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Synthesis, crystal structures and properties of new chloroniobium cluster hydroxides with co-ordinated and non-coordinated OH- groups. The presence of H3O2- intercluster bridges

The isostructural, trigonal clusters of the composition [Nb6Cl12(H2O)(6)](OH)(2) . 1/4CH(3)OH . 6H(2)O 1 and [Nb6Cl12(H2O)(6)](OH)(2) 6H(2)O 2 have been isolated from alkaline solutions of [Nb6Cl12](2+) cluster in alcohol/water (1:3) in the presence of NMe(4)OH, while the presence of NEt(4)OH yielded NEt(4)[Nb6Cl12(H3O2)(6/2)]. 3H(2)O 3. Compound 1 crystallizes in trigonal space group R(3) over barm$ with a = 21.166(5)Angstrom and c = 23.812(4)Angstrom, gamma = 120 degrees, U = 9238.6(3) Angstrom(3), Z = 12. Two crystallographically independent cluster octahedra (I and II) have been found in the unit cell of 1 in the ratio 3:1. The Nb-O distances of 2.211(11)Angstrom and 2.217(16)Angstrom for I and 2.238(19)Angstrom for II indicate six co-ordinated water molecules. The cluster units of I are connected by hydrogen bonds of 2.49(1)Angstrom into a two-dimensional framework. Compound 3 is monoclinic, space group P2(1)/n, a = 10.085(5) Angstrom, b = 11.446(4)Angstrom, c = 14.971(6)Angstrom, beta = 102.95(6)degrees, U = 1684.2(1)Angstrom(3), Z = 2. The short Nb-O distances at 2.167(6), 2.177(8) and 2.187(7)Angstrom and considerable reduction of the Nb-O stretching frequency in the IR spectra support the presence of H3O2- (co-ordinated water molecule from one cluster unit and co-ordinated OH- group from the neighbouring cluster unit) bridges. Each cluster unit is joined to the six neighbouring units by intermolecular hydrogen bonds of distances 2.540(11)Angstrom and 2.594(10)Angstrom in a three-dimensional network.

niobium ; clusters ; cluster hydroxides ; intercluster bridges ; synthesis ; crystal structures

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