EVIDENCE ON LIGAND STRENGTHS FROM THE CRYSTAL-STRUCTURES OF [INCL3(DMF)3], [INCL3(DMA)3], [(INCL3(PHCHO)3)2].PHCHO AND [INCL3(PHCOME)2] FROM DIMETHYLFORMAMIDE (DMF), DIMETHYLACETAMIDE (DMA), BENZALDEHYDE AND ACETOPHENONE

X-Ray crystal structure determinations have been made for the fac octahedral complexes [InCl3(dmf)3] 1, [InCl3(dma)3] 2 and [{InCl3(PhCHO)3}2].PhCHO 3, from dimethylformamide (dmf), dimethylacetamide and benzaldehyde and the trigonal-bipyramidal complex [InCl3(PhCOMe)2] 4 from acetophenone. The average In-O bond length for 3 is ca. 0.07 angstrom greater than for 1 or 2. In 4, In-O is 0.07 angstrom longer than that known for [InCl3(tmu)2] from tetramethylurea (tmu). An extension of the comparison to structures involving other ligands shows there to be a general correspondence between In-O bond lengths and ligand donor values. By contrast with the weak co-ordination of aldehydes and ketones, co-ordination of an amide is enhanced through polarisation. In the crystal of 3, individual [InCl3(PhCHO)3] molecules are paired, almost centrosymmetrically, with intermeshing of their PhCHO ligands.