The crystal and molecular structure of pentaethylcyclopentaphosphinemolybdenum tetracarbonyl, (EtP)5Mo(CO)4

Abstract

The crystal structure of pentaethylcyclopentaphosphinemolybdenum tetracarbonyl has been elucidated by single-crystal X-ray analysis. The triclinic unit cell (a= 10·16, b, = 12·96, c= 17·77 A, α= 80°12′, β= 85°47′, γ= 80°24′, Z= 4, space group P) contains two pairs of crystallographically distinct molecules. The only important structural difference between these molecules lies in the conformation of the terminal carbon atoms of the ethyl groups. The pentaphosphine ring is extremely puckered and is 1 : 3 co-ordinated to the molybdenum atom; the P–Mo–P angle is approximately 66°. Otherwise the configuration around the molybdenum atom is approximately octahedral. The Mo–C bonds of each molecule comprise two pairs which have significantly different average bond lengths. If the two carbonyl groups which lie in the same plane as the molybdenum atom and the two co-ordinated phosphorus atoms are regarded as ‘equatorial,’ and the other two carbonyl groups as ‘axial,’ the weighted mean Mo–Ceq= 1·931± 0·018 A, while Mo–Cax= 2·012± 0·015 A. Within experimental error the P–P bonds in the pentaphosphine ring are all equal, as are the Mo–P distances; the mean values are 2·20 and 2·52 A, respectively.