Co-ordination chemistry of higher oxidation states. Part 11. The reaction of nickel(II) iodo-complexes with molecular iodine; crystal and molecular structure of [Ni{o-C6H4(PMe2)2}2][I3]2·2I2

Abstract

The reaction of excess of elemental iodine with the nickel(II) iodo-complexes [Ni(L–L)₂I₂][L–L = H₂NCH₂CH₂NH₂, o-C₆H₄(PMe₂)₂, o-C₆H₄(AsMe₂)(PMe₂), or o-C₆H₄(AsMe₂)₂] in CH₃CN–CH₂Cl₂ solution produces diamagnetic Ni(L–L)₂I₆ materials formulated as [Ni^II(L–L)₂][I₃]₂ and containing tri-iodide(1–) anions. From neat CH₂Cl₂ solution the complex Ni[o-C₆H₄(PMe₂)₂]₂I₁₀ was obtained, and has been shown by single-crystal X-ray studies to be triclinic, space group P, with unit-cell dimensions a= 9.672(2), b= 12.369(2), c= 9.574(3)Å, α= 106.55(2), β= 107.70(2), γ= 99.48(1)°, and Z= 1. 2 914 Observed reflections [F 4σ(F)] refined to R 0.032. The complex contains planar [Ni{o-C₆H₄(PMe₂)₂}₂]²⁺ cations [Ni–P 2.210(2) and 2.200(2)Å], linear I₃^– anions [I–I 2.910(1) and 2.932(1)Å], and di-iodine [I–I 2.728(1)Å]. Weak secondary interactions between the iodine atoms of I₃^– and I₂[I ⋯ I 3.442(1) and 3.576(1)Å] lead to the formation of bifurcated chains. Other nickel(II) polyiodides obtained include the paramagnetic [Ni(L–L)₂(I₃)₂](L–L = MeSCH₂CH₂SMe or MeSeCH₂CH₂SeMe) and the diamagnetic [Ni(L–L)I₄][L–L =o-C₆H₄(AsMe₂)₂ or o-C₆H₄(AsPh₂)₂] and [Ni(Ph₂PCH₂CH₂PPh₂)I₆]. The reaction of the nickel-(III) and -(IV) species [Ni{o-C₆H₄(AsMe₂)₂}₂Cl₂]ⁿ⁺(n= 1 or 2) with I^– gives a compound of composition [Ni{o-C₆H₄(AsMe₂)₂}₂I₃] which is considered to be a nickel(II) derivative. The complexes have been characterised by electronic and e.s.r. spectroscopy, magnetic and conductance measurements. No evidence for the formation of nickel(III) iodo-complexes has been obtained.