Derivatives of bivalent germanium, tin, and lead. Part XVIII. Crystal and molecular structure, and variable-temperature Mössbauer effect of octakis-µ-(o-nitrobenzoato)-di-µ3-oxo-bis(tetrahydrofuran)ditin(II)-ditin(IV)

Abstract

The crystal and molecular structure of the title compound has been determined by Patterson and Fourier methods from diffractometer data to a final R value of 0.062 for 5 146 independent, non-zero reflections. Crystals are mono-clinic, space group P2₁/c, a= 13.426(4), b= 14.666(3), c= 22.029(5)Å, β= 115.51 (2)°, Z= 2. The structure consists of independent tetranuclear cluster molecules containing two tin(II) and two tin(IV) atoms. The central feature of the macromolecule is a lozenge-shaped four-membered Sn^IV₂O₂ ring. Octahedral co-ordination at each tin(IV) atom is completed by oxygen atoms from four o-nitrobenzoate groups [r(Sn^IV–O) 2.047(6)–2.067(7)Å], which form bridges between the tin atoms in each valence state. The geometry at the bivalent tin atoms is that of a distorted pentagonal pyramid with oxygen atoms from four bridging carboxylate groups and tetrahydrofuran occupying equatorial positions at bond distances in the range 2.409(8)–2.661 (9)Å. The apical site of the pentagonal pyramid is occupied by the oxygen atom of the four-membered Sn₂O₂, ring at the extremely short tin(II)-oxygen distance of 2.113(7)Å. The tin(II) lone-pair electrons are presumably in the remaining apical position. The partial oxidation of tin(II), which takes place in the synthesis of the compound, is deduced to take place by interaction with the o-nitrobenzoate groups. From the variable-temperature Mössbauer effect, the Debye temperatures for the tin(II) and rin(IV) atoms were determined to be 104.1 and 119.6 K.