The coordination chemistry of divalent cobalt, nickel and copper. Part 8. Selected complexes containing N-substituted pyridine-2,6-dicarboxamide ligands; crystal structure of dibromo( N,N′-dimethyl- N,N′-diphenylpyridine-2, 6-dicarboxamide)nickel(II)

Abstract

Diverse complexes of divalent cobalt, nickel and copper and the ligands N,N,N′,N′-tetramethylpyridine-2,6-dicarboxamide (tdpa), N,N′-dimethyl- N,N′-diphenylpyridine-2,6-dicarboxamide (dpda) and N,N,N′,N′-tetraisopropylpyridine-2 ,6-dicarboxamide (ppda) were discussed in order to illustrate the properties of these ligands. The complexes [M-(ppda) 2](ClO 4) 2 (M = Co, Ni and Cu) and [Co-(ppda) 2] (ClO 4) 2(acet) (acet = acetone), had distorted octahedral chromophores. The distortion was most pronounced in [Cu(ppda) 2](ClO 4) 2. This severe distortion was not present in octahedral [Ni(tdpa) 2]-(CIO 4) 2. Isostructural, crystalline (MCl 2) 3(tdpa)1 2 (M= Ni and Co) were isolated from hot solutions. The solid reflectance spectra were resolved into gaussian components. This data, in conjunction with infrared and magnetic measurements, enabled the assignment of the formula [MCl(tpda)] 2[MCl 4] to these complexes. The anion was found to be tetrahedral while the cation had a distorted tetrahedral chromophore. The reaction of NiBr 2 with dpda produced two complexes; green αNiBr 2(dpda) was isolated at room temperature while red βNiBr 2(dpda) was obtained from hot solution. Characterisation data indicated αNiBr 2(dpda) to have a pentacoordinate chromophore. The characterisation data for βNiBr 2(dpda) was ambiguous and a crystal structure determination was performed (monoclinic crystal, space group P2 1/ a with a = 13.871, b = 16.019, c = 9.878Å, β = 95.492°, final R factor = 0.0549 and N obs = 2221). The Ni was in a distorted square pyramidal environment with the donor atoms of dpda and a bromine atom constituting the basal plane and the remaining bromine atom occupying the apical position. The coordination spheres of the crystalline complexes NiBr 2(dpda)(dmp) (dmp = 2,2-dimethoxypropane) and NiBr 2(dpda)(acet) were analogous to those of αNiBr 2(dpda) and βNiBr 2(dpda) respectively.