Isolation of first row transition metal-carboxylate zwitterions

Zwitterionic 3d metal carboxylates of Zn(ii), Cu(ii), Ni(ii) and Co(ii) have been isolated and structurally authenticated by X-ray crystallography. A series of 2-hydroxymethylpyridine-carboxylate ligands with different sizes and shapes demonstrate variable coordination modes with first row transition metals under different conditions, yielding a class of 17 complexes, predominantly zwitterions. The nature of the ligands permits the carboxylates to be un-coordinated, anionic and conjugated, thereby balancing the positive charges on the metal centers.