The substitution pattern determines whether distilbenylazobenzene compounds 1 or their subsequent products, the dihydrocinnolines 2, are isolated in the cobalt‐catalyzed solvent‐free reaction of azo compounds with diphenylacetylene. For several derivatives a photochromic equilibrium exists between the two forms.

group P b m . u = 11.544(4). h = 13.206(8), c = 13.784(3) 8, ix = fi = 7 = 90 . V = 2101(2) A'. Z = 4. pLalCs = 1.298 Mgm-3, data collection on a Nicolet R3mv four-circle diffractometer with monochromated Mo,, radiation. (i = 0.71073) in the range 4 < 20 < 57"; 3505 reflections measured of which 2525 independent: structure solution with direct methods (SHELXTL Plus 4.1 1 ); data refinement using full matrix against F2 using the least squares method (SHELXL 93, G. M. Sheldrick. Universitlt Gottingen. 1993). All non-hydrogen iitoms were refined anisotropically; all hydrogen atoms were localized using difference Fourier syntheses and independently refined isotropically; 191 refined parameters: R values for [I > 2u(I)]: R1 = 0.0594: uR2 = 0. I51 1. b) Further details of the crystal structure investigations may be obtained from the Director ofthe Cambridge Crystallographic Data Centre, 12 ), VCH, Weinheim. 1994, pp. 431 -500. Crystal structure analysis of 7 (C,,H,,CIN,O,); M = 391.9, monoclinic. space groupP2,:ri.o =7.1360(9),h=19.332(5),c=15.975(4)~,~= 94.45(2)". V =

Two translationally independent electron-rich particles would principally repel each other, unless they had opposing electrical charge and would thus form an ion pair in a suitable solvent. Under these conditions, a novel interionic strain could build up, which would result from the intkrionic orbital repulsion and should express itself in the increased reactivity of both ionic components towards other reagents. In order to confirm this, salts would have to be synthesized in which electron-rich cations are combined with electron-rich anions. Cations are generally, however, electron-deficient systems; the notable exception to this rule are the tris(dialkylamin0)-substituted cyclopropenylium ions, which according to Gerson et al. can be considered as electron-excess systems."l These electronic properties are the cause of their unusual behavior in comparison to other carbenium ions: For example, the tris(dimethy1amino)cyclopropenylium ion (TDA cation) functions as the donor component in deeply colored charge transfer (CT) salts with tetracyanoethylene (TCNE) or 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) .[*% The TDA cation also behaves as a donor with respect to electron-deficient anions of the type EICI; (El = Sb, Nb, Ta); in these reactions deeply coloured "inverse CT salts" with one-dimensionally stacked structures r e s~l t . [~-~~ TDA salts can be readily oxidized to give stable isolable radical dicationic salts.'9-If this cation is combined with donor anions (e.g. halide ions), ion pairs of the type 1 are obtained which contain-as required above-two oppositely charged electron-excess systems as electronic antagonists (Scheme 1 a). This is demonstrated in that the E l l , values of about 1.4 V (vs Ag/AgCI; 0.1 N NEt,CI/CH,CN) for the oxidation of both the TDA cation and the chloride ion are almost the same, in spite of the opposing charges of these ions.[t2, I 3 l At the point of maximum electrostatic attraction between the constituent ions of 1 (centrosymmetric arrangement), the orbital repulsion of the two would also have its maximum effect. The latter should be especially pronounced for the corresponding HOMO/HOMO interaction since the interacting orbitals have the same local symmetry (see Scheme 1 b).We inferred from this, that TDA halides should exhibit a distinctly lower tendency to form inner ion pairs in dipolar aprotic solvents than other known saltlike halides. They are possibly, therefore. highly effective sources of naked halide ions. In order to check this hypothesis. we treated the readily accessible[91 tris(dimethybamino)cyclopropenylium chloride (TDACI) 1 a with accep-

The complex adducts [M(acac)2(PhHgOHgPh)]2 (M = Co, Ni) have been obtained by incorporation of PhHgOH into the coordination sphere of M(acac)2 at ambient temperature. The X-ray crystal structure of [Ni(acac)2(PhHgOHgPh)(Et2O)]2 (1c) reveals a dimeric nickel complex coordinated by the acetylacetonate oxygen and the bridging oxygen of bis(phenylmercuric) oxide. Refluxing a THF solution of compound 1c gave diphenylmercury, HgO, and Ni(acac)2(THF)2. With PhHgOH or PhHgSH the symmetrization reactions also occurred when catalytic amounts of Ni(acac)2 were used. In contrast, triphenyltin derivatives (hydroxide, acetate, oxide) on treatment with M(acac)2 in aqueous THF gave the stable complexes [M(acac)2(Ph3SnOH)]2 (M = Co, Ni). The structure of [Ni(acac)2(Ph3SnOH)]2 (2) was also determined by X-ray crystallography.

Gd(HSO4)3 is obtained on treatment of Gd2(SO4)3 in conc. H2SO4 in closed vessels at 200 °C. The extremely moisture-sensitive crystals belong to the orthorhombic space group Pbca. Lattice constants are a = 12.080(8), b = 9.574(8), c = 16.513(8)Å and Z = 8. Gadolinium is coordinated by eight oxygen atoms of the hydrogensulfate ligands forming a distorted square antiprism. There are three different HSO4- anions within the structure. One of them is coordinated with two Gd atom s while two HSO4- anions bridge three Gd atoms. The Gd-O bond lengths vary in the range of 2.334(6)-2.423(5)Å .