Review pubs.acs.org/CR

Magnetic Susceptibility of Uranium Complexes Douglas R. Kindra and William J. Evans* Department of Chemistry, University of California, Irvine, California 92697-2025, United States where the ligand field effects are strong and can diminish the contribution of the orbital angular momentum to the magnetic moment (orbital quenching). However, an operational solution exists for transition metal complexes: a spin-only approximation, μS = 2[S(S + 1)]1/2, can be used as a starting point and then modified for orbital contributions depending on the dn configuration and symmetry.7−10 The actinides are intermediate between lanthanides and transition metals in the sense that the greater radial extension of CONTENTS the 5f orbitals means that ligand field effects cannot be ignored, yet spin−orbit coupling is large.1−3,6,8,11−15 In a case where two 1. Introduction 8865 effects can be comparable, finding a simple model is usually 2. Results 8873 more difficult. Neither the spin-only μS approximation used for 3. Discussion 8873 transition metals nor the total angular momentum μ J 4. Conclusion 8877 approximation used for the lanthanides is adequate for uranium, Author Information 8878 although μJ is often used as an approximate starting point. A Corresponding Author 8878 detailed theoretical analysis on actinide magnetism has recently Notes 8878 been published that defines these issues more formally.3 Biographies 8878 A further complication for uranium is that the μJ values of Acknowledgments 8878 3.62 and 3.58 μB often used to approximate magnetism for U3+ List of Abbreviations 8878 and U4+, respectively, are similar enough to be within the References 8879 experimental error of typical measurements. It is therefore difficult to differentiate U3+ and U4+ from room-temperature magnetic moments.11−15 As a consequence, it is preferable to obtain variable-temperature data with a superconducting 1. INTRODUCTION quantum interference device (SQUID) or vibrating sample Since uranium has several common paramagnetic oxidation magnetometer (VSM) since the magnetic moment of a 5f 2 U4+ 1 5+ 2 4+ 3 3+ states, i.e., 5f U , 5f U , and 5f U , one of the analytical ion typically approaches zero at low temperature due to a methods commonly used for characterizing uranium complexes singlet ground state. This does not occur with half-integral 5f 3 1−10 is measurement of magnetic susceptibilities. A variety of U3+ and 5f 1 U5+. Unfortunately, although variable-temperature solid state and solution methods have been used to obtain analysis is the state-of-the-art method to evaluate the magnetic data on uranium complexes under different magnetism of uranium complexes, such data are not always conditions at both room and low temperature, and data are easily obtained by all research groups and even the shapes of often cited to support the assignment of oxidation state. variable-temperature plots are not always consistent for a given Statements like “the magnetic moment of compound X is ion.17−25 consistent with Un+” are common in uranium papers. Despite these difficulties, many claims of oxidation state However, it has been pointed out repeatedly in the 1−3,5,6,11−15 based on room-temperature magnetic moments are in the literature that evaluating the magnetic susceptibility literature. These claims often cite other papers with similar of uranium complexes is not as straightforward as it is for magnetic moments to support the oxidation state assignment transition metal and lanthanide complexes. For any metal without mentioning the papers in which different magnetic complex, the magnetic moment arises from the sum of the moments were observed for that oxidation state. contributions of the ground state and the low-lying thermally To our knowledge, no comprehensive collection of magnetic accessible excited states as well as any temperature-independent data on uranium complexes has been assembled to survey the magnetism in the system. For most 4fn lanthanides, the ground actual range of data in the literature. To remedy this deficiency, state is defined by a 2S+1LJ Russell−Saunders term because the data in this review were compiled. It was of interest to spin−orbit coupling is large and ligand field splitting is small determine if there were any trends in the ranges of magnetic due to the limited radial extension of the 4f orbitals. Roommoments reported for uranium complexes and the frequency of temperature magnetic moments can be approximated for most typically observed values. Magnetic data on over 500 complexes of the lanthanides by μJ = g[J(J + 1)]1/2 and correlated with 7−10,16 of uranium in the common +3, +4, and +5 oxidation states as oxidation state. This approximation does not apply to 3+ 3+ Sm and Eu because they have low-lying excited states, but the range of their experimental values is well defined.7−10,16 Received: May 3, 2014 Published: August 19, 2014 The situation is more complicated for dn transition metals © 2014 American Chemical Society

8865

dx.doi.org/10.1021/cr500242w | Chem. Rev. 2014, 114, 8865−8882

Chemical Reviews

Review

Table 1. Room-Temperature (RT) and Low-Temperature (LT) Magnetic Moments (μB) of Monometallic Uranium Complexes in various Formal Oxidation States, Un+, and Formal Coordination Numbers (CN) Determined by Various Methodsa compound

oxidation state

CNb

method

RT μ

+3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3

6 6 10 9 8 7 4 6 7 3 3 3 6 8 7 7 7

S S E S

1.75 1.92 2.33 2.37 2.37 2.37 2.38 2.49 2.5 2.51 3.07 3.354 2.52 2.53 2.59 2.6 2.6 2.60 2.6† 2.63 2.7 2.7 2.80 2.80 2.8 2.83 2.87 2.9 2.90 2.9 2.9 2.91 2.91 2.92 2.92 2.95 2.95 2.95 2.97 3.0 3.0† 3.01 3.01 3.02 3.04 3.06 3.07 3.1 3.11 3.12 3.13 3.13 3.14 3.2 3.20 3.20 3.25 3.25 3.27 3.28

Ad,Me

ArO)3mes}U] [{( [((tBuArO)3mes)U] U(C5H5)3·THF [U(Cp*)2(terpy)]I Cp*2U(2,2′-bpy) [(Ar*O)3U(THF)] [U{OSi(OtBu)3}4K] [((Neop,MeArO)3tacn)U] Tp*2UCH2Ph U[N(SiMe3)2]3 U[N(SiMe3)2]3 U[N(SiMe3)2]3 [(Ar*O)3U] [U(TpMe2)2(bipy)]I [(Ad(ArO)3tacn)U(Me4IMC:)] Tp*2U(CH2SiMe3) Tp*2U(CH3) K5Li2UF10 U(Ph2BPz2)3 [K(18c6)][U(OSi(OtBu)3)4] Tp*UI2(2,2′-bpy) U(H3BNMe2BH3)3(PMe3)2 [U(NN′3){OP(NMe2)3}] [(Et8-calix[4]tetrapyrrole)U(dme)][K(dme)] U(H3BNMe2BH3)3 [((AdArO)3tacn)U] UI3(THF)4 Tp*UI2(THF)2 [((t‑BuArO3)tacn)U(NCCH3)] [((AdArO)3tacn)U(η1-NNCPh2)] U(H3BNMe2BH3)3(thf) U(ArFTPA)(py)3 UCl3(cyclohexyl-15-crown-5) [((t‑BuArO)3tacn)U] Cs2NaUCl6 UCl3(H2O)7 [U(NN′3)(NC5H5)] U(THF)(N[R]Ar)3 [U(tmma)4][BPh4]3 U[CH(SiMe3)2]3 [((AdArO)3N)U] [U(TpMe2)2I] U(CH2PPh3)(NR2)3 [U(BIPMTMS)(I)2(THF)] [((DiaArO)3tacn)U] U(NN′3) U(Lme)I{N(SiMe3)2} [U(C5Me5)3] U{N(SiMe2Ph)2}3 [U(TrenTIPS)] CsUCl4 U(Lme)I2(THF)2 Cp″3U·(tBuNC) Tp*2U(2,2′-bpy) [((Me3Si)2N)3U(Me4IMC:)] (THF)U(N[Ad]Ar)3 Cp″3U·(C6H11NC) Ba2UCl7 CsUCl4·4H2O Cp′3U 8866

6 4 7 8 5 10 6 6 7 7 7 7 7 7 6

5 4 3 4 7 4 6 6 4 4 9 4 4 6 10 8 4 4 10

9

S E S G E S S S S G G S E G E E E S S G S S E S F S V F E E G S S S S S E E E E S F E G S S

F E

LT μ (temp, K) 1.00 (5) 1.15 (5) 1.26 (2) 1.21 (2) 1.54 (2)

2.06 (5) 1.27 (2) 1.60 (1.8) 1.81 (5)

1.7† (1.8)

1.74 (5) 2.23 (1.8) 1.66 (5) 1.9 (5) 2.1† (2) 1.77 (5) 2.49 (4)

1.6† (5) 2.0 (1.8) 2.12 (4) 2.00 (1.8) 1.26 (5)

2.22 (1.8)

1.78 (5) 2.31 (5) 1.76 (5)

ref 29 30 31 32 33 34 35 36 37 38 39 40 34 41 39 37 37 42 43 44 45 46 47 48 46 11 49 45 11 50 46 51 52 11 53 54 47 55 56 57 58 59 23 49 13 60 61 62 63 64 65 61 3 45 39 66 3 42 67 26c

dx.doi.org/10.1021/cr500242w | Chem. Rev. 2014, 114, 8865−8882

Chemical Reviews

Review

Table 1. continued compound

oxidation state

CNb

method

RT μ

LT μ (temp, K)

ref

+3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4

3 3 3 9

S S E

3.3† 3.3† 3.3 3.32 3.33 3.34 3.36 3.37 3.39 3.40 3.4 3.42 3.44 3.44 3.46 3.47 3.47 3.49 3.5 3.52 3.53 3.56 3.56 3.56 3.57 3.57 3.60 3.61 3.65 3.65 3.67 3.67 3.70 3.70 3.70 3.7† 3.71 3.72 3.73 3.74 3.75 3.77 3.8† 1.36 1.76 1.79 1.91 1.93 1.98 1.99 2.01 2.03 2.04 2.04 2.07 2.10 2.14 2.14 2.15 2.17 2.19

2.1† (1.8) 1.9† (1.8)

68 68 69 3 42 42 42 3 70 71 69 72 73 74 75 76 74 75 77 78 79 71 65 75 80 81 47 61 80 42 82 71 80 81 83 84 81 79 75 79 75 74 85 86 87 88 88 33 25 89 64 89 33 90 33 91 92 93 94 95 29

Me

U(Bp )3 U(BcMe)3 U(ODtbp)3 Cp″3U K2UBr5·2CH3CN·6H2O Rb2UBr5·CH3CN·6H2O [(CH3)3N]3UCl6 Cp‡3U UCl3·CH3CN·5H2O UOCl U(OTtbp)3 {[(−CH2−)5]4-calix[4]tetrapyrrole}UK(DME)2 UI3(CH3CN)4 Rb2UCl5 Rb2UBr5 (C5Me5)2U(dmpe)(H) (NH4)2UCl5 Rb2UCl5 U(BH4)3(2.2.2-cryptand) K2UBr5 NH4UCl4·4H2O UOI Cs2LiUCl6 K2UCl5 UBr3 RbUCl4·3H2O [U(NN′3)(CH2PMe3)] U(Lme)(Cp*)I UI3 SrUCl5 UF3 UOBr UCl3 KUCl4·3H2O U(HCOO)3 U(dpp-BIAN)2(THF) [solid state] NH4UCl4·3H2O KUCl4·4H2O Rb2UI5 RbUCl4·4H2O K2UI5 K2UCl5 [U(BIPMTMSH)(I)2(THF)] (C5Me4H)3UNO UI4·(1-phenylpiperazine) Cp2U(MesDABMe) (MesDABMe)2U(THF) Cp*2U(2,2′-bpy)(COPh2) [Li(THF)]2[U(OtBu)6] (η2-Ph2PNiPr)3UCl [UCl(TrenTIPS)] (η2-Ph2PNiPr)4U Cp*2U(2,2′-bpy)(COHPh) U(SO4)2·2.2 DMF Cp*2U(2,2′-bpy)(COH(furan)) [U(TrenTMS)(THF)2][BPh4] [((AdArO)3N)U(N3)] [(NN′3)U(CCPh)2(Li·THF)] UI4(Et2O)2 [U{BIPMTMS[C(O)(CHCHC6H4O-2)]-κ3-N,O,O′}(Cl)2(THF)] [{(Ad,MeArO)3mes}U][(15C5)Na(THF)], 3-Na 8867

9 9 3 10 7 6 9

6

9 5 6 9 9 9 9 9 5

6 6 6 10 8 5 9 6 7 5 8 9

F F E G F F S E F S F S F F F S V F E E V G F V F G S F F S F S F S S V S S S E S E G

9 6 7 6 6 6

E S S E S S

2.03 (5)

2.13 (5)

2.67 (5)

1.3† (2)

3.1† (1.8) 0.33 (1.8) 0.40 (2) 0.68 (2) 0.20 (2) 0.50 (1.8)

0.34 (2) 0.5† (2) 0.41 (1.8) 0.71 (5)

dx.doi.org/10.1021/cr500242w | Chem. Rev. 2014, 114, 8865−8882

Chemical Reviews

Review

Table 1. continued compound

oxidation state

CNb

method

RT μ

+4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4

10 7 6 7

V S S S S V E E E S G S V G V S S S E S S S S E V V G V V S G S V G F E G

2.2 2.21 2.22 2.22 2.22 2.22 2.3 2.3 2.3 2.32 2.32 2.33 2.34 2.35 2.36 2.37 2.37 2.39 2.4 2.4† 2.4† 2.4† 2.4† 2.4 2.4 2.42 2.42 2.43 2.44 2.45 2.45 2.45 2.45 2.46 2.47 2.48 2.48 2.49 2.5† 2.5† 2.50 2.5 2.52 2.53 2.54 2.55 2.56 2.58 2.59 2.59 2.59 2.6 2.6 2.6† 2.6† 2.6 2.60 2.6 2.61 2.62 2.62

[(CH3)4COT]2U [{(Ad,MeArO)3mes}U][K], 2-K [{(Ad,MeArO)3mes}U][(18C6)K(THF)], 3-K [U(BIPMDipp)(Cl)2(THF)2] [Ph3BuP]2[UCl6] U(ClO4)4·2(1,4-dimethylpiperazine)THF (C5Me5)3UBr (C5Me5)3UCl Cp*U(PDI)(THF) [{(Ad,MeArO)3mes}U][Na], 2-Na UCl4·3DPA [Ph3BuP]2[UBr6] U(NCS)4·(1,4-dimethylpiperazine) UCl4·2.5DMA dicyclobutenouranocene [((tBuArO)3mes)U(dbabh)] [Cp*2Co]2[U{OB(C6F5)3}2(Aracnac)2] (dippap)U(CH2Ph)2(THF)2 (C5Me5)3UF [U(TrenTIPS)(PH)(K-2,2,2-cryptand)] [U(I)(TrenTIPS)] [U(F)(TrenTIPS)] [U(NH2)(TrenTIPS)] [DIPPNCOCN]UCl2·0.5C7H8 U[C8H6(CH2)3]2 U(C5Me5)2Cl(pz−) UCl4·3MFA U(COT)2 U(N(CH2CH2CH2CH3)2)4 [U(TrenTIPS)(PH)][K(B15C5)2] Cp3UOH [Li(THF)2][U(NCtBuPh)5] U(NCS)4·(2,5-dimethylpiperazine) UCl4·2.5DEA UCl4·2.5MCaL [U(I){HC(SiMe2NAr′)3}(THF)] UCl4·2.5DMF Cp*2U(2,2′-bpy)(COMe2) [((t‑BuArO)3tacn)U(OMe)] [((AdArO)3tacn)U(OMe)] [U(NN′3)(NEt2)] [(C6H5)4COT]2U UCl4·2.5MBuL [U(Cp*)2{NC5H4(py)2}][BPh4] [U(Cl)(C5H4N-2-NSiMe3)3] UCl4·4BAN UI2Cl2·5DMA {[(−CH2−)5]4-calix[4]tetrapyrrole*}ULi(OC2H5)(THF)2 [U{N(CH2CH2NSiMe3)2(CH2CH2NSiMe2CHBPh2)}(THF)] (C8H8)2U UCl4·3MAA [U{N(SiMe3)2}3H] BH4U[N(SiMe3)2]3 [U(N3)(TrenTIPS)] [U(TrenTIPS)(PH2)] {N[ο-(NCH2PiPr2)C6H4]3}UCl U(CH2C6H5)4 Tp*2U(NPh) [U{C(PPh2NMes)2}2] [U{C(PPh2NSiMe3)2}(Cl)(μ-Cl)2Li(thf)2] U(salen)Cl2·bipy 8868

10 10 7 7

10 7 6 6 10 5 5 5 5 5 10 9 10 4 5 10 5

5 9 7 7 5 10 9 7

9 6 10 4 3 5 5 8 4 7 6 6 8

S S E S F S E G G G E G E E S S S G G E S S

LT μ (temp, K) 0.85 (5) 0.65 (5) 0.75 (1.8)

0.64 (5)

0.54 (5) 0.8† (2) 0.47 (2) 0.8† 0.6† 0.5† 0.6†

(1.8) (1.8) (1.8) (1.8)

1.04 (1.8) 0.56 (4.2) 0.94 (4)

1.3† (5) 1.1† (5)

0 (2)

1.21 (5)

0.4† (1.8) 0.6† (1.8) 0.4† (1.8)

0.34 (1.8)

ref 96 29 29 97 25 87 98 98 99 29 100 25 87 100 101 30 102 103 98 104 17 17 17 105 106 107 100 108 109 104 110 18 87 100 111 112 100 33 19 19 113 96 111 32 114 100 100 72 115 116 100 63 117 17 104 118 119 120 121 122 123

dx.doi.org/10.1021/cr500242w | Chem. Rev. 2014, 114, 8865−8882

Chemical Reviews

Review

Table 1. continued compound

oxidation state

CNb

method

RT μ

+4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4

5

E S G V V V E G

2.63 2.64 2.65 2.65 2.65 2.67 2.67 2.67 2.68 2.69 2.69 2.7† 2.7 2.7 2.7 2.7 2.70 2.70 2.7 2.7 2.7 2.71 2.71 2.72 2.72 2.72 2.72 2.73 2.73 2.73 2.74 2.75 2.75 2.75 2.76 2.76 2.77 2.78 2.79 2.79 2.79 2.79 2.79 2.79 2.8 2.8 2.8† 2.8† 2.8† 2.80 2.80 2.8 2.80 2.81 2.81 2.81 2.81 2.82 2.82 2.82 2.82

but

(L )UI3 [U{BIPMTMS[C(NCy)2]-κ4-C,N,N′,N′′}(Cl)(μ-Cl)2Li(THF)2] Cp3USH [C6H5COT]2U bis(tetrahydrobenzo[8]annulene)uranium UCp3(C3H3N2) (η2-iPr2PNMes)3UI UCl4·4VaL U(O-2,6-But2C6H3)4 U(N(CH2CH2CH3)2)4 Na3UF7 (C5Me5)2U[-NC(CH3)(3-F-C6H4)]2 [{N(SiMe3)2}2U(CH2Si)N(SiMe3)] MeU[N(SiMe3)2]3 [((AdArO)3tacn)U(η2-3-phen(Ind))] [tBuNON]U(η5-C5Me5)CH3 [U{HC[C(Me)NDipp][C(CH2)Ndipp]}{N(SiMe3)2}2] (dmpe)U(CH2C6H5)4 Tp*2U(NMes) Tp*2U(NAd) U(OSiMe3)2I2(bipy)2 [{(DMB,DMBArO)3tacn}UCl] U[OC(CMe3)2H]4 [((tBuArO3)tacn)U(dbabh)] [U(I){HC(SiMe2NAr)3}(THF)2] UCl4·3DMBA [UL4] LOCMe2CH2[1-C(NCHCHNiPr)] [Cp*2Co][U(O)(N(SiMe3)2]3] [(dmpe)(dmbpy)UCl4] UCl4·4MA U(N(CH2CH3)2)4 (C5Me4H)3UCl [{(tAmyl,tAmylArO)3tacn}UCl] UCl4·6AA UCp4 UCl4·4BuL U(dpp-BIAN)2 (C5Me5)2U[-NC(CH3)(C6F5)]2 [(TrenTMS)U(I)(THF)] [U(TrenTMS)(NCy2)] U(dpp-BIAN)2(THF) (solution) UCl4·CaL U(NO3)4(1,4Me2-pipz)2 U(gu)2Cl2 ClU[N(SiMe3)2]3 [U(TrenTIPS)(NH)][K(15C5)2] [((AdArO)3tacn)U(N3)] [((AdArO)3tacn)U(NCNCH3)] [(tren-TMS)UCl(thf)] [U(I)(C5H4N-2-NSiMe3)3] [tBuNON]U(C5Me5)Cl [tBuNON]U(CH2Si(CH3)3)2 U(NO3)4(2,5Me2-pipz)2 [((t‑BuArO)3tacn)U(OCHt‑BuPh2)] UCl3·5DMSO(ClO4) U(NO3)4(1Ph-pipz)2 U(NO3)4(2,6Me2-pipz)2 U(NO3)4(1Me-pipz)2 U(NO3)4(2Me-pipz)2 U(LH)LCl3 U[OSi(CMe3)3]4 8869

10 10 10 11 7 4 4 8 4 4 8 7 4 6 7 7 8 7 4 7 6 7 4 8 4 10 7

V S E E S E E G G G E S S E G E S S G V S S G

12 4 8 6 5 5

4 5 7 7 6 7 7 5 7

4

F S S E E E F V F E S S S S E S E V S F V V V V F

LT μ (temp, K) 0.22 (1.8) 0.52 (4.2)

0.6† (2)

1.2 (5)

0.40 (2) 1.16 (5)

2.00 (4) 0.6† (2)

0.33 (1.8) 0.43 (2)

0.8† (2) 0.6† (2)

1.5 (1.8) 0.6† (5) 1.2† (5) 0.3† (1.8) 0.91 (5)

1.14 (5)

ref 61 95 110 96 124 125 89 111 126 109 127 128 63 117 50 129 61 119 120 120 130 131 3 30 112 100 132 21 133 100 109 86 131 100 134 111 84 128 135 91 84 111 136 137 117 138 139 14 140 114 129 129 136 141 142 136 136 136 136 143 3

dx.doi.org/10.1021/cr500242w | Chem. Rev. 2014, 114, 8865−8882

Chemical Reviews

Review

Table 1. continued compound

oxidation state

CNb

method

RT μ

+4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4

4

S G V V E S

2.83 2.83 2.83 2.83 2.83 2.84 2.84 2.85 2.85 2.86 2.87 2.88 2.88 2.88 2.89 2.89 2.9† 2.9† 2.9† 2.9 2.90 2.90 2.90 2.91 2.92 2.92 2.93 2.94 2.94 2.96 2.96 2.98 2.99 3.00 3.0† 3.0 3.01 3.03 3.04 3.05 3.08 3.08 3.08 3.08 3.09 3.09 3.11 3.11 3.12 3.12 3.12 3.13 3.13 3.13 3.13 3.14 3.14 3.15 3.15 3.16 3.16

[Ph3PCH3][U(Te)(N(SiMe3)2)3] UCl4·4AAN U(NO3)4(pipz)2 CsLiU(PS4)2 [UC12{N(CH2CH2PPri2)2}2] U(CHPPh3)[N(SiMe3)2]3 U[(C6H5)2N]4 [((ArO)3tacn)U(OAr)] UsalenCl2(THF)2 [DIPPNCOCN]UCl3Li(THF)2 [U(C5H4N-2-NSiMe3)4] [U(Cl){HC(SiMe2NAr)3}(THF)] UCl4·4BAM UCl4·4EA [((AdArO)3tacn)U(CO2)] [U{(NHCMe2SiPri2NCH2CH2)N(CH2CH2NSiPri3)2}] [((AdArO)3tacn)U(I)] [((AdArO)3tacn)U(Br)] [((AdArO)3tacn)U(Cl)] [tBuNON]U(C3H5)2 [U{N(CH2CH2NSiPri3)2(CH2CH2NSiPri2C[H]MeCH2)}] UPn*2 [Et4N][U(NCS)5(bipy)2] FU[N(Me3Si)2]3 U(I)(N[R]Ar)3 U(acac)4 [U(BIPMDipp)(Cl)(μ-Cl)2(Li)(tmeda)(OCPh2)] U[N(SiMe3)2]4 [U{N(SiMe2H)2}4] [Li(DME)3][U(CH2SiMe3)5] UCl4·6AcA Tp*2U(η2-Se2) (PNP)2U[η2-(N,N′)N−NCPh2] [({(tBuArO)2(CH2Ph)}tacn)U(enolate)] [U(BIPMTMSH)(Cl)3(THF)] U(ClO4)4·(1,4-dimethylpiperazine) U(TTA)4 [U(TrenTMS){N(SiMe3)2}] [U(NCy2){HC(SiMe2NAr)3}(THF)] UBr4·(1,4-dimethylpiperazine)) [U(BIPMDipp)(μ-Cl)4(Li)2(tmeda)(OCPhBut)] [U(NN′3)I] U(bac)4 UCl4·4DPF [(TsXy)UN(SiMe3)2] [Li(THF)4][U(CH2tBu)5] Cp‡2UF2 UO2 CpPUI2(MesPDIMe) [(NN′3)U(CCPh)] U{N(SiMe3)SiMe2CH2BBNH}2 UOCl2 [((DiaArO)3tacn)U(Cl)] [U(BIPMDipp)(μ-Cl)4(Li)2(OEt2)(tmeda)] UCl4·4MF [U(NN′3)Br] U(SO4)2·4H2O [U(TrenTIPS)(THF)][BPh4] MeU[OC(CMe3)3]3 (C5H5)3UCl (η2-iPr2PNMes)4U 8870

7 4 4 7 6 8 5

7 5 7 7 7 5 5 10 4 4 8 7 4 4 5 8 7 8 7 8 5 5 7 5 8 4 5 8 8 8 5 4 7 7 5 8 4 4 10 8

S S E E G G S S S S S E E S S E S E S E S G S E S S V S E E V E E S G E S S S S E F S S G E S E

E

LT μ (temp, K) 0.79 (4)

0.97 (4) 1 (5) 0.7† (2)

1.51 (5) 0.74 (1.8) 0.7† (5) 0.7† (5) 0.7† (5)

1.6† (5) 0.35 (2)

1.3† (2) 1.89 (2) 0.94 (4) 0.47 (3.5) 0.4† (1.8)

2.36 (2)

1.25 (5) 0.5† (2)

0.69 (2) 0.66 (1.8)

ref 21 100 136 144 145 23 146 147 148 105 114 112 100 100 139 17 139 139 139 129 149 150 151 3 55 152 97 153 63 25 100 154 155 156 85 87 152 91 112 87 97 113 152 100 157 25 3 152 158 93 159 160 13 97 100 113 152 104 3 161 89

dx.doi.org/10.1021/cr500242w | Chem. Rev. 2014, 114, 8865−8882

Chemical Reviews

Review

Table 1. continued compound

oxidation state

CNb

method

RT μ

(N″)2U{κ -N(SiMe3)SiMe2CH2BBN-H} U(tfac)4 (1,4,7-(CH3)3-C9H4)3UCl IU(N[tBu]Ar)3 [Li(DME)][U(NC5H10)5] γ-Na2UF6 (1-C2H5-C9H6)3UCl MeU[(Me3Si)2N]3 [((tBuArO)3tacn)U(benzyl•−)] [U(NN′3)Cl] (C5Me5)2U[−NC(CH3)(3,5-F2-C6H3)]2 [U(BIPMMes)(Cl)2(THF)2] [Ph3PCH3][U(Se)(N(SiMe3)2)3] [(dmpe)2UMe4] (dippisq)UI3(THF)2 K4U(NCS)8 CpPU(O2C2Ph4)(MesPDIMe) [U{BIPMTMS[C(NBut){OLi(THF)2(μ-Cl)Li(THF)3}]-κ4-C,N,N′,N′′}(Cl)3] UOBr2 UCl4 UF4 [((AdArO)3tacn)U(NCO)] Cp‡2UCl2 U(ArF3TPA)(py)2Cl [Li(DME)3][U(OtBu)2(CH2SiMe3)3] UOI2 Tp*2U(η2-S2) U(I)[N(SiMe3)2]3 [U(OTf)3(OH)(py)4] [(dmpe)2UCl4] UCp*2Cl2(pz) U(dbm)4 UCp3Cl [tBuNON]UI3Li(THF)2 [Li][U(2,3-C6H3CH2NMe2)(2-C6H4CH2NMe2)3] [((t‑BuArO)3tacn)U(OC·t‑BuPh2)] [((t‑BuArO)3tacn)U(η2-NNCPh2)] U(cupf)4 IU(N[Ad]Ar)3 [((t‑BuArO)3tacn)U(N3)] [U(BIPMMesH)(Cl)3(THF)] UCl4·5DMSO NaUO3 UCl5 LiUO3 UCl5·SOCl2 [Li(DME)3][U(NC5H10)6] K(UO)Si2O6 [Li][U(NCtBuPh)6] [Ph3PI][U(OSiMe3)2I4] [Li(DME)3][U(OtBu)2Cl4] [U(NN′3)(O)] U[(μ-CH2-SiMe2)N(SiMe3)]2[N(SiMe3)2] UCl2[N(SiMe3)2]2 [U{(SiMe2NPh)3tacn}(η2-S2)] [Cp*2Co][UO2(Aracnac)2]; Ar = 2,4,6-Me3C6H2 U(OSiMe3)2I2(Aracnac) UCl5·TCAC [Li(THF)4][U(CH2SiMe3)6] [((AdArO)3N)U(NTMS)] U(O)[N(SiMe3)2]3

+4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5

4 8 10 4 5 8 10 4 8 5 8 7 4 8 7 8 8

E S G S S S G

3.16 3.16 3.17 3.18 3.18 3.18 3.18 3.18 3.19 3.19 3.2† 3.23 3.23 3.23 3.23 3.26 3.27 3.27 3.27 3.29 3.30 3.3† 3.32 3.32 3.33 3.34 3.34 3.35 3.35 3.40 3.42 3.43 3.44 3.46 3.47 3.48 3.5† 3.5 3.52 3.55 3.55 3.79 1.24 1.26 1.28 1.29 1.3 1.32 1.38 1.4 1.44 1.47 1.48 1.5 1.50 1.5 1.52 1.54 1.54 1.57 1.59

2

8871

8 8 7 8 6 5 9 8 4 8 9 8 10 6 8 7 8 8 4 7 7

S E S S S S S S S S F S S S S S F S S S S V S S S S S S S S S F

6

6 6 6 6 5 5 5 8 6 6

S S S E S E G S S E E

6 6 4

S S S

LT μ (temp, K)

1.81 (2)

1.59 (2) 0.6† (2) 0.32 (1.8) 0.96 (4) 0.5† (2) 1.50 (2) 1.44 (5) 0.31 (1.8)

0.8† (5) 0.6† (2) 3.2† (4) 1.04 (4) 2.16 (4) 0.6† (2)

0.6† (2) 0.78 (4) 1.61 (5) 1.75 (5)

0.4 (5) 0.32 (1.8)

0.96 (4) 1.09 (4) 1.0† (4)

1.0† (2) 1.23 (2)

1.2† (4) 0.90 (2) 0.94 (4)

ref 159 152 162 66 163 152 162 3 156 113 128 97 21 133 103 152 158 95 160 152 152 14 3 51 22 160 154 164 165 133 107 152 134 105 166 141 50 152 66 167 97 142 168 169 169 169 163 170 18 130 22 47 171 172 173 174 175 169 22 92 164

dx.doi.org/10.1021/cr500242w | Chem. Rev. 2014, 114, 8865−8882

Chemical Reviews

Review

Table 1. continued compound Ar

oxidation state

CNb

method

RT μ

+5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5

6 6 6 5

E E G S S

5

S S

8 5 5 5 4 4 10

E S S S S E

7

S G G

1.6 1.61 1.62 1.63 1.64 1.67 1.68 1.69 1.71 1.75 1.76 1.8† 1.8† 1.81 1.82 1.83 1.86 1.92 1.94 1.95 1.96 1.96 1.97 1.98 1.99 2.0† 2.03 2.03 2.04 2.04 2.04 2.09 2.12 2.13 2.14 2.16 2.17 2.20 2.2 2.22 2.22 2.23 2.25 2.26 2.27 2.28 2.30 2.33 2.34 2.34 2.34 2.35 2.37 2.38 2.40 2.42 2.42 2.46 2.48 2.51 2.53

t

[Cp*2Co][UO2( acnac)2]; Ar = 3,5- Bu2C6H3 UC12[N(CH2CH2PPri2)2]3 Me4NUCl6 [U(μ-N)(μ-Na15C5)(TrenTIPS)] {[UO2(dbm)2][μ-K(MeCN)2][μ8-K]} N2H6UF7 [((AdArO)3N)U(NMes)] [UO2(dbm)2K(18C6)] CsUCl6 Cp*U(PDI)(NPh)2 [U(O)(TrenTIPS)] [U(NSiMe3)(TrenTIPS)] [U(NAd)(TrenTIPS)] (Me3SiN)U(N[Ad]Ar)3 U(O)[N(SiMe3)2]3 Cp3UNSiMe3 Na3UF8 [((AdArO3)tacn)U(O)] UCl4T·HT UCl5(oxineH)2 (MeC5H4)3UNPh [(Ar*O)3U(O)(THF)] [Ph3PCH3][U(O)(CH2SiMe2NSiMe3)(N{SiMe3}2)2] [((t‑BuArO3)tacn)U(O)] [UN(TrenTIPS)][Na(12C4)2] [((AdArO)3tacn)U(NSiMe3)] [UO{OSi(OtBu)3}4K] (C5Me5)2U(N-2,6-iPr2-C6H3)(NCPh2) Br3OU [(Me3Si)2N]3UNSiMe3 UCl5(pyrazine)2 (Me2H2N)UCl6 [K(18C6)][U(NSiMe3)(OSi(OtBu)3)4] UCl5·Ph3PO Ph4AsUCl6 [U{C(PPh2NSiMe3)2}(Cl)2(I)] [U(NN′3)(NSiMe3)] [UO2(salan-tBu2)(py)(K18C6)] [UO2(salan-tBu2)(Py)μ-K] (C5Me5)2U(N-2,6-iPr2-C6H3)(CCPh) (C5Me5)2U(N-2,6-iPr2-C6H3)(F) [UO2(salophen-tBu2)(py)K] NH4UF6 [(Me3Si)2N]3UN(p-C6H4CH3) (C5Me5)2U(N-2,6-iPr2-C6H3)(NPh2) UCl5(phthalazine)2 (C5Me5)2U(N-2,4,6-tBu3-C6H2)(Br) [U(BIPMDipp)(Cl)2(μ-Cl)2(Li)(THF)2] (C5Me5)2U(N-2,6-iPr2-C6H3)(I) [((t‑BuArO)3tacn)U(NSiMe3)] [K(18C6)][U(NAd)(OSi(OtBu)3)4] [((t‑BuArO3)tacn)U(NMes)] α-UF5 (C5Me5)2U(N-2,6-iPr2-C6H3)(OPh) [((AdArO3)tacn)U(NMes)] (C5Me5)2U(N-2,6-iPr2-C6H3)(Cl) (C5Me5)2U(N-2,6-iPr2-C6H3)(Br) (C5Me5)2U(N-2,4,6-tBu3-C6H2)(F) (C5Me5)2U(N-2,6-iPr2-C6H3)(SPh) (C5Me5)2U(N-2,4,6-tBu3-C6H2)(Cl) (C5Me5)2U(N-2,4,6-tBu3-C6H2)(I) 8872

10 5 5 7 5 7 5 8

6 5

S S S S S S S G S G G E

6 6 5 7 7 8 8 7

G S E S E S S S

4 8

S S G S S S S E S F S S S S S S S S

4

8 7 8 7 5 7 6 8 7 8 8 8 8 8 8

LT μ (temp, K)

1.58 (10) 1.3† (5) 1.0 (5) 0.7† (5)

1.2 (1.8) 1.3† (1.8) 1.4† (1.8)

1.19 (5) 1.49 (5)

1.25 (5) 0.86 (2) 1.47 (4) 1.61 (5) 1.31 (1.8) 1.3† (5) 0.75 (2) 1.1† (2) 1.61 (5)

0.9 (1.8) 1.05 (6) 1.1† (2) 1.35† (2) 0.72 (6) 1.49 (5) 1.1† (2) 1.0† (2) 1.10 (1.8) 1.4† (2) 1.46 (5) 1.67 (5) 1.1† (2) 1.64 (5) 1.4† (2) 1.4† (2) 1.0† (2) 1.1† (2) 1.0† (2) 1.0† (2)

ref 174 176 177 17 178 169 92 178 169 99 179 17 17 66 38 180 169 181 182 182 180 34 24 181 64 14 35 183 184 3 185 177 44 169 177 122 47 186 187 183 188 186 169 3 183 185 188 97 188 167 44 181 189 183 181 188 188 188 183 188 188

dx.doi.org/10.1021/cr500242w | Chem. Rev. 2014, 114, 8865−8882

Chemical Reviews

Review

Table 1. continued compound

oxidation state

CNb

method

RT μ

+5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5

7

S E S G G G G G G G G S G S G

2.55 2.6 2.65 2.68 2.70 2.74 2.76 2.78 2.84 2.84 2.86 2.86 3.10 3.70 3.77

Dia

[(( ArO)3tacn)U(NTMS)] [UO2py5]I·py (C5Me5)2U(N-2,6-iPr2−C6H3)(OTf) UCl5(2-mcpy)2 UCl5diphos UCl5(py)2 UCl5(EBDPP) [UCl4(dipy)]Cl UCl5PhTeTePh UCl5(oxineH)4 UCl5(ophen)2 [Li(THF)][(THF)(Me3Si)2NLiOUO(THF){Li(THF)}2(L)] UCl5PhSeSePh [U(dbabh)6][nBu4N] UCl5(enbissal)2

8

7 6

LT μ (temp, K) 1.26 (5) 1.1† (2)

0.88 (2) 1.16 (5)

ref 13 186 183 182 185 182 182 182 185 182 182 190 185 191 182

a E = Evans method; F = Faraday method; G = Gouy balance; S = SQUID; V = VSM. Values determined from graphs of χT or μ vs temperature are denoted with a † superscript. bFormal coordination number for inorganic salts given when available in the literature.192 cMagnetic measurement performed for this work.

well as the newly discovered +2 oxidation state26,27 are presented here along with a statistical analysis of the values versus the oxidation state assigned to each complex. This compilation will allow magnetic data on new uranium complexes to be compared to the full range of data in the literature. This should aid in determining if the new complexes exhibit typical or unusual magnetic properties.

temperature are presented in Table 3. For each oxidation state, the following values are given: the average, the median, the standard deviation, σ,218 the upper and lower quartile,219 qu and ql, respectively, and the number of measurements, n.

3. DISCUSSION Table 1 shows that the range of room-temperature magnetic moments for each of the common paramagnetic uranium ions is large and the overlap is extensive: reported data range from 1.75 to 3.8, 1.36 to 3.79, and 1.24 to 3.77 μB for U3+, U4+, and U5+, respectively. As a consequence, any room-temperature magnetic moment between 1.75 and 3.77 μB could be claimed to be within the full range of U3+, U4+, or U5+! However, the histograms show trends that follow the number of unpaired electrons: the moments for U3+ tend to be higher than those of U4+, which tend to be higher than those of U5+ (Figures 2 and 3). The range of values between the upper and the lower quartiles, i.e., the middle 50% of the values, shows ranges with less overlap: 2.90−3.49, 2.50−3.08, and 1.64−2.38 μB for U3+, U4+, and U5+, respectively. There is still significant overlap between U3+ and U4+ at this 50% population level, but there is no overlap with U5+. This overlap reflects statements in earlier papers indicating that room-temperature magnetic moments are inadequate for differentiating U3+ and U4+.11−15 The ranges of the low-temperature magnetic moments for U3+, U4+, and U5+ also overlap: 1.00−3.1, 0.0−3.2, and 0.7− 1.67 μB, respectively. These are more difficult to compare since the lowest temperature reported is not uniform from one complex to another. The ranges of low-temperature magnetic moments for the middle 50% of each ion are more distinct: 1.57−2.11, 0.50−1.10, and 1.00−1.40 μB for U3+, U4+, and U5+, respectively. There is no overlap between the range for U3+ and U4+, and the overlap between U4+ and U5+ is minimal. Hence, low-temperature data, when available, are the most valuable. Moreover, as pointed out in numerous papers on variabletemperature magnetic data, the shape of the curve in a magnetic moment or χT versus temperature plot is often more informative in differentiating oxidation states. The susceptibility of a 5f2 U4+ complex should drop drastically toward a diamagnetic ground state at some low temperature (typically around 50 K), whereas the susceptibility of the half integral spin

2. RESULTS Table 1 contains the room-temperature magnetic moment of each monometallic uranium complex surveyed as well as the moment measured at low temperature (1.8−5 K) when variable-temperature studies were reported. Complexes are named as they are in the original literature, and data are grouped according to the oxidation state assigned by the authors. The formal oxidation state28 assignment by the original authors, which is usually based on other data including spectroscopic, crystallographic, and DFT studies, is maintained in this review. Data are listed in order of increasing roomtemperature magnetic moments for each oxidation state as lowtemperature data are not always available and the lowest temperatures examined are not always the same. Complexes described only on the basis of synthesis and elemental analysis are reported as well as complexes fully characterized by X-ray crystallography and other spectroscopic methods. Magnetic moments not directly given in the text of papers were determined from plots of χT or μ versus temperature. Only monometallic complexes are included in the statistical survey to avoid complications of metal−metal interactions in polymetallic species. However, data on homovalent bimetallic complexes are presented in Table 2 for comparison with data collected on bimetallic species in the future. Figure 1 presents a histogram of the room-temperature magnetic moments for monometallic U3+, U4+, and U5+ complexes to allow visualization of the range of data on complexes of the different uranium ions. Figure 2 presents histograms of the room-temperature magnetic moments for each oxidation state individually. Figure 3 presents analogous histograms of the low-temperature magnetic moments. Statistical analyses of the data on the monometallic complexes for each oxidation state at both room and low 8873

dx.doi.org/10.1021/cr500242w | Chem. Rev. 2014, 114, 8865−8882

Chemical Reviews

Review

Table 2. Room-Temperature (RT) and Low-Temperature (LT) Magnetic Moments (μB) of Bimetallic Uranium Complexes in Various Formal Oxidation States, Un+, and Formal Coordination Number (CN) Determined by Various Methodsa oxidation state

compound t

(μ-toluene)U2(N[ Bu]Ar)4 (NNfc)2U2(μ-η6:η6-C7H8) {[(Me3Si)2N][C5Me5]U}2(μ-η6:η6-C6H6) [Li(THF)4]2{U2[(−CH2−)5]4-calix[4]tetrapyrrole}[μ-I] [(C5Me5)2U]2(μ-η6:η6-C6H6) [{(DtbpO)2U}2(η6-η6-C6H6) {[(SiMe3)2N]2U}2(η6-η6-C6H6) [U(OSi(OtBu)3)2(μ-OSi(OtBu)3)]2 [{U(NN′3)}2μ2-η2:η2-N2)] {U[N(Me3Si)2]2}2[μ-N(H)(2,4,6-Me3C6H2)]2 RbU2Cl7 [(U(BIPMTMSH)(I))2(μ-η6:η6-C6H5CH3)] [{((AdArO)3N)U}2(μ-S2)2] [(NNfc)U]2(μ-NPh)2 [UF3(H2O)(C2O4)0.5]2 [{U(TrenTMS)}2(μ-O)] {[K(THF)]3[K(THF)2][U(CH2C6H5)6]2} [K2{U(OSi(OtBu)3)3}2(μ-η6:η6-C7H8)] (DtbpO)3UOCCOU(ODtbp)3 [{((AdArO)3N)U}2(μ-η3: η3-Se4)] [Cp′2U(OCH3)]2PH [U(μ-bis-menaphthquinolen)]2 [{U(TrenTMS)(THF)}2(μ-Cl)][BArf4] [(C5H4Me)3U]2[[μ-η1:η2-PhNCO]] [U(μ-NR)(Cl)2(THF)2]2 [R = 2-tBuC6H4 ] {[tBuNON]UCl2}2 [U(μ-NR)(Cl)2(THF)2]2 [R = Dipp] [U2(cyclo-salophen)(py)4] [{((AdArO)3N)U}2(μ-Se2)(μ-DME)] [U2(cyclo-salophen)(THF)4] [(N(SiMe3)2)3U]2(μ-O) (Mes2(p-OMePh)corrole)2U2(μ-Cl)2(DME)2 [{U(TrenTMS)(μ-I)}2] [C2N2H10][U2F6(HPO3)2] [{((AdArO)3N)U(THF)}2(μ-η2: η2-Se4)] [{(MeC5H4)3U}2(μ-Se)] [C4N2H12][U2F6(HPO3)2] [{(MeC5H4)3U}2(μ-PhNCO)] [{(MeC5H4)3U}2(μ-S] [Na(DME)2(TMEDA)][(N(SiMe3)2)2U(μ-N)(CH2SiMe2N(SiMe3))U(N (SiMe3)2)2] [{(MeC5H4)3U}2(μ-CS2)] [{(MeC5H4)3U}2(μ-Te)] [U(BIPMTMS)(Cl)(μ-Cl){OC(Ph)(But)}]2 [{U(NN′3)}2(μ-Cl)] (C5H14N2)2U2F12·2H2O [(NN′3)2U2(p-DEB)] [(NN′3)2U2(m-DEB)] [{((ArO)3tacn)U}2(μ-O)] (C2H10N2)U2F10 Te{U[N(Me3Si)2]3}2 [(NN′3)2U2(p-DEB)(THF)] {U[N(Me3Si)2]2}2[μ-N(p-tolyl)]2 [(C4N2H12)2(U2F12)·H2O] (H3N(CH2)4NH3)U2F10·2H2O [(C5N2H14)2(U2F12) ·2H2O] [(C5N2H14)2(H3O)(U2F11)] (H3N(CH2)6NH3)U2F10·2H2O (H3N(CH2)3NH3)U2F10·2H2O

+3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +3 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 8874

CNb method 5 5 7 8 9 5 5 5 5

7 8 4 5 6 6 4 7 8 6 6 10 6 6 6 8 7 8 4 8 6 7 10 10 10 4 10 10 7 5 5 5 7 4 6 4

RT μ (μB)

S S E S E E E S E S S S S S S E S S E S E E E S S S S E S E S S E S S S S S S S

1.5 1.8 1.8 1.99 2.1 2.7 2.7 2.78 3.22 3.53 3.74 3.50§ 1.65 1.9 2.04 2.09 2.11 2.23 2.3 2.30 2.42 2.44 2.48 2.53 2.58 2.63 2.65 2.68 2.69 2.70 2.71 2.7† 2.74 2.75 2.82 2.85 2.85 2.87 2.93 2.93

S S S E S S S S S S S S S S S S S S

3.01 3.02 3.03 3.08 3.09 3.15 3.17 3.22 3.24 3.28 3.34 3.34 3.35 3.47 3.59 3.72 3.94 4.00

LT μ (μB) (temp, K) 0.25 (5) 0.74 (5) 0.55 (2)

2.17 (1.8) 0.26 (2) 0.6† (5) 0.2† (5) 0.34 (2) 0.4† (2) 0.39 (2)

0.6† (2) 0.81 (2) 0.63 (2) 0.30 (2) 0.94 (4) 0.65† (2) 0.6† (2) 0.33 (2) 0.6† (2)

1.1† (2)

0.33 (1.8 K)

0.7 (5)

ref 66 193 194 195 194 196 196 15 60 3 3 85 197 198 199 91 25 15 69 197 200 201 91 202 203 129 203 204 197 204 164 205 91 206 197 207 206 207 207 208 207 207 95 209 3 93 93 147 3 3 93 3 3 3 3 3 3 3

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Table 2. continued oxidation state

compound (Cp3U)2O [{U(BIPMTMS)(μ-I)(I)}2] [U(NN′3)]2(μ-O) (Cp3U)2S [{U(BIPMTMS)(Cl)(μ-Cl)(THF)}2] [{HC(SiMe2NAr′)3}U(Cl)(μ-Cl)U(THF)2-{(Ar′NSiMe2)3CH}] [U(NEt2)4]2 [(BIPMTMS)U(Cl)(μ-Cl)3(Cl)U(BIPMTMSH)] [Na(DME)3]2[{((AdArO)3N)U}2(μ-S)2] Na[(μ-N)(U(N[t-Bu]Ar)3)2] [U{N(CH2CH2NSiMe3)(CH2CH2NSiMe2CH2)2}U{N(CH2CH2NSiMe3)}] [N(n-Bu)4][(μ-N)(U(N[t-Bu]Ar)3)2] {((AdArO)3N)U}2(μ-η2:η1-1,2-(CH)2-cyclohexane) [Na(DME)3]2[{((AdArO)3N)U}2(μ-Se)2] {((AdArO)3N)U2(μ-η2(C1):η1(C4)-2-nBu-1,3-octadiene) {((AdArO)3N)U}2(μ-η2(C4):η1(C1)-1,3-di(p-tBu-phenyl)butadiene)) {((AdArO)3N)U}2(μ-η2:η2-1,2-(CH)2-cyclopentane) [{((t‑BuArO)3mes)U}2(μ-κ2:κ2-CO3)] [{((AdArO)3N)U}2(μ-O)] [{((AdArO)3N)U}2(μ-Se)] [Na(DME)3]2[{((AdArO)3N)U}2(μ-Te)2] [((Neop,MeArO)3tacn)U]2(μ-O) [{((AdArO)3N)U}2(μ-S)] [{((AdArO)3N)U}2(μ-η1:κ2-CO3)] [U{N(CH2CH2NSiMe3)2(μ-CH2CH2NCN)}{N(SiMe3)2}]2 [((Neop,MeArO)3tacn)U]2(μ-CO3) [{U(BIPMTMSH)(Cl)2(μ-Cl)}2] [{((t‑BuArO)3tacn)U}2(μ-Se)] [{U(TrenDMSB)}2(μ-η1:η1-OCHCO)] [{((t‑BuArO)3tacn)U}2(μ-S)] {[{[(−CH2−)5]4-calix[4]tetrapyrrole}-UK(THF)3]2(μ-O)}·2THF [U(OSi(OtBu)3)3]2(μ-C7H8] [(R3SiOUO)2(LSiMe3)] {U-μ-Cl[N(SiMe3)2]2[N(SiMe3)]}2 [(MeC5H4)3U]2[μ-1,4-N2C6H4] [(MeC5H4)3U]2[μ-1,3-N2C6H4] [K{U(OSi(OtBu)3)3}2(μ-η6:η6-C7H8)] [{U(μ-N)(μ-Na)(TrenTIPS)}2] [{U(TsXy)}2(μ-η6:η6-C6H5Me)] [U2Cl9(Ph3As)]Cl [{((AdArO)3N)U}2(μ-O)2] [(μ-N)(U(N[t-Bu]Ar)3)2][B(ArF)4] [{U(TsTol)}2(μ-η6:η6-C6H5Me)]

+4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +4 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5 +5

CNb method 10 6 5 10 7 6 4 7 6 4 6 4 6 6 6 6 7 8 7 7 6 7 7 6 6 8 7 7 5 7 5 6 7 5 10 10 6 5 6 7 4 6

G S E G S E S S S E E E S S S S S S S S S S S S E S E S S S G S S G S S S S S G S E S

RT μ (μB) 2.17§ 2.3§† 2.55§ 2.64§ 2.7§† 2.79§ 2.81§ 3.1§† 3.2§† 3.22§ 3.23§ 3.23§ 3.3§† 3.4§† 3.4§† 3.4§† 3.5§† 3.49§ 3.5§ 3.5§† 3.5§† 3.52§ 3.6§† 3.64§ 3.74§ 3.75§ 3.82§ 3.8§† 4.00§ 4.0§† 5.17§ 1.35 1.53 1.54 2.08 2.12 2.13 2.26 2.40 3.40§ 2.2§† 2.86§ 3.32§

LT μ (μB) (temp, K) 0.63 (4.2) 0.2† (1.8) 0.58 (4.2) 0.3† (1.8)

0.7† (1.8) 0.4† (2)

0.4† (2) 0.4† (2) 0.5† (2) 0.5† (2) 0.5† (2) 0.61 (5) 0.6 (5) 0.5† (2) 0.5† (2) 0.73 (2) 0.6† (2) 0.93 (5) 0.71 (2) 0.7† (2) 0.69 (1.8) 1.1† (2) 0.31 (2)

1.30 (5) 0.97 (2) 0.8† (1.8) 0.59 (1.8) 0.5† (2) 0.88 (1.8)

ref 110 85 47 110 85 112 210 85 211 212 115 212 213 211 213 213 213 58 58 211 211 36 211 58 214 36 85 211 20 211 72 15 215 171 180 180 15 64 216 182 211 212 217

E = Evans method; F = Faraday method; G = Gouy balance; S = SQUID; V = VSM. Values determined from graphs of χT or μ vs temperature are denoted with a † superscript. Values reported without specifying if per uranium metal or per formula unit are denoted with a § superscript. bFormal coordination number for inorganic salts given when available in the literature.192 a

The medians of the two populations were within 0.1 μB of each other for each ion. For the U5+ ion, however, a significant difference was present between the solid and the solution state room-temperature moments. The median solution state value was 1.75 μB vs a solid state value of 2.18 μB, a difference nearly four times that seen for the other ions. It is unclear what could cause this difference, and it may be a statistical artifact from unusually large U5+ values reported in some solid state measurements (cf. 3.10,185 3.70,191 3.77182 μB) and the small sample size (n = 13) for solution state U5+ ion measurements. It should also be noted that in the rare instances in which both solid state and solution state room-temperature magnetic moments are reported, across all oxidation states the magnetic

systems, 5f 3 U3+ and 5f 1 U5+, should go to nonzero values at low temperature.11,13,15,88,92 At the suggestion of the referees, three representative variable-temperature plots for complexes of U3+, U4+, and U5+ are shown in Figure 4. The results of Meyer and co-workers11 on a series of related (AdArO)3tacn complexes are used to illustrate the relative shape and slope of the curves found in typical variable-temperature plots for the three uranium ions. Data were examined further to see if other trends could be discerned. Comparison of the room-temperature magnetic moments determined in the solid state (SQUID, VMS, Gouy balance) versus solution state (Evans method) revealed no significant difference for either the U3+ or the U4+ complexes. 8875

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Figure 1. Histogram of the uranium magnetic moments for monometallic complexes of the three common oxidation states with U3+, U4+, and U5+ in white, gray, and black, respectively. Histogram bin widths are 0.20 μB.

Figure 3. Low-temperature (1.8−5 K) magnetic moments (μB) of monometallic U3+ (top, green), U4+ (middle, orange), and U5+ (bottom, blue) complexes in μB. Histogram bin widths of 0.20; y axis is not to scale.

Table 3. Statistical Analysis of All Monometallic Uranium Complexes Reported for Room Temperature and Low Temperature (1.8−5 K)

room-temp

low-temp

3+

U U4+ U5+ U3+ U4+ U5+

average

median

std dev218

ql219

qu219

n

3.13 2.77 2.07 1.84 0.84 1.18

3.14 2.79 2.04 1.81 0.69 1.13

0.44 0.39 0.51 0.46 0.54 0.25

2.90 2.50 1.64 1.57 0.50 1.00

3.49 3.08 2.38 2.11 1.10 1.40

103 243 95 33 91 50

moment based on ligand field strength. Variation in magnetic moments is sometimes explained by suggesting that stronger field ligands can quench orbital contributions to magnetism, and this is used as evidence for 5f covalency. Ligand trends are discussed below as a function of metal oxidation state. Data on four simple trivalent uranium halide salts, UX3, are available. The 3.67, 3.7, 3.57, and 3.65 μB values for X = F,82 Cl,80 Br,80 and I,80 respectively, are all considerably higher than the average U3+ value of 3.13 μB, and they do not follow a periodic trend. The common trivalent uranium starting material U[N(SiMe3)2]3 has three reported values: 2.51, 3.07, and 3.354 μB. Comparing the median and most recent value for U[N(SiMe3)2]3 with other simple trivalent homoleptic coordination compounds also fails to give a correlation of

Figure 2. Room-temperature magnetic moments of monometallic U3+ (top, green), U4+ (middle, orange), and U5+ (bottom, blue) complexes in μB. Histogram bin widths of 0.20; y axis is not to scale.

moments from the two methods can deviate by as much as 0.7 μ B , although 0.1−0.3 μ B differences are more typical.17,85,86,97,161,186 The compilation of data contained several series of closely related complexes that allowed inspection of trends in magnetic 8876

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strength since they are equivalent.152 A series of U4+ tacn halide complexes [((AdArO)3tacn)U(X)] (X = Cl, Br, and I) all have measured moments of approximately 2.9 μB,139 thereby showing no significant ligand effects. Tris(2-aminoethyl)amine (tren)-based tetravalent uranium complexes, [N(CH2CH2NR)3]U(X), show inconsistency despite only slight modifications to the R groups of the tren ligands: R = SiMe2But,113 X = Cl (3.19 μB), Br (3.14 μB), and I (3.08 μB); R = SiiPr3,17,64 X = F (2.4 μB), Cl (2.01 μB), and I (2.4 μB); R = SiMe3,130,135 X = Cl (2.8 μB) and I (2.79 μB). On the other hand, the U[N(SiMe3)2]3X complexes with X = Cl (2.8 μB),117 F (2.91 μB),3 BH4 (2.6 μB),117 Me (2.7 μB),117 H (2.6 μB),63 and N(SiMe3)2 (2.94 μB)153 have more variation, but the values do not follow ligand field strength. However, several pairs of U4+ complexes do have lower magnetic moments for the member with the stronger ligand field: 3.32 and 3.11 μB for [C5H3(CMe3)2]2UCl2 and [C5H3(CMe3)2]2UF2,3 2.65 and 2.45 μB for (C5H5)3USH and (C5H5)3UOH,101 and 2.9 and 2.7 μB for Tp*UI2(THF) and Tp*UI2(2,2′-bpy),45 respectively. Unlike the simple trivalent and tetravalent uranium halides, which all have magnetic moments higher than the average for the oxidation state, the pentavalent halides, UX5, have magnetic moments that bracket the 2.07 μB average for U5+: 1.26 and 2.37 μB for UCl5169 and α-UF5,189 respectively. Again, these compounds do not show a trend of lower moment with increased ligand field strength; the example higher in the spectrochemical series of ligand field strengths has the higher moment. The family of pentavalent complexes [((AdArO)3tacn)U(NSiMe3)], [((t‑BuArO)3tacn)U(NSiMe3)], [((DiaArO)3tacn)U(NSiMe3)], [((AdArO)3tacn)U(NMes)], and [((t‑BuArO)3tacn)U(NMes)] has a wide range of roomtemperature magnetic moments of 2.0,14 2.34,167 2.55,13 2.40,181 and 2.35 μB,181 respectively, and the values are not regular in terms of either the tacn ligand or the imido ligand. An extensive series of pentavalent uranium complexes of the formula (C5Me5)2U(N-2,6-iPr2-C6H3)(X) where X = OTf (2.65 μB), SPh (2.48 μB), OPh (2.38 μB), NPh2 (2.27 μB), CCPh (2.22 μB), and NCPh2 (2.03 μB) shows magnetic moments that decrease with increasing ligand field strength.183 However, the halide series of the same parent compound (C5Me5)2U(N-2,6-iPr2-C6H3)(X) where X = F (2.22 μB), Cl (2.42 μB), Br (2.42 μB), and I (2.34 μB) does not show a periodic trend based on ligand.188 Hence, currently there is no evidence of consistent correlation between ligand field strength and magnetic moment for any of the uranium oxidation states.

Figure 4. Examples of μB versus temperature plots for a series of related (AdArO)3tacn complexes from Meyer and co-workers:11 (A) U3+ complexes [((t‑BuArO)3tacn)U] (1), [((AdArO)3tacn)U] (1-Ad), and [(( t‑Bu ArO) 3 tacn)U(NCCMe 3 ] (4); (B) U 4+ complexes [((AdArO)3tacn)U(N3)] (U(IV)-N3), [((AdArO)3tacn)U(Cl)] (U(IV)-Cl), [((AdArO)3tacn)U(Br)] (U(IV)-Br), and [((AdArO)3tacn)U(I)] (U(IV)-I); (C) U5+ complex [((AdArO)3tacn)U(NSi(CH3)3)]. Reprinted with permission from Chemical Communications 2006, 1353.

moment versus ligand field strength: U[N(SiMe3)2]3 (3.07 μB),39 U[CH(SiMe3)2]3 (3.0 μB),57 and U(OC6H3−But2-2,6)3 (3.3 μB).69 Comparison of the magnetic moments of the trivalent cyclopentadienyl series (C5Me5)3U (3.1 μB),62 (C5H4SiMe3)3U (3.28 μB),26 [C5H3(SiMe3)2]3U (3.32 μB),3 and [C5H3(CMe3)2]3U (3.37 μB)3 reveals there is not a large variation as a function of ligand. Likewise, the 2.6, 2.5, and 2.6 μB37 values for the U3+ hydrotris(3,5-dimethylpyrazolyl)borate (Tp*) complexes, Tp*2U(CH3), Tp*2U(CH2Ph), and Tp*2U(CH2SiMe3) are similar. In contrast, a significant variation in magnetic moments is found for the tacn series [((t‑BuArO)3tacn)U] (2.92 μB),11 [((AdArO)3tacn)U] (2.83 μ B ), 1 1 [ ( ( N e o p , M e A rO ) 3 t ac n )U ] ( 2 .4 9 μ B ), 3 6 a n d [((DiaArO)3tacn)U] (3.04 μB)13 even though the differences in ligands are distant from the metal center. A mixed picture of ligand effects is also found with U4+ complexes. The salts, UF4 and UCl4, both have similar measured moments of 3.29 and 3.30 μB, respectively, which like the trivalent analogs are significantly higher than the U4+ average (2.77 μB) and show no correlation with ligand field

4. CONCLUSION This study has examined the actual magnetic moment data in the literature to evaluate statements in the literature correlating magnetism with composition of uranium complexes. A survey of the magnetic moment data reported on over 500 uranium complexes shows that there is significant overlap between measured values of complexes of U3+, U4+, and U5+. Since each ion has a large range of values and since there is so much overlap between the ranges, it is difficult to use roomtemperature values to assign oxidation states based on comparisons with other complexes. Since the overlap observed in the ranges of the low-temperature magnetic moments of U3+, U4+, and U5+ is smaller, low-temperature (1.8−5.0 K) values are more useful in assigning oxidation state. Ultimately, the shape of the μ versus T curves and the tendency of μ to approach zero (U4+) or not (U3+ and U5+) are the most valuable magnetic indicators of oxidation state. These conclusions can now be 8877

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made on the basis of all the magnetic data on uranium complexes currently in the literature. This survey also shows that there is no simple correlation of magnetic moment and ligand field strength. This compilation will also allow future data to be evaluated in terms of how typical a newly determined magnetic moment is for a given type of complex. If further correlations can be made, this compilation should provide the basis for discerning them as more data are collected.

different from his training and experience, namely, the chemistry of the rare earth metals and actinides, with the central thesis that the special properties of these metals should lead to unique chemistry. After receiving tenure at the University of Chicago in 1982, he was recruited to the University of California, Irvine, where he has been a professor since 1983.

ACKNOWLEDGMENTS We thank the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences of the Department of Energy (DE-SC0004739) for support and Lindsay Kindra for assistance with graphical analysis and helpful discussion.

AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

LIST OF ABBREVIATIONS 18C6 18-crown-6 ether 12C4 12-crown-4 ether AA acetamide AAN acetanilide AcA acrylamide dipp ap 4,6-di-tert-butyl-2-[(2,6-diisopropylphenyl)amido]phenolate B15C5 benzo-15-crown-5 ether bac benzoylacetonato BAM benzamide BAN benzanilide BcMe dihydrobis(methylimidazolyl)borate BpMe dihydrobis(methypyrazolyl)borate bpy; bipy 2,2′-bipyridine BIPMDipp C(PPh2NDipp)2}2; Dipp = C6H3-2,6-iPr2 BIPMmes C(PPh2NMes)2}2; Mes = C6H2-2,4,6-Me3 BIPMTMS C(PPh2NSiMe3)2 BuL γ-butyrolactam CaL ε-caprolactam COT C8H8 Cp C5H5 Cp* C5Me5 Cp′ C5H4SiMe3 Cp″ 1,3-(Me3Si)2C5H3 Cp‡ 1,3-(Me3C)2C5H3 CpP 1-(7,7-dimethylbenzyl)cyclopentadienide cupf cupferronato Mes DABMe ArN=C(Me)C(Me)=NAr; Ar = 2,4,6-trimethylphenyl dbm dibenzoylmethanato DEB diethynylbenzene DEA N,N′-diethylacetamide dipp C6H3-2,6-iPr2 DMA N,N′-dimethylacetamide DMBA N,N′-dimethylbenzmide DMF N,N′-dimethylformamide dmpe 1,2-bis(dimethylphosphino)ethane DPA N,N′-diphenylacetamide DPF N,N′-diphenylformamide dpp-BIAN 1 , 2 - b i s ( 2 , 6 - d i i s o p r o p y l p h e n y l i m i n o ) acenaphthylene EA N-ethylacetamide enbissal ethylenebis(salicylaldimine) gu guanine Hdbabh 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5diene IMC: tetramethylimidazol-2-ylidene

Biographies

Douglas Kindra is a native of Chicago, IL, who graduated in 2010 from Michigan State University with his B.S. degree in Chemistry. In his undergraduate studies he had the privilege to work with both Professors David P. Weliky and James K. McCusker. He is currently pursuing his Ph.D. studies at the University of California, Irvine with Professor William J. Evans, where he is investigating small molecule activation with samarium, uranium, and bismuth organometallic compounds.

William Evans was born in Madison, WI, and raised in Menomonee Falls, WI. He received his B.S. degree from the University of Wisconsin, where he did undergraduate research on pentaboranes with Professor Donald F. Gaines. He obtained his Ph.D. degree from UCLA under the direction of Professor M. Frederick Hawthorne studying metallocarboranes. He did postdoctoral research on transition metal phosphite complexes with the late Professor Earl L. Muetterties at Cornell University. When he began his independent career in 1975 at the University of Chicago, he chose an area of research completely 8878

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Chemical Reviews isq MA MAA MBuL MCaL mcpy MF MFA tBu NON ODtbp ophen OTtbp Oxine PDI Mes PDIMe Pipz Pn* Pz T terpy tfac tmma Tp*; TpMe2 tren TTA Val

Review

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iminosemiquinone N-methylacetamide N-methylacetanilide N-methyl-γ-butyrolactam N-methyl-ε-caprolactam 2-mercaptopyridine N-methylformamide N-methylformanilide [tBuNH(SiMe2)]2O OC6H3-But2-2,6 o-phenanthroline OC6H2-But3-2,4,6 8-hydroxyquinoline pyridine-(diimine) 2,6-((Mes)N=CMe)2-C5H3N; Mes = C6H2-2,4,6Me3 piperazine C14H18 pyrazolate tropolono 2,2′:6′,2″-terpyridine trifluoroacetylacetonato N,N,N′,N′-tetramethylmalonamide hydrotris(3,5-dimethylpyrazolyl)borate) tris(2-aminoethyl)amine thenoyltrifluoroacetonato δ-valerolactam

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σ=

∑ [(xi − x ̅ )2 /(n − 1)]1/2 i=1

(219) The upper quartile (qu) has the property that 75% of the observations fall short of qu and 25% exceed it. The lower quartile (ql) has the analogous property in that 75% of the observations exceed ql and 25% fall short.

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