The coordinating environments provided by the 1-(5,6-dimethylbenzimidazolyl)-3-benzimidazolyl-2-thiapropane (1), 1-(5,6-dimethylbenzimidazolyl)-3-benzimidazolyl-2-oxapropane (2), 1-(N-methyl)benzimidazolyl-3-benzimidazolyl-2-oxapropane (3), and 1,7-bis(benzimidazol-2-yl)-2,6-dithiaheptane (4) ligands for a series of soft-to-borderline metal ions have been demonstrated by crystallographic structure determination in the solid state, supplemented by multinuclear NMR studies in solution. Structures of [Zn(3)(H2O)(MeCN)](ClO4)2 ([C19H21N5O2Zn](ClO4)2, monoclinic, space group P21/c, a = 10.3247(11) Å, b = 11.0320(12) Å, c = 20.761(2) Å, β = 96.465(3)°, V = 2349.7(4) Å3, Z = 4), [Zn(1)Cl2]·CH3OH ([C18H18Cl2N4SZn]·CH4O, triclinic, space group P1̄, a = 9.0917(9) Å, b = 9.9186(10) Å, c = 12.2079(12) Å, α = 99.710(3)°, β = 94.252(2), γ = 95.598(3)°, V = 1075.3(2) Å3, Z = 2), [Hg(1)Br2]·CH3OH ([C18H18Br2HgN4S]·CH4O, triclinic, space group P1̄, a = 9.1956(12) Å, b = 9.9775(13) Å, c = 12.462(2) Å, α = 99.239(3), β = 97.676(3)°, γ = 94.036(3)°, V = 1113.4(3) Å3, Z = 2), [Cd(1)Cl2] ([C18H18CdCl2N4S], monoclinic, space group P21/n, a = 14.5219(11) Å, b = 8.5315(7) Å, c = 15.6182(12) Å, β = 92.063(2)°, V = 1933.7(3) Å3, Z = 4), and [Ag(4)](NO3) ([C19H20AgN4S](NO3), monoclinic, space group C2/c, a = 13.7339(3) Å, b = 17.2710(1) Å, c = 9.8866(2) Å, β = 115.399(1)°, V = 2118.4(1) Å3, Z = 4) have been determined. Ligand 3 provided the expected N2O donor set to Zn(II) forming part of a pseudo-trigonal bipyramidal coordinating environment, tentatively extrapolated to the Zn(II), Cd(II), and Hg(II) complexes of ligand 2 from 1H NMR studies. The thioether-bridged ligands (1 and 4) displayed a strikingly different coordination mode; in none of these structures was the thioether found to be coordinated to the central metal ion, resulting in pseudotetrahedral structures for the Zn(II) and Hg(II) complexes of ligand 1, a bis(chloro)-bridged dimeric five-coordinate complex of Cd(II) with ligand 1, and a near-linear coordination mode for the Ag(I) complex of ligand 4. No significant distinction in geometric parameters around the metal ions could be observed resulting from the introduction of asymmetry and a change of pK a within the bis(benzimidazole) ligands. Using 199Hg NMR spectroscopy, it was demonstrated that the thioether of ligand 1 did not coordinate in solutions of the 1:1 HgBr2 complex; negligible shifts of the signals corresponding to the aliphatic bridging protons in the 1H NMR spectra of ligand 1 when coordinated to Zn(II), Cd(II), and Hg(II) also suggested a noncoordinating behavior. Exchanges occurring in mixtures of HgBr2 and ligand 1 were examined using 199Hg, 13C, and 1H NMR. It is considered that there is little or no exchange occurring in a region of excess mercury on the 199Hg NMR time scale, and in a region of excess ligand 1 the 1/1 complex predominates.

Reaction of para-bonded hexamethylbenzene, hexamethylbicyclo[2,2,0] hexa-2,5-diene, with rhodium trichloride trihydrate in methanol gives a red solid, also obtained in high yield from the reaction of pentamethylcyclopentadiene with RhCI3,3H20 under similar conditions, and now considered to be di-p-chloro-dichloro(pentamethy1cyclopentadienyl)dirhodium(lll), (C5Me,RhC12)2, rather than the arene complex previously suggested. The same compound has also been obtained in good yields from the reactions of 1 -(I -methoxyethyl)-, 1 -(I -chloroe t h y I )or 1 -( 1 -ace tox y e t h y I)pen ta met h y I cyc I o p e n ta -2,4 -die n e and endo -1 ,2,3,5,6pent a m e t h y I -4met h y le n ebicyclo [3,1 ,O] hex-2-ene with RhC1,,3H20 under similar conditions. Evidence is presented that these last reactions and that of hexamethylbicyclo[2,2,0] hexa-2.5-diene occur via a rearrangement to pentamethylcyclopentadiene catalysed by the hydrochloric acid formed in the reaction of methanol with rhodium trichloride. Reaction of the compound (C5Me5RhC12)2 with sodium iodide gives the corresponding iodo-complex, (C5Me5Rh12),, and pyridine yields the compound (C5Me,) RhCI2(C5H5N).

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We describe some crowns (dinaphthopolyoxacycloalkanins) containing the phenyldinaphthylmethane subunit, regarded as a propeller, the aryl rings (blades) of which are fluxional, twisting about the arylmethine bonds. This torsional propeller movement is fluxional at room temperature on the n.m.r. timescale for some crowns, with AGf2+2M of ca. 10-1 1 kcal mol-', while for others (regarded as locked propellers at room temperature), A G f , is ca. 19 kcal mol-'. Whether fluxional in solution or no, the crowns and their salt complexes commonly exhibit just one propeller isomer in the solids; X-ray crystal structures of one example of a crown (4), and one example of a salt complex ( 7 ) , are described in this paper. Crystal data for (4): C,H4,0,~0.5(CH3)2C0, monoclinic, space group P2,/n, a = 14.403(2), b = 13.428(1), c = 17.797(3)A, p = 93.18(1)", R = 0.070. Crystal data for (7):C4,H440,KNCS~(CH3),C0, monoclinic, space group P2,/c, a = 12.721 (1 ), b = 15.1 97(1), c = 22.038(3) A, p = 92.55(1)", R = 0.065. N.m.r. spectroscopic evidence in solution suggests more than one propeller isomer in solution for fluxional crowns with six oxygen donors, while for locked crowns there is only one. The single observable process (two-ring flip) for the fluxional crowns with 5 and 7 oxygen donors exchanges environments of the two differentiable naphthyl rings and phenyl edges for pairs of isomers which cannot themselves be differentiated by n.m.r. spectroscopy.A lower energy flip exchanges differentiable isomers via a flip of one naphthyl and one phenyl ring for the six-donor crowns. The flexing of the polyether segments in it locked propeller has been shown to be correlated with the twisting of its propeller, using a combination of dynamic n.m.r. studies with 'H and 2H nuclei.

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