Crystal structure and stereochemistry of the solvated complex dichlorodipyridine-[o-(di-o-tolylphosphino)benzyl]rhodium(III)–0·61 chloroform: the trans-influence of ligands in octahedral complexes
The complex [RhCl2(C6H5N)2{P(o-C6H4Me)2(o-C6H4CH2)}] crystallises from chloroform–ethanol as monoclinic crystals containing a monstoicheiometric amount of chloroform. The cell dimensions are a= 18·43, b= 10·22, c= 19·15, β= 112·4 ± 0·1°; the space group is P21/c with one molecule of metal complex per asymmetric unit. A three-dimensional X-ray analysis, based on 2430 independent diffractometer-measured reflections, has converged to a final weighted R of 0·077. The value of σ for the Rh–Cl and Rh–P bond distances is 0·004 Å, and for Rh–C and Rh–N is 0·013–0·016Å; within the pyridine and tolyl groups the mean σ for bond distances is 0·027 Å. The steric requirements of the five-membered chelate ring and the methyl groups of the nonchelating tolyl groups give rise to several significant deviations from the C2v symmetry of the carbon skeleton of free toluene. The trans-influence exerted by a saturated carbon ligand is evidenced by the significant difference between the Rh–Cl bond lengths, one chlorine being trans to a pyridine (Rh–Cl 2·339 Å), the other trans to the benzyl carbon (Rh–Cl 2·531 Å). A general discussion of the trans-influence in octahedral complexes is provided. The molar ratio, within the crystal, complex:chloroform, determined from a least squares refinement of the chloroform group population parameter, is 1 :0·61 ± 0·02. Complete disorder of the solvents chloroform appears to be prevented by a weak hydrogen bond between the proton of the chloroform group and one of the chlorine atoms co-ordinated to the metal.