Interaction of metal ions with humic-like models. Part. I. Synthesis, spectroscopic and structural properties of diaquabis(2,6-dihydroxybenzoato) copper(II) and hexaaquaM(II) bis(2,6-dihydroxybenzoate) dihydrate (M = Mn, Fe, Co, Ni, Cu and Zn)

Compounds of the type M(2,6-DHB)2·8H2O (M = Mn, Fe, Co, Ni, and Zn; 2,6-DHB = 2,6-dihydroxybenzoate ion) and Cu(2,6-DHB)2(H2O)2 were prepared and characterized by means of infrared and electronic spectroscopy, electron spin resonance and thermal analysis. For Cu(2,6-DHB)2(H2O)2 (1) and Zn(2,6-DHB)2·8H2O (2) the crystal structure was also determined by single-crystal X-ray diffraction methods. The compound (1) has a polymeric nature, the coordination around each copper atom being tetragonally-distorted octahedral, with two water oxygens [CuO, 1.966(3) Å] and two carboxyl oxygens [CuO, 1.935(2) Å] from 2,6-DHB molecules about the square plane and two phenolic groups from adjacent units in the axial positions. The structure of (2) consists of almost regular octahedral [Zn(H2O)6]2+ cations surrounded by 2,6-DHB anions. The remaining two water molecules are involved in hydrogen bonding with the coordinated water molecules. X-ray data show that all the M(2,6-DHB)2·8H2O are isomorphous with (2). The thermal, spectroscopic and magnetic properties are interpreted on the basis of the crystal structures. In particular, the ESR and absorption data of the copper(II) compounds are compared with those of the salicylate complexes. © 1983.