The synthesis and X-ray crystal structures of rare earth(III) perfluoroadipate complexes — Novel coordination polymers

Abstract

A representative series of polymeric hydrated lanthanoid perfluoroadipates [Ln2(pfad)3(H2O)n]·mH2O (Ln = La, Ce, Nd, Gd, Yb) has been prepared from the reaction of perfluoroadipic acid with either the appropriate lanthanoid oxide or Ce2(CO3)3 in water. X-ray crystal structures showed [Ln2(pfad)3(H2O)10]·4H2O (La, Nd) to be two-dimensional inorganic polymers, which contain nine-coordinate Ln atoms to which are attached five water molecules and four carboxylate oxygen atoms. Two pfad ligands bridge two Ln atoms through one carboxylate group, the other being free, whilst one pfad ligand bridges four Ln atoms in a µ4-(η1,η1/η1,η1) manner. In two-dimensional polymeric [Yb2(pfad)2(H2O)8](pfad)·6H2O, each eight-coordinate ytterbium atom has four water ligands and four carboxylate oxygen donor atoms. The two carboxylate ligands bind in a µ4-(η1,η1/η1,η1) manner, and there is one pfad counter-ion per two ytterbium atoms. These structures show features quite different from those of many lanthanoid adipate complexes [Ln2(ad)3(H2O)n]·mH2O, but there is no F-Ln coordination. From the reaction of [Nd2(pfad)3(H2O)10]·4H2O with benzene-1,2-disulfonic acid (H2bds), the mixed ligand complex [Nd2(bds)2(pfad)(H2O)8] was isolated. This is a one-dimensional polymer featuring Nd2(bds)2 units linked together by µ-η2,η2 pfad ligands. Each Nd atom is nine-coordinate with three sulfonate oxygen donors, two carboxylate oxygen atoms, and four water ligands, and the bds ligands bind in the new µ-η2(O,O′),η1(O′′) manner for Ln complexes. Surprisingly, [Na2pfad] was isolated unhydrated from water, the six-coordinate Na atoms being coordinated by four carboxylate oxygen atoms and two (C)-F atoms in an octahedral array. The ligands are duodecadentate, each –CF2CO2 unit binding to five different sodium ions through four oxygen and one α-F atom with the second α-F atom bound to a sodium ion in a OC(O)CF-Na chelate ring.Key words: rare earths, lanthanoid, X-ray crystal structures, adipates, carboxylates.