2-diphenylphosphino-phenol as a ligand for mono- and poly-nuclear complexes of manganese, cobalt, nickel, zinc, and cadmium

2-Diphenylphosphino-phenol was chosen as an ambivalent (hard/soft) chelatin g ligand for biologically important first row transition metals. The expect ed mode of complexation is relevant to trapping of metal ions in humic acid s and related environmental ion exchange systems with phenolate functions. The 1:2 complex with nickel(II) is known to have a standard mononuclear squ are-planar structure, and experimental evidence suggests that the new cobal t(II) complex is analogous. By contrast, zinc and cadmium were found to giv e novel trinulear complexes [M-3(2-Ph2P-C6H4O)(6)], M = Zn, Cd. In a chain of three metal atoms, the octahedrally coordinated central atom resides on a center of inversion and is solely oxygen-bound [MO6], while the two perip heral metal atoms are in a mixed coordination environment [fac-MO3P3]. The analogous manganese(II) complex crystallizes as a net trihydrate, where two different trinuclear units are present in the lattice. One is of a new typ e and represents a centrosymmetrical hexahydrate [Mn-3(2-Ph2P-C6H4O)(6)(OH2 )(6)]. The central part is an octahedral [Mn(OH2)(6)](2+) dication, which i s hydrogen-bonded to two [Mn(2-Ph2P-C6H4O)(3)](-) anions. The nickel(II) co mplex was found to form 1:1 adducts with ZnCl2 or ZnBr2. The two complexes are isomorphous. In the adduct structure the zinc atom is attached to the t wo oxygen atoms of the nickel compound leaving the remainder of the molecul ar geometry largely unchanged. Together with the two halogen atoms a tetrah edral environment [ZnO2X2] is formed (X = Cl, Br), while the nickel atom re tains its square planar [NiO2P2] environment.