EPR Spectra Of Crystals Research Articles

Structural and functional characterization of the catalytic domain of a cell-wall anchored bacterial lytic polysaccharide monooxygenase from Streptomyces coelicolor

Bacterial lytic polysaccharide monooxygenases (LPMOs) are known to oxidize the most abundant and recalcitrant polymers in Nature, namely cellulose and chitin. The genome of the model actinomycete Streptomyces coelicolor A3(2) encodes seven putative LPMOs, of which, upon phylogenetic analysis, four group with typical chitin-oxidizing LPMOs, two with typical cellulose-active LPMOs, and one which stands out by being part of a subclade of non-characterized enzymes. The latter enzyme, called ScLPMO10D, and most of the enzymes found in this subclade are unique, not only because of variation in the catalytic domain, but also as their C-terminus contains a cell wall sorting signal (CWSS), which flags the LPMO for covalent anchoring to the cell wall. Here, we have produced a truncated version of ScLPMO10D without the CWSS and determined its crystal structure, EPR spectrum, and various functional properties. While showing several structural and functional features typical for bacterial cellulose active LPMOs, ScLPMO10D is only active on chitin. Comparison with two known chitin-oxidizing LPMOs of different taxa revealed interesting functional differences related to copper reactivity. This study contributes to our understanding of the biological roles of LPMOs and provides a foundation for structural and functional comparison of phylogenetically distant LPMOs with similar substrate specificities.

Ligand hyperfine coupling and electron structure features in the EPR spectra of Cu-doped multicomponent borate crystals: an interpretation based on the concept of the Jahn–Teller effect

Ligand hyperfine coupling and electron structure features in the EPR spectra of Cu-doped multicomponent borate crystals: an interpretation based on the concept of the Jahn–Teller effect

Iridium(III) Complex Radical and Corresponding Ligand Radical Functionalized by a Tris(2,4,6-trichlorophenyl)methyl Unit: Synthesis, Structure, and Photophysical Properties

Organic radical luminescent materials with doublet excited state character based on tris(2,4,6-trichlorophenyl)methyl (TTM) have attracted extensive attention in recent years. However, how they affect the phosphorescent iridium(III) complex characterized by the triplet excited state has not been studied yet. Herein, a new iridium(III) complex radical (Ir-TTM) and corresponding ligand radical (ppy-TTM) with a TTM unit have been designed and synthesized, and their radical properties were confirmed by the single crystal structure and EPR spectra. Notably, the ligand radical ppy-TTM shows an efficient red light emission, whereas the iridium complex radical Ir-TTM emits no light, which resulted from the intramolecular quenching effect of the TTM radical unit on the iridium luminescence center. DFT calculations demonstrate that the lowest doublet (D1) excited state of ppy-TTM shows an intramolecular charge transfer character from the 2-phenylpyridine moieties to the TTM unit, whereas the D1 of Ir-TTM exhibits a significant charge transfer character from the iridium luminescence center moieties to the TTM unit, which further explains the luminescence quenching mechanism of the phosphorescent iridium complex radical.

Proton-Coupled Oxidation of Aldimines and Stabilization of H-Bonded Phenoxyl Radical-Phenol Skeletons.

Stable phenoxyl radicals H-bonded to phenols were successfully isolated. The effect of the intermolecular H-bonding to the concerted proton coupled electron transfer (CPET) reactions of the aldimines and the stability and spin distribution of the H-bonded phenoxyls are reported. Salts of iminium-phenol derivatives as cations and the corresponding imine-phenolato derivatives coordinated to zinc(II) as anions, [ZnII(ArRO)Cl2]-[ArROH2]+, were isolated, where ArOH are aldimine derivatives. Notably, [ZnII(ArRO)Cl2]-[ArROH2]+ salts undergo CPET reactions in air affording phenoxyl analogues, [ZnII(ArOH)Cl2].ArO●·CH3CN. [ZnII(ArRO)Cl2]-[ArROH2]+ salts incorporate intermolecular iminium-phenolato, [(Zn)Ar-O--+HN═CH-] H-bonds, while [ZnII(ArOH)Cl2].ArO●·CH3CN moieties contain intermolecular phenoxyl-phenol, [Ar-O-HO-Ar]●, H-bonds. The phenoxyls are presented in two forms, [(Zn)Ar-O●---HO-Ar (zinc phenoxyl) ↔ (Zn)Ar-OH---●O-Ar (free phenoxyl)]. In crystals, the spin density scatters on both phenolic fragments corresponding to a delocalized state, while in solution the latter form has been calculated as a ground electronic state. The X-band EPR spectra of crystals, solutions and frozen glasses were analyzed. The powder spectra at g = 2.0030 ± 0.0005 and the frozen glass spectra at g = 2.0075 ± 0.0003 follow the hyperfine patterns due to 14N (I = 1) nuclei. In fluid solutions, the g values of the hyperfine signals due to 14N and 1H nuclei are 2.0078 ± 0.0001. 1-3 exhibit absorption bands at 350-390 nm due to π → π* intraligand charge transfer (ILCT) transitions, while the radical species, in addition to π → π transitions at 405-440 nm, display phenol to phenoxyl intervalence charge transfer (IVCT) transitions at 600-650 nm. The cyclic voltammograms (CVs) of 1-3 depend on the scan rates; at lower scan rates (100-400 mV/s) the CPET reactions occur at -0.92 to -0.96 V versus Fc+/Fc couple, whereas at higher scan rates (1000-2400 mV/s), the oxidation occurs by the electron transfer (ET) path at 0.05-0.12 V. Thus, a potential shift of ∼1.0 V is recorded due to CPET reactions facilitated by H-bonding.

Structure and magnetic properties of trinuclear copper(II) complex [Cu 3 (bipy) 6 (μ 3 -CO 3 )][B 12 H 12 ] 2 ·4.5DMF·2H 2 O

Abstract Trinuclear copper(II) complex [CuII3(bipy)6(μ3-CO3)][B12H12]2·4.5DMF·2H2O is isolated as a result of the redox reaction proceeding when [AgI2B12H12] was allowed to react with CuICl in the presence of bipy. Crystal structure, magnetic properties, and EPR spectrum of the compound are studied. It has been found that in the range 300–2 K, magnetic moment decreases from 1.98 to 1.33 µB with decreasing the temperature. In the EPR spectrum, the transition ΔM = ±3 transition is observed indicating the existence of the S = 3/2 state. This transition is explained by the effect of fine coupling tensor which admixes the |−1/〉 state into the |3/2〉 state and the |1/2〉 state into the |−3/2〉 state. The EPR spectrum is simulated by the spin Hamiltonians for S = 3/2 and S = 1/2.

EPR Investigation Of Mn (II) Probe In Diaquamalonatozinc(II) Single Crystals - Usage In Enrichment Of Dental Cement

Single crystal EPR studies on Cu(II) and VO(II) doped Diaquamalonatozinc(II) are already studied and published. Inorder to understand the effect of Mn(II) in the host lattice Diaquamalonatozinc(II), single crstal EPR studies of Mn(II) doped Diaquamalonatozinc(II) are carried out at room temperature to identify the local structure of the host ion. Angular variation of Mn(II) hyperfine lines in the three orthogonal planes shows the presence of a two sites. The spin-Hamiltonian parameters calculated from the single crystal EPR spectra are: gxx = 1.989, gyy = 1.999, gzz = 2.023; Axx = 8.72, Ayy = 9.28; Azz = 9.34 mT, Dxx = -33.36, Dyy = -7.25, Dzz = 40.61 mT and E = 13.05 mT. The spin-Hamiltonian parameters calculated from the powder EPR spectrum are: g = 1.995, A = 9.25 mT, D = -53.6. The percentage of covalency obtained is around 8.5%.

Crystal structure, infrared and EPR spectra and anticancer activity in vitro of the novel manganese(II) complexes of indolecarboxylic acids

The new complexes of 5-methoxyindole-2-carboxylic acid (5-MeOI2CAH) and indole-2-carboxylic acid (I2CAH) with manganese(II): catena-poly[diaquamanganese(II)-bis(μ2-5-methoxyindole-2-carboxylato-O:O′)], [Mn(5-MeOI2CA)2(H2O)2]n (1) and catena-poly[diaquamanganese(II)-bis(μ2-indole-2-carboxylato-O:O′)], [Mn(I2CA)2(H2O)2]n (2) have been prepared. A single crystal X-ray analysis of 1 shows that the complex crystallizes in the monoclinic system, space group P21/c. The 5-MeOI2CA anion acts as a bidentate bridging ligand coordinated to Mn(II) in an abnormal non-planar skew–skew mode, which differs from the coplanar syn–syn, syn–anti and anti–anti bridging modes commonly occurring in metal carboxylates. The FTIR and EPR spectroscopic studies of Mn(II) complexes are reported. In vitro cytotoxicities of 1, 2, 5-MeOI2CAH, I2CAH and their Zn(II) complexes have been evaluated by an MTT assay against the selected human leukemia cell lines: HL-60, MV-4-11, U937, Jurkat, KG-1, U2932 and murine melanoma B16-F0. The results have revealed that the two manganese(II) complexes are cytotoxic and their antiproliferative activity against some cell lines (e.g. Jurkat derived from an acute T cell leukemia) is similar to that of cisplatin.

Single Crystal EPR of the Mixed-Ligand Complex of Copper(II) with l-Glutamic Acid and 1,10-Phenanthroline: A Study on the Narrowing of the Hyperfine Structure by Exchange

We report an EPR study at X- and Q-bands of polycrystalline and single crystal samples of the mixed copper(II) complex with L-glutamic acid (glu) and 1,10-phenantroline (phen), [Cu(glu)(phen)(H(2)O)](+) NO(3)(-)·2(H(2)O). The polycrystalline sample spectrum at Q-band showed well resolved g(∥ )and g(⊥) features and partially solved hyperfine structure at g(∥), typical for weakly exchange coupled systems. This is confirmed from the angular variation of the EPR spectra which shows for certain magnetic field orientations a partially solved hyperfine structure characteristic of weak exchange, whereas a single Lorentzian line corresponding to strong exchange is observed for others. Analysis and simulation of the single crystal EPR spectra were performed using the random frequency modulation model of Anderson. Numerical simulations of the angular variation of the EPR spectra showed that the narrowing of the hyperfine structure is due to an exchange-mediated mechanism in which transitions between any pair of lines are equally likely. The exchange interaction responsible for this process is mediated by hydrophobic interactions between two phen molecules and a mixed chemical path of the type CuA-O(ap)H···O-C-O(eq)-CuB, for which we evaluated an average isotropic exchange parameter |J| ≈ 25 × 10(-4) cm(-1).

A bimetallic CoII–DyIII complex bridged by oxydiacetate ligand: Synthesis, structure, magnetic, spectral and TG properties of {[DyCo(oda)3]4[Co(H2O)6]2·6H2O}n

Abstract A novel 3d–4f heteronuclear coordination polymer containing cobalt and dysprosium, {[DyCo(oda)3]4[Co(H2O)6]2·6H2O}n (1) (H2oda = oxydiacetic acid), has been synthesized and characterized by X-ray crystal diffraction, magnetic analysis, fluorescence and EPR spectrum as well as TGA studies. The single-crystal analysis shows that compound 1 displays unique hexadecagonal and octagonal channel structure. The photoluminescent spectrum of 1 indicates that the emissions come from intraligand π–π⁎ transitions. Temperature-dependent magnetic susceptibilities, EPR and TG properties for 1 also have been discussed.

Single Crystal EPR Study of the Dinuclear Cu(II) Complex [Cu(tda)(phen)]2·H2tda (tda = Thiodiacetate, phen = Phenanthroline): Influence of Weak Interdimeric Magnetic Interactions

We report powder and single crystal EPR measurements of [Cu(tda)(phen)](2)·H(2)tda (tda = thiodiacetate, phen = phenanthroline) at 9.7 GHz. This compound consists of centrosymmetric copper(II) ion dimers, weakly ferromagnetically exchange-coupled (J = +3.2 cm(-1)), in which the dimeric units are linked by hydrophobic chemical paths involving the phen molecules. EPR revealed that the triplet spectra are collapsed by interdimeric exchange interactions mediated by that chemical path. Analysis and simulation of the single crystal EPR spectra were performed using Anderson's exchange narrowing model, together with statistical arguments. This approach allowed us to interpret the spectra modulated by the interdimeric interactions in situations of weak, intermediate, and strong exchange. We evaluated an interdimeric exchange constant J' = 0.0070(3) cm(-1), indicating that hydrophobic paths can transmit weak exchange interactions between centers at relatively long distances of the order of ∼10 Å.

Spectroscopic, magnetic, and electrochemical studies of a dimeric N-substituted-sulfanilamide copper(II) complex. X-ray and molecular structure of the Cu 2( N-(pyridin-2-yl)biphenyl-4-sulfonamidate) 4 complex

A dinuclear copper(II) complex with a N-substituted sulfonamide as ligand has been investigated. The new N-(pyridin-2-yl)biphenyl-4-sulfonamide ligand has been prepared and structurally characterized. The copper(II) complex has been synthesized and its crystal structure, magnetic properties and EPR spectra were studied in detail. The metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the copper(II) ions in the dinuclear entity is distorted square planar with two N-pyridyl and two N-sulfonamido atoms. Magnetic susceptibility data show a moderate antiferromagnetic coupling, with −2 J = 284 cm −1. The EPR spectrum of the polycrystalline sample of the title compound has been measured at the X-band frequency at different temperatures.

New copper(II)-radical one dimensional chain: Synthesis, crystal structure, EPR, magnetic properties and DFT calculations

The novel chain compound [Cu(Phtfac)(2)(NITpPy)](n) (where NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and Phtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione) was synthesized and characterized structurally, magnetically and by EPR. The compound contains two non equivalent Cu(II) ions, Cu1 and Cu2, located at inversion centers and bridged by a NITpPy ligand coordinating Cu1 through the pyridine donor atom, and Cu2 through a N-O group, resulting in a head-to-head chain structure. The chain exhibits an unusual spin topology with two alternating pairs of magnetic coupling constants. The magnetic behavior was modeled considering a 16-membered ring with alternating exchange couplings. The best fit parameters indicate a ferromagnetic (J(1) = 29.4 cm(-1)), and antiferromagnetic (J(2) = -4.6 cm(-1)) couplings and an average g = 2.05, corresponding to a ground state with three parallel and one anti-parallel spin for each Cu(2)NITpPy(2) unit. DFT calculations allowed assigning the ferromagnetic coupling to Cu-O-NITpPy and the antiferromagnetic coupling to Cu-N(Py)-NITpPy. Single crystal EPR spectra display only one resonance for most field orientations, as a consequence of the collapse of the signals of the different spins produced by the exchange interactions. The observed g-tensor of this resonance is related to those expected for the Cu(II) and radical ions. Comparison of this compound with other Cu-NIT radicals chains bearing different substituents in the organic radicals, highlights that the beta-diketonate ligand plays an important role in determining the final architecture. Moreover, we show how a knowledge of the spin density distribution in the initial building blocks is essential to rationalize the magnetic behavior of the resulting product.

Multi-range high-frequency EPR spectroscopy of LiYF4 and LiLuF4 crystals doped by rare-earth ions

EPR spectra of isostructural LiYF4 and LiLuF4 crystals doped by Dy3+, Er3+, and Ho3+ ions are measured at 4.2 K in the frequency range 40–800 GHz. The effects caused by isotopic disorder in the lithium sublattice, the random crystal field, and the interaction between paramagnetic impurity ions are detected and studied. The results of the measurements are used to determine the spectral characteristics of the compounds and the crystal field parameters. It is demonstrated that the formation of the isotope structure of the EPR signal is dominated by local deformations of the crystal lattice induced by mass defects.

Deep levels of intrinsic point defects and the nature of “anomalous” optical absorption in ZnGeP2

Deep levels of single vacancies and antisite defects in the structure of the ZnGeP2 compound are investigated using the pseudopotential method and an extended unit cell. The data obtained are compared with those for the GaP isoelectronic analog. It is demonstrated that, in the case of the ZnGeP2 crystal, deep levels (degenerate in the GaP structure) are substantially split as a result of lowering the lattice symmetry and anisotropy of the chemical bonding. In particular, the splitting of the V P 0 (t 2) level is equal to 1.58 eV. The averaged levels of defects in the ZnGeP2 compound are in close agreement with the levels of defects in the GaP compound. The absorption coefficients for polarized light are calculated with allowance made for the neutral and charged states of the defects. The optical transitions responsible for the absorption peaks in the IR range of the spectrum of the ZnGeP2 compound are revealed. It is shown that the first peaks are associated with the transitions of electrons from the valence band states located deep in the Brillouin zone to the V Zn −1 and V P 0 deep levels. This leads to a considerable shift (by ∼0.3 eV) of these peaks toward the high-energy range as compared to the energy positions of the deep levels in the band gap with respect to the top of the valence band. The experimental data on the photoinduced EPR spectra of postgrowth and electron-irradiated ZnGeP2 crystals are consistently interpreted by analyzing the electron density.

Synthesis, X-ray crystal structure and X-band EPR of [Cu(H 2O) 2(imH) 4]·Sq single crystals

The copper salt [Cu(H 2O) 2(imH) 4]·Sq has been synthesized at room temperature. Crystal structure of the [Cu(H 2O) 2(imH) 4]·Sq (Sq is squarete dianion (C 4O 4 2−) and imH is imidazole (C 3H 4N 2)) complexes has been investigated by single-crystal X-ray diffraction analyses and the environment of copper ion has been identified by EPR. The single crystal is triclinic with the space group P1. The unit cell dimensions of the crystals are a = 9.317 Å, b = 9.958 Å, c = 12.130 Å, α = 69.99°, β = 76.61° and γ = 78.13°. The unit cell contains two molecules. The Cu(II) atom has an octahedral arrangement in which the Cu(II) ion lies on the inversion canter and is coordinated by four imidazole ligands with the equatorial plane and two water molecules with the octahedral axial. The complex shows a normal magnetic moment and the single crystal EPR spectra consist of two sets of four hyperfine lines of copper. The ground wave function of the hole of the Cu 2+ is an admixture of d x 2 − y 2 and d z 2 states.

Crystal structure and EPR of the RbNd(WO 4) 2 single crystal

Crystal structure and EPR spectra in a RbNd(WO 4) 2 single crystal have been studied. RbNd(WO 4) 2 crystallizes in the monoclinic structure with the unit cell parameters: a = 1 0.7 9 2 ( 2 ) Å , b = 1 0.6 7 3 ( 2 ) Å , c = 7.6 7 0 3 ( 1 5 ) Å , β = 1 3 0.5 1 ( 3 ) ° . Using the X-ray diffraction measurements, the fractional atomic coordinates, displacement parameters and interatomic distances have been determined. The EPR spectra are described in terms of the main g-tensor values: g z = 3.2 9 1 ± 0.0 0 5 , g x = 0.7 2 6 ± 0.0 0 5 , g y = 1.5 3 3 ± 0.0 0 5 . Both the magnetic dipole–dipole and isotropic exchange interactions have been calculated. The exchange interactions are shown to exceed the magnetic dipole–dipole interactions and to have an opposite sign. These results suggest an appeareance of an antiferromagnetic ordering in RbNd(WO 4) 2 at low temperatures.

A novel three-dimensional molybdenum(V) phosphate decorated with zinc coordination cations: Zn[Mo 6O 12(OH) 3(PO 4) 4] 2{Zn 4(H 2O) 5(2,2′-bipy) 2} 2·2H 2O

A novel three-dimensional molybdenum(V) phosphate decorated with zinc complex cations, Zn[Mo 6O 12(OH) 3(PO 4) 4] 2{Zn 4(H 2O) 5(2,2′-bipy) 2} 2·2H 2O (2,2′-bipy=2,2′-bipyridine) 1, has been hydrothermally synthesized and characterized by single crystal X-ray diffraction, IR, TGA and EPR spectrum. The crystal data are triclinic, space group P 1 ¯ , a=13.0842(7) Å, b=14.0065(11) Å, c=14.3344(10) Å, α=64.445(3)°, β=88.805(3)°, γ=74.099(3)°, V=2264.9(3) Å 3, Z=1, R=0.0283, wR=0.0749. The Zn[Mo 6P 4] 2 units are connected together via additional zinc coordination complex ions to give a novel three-dimensional molybdenum(V) phosphate framework.

Interstitial substitutions of vanadyl ions doped in single crystals of hexaimidazole cobalt sulphate: An EPR study

AbstractElectron paramagnetic resonance studies on single crystals of hexaimidazole cobalt(II) sulphate doped with VO(II) are carried in the temperature range 77–300 K at X‐band frequencies. Single crystal EPR spectra indicate the presence of vanadyl impurity positioned in four sites with intensity ratios of 45:36:6:1. Angular variation studies in all the three orthogonal planes confirm that both the intense vanadyl sites have occupied interstitial positions in the lattice. The spin Hamiltonian parameters, calculated for the two sites, indicate orthorhombic nature for the impurity. However, the analysis of powder spectrum reveals the presence of only one site. The spin‐lattice relaxation parameters have been calculated at various temperatures from line width measurements. The admixture coefficients have also been calculated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Functional superoxide dismutase mimics. Structural characterization and magnetic exchange interactions of copper(II)-N-substituted sulfonamide dimer complexes.

Dinuclear copper(II) complexes with N-substituted sulfonamide ligands as superoxide dismutase (SOD) mimics have been investigated. The new N-(thiazol-2-yl)toluenesulfonamide (Htz-tol) and N-(thiazol-2-yl)naphthalenesulfonamide (Htz-naf) ligands have been prepared and structurally characterized. The complexes derived from these ligands, [Cu(2)(tz-tol)(4)] (1) and [Cu(2)(tz-naf)(4)] (2), have been synthesized, and their crystal structure, magnetic properties, and EPR spectra were studied in detail. In both compounds the metal centers are bridged by four nonlinear triatomic NCN groups. The coordination geometry of the coppers in the dinuclear entity of 1 and 2 is distorted square planar with two N-thiazole and two N-sulfonamido atoms. Magnetic susceptibility data show a strong antiferromagnetic coupling, with -2J = 121.3 cm(-1) for compound 1 and -2J = 104.3 cm(-1) for compound 2. The EPR spectra of the polycrystalline samples of compounds 1 and 2 have been measured at the X- and Q-band frequencies at different temperatures. Above 20 K the spectra are characteristic of S = 1 species with zero-field splitting parameter D = 0.230 cm(-1) for compound 1 and 0.229 cm(-1) for compound 2. The EPR parameters are discussed in terms of the known binuclear structures. The complexes exhibit high SOD activity, as shown by the low IC(50) values obtained with the xanthine/xanthine oxidase/NBT assay: 0.13 microM for compound 1; 0.17 microM for compound 2.

Synthesis, structural, and magnetic characterization of substituted benzoimidazole-l-yl N,N′-dioxides

The crystal structures, EPR spectra and magnetic properties of the novel halogen- and cyano-substituted nitronyl nitroxide radicals 2-(2,6-dichlorophenyl)benzimidazolyl N,N′-dioxide, 6, 2-(2,6-difluorophenyl)benzimidazolyl N,N′-dioxide, 7, 2-(2-chloro-6-fluorophenyl)benzimidazolyl N,N′-dioxide, 8, 2-(2,3,6-trichlorophenyl)benzimidazolyl N,N′-dioxide, 9, 2-(2,3,4,5,6-pentafluorophenyl)benzimidazolyl N,N′-dioxide, 10, and 2-(3-cyanophenyl)benzimidazolyl N,N′-dioxide, 11, are reported. Compound 6 crystallizes in the triclinic crystal system in space group P. The molecules of 6 are arranged in pairs with short intermolecular distances between the NO groups. 7 crystallizes in two different modifications: polymorph α is orthorhombic, space group Pbca; polymorph β is monoclinic, space group P21/c. 8 crystallizes in two modifications: the α polymorph is monoclinic, space group P21/c; and the β polymorph is monoclinic, space group P21/n. 9 crystallizes in the monoclinic system, space group P21/c. 10 crystallizes in the monoclinic system, space group C2/c. The molecules of 10 are packed in pairs of two types that form a chain perpendicular to the c-axis. 11 crystallizes in the monoclinic crystal system in space group P21/c. The rotation angle between the two rings in compounds 6–10 is 54.2–76.7°. The rotation angle between the two rings is only 21.0° in 11 and it strongly affects the packing of the molecules that adopt the stacking mode. The magnetic measurements show that 6, 7, 10 and 11 exhibit large magnetic coupling. The best fitting with the experimental data for 6 and 11 was obtained using the Bleaney–Bowers singlet–triplet model plus the Curie–Weiss spin impurity (S = 1/2; H = −2JS1·S2) J/kB = −84.2 K and θimp = 0.3 K and J/kB = −95.3 K, θimp = 1.8 K, respectively. A Pade expression for 7 revealed Jintra/kB = 66.0 K and zJinter/kB = −14.0 K. Compound 10 shows evidence for large antiferromagnetic spin coupling (θ = −37.0 K Curie–Weiss model).