Crystal structure and magnetic properties of two new zoledronate complexes: A Mn dimer [Mn(II)(H3Zol)2·(H2O)2] and a Fe15 molecular cluster [Fe(III)15(HZol)10(H2Zol)2 (H2O)12(Cl4:(H2O)2)·Cl7·(H2O)65] (where H4Zol: C5H10N2O7P2 is zoledronic acid)

Abstract

The synthesis, X-ray structure and magnetic properties of two new zoledronato complexes are presented: Mn(II)(H3Zol)2(H 2O)2, (I) and Fe(III)15(HZol) 10(H2Zol)2 (H2O)24 (2/3Cl:1/3H2O)6·7Cl·65(H2O) (II), where H4Zol = zoledronic acid = C5H10N 2O7P2. Complex (I) is a dimer, built up around an inversion centre where the cation is located, surrounded by two chelating zoledronate anions and two water molecules. The structure is isomorphous to the Co, Ni and Zn isologues. A quite different structure is the Fe(III) complex which consists of a centrosymmetric cluster with 15 Fe(III) cations (one of them at the inversion centre), 12 zoledronate anions, in different protonation states and 26 coordinated water molecules, 24 of which show full occupancy and the remaining 2 share 6 coordination sites with 4 chlorine anions. There are in addition 7 chlorine counterions and a not well determined number of hydration water molecules, their number being adjusted as to match the chemical and TGA analysis. The general shape of the molecule is that of a 6 arm propeller with a Fe(III) cation at its center and two FeO6 coordination polyhedra sitting above and below, defining some sort of "paddle wheel axis", perpendicular to the wheel plane. Around this axis there is an almost perfect circular structure formed by other six FeO6 octahedra, to which the "paddles", defined by the remaining six FeO6 groups attach. The ensemble presents some unusual (Fe···OPO)n loops (n = 2,3,4), some of them unreported, and displays a striking non-crystallographic -3 symmetry. The protonation state of the zoledronato ligands were inferred from the counterions effectively found and charge balance considerations. Both compounds present a paramagnetic behaviour at R.T, and obey a Curie Weiss law down to rather low temperatures (15 K for (I), 100(K) for (II)) with a tendency to different types of interactions viz., ferromagnetic for (I) and antiferromagnetic for (II). The geometry of the F15 cluster is analyzed. © 2012 Elsevier B.V. All rights reserved.