A stable yellow derivative of cobyrinic acid heptamethyl ester, (5R,6R)-Coα,Coβ-dicyano-5,6-dihydro-5-hydroxy-heptamethylcob(III)yrinate-c,6-lactone (DCSYCbs), was prepared from dicyanocobyrinic acid heptamethyl ester (DCCbs). The C5 carbon is oxidized and the c side chain cyclized to form a lactone at C6; the 13 atom, 14 π-e(-) delocalized system of corrins is interrupted, giving a triazamethine system with four conjugated double bonds between N22 and N24 and an isolated double bond between N21 and C4. Stable yellow aquacyanocobyrinic acid heptamethyl ester (ACSYCbs) was prepared by driving off HCN with N(2) in a methanol/acetic acid solution. The electronic spectra of DCCbs and DCSYCbs appear similar except that the bands in DCSYCbs are shifted to shorter wavelengths and the γ-band is much less intense. The experimental spectra were adequately modeled using TD-DFT at the PBE1PBE/6-311G(d,p) level of theory. DCSYCbs crystallizes in the space group P2(1)2(1)2(1) (R(1) = 6.08%) with Z = 4, including one methanol solvent molecule and one water molecule per cobester. The addition of a hydroxyl group at C5 causes loss of the double bond between C5 and C6 and elongation of the C5-C6 bond. From a combination of two-dimensional (1)H TOCSY and ROESY NMR spectra and (1)H/(13)C HSQC and HMBC data, the complete (1)H and (13)C NMR assignments of DCSYCbs were possible, except for two of the ester methyl groups and the (13)C resonances of the two axial cyanide ligands. The latter were assigned using relative chemical shifts calculated by GIAO-DFT methods. The (59)Co resonance of DCCbs was observed at 4074 ppm while that of DCSYCbs is shifted downfield to 4298 ppm. Comparison with available (59)Co data of analogous systems suggests that the more π-conjugated corrin of DCCbs interacts more strongly with the metal than the less extensively conjugated macrocycle of DCSYCbs. As the strength of the interaction between Co(III) and an equatorial macrocycle increases, ν(CN) of axially coordinated CN(-) shifts to lower frequency; in DCSYCbs and DCCbs ν(CN) occurs at 2138 and 2123 cm(-1), respectively. Hence the corrin ligand in DCCbs interacts more strongly with the metal than the stable yellow corrin ligand, with its diminished conjugation. The UV-vis spectral data and DFT-calculated MOs are consistent with greater overlap between the corrin and the metal orbitals in DCCbs relative to DCSYCbs, which gives the metal in the former a softer, more covalent character.

Treatment of [Pt(trpy)Cl]SbF(6) with AgSCN in a metathesis reaction affords after work-up yellow crystals of [Pt(trpy)(NCS)]SbF(6).CH(3)CN where trpy is 2,2':6',2''-terpyridine. A single crystal structure determination of the solvate shows that the SCN(-) ion is N-bound to the Pt atom, and that the planar cations stack as Pt(2) dimers with a PtPt separation of 3.293(1) A. The crystals rapidly de-solvate under ambient conditions to give a polycrystalline maroon material characterised as [Pt(trpy)(NCS)]SbF(6) (). A (15)N NMR spectroscopic study of a solution of isotopically labeled [Pt(trpy)((15)N(13)CS)]SbF(6) in CD(3)CN shows that both linkage isomers of the SCN(-) ion co-exist in solution with the N-bound isomer dominant, and the S-bound isomer present at a much lower concentration. Compound exhibits temperature dependent (3)MMLCT emission in the solid state; at 280 K the emission maximises at 692 nm, but red-shifts systematically on cooling to reach 762 nm at 80 K. Compound shows vapochromic behaviour that is selective and reversible for vapours of acetonitrile, DMF and pyridine. The colour change is from maroon for to yellow for all three solvates. The emission spectra recorded for the solvates maximise at wavelengths that are all significantly blue-shifted compared to lambda(em)(max) recorded for : the blue-shifts measured at 77 K are 90, 115 and 155 nm for the acetonitrile, DMF and pyridine solvates respectively. The origin of the vapochromic properties of compound is likely to do with the breaking and making of metallophilic PtPt interactions in the solid state.

Multiple techniques have been used to delineate the self-assembly of a bis(pyrrole) Schiff base derivative (compound 4, C(16)H(14)N(4)), which forms an unusual dimer through complementary N-H...N=C hydrogen bonds between twisted, C2-symmetric monomer units. The asymmetric unit of the crystal structure comprises one and a half dimer units, with one dimer exhibiting approximate D2 point-group symmetry and the other exact D2 symmetry (space group C2/c). The dimers pack into columns whose axes are collinear with the a axis of the unit cell. The columns assemble into discrete layers with two distinct types of hydrogen-sized voids residing between the layers. Despite the promising architecture of the voids within the lattice of 4, the absence of genuine channels to interconnect the voids precludes the uptake of hydrogen gas, even at elevated pressures (10 bar). AM1 calculations of the structure of dimeric 4 indicate that self-recognition through hydrogen bonding depends primarily on favorable electrostatic interactions. The potential-energy surface for monomeric 4 mapped by counter-rotation of an adjacent pair of C=C-N=C torsion angles indicates that the X-ray structures of the four monomeric units are global minima with highly nonplanar conformations that are preorganized for self-recognition by hydrogen bonding. The in vacuo enthalpy of association for the dimer was calculated to be significantly exergonic (DeltaG(assoc)=-21.9 kJ mol(-1), 298 K) and in excellent agreement with that determined by 1H NMR spectroscopy in CDCl3 (DeltaG(assoc)=-16.6(4) kJ mol(-1), 298 K). Using population and bond order analyses, in conjunction with the conformation dependence of the frontier MO energies, we have been able to show that pi-electron delocalization is only marginally diminished in the nonplanar conformers of 4 and that the electronic structures of the constituent monomers of the dimer are well mixed.

NAMFIS (NMR Analysis of Molecular Flexibility In Solution) has been applied to curcumin dissolved in DMSO. Quantitative H-H distance constraints reduce a pool of candidate conformations to a solution collection of four enol conformations-two of these match curcumin crystallized with human transthyretin, and one is closely related to a single-crystal structure of curcumin.

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