Nitrogen-14 nuclear quadrupole resonance study of bonding in transition-metal cyanides

Abstract

Nitrogen-14 n.q.r. frequencies were measured for K₄[Mo(CN)₈]·2H₂O, K₃[Fe(CN)₆], K₄[Fe(CN)₆]·3H₂O, Ba₂[Fe(CN)₆]·3H₂O, K₄[Ru(CN)₆]·3H₂O, K₂[Ni(CN)₄], Na₂[Ni(CN)₄], K₂[Pd(CN)₄], Na₂[Pd(CN)₄], K[Ag(CN)₂], and K[Au(CN)₂] at 77 K. Two sets of cyanides with different σ- but equal π-orbital populations were found in K₄[Mo(CN)₈]·2H₂O. Changing from Mn to Co in hexacyanides produced an increase in back bonding and a decrease in σ bonding. In the nickel to platinum group cyanides no back bonding was found and the changes in the principal quantum number produced variations only in the nitrogen σ population. In the zinc to mercury group cyanides almost no change was found with variation of the principal quantum number in either σ or π populations. In dicyanides of Hg, Ag, and Au, back bonding increased in that order. It was found also that the variations in the metal charge caused important modifications in the population of the σ and π orbitals of the –CN group.