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Oxamato-Bridged Trinuclear NiIICuIINiII Complexes with Irregular Spin State Structures and a Binuclear NiIICuII Complex with an Unusual Supramolecular Structure:  Crystal Structure and Magnetic Properties

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posted on 18.05.2001, 00:00 by En-Qing Gao, Jin-Kui Tang, Dai-Zheng Liao, Zong-Hui Jiang, Shi-Ping Yan, Geng-Lin Wang
Four oxamato-bridged heterotrinuclear NiIICuIINiII complexes of formula {[Ni(bispictn)]2Cu(pba)}(ClO4)2·2.5H2O (1), {[Ni(bispictn)]2Cu(pbaOH)}(ClO4)2·H2O (2), {[Ni(cth)]2Cu(pba)}(ClO4)2 (3), and {[Ni(cth)]2Cu(opba)}(ClO4)2·H2O (4) and a binuclear NiIICuII complex of formula [Cu(opba)Ni(cth)]·CH3OH (5) have been synthesized and characterized by means of elemental analysis, IR, ESR, and electronic spectra, where pba = 1,3-propylenebis(oxamato), pbaOH = 2-hydroxyl-1,3-propylenebis(oxamato), opba = o-phenylenebis(oxamato), bispictn = N,N‘-bis(2-pyridylmethyl)-1,3-propanediamine, and cth = rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. The crystal structures of 1, 3, and 5 have been determined. The structures of complexes 1 and 3 consist of trinuclear cations and perchlorate anions, and that of 5 consists of neutral binuclear molecules which are connected by hydrogen bonds and π−π interactions to produce a unique supramolecular “double” sheet. In the three complexes, the copper atom in a square-planar or axially elongated octahedral environment and the nickel atom in a distorted octahedral environment are bridged by the oxamato groups, with Cu···Ni separations between 5.29 and 5.33 Å. The magnetic properties of all five complexes have been investigated. The χMT versus T plots for 14 exhibit the minimum characteristic of antiferromagnetically coupled NiCuNi species with an irregular spin state structure and a spin-quartet ground state. The χMT versus T plot for 5 is typical of an antiferromagnetically coupled NiCu pair with a spin-doublet ground state. The NiII−CuII isotropic interaction parameters for the five complexes were evaluated and are between 102 and 108 cm-1 (Ĥ = −JŜCu·ŜNi).