The coordination chemistry of divalent cobalt, nickel and copper. Part II. The characterisation of a mixed ligand nickel(II) species and its thermal decomposition products. The crystal structure of (pyridine-2,6-dicarboxylato)(N,N,N′,N′-tetramethyl-1,2-diaminoethane)nickel(II) dihydrate

Abstract

The magnetic and spectral properties of the complex Ni(pydca)(tmen)·2H 2O (1) and those of the thermally-derived species Ni(pydca)(tmen)·H 2O (2) and Ni(pydca)(tmen) (3) have been studied (pydca = pyridine-2,6-dicarboxylate, tmen = N,N,N,′,N′-tetramethyl-1,2-diaminoethane). Conflicting features in the electronic spectra prevented unambiguous stereo-chemical assignments. The presence of split ν 8(COO) and ν as(COO) infrared absorption bands in the regions 1350–1400 cm −1 and 1610–1680 cm −1 respectively suggested dissimilar co-ordination of the carboxylate groups. The structure of (1) has been determined by the heavy-atom technique and refined by least-squares. Crystals are triclinic, space group P 1 , with a = 10.806(5), b = 8.626(4), c = 9.825(5) Å, α = 114.32(2), β = 91.52(2), γ = 96.67(2)°, d obs = 1.50 (by flotation), d calc = 1.51 g cm −3 and Z = 2. With N obs = 2218, the final R factor was 0.047. Complex (1) is properly formulated as [Ni(pydca)(tmen)(H 2O)]·H 2O with Ni in a distorted octahedral environment, being bonded to two O atoms and the N atom of pydca, the two N atoms of tmen and one water molecule. The NiN(amine) distances differ significantly but structural parameters for the two carboxylate groups agree within experimental error. The anomalous spectral splitting appears to be common to analogous species containing fully-substituted diamines. Distorted octahedral and distorted square pyramidal symmetries are assigned to (2) and (3) respectively.