Theoretical Studies on the Spin Exchange Interaction in Copper(II) Complexes Coordinated with Nitronyl Nitroxide

In the recent years, a wide variety of transition metal complexes with the nitronyl radical ligands have been reported1,2. These systems display the various magnetic behaviors (ferro- or antiferro-magnetism) between the unpaired electrons on the radical ligands and on the paramagnetic metal ion center. However, few theoretical studies on the metal-radical complexes were reported and quite few are known about the nature of the exchange coupling interactions. In this work, we are interested i…     

Intermolecular Ferromagnetic and Antiferromagnetic Interactions in Halogen-Bridged Copper(I) Imino Nitroxides: Crystal Structures and Magnetic Properties of [Cu(I)(&mgr;-X)(imino nitroxide)](2) (X = I or Br)

Reaction of CuI or CuBr with some imino nitroxides in methanol gave the halogen bridged dinuclear Cu(I) complexes [Cu(&mgr;-I)(impy)](2) (1), [Cu(&mgr;-I)(immepy)](2) (2), [Cu(&mgr;-Br)(immepy)](2) (3), and [Cu(&mgr;-Br)(imph-NO(2))](2) (4), respectively (impy = 2-(2'-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl, immepy = 2-(6'-methyl-2'-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl, imph-NO(2) = 2-(4'-nitrophenyl)-4,4,5,5-tetramethyl-4,6-dihydro-1H-imidazolyl-1-oxyl). Crystal structures and magnetic properties have been studied. Complexes 1-4 have dimeric structures where two copper ions are doubly bridged by halide ions in a &mgr;(2) fashion. In 1-3, each copper ion is tetrahedral with a bidentate imino nitroxide and two halide ions, and the two copper ions are separated by 2.592(2), 2.6869(8), and 2.7357(6) ?, respectively. In 4, triangular coordination sites of the copper ions are completed with a nitrogen atom from the imino nitroxide and two bromide ions bridging the two copper ions with a separation of 3.074(2) ?. Ligand imino nitroxides in 1-4 form one-dimensional radical chains, and the chains are linked with halocuprate dimer units. Structural and magnetic susceptibility data support that radicals in 1 and 4 are ferromagnetically stacked, while radicals in 2 and 3 form an antiferromagnetic chain. The magnetic behaviors are discussed in connection with the stacking modes of the radicals and bridging conformations. Crystal data (Mo Kalpha, lambda = 0.71069 ?): 1, orthorhombic, space group P2(1)2(1)2(1), a = 17.807(2) ?, b = 8.595(2) ?, c = 19.336(6) ?, and Z = 4; 2, monoclinic, space group P2(1)/c, a = 9.941(2) ?, b = 18.482(2) ?, c = 8.337(2) ?, beta = 96.41(2) degrees, and Z = 2; 3, monoclinic, space group P2(1)/c, a = 9.964(6) ?, b = 18.167(4) ?, c = 8.009(7) ?, beta = 95.81(6) degrees, and Z = 2; 4, monoclinic, space group P2(1)/c, a = 11.991(7) ?, b = 17.998(8) ?, c = 7.215(6) ?, beta = 104.07(6) degrees, and Z = 2.     

Crystal structures and magnetic properties of metal complexes bearing four nitronyl nitroxide moieties in the same coordination sphere

Mononuclear transition metal complexes of the type [M(2,6-NITpy)2](ClO4)2 x solvent (2,6-NITpy = 2,6-bis-(3'-oxide-1'-oxyl-4',4',5',5'-tetramethylimidazolin-2'-yl)pyridine; M = Ni (1), Co (2), Zn (3), Mn (4), Cu (5)) have been synthesized and characterized by single-crystal X-ray diffraction studies. Crystal data: 1, monoclinic, P2(1)/c, Z = 4, a = 20.946(2) A, b = 12.0633(2) A, c = 21.173(2) A, beta = 113.55(1) degrees; 2, monoclinic, P2(1)/c, Z = 4, a = 20.902(2) A, b = 12.0981(8) A, c = 21.215(2) A, beta = 113.130(9) degrees; 3, triclinic, P1, Z = 2, a = 11.410(1) A, b = 12.932(1) A, c = 21.609(2) A, alpha = 96.040(2) degrees, beta = 102.24(1) degrees, gamma = 114.98(1); 4, monoclinic, P2(1)/n, Z = 4, a = 11.5473(8) A, b = 19.212(1) A, c = 25.236(2) A, beta = 98.772(9) degrees; 5, triclinic, P1, Z = 2, a = 12.1604(9) A, b = 12.6961(9) A, c = 18.103(2) A, alpha = 84.191(8) degrees, beta = 73.392(8) degrees, gamma = 66.072(8). The two 2,6-NITpy biradicals behave as terdentate ligands and bind almost perpendicular to each other in meridional positions. In compounds 1-4, the pyridine rings are axially ligated and four different nitronyl nitroxide radicals bind to the metal center through their O(nitroxyl) atoms, forming the equatorial plane of a distorted octahedron. On the contrary, in the copper(II) complex (5), the two N(pyridyl) atoms are found in equatorial positions. Only two nitroxide groups are then bound to the copper(II) ion in the equatorial plane, the other two being axially ligated. The two axially bound nitronyl nitroxide radicals couple ferromagnetically to the copper center (JCu-rad(ax) = + 10 K), whereas a strong antiferromagnetic coupling between this metal ion and the equatorial nitroxide groups (JCu-rad(eq) = -460 K) is observed. The other complexes exhibit strong antiferromagnetic metal-radical interactions: JNi-rad = -240 K, for 1; JMn-rad = -120 K, for 4. Interestingly, the study of the diamagnetic zinc(II) compound (3) reveals a moderate intramolecular antiferromagnetic interaction between radicals coordinated to the same metal center (Jrad-rad = -27.7 K). This interaction is transmitted through space and is also present in the other complexes: Jrad-rad = -14 K, for 1; Jrad-rad = -10 K, for 4; Jrad-rad = -20.5 K, for 5. Antiferromagnetic intermolecular interactions are also present in all the complexes herein studied.     

Magnetic and electronic properties in novel terpyridine-based nitroxide complexes: strong radical-metal interaction via a pyridyl ring

Transition metal complexes of 2-[4'-(2,2':6',2' '-terpyridyl)]-(4,4,5,5-tetramethylimidazolinyl-3-oxide-1-oxyl) (terpy-NIT) and 2-[4'-(2,2':6',2' '-terpyridyl)]-(4,4,5,5-tetramethylimidazolinyl-1-oxyl) (terpy-IM) have been prepared. Whereas the pyridyl fragments of the free ligands are in an anti conformation, the complexes are obtained by coordination of two terpyridines in a syn conformation, forming a distorted octahedron around the metal center: [M(terpy-NIT)(2)](ClO(4))(2) (M = Ni(II) 1, Zn(II) 2, Cu(II) 3) and [M(terpy-IM)(2)](ClO(4))(2) (M = Ni(II) 4, Zn(II) 5). The ligands and their complexes have been characterized by FAB-MS, UV-vis, FT-IR spectroscopies, elemental analysis, and by EPR spectroscopy and susceptibility measurements. Single-crystal X-ray diffraction have been performed on the terpy-NIT ligand and on complexes 1, 4, and 5 giving following crystal data: terpy-NIT, monoclinic, P2(1)/c, Z = 4, a = 14.2186(5), b = 12.9129(6), c = 11.704(1) A, beta = 108.615(4) degrees; 1, orthorhombic, P(n a 2(1)), Z = 4, a = 23.6367(6), b = 8.7836(1), c = 24.2748(7) A; 4, monoclinic, P2(1), Z = 1, a = 8.738(1), b = 25.010(1), c = 11.704(1) A, beta = 102.849(3) degrees; 5, monoclinic, P2(1), Z = 1, a = 8.7463(2), b = 25.0833(5), c = 11.8168(3) A, beta = 102.757(3) degrees. For complexes 1 and 3, an antiferromagnetic behavior has been found and parametrized by considering a symmetric magnetic trimer, highlighting a strong intramolecular coupling between the metal and the radicals (average values 2J(M-NIT) = -19.6 K for M = Ni and -22.8 K for M = Cu). In the case of compound 4, an asymmetric magnetic trimer has been used to model the antiferromagnetic interactions (2J(Ni-IM1) = -13.0 K, 2J(Ni-IM2) = -5.6 K). The shape of the EPR spectra of complexes 2, 3, and 5 in solution indicates the intermediate exchange limit, of the order of a few mK, between the two nitroxide radicals through the pyridyl-metal-pyridyl fragment.     

Aminomethyl-bipyridine bearing two flexible nitronyl-nitroxide arms: a new podand for complexation of transition metals in a facial or meridional conformation

Transition metal complexes of 6-aminomethyl-bis[methyl-2-(4,5-dihydro-4,4,5,5- tetramethylimidazolinyl-3-oxide-l-oxy)]-2,2'-bipyridine, bpyN(NIT)(2), 1, have been synthesized and characterized by FAB-MS, UV-vis, FT-IR, and EPR spectroscopies, elemental analysis, and susceptibility measurements. Single-crystal X-ray diffraction studies have been performed on all compounds giving the following crystal data: bpyN(NIT)(2), 1, triclinic, P(-)1, Z = 2, a = 10.7224(4) A, b = 11.0995(4) A, c = 13.1134(3) A, alpha = 114.101(9) degrees, beta = 97.476(9) degrees, gamma = 99.667(9) degrees; ZnbpyN(NIT)(2), 2, hexagonal, P3(2), Z = 3, a = 15.4545(3) A, b = 15.4545(3) A, c = 13.5594(3) A; NibpyN(NIT)(2), 3, hexagonal, P3(2), Z = 3, a = 15.2867(1) A, b = 15.2867(1) A, c = 13.7160(1) A; CubpyN(NIT)(2), 4, triclinic, P(-)l, Z = 2, a = 11.8640(4) A, b = 13.2023(4) A, c = 13.2661(5) A, alpha = 90.539(9) degrees, beta = 104.983(9) degrees, gamma = 113.252(9) degrees. The two radicals of the free ligand 1 are almost perpendicular to one another in the solid state, favoring a weak ferromagnetic interaction (J/k(B) = 8.8 K). The complexes obtained by wrapping the ligand around a single metal center gave rise to two different coordination schemes where the two radicals of 1 adopt a ON(3)O meridional (with Ni and Zn) or a ON(3)O facial conformation (with Cu), which strongly affects the magnetic and electronic properties (O accounts for the coordinated oxygen atoms of the nitroxide radicals and N(3) accounts for the tertiary amine). For 2, a model of a dimer has been used giving rise to a weak antiferromagnetic interaction between the radicals (J/k(B) = -5.3 K). For 3, a very strong intramolecular antiferromagnetic coupling has been found and estimated at J/k(B) = -230 K and J'/k(B) = -110 K between the nickel and each radical using an asymmetric model of a trimer. For 4, an unusual magnetic behavior is observed, dominated by antiferromagnetic interactions with a residual plateau at chiT = 0.63 emu.K.mol(-)(1). Molecular modeling at the CASSCF level is in keeping with an antiferromagnetic coupling of the radical bound with the Cu(II) in the equatorial position. The combined structural, electronic, and magnetic characteristics suggest that the use of a flexible molecule provide an additional approach for fine-tuning magnetic interactions.     

Novel copper(II) induced formation of a porphyrinogen derivative: X-ray structural,spectroscopic, and electrochemical studies of porphyrinogen complexes of Cu(II) and Co(III) complex of a trispyrazolyl tripodal ligand

Copper(II) complexes of a novel pyrazole containing porphyrinogen and cobalt(III) and zinc(II) complexes of a pyrazole containing tripodal ligand having N-donor atoms have been investigated. 5-Methyl-3-formylpyrazole (MPA) on reaction with copper(II) nitrate or perchlorate in the presence of tris(2-aminoethyl)amine (tren) forms novel pyrazole-based porphyrinogen complexes [Cu(T(3)-porphyrinogen)(H(2)O)](NO(3))(2) (1a) and [Cu(T(3)-porphyrinogen)(H(2)O)](ClO(4))(2) (1b) where T(3)-porphyrinogen is 1,6,11,16-tetraaza-5,10,15,20-tetrahydroxy-2,7,12,17-tetramethylporphyrinogen. The same products are also obtained when tren is replaced by triethylamine. By contrast, the reaction between MPA, tren, and cobalt(II) perchlorate produces the cobalt(III) complex [Co(HMPz(3)tren)]ClO(4) (2) derived from the tripodal Schiff base tris[4-(3-(5-methyl-pyrazolyl)-3-aza-3-butenyl]amine (H(3)MPz(3)tren). The X-ray crystal structures of the copper(II) complexes (1a and 1b) and the cobalt(III) complex (2) have been determined. The structures show distorted square pyramidal coordination environments for 1a and 1b with the water molecule occupying the apical site, while for complex 2 a distorted octahedral geometry is obtained. Data for 1a follow: a = 19.476(3) A, b = 9.4116(8) A, c = 14.204(3) A; alpha = 90 degrees = gamma, beta = 107.58(2) degrees; V = 2482.0(7) A(3), Z = 4. Data for 1b follow: a = 20.967(3) A, b = 9.1563(18) A, c = 14.858(4) A; alpha = 90 degrees = gamma, beta = 108.44(3) degrees; V = 2706.0(10) A(3), Z = 4. Data for 2 follow: a = 21.293(3) A, b = 12.724(2) A, c = 19.777(4) A; alpha = 90 degrees = gamma, beta = 93.03(2) degrees; V = 5350.6(15) A(3), Z = 8. All three complexes crystallize in the monoclinic crystal system with the C2/c space group. The complexes are further characterized by UV-vis, IR, EPR, and electrochemical studies.     

Radical-copper wheels: structure and magnetism of hexanuclear hybrid arrays

Complexation of copper(II) bromide and chloride with 4-pyrimidinyl nitronyl nitroxide (4PMNN) as a bridging ligand gave discrete hexanuclear complexes carrying 12 spins, [CuX(2).(4PMNN)](6) [X = Br (1), Cl (2)], which crystallize in a trigonal space group. The crystallographic parameters are C(11)H(15)Br(2)CuN(4)O(2).0.3H(2)O, a = 28.172(2), c = 12.590(2) A, V = 8653(2) A(3), and Z = 18 for 1, and C(11)H(15)Cl(2)CuN(4)O(2).0.3H(2)O, a = 28.261(2), c = 12.378(1) A, and Z = 18 for 2. The hexanuclear arrays construct a perfect column perpendicular to the molecular plane. The diameter of the resultant honeycomblike channel is ca. 11.5 A defined by the interatomic distance of two opposing copper ions. Their magnetic behavior is interpreted as the simultaneous presence of ferro and antiferromagnetic couplings. The ferromagnetic couplings are attributed to the interactions between a copper spin and the axially coordinated nitronyl nitroxide spin and between nitronyl nitroxide groups through van der Waals contacts. The antiferromagnetic coupling is due to the interaction between copper ions across the pyrimidine bridges.     

Copper(I) complexes, copper(I)/O(2) reactivity, and copper(II) complex adducts, with a series of tetradentate tripyridylalkylamine tripodal ligands

Copper(I) and copper(II) complexes possessing a series of related ligands with pyridyl-containing donors have been investigated. The ligands are tris(2-pyridylmethyl)amine (tmpa), bis[(2-pyridyl)methyl]-2-(2-pyridyl)ethylamine (pmea), bis[2-(2-pyridyl)ethyl]-(2-pyridyl)methylamine (pmap), and tris[2-(2-pyridyl)ethyl]amine (tepa). The crystal structures of the protonated ligand H(tepa)ClO(4), the copper(I) complexes [Cu(pmea)]PF(6) (1b-PF(6)), [Cu(pmap)]PF(6) (1c-PF(6)), and copper(II) complexes [Cu(pmea)Cl]ClO(4).H(2)O (2b-ClO(4).H(2)O), [Cu(pmap)Cl]ClO(4).H(2)O (2c-ClO(4).H(2)O), [Cu(pmap)Cl]ClO(4) (2c-ClO(4)), and [Cu(pmea)F](2)(PF(6))(2) (3b-PF(6)) were determined. Crystal data: H(tepa)ClO(4), formula C(21)H(25)ClN(4)O(4), triclinic space group P1, Z = 2, a = 10.386(2) A, b = 10.723(2) A, c = 11.663(2) A, alpha = 108.77(3) degrees, beta = 113.81(3) degrees, gamma = 90.39(3) degrees; 1b-PF(6), formula C(19)H(20)CuF(6)N(4)P, orthorhombic space group Pbca, Z = 8, a = 14.413(3) A, b = 16.043(3) A, c = 18.288(4) A, alpha = beta = gamma = 90 degrees; (1c-PF(6)), formula C(20)H(22)CuF(6)N(4)P, orthorhombic space group Pbca, Z = 8, a = 13.306(3) A, b = 16.936(3) A, c = 19.163(4) A, alpha = beta = gamma = 90 degrees; 2b-ClO(4).H(2)O, formula C(19)H(22)Cl(2)CuN(4)O(5), triclinic space group P1, Z = 4, a = 11.967(2) A, b = 12.445(3) A, c = 15.668(3) A, alpha = 84.65(3) degrees, beta = 68.57(3) degrees, gamma = 87.33(3) degrees; 2c-ClO(4).H(2)O, formula C(20)H(24)Cl(2)CuN(4)O(5), monoclinic space group P2(1)/c, Z = 4, a = 11.2927(5) A, b = 13.2389(4) A, c = 15.0939(8) A, alpha = gamma = 90 degrees, beta = 97.397(2) degrees; 2c-ClO(4), formula C(20)H(22)Cl(2)CuN(4)O(4), monoclinic space group P2(1)/c, Z = 4, a = 8.7682(4) A, b = 18.4968(10) A, c = 13.2575(8) A, alpha = gamma = 90 degrees, beta = 94.219(4) degrees; 3b-PF(6), formula [C(19)H(20)CuF(7)N(4)P](2), monoclinic space group P2(1)/n, Z = 2, a = 11.620(5) A, b = 12.752(5) A, c = 15.424(6) A, alpha = gamma = 90 degrees, beta = 109.56(3) degrees. The oxidation of the copper(I) complexes with dioxygen was studied. [Cu(tmpa)(CH(3)CN)](+) (1a) reacts with dioxygen to form a dinuclear peroxo complex that is stable at low temperatures. In contrast, only a very labile peroxo complex was observed spectroscopically when 1b was reacted with dioxygen at low temperatures using stopped-flow kinetic techniques. No dioxygen adduct was detected spectroscopically during the oxidation of 1c, and 1d was found to be unreactive toward dioxygen. Reaction of dioxygen with 1a-PF(6), 1b-PF(6), and 1c-PF(6) at ambient temperatures leads to fluoride-bridged dinuclear copper(II) complexes as products. All copper(II) complexes were characterized by UV-vis, EPR, and electrochemical measurements. The results manifest the dramatic effects of ligand variations and particularly chelate ring size on structure and reactivity.     

Synthesis, structural and magnetic properties of a series of copper(II) complexes containing a monocarboxylated perchlorotriphenylmethyl radical as a coordinating open-shell ligand

A series of complexes of copper(II)-containing a perchlorotriphenylmethyl radical functionalized with a carboxylic group as a new ligand is reported. The compounds [Cu(PTMMC)(2)(L)(3)](PTMMC = (tetradecachloro-4-carboxytriphenyl)methyl radical; L =(1) H(2)O, (2) pyrimidine and ethanol or (3) pyridine), [Cu(2)(PTMMC)(2)(MeCOO)(2)(H(2)O)(2)](4) and [Cu(HPTMMC)(2)(L)(3)](HPTMMC =alpha-H-(tetradecachlorotriphenyl)methane-4-carboxylic acid; L = pyridine)(5) were structurally characterized. In complexes 1, 2, 3, and 5, the copper(II) ion is coordinated to two PTMMC (or HPTMMC) units in a slightly distorted square planar surrounding, while 4 shows a paddle-wheel copper(II) dimer structure, where each Cu metal ion has four O atoms of different carboxylate groups, two of them belonging to two PTMMC radicals. The copper(II)-radical exchange couplings are antiferromagnetic for complexes 1, 2 and 3. A linear three-spin model was applied to complexes 1, 2 and 3 to give J/k(B)=-24.9, -15.0 and -20.7 K, respectively. Magnetic properties of 4 show that it is one of the scarce examples of a spin-frustrated system composed of organic radicals and metal ions. In this case, experimental data were fitted to a magnetic model based on a symmetrical butterfly arrangement to give a copper(II)-copper(II) exchange coupling of J/k(B)=-350.0 K and a copper(II)-radical exchange coupling of J/k(B)=-21.3 K, similar to that observed for the copper(II)-radical interactions in complexes, and.     

Syntheses, crystal structures, magnetic properties, and EPR spectra of tetranuclear copper(II) complexes featuring pairs of "roof-shaped" Cu2X2 dimers with hydroxide, methoxide, and azide bridges

Hydroxo- and methoxo-bridged tetranuclear copper(II) complexes of the tetramacrocyclic ligand 1,2,4,5-tetrakis(1,4,7-triazacyclonon-1-ylmethyl)benzene (Ldur), have been prepared from [Cu4Ldur(H2O)8](ClO4)8.9H2O (1). Addition of base to an aqueous solution of 1 gave [Cu4Ldur(mu2-OH)4](ClO4)4 (2). Diffusion of MeOH into a DMF solution of 2 produces [Cu4Ldur(mu2-OMe)4](ClO4)4.HClO4.2/3MeOH (3), a complex which hydrolyzes on exposure to moisture regenerating 2. The structurally related azido-bridged complex, [Cu4Ldur(mu2-N3)4](PF6)4.4H2O.6CH3CN (4), was produced by reaction of Ldur with 4 molar equiv of Cu(OAc)2.H2O and NaN3 in the presence of excess KPF6. Compounds 2-4 crystallize in the triclinic space group P1 (No. 2) with a = 10.248(1) A, b = 12.130(2) A, c = 14.353(2) A, alpha = 82.23(1) degrees, beta = 80.79(1) degrees, gamma = 65.71(1) degrees, and Z = 1 for 2, a = 10.2985(4) A, b = 12.1182(4) A, c = 13.9705(3) A, alpha = 89.978(2) degrees, beta = 82.038(2) degrees, gamma = 65.095(2) degrees, and Z = 1 for 3, and a = 12.059(2) A, b = 12.554(2) A, c = 14.051(2) A, alpha = 91.85(1) degrees, beta = 98.22(1) degrees, gamma = 105.62(1) degrees, and Z = 1 for 4. The complexes feature pairs of isolated dibridged copper(II) dimers with "roof-shaped" Cu2(mu2-X)2 cores (X = OH-, OMe-, N3-), as indicated by the dihedral angle between the two CuX2 planes (159 degrees for 2, 161 degrees for 3, and 153 degrees for 4). This leads to Cu.Cu distances of 2.940(4) A for 2, 2.962(1) A for 3, and 3.006(5) A for 4. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -27 cm(-1)) for the hydroxo-bridged copper(II) centers in 2 and very strong antiferromagnetic coupling (J = -269 cm(-1)) for the methoxo-bridged copper(II) centers in 3. Pairs of copper(II) centers in 4 display the strongest ferromagnetic interaction (J = 94 cm(-1)) reported thus far for bis(mu2-1,1-azido)-bridged dicopper units. Spectral measurements on a neat powdered sample of 4 at 33.9 GHz or 90 Ghz confirm the spin-triplet ground state for the azido-bridged copper(II) pairs.     

Solvent-dependent coordination polymers: cobalt complexes of 3,5-dinitrobenzoic acid and 3,5-dinitro-4-methylbenzoic acid with 4,4'-bipyrdine

The synthesis, structure elucidation, and analysis of the self-assembly of Co(II) complexes of 3,5-dinitrobenzoic acid and 3,5-dinitro-4-methylbenzoic acid with 4,4'-bipyridine have been reported. Formation of the complexes and the self-assembly in the three-dimensional structures have been found to be dependent on the solvents (such as acetone, dimethly sulfoxide, etc.) employed for the synthesis of the aggregates. 3,5-Dinitrobenzoic acid forms two coordination polymers, 1a and 1b, from methanol and a mixture of methanol and acetone solvents, respectively, with entirely different recognition patterns. Similarly, 3,5-dinitro-4-methylbenzoic acid also forms two coordination complexes, 2a and 2b, incorporating the solvent of the reaction medium into the crystal lattice. Complex 2a forms a solvated channel structure, whereas 2b gives a bilayered structure, with the layers being separated by solvent of crystallization (dimethyl sulfoxide) molecules. All the complexes have been characterized by single-crystal X-ray diffraction studies. Complexes 1b, 2a, and 2b crystallize in a monoclinic lattice, but 1a adopts a tetragonal lattice. The unit cell dimensions are, for 1a, a = 8.095(1) A, b = 8.095(1) A, c = 46.283 (6) A, alpha = 90 degrees, beta = 90 degrees, and gamma = 90 degrees (space group P4(3)2(1)2, Z = 4), for 1b, a = 22.774(2) A, b = 11.375 (1) A, c = 22.533(2) A, alpha = 90 degrees, beta = 104.15(1) degrees, and gamma = 90 degrees (space group P2(1)/c, Z = 4), for 2a, a = 17.657(6) A, b = 18.709(4) A, c = 21.044(6) A, alpha = 90 degrees, beta = 108.68(3) degrees, and gamma = 90 degrees (space group, C2/c, Z = 8), and, for 2b, a = 11.025(5) A, b = 15.139(4) A, c = 11.443(4) A, alpha = 90 degrees, beta = 97.48(3) degrees, and gamma = 90 degrees (space group P2/n, Z = 2). In all the complexes 1a, 1b, 2a, and 2b, the basic interaction between Co(II) and 4,4'-bipyridine remains the same with the formation of linear Co-N dative bonds, but the carboxylates display various modes of interaction with Co(II). The average Co-N and Co-O distances are 2.161 and 2.108 A, respectively.     

Syntheses,crystal engineering,and magnetic property of a dicyanamide bridged three-dimensional manganese(II)-nitronyl nitroxide coordination polymer derived from a new radical

Syntheses, structural characterization, crystal engineering, and variable-temperature magnetic study at fixed field strength of a novel dicyanamide bridged three-dimensional manganese(II)-nitronyl nitroxide compound, [Mn(II)(NIT-tz)(dca)(2)] (1), (NIT-tz = 2-(2-thiazole)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide, a new Ullman type radical) have been described. The compound crystallizes in the orthorhombic P2(1)2(1)2(1) space group with the following unit cell parameters: a = 11.015(2) A, b = 12.6134(14) A, c = 13.7652(9) A, and Z = 4. In this complex, the radical behaves as a bidentate chelating ligand, while four single end-to-end dicyanamide (dca) units construct the three-dimensional structure. Inside the structure, there exist diamond-shaped channels, spiral networks, and helical chains. Variable-temperature (5-300 K, 1 T) magnetic susceptibility data reveal the existence of antiferromagnetic interaction in this molecule. The magnetic behavior is explained by considering the exchange-coupled manganese(II)-radical system, which is subjected to the Mn(II)-dca-Mn(II) intermolecular interactions (H = -2JS(1).S(2) - 2zJ'S). The least-squares fitting of the data results J = -73 cm(-)(1), g = 1.99, and J' = -0.17 cm(-)(1) (z = 4).     

Design of high-dimensional copper(II) malonate complexes with exo-polydentate N-donor ligands

Two polymeric malonato-bridged copper(II) complexes of formulas [(H(2)bpe)[Cu(mal)2]]n.4nH2O (1) and [Cu(4")(mal)(4)(bpe)(3)]n.6nH(2)O (2) [mal = malonate dianion; bpe = 1,2-bis(4-pyridyl)ethylene] have been synthesized and characterized by X-ray diffraction. Complex 1 crystallizes in triclinic space group P(-)1, Z = 1, with unit cell parameters a = 4.8831(10) A, b = 9.585(2) A, c = 11.813(2) A, alpha = 77.29(3) degrees, beta = 82.18(3) degrees, and gamma = 84.92(3) degrees, whereas complex 2 crystallizes in the monoclinic space group P2(1)/n, Z = 4, with unit cell parameters a = 13.462(3) A, b = 10.275(5) A, c = 19.579(4) A, and beta = 105.21(3) degrees. The structure of 1 consists of anionic malonato-bridged uniform copper(II) chains which are connected through hydrogen bonds involving malonate-oxygen atoms, noncoordinated water molecules, and H(2)bpe(2+) cations. The intrachain copper-copper separation through carboxylate-malonate bridge in the anti-syn conformation is 4.8831(10) A. Complex 2 possesses a three-dimensional structure made up of neutral corrugated malonated-bridged copper(II) layers linked through bis-monodentate bpe molecules. The copper(II) atoms within each layer are bridged by a double mu-oxo and four carboxylato-malonate bridges with copper-copper separations of 3.4095(7) A (through oxo) and 4.9488(11)-6.5268(13) A (through carboxylato). The shortest interlayer copper-copper separation across bridging bpe is 13.434(3) A. Variable-temperature magnetic measurements (2-290 K) show an overall ferromagnetic behavior for both compounds. The magnetic pathway of complex 1 is through a single carboxylate-malonate bridge connecting apical and equatorial positions of adjacent copper(II) atoms, and the value of the magnetic coupling (J) for 1 through a numerical expression for a ferromagnetic uniform chain of interacting local doublets is J = +0.049(1) cm(-1). The values for the magnetic couplings through the main intralayer exchange pathways in 2 which correspond to carboxylate-malonate bridges connecting equatorial-equatorial (J(1)) and equatorial-apical (J(2)) coordination sites and to the double mu-oxo bridge linking equatorial-apical (J(5)) positions have been determined through a simplified model. The three magnetic couplings are weak, two of them being ferromagnetic (J(1) = +23(1) cm(-1) and J(2) = +6.5(1) cm(-1)) and the other one antiferromagnetic [zJ' = -1.0(1) cm(-1)]. The values of the magnetic couplings in 1 and 2 compare well with those previously reported for similar malonato-bridged copper(II) complexes of different dimensionalities.     

含羟基基团取代的氮氧自由基构筑的三个双核稀土化合物的结构及磁性表征

以三氟乙酰丙酮(tfac)为共配体的稀土配合物分别与5-溴-2-羟基苯取代的自由基配体和5-硝基-2-羟基苯取代的自由基配体进行反应,合成3个稀土-自由基配合物[Ln2(tfac)4(NIT-5Br-2PhO)2](Ln=Gd (1),Dy(2))和[Dy2(tfac)4(NIT-5NO2-2PhO)2](3)(NIT...     

Synthesis, Structure, and Reactivity of Model Complexes of Copper Nitrite Reductase

The copper(I) and copper(II) complexes with the nitrogen donor ligands bis[(1-methylbenzimidazol-2-yl)methyl]amine (1-BB), bis[2-(1-methylbenzimidazol-2-yl)ethyl]amine (2-BB), N-acetyl-2-BB (AcBB), and tris[2-(1-methylbenzimidazol-2-yl)ethyl]nitromethane (TB) have been studied as models for copper nitrite reductase. The copper(II) complexes form adducts with nitrite and azide that have been isolated and characterized. The Cu(II)-(1-BB) and Cu(II)-AcBB complexes are basically four-coordinated with weak axial interaction by solvent or counterion molecules, whereas the Cu(II)-(2-BB) and Cu(II)-TB complexes prefer to assume five-coordinate structures. A series of solid state structures of Cu(II)-(1-BB) and -(2-BB) complexes have been determined. [Cu(1-BB)(DMSO-O)(2)](ClO(4))(2): triclinic, P&onemacr; (No. 2), a = 9.400(1) ?, b = 10.494(2) ?, c = 16.760(2) ?, alpha = 96.67(1) degrees, beta = 97.10(1) degrees, gamma = 108.45(1) degrees, V = 1534.8(5) ?(3), Z = 2, number of unique data [I >/= 3sigma(I)] = 4438, number of refined parameters = 388, R = 0.058. [Cu(1-BB)(DMSO-O)(2)](BF(4))(2): triclinic, P&onemacr; (No. 2), a = 9.304(5) ?, b = 10.428(4) ?, c = 16.834(8) ?, alpha = 96.85(3) degrees, beta = 97.25(3) degrees, gamma = 108.21(2) degrees, V = 1517(1) ?(3), Z = 2, number of unique data [I >/= 2sigma(I)] = 3388, number of refined parameters = 397, R = 0.075. [Cu(1-BB)(DMSO-O)(NO(2))](ClO(4)): triclinic, P&onemacr; (No. 2), a = 7.533(2) ?, b = 8.936(1) ?, c = 19.168(2) ?, alpha = 97.66(1) degrees, beta = 98.62(1) degrees, gamma = 101.06(1) degrees, V = 1234.4(7) ?(3), Z = 2, number of unique data [I >/= 2sigma(I)] = 3426, number of refined parameters = 325, R = 0.081. [Cu(2-BB)(MeOH)(ClO(4))](ClO(4)): triclinic, P&onemacr; (No. 2), a = 8.493(3) ?, b = 10.846(7) ?, c = 14.484(5) ?, alpha = 93.71(4) degrees, beta = 103.13(3) degrees, gamma = 100.61(4) degrees, V = 1270(1) ?(3), Z = 2, number of unique data [I>/= 2sigma(I)] = 2612, number of refined parameters = 352, R = 0.073. [Cu(2-BB)(N(3))](ClO(4)): monoclinic, P2(1)/n (No. 14), a = 12.024(3) ?, b = 12.588(5) ?, c = 15.408(2) ?, beta = 101,90(2) degrees, V = 2282(1) ?(3), Z = 4, number of unique data [I >/= 2sigma(I)] = 2620, number of refined parameters = 311, R = 0.075. [Cu(2-BB)(NO(2))](ClO(4))(MeCN): triclinic, P&onemacr; (No. 2), a = 7.402(2) ?, b = 12.500(1) ?, c = 14.660(2) ?, alpha = 68.14(1) degrees, beta = 88.02(2) degrees, gamma = 78.61(1) degrees, V = 1233.0(4) ?(3), Z = 2, number of unique data [I>/= 2sigma(I)] = 2088, number of refined parameters = 319, R = 0.070. In all the complexes the 1-BB or 2-BB ligands coordinate the Cu(II) cations through their three donor atoms. The complexes with 2-BB appear to be more flexible than those with 1-BB. The nitrito ligand is bidentate in [Cu(2-BB)(NO(2))](ClO(4))(MeCN) and essentially monodentate in [Cu(1-BB)(DMSO-O)(NO(2))](ClO(4)). The copper(I) complexes exhibit nitrite reductase activity and react rapidly with NO(2)(-) in the presence of stoichiometric amounts of acid to give NO and the corresponding copper(II) complexes. Under the same conditions the reactions between the copper(I) complexes and NO(+) yield the same amount of NO, indicating that protonation and dehydration of bound nitrite are faster than its reduction. The NO evolved from the solution was detected and quantitated as the [Fe(EDTA)(NO)] complex. The order of reactivity of the Cu(I) complexes in the nitrite reduction process is [Cu(2-BB)](+) > [Cu(1-BB)](+) > [Cu(TB)](+) > [Cu(AcBB)](+).     

Structurally reinforced tetraazamacrocyclic complexes

The reaction between alkyl or aryl aldehydes and macrocyclic ligands with pendant amine groups produced imidazolidine-containing bi- or tricyclic ligands. The copper complexes of three of these ligands were structurally characterized: [CuL3Cl].3H2O (triclinic, P1, a = 10.041(2) A, b = 10.172(1) A, c = 11.202(1) A, alpha = 92.07(1) degrees, beta = 96.76(2) degrees, gamma = 92.99(1) degrees, Z = 2), [Cu(H2L4)Cl]Cl.2H2O (monoclinic, P2(1)/n, a = 15.159(5) A, b = 10.645(1) A, c = 19.094(6) A, beta = 93.78(1) degrees, Z = 4), [CuL5].2H2O.NaNO3 (monoclinic, P2(1)/n, a = 10.649(8) A, b = 7.261(2) A, c = 15.25(1) A, beta = 94.77(4) degrees, Z = 2). The conformational rigidity and stereochemical activity of these macrocycles and their complexes are discussed in comparison with close analogues.     

Synthesis,structures, and magnetic properties of a series of lanthanum(III) and gadolinium(III) complexes with chelating benzimidazole-substituted nitronyl nitroxide free radicals. Evidence for antiferromagnetic Gd(III)-radical interactions

This paper reports the synthesis, crystal structures, and magnetic properties of a series of lanthanide complexes with nitronyl nitroxide radicals of general formula [[Ln(III)(radical)(4)] x (ClO(4))(3) x (H(2)O)(x) x (THF)(y)] (1-4) and [Ln(III)(radical)(2)(NO(3))(3)] (5, 6) [Ln = La (compounds 1, 3, 5) or Gd (compounds 2, 4, and 6); radical = 2-(2'-benzymidazolyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITBzImH, compounds 1, 2, 5, 6) or 2-[2'-[(6'-methyl)benzymidazolyl]]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (NITMeBzImH, compounds 3, 4)]. (1) C(64)H(88)Cl(3)LaN(16)O(24), fw = 1710.76, orthorhombic, Fddd, a = 11.0682(8) A, b = 34.240(3) A, c = 42.787(3) A, V = 16215(2) A(3), Z = 8, R = 0.0876, R(w) = 0.2336. (2) C(64)H(88)Cl(3)GdN(16)O(24), fw = 1729.10, tetragonal, P 4 macro 2c, a = 16.0682(4) A, b = 16.0682(4) A, c = 18.7190(6) A, V = 4833.0(2) A(3), R = 0.0732, R(w) = 0.2218. (3) C(68)H(94)Cl(3)LaN(16)O(23), fw = 1742.80, tetragonal, P 4 macro 2(1)m, a = 21.125(3) A, b = 21.125(3) A, c = 10.938(2) A, V = 4881.5(14) A(3), R = 0.1017, R(w) = 0.3126. (5) C(28)H(34)LaN(11)O(13), fw = 871.57, orthorhombic, Pna2(1), a = 19.5002(12) A, b = 13.0582(8) A, c = 14.5741(9) A, V = 3711.1(4) A(3), R = 0.0331, R(w) = 0.1146. (6) C(28)H(34)GdN(11)O(13), fw = 889.91, orthorhombic, Pna2(1), a = 19.1831(10) A, b = 13.1600(7) A, c = 14.4107(7) A, V = 3638.0(3) A(3), Z = 4, R = 0.0206, R(w) = 0.0625. Compounds 1-4 consist of [M(III)(radical)(4)](3+) cations, uncoordinated perchlorate anions, THF, and water crystallization molecules. In these complexes, the coordination number around the lanthanide ion is eight, and the polyhedron is either a distorted dodecahedron (1) or a distorted cube (2, 3). The crystal structures of 5 and 6 consist of independent [M(III)(radical)(2)(NO(3))(3)] entities in which the lanthanide is ten-coordinated and has a distorted bicapped square antiprism coordination polyhedron. For the lanthanum(III) complexes, the temperature dependence of the magnetic susceptibility indicates that radical-radical magnetic interactions are negligible either for compounds 1 and 3, while for compound 5 it is simulated considering dimers of weakly antiferromagnetically coupled radicals (J(rad-rad) = -1.1 cm(-1)). In the case of the gadolinium(III) compounds (2, 4, 6), each magnetic behavior gives unambiguous evidence of antiferromagnetic Gd(III)-radical interaction (2, J(Gd-rad) = -1.8 cm(-1); 4, J(Gd-rad) = -3.8 cm(-1); 6, J(Gd-rad1) = -4.05 cm(-1) and J(Gd-rad2) = -0.80 cm(-1)), in contrast to the ferromagnetic case generally observed. The nature of the Gd(III)-radical interaction is explained in relation to the donor strength of the free radical ligand.     

Diverse solid-state and solution structures within a series of hexaamine dicopper(II) complexes

Mono- and dicopper(II) complexes of a series of potentially bridging hexaamine ligands have been prepared and characterized in the solid state by X-ray crystallography. The crystal structures of the following Cu(II) complexes are reported: [Cu(HL3)](ClO4)(3), C11H31Cl3CuN6O12, monoclinic, P2(1)/n, a = 8.294(2) A, b = 18.364(3) A, c = 15.674(3) A, beta = 94.73(2) degrees, Z = 4; ([Cu2(L4)(CO3)](2))(ClO4)(4).4H2O, C40H100Cl4Cu4N12O26, triclinic, P1, a = 9.4888(8) A, b = 13.353(1) A, c = 15.329(1) A, alpha = 111.250(7) degrees, beta = 90.068(8) degrees, gamma = 105.081(8) degrees, Z = 1; [Cu2(L5)(OH2)(2)](ClO4)(4), C13H36Cl4Cu2N6O18, monoclinic, P2(1)/c, a = 7.225(2) A, b = 8.5555(5) A, c = 23.134(8) A, beta = 92.37(1) degrees, Z = 2; [Cu2(L6)(OH2)(2)](ClO4)(4).3H2O, C14H44Cl4Cu2N6O21, monoclinic, P2(1)/a, a = 15.204(5) A, b = 7.6810(7) A, c = 29.370(1) A, beta = 100.42(2) degrees, Z = 4. Solution spectroscopic properties of the bimetallic complexes indicate that significant conformational changes occur upon dissolution, and this has been probed with EPR spectroscopy and molecular mechanics calculations.     

Verdazyl radicals as oligopyridine mimics: structures and magnetic properties of M(II) complexes of 1,5-dimethyl-3-(2,2'-bipyridin-6-yl)-6-oxoverdazyl (M = Mn,Ni, Cu,Zn)

The verdazyl radical 1,5-dimethyl-3-(2,2'-bipyridin-6-yl)-6-oxoverdazyl (3) was prepared, and its homoleptic metal complexes M(3)(2)(2+).2X(-) (5, M = Mn(II); 6, M = Ni(II); 7, M = Cu(II); 8, M = Zn(II); X = ClO(4), PF(6)) were characterized by single-crystal X-ray diffraction and variable-temperature magnetic susceptibility measurements. Relevant crystallographic parameters are as follows: 5, monoclinic space group Pna2(1), a = 18.755(4) A, b = 11.154(3) A, c = 16.594(4) A, alpha = 90.00 degrees, beta = 90.00 degrees, gamma = 90.00 degrees, V = 3471.4(13) A(3), and Z = 4; 7, triclinic space group Ponedblac;, a = 9.4638(18) A, b = 9.8442(19) A, c = 18.769(4) A, alpha = 103.746(3) degrees, beta = 92.925(3) degrees, gamma = 94.869(3) degrees, V = 1687.8(6) A(3), and Z = 2; 8, triclinic space group Ponedblac;, a = 9.4858(14) A, b = 9.7919(14) A, c = 18.889(3) A, alpha = 104.196(3) degrees, beta = 92.855(3) degrees, gamma = 94.216(3) degrees, V = 1692.1(4) A(3), and Z = 2. In all cases, the two verdazyl-based ligands bind almost perpendicular to each other in meridional positions, yielding pseudooctahedral metal complexes whose general structural features are strongly reminiscent of metal bis(terpyridine) complexes. The intramolecular metal-verdazyl magnetic exchange coupling is strongly ferromagnetic in 6 (J(Ni-vd) = +240 cm(-1)), and strongly antiferromagnetic in 5 (J(Mn-vd) = -93 cm(-1)). Complex 7 exhibits weak ferromagnetic coupling (J(Cu-vd) = -4.5 cm(-1)). Intramolecular radical-radical coupling in the zinc complex 8 was found to be weakly antiferromagnetic (J(vd-vd) = -8 cm(-1)). Intramolecular radical-radical exchange was generally weak in the four metal complexes, ranging from -10 cm(-1) (for 5) to +2 cm(-1) (for 7). The low-temperature magnetic behavior of 7 and 8 is complex, possibly arising from a combination of intra- and intermolecular interactions.     

A Novel Binuclear Cu（Ⅱ） Complex with Nitroxide Radicals Exhibiting Ferromagnetic Interactions

A new binuclear Cu(Ⅱ) complex with nitronyl nitroxide radicals [Cu(NIT3Py)2Cl2]2(NIT3Py = 2-(3'-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been synthesized and structurally characterized by X-ray diffraction analysis.It crystallizes in monoclinic,space group C2/c with a = 38.483(4),b = 7.2450(8),c = 27.559(3) ,β = 134.0180(10)°,V = 5525.6(10) 3,C48H64Cl4Cu2N12O8,Mr = 1206.00,Z = 4,Dc = 1.450 g/cm3,μ(MoKα) = 1.025 mm-1,F(000) = 2504,S = 1.066,the final R = 0.0471 and wR = 0.1121 for 3286 observed reflections(I > 2σ(I)).The title complex consists of centrosymmetric dinuclear units [Cu(NIT3Py)2Cl2]2,in which the copper ions are square-pyramidally coordinated by two pyridyl nitrogen atoms of two radical ligands and three chlorine anions,two of which bridge the copper ions.The magnetic measurements show ferromagnetic interactions between the copper ions and the radical ligands.