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Copper-Linked Hexaniobate Lindqvist ClustersVariations on a Theme

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journal contribution
posted on 28.05.2007, 00:00 by Ranko P. Bontchev, Eugene L. Venturini, May Nyman
Four new one-dimensional materials and one dimer complex based on the linkage of [Nb6O19] clusters and [CuLx] (L = ethylenediamine (en), NH3, H2O) assemble under ambient conditions. These phases include the following:  Rb4[Cu(en)2(H2O)2]3[(Nb6O19H2)2Cu(en)2]·24H2O (1), space group P1̄; [Cu(en)2(H2O)2]2[(Nb6O19H2)Cu(en)2]·14H2O (2), space group P1̄; Rb2[Cu(NH3)2(H2O)4][Cu(NH3)4(H2O)2]2{[Nb6O19][Cu(NH3)]2}2·6H2O (3), space group P1̄; {[Nb6O19][Cu(NH3)2(H2O)]2[Cu(H2O)4]2}·3H2O (4), space group P2/n; and {[Nb6O19][Cu(NH3)2(H2O)]2[Cu(H2O)4]2} (5), space group C2/m. All structures have been solved by single-crystal methods, and compounds 15 were characterized by thermogravimetric analysis, Fourier transform IR, chemical analysis, and magnetic measurements. It has been demonstrated that the conformation, charge, and geometry of the [Nb6O19]−[CuLx] chains can be modulated by varying the type and amount of the [CuLx]2+ species. The charge balance is provided by mixed Rb+/[CuLx]2+ or [CuLx]2+ cations only for structures 13, whereas 4 and 5 are neutral chains with no counterions. There are weak antiferromagnetic Cu2+−Cu2+ interactions in all phases. Compounds 25 represent the first examples in which the [Nb6O19] Lindqvist ion forms extended solids rather than dimers or decorated monomers when reacted with transition-metal, cationic complexes.