Question

Which among iron cobalt nickel and manganese forms octahedral conolex?

Answer 1

Methyl cyanide forms complexes with manganese, cobalt, and nickel either by recrystallisation of anhydrous halides from methyl cyanide or by reactions of the metals with halogens in methyl cyanide solution. Manganese and nickel chlorides and bromides form octahedral complexes, MX3,2MeCN; while cobalt forms tetrahedral complexes CoX2,3MeCN, which contain a mole of unco-ordinated methyl cyanide, and which give CoX2,2MeCN when pumped under vacuum. The iodides of all three metals form complexes MI 2.SMeCN, which are formulated as [M(MeCN)62+][MI42-]. The formation of [MI,2! ions is probably dominated by the polarisability of the iodide ion and the high degree of covalent bonding associated with this anion, whereas the formation of tetrahedral cobalt chloride and bromide complexes is determined by the stable e4t23 electron configuration. The reaction of these metals with bromine in methyl cyanide gives a series of complexes [M(MeCN)62+](Br3-)2, although only the nickel complex is stable. Evidence for the structures of these complexes has been sought from their reflectance spectra and magnetic properties. The splitting of the 3T2g(F) level in nickel(II) by non-equivalent ligands and the position of methyl cyanide in the spectrochemical series are discussed.