almost the same as the Mo-Mo distance (2-61-2-64 A) in (M06X8)4f.5-7 In contrast, the two-electron oxidation of the more weakly bound (Nb6X12)2+ increases the Nb-Nb distance from 2.92 to 3.016 and decreases the Nb-(axia1)Cl distance from 2-60 to 2.48 A.

The crystal structure of the title compound has been determined by single-crystal X-ray diffraction by use of conventional heavy-atom methods. The structure was refined by a block-diagonal least-squares procedure to R 0.08 for 345 independent visually estimated reflections. Crystals are rhombohedral, space group R3, a = 9.77 * 0.01 8, cc = 80.7 f 0.1' (hexagonal cell : a = 12.64, c = 19.47 8). 2 = I .The structure consists of cubic close-packed layers of [Hg(C5H5NO)s]2+ cations with the CIO.i-ions in ' trigonal holes ' of the array. The mercury has regular octahedral co-ordination, d(Hg-0) 2.35 8. Distances and angles within the ligand and the perchlorate ion are as expected. The i.r. spectrum of the perchlorate ion shows bandsplitting consistent with its C3?, symmetry.

The synthesis. properties, and structures of cationic dimeric dithiocarbamato-complexes (dtc) of cobalt(iii) are described. The complexes [Co,(R,dtc),] BF, were prepared by reaction of [Co( R,dtc),] with boron trifluoride. The crystal structure of [Co,(Et,dtc),] BF, was determined from three-dimensional counter data. Crystals are orthorhombic, space group P212121. with a = 14.301 (5). b = 16.819(3), c = 18.048(4) A, and 2 = 4. The structure was solved by conventional Patterson and Fourier techniques and refined by block-diagonal leastsquares to R 0.092 for 1 141 independent reflections. The green-brown diamagnetic [C~,(R,dtc)~]+ species is comprised of an electrophilic [Co(R,dtc),]+ fragment co-ordinated in the cis-positions by sulphur atoms from an octahedral [Co( R,dtc),] molecule of opposite chirality. The lability of the bridging groups renders the dimer susceptible to attack by other nucleophiles and representative mixed chelates of the type [Co( R,dtc),(chel)] have been synthesised (chel = xanthate, dithiocarbamate. acetyl-, and dithioacetyl-acetonate).INTEREST in the unsuspected capacity of the dithiocarbamate ligand (I) to stabilize complexes in unusually high oxidation states has lead to the isolation of dithiocarbamate complexes of CuIII, NiIv, FeIV, and MnW.l-7 [I)For [Co(R,dtc),] oxidation of the 3d6 ion would be expected to be difficult. Indeed, preliminary electrochemical results confirm that these complexes are difficult to oxidize electrochemically * although the detailed nature of the oxidation process is still being s t ~d i e d . ~ Chemical oxidation of dithiocarbamate complexes with BF, has afforded the well characterized FeIV salts, [Fe(R2dtc),]BF4 and Pasek and Straub suggested they also obtained the species [Mn(Et2dtc),]BF4 and [Co(Et,dtc),]BF,., By a similar method ([Co(R,dtc),] and BF,), Gahan and O'Connor have extended the series of presumed Corn species, [Co(R2dtc),]BF4, and report unusual and unexpected properties, the complexes being diamagnetic and oligomeric with molecular complexities of 2-4 in chloroform.1° These anomalies and the structure of the ' oxidized cobalt species must be resolved before the electron-transfer behaviour of the cobalt dithiocarbamates can be interpreted. Accordingly, we have employed a BF, oxidation procedure, which has successfully provided complexes of CuIII, FeIV, and MnIv,4 on the [Co(%dtc),] species. In a preliminary communication l1 we summarized spectroscopic and other physicochemical evidence that the complexes we obtain

No abstract

Crystals of hexakis(2-pyridone)copper(II) perchlorate, [Cu(C5H5NO)6] (ClO4)2, are monoclinic, a 9.453(2), b 10.492(3), c 17.794(4) Ǻ, β 95.57(2)�, space group P21/c with Z = 2. The structure was solved by Fourier methods using X-ray diffractometer data and refined by block-diagonal least-squares to convergence at R 0.037, Rw 0.044 for 3054 independent reflections. The octahedral coordination of the copper atom in the centrosymmetric cation is tetragonally distorted with Cu-O bond lengths of 1.922(2), 1.952(2) and 2.546(2) Ǻ. The ligands are in the pyridone tautomeric form and coordinate the copper atom through the exocyclic oxygen atoms. There are N-H...O bonding interactions between the ligands in the equatorial plane and the axial ligands (N...O distances of 2.781(3) and 2.894(3) Ǻ). The perchlorate ions (Cl-O, 1.412-1.436 Ǻ) are hydrogen-bonded to the N-H groups of the axial ligands (N...O 2.958 Ǻ.