Synthesis,structure and magnetic properties of an iron(II) complex with nitronyl nitroxides

An iron(II) complex with nitronyl nitroxides, [Fe^II(dppNN)₂](BF₄)₂ · CH₃COCH₃ (1) (dppNN = 2,6-di(pyrazol-1-yl)-4-(4,4,5,5-tetramethyl-1-oxido-3-ylooxy-4,5-dihydro-3H-imidazol-2′-yl)pyridine) was synthesized. In 1 the central iron(II) ion was coordinated by two tridentate ligands with nitronyl nitroxides. Magnetic susceptibility measurements showed that χ_mT values below 130 K was almost temperature independent, while upon increasing temperature χ_mT values showed gradual increase, suggesting an occurrence of a spin transition from low to high spin state. Green light irradiation on powder sample at 5 K resulted in spin conversion (LIESST).     

Low-dimensional quantum magnetic systems: Synthesis,structure and magnetic behavior of (2,5-dimethylpyrazine)copper(II) chloride and synthesis and magnetic behavior of bis(2,6-dimethylpyrazine)copper(II) chloride

The synthesis, X-ray structure and magnetic susceptibility of (2,5-dimethylpyrazine)copper(II) chloride (1), and the synthesis and magnetic susceptibility of (2,6-dimethylpyrazine)₂copper(II) chloride (2), are reported. Compound 1 crystallizes in the space group P2₁/c as a coordination polymer of Cu(II) ions bridged by 2,5-methylpyrazine. The resulting chains are magnetically linked via short chloride–chloride contacts. The magnetic susceptibility responds as a uniform Heisenberg chain (2J/k = −20(5) K) with a phase transition to three dimensional order near 5 K. Susceptibility data for compound 2 show that the compound is a linear chain coordination polymer with the copper ions linked by bihalide bridges. A fit to the model for a uniform Heisenberg chain yields 2J = −22.7(2) K.     

Synthesis,structure and magnetic properties of pyrazolate-bridged dinuclear complexes [{M(NCS)(4-Phpy)}2(μ-bpypz)2] (M = Co2+ and Fe2+)

The synthesis and magnetic characterization of pyrazolato-bridged dinuclear complexes [{M(NCS)(4-Phpy)}₂(μ-bpypz)₂] (Hbpypz = 3,5-bis(2-pyridyl)-pyrazole; 4-Phpy = 4-phenylpyridine; M = Co²⁺ (1) and Fe²⁺ (2)) are described together with the X-ray crystal analysis of the cobalt complex. The structure of 1 shows that the desired coordination has been achieved with the cobalt atoms being coordinated to two bpypz to form the dimer. The X-ray diffraction patterns show 1 and 2 to be isomorphous at room temperature. 2 displays a single spin-crossover transition between the [HS–HS] and [LS–LS] states with T_c = 150 K.     

Spin-crossover in cobalt(II) compounds containing terpyridine and its derivatives

In this review article we discuss the unique and novel magnetic properties for the cobalt(II) compounds with a variety of terpy derivatives including substituents at the 4-position. These are also compared with the unsubstituted terpy cobalt(II) complex. Since the first SCO cobalt(II) complex with terpy ligand was reported, this system has been widely studied. SCO cobalt(II) complexes possessing terpy or OH-terpy ligand reveal incomplete or gradual SCO behavior. The pyterpy-appended cobalt(II) complex shows SCO depending on the guest molecules involved. Cobalt(II) complexes with long-alkylated terpy ligands, [Co(Cn-terpy)₂](BF₄)₂ (n = 16, 14 and 12) have been synthesized and some were characterized by single crystal X-ray analysis. Furthermore, variable-temperature magnetic susceptibility indicated that the non-solvated compounds [Co(Cn-terpy)₂](BF₄)₂ (n = 16, 14 and 12) exhibit “reverse spin transition” phenomenon with wide thermal hysteresis around room temperature. In addition, the solvated compound [Co(C12-terpy)₂](BF₄)₂·EtOH·0.5H₂O shows “re-entrant SCO” behavior. The long alkyl chains in SCO cobalt(II) complexes can lead to novel physical properties resulting from a synergetic effect between SCO and response of the flexibility toward external stimuli.     

Synthesis,crystal structure and thermal behaviour of [La(hfa)3(Phen)2] (hfa = hexafluoroacetylacetonate,Phen = o-phenanthroline)

The mixed ligand complex [La(hfa)₃(Phen)₂] (I) was obtained by the interaction of La(hfa)₃ and Phen; its composition does not depend on the stoichiometry of the reagents. According to the X-ray single crystal analysis data, complex I crystallizes in the monoclinic space group P2₁/n, with a = 13.583(3) Å, b = 16.959(3) Å, c = 18.860(4) Å, β = 94.71(3)° and Z = 4. The structure of I consists of isolated mononuclear molecules, the coordination number of La being 10. Thermal behaviour and composition of the vapor phase have been studied for I by thermal analysis and mass-spectrometry using a Knudsen cell. The mixed ligand complex I was found to sublime congruently in the temperature range 370–460 K: [La(hfa)₃(Phen)₂]_(s) = [La(hfa)₃(Phen)]_(g) + Phen_(g), Δ_rH⁰(T) = 316.2 ± 1.8 kJ/mol.     

Electrochemical and magnetic properties of inorganic polymers constructed from Mn(II)/Co(II)-substituted heteropolymolybdates

Two inorganic polymers constructed from transition metal-substituted heteropolymolybdates, [(CH₃)₃NH]_5n[PMo₁₁MO₃₉]_n·xH₂O (M = Mn²⁺, x = n (1); M = Co²⁺, x = 2n (2)), have been synthesized in aqueous solutions and characterized by IR, TGA, and single-crystal X-ray diffraction analysis. Crystal data: 1, monoclinic, C2/c, a = 17.1322(7) Å, b = 17.6062(7) Å, c = 17.6459(7) Å, β = 103.2220(10)°, V = 5181.5(4) Å³ and Z = 4; 2, triclinic, P-1, a = 12.1986(7) Å, b = 13.0973(7) Å, c = 16.7736(9) Å, α = 97.1810(10)°, β = 98.5040(11)°, γ = 96.3920(10)°, V = 2606.5(2) Å³ and Z = 2. The cyclic voltammograms of 1 and 2 show irreversible redox peaks in DMF solution and there are three reversible couples after addition of 0.1 M H₂SO₄ aqueous solutions. The cyclic voltammograms of 1/2-modified carbon paste electrode (1-CPE/2-CPE) show two consecutive reversible two-electron redox processes. Especially, 2-CPE shows good electrocatalytic activity toward the reduction of nitrite and hydrogen peroxide. The magnetic properties of the two complexes have also been investigated.     

Ferromagnetic coupling of copper(II) and nickel(II) complexes with a cyclam-based paramagnetic host

Bis(NN–CH₂)-substituted dimethylcyclam (cyclamNN₂) was designed and synthesized as a paramagnetic host, where NN stands for 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide. We prepared transition-metal complexes [M(cyclamNN₂)](ClO₄)₂ (M = Cu (1), Ni (2)) and investigated their metal–radial exchange couplings. The copper ion in 1 is located at the center of the cyclam cavity and one radical arm is coordinated at an axial position. Compound 1 showed ferromagnetic coupling (2J/k_B = +44(3) K), which is ascribable to the NN–Cu coupling. Ferromagnetic coupling was also observed in 2, but the molecular structure was unknown at present. The Curie–Weiss analysis gave the Weiss temperature (θ) of +13.5(6) K for 2.     

Crystal structures,luminescence, and thermal properties of lanthanide complexes with 2,3,4-trimethoxybenzoic acid and 1,10-phenanthroline

The complexes of [Ln(2,3,4-tmoba)₃phen]₂ (Ln = Dy (1), Eu (2), Tb (3); 2,3,4-tmoba = 2,3,4-trimethoxybenzoate; phen = 1,10-phenanthroline) were synthesized and characterized by a series of techniques including the elemental analysis, IR and fluorescent spectra and TG/DSC-FTIR technology. The crystal structures were determined by X-ray crystallography. Each complex include two Ln³⁺ ions, six 2,3,4-tmoBA and two phen molecules forming a binuclear structure, giving the coordination number of nine. The three-dimensional IR accumulation spectra of gaseous products for the complexes 1 to 3 are analyzed and the thermal decomposition processes are further authenticated. Through means of differential scanning calorimeter (DSC), two solid-solid phase transition endothermic peaks were found in the complex 2, which was different from the complexes 1 and 3. The heat capacities of these complexes were measured and fitted to a polynomial equation with the least squares method for each complex on the basis of the reduce temperature x (x = [T − (T_max + T_min)/2]/[(T_max − T_min)/2]) over the range from (256.15 to 476.15) K. Subsequently, the smoothed molar heat capacities and thermodynamic functions (H_T−H_298.15 K), (S_T−S_298.15 K), and (G_T−G_298.15 K) of the complexes 1 to 3 were calculated based on the fitted polynomial of the heat capacities. The fluorescent intensity of the complexes 2 and 3 are markedly improved as well.     

Ferromagnetic interaction in iron(II)–bis-Schiff base complexes

The preparation and magnetic properties of three Fe(II)–bis-Schiff base complexes, [Fe₂(L1)2(4,4′-bpy)] · MeOH (1), [Fe(L2)(EtOH)] (2) and [Fe(L3)(MeOH)] (3) (L1 = N,N′-bis(2-hydroxy-1-naphthaldehyde)-1,2-phenylenediimine; L2 = N,N′-bis(salicylidene)-1,2-phenylenediamine; L3 = N,N′-bis(5-Cl-salicylidene)-1,2-phenylenediamine; 4,4′-bpy = 4,4′-bipyridine) are reported. X-ray single crystal structure analyses for 1–3 reveal that 1 shows a dinuclear Fe(II)–bis-Schiff base complex bridged by 4,4′-bpy, while 2 and 3 show mononuclear structures. Molecular packing of 2 shows a uniform one-dimensional chain structure through hydrogen bonds and Fe?π interaction and that of 3 indicates significant π–π interaction to form a dimmer structure. The χT–T plots of 1–3 show all ferromagnetic interaction at low temperature. The origin of the ferromagnetic interaction observed in 2 is tentatively ascribed to the dimer formation through Fe?π interaction at low temperature.     

Magnetic properties of hybrid organo-inorganic copper(II) oxovanadate(V) phosphate and phosphonate bridged systems

The hybrid organo-inorganic compounds [Cu₄(bipy)₄V₄O₁₁(PO₄)₂]nH₂O (n ∼ 5) (1), [Cu₂(phen)₂(PO₄)(H₂PO₄)₂(VO₂) · 2H₂O] (2) and [Cu₂(phen)₂(O₃PCH₂PO₃)(V₂O₅) (H₂O)]H₂O (3) which present different bridging forms of the phosphate/phosphonate group, show different bulk magnetic properties. We herein analyze the magnetic behaviour of these compounds in terms of their structural parameters. We also report a theoretical study for compound (1) assuming four different magnetic exchange pathways between the copper centres present in the tetranuclear unit. For compound (1) the following J values were obtained J₁ = +3.29; J₂ = −0.63; J₃ = −2.23; J₄ = −46.14 cm⁻¹. Compound (2) presents a Curie–Weiss behaviour in the whole range of temperature (3–300 K), and compound (3) shows a maximum for the magnetic susceptibility at 64 K, typical for antiferromagnetic interactions. These data where fitted using a model previously reported in the literature, assuming two different magnetic exchange pathways between the four copper(II) centres, with J₁ = −30.0 and J₂ = −8.5 cm⁻¹.     

Iron(II) spin transition 1,2,4-triazole chain compounds with novel inorganic fluorinated counteranions

New one-dimensional spin transition coordination polymers of formula [Fe(NH₂trz)₃](AF₆) · nH₂O (A = Ti, Zr, Sn; NH₂trz = 4-amino-1,2,4-triazole) have been synthesized in MeOH and EtOH media. These materials display an abrupt and hysteretic spin transition around 200 K as well as a reversible thermochromic effect on cooling. A preliminary evaluation of the lattice dynamics in the high-spin and low-spin states is presented.     

Mesogenic and magnetic behavior in cobalt(II) and iron(II) compounds with long alkyl chains

Abstract  Metal complexes with long alkyl chains [Co(C16-terpy)₃](BF₄)₂ (1), [Fe(C16-terpy)₂](BF₄)₂ (2), [Co(C16-terpy)₂](BPh₄)₂ (3), [Co(C14-terpy)₂](BF₄)₂ (4), and [Fe(C12C10C5-terpy)₂](BF₄)₂ (5) were synthesized and their physical properties characterized, where C16-terpy, C14-terpy, and C12C10C5-terpy are 4′-hexadecyloxy-2,2′:6′,2′′-terpyridine, 4′-tetradecyloxy-2,2′:6′,2′′-terpyridine, and 4′-5′′′-decyl-1′′′-heptadecyloxy-2,2′:6′,2″-terpyridine, respectively. Complexes 1, 2, and 5 exhibited liquid–crystal properties in the temperature ranges of 371–528 K and 466–556 K, and 88–523 K, respectively. Variable-temperature magnetic susceptibility measurements revealed that the Co(II) complexes 1 and 4 exhibited unique spin transitions (T _1/2↓ = 217 K and T _1/2↑ = 260 K for 1 and T _1/2↓ = 250 K and T _1/2↑ = 307 K for 4), so-called ‘reverse spin transition,’ induced by structural phase transitions. Complex 3 exhibited gradual spin-crossover behavior (T _1/2 = 160 K.), and complex 5 exhibited spin transitions (T _1/2↑ = 288 K and T _1/2↓ = 284 K) at the liquid crystal transition temperature. Compounds with multifunction, i.e., magnetic and liquid–crystal properties, are important in the development of molecular materials. Graphical Abstract  

Mechanism of reversible spin transition with a thermal hysteresis loop in [FeIII(qsal)2][Ni(dmise)2] · 2CH3CN: Selenium analogue of the precursor of an Fe(III) spin-crossover molecular conducting system

A novel Fe(III) spin-crossover complex, [Fe(qsal)₂][Ni(dmise)₂] · 2CH₃CN 1 [qsalH = N-(8-quinolyl)-salicylaldimine, dmise = 4,5-dithiolato-1,3-dithiole-2-selone] was prepared. The magnetic susceptibility measurements revealed 1 exhibited a cooperative spin transition with a thermal hysteresis loop of 15 K. The high and the low temperature structures of 1 indicated three-dimensional intermolecular π?π interactions play a key role in the cooperative spin transition, accompanying a reversible molecular slipping of π-dimer of Ni(dmise)₂ along the molecular long axis. The transfer integral calculation for 1 suggested the π-dimer of Ni(dmise)₂ is in the spin singlet state.     

Dimeric and monomeric palladium(II) parent-amido (NH2) complexes: Synthesis,characterization, and reactivity

The treatment of [PdL₃(NH₃)]OTf (L₃ = (PEt₃)₂(Ph) (1), (2,6-(Cy₂PCH₂)₂C₆H₃) (3)) with NaNH₂ in THF afforded dimeric and monomeric parent-amido palladium(II) complexes with bridging and terminal NH₂, respectively, anti-[Pd(PEt₃)(Ph)(μ-NH₂)]₂ (2) and Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₂) (4). The dimeric complex 2 crystallizes in the space group P2₁/n with a = 13.228(2) Å, b = 18.132(2) Å, c = 24.745(2) Å, β = 101.41(1)°, and Z = 4. It has been found that there are two crystallographically independent molecules with Pd(1)–Pd(2) and Pd(3)–Pd(4) distances of 2.9594 (10) and 2.9401(9) Å, respectively. The monomeric amido complex 4 protonates from trace amounts of water to give the cationic ammine species [Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₃)]⁺. Complex 4 reacts with diphenyliodonium triflate ([Ph₂I]OTf) to give aniline complex [Pd(2,6-(Cy₂PCH₂)₂C₆H₃)(NH₂Ph)]OTf (5). Reaction of 4 with dialkyl acetylenedicarboxylate (DMAD, DEAD) yields diastereospecific palladium(II) vinyl derivative (Z)–(Pd(Cy₂PCH₂)₂C₆H₃)(CR = CR(NH₂)) (R = CO₂Me (6a), CO₂Et (6b)). Reacting complexes 6a and 6b with p-nitrophenol produces (Pd(Cy₂PCH₂)₂C₆H₃)(OC₆H₄–p-NO₂) (8) and cis-CHR = CR(NH₂), exclusively.     

Two highly unsymmetrical tetradentate (N3O) Schiff base copper(II) complexes: Template synthesis,structural characterization,magnetic and computational studies

Two new copper(II) complexes, [Cu₂(L¹)₂](ClO₄)₂ (1) and [Cu(L²)(ClO₄)] (2), of the highly unsymmetrical tetradentate (N₃O) Schiff base ligands HL¹ and HL² (where HL¹ = N-(2-hydroxyacetophenone)-bis-3-aminopropylamine and HL² = N-(salicyldehydine)-bis-3-aminopropylamine) have been synthesised using a template method. Their single crystal X-ray structures show that in complex 1 two independent copper(II) centers are doubly bridged through phenoxo-O atoms (O1A and O1B) of the two ligands and each copper atom is five-coordinated with a distorted square pyramidal geometry. The asymmetric unit of complex 2 consists of two crystallographically independent N-(salicylidene)-bis(aminopropyl)amine-copper(II) molecules, A and B, with similar square pyramidal geometries. Cryomagnetic susceptibility measurements (5–300 K) on complex 1 reveal a distinct antiferromagnetic interaction with J = ?23.6 cm^?1, which is substantiated by a DFT calculation (J = ?27.6 cm^?1) using the B3LYP functional. Complex 1, immobilized over highly ordered hexagonal mesoporous silica, shows moderate catalytic activity for the epoxidation of cyclohexene and styrene in the presence of TBHP as an oxidant.     

Molecular spin ladders self-assembly from [Ni(dmit)2]− building blocks: Syntheses,structures and magnetic properties

Two ion-pair compounds, consisting of 1-(4′-R-benzyl)pyridinium ([RBzPy]⁺, R = NO₂ (1) and Br (2)) and [Ni(dmit)₂]⁻ (dmit²⁻ = 2-thioxo-1,3-dithion-4,5-dithiolato), have been synthesized and structurally characterized. The anions of [Ni(dmit)₂]⁻ stack into dimers, which further construct into two-leg ladder through terminal S⋯S interactions in 1, lateral S⋯S interactions in 2. The weak H-bonding interactions of C–H⋯S were observed in 2, while only weak van de Waals interactions between anion and cations in 1. The magnetic susceptibilities measured in 2–300 K indicate AFM exchange interaction domination both two compounds. A peculiar magnetic transition at ∼100 K was observed in 1. An AFM ordering below ∼11 K was found in 2, and the best fit to magnetic susceptibility above 45 K in this compound, using a dimer model with s = 1/2, give rise to Δ/k_B = 36.1 K, zJ = −0.91 K, C = 3.2 × 10⁻³ emu K mol⁻¹ and χ₀ = −4.0 × 10⁻⁶ emu mol⁻¹ with g of 2.0 fixed.     

Benign synthesis of N-(8-quinolyl)pyridine-2-carboxamide) ligand (Hbpq), and its Ni (II) and Cu (II) complexes. A fluorescent probe for direct detection of nitric oxide in acetonitrile solution based on Hbpq copper(II) acetate interaction

The ligand Hbpq = N-(8-quinolyl)pyridine-2-carboxamide) has been prepared using tetrabutylammonium bromide (TBAB) as an environmentally friendly reaction medium. Four new complexes of this ligand, [M(bpq)X] (M = Cu(II), X = SCN̄ (1), N₃̄ (2); M = Ni(II), X = SCN̄ (3), N₃̄ (4)), have also been synthesized and fully characterized. The crystal and molecular structures of [Cu(bpq)(NCS)]_n (1) have been determined by X-ray crystallography. Copper(II) ion adopts a distorted square pyramidal (4 + 1) coordination in this complex. Hbpq ligand shows a strong emission at 500 nm in acetonitrile solution. The emission is quenched in the presence of copper(II) acetate, apparently because of the formation of [Cu(L)(OAc)(H₂O)] complex. Introduction of nitric oxide (NO) into the acetonitrile solution at room temperature induces an increase in the fluorescence intensity, presumably due to the reduction of Cu(II) to Cu(I). This process is reversible and can form a basis for direct detection of NO.     

Coordination polymers incorporating copper(II) and manganese(II) centers bridged by pyridinedicarboxylate ligands: Structure and magnetism

Two heterobimetallic coordination polymers, [Cu(2,4-pydc)₂Mn(H₂O)₄]_x (1) and [Cu(2,5-pydc)₂Mn(H₂O)₂]_x · 4xH₂O (2), have been synthesized and structurally characterized by single crystal X-ray diffraction. Both compounds have extended 2-D sheet structures. In 1 the copper centers are linked in chains by double ligand bridges and these chains are cross-linked through the manganese coordination spheres and O–C–O bridges to form polymeric sheets. In 2 separate O–C–O bridged Cu and Mn chains are connected in an alternating array by additional ligand bridging to generate the overall 2-D structure. Analysis of magnetic data of 1 reveals that ferromagnetic exchange between the O–C–O bridged copper and manganese centers dominates the magnetic properties of this system. The magnetic data for 2 fit well to a model incorporating antiferromagnetic exchange in independent S = 1/2 and S = 5/2 linear chains with J(Cu) = −0.073 cm⁻¹ and J(Mn) = −0.32 cm⁻¹. Unlike the situation in 1, there is no evidence for heterometallic exchange. In both 1 and 2 the significant exchange occurs via O–C–O bridges. To study the effect of thermal dehydration on the magnetic properties of these systems, the compounds Cu(2,4-pydc)₂Mn · H₂O (1d) and Cu(2,5-pydc)₂Mn · H₂O (2d) were synthesized and studied.     

A new luminescent sulfate bridged dimeric copper(II) complex with DNA binding and SO2 fixation ability: Synthesis and structure

New luminescent mononuclear and dinuclear copper(II) (S = 1/2) complexes [Cu(HL)(H₂O)₂](ClO₄)₂ (1a) and [Cu₂(HL)₂(μ-SO₄)₂]·2H₂O (1b) were synthesized with the acyclic tridentate pyridine-2-carboxaldehyde-2-pyridylhydrazone ligand, HL (1). Interestingly, the mononuclear complex 1a can be converted into the disulfate bridged dimeric copper(II) complex 1b by passing freshly prepared SO₂ through the basic medium. On excitation at 290 nm, the ligand fluoresces at 364 nm due to an intraligand ¹(π–π1) transition. Upon complexation with copper(II), the emission peak is slightly blue shifted (356 nm, F/F₀ 0.76 for 1a and 354 nm, F/F₀ 0.89 for 1b) with a little quenching in the emission intensity. The association constants (K_ass (5.06 ± 0.004) × 10⁴ for 1a and K_ass (5.46 ± 0.006) × 10⁴ for 1b at 298 K) and the thermodynamic parameters have been determined by UV–Vis spectroscopy. The molecular structure of the complex 1b (Cu?Cu 4.456 Å) has been determined by single crystal X-ray diffraction studies. The complex 1b exhibits a strong interaction towards DNA as revealed from the K_b (intrinsic binding constant) 6.3 × 10⁴ M^?1 and K_sv (Stern–Volmer quenching constant) 2.93 values.     

Crystal structures and magnetic properties of complexes of M(NO3)2; M = MnII,CoII, NiII,and CuII,with pyridine ligands carrying an aminoxyl radical

Four complexes of M(NO₃)₂(4NOPy-OMe)₂, (4NOPy-OMe = 4-(N-tert-butyloxylamino)-2-(methoxymethylenyl)pyridine, and M = Mn^II, 1; Co^II, 2; Ni^II, 3; Cu^II, 4), were prepared and fully characterized. X-ray single crystal analysis reveals that four complexes are isostructural. The molecular structures are distorted octahedral in which the methoxy oxygen atoms coordinate to the metal ion by trans-configuration while the pyridyl nitrogen atoms and the nitrate oxygen atoms coordinate by cis-configuration. The magnetic properties of all complexes were investigated by SQUID magneto/susceptometry. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K indicated that the magnetic coupling between aminoxyl radicals and metal ion was antiferromagnetic in the complex 1 and were ferromagnetic in the complexes 2–4. The quantitative analysis based on the spin Hamiltonian, H = −2J(S₁S_M + S_MS₂) yielded the best fit as J/k_B = −13.4 ± 0.1 K, g = 1.94 ± 0.002, and θ = −0.78 ± 0.02 K for the complex 1, J/k_B = 48.7 ± 2.1 K, g = 2.07 ± 0.02, and θ = −2.83 ± 0.41 K for the complex 3 (the data in the temperature range 300–50 K were used), and J/k_B = 57.0 ± 1.2 K, g = 2.002 ± 0.004, and θ = −9.8 ± 0.1 K for the complex 4.