Crystallographic studies of problems in stereochemistry

Abstract

The structure proposed earlier for ZnCl₂ terpyridyl has been refined by least squares techniques. Though no basic differences in the trigonal biprymidal stereochemistry about the zinc atom have been found, significant departures from planarity have been detected within the terpyridyl ligand. A crystal structure analysis of Sn₂Me₄Cl₄ terpyridyl has confirmed that it is monochloro bismethyl 2,2;2” terpyridyl tin(IV) trichloro bismethyl stannate(IV) and is therefore made up of tin-based 5-coordinate anions and 6-coordinate cations. The 5-coordinate anion is trigonal bipyramidal in shape, with two methyl groups and one chlorine atom in the equatorial plane, apical positions being occupied by chlorine atoms. The 6-coordinate cation has a distorted octahedral shape. Nitrogen atoms of the terpyridyl group, the tin atom and the chlorine atom all make up one plane. Two trans methyl groups are linked to the tin atoms by bonds approximately normal to this plane. A phase showing variable composition in the range P₄8₅ to P₄S₆.₉ is found from crystal structure analysis to be made up of molecules isostructural with P₄S₇. Explanation of the variable composition is provided by the partial absence of some of the terminal sulphur atoms. A crystal structural analysis of the compound P₂S₆Br₂ has established the presence of a new six membered ring. Two units each made up of a phosphorus atom surrounded tetrahedrally by three sulphur atoms and one bromine atom are linked together by two sulphur-sulphur bonds making up a P₂S₄ ring. Terminal sulphur and bromine atoms bonded to the ring phosphorus atom show disorder.