Bidentate group vb ligands. Part XIII. Divalent cobalt, nickel, and palladium complexes of 1,2-bis(methylphenylarsino)ethane and 1,3-bis(methylphenylarsino)propane. Stoichiometric and structural effects of chelate chain length

Article abstract of DOI:10.1016/S0020-1693(00)93852-0

Thirtyfour complexes of 1,2-bis(methylphenylarisino)ethane (dase) and 1,3-bis(methylphenylarsino)propane (dasp) have been characterised. Interesting differences are observed in the complexing properties of these chelates. Thus, with cobalt(II) halides [Co(dase)₂][CoX₄], which contain planar cations, and pseudotetrahedral [Co(dasp)X₂] are obtained. Nickel (II) halides form planar [NiLX₂] complexes with dase, but with dasp form [Ni(dasp)X₂]_n (X = Cl, Br) which are pseudooctahedral in the solid state and planar in solution, and the pseudotetrahedral [Ni(dasp)I₂]. The [Ni(dasp)₂X] ClO₄ are trigonal bipyramidal in the solid state (X = Cl, Br, I, NCS), but in solution [Ni(dasp)₂(NCS)]⁺ appears to be square pyramidal, whilst the [Ni(dase)₂X] ClO₄ are square pyramidal in both the solid state and solution. The planar [Ni(dasp)(NCS)₂] complex differs from the analogous dase species by losing ligand on recrystallisation to form the dimeric Ni₂(dasp)₃(NCS)₄moiety. Planar [PdLX₂] (L = dase, dasp, X = Cl, Br, I) species are formed, but no [PdL₂X]⁺ complexescould be isolated. In the solid state [PdL(NCS)(SCN)] complexes are formed, and the dase species isomerises to [Pd(dase)(SCN)₂] in dichloromethane. An attempt is made to relate the structural differences in the complexes to the chain length of the chelates.