Generation and Stabilization of D(6h) and C(2v) Valence Tautomeric Structures of the Rhodizonate Dianion in Hydrogen-Bonded Host Lattices This work was supported by the Hong Kong Research Grants Council Earmarked Grant (CUHK 4206/99P)

Coordination chemistry of polyoxo-carbocyclic compounds containing one or more neighboring oxo-groups

This is a review of publications concerning the results of X-ray analysis of single crystals and spectrochemical characteristics of metal complexes containing polyoxo-carbocyclic compounds with one or more neighboring oxo-groups. The features of lattice characteristics and coordination modes, depending on the nature of the organic dianion, are shown here. The squarate anions, ${{\rm{C}}_{\rm{4}}}{\rm{O}}_{\rm{4}}^{{\rm{2 - }}}$ are predominantly involved in monodentate bridging coordination, and the derivatives containing five or six C-atoms in the cycle (croconate and rhodizonate anions) usually form bidentate chelating bridged modes. The stabilization of the crystal lattices of the metal complexes is due to the formation of hydrogen bonds and π-π stackings, which produce self-assembled three-dimensional (3D) structures with cavities and intercalation of some small molecules. The strong interlayer interactions lead to appearance of specific conductometric and magnetic properties, which together with their high thermal stabilities, make the oxocarbon complexes new and perspective materials for electronics and related areas.

Solid-state linear polarized IR-spectroscopy of croconic and rhodizonic acids

The applications of linear-polarized IR-spectroscopy to oriented colloid suspensions in a nematic host are demonstrated with croconic and rhodizonic acids. The experimental IR vibrational assignments of the solid-state of both neutral compounds are presented. Assignments are supported by theoretical quantum chemical calculations and vibrational analysis at the DFT level of theoretical approximation with the 6-311++G** basis set.

Silver(I) Double and Multiple Salts Containing the 1,3-Butadiynediide Dianion: Coordination Diversity and Assembly with the Supramolecular Synthon Ag4⊂CCCC⊃Ag4

A series of 13 silver(I) double and multiple salts containing 1,3-butadiynediide, C4(2-), were synthesized by dissolving the silver carbide Ag2C4 in a concentrated aqueous solution of one or more of the silver salts AgNO3, AgCF3CO2, AgC2F5CO2, AgF, AgBF4, and AgPF6. The 1,3-butadiynediide anion invariably adopts a mu4,mu4 coordination mode in these compounds, which indicates that the Ag4[cap]C[triple bond]C-C[triple bond]C[cap]Ag4 moiety can be used as a new type of metalloligand supramolecular synthon for the construction of coordination networks. Fine-tuning with various ancillary anionic ligands caused the Ag4 aggregate at each ethynide terminus to adopt a butterfly-shaped, planar, or barblike configuration, within which the silver-ethynide interactions can be classified into three types: sigma, pi, and mixed (sigma,pi). The effect of coexisting nitrile ligands and quaternary ammonium salts on supramolecular assembly with the above synthon was also explored. The hydrolysis of PF6(-) and BF4(-) led to the formation of the quadruple salt Ag2C4 x 4 AgNO3 x AgPF2O2 x Ag3PO4 and a novel (F)2(H2O)18 hydrogen-bonded tape in the triple salt Ag2C4 x 2 AgF x 10 AgC2F5CO2 x CH3CN x 12 H2O, respectively. The largest silver-ethynide cluster aggregate described to date, (C4)3@Ag18, occurs in 3 Ag2C4 x 12 AgC2F5CO2 x 5 [(BnMe3N)C2F5CO2] x 4 H2O (Bn = benzyl).

Solvent-induced supramolecular isomerism in [Pt(SC(NH2)2)4]2+ croconate salts

The role of solvent (and other species) in the formation of networks from tetrakis(thiourea)platinum(II) cations and croconate anions is examined, with crystallisations from DMSO giving rise to a structure containing solvent filled channels.

Stabilization of D5hand C2vvalence tautomers of the croconate dianion

The non-benzenoid aromatic D(5h) and enediolate C(2v) form of C5O5(2-) have been stabilized by hydrogen bonding with urea and 1,3-dimethylurea, respectively, in the host lattices of two novel crystalline inclusion compounds.

Are neutral oxocarbons stable?

A set of novel oligomeric polycyclic neutral oxocarbons has been computed at the B3LYP level of density functional theory. On the basis of the calculated dissociation enthalpies, the most stable structures are C(9)O(9) and C(12)O(12) with benzene-like central ring, in agreement with the experimental finding, and the enhanced stability is due to their aromaticity. Several other oxocarbons also have been identified as stable and are targets for further experimental investigations.