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The isolation and structural characterization of 1 : 1 adducts of copper(1) chloride (1) and bromide (2) with pyridine-4-carbonitrile (L) is described; crystals of the two complexes are isomorphous (monoclinic, P21/c, a ≈ 3.9, b ≈ 14.7, c ≈ 13.0 � , β ≈ 96°, Z 4; R0.047, 0.063 for No 630, 707 'observed' reflections respectively). Unlike the 1 : 1 adducts with the parent pyridine and benzonitrile ligands which are 'stair' polymers, these complexes comprise 'split-stair' strands woven into a two-dimensional sheet by crosslinking ambidentate ligands. Cu-N ( nitrile ) (1.942(9), 1.96(1) � ) are appreciably shorter than Cu-N (pyridine) (2.066(8), 2.04(1) � ), as in the parent base complexes. The two Cu-X are similar in each case: 2.336(6), 2.366(3) � (CI); 2.460(3), 2.486(3) � (Br). The iodide adduct (3) isolated is of novel stoichiometry (Cul : L, 4 : 5) (monoclinic, P21/c; a 10.140(5), b 12.214(6), c 15.157(8) � , β 99.99(4)° Z 2; R 0.048, No 2416). It is a linear polymer, comprising tetranuclear Cu414L4 'step' units, crosslinked across inversion centres by disordered ambidentate ligands.

r/-Allyl)bromodicarbonyl(N,N'-dicyclohexylethanediimine)molybdenum(II), [MoBr(CaHs)-(CO)2(C~4H24N2)], M r = 493.30, orthorhombic, Pnam, a = 12.541 (1), b= 8.318 (1), c= 19.503 (1)A, V= 2034.5A 3, Z=4, D x= 1.611Mgm -3, 2(CuK~t)= 1.5418 A, ~= 7.322mm -1, F(000)= 1000, T= Mo Br 293K, final R=0.088 for 1267 unique observed c(1) reflections. The Mo atom shows octagonal coordination c(2) C(3) with a mirror plane passing through it, the Br atom and c(10) the central C atom of the r/-allyl group. Bonds to C(ll) Mo are Mo--Br = 2.649 (2), Mo--N = 2.221 (8), c(12) C(13) Mo-C(allyl) = 2.179 (17), and Mo-C(carbonyl) = c(14) 1.965 (14) A. C(15) C(16) O(l) N(I) Experimental. Tabular crystal, 0.13 x 0.10 x 0.05 mm, non-standard setting of space group Pnma (No. 62) used, Enraf-Nonius CAD-4 diffractometer, Ni-filtered radiation, moving-crystal/moving-counter technique, 20< 140 °, lattice parameters from measurements on 45 reflections, no absorption corrections, h=-15 to 15, k=-10 to 10, l=0 to 23, reflection 402 as intensity standard, average count 5484.5 with a (calculated from distribution of measurements) = 103.9. 4215 reflections measured and merged using SHELX76 (Sheldrick, 1976), 1651 unique reflections, merging Rin t = 0.072, 384 excluded during refinement [F o < 3a(Fo)]. Mo and Br positions from Patterson function, other non-H atoms from Fourier syntheses, based on phases defined by Mo and Br; least-squares refinement, F magnitudes; isotropic and then anisotropic temperature factors gave R = 0.088, wR = 0.0676 including H atoms at calculated positions. Weights given by w = I/[a2(F) +

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The structure of KB[ Re0,(CN)4] has been determined by three-dimensional single-crystal neutron diffraction, and has been refined to R 0.1 45 for 670 independent reflections. The complex crystallizes in the triclinic space group PT with a = 0.766, b = 0,745. c = 0.629 nm. a = 109.6, 6 = 105.9, y = 11 5.4" and Z = 1. The [Re0,(CN),]3ion possesses an approximate octahedral arrangement around the rhenium, and contains a crystallographic centre of symmetry. The cyanide groups are carbon bonded with Re-C distances 0.21 15 and 0.21 32 nm, C-N distances 0.1 148 and 0.1 164 nm and Re-C-N angles of 179.2 and 173.7". The Re-0 distance is 0.1 773 nm.PREVIOUS work using X-ray diffraction techniques has shown that in the crystal structure of K,[ReN- (CN),],H,O, the cyanide ligands are bent. There was also evidence to suggest that the cyanide groups might be nitrogen bonded to the rhenium. We were unable to grow crystals of this complex sufficiently large for investigation by neutron diffraction, but suitable specimens of the complex K3[Re02(CN),] were obtained. Both the ions [ReN(CN), ,-J3-contain octahedrally co-ordinated dia-