Crystal structure determination of an organometallic compound from synchrotron radiation Laue diffraction photographs

Abstract

Laue diffraction patterns for a small single crystal of the organometallic compound [FeRhCl(CO)sdppee] [dppee is PhEPCH(=CHE)PPh2] were recorded with the SRS wiggler beam at SERC Daresbury Laboratory. The intensities were measured from these photographs and the structure determined by Patterson and Fourier methods. The crystal had previously given weak Cu Ka Weissenberg photographs from which the unit-cell dimensions and space group were determined. The diffraction data did not extend to plane spacings much less than 1.2,~ and the crystals were found to be disordered; refinement with stereochemical restraints gave R = 0.14. This is a pilot study; the technique could have uses for very small crystals or for 'kinetic crystallography'. The crystals of [FeRhCI(CE6HE2P2)(CO)s], Mr= 730.7, are monoclinic, a=8.26, b= 19.81, c = 9.77 A, fl = 111.3 (2) ° (e.s.d. of ratio of cell edges ca O. 1% from Laue diffraction pattern fitting, e.s.d, of absolute values ca 1% from weak, lowresolution Weissenberg photograph), U= 1489.5 t13, F(000) = 732, space group P2~ or P21/m from systematic absences (in Weissenberg photograph, not accessible from Laue), Z= 2, D,, (flotation)= 1.62, D x-- 1.63 g cm -3. The molecule has an Fe-Rh bond, 2.7 A, and a bridging diphosphine group.