Zheng He

Crystal structures and magnetic behaviour of three new azido-bridged dinuclear cobalt(II) and copper(II) complexes

Three dinuclear cobalt(II) and copper(II) complexes with double end-on (EO) azido bridges, [Co2(DMP)2(N3)4] (1), [Cu2(DMP)2(N3)4] (2) and [Cu2(PAP)2(N3)4] (3) (DMP = 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine; PAP = 1-phenyl-2-(2-pyridyl)-1-azapropylene) have been synthesized and characterized by single-crystal X-ray diffraction and magnetic analyses. The EPR spectra of powder samples for the two copper(II) complexes have also been examined at room temperature and 77 K, respectively. In the isomorphous complexes 1 and 2, the metal ions are penta-coordinated with distorted trigonal bipyramidal geometries, and the EO azido bridges assume an equatorial–axial disposition between metal ions. In contrast, the copper(II) ion in complex 3 adopts a distorted square pyramidal geometry, and the EO azido bridges assume a basal–apical disposition between metal ions. According to magnetic studies, the double end-on azido bridges mediate ferromagnetic coupling with J = 18.1 cm−1 in 1, antiferromagnetic coupling with J = −27.6 cm−1 in 2, and ferromagnetic coupling with J = 35.0 cm−1 in 3.

Ligand-controlled dimensionality: 1D, 2D and 3D Gd(III) coordination polymers based on SO42− and pyridine carboxylate N-oxide ligands

Three Gd(III)-sulfate polymers [Gd(PNO)(H2O)2(SO4)]n (1), [Gd(NNO)(H2O)2(SO4)]n (2), and [Gd(INO)(H2O)(SO4)]n (3) exhibiting a systematic variation in framework dimensionality have been hydrothermally synthesized by using three isomeric pyridine carboxylate N-oxides, PNO = picolinate N-oxide, NNO = nicotinate N-oxide, and INO = isonicotinate N-oxide, as organic components. Compound 1 comprises 1D coordination chains that are unable to propagate to higher dimensionalities due to the convergent endo PNO ligand. The structure of compound 2 consists of hydrogen-bonded layers. The formation of the 2D layer is attributed to the more divergent NNO than PNO. Compound 3 consists of a 2-fold interpenetrating “3D herringbone” framework, in which the most divergent exo ligands of INO connect the individual Gd-sulfate inorganic chains to produce the 3D coordination network. It is demonstrated that the convergence or divergence of the three isomeric ligands of the pyridine carboxylate N-oxide can be used to engineer the dimensionality of the coordination polymers.

Chelating Schiff base assisted azide-bridged Mn(II), Ni(II) and Cu(II) magnetic coordination polymers

Four new Mn(II), Ni(II) and Cu(II) coordination polymers [Mn2(L1)(μ(1,1)-N3)2(μ(1,3)-N3)2]n (1), [Ni(L2)2(μ(1,3)-N3)]n(ClO4)n (2), [Cu(L3)(μ(1,1)-N3)(N3)]n (3) and [Cu(L4)(μ(1,1)-N3)2]n (4) (L1 = N,N′-bis(2-pyridylmethylene)ethane-1,2-diamine, L2 = N-(2-pyridylmethylene)methylamine, L3 = N-(2-pyridylmethylene)-3-pyridylamine, L4 = N-(2-pyridylmethylene)-tbutylamine) have been synthesized and characterized by single-crystal X-ray analysis and magnetic measurements. Complex 1 indicates a stoichiometry-dependent structural change (based on Mn:L1:N3 = 2:1:4 molar ratio) and consists of two-dimensional (2-D) (4,4) net layers, in which Mn(II) centers are co-bridged by single end-to-end (EE), double end-on (EO) azide and chelate-bridging L1 ligands. Complex 2 shows a single EE azide-bridged one-dimensional (1-D) Ni(II) chain. Complexes 3 and 4 indicate single EO and double EO azide-bridged 1-D Cu(II) chains, respectively. Complex 1 exhibits weak ferromagnetism due to its intra-layer spin-canting with T(c) = 20 K. Complex 2 shows an unusual intra-chain ferromagnetic coupling and spin-canting behaviour. Both complexes 3 and 4 exhibit intra-chain antiferromagnetic interactions. Magneto-structural parameters for these related complexes were also discussed.

High-dimensional azido-bridged cadmium(II) polymeric complexes with bis(bidentate) diazine ligands

Five new Cd(II)-azido polymeric complexes with bis(bidentate) diazine Schiff bases as auxiliary bridging ligands have been synthesized and crystallographically characterized. The differences in side constituents of the coligands lead to different diazine-bridged binuclear units and hence to three different types of polymeric networks, all being 3-connected nets. In complex 1, [Cd2(L1)2(N3)4]n (L1 = 1,4-bis(2-pyridyl)-2,3-diaza-1,3-butadiene), a single diazine ligand links two metal ions into a centrosymmetric binuclear unit, and each unit is connected with four neighbors via double azido bridges in the end-on (EO) mode, yielding 2-D layers with the (6,3) net topology. Complex 2, [Cd2(L2)2(N3)2]n(ClO4)n·nH2O (L2 = 1,4-bis(2-pyridyl)-1-amino-4-methyl-2,3-diaza-1,3-butadiene), shows a layer structure with the (6,3) net topology, but the binuclear unit contains two diazine bridges and the neighboring units are interlinked via single azido bridges in the end-to-end (EE) mode. The remaining three complexes, [Cd2(L)2(N3)4]n (L = 1,4-bis(2-pyridyl)-1-amino-2,3-diaza-1,3-butadiene for 3, 1-(2-pyridyl)-4-(2-pyrazinyl)-4-amino-1-methyl-2,3-diaza-1,3-butadiene for 4, and 2,5-bis(2-pyridyl)-3,4-diaza-2,4-hexadiene for 5), are isostructural and form the 3-D (10,3)-b net with three different connectors around each node (the cadmium ion): adjacent cadmium ions are alternately bridged by double EO azido bridges and mixed EO azido-diazine double bridges to produce a chain, and each chain is connected to four neighboring chains by single EE azido bridges to generate the 3D framework.

Azide-bridged Cd(II) 1D coordination polymer with Cd13 nano-crown-like cluster

A novel polymeric one-dimensional 2-acetylpyridine-supported cadmium(II)–azide shows tridecanuclear Cd13 crown-like clusters with defective supercubane cores, in which the azide ligands show μ-1,1- and μ-1,1,1-N3 bridging modes.

Four one-dimensional cadmium(II) polymers: one chairlike chain containing four azido bridging modes and three double end-on azido-bridged uniform chains

Four new azido-bridged cadmium(II) complexes have been synthesized and characterized by spectroscopy and crystallographic methods. Compounds [Cd3(L1)2(N3)6(H2O)(CH3OH)0.5]n (1), [Cd(L2)(N3)2]n (2), [Cd2(L3)(DMF)(N3)4]n (3) and [Cd(L4)(N3)2]n (4) (L1 = 2-acetylpyridine, L2 = 2-(pyrazol-1-ylmethyl)pyridine, L3 = 2-(3-methylpyrazol-1-ylmethyl)pyridine and L4 = 1-(2-pyridyl)-2-aza-1-amylene) show one-dimensional (1-D) polymeric structures in the lattice with the distorted octahedral coordination environment of the cadmium(II) ions in the four complexes. Compound 1 contains hexanuclear chairlike unit with defective dicubane-like core, which is further linked by azido bridges into a novel 1-D chain. It is interesting that four different azido bridging modes exist simultaneously in 1. Zigzag chains with double end-on (EO) azido bridged Cd(II) ions are formed in compound 2. Compounds 3 and 4 consist of uniform double EO azido bridged helical chains with screw-pitches of 18.91 and 26.04 A, respectively. It should be noted that the longer pitch in 4 is unusual in inorganic–organic hybrid complexes. Further comparison within the four chains shows that the rigidity of the chains increases with the steric effect of the co-ligands coordinated to the central Cd(II) ions.

Self-assembly of molecular squares based on easy-to-prepare multidentate Schiff base ligands

The choice of ligands with different spacer length and coordination orientation leads to size, shape and packing differences between two self-assembled molecular squares [Zn4H8L1(4)][PF6]5[NO3]3.S (1) and [Zn4H8L2(4)][PF6]6[NO3]2.S (2) (S = solvent), formed from Zn(NO3)2 and two easy-to-prepare bistridentate Schiff-base ligands.