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The crystal and molecular structure of [(Fe salen),0],2py (salen = NN'-ethylenebis(salicylideneiminato, py = pyridine) has been determined by single-crystal X-ray analysis. The crystallographic asymmetric unit comprises one dimeric molecule and two non-bonded pyridine molecules in a triclinic cell of dimensions, a = 12.73, b = 13-73, c = 13-92 8, cc = 11 8.75, p = 74.1 5, y = 11 6.1 7" ; space group PT. The iron atoms are joined by a single oxygen atom and both are five-co-ordinate with a distorted square pyramidal geometry. The mean Fe-O(bridge) bond length is 1-80 a and the bridging angle Fe-O-Fe is markedly bent a t 139". The properties of the dimeric molecule are compared with those of other oxo-bridged iron(ttl) and manganese(li1) dimers and also with the closely related [Fe salen CI], dimer and Fe salen CI monomer.

The structures of the hydrated zinc(I1) and nitrate ions in 3.72 mo! dm-3 aqueous ZniN03)z have been determined bv X-ray diffraction. Octahedral coordination in Zn;; is confirmed and the average Zn-Owater distance is 2.17 (4) A; there is no evidence for coordination by NO;. Approximately three water molecules are hydrogen bonded to each nitrate 0-atom.The use of X-ray diffraction for determining the molecular geometry of metal complexes in solution has been very limited compared with the solid-state applications, and such studies as have been reported have largely involved the heavier metals and simple monodentate ligands. A major reason for our interest in it is the possibility of directly determining the coordination of zinc in its complexes in solution. While it is generally agreed that the important role played by Zn" in enzyme chemistry is linked with its ability to adopt a coordination number (CN) of 4, 5 or 6 and to change its coordination geometry comparatively easily according to the circumstances, its d lo configuration has so far precluded the direct determination of its CN by spectroscopic techniques. We have developed a simple but accurate photographic technique which uses Cu K, radiation and an enclosed cylindrical sample and have applied it initially to a study of aqueous Z I I ( N O~)~. Its use to determine the coordination geometry of the 2,2',2"-triaminotriethylamine (tren) complex of zinc (chloride) will be reported elsewhere.A full single-crystal structural analysis of Zn(N03j2.6H20 has been reported by Ferrari et al.,' who showed that the the coordination at the metal ion is octahedral. The only X-ray report on solutions of this salt has been by Bol et L Z~. ,~ who compared the diffraction pattern of a unimolar aqueous solution with that of the same concentration of Mg(NO3)2. Assuming both metals to be octahedrally hydrated, Bol et al. argued that the anion-solvent, solvent-solvent and anion-anion interactions would be same in the two cases and would therefore be eliminated by subtracting one radial distribution function (r.d.f.) from the other. They determined the inner-sphere zinc-oxygen distance but were unable to comment on any other characteristic distances other than to suggest that there might be 12k2 water molecules in the second hydration shell, with rZn-o of ca. 4.2 A.The only other reports on X-ray diffraction studies of solutions of aqua-zinc have been by Shapovalov3 on the sulphate and Ohtaki et al.4 on the sulphate and perchlorate. In the former case, three concentrations were studied (corresponding to mole ratios xH20:xZn of 31, 50 and 100) and the inner-sphere rZn-0 was determined for all three. The CN of zinc was assumed to be six throughout, and no evidence was found to indicate any deviation from this, or of sulphate coordination; no other distances were reported. Ohtaki et al. found the CN of zinc to be close to 6 for both the sulphate (xHz0 : x Z n = 19.2) and the perchlorate (15.4), and also found no evidence of sulphate coordination. They reported the zinc-oxygen distan...

The complex [RhC12(C6H5N)2(P(o-C6H4Me)2(o-C6H4CH2))] crystallises from chloroform-ethanol as monoclinic crystals containing a nonstoicheiometric amount of chloroform. The cell dimensions are a = 18.43, b = 10.22. c = 19.1 5, p = 11 2.4 f 0.1 ; the space group is P2Jc with one molecule of metal complex per asymmetric unit.A three-dimensional X-ray analysis, based on 2430 independent diffractometer-measured reflections, has converged to a final weighted R of 0.077. The value of u for the Rh-CI and Rh-P bond distances is 0.004 8, and for Rh-C and Rh-N is 0.01 3-0.01 6 8 ; within the pyridine and tolyl groups the mean o for bond distances is 0.027 8.The steric requirements of the five-membered chelate ring and the methyl groups of the nonchelating tolyl groups give rise to several significant deviations from the C,, symmetry of the carbon skeleton of free toluene. The transinfluence exerted by a saturated carbon ligand is evidenced by the significant difference between the Rh-CI bond lengths, one chlorine being trans to a pyridine (Rh-CI 2.339 A), the other trans to the benzyl carbon (Rh-CI 2.531 8). A general discussion of the trans-influence in octahedral complexes is provided.The molar ratio, within the crystal, complex: chloroform, determined from a least-squares refinement of the chloroform group population parameter, is 1 :0-61 f 0.02. Complete disorder of the solvated chloroform appears to be prevented by a weak hydrogen bond between the proton of the chloroform group and one of the chlorine atoms coordinated to the metal.