Theoretical studies of magnetic interactions in Mn(II)(hfac)(2)[di(4-pyridyl)phenylcarbene] and Cu(II)(hfac)(2)[di(4-pyridyl)phenylcarbene].

Bis(hexafluoroacetylacetonato(hfac))manganese(II) coordinated with di(4-pyridyl)phenylcarbene, Mn(II)(hfac)(2)[di(4-pyridyl)phenylcarbene] (1a) and its copper analogue Cu(II)(hfac)(2)[di(4-pyridyl)phenylcarbene] (2a) have attracted great interest from the viewpoint of photoinduced magnetism. The complexes 1a and 2a are regarded as the new d-pi-p conjugated systems containing transition metal ion and carbene as spin sources. The magnetic measurements demonstrated antiferromagnetic and ferromagnetic effective exchange interactions for 1a and 2a, respectively. Here, we have performed UHF and UHF plus DFT hybrid calculations (UB3LYP) to elucidate the nature of the through-bond effective exchange interaction between Mn(II) (or Cu(II)) ion and triplet carbene sites in 1a (or 2a) and their model complexes. The natural orbital analysis of the UHF and UB3LYP solutions and CASCI calculations for the simplest models of 1a and 2a are performed to elucidate relative contributions of spin polarization (SP) and spin delocalization (SD) (or superexchange (SE)) interactions for determination of the sign of J(ab) values. Mn(II) carbene complex 1a shows an antiferromagnetic interaction because of the pi-type antiferromagnetic SE effect and the pi-type SP effect, while the positive J(ab) value for Cu(II) carbene complex 2a can be explained by the fact that ferromagnetic SE and SP interactions due to orbital orthogonality are more effective than the sigma-type antiferromagnetic SE interaction. The ligand coordination effects of both 4-pyridylcarbene and hfac play crucial roles for determination of the J(ab) values, but the ligand coordination effect of hfac is more important for the active control of charge or spin density distributions than that of 4-pyridylcarbene. The spin alignment mechanisms of 1a and 2a are indeed consistent with SE plus SP rule, which is confirmed with the shape and symmetry of natural orbitals, together with charge and spin density distributions.     

Coordination complexes of 2-(4-quinolyl)nitronyl nitroxide with M(hfac)(2) [M = Mn(II), Co(II), and Cu(II)]: syntheses, crystal structures, and magnetic characterization

Three new complexes of the formula M(2)L(2) derived from 2-(4-quinolyl)nitronyl nitroxide (4-QNNN) and M(hfac)(2) [M = Mn(II), Co(II), and Cu(II)], (4-QNNN)(2).[Mn(hfac)(2)](2) (1), (4-QNNN)(2).[Co(hfac)(2)](2).2H(2)O (2), and (4-QNNN)(2).Cu(hfac)(2).Cu'(hfac)(2) (3), were synthesized and characterized structurally as well as magnetically. Complexes 1 and 2 are four-spin complexes with quadrangle geometry, in which both the nitrogen atoms of quinoline rings and oxygen atoms of nitronyl nitroxides are involved in the formation of coordination bonds. For complex 3, however, the nitrogen atoms of quinoline rings are coordinated with Cu(II) ion to afford a three-spin complex, which is further linked to another molecule of Cu(hfac)(2) (referred to as Cu'(hfac)(2)) to form a 1D alternating chain. The magnetic behaviors of the three complexes were investigated. For complex 1, as the nitronyl nitroxides and Mn(II) ions are strongly antiferromagnetically coupled, consequently its temperature dependence of magnetic susceptibility was fitted to the model of spin-dimer with S = 2, yielding the intradimer magnetic exchange constant of J = -0.82 cm(-1). For complex 2, the temperature dependence of the magnetic susceptibility in the T > 50 K region was simulated with the model of two-spin unit with S(1) = 3/2 and S(2) = 1/2, leading to J = -321.9 cm(-1) for the magnetic interaction due to Co(II).O coordination bonding, D = -16.3 cm(-1) (the zero-field splitting parameter), g = 2.26, and zJ = -3.8 cm(-1) for the magnetic interactions between Co(II) ions and nitronyl nitroxides through quinoline rings and those between nitronyl nitroxides due to the short O.O short contacts. The temperature dependence of magnetic susceptibility of 3 was approximately fitted to a model described previously affording J(1) = -6.52 cm(-1) and J(2) = 3.64 cm(-1) for the magnetic interaction between nitronyl nitroxides and Cu(II) ions through the quinoline unit via spin polarization mechanism and the weak O.Cu coordination bonding, respectively.     

Syntheses, structure, and magnetic properties of hexanuclear Mn(III)(2)M(III)(4) (M = Y, Gd, Tb, Dy) complexes

The synthesis and characterizations of a family of isomorphous [Mn(III)(2)M(III)(4)L(2)(μ(4)-O)(2)(N(3))(2)(CH(3)O)(2)(CH(3)OH)(4)(NO(3))(2)]·2H(2)O (M = Y(1), Gd(2), Tb(3), Dy(4)) are reported, where H(4)L = N,N'-dihydroxyethyl-N,N'-(2-hydroxy-4,5-dimethylbenzyl)ethylenediamine. They were obtained from the reactions of H(4)L with M(NO(3))(3)·6H(2)O, Mn(ClO(4))(2)·6H(2)O, NaN(3) and NEt(3) in a 1?:?1?:?1?:?2?:?2 molar ratio. The core structure consists of a Mn(2)M(4) unit. The four M(III) ions that are held together by two μ(4)-bridging oxygen atoms form a butterfly M(4) moiety. The M(4) core is further connected to the two five-coordinate trigonal-bipyramidal Mn(III) ions via one μ(4)-O(2-), two alkyloxo and one methoxo triple bridges. Magnetic susceptibility measurements indicate the presence of intramolecular antiferromagnetic interactions in complex 2, and overall intramolecular ferromagnetic interactions in complexes 3 and 4. The alternating current (AC) magnetic susceptibility studies revealed that complexes 3 and 4 showed frequency-dependent out-of-phase signals, which indicates that they exhibit slow relaxation of the magnetization.     

A rational design for imidazolate-bridged linear trinuclear compounds from mononuclear copper(II) complexes with 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL): syntheses, structures, and magnetic properties of [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = ZnII, CuII, MnII)

Two mononuclear copper(II) complexes with the unsymmetrical tridentate ligand 2-[((imidazol-2-ylmethylidene)amino)ethyl]pyridine (HL), [Cu(HL)(H2O)](ClO4)2.2H2O (1) and [Cu(HL)Cl2] (2), have been prepared and characterized. The X-ray analysis of 2 revealed that the copper(II) ion assumes a pentacoordinated square pyramidal geometry with an N3Cl2 donor set. When 1 and 2 are treated with an equimolecular amount of potassium hydroxide, the deprotonation of the imidazole moiety promotes a self-assembled process, by coordination of the imidazolate nitrogen atom to a Cu(II) center of an adjacent unit, leading to the polynuclear complexes [[Cu(L)(H2O)](ClO4)]n (3) and [[Cu(L)Cl].2H2O]n (4). Variable-temperature magnetic data are well reproduced for one-dimensional infinite regular chain systems with J = -60.3 cm(-1) and g = 2.02 for 3 and J = -69.5 cm(-1) and g = 2.06, for 4. When 1 is used as a "ligand complex" for [M(hfac)2] (M = Cu(II), Ni(II), Mn(II), Zn(II)) in a basic medium, only the imidazolate-bridged trinuclear complexes [Cu(L)(hfac)M(hfac)2Cu(hfac)(L)] (M = Zn(II), Cu(II)) (5, 6) can be isolated. Nevertheless, the analogous complex containing Mn(II) as the central metal (7) can be prepared from the precursor [Cu(HL)Cl2] (2). All the trinuclear complexes are isostructural. The structures of 5 and 6 have been solved by X-ray crystallographic methods and consist of well-isolated molecules with Ci symmetry, the center of symmetry being located at the central metal. Thus, the copper(II) fragments are in trans positions, leading to a linear conformation. The magnetic susceptibility data (2-300 K), which reveal the occurrence of antiferromagnetic interactions between copper(II) ions and the central metal, were quantitatively analyzed for symmetrical three-spin systems to give the coupling parameters JCuCu = -37.2 and JCuMn = -3.7 cm(-1) with D = +/-0.4 cm(-1) for 6 and 7, respectively. These magnetic behaviors are compared with those for analogous systems and discussed on the basis of a localized-orbital model of exchange interactions.     

Syntheses, structures, and properties of trinuclear complexes [M(bpca)(2)(M'(hfac)(2))(2)], constructed with the complexed bridging ligand [M(bpca)(2)] [M, M' = Ni(II), Mn(II); Cu(II), Mn(II); Fe(II), Mn(II); Ni(II), Fe(II); and Fe(II), Fe(II); Hbpca = Bis(2-pyridylcarbonyl)amine, Hhfac = Hexafluoroacetylacetone

Five trinuclear complexes [M(bpca)(2)(M'(hfac)(2))(2)] (where MM'(2) = NiMn(2), CuMn(2), FeMn(2), NiFe(2), and FeFe(2); Hbpca = bis(2-pyridylcarbonyl)amine; and Hhfac = hexafluoroacetylacetone) were synthesized almost quantitatively by the reaction of [M(bpca)(2)] and [M'(hfac)(2)] in 1:2 molar ratio, and their structures and magnetic properties were investigated. Three complexes, with M' = Mn, crystallize in the same space group, Pna2(1), whereas two complexes, with M' = Fe, crystallize in P4(1), and complexes within each set are isostructural to one another. In all complexes, [M(bpca)(2)] acts as a bis-bidentate bridging ligand to form a linear trinuclear complex in which three metal ions are arranged in the manner M'-M-M'. The central metal ion is in a strong ligand field created by the N(6) donor set, and hence the Fe(II) in the [Fe(bpca)(2)] moiety is in a low-spin state. The terminal metal ions (M') are surrounded by O(6) donor sets with a moderate ligand field, which leads to the high-spin configuration of Fe(II). Three metal ions in all complexes are almost collinear, and metal-metal distances are ca. 5.5 A. The magnetic behavior of NiMn(2) and NiFe(2) shows a weak ferromagnetic interaction between the central Ni(II) ion and the terminal Mn(II) or Fe(II) ions. In these complexes, sigma-spin orbitals of the central Ni(II) ion and those of terminal metal ions have different symmetry about a 2-fold rotation axis through the Ni-N(amide)-M'(terminal) atoms, and this results in orthogonality between the neighboring sigma-spin orbitals and thus ferromagnetic interactions.     

Preparation and magnetic properties of Mn(hfac)(2)-complexes of 2-(5-pyrimidinyl)- and 2-(3-pyridyl)-substituted nitronyl nitroxides

Mn(hfac)(2) complexes of [2-(5-pyrimidinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H- imidazoline-1-oxyl 3-oxide] (1) and its 2-(3-pyridyl) analogue (2) were prepared. Both complexes formed similar dimer structures. However, their packing patterns were considerably different. The pyrimidine dimers were aligned to form a linear chain structure, and each dimer was weakly bound by two sets of O6-C2 short contacts. In the pyridine dimer complex, two structurally similar but independent dimers were alternatively arranged, and two dimer-dimer contacts, O6-C2 (3.13 A) and O6-C3 (3.30 A), were observed. The pyrimidine complex showed strong antiferromagnetic behavior in the high temperature region (150-300 K) and weak ferromagnetic behavior below 100 K. Two models were used to analyze these magnetic properties. One is a quintet-septet thermal equilibrium model with mean-field approximation, which can reproduce the round minimum observed at about 150 K in chi(p)T plots (J(1)/k(B) = -148 +/- 2 K with theta = +2.5 +/- 0.1 K). The other is a ferromagnetic S = 2 chain model to fit the chi(p)T values in the lower temperature region (J(S=2)/k(B) = +0.31 +/- 0.01 K). The pyridine complex showed antiferromagnetic interactions both in the high and low temperature regions. The magnetic behavior was similarly analyzed with the following parameters: J(1)/k(B) = -140 +/- 2 K with theta = -0.55 +/- 0.05 K, and J(S=2)/k(B) = -0.075 +/- 0.003 K. The ligand-ligand interactions for both of the complexes were theoretically analyzed. The calculated results agreed well with the experiments. The stronger antiferromagnetic behavior observed in both the complexes at high temperatures was attributed to the magnetic interaction between the Mn(II) and the coordinating nitroxide oxygen atom. The weaker ferromagnetic interaction, J(S=2)/k(B) = +0.31 +/- 0.01 K, in the pyrimidine complex was attributed to the coulombic O6-C2 contact. Antiferromagnetic interaction J(S=2)/k(B) = -0.075 +/- 0.003 K in the pyridine complex was attributed to the O6-C3 contact.     

Heterocycle-substituted stable thioaminyl radicals: isolation, ESR spectra, and magnetic properties(1)

N-[(2-Benzothiazolyl)thio]- (1), N-[(2-benzoxazolyl)thio]- (2), and N-(2-pyrimidylthio)-2,4,6-trisubstituted-phenylaminyls (3) were generated by oxidation of the corresponding amines. Although 2 and 3 were not sufficiently persistent to be isolated, 1 was very persistent and could be isolated as radical crystals. The ESR spectra of nondeuterated and partially deuterated 1-3 radicals were measured, and the spin density distributions were estimated from the hyperfine coupling constants. Ab initio molecular orbital calculations were made for 1 to discuss the spin density distribution in more detail. Single-crystal X-ray crystallographic analysis was performed for one radical. Magnetic properties were measured for isolated four radicals with a SQUID. Two radicals showed ferromagnetic interaction, and analyses of chiT vs T plots with the one-dimensional regular Heisenberg model gave 2J/k(B) = 5.8 and 8.6 K. The remaining two radicals showed antiferromagnetic interaction. Analyses of the chiT vs T plots with the Curie-Weiss law or dimer model gave theta = -1.4 K and 2J/k(B) = -1370 K. The strong antiferromagnetic interaction could be explained in terms of the X-ray crystallographic results.     

Preparation, structure, and magnetic interaction of a Mn(hfac)2-bridged [2-(3-pyridyl)(nitronyl nitroxide)-Mn(hfac)2]2 chain complex

A new one-dimensional chain complex, Mn(hfac)(2)-bridged [2-(3-pyridyl)(nitronyl nitroxide)Mn(hfac)(2)](2), was prepared and its structure and magnetic properties were elucidated; the complex exhibited a large antiferromagnetic interaction of J(1)=-185 K between the three Mn(ii) atoms and the two nitronyl nitroxides to give S=13/2 spin units and a small ferromagnetic interaction of J(3)'=+0.02 K between these spin units at low temperatures (50-1.9 K), compatible with the theoretical analysis for model compounds.     

Synthesis and magnetic properties of heterometal cyclic tetranuclear complexes [Cu(II)LM(II)(hfac)]2 (M(II) = Zn,Cu, Ni,Co, Fe,Mn; H3L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane; Hhfac = hexafluoroacetylacetone)

A series of heterometal cyclic tetranuclear complexes [Cu(II)LM(II)(hfac)](2) (M(II) = Zn (1), Cu (2), Ni (3), Co (4), Fe(5), and Mn (6)) have been synthesized by the assembly reaction of K[CuL] and [M(II)(hfac)(2)(H(2)O)(2)] with a 1:1 mole ratio in methanol, where H(3)L = 1-(2-hydroxybenzamido)-2-((2-hydroxy-3-methoxybenzylidene)amino)ethane and Hhfac = hexafluoroacetylacetone. The crystal structures of 2, 4, and [Cu(II)LMn(II)(acac)](2) (6a) (Hacac = acetylacetone) were determined by single-crystal X-ray analyses. Each complex has a cyclic tetranuclear Cu(II)(2)M(II)(2) structure, in which the Cu(II) complex functions as a "bridging ligand complex", and the Cu(II) and M(II) ions are alternately arrayed. One side of the planar Cu(II) complex coordinates to one M(II) ion at the two phenoxo and the methoxy oxygen atoms, and the opposite side of the Cu(II) complex coordinates to another M(II) ion at the amido oxygen atom. The temperature-dependent magnetic susceptibilities revealed spin states of S(M) = 0, 1/2, 1, 3/2, 2, and 5/2 for the Zn(II), Cu(II), Ni(II), Co(II), Fe(II), and Mn(II) ions, respectively. Satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a rectangular arrangement with two different g-factors for the Cu(II) and M(II) ions, two different isotropic magnetic exchange interactions, J(1) and J(2), between the Cu(II) and M(II) ions, and a zero-field splitting term for the M(II) ion. In all cases, the antiferromagnetic coupling constants were found for both exchange interactions suggesting nonzero spin ground states with S(T) = 2/S(M) - S(Cu)/, which were confirmed by the analysis of the field-dependent magnetization measurements.     

Crystal structure and magnetic properties of dicarboxylate-bridged linear chain Mn(II) complexes

Two manganese(II) complexes, [Mn(mtm)(CH₃OH)₂(H₂O)]_n (1) and [Mn₂(mtm)₂(2,2′-bipy)₂]_n (2) (bipy=bipyridine, mtm=[bis(methylthio)methylene]malonate) were synthesized and characterized by X-ray crystallography. Structure of 1 consists of octahedral manganese(II) species which are extended by carboxylate bridges in syn–anti fashion along the c-axis. Chains of 1 are associated by hydrogen bonding among coordinating water and methanol molecules and carboxylate oxygen atoms, forming two-dimensional structures. The crystallographic asymmetric unit of 2 comprises two [Mn(2,2′-bipy)(mtm)] units in which Mn(II) atoms are bridged by μ₂-oxygens from carboxylate to form Mn₂O₂ rhombus. The dimeric units are linked doubly by second carboxylates in syn–anti fashion, resulting in a chain structure. The antiferromagnetic coupling of Mn(II) ions in 1 (−0.2 cm⁻¹) and 2 (−1.57 cm⁻¹) was determined from variable-temperature magnetic susceptibility data in the temperature range of 2–300 K.     

Syntheses, crystal structures, and magnetic properties of one-dimensional oxalato-bridged Co(II), Ni(II), and Cu(II) complexes with n-aminopyridine (n = 2-4) as terminal ligand

The reaction of M(ox) x 2H(2)O (M = Co(II), Ni(II)) or K(2)(Cu(ox)(2)) x 2H(2)O (ox = oxalate dianion) with n-ampy (n = 2, 3, 4; n-ampy = n-aminopyridine) and potassium oxalate monohydrate yields one-dimensional oxalato-bridged metal(II) complexes which have been characterized by FT-IR spectroscopy, variable-temperature magnetic measurements, and X-ray diffraction methods. The complexes M(mu-ox)(2-ampy)(2) (M = Co (1), Ni (2), Cu (3)) are isomorphous and crystallize in the monoclinic space group C2/c (No. 15), Z = 4, with unit cell parameters for 1 of a = 13.885(2) A, b = 11.010(2) A, c = 8.755(1) A, and beta = 94.21(2) degrees. The compounds M(mu-ox)(3-ampy)(2).1.5H(2)O (M = Co (4), Ni (5), Cu (6)) are also isomorphous and crystallize in the orthorhombic space group Pcnn (No. 52), Z = 8, with unit cell parameters for 6 of a = 12.387(1), b = 12.935(3), and c = 18.632(2) A. Compound Co(mu-ox)(4-ampy)(2) (7) crystallizes in the space group C2/c (No. 15), Z = 4, with unit cell parameters of a = 16.478(3) A, b = 5.484(1) A, c = 16.592(2) A, and beta = 117.76(1) degrees. Complexes M(mu-ox)(4-ampy)(2) (M = Ni (8), Cu (9)) crystallize in the orthorhombic space group Fddd (No. 70), Z = 8, with unit cell parameters for 8 of a = 5.342(1), b = 17.078(3), and c = 29.469(4) A. All compounds are comprised of one-dimensional chains in which M(n-ampy)(2)(2+) units are sequentially bridged by bis-bidentate oxalato ligands with M.M intrachain distances in the range of 5.34-5.66 A. In all cases, the metal atoms are six-coordinated to four oxygen atoms, belonging to two bridging oxalato ligands, and the endo-cyclic nitrogen atoms, from two n-ampy ligands, building distorted octahedral surroundings. The aromatic bases are bound to the metal atom in cis (1-6) or trans (7-9) positions. Magnetic susceptibility measurements in the temperature range of 2-300 K show the occurrence of antiferromagnetic intrachain interactions except for the compound 3 in which a weak ferromagnetic coupling is observed. Compound 7 shows spontaneous magnetization below 8 K, which corresponds to the presence of spin canted antiferromagnetism.     

Syntheses,structures and magnetic properties of Mn(II) containing 3D polymeric networks

Two novel 3D coordination polymers {[Mn(aip)(DMF)]}_n, CPO-9, and {[Mn₃(Hatp)₂(atp)₂](H₂O)₂(DEF)₄}_n CPO-10 (aip = 5-aminoisophthalate, atp = 2-aminoterephthalate, DMF = dimethylformamide, DEF = diethylformamide) have been synthesized by solvothermal methods. Their properties have been studied by single-crystal X-ray diffraction, thermogravimetric analysis, high-temperature powder X-ray diffraction and magnetic susceptibility measurements. The crystal structure of CPO-9 is based on infinite chains of carboxylato-bridged five-coordinated Mn(II) ions that are crosslinked via the aip ligands to form a 3D structure. CPO-10 is based on linear trinuclear building units of carboxylato-bridged octahedral Mn(II) ions that are crosslinked by the atp ligands into a 3D structure. Both compounds have 1D channels that contain solvent molecules. The solvent accessible void volume for CPO-10 is 51.9% of the unit cell volume. For both compounds, however, the solvent molecules cannot be removed without the collapse of the structures into amorphous phases at 250 °C. The magnetic susceptibility measurements indicate antiferromagnetic couplings between the Mn(II) ions in both compounds. The magnetic data have been fitted using theoretical approaches.     

2D and 3D Cu(hfac)2 complexes with nitronyl nitroxide biradicals

Reactions between Cu(hfac)2 and nitronyl nitroxide biradicals 1,4-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]butane (L4) and 1,8-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]octane (L8) gave respectively a framework compound [Cu(hfac)2]2L4 and a layered polymer compound [Cu(hfac)2]2L8. The framework of [Cu(hfac)2]2L4 consists of 66-membered condensed metallocycles. Inside the framework, the structure has macrohelixes (pitch approximately 25 A) extending along the [001] crystallographic direction. All the helixes have the same direction of winding; the crystals, therefore, are optically active, the structure corresponding either to P-isomer (P4(1)2(1)2) or to M-isomer (P4(3)2(1)2). The long distances between the Cu atoms and the O atoms of the coordinated >N-O groups (Cu-O 2.351-2.467 A) are responsible for ferromagnetic exchange interactions in Cu2+-O-N< and >N-O-Cu2+-O-N< exchange clusters.     

Magnetic resonance in Cu(hfac)2LR heterospin chain polymer complexes

Cu(hfac)₂ chain polymer heterospin complexes with pyrazole-substituted nitronylnitroxides (L^R, where R = Me, Et) with a composition Cu(hfac)₂L^R, exhibiting structural rearrangements with magnetic effects in the solid state at reduced temperatures, were studied by magnetic resonance. The magnetic resonance spectrum changes substantially for substituents of different types. The results of this study are discussed in the context of the cluster approach in view of the specific crystal structure of the compounds.     

TG,DTA and electrical conductance properties of some Cu(II) AND Mn(II) bisazo- dianils complexes

The TG and DTA of a new series of Mn(II) and Cu(II) complexes with a number of newly prepared bisazo-dianil ligands were studied in the temperature range (20-700°C). The TG and DTG curves display to main steps, the first one within the temperature range (25-330°C) correspond to the elimination of water or and ethanol from the complexes. The second step within the range (350-625°C) is due to the decomposition of the complexes yielding the metal oxides as the final product. The rate constants of the dehydration and decomposition reactions were determined, from which some kinetic parameters were evaluated. The DTA curves show that the dehydration of the metal complexes is an endothermic reaction. In all cases the anhydrous metal complexes undergo exothermic decomposition reactions to give the metal oxide. The thermodynamic parameters (ΔE, ΔH, ΔS, ΔG) for the occurring processes are calculated. The electrical conductivities of the solid complexes were measured and the activation energy of the complex and its free ligand are also calculated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ferromagnetic Mn(II).Cu(II) Exchange in the New Bimetallic Quasi-2-D Compound Cu(op)(2)MnCl(4) (op = 1,4-Diazacycloheptane)

The synthesis, crystal structure, and magnetic properties are reported for the new bimetallic compound Cu(op)(2)MnCl(4), where op = HN(CH(2))(5)NH. The compound, C(10)H(24)N(4)Cl(4)CuMn, crystallizes in the monoclinic space group P2(1)/n. Cell dimensions are as follows: a = 15.316(3) ?, b = 16.608(3) ?, c = 7.141(2) ?, beta = 100.01(5) degrees, Z = 4. The structure consists of well-separated and magnetically equivalent layers which are composed of chloride-bridged Cu(op)(2)MnCl(4) binuclear units connected by rather loose Cu-N-H.Cl-Mn contacts. The MnCl(4) fragment approximates tetrahedral symmetry. The Cu(II) geometry is (4 + 1) square-pyramidal with the apical position occupied by a bridging chloride ligand and the basal ones by the nitrogen atoms from the organic ligands. The shortest interlayer M.M separations, approximately 7 ?, are of the Mn.Cu type. Magnetic susceptibility and single-crystal EPR measurements for the compound have been carried out over the range 4-300 K. At room temperature the chiT product (per MnCu unit) has a value of 4.84 emu.mol(-)(1).K, close to that expected for uncoupled S = (5)/(2) and S = (1)/(2) spins. When the temperature is lowered, chiT remains almost constant until 80-90 K, slightly increases to reach a maximum at approximately 13 K (5.21 emu.mol(-)(1).K), and then rapidly decreases. Comparison between theory and experiment, made with use of both a mean field corrected dimer model and an approximate 2-D model, indicates that Mn(II).Cu(II) exchange is ferromagnetic within the dimers (J(1) approximately 2.6 cm(-)(1)) and antiferromagnetic among dimers, with J values between -0.07 and -0.03 cm(-)(1) (the interaction Hamiltonian is of the form H = -2JS(A).S(B)). Single-crystal EPR spectra recorded along the a, b, and c axes show a large temperature dependence of the g factors: at 4.2 K, g(a) = 2.10, g(b) = 1.96, and g(c) = 2.01. This pattern substantiates the presence of a 2-D magnetic structure with ferromagnetic intradimer exchange and interdimer antiferromagnetic exchange of weaker magnitude. The opposite signs of the interactions are ascribed to the local symmetries of the Cu(II) and Mn(II) ions.