Dalton Transactions (Print Edition) 2015-02-21

Four linear Cu(II)3 subunit-based coordination polymers with various inter-subunit connections, spin ground-states and intra-/inter-subunit magnetic couplings.

En-Cui Yang, Zhong-Yi Liu, Si-Hang Chen, Yan-Hong Su, Yan-Yan Zhang, Xiao-Jun Zhao

Index: Dalton Trans. 44(7) , 3190-9, (2015)

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Abstract

Four new 4-amino-1,2,4-triazole (atr)-based coordination polymers, {[Cu2(atr)(H2O)(μ-OH)2(pa)]·H2O}n (), {[Cu3(atr)2(H2O)2(μ-OH)2(npa)2]·2H2O}n (), {[Cu3(atr)5(dca)(μ-OH)(ClO4)2](ClO4)2}n () and {[Cu3(atr)2(H2O)(μ3-OH)(μ-OH)2(spa)]·1.5H2O}n () (pa(2-) = phthalate, npa(2-) = 3-nitrophthalate, dca(-) = dicyanamide and spa(3-) = 4-sulfophthalate), were successfully obtained by varying the carboxylate- and cyanide-modified magnetic bridges. Structural determinations reveal that the former three samples are bent one-dimensional chains constructed from linear Cu(II)3 subunits and different inter-subunit connections. In , linear {Cu3(μ-N1,N2-atr)2(μ-OH)2}(4+) and {Cu3(μ-COO)2(μ-OH)2}(4+) subunits are alternately connected in a sharing-vertex manner to give a ferrimagnetic S = 1/2 spin ground-state. The linear {Cu3(μ-N1,N2-atr)2(μ-OH)2}(4+) building block of is repeatedly bridged by pairs of single-atom bridging carboxylate groups of the npa(2-) ligand leading to a paramagnetic S = 1/2 spin ground-state. By contrast, each linear {Cu3(μ-N1,N2-atr)4}(6+) core in is periodically propagated by four-fold heterobridges (μ-OH(-), μ-ClO4(-), μ-N1,N2-atr and μ-dca(-)) to generate an overall diamagnetic S = 0 spin ground-state. Complex is a three-dimensional pillared-layer framework composed of linear {Cu3(μ-N1,N2-atr)2(μ-OH)2}(4+)-based layers and ditopic spa(3-) connectors, which exhibits a ferrimagnetic S = 1/2 spin ground-state and a metamagnetic transition resulting from the competition between the weak interchain/interlayer antiferromagnetic interaction and the enhanced external magnetic field. In addition, different intra- and inter-subunit magnetic strengths are observed in with the coupling constants 182 < -Jintra < 43 and -127 < Jinter < 51.2 cm(-1). These interesting magnetostructural results are significant and helpful for the cyclic polyazolate-based magnetic materials.