Crystal structures of trans-di(2-fluorobenzoato-O)di-(1,3-diaminopropane-N,N')nickel(II) and its copper(II) analogue. Variation in the coordination modes

Article abstract of DOI:10.1016/0020-1693(95)04970-3

The structures of di(2-fluorobenzoato-O)di(1,3-diaminopropane-N,N')copper(II) (1) and trans-di(2-fluorobenzoato-O)bis(1,3-diaminopropane-N,N')nickel(II) (2) were determined by single-crystal X-ray methods. 1: [Cutn₂(2FbzO)₂] (tn=1,3-diaminopropane; 2FbzO=ortho-fluorobenzoate), C₂₀H₂₈F₂CuN₄O₄, M_r=490.01, monoclinic, space group P2₁/n No, 14, a=15.189(3), b=8.446(4), c=26.846(4) A, β=106.20(1)°, V=3307(2) A³, Z=6, D_c=1.476 g cm^-3.2: [Ni(tn)₂(2FbzO)₂],C₂₀H₂₈F ₂NiN₄O₄, M_r=485.15, monoclinic, space group P2₁/a No. 14, a=11.280(2), b=8.423(2), c=11.568(3) A, β=96.37(2), V=1092.3(9) A³, Z=2, D_c=1.512 g cm^-3. In compounds 1 and 2 the chelate rings display a chair conformation and there is trans coordination around the central metal cation. In 1 there are two crystallographically independent complex units, which represent different modes of conformational isomerism. In the first one the central copper(II) ion sits at a centre of symmetry, whereas in the second the site symmetry is only C¹ In 2 the site symmetry around the central nickel (II) cation is C_i. All the axial M-O bond lengths exhibit axial elongation. Extended Hueckel calculations suggest that the nature 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 negligible. The effect of axial bonding is seen also in the geometry of the carboxylate groups. The most noticeable changes occur in the O-C-O angle of the carboxylate group. The effect of ortho substitution upon the benzoic 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 of the carboxylate group.