X-ray structural studies of lanthanide alkoxides

Abstract: A number of homo- and hetero-metallic lanthanide (oxo-)isopropoxides with the general composition LnxMyO(OiPr)p(HOiPr)q has been structurally characterized by means of single crystal X-ray diffraction. The studied compounds may be divided into five groups by the geometry of their metal-oxygen core.1) M5O(OiPr)13 (M = Er, Eu, Gd) and [(Eu2+)(Eu3+)4O(OiPr)12(HOiPr)]'(HOiPr). In this system the flexibility of the close-packed molecular framework with respect to orientation of the molecules and the possibility to incorporate solvent molecules has been shown.2) (Tb0.9Er0.1)4TiO(OiPr)14, Er4SbO(OiPr)13 and Er2M2TiO(OiPr)14 (M = La, Sc). Three geometrically distinct metal positions may be identified in the common M4TiO(OiPr)14 system, so that metal composition may be stated as M2M’2Ti. The successful substitution in the Er4TiO(OR)14 molecule of Ti for Sb and of two Er atoms for La has been performed.3) M[Al(OiPr)4]3 (M = Nd, Eu). The phase transition from orthorhombic modification at room temperature to monoclinic at 110 K has been observed when M = Nd. Both compounds form pseudo-merohedrally twinned crystals at low temperature.4) [(Eu3+)2(Eu2+)2(OiPr)10(HOiPr)3]'2(HOiPr) is probably the first mixed valence Eucontaining alkoxide structurally characterized. It also exhibits rare four-dentate [OiPr]1- ligand.5) Er4Cs2O(OiPr)12 and Er4(Na0.75Er0.25)2O(OiPr)13(HOiPr). The two chemically related phases display similar molecular geometry with distorted octahedral configuration of metal atoms. Yet the relative arrangement of two alkali elements within the octahedron is different: trans for Na and cis for Cs.