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Effect of the Distant Substituent to Slow Magnetic Relaxation of Pentacoordinate Fe(III) Complexes Cyril Rajnaḱ , Jań Titiš, Jań Moncol’, Dušan Valigura, and Roman Bocǎ * Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c00647

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ABSTRACT: Pentacoordinate Fe(III) complexes [Fe(LMeO)2X] and [Fe(LEtO)2X], X = Cl and Br, show the slow magnetic relaxation that is enhanced by the applied static magnetic field. A substitution of the distant ethoxy group to the methoxy group residing at the phenyl ring of a Schiff base N,O-donor ligand (LMeO vs LEtO) considerably influences the relaxation characteristics. In the chlorido complex [Fe(LMeO)2Cl], the following three slow relaxation channels are recognized as possessing different relaxation times: τLF = 0.47 s, τIF = 13 ms, and τHF = 26 μs at the static field BDC = 0.2 T and T = 1.9 K. In the bromido complex [Fe(LMeO)2Br], only the following two relaxation channels are seen: τLF = 0.30 ms and τHF = 139 μs at BDC = 0.15 T and T = 1.9 K. Due to D > 0, the Orbach relaxation mechanism does not apply, and the temperature dependence of the high-frequency relaxation time can be described by two Raman-like terms.



INTRODUCTION Single-molecule magnets have attracted much attention in the last decades because of their high application potential.1−3 The former period on focusing on the metal clusters of a high nuclearity has been followed by investigating mononuclear species that exhibit a slow magnetic relaxation as a prerequisite of single ion magnetism (SIM). Though Co(II) mononuclear complexes have been investigated to a great extent, examples of SIM can be found also among V(IV), Cr(III), Cr(II), Cr(I), Mn(IV), Mn(III), Mn(II), Fe(III), Fe(II), Fe(I), Co(II), Co(I), Ni(III), Ni(II), Ni(I), and Cu(II) complexes.4−32 Mononuclear iron complexes exhibiting a slow magnetic relaxation (SMR) represent a rather small family. It covers a few Fe(III), Fe(II), and Fe(I) systems of different geometries ranging from two- to pentacoordination.33−37 The high-spin Fe(III) complexes always possess the orbitally nondegenerate ground state 6A, with an additional subscript depending on the actual geometry of the coordination polyhedron (e.g., 6A1′ and 6 A1 for trigonal bipyramidal and square pyramidal, respectively). For the S = 5/2 spin systems, the axial zero-field splitting D is small, which implies that the barrier to the reversal of the spin, Ueff = |D|(S2 − 1/4), is also small. Small D values are confirmed by magnetization and DC susceptibility data as well as ab initio CASSCF/NEVPT2 calculations. Despite to this fact, slow magnetic relaxation was detected in the pentacoordinate complex [FeIII(LEtO)2Cl] (hereafter 2), where LEtO is the bidentate Schiff base N,O-donor ligand with an ethoxy group situated at position 6 of the phenyl ring.38 We will show hereafter that the alteration of this distant ethoxy © XXXX American Chemical Society

group to the methoxy substituent is no longer innocent for the dynamic (AC) magnetic susceptibility such that the complex under study, [FeIII(LMeO)2Cl] (1), shows a fairly different relaxation behavior. Additionally, the bromido analogues [FeIII(LMeO)2Br] (3) and [FeIII(LEtO)2Br] (4) were prepared, characterized, and subjected to magnetometry and susceptometry experiments.



EXPERIMENTAL SECTION

Synthetic Procedures. For the preparation of complex [FeIII(LMeO)2Cl], 1, a reaction mixture was formed by combining 3methoxysalicylaldehyde (0.63 g, 4.12 mmol), 2-aminomethylfuran (0.36 cm3, 4.12 mmol), and 20 cm3 of MeOH. It was stirred for 1 h at 70 °C, with a color change to yellow. FeCl3 (0.33 g, 2.06 mmol) was added once following the previous steps. After 4 days, dark blackgreen crystals were isolated by filtration from the mother liquid with a yield of 12%. The bromido analogues 3 and 4 were prepared in a similar way. A CHNS analyzer (Thermo Scientific, Flash 2000) was used for the elemental analysis. For FT-IR (ATR) spectra, freshly grown crystals were used. The UV−vis absorption spectra were measured in the range 190−1100 nm at room temperature in the Nujol suspension using an electron spectrometer equipped with a DAD detector (Analytical Jena, Specord 250 Plus). Received: February 29, 2020

A

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X-ray Data Collection and Structure Determination. A Stoe StadiVari diffractometer with a PILATUS3R 300 K HPAD detector was used for the data collection and cell refinement of suitable single crystals of 1, 3, and 4. The microfocused X-ray source Xenocs Genix3D Cu HF was used at 100 K. Raw data were corrected for the Lorentz, polarization, and multiscan absorption effects. A chargeflipping method was utilized for the structure solution that was refined anisotropically by least-squares methods. The program packages SUPERFLIP SHELXL (ver. 2018/3), OLEX2, and MERCURY were used for structure determination, refinement, and drawing, respectively.39−42 The positions of the hydrogen atoms were refined using fixed distances from the mother carbon atoms. Characterizations using Hirschfeld surface and fingerprint plots were made through the CrystalExplorer17.5 program.43−47 Transparent surfaces were selected, allowing a clear viewing of the molecules and the crystal interaction environment. Selected crystal data and detailed analysis of the Hirschfeld surface are presented in the Supporting Information. Ab Initio Calculations. The ORCA package ver. 4.1.2 was utilized for the quantum-chemical calculations at the ab initio and DFT levels using the experimental geometry of the studied complexes.48,49 The relativistic effects were recovered by the zero-order regular approximation. The scalar relativistic contracted version of the def2TZVPP functions for the Fe atom and def2-SV(P) for the other elements were used as the basis set. The hybrid PBE0 exchangecorrelation functional was used in the DFT calculation, and the operator of the spin−orbit coupling was expressed via the spin−orbit mean field approach. Zero-field splitting (zfs) was treated using the coupled-perturbed method.50−52 SA-CASSCF (state-average complete active space self-consistent field) wave functions were based on five electrons in the d orbitals of iron, yielding equally weighted 75 doublets, 24 quartets, and 1 sextet. In the next stage, NEVPT2 (the nelectron valence second-order perturbation theory) was applied.53−59 The RI approximation with a decontracted auxiliary basis set and the chain-of-spheres (RIJCOSX) approximation to exact the exchange were utilized. Finally, the zero-field splitting parameters were evaluated through the quasi-degenerate perturbation theory, where a SOMF approximation to the Breit−Pauli operator of the spin−orbit and the theory of the effective Hamiltonian were exploited. SQUID Magnetometry and Susceptometry. DC and AC magnetic data was collected with the SQUID magnetometer (Quantum Design, model MPMS-XL7) using the diamagnetic gelatin cup as a sample holder. The RSO detection mode was used in data acquisition at the magnetic field BDC = 0.1 T. After a correction to the underlying diamagnetism, the susceptibility data were transformed to the effective magnetic moment. The dependence of the magnetization per formula unit at low temperatures was scanned up to BDC = 7 T. The AC susceptibility data were taken at an oscillating field with an amplitude BAC = 0.38 mT by applying various DC field-frequency− temperature regimes.

Article

Figure 1. Structure of Fe(III) complex 1.

there is a number of intermolecular contacts. The 3D Hirshfeld surfaces of 1 mapped over the shape index is drawn in Figure 2.

Figure 2. 3D Hirschfeld surface of 1 plotted over the shape index showing π−π stacking interactions.

The 3D surface mapped over dnorm represents the circular depressions indicative of C−H···O, C−H···Cl, and C−H···π contacts (deep red). Other visible spots in the Hirchfeld surfaces refer to H···H contacts. The bromido complex 3 is a structural analogue of 1, and that of 4 resembles 2 (the same space groups). The SHAPE agreement factor in 3 for SPY is 1.216, and that in 4 for TBPY amounts to 1.082 (Figure 3).



RESULTS Structure Description. Single crystals of 1 reveal the monoclinic system and the space group P21/n. The molecular structure of 1 is shown in Figure 1. The chromophore {FeN2O2Cl} forms a square pyramid (SPY) with an approximate C4v symmetry. The Fe−N bond distances are 2.129 and 2.131 Å, and the Fe−O bond distances are 1.894 and 1.903 Å. The chlorido ligand is situated at the apical position at the distance Fe−Cl of 2.228 Å. The SHAPE agreement factor for SPY is 1.003.60 This is in contrast to the previously characterized analogue [FeIII(LEtO)2Cl], which adopts a tetragonal bipyramidal geometry (TBPY) with the agreement factor of 0.976.38 Detailed structural data are presented in the Supporting Information and can be compared with analogous systems.61 The actual symmetry of 1 is lower than C4v and the electronic ground term that stays orbitally nondegenerate 6A. As expected for the complexes containing the aromatic rings,

Figure 3. Structure of the Fe(III) complexes 3 and 4.

DC Magnetic Data. According to the expectations, the DC magnetic data for 1 match behavior typical for the S = 5/2 spin system (Figure 4). At room temperature, the effective magnetic moment is μeff = 5.53 μB, and it stays nearly constant down to 10 K; on further cooling, it decreases due the zero-field splitting. Again, owing to some zfs, the spin-only value for the magnetization M1 = Mmol/NAμB = 5 is not approached at B = 7.0 T and T = 2.0 K Magnetic susceptibility and magnetization were fitted simultaneously according to the standard model of the zfs (the E-parameter was omitted). The optimization routine converged to geff = 1.91(6), D/hc = +3.7(12) cm−1, the minor B

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magnetic field was set to BDC = 0.20 to 1.20 T. A three set Debye model containing 10 free parameters was used in the AC data fitting (Supporting Information). The experimental points are displayed in Figure 5 along with the lines generated for the set of optimized parameters.

Figure 4. Effective magnetic moment, molar susceptibility, and the magnetization per formula unit for 1. Lines are fitted.

correction to the molecular field (zj)/hc = +0.031 cm−1, and the overall temperature-independent magnetism χTIM = −10 × 10−9 m3 mol−1 (the sign reversal of the D parameter gave almost the same results, and the negative χTIM value compensates for uncertainties in estimating the corrections for the underlying diamagnetism and an eventual temperatureindependent paramagnetism.) DC magnetic data for 3 and 4 are analogous; they are deposited in the Supporting Information. A subnormal g value can reflect the presence of chain-like weak exchange interactions via the π−π stacking of the aromatic rings. Results of Ab Initio Calculations. The CASSCF and NEVPT2 calculations gave the following parameters of the zfs Hamiltonian for 1: g = {2.0015, 2.0015, 2.0017}, D/hc = +1.06 cm−1, and E/D = 0.074. Main contributions to the zfs arise from the lowest sextet-to-quartet excitations. The low-lying quartet term appears 13669 cm−1 above the ground sextet and its contribution is D0 = +2.6 cm−1. The higher excitations contribute with smaller negative values and thus partially compensate the former D0 value. It is also worth mentioning the existence of high-energy excitations above 30000 cm−1 with significant but compensated contributions. The lowest Kramers doublets (spin−orbit multiplets) lie at zero, 2D ∼ 2.2, and 6D ∼ 6.4 cm−1. For comparison, DFT calculations yielded D/hc = +1.26 cm−1 and E/D = 0.15, supporting the NEVPT2 results. For 3 and 4, the NEVPT2 calculation gave very similar results (g = {2.0015, 2.0015, 2.0018}, D/hc = +1.53 cm−1, and E/D = 0.047 for 3 and g = {2.0013, 2.0014, 2.0016}, D/hc = +1.54 cm−1, and E/D = 0.213 for 4). The significant similarity to complex 1 was also confirmed by the calculated magnetic functions (Supporting Information). Slightly different results were provided by DFT calculations (D/hc = +2.5 cm−1 for 3 and D/hc = +2.9 cm−1 for 4). In 3 and 4, the dominant spin−orbit coupling contribution to D originates from doubly occupied to singly occupied molecular orbitals, as presented in the Supporting Information. This is in contrast to complex 1. Notice that Ueff is absent, owing to the D > 0 barrier to spin reversal. Differences in the ab initio results relative to the magnetometric determination can originate in a different environment, such as a single molecule in vacuo vs the solid state where some intermolecular interactions also assist. An additional effect may originate in the spin admixed states typical for pentacoordinate Fe(III) complexes; this is naturally involved in the ab initio calculations but omitted in the zfs model. AC Susceptibility. Dynamic susceptibility measurements were taken at low temperatures for 22 frequencies of the oscillating field between f = 0.1 and 1500 Hz; the external

Figure 5. Components of the AC susceptibility for 1 at T = 1.9 K and a set of external magnetic fields as a function of the frequency. Lines are the results of the Debye model with three components.

The absorption components (the out-of-phase susceptibility) show a well-developed peak with a maximum at f ″ ∼ 0.40 Hz, yielding the low-frequency relaxation time τ(LF) = 1/ (2πf″) ∼ 0.40 s. At the higher frequency, an intermediatefrequency (IF) peak is also recognized along with the onset of the high-frequency (HF) peak lying above f > 1500 Hz. The low-frequency relaxation channel is supported by the external magnetic field until BDC = 0.80 T when the mole fraction of the slowly relaxing species adopts a value of x(LF) = 0.51; then, the opposite field effect is seen. The frequency dependence of the AC susceptibility for a number of temperatures was analyzed for two external fields (Figure 6). At T = 1.9 K, the LF peak at the absorption

Figure 6. Components of the AC susceptibility for 1 at BDC = 0.20 and 0.60 T and a set of temperatures as a function of the frequency. Lines are the results of the Debye model with three or two relaxation modes. C

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component is well developed. A shoulder at higher frequencies refers to the IF mode, and only the onset of the HF peak is seen below 1500 Hz. On heating, the LF peak tends to disappear; however, its position is nearly constant. The IF peak attenuates above T > 2.5 K so that the data fitting proceeds according to the two set Debye model. At BDC = 0.60 T, the LF peak is better developed and well fitted; again, it holds its position at f ″ ∼ 0.25 Hz so that τ(LF) ∼ 0.64 s. The IF and HF peaks are fitted less accurately, mainly due to a number of “bad points”. At higher DC fields, the fluctuations in the superconducting magnet cause a loss of accuracy during the accumulation of AC susceptibility data for which only a small amplitude BAC = 0.38 mT is available. Especially, the data above T > 3.5 K do not allow for a reliable fitting of the IF and HF channels. The Argand diagram and the Arrhenius-like plot are drawn in the left and right panels of Figure 7, respectively. With D >

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Figure 8. Analysis of the relaxation time for the high-frequency relaxation mode of 1. Dashed lines are linearized LT and HT edges, and solid lines are fitted via eq 1.

The bromido analogues of 1 and 2, i.e. 3 and 4, respectively, display different AC susceptibility profiles; for BDC = 0.15− 0.20 T, the high-frequency peaks are positioned at f ″ ∼ 1000 Hz, and with an increasing field they are moved to even higher frequencies (Supporting Information). The low-frequency peaks are oddly visible and do not show a definite field effect.



DISCUSSION The relaxation properties of the mononuclear transition metal complexes are somehow different from the behavior of the former class of polynuclear systems discovered and classified as single-molecule magnets. Just the class of mononuclear Co(II) complexes, owing to the accumulation of a huge number of data, allows some generalization as follows: (i) there are more than a single relaxation channel, and two or three are typical. (ii) The applied static field (e.g., BDC = 0.6 T) strongly supports the low-frequency relaxation channel (around fAC ∼ 1 Hz). (iii) The temperature evolution of the LF mode does not follow traditional relaxation mechanisms. (iv) On heating, the low-frequency and intermediate-frequency relaxation channels are attenuated more rapidly than the high-frequency one. (v) The high-frequency relaxation time used to be analyzed by considering the Orbach, direct, Raman, and quantum tunneling processes. (vi) The retrieved Ueff value does not correlate with the zero-field splitting parameter D. (vii) Slow magnetic relaxation is also detected when the D-parameter is positive, small, negligible, or absent for S = 1/2 spin systems. (viii) In some cases, a reciprocating thermal behavior is detected at low temperatures when the relaxation time is shortened on further cooling. (ix) As a rule, the slow magnetic relaxation in mononuclear complexes manifests itself under an external field; however, examples of SIMs in the zero field are also known. In the series of [Co(PPh3)2X2] complexes where X = Cl, Br, I, and [Co(AsPh3)2I2], it was observed that the relaxation time increases with the proton number of the halido ligand and that of the donor atom P/As; this was interpreted as an effect of the spin−orbit coupling that rises |D| and consequently Ueff.62−64 On the contrary, for [Co(biq)X2] complexes (biq = 2,2′biquinoline) the relaxation time is shortened along the series of halide coligands.65 In the series [Co(bcp)X2] (bcp = 4,7diphenyl-2,9-dimethyl-1,10-phenantroline), only the chlorido complex shows SMR; the bromido and iodido complexes do not show SMR, owing to the antiferromagnetic exchange coupling.66 In the series of [Co(dmphen)X2] complexes (dmphen = 2,9-dimethyl-1,10-phenantroline), only bromido and iodido complexes display manifold SMR, whereas the chlorido complex does not show SMR due to the antiferromagnetic exchange interaction.67 These examples point to the complexity of the relaxation processes in SIMs.

Figure 7. Argand diagrams (left) and Arrhenius plots (right) for 1. Solid lines are fitted, and dashed lines are a guide for the eyes.

0, the Orbach process is discriminated because of a lack of the barrier to spin reversal. Therefore, two Raman-like processes were probed via eqn 1 τ −1 = CT n + C′T l

(1)

where n = 7−9 is expected for the net Raman process, l = 1 refers to the direct relaxation process, and l ∼ 2 is typical for the phonon bottleneck process. Two linearized forms lnτ = b[0] + b[1]·lnT = −lnC − n·lnT were used in estimating trial parameters for the optimization routine, which finally gave C = 10.4 K−n s−1, n = 9.77, C′ = 9.7 × 105 K−l s−1, and l = 2.16. This analysis is envisaged in Figure 8. Relaxation times for complexes 2−4 are analyzed in Figure S20. A comparison of 1 with 2 shows that in 2 the high-frequency peak is caught below the hardware limit at ca. f ″ ∼ 520 Hz (τHF = 232 μs) at BDC = 0.15 T and T = 1.9 K. Its thermal development can be analyzed in terms of the eq 1. The lowfrequency relaxation times at these conditions are τ(LF) = 500−600 ms. D

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absorption component is seen between frequencies f = 10 and 1000 Hz. The above three reports on hexa- and tricoordinate Fe(III) complexes differ from the present communication for pentacoordinate systems.26,37,70 They possess D < 0 and confirm a linear dependence lnτ vs T−1 in a broad temperature interval, referring to the Orbach process only. This is in contrast to curved dependences observed for complexes 1−4 recovered by one or two Raman-like terms. The absence of the barrier to spin reversal owing to D > 0 means that the contributions to the spin−lattice relaxation originate mostly in the coupling with phonons of sufficiently low energy, although the spin−spin interaction also can be in the play. Just the acoustic phonons of an intramolecular origin can play a role in determining the relaxation mechanism for magnetically isolated spins at sufficiently high applied fields.71,72 The first-principle calculations allow the determination of individual contributions, such as the Zeeman term, the hyperfine term, and the spin−spin dipolar term, to the overall relaxation process. Differences in the space group and different intermolecular contacts of π−π character can manifest themselves in the alteration of the phonon spectrum and consequently the spin−lattice relaxation.

It is worth noting that mononuclear complexes studied as SIMs often contain aromatic rings that cause manifold intermolecular contacts, e.g. π−π or π−H interactions. They are responsible for forming dimers, oligomers, chains, and 2D or 3D supramolecular networks in the solid state. In such a case, especially at low temperatures, the individual centers feel their neighbors via the weak exchange interactions. This kind of interaction is supported by the magnetic field such that at low temperatures and higher fields some aggregates of a variable size are formed. Such a nucleation can be the raison d’être for the second or third slower relaxation channel in those SIMs. The low-frequency relaxation mode can be suppressed by the dissolution of the parent compound in a diamagnetic Zn(II) matrix.68,69 The present series of Fe(III) complexes also shows the complexity of the slow magnetic relaxation. Even a small modification outside the donor set can manifest itself in an alteration of the relaxation mechanism. The chlorido complex 1 (P21/n, SPY = 1.003) shows structural similarities with its bromido analogue 3 (P21/n, SPY = 1.216). There is π−π stacking between the adjacent molecular units, leading to a chain-like structure (Figure S7) with short C−C contacts of 3.43 and 3.40 Å. Notice the positioning of the furanyl rings that are perpendicular to the base of the square pyramid (angle N−C−C ∼ 111 deg). The analysis of the DC susceptibility reveals some (overall) intermolecular ferromagnetic exchange coupling (zj)/hc = +0.031 cm−1 in 1 that is absent in 3. In 1, the absorption component of the AC susceptibility referring to the HF relaxation channel shows only the onset of the peak until the hardware limit; at BDC = 0.20 T and T = 1.9 K, the estimate of the relaxation time is τ(HF) ∼ 26 μs. In 3, the HF peak is well seen at ca. f ∼ 1000 Hz, which yields τ(HF) = 139 μs at BDC = 0.15 T and T = 1.9 K. The AC susceptibility data for 3 allow the analysis of the HF relaxation time in terms of the double Raman process with C = 107 K−n s−1, n = 5.52, C′ = 8.1 × 104 K−l s−1, and l = 2.30. The chlorido complex 2 (C2/c, TBPY = 0.976) and its bromido analogue 4 (C2/c, TBPY = 1.082) span different point groups than 1 and 3, and their coordination polyhedron resembles the trigonal bipyramid. Additionally, these complexes show π−π interactions of the chain-like character between adjacent molecular units at C−C = 3.38 and 3.40 Å (Figure S7); these, however, are not reflected in the DC susceptibility data, which can be well fitted by omitting the molecular field correction. There are reports on hexacoordinate Fe(III) centers with a highly distorted octahedral geometry incorporated into polyoxometalates. In TBA4H6[Aα-SiW9O34]·2H2O (TBA = tetra-n-butylammonium), the DC magnetic data yielded a negative D/hc = −1.20 cm−1 and g = 1.90, and the analysis of the AC susceptibility revealed Ueff/kB = 9.2 K and τ0 = 8.2 μs.26 The report on TBA7H10[(Aα-XW9O34)2Fe] with heteroatoms X = Ge and Si confirmed a slight magnetic anisotropy, with values of D/hc = −1.26 cm−1, gxy = 1.58, gz = 2.53 and D/hc = −1.22 cm−1, gxy = 1.80, gz = 2.05 for the Ge- and Si-contained cluster, respectively.70 The Orbach process parameters are Ueff/kB = 11.4 (9.2) K and τ0 = 1.3 (3.3) μs. These systems can be considered insulated from the intermolecular contacts such that the presence of only a single out-of-phase susceptibility peak is understandable. The complex [Fe{N(SiMe3)2}3] with a trigonal planar geometry possesses values of D/hc = −1.12 cm−1, Ueff/kB = 9.9 K, and τ0 = 28.5 μs.37 A single peak of the



CONCLUSIONS The pentacoordinate complex [Fe(LMeO)2Cl] containing the {FeIIIN2O2Cl} chromophore displays some similarities with the [Fe(LEtO)2Cl] complex characterized previously. However, there are some differences in the geometry of the coordination sphere, since the SHAPE agreement factor classifies the methoxy-complex as square pyramidal (SPY 1.003) whereas the ethoxy counterpart refers to the trigonal bipyramidal (TBPY 0.986) geometry. The ab initio calculation show the small zfs parameter D/hc = +1.1 cm−1, and the positive value of +3.1 cm−1 was also given in the analysis of the DC magnetic data. The absorption component is silent in the zero static field. With an applied external field, it passes through a maximum and then escapes. There are three relaxation channels in the chlorido systems and only two in the bromido complexes. The static magnetic field strongly supports the low-frequency relaxation mode. The positive D value menas that the Orbach relaxation mechanism does not apply in the present series of pentacoordinate Fe(III) complexes. At BDC = 0.6 T and T = 1.9 K, the relaxation time adopts a value of τ(LF) = 733 ms for 1 and of 618 ms for 2. However, the profile of the frequency dependence of the absorption component of the AC susceptibility is different. The HF channel indicates a much shorter relaxation processes for 1 relative to that of 2. To this end, a small change in the composition of the complex could manifest itself in a visible alteration of the slow relaxation processes in mononuclear pentacoordinate Fe(III) complexes.



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* Supporting Information sı

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00647. Details about the chemicals, synthesis, and physical measurements; IR and UV−vis spectra; X-ray structure determination, XPD patterns; Hirschfeld analysis; magnetic DC and AC data; DFT and ab initio E

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calculations; and details on the AC susceptibility analysis (PDF) Accession Codes

CCDC 1855297 and 1960376−1960377 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/ cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.



AUTHOR INFORMATION

Corresponding Author

Roman Boča − Department of Chemistry, Faculty of Natural Sciences, University of Ss. Cyril and Methodius, 917 01 Trnava, Slovakia; orcid.org/0000-0003-0222-9434; Email: [email protected]

Authors

Cyril Rajnák − Department of Chemistry, Faculty of Natural Sciences, University of Ss. Cyril and Methodius, 917 01 Trnava, Slovakia; orcid.org/0000-0003-2173-6220 Ján Titiš − Department of Chemistry, Faculty of Natural Sciences, University of Ss. Cyril and Methodius, 917 01 Trnava, Slovakia; orcid.org/0000-0003-2530-7722 Ján Moncol’ − Institute of Inorganic Chemistry, FCHPT, Slovak University of Technology, 812 37 Bratislava, Slovakia; orcid.org/0000-0003-2153-9753 Dušan Valigura − Department of Chemistry, Faculty of Natural Sciences, University of Ss. Cyril and Methodius, 917 01 Trnava, Slovakia; orcid.org/0000-0001-7834-7395

Complete contact information is available at: https://pubs.acs.org/10.1021/acs.inorgchem.0c00647 Author Contributions

The manuscript was written through contributions of all authors. Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS Slovak grant agencies (Grants VEGA 1/0919/17, VEGA 1/ 0013/18, APVV 16-0039, and APVV 18-0016) and the project ITMS no. 26240220084 cofounded by the European Regional Development Fund are acknowledged for financial support. Prof. Vladimiŕ Joriḱ (Slovak University of Technology, Bratislava) is acknowledged for the X-ray powder diffraction experiments.



Article

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pubs.acs.org/IC Article Effect of the Distant Substituent to Slow Magnetic Relaxation of Pentacoordinate Fe(III) Complexes Cyril Rajnaḱ , Jań Titis...
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