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The Schiff-base dianion N,N'-2,2-dimethyltrimethylenebis[salicylideneiminate(2-)] (salnptn) coordinates to vanadium( w ) to form [VO(salnptn)] whose crystal structure has been determined. The compound is polymeric in the solid state with -. V=O ---V=O -+ V=O chains, the salnptn donor atoms being coplanar and the salnptn framework umbrella-shaped. In the derivative [VO(OMe)(salnptn)], the crystal structure of which has also been determined, the OMe and the vanadyl oxygen are co-ordinated cis to each other, and the salnptn now occupies three equatorial and one axial coordination positions. Even N,N'-ethylenebis(salicy1ideneiminate) seems to behave analogously, though it is normally planar.We have recently described a series of vanadium(1v) complexes of tetradentate dianionic Schiff bases.' It is now well established that vanadyl(rv) compounds with such ligands are essentially five-co-ordinate, but they fall into two classes, one of green compounds with v(V=O) ca. 980 cm-' in which the five-coordinate species are without obvious intermolecular interactions in the crystal, and another which are yellow-brown, with v(V=O) ca. 880 cm-l and which appear to 'polymerise' in the crystal, forming V=O --+ V=O --V=O chains, though the 0 -V co-ordinate bond is rather long, ca. 2.2 8, compared with ca. 1.6 8, for V=0.2 Among the compounds we prepared was wO(2-OC6H4-CH=NCH,CMe2CH2N=CHC6H40-2)] ' or wO(salnptn)] which shows v(V=O) at 871 cm-' and is orange, suggesting a polymeric structure in the solid, but its solubility in organic solvents is nevertheless very high. Accordingly we undertook an X-ray crystal-structure analysis to determine whether the colour and IR data, or the solubility, is the more reliable indicator of the solid-state configuration.

The preparation and some physical properties of complexes of the types [MX,L,] where M = Re, Ru, or 0 s and [MX,L,] where M = Re, 0 s . or Ir and L = tertiary monophosphines are described. A few tertiary monoarsine analogues are also included.

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