Synthetic and structural chemistry of gadolinium and holmium catecholates

As part of a study to characterize the complexes formed by catechol (1,2-dihydroxybenzene) with lanthanides in aqueous solution, crystalline samples of three gadolinium(III) complexes and a holmium(III) complex have been prepared and characterized by structural, analytical, and spectroscopic techniques. Only 1:1 complexes are isolated at pH < 8, but bis-, tris- and tetrakis(catecholato)gadolinium complexes have been prepared in basic (pH > 11) solutions. The structures of tris- and tetrakis(catecholate)gadolinium compounds have been determined by single-crystal X-ray diffraction methods using counter data. Molecular and crystal structure data are tabulated.