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

Abstract

The structures of di(2-fluorobenzoato- O)di(1,3-diaminopropane- N, N′)copper(II) ( 1) and trans-di(2-fluorobenzoato- Obis(1,3-diaminopropane- N, N′)nickle(II) ( 2) were determined by single-crystal X-ray methods. 1: [Cutn 2(2FbzO 2] (tn = 1,3,-diaminopropane 2FbzO = ortho-fluorobenzoate), C 20H 28F 2CuN 4O 4, M 1 = 490.01, monoclinic, space group P2 1/ n No. 14 a = 15.189(3), b = 8.446(4), c = 26.846(4) A ̊ , β = 106.20(1)°, V = 3307(2) A ̊ 3, Z = 6, D c = 1.476 g cm −3 2: [Ni(tn) 22FBzO) 2], C 20F 2NiN 4O 5, M t = 485.15 , monoclinic, space group P2 1/ a No. 14, a = 11.280(2), b = 8.423(2), c = 11.568(3) A ̊ , β = 96.37(2), V = 1092.3(9) A ̊ 3, Z = 2, D = 1.512 g cm −3 . In compounds 1 and 2 the chelate rings display a chair conformation and their is rans 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 C 1. In 2 the site symmetry around the central nickel(II) cation is C 1. All the axial MO bond lengths exhibit axial elongation Extended Hückel 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 mean variations are seen in the torsion angle of the carboxylate group.