CRYSTAL-STRUCTURES OF BENZOATO-O)-DI-(1,3-DIAMINOPROPANE-N,N')NICKEL(II) AND ITS COPPER(II) ANALOG - VARIATION IN THE COORDINATION MODES

The structures of robenzoato-O)di(1,3-diaminopropane-N,N')copper(II) ( 1) and di(2-fluorobenzoato-O)bis(1,3-diaminopropane-N,N') nickel(II) ( 2) were determined by single-crystal X-ray methods. 1: [Cutn(2)(2Fbz0) (2)] (tn = 1,3-diaminopropane; 2FbzO = ortho-fluorobenzoate), C20H28F2 CuN4O4, M(r) = 490.01, monoclinic, space group P2(1)/n No. 14, a = 15. 189(3), b = 8.446(4), c = 26.846(4) Angstrom, beta = 106.20(1)degrees, V = 3307(2) Angstrom(3), Z = 6, D-c = 1.476 g cm(-3).2: [Ni(tn)(2)(2F bzO)(2)], C20H28F2NiN4O4, M(r) = 485.15, monoclinic, space group P2(1) /a No. 14, a = 11.280(2), b = 8.423(2), c = 11.568(3) Angstrom, beta = 96.37(2), V = 1092.3(9) Angstrom(3), Z = 2, D-c = 1.512 g cm(-3) In c ompounds 1 and 2 the chelate rings display a chair conformation and th ere is trans coordination around the central metal cation. In 1 there are two crystallographically independent complex units, which represen t different modes of conformational isomerism. In the first one the ce ntral copper(II) ion sits at a centre of symmetry, whereas in the seco nd the site symmetry is only C-1. In 2 the site symmetry around the ce ntral nickel(II) cation is C-i. All the axial M-O bond lengths exhibit axial elongation. Extended Huckel calculations suggest that the natur e of the axial bonding in the two compounds is essentially different. In the copper(II) complex units it is affected by d-s mixing, whereas in the nickel(II) analogue the amount of d-s mixing is almost negligib le. The effect of axial bonding is seen also in the geometry of the ca rboxylate groups. The most noticeable changes occur in the O-C-O angle of the carboxylate group. The effect of ortho substitution upon the b enzoic acid and benzoate anion was investigated at the HF/6-31 + + G(d ) level of theory. The main variations are seen in the torsion angle o f the carboxylate group.