X-Ray investigations on spin-state equilibria. Crystal and molecular structure of two five-co-ordinate cobalt(II) complexes with an N4P donor set

Abstract

The crystal and molecular structures of two complexes of cobalt(II) isothiocyanate with the ligand N[(diphenyl-phosphino)ethyl]-N′-diethylethylenediamine (nnp) and its methyl derivative (nnpMe), have been determined. Crystals of Co(nnp)(NCS)₂(I) are triclinic, space group P, With a= 15·896(4),b= 8·786(2),c= 9·402(2)Å, α= 111·3(1), β= 94·6(1),γ= 90·5(1 )°.Z= 2. Crystals of Co(nnpMe)(NCS)₂, (II) are monoclinic, space group Cc, witha= 13·485(4),b= 13·503(4), c= 16·034(6)Å, β= 116·22(2)°. Counter methods were used to collect 1437 (I) and 1815 (II) reflections and the structures solved by the heavy-atom method; least-squares refinement gave R 7·4 (I) and 6·2%(II).

In both complexes the cobalt atom is five-co-ordinated by the two nitrogen and the phosphorus atoms of the ligand and the two nitrogen atoms of the thiocyanate groups, The two co-ordination polyhedra can be described as distorted trigonal bipyramids, that of (I) tending towards an elongated square pyramid, that of (II) towards the tetrahedron. The magnetic moment of (I) varies reversibly with temperature whereas (II) is constantly high spin. These differences are ascribed to different distortions of the two co-ordination polyhedra