The Synthesis, and the Crystal and Molecular Structures of Tetraethylammonium [Aquaheptakis(thiocyanato)lanthanoidate(III)], [(C2H5)4N]4[M(SCN)7(H2O)], (M=La, Ce, Pr; Nd, Dy, Er): The Complexes in a Cubic Octa-Coordination Geometry

Abstract

Abstract The title complexes have been synthesized, and their crystal and molecular structures were determined by the X-ray diffraction method using their single crystals. Among them, the crystals of the La, Ce, and Pr complexes are isomorphous; cubic, space group Pm\bar3, Z=1, and the cell constants of the Pr complex, for example, are a=11.513(2) Å, U=1526.1(5) Å3, and the final R value was 0.093. The Nd, Dy, and Er complexes, another group of the isomorphous complexes obtained almost by the same synthetic method, are tetragonal, space group I4/m, Z=2, and the cell constants of the Er complex, for example, are a=1.564(2), c=22.627(4) Å, U=3026(3) Å3, and the final R value was 0.071. The coordination geometry around the metal atoms of both types of complexes are almost the same: seven thiocyanato nitrogen and one water oxygen atoms are coordinated in a cubic geometry, being disordered as if each ligating atomic position is equally occupied by 1/8 atom of the water oxygen and 7/8 atoms of the thiocyanato nitrogen. In the lattice of the former three complexes, the tetraethylammonium nitrogen atoms occupy all Cl− ionic positions of the NaCl-type lattice, while the metal atoms only the apex Na+ ionic positions; not the face-center ones. The unit cells of the latter three complexes are apparently consist of the two former cubic type cells being piled on the c-axis direction, where the arrangement of the atoms is different from the former only on the plane where two original cells are contact: metal and ammonium nitrogen positions slide 0.5 both to a- and b-axis directions. Thus each metal atom of the both type complexes is surrounded by six tetraethylammonium nitrogen atoms on both sides of the a, b, and c-axis directions.