Acceptor properties of halides of elements of groups IV and V
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
2,2’-Bipyridyl forms equimolar complexes, MX₃.bipy, with the trihalides of arsenic, antimony and bismuth, and also with the mono-organosubstituted halides of these elements, RMX₂.bipy. Most of the crystalline compounds are covalent, but are partially ionised in nitrobenzene solution as (MX₂.bipy)+X-. Ionisation increases from chlorides to iodides, but decreases from arsenic to bismuth. The first trend can be correlated with decreasing strength of the metal-halogen bond, and the second with an increasing preference for higher coordination numbers down the Group. Diphenylgermanium halides do not react with 2,2’-bi-pyridyl, but germanium tetraiodide forms the adduct GeI₄.2bipy. With various organotin halides and the diphenyl-lead halides, 2,2’-bipyridyl forms six-coordinate complexes, RnSnX₄-n.bipy and Ph₂PbX₂.bipy. These are non-electrolytes in nitrobenzene, although slight ionisation is apparent among the tin complexes. 2,2’ 2”-Terpyridyl does not react with germanium tetra-chloride, but forms a 1:1 adduct with germanium tetraiodide, GeI₄.terpy. This tridentate ligand also reacts with tow molecules of dimethyltin and diphenyltin chlorides and bromides to form compounds containing six-coordinate tin cations, (R₂SnX.terpy)+, and unusual five-coordinate tin anions, R₂SnX-3. No corresponding complex anion is formed with dimethyltin diiodide. The diphenyl-lead halides all coordinate one molecule of 2,2’, 2”-terpyridyl to form complexes Ph₂PbX₂.terpy, which show only a slight tendency to ionise in nitrobenzene, and are presumably seven-coordinate. Differences in the acceptor behaviour of Group IV halides can again be related to performance for higher coordination numbers at the bottom of the Group.