A comparison of the molecular and crystal structures of the dimethylacetamide complexes from zinc chloride, bromide, and iodide

The dimethylacetamide complexes ZnCl 2 (dma) 2 and ZnI 2 (dma) 2 crystallise according to the respective space groups P2 1 2 1 2 1 and P2 1 /c. The molecules of the two compounds are conformationally different through differing ligand rotations about the Zn-O bonds. These are such as to enable a molecular packing in which there is a balance of the predominant CH 3 --X attractions and CH 3 --CH 3 repulsions. The bromide is P1 triclinic, now with two conformationally different molecules in the asymmetric unit, but its molecular packing is similar to that of the iodide, again to balance the same attractions and repulsions. Approach distances to the amide carbon atoms are discussed.