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 NiX 2 ⋯(N 2 ) n with a physisorbed type of interaction between the nitrogen and the nickel centre. These can be converted by photolysis into pseudo-tetrahedral NiX 2 (η 1 -N 2 ) 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 CoBr 2 only very very weak new bands were observed after photolysis in a nitrogen matrix, and no new bands were observed after photolysis for NiF 2 , FeBr 2 or ZnBr 2 in nitrogen matrices.