engleski

Tris[1-(benzyliminomethyl)-2-naphtholato-N, O]cobalt(III)-DMSO (1/2)

The Schiff bases are good structural models for studying the free ligand conformational changes after chelation to the metal centre. The Co(II) and Co(III) salicylaldimine complexes were investigated extensively. On the contrary, there is only one naphthaldiminato Co complex structurally characterized so far [Xu Xiaojie et al., J.Inorg.Chem. 2 (1986) 11]. Similarly to the salicylaldiminato derivatives the Co naphthaldimine complexes with R being either alkyl or aryl belong to the structural type I [Co(II): n = 2 ; Co(III): n = 3, usually m = 0 in both cases]. The dark red tris-bidentate complex crystallizes from a DMSO solution with two solvent molecules of crystallization. The Co(III) is octahedrally surrounded by three N and three O donor six-membered chelate ring atoms [Co-O1 188.2(3), Co-O2 189.5(3), Co-O3 189.4(3), Co-N1 194.5(3), Co-N2 193.3(3), Co-N3 194.8(3) pm]. The chelate ring N� O bite distances are 279.0(4), 277.7(5) and 275.8(4) pm, respectively. The most interesting feature of tris-bidentate metal complexes is the possibility of geometrical fac-mer isomerism. Fac (OC-6-22) isomer has a threefold rotation axis, and the title complex is a mer isomer due to significant ligands conformation differences. The interplanar angles between N-substituent phenyl and naphthalene planes in any particular ligand amounting 98.4(2), 111.4(2), 63.1(2) degrees exhibit the remarkable discrepancy in comparison to the analogous dihedral angle [83.1(6) degrees] in non-coordinated ligand. The later is the result of steric overcrowding. The crystal structure is dominated by nonbonding attractive van der Waals interactions. The shortest intermolecular contact found is at the border of 350 pm between a complex molecule and DMSO [O5-C23* 351.2 pm ; (*) = 1-x, -y, -z].

tris-chelate cobalt(III) complexes; naphthaldiminic Schiff base ligands; structural isomerism; X-ray structure determination

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