Dinitrogen bonding modes to molecular nickel(II) halides: a matrix isolation IR and DFT study

A combination of matrix isolation IR and DFT studies has shown that when monomeric nickel dihalides (NiX2, X=Cl, Br) are condensed in solid nitrogen matrices the initial species formed are NiX2⋯(N2)n with a physisorbed type of interaction between the nitrogen and the nickel centre. These can be converted by photolysis into pseudo-tetrahedral NiX2(η1-N2)2 moieties with end-on bonded dinitrogen ligands in a chemisorbed type of interaction, but only if the matrix is deposited at less than 10 K. On warming to ca. 20 K the chemisorbed species revert to the physisorbed state. For CoBr2 only very very weak new bands were observed after photolysis in a nitrogen matrix, and no new bands were observed after photolysis for NiF2, FeBr2 or ZnBr2 in nitrogen matrices.