Uniaxial negative thermal expansion and metallophilicity in Cu3[Co(CN)6]

We report the synthesis and structural characterisation of the molecular framework copper(I)hexacyanocobaltate(III), Cu3[Co(CN)6], which we find to be isostructural to H3[Co(CN)6] and the colossalnegative thermal expansion material Ag3[Co(CN)6]. Using synchrotron X-ray powder diffraction measurements,we find strong positive and negative thermal expansion behaviour respectively perpendicular and parallel to thetrigonal crystal axis:α= 25.4(5) MKa−1andα= − 43.5(8) MKc−1. These opposing effects collectively result in avolume expansivityα= 7.4(11) MKV−1that is remarkably small for an anisotropic molecular framework. Thisthermal response is discussed in the context of the behaviour of the analogous H- and Ag-containing systems.We make use of density-functional theory with many-body dispersion interactions (DFT + MBD) todemonstrate that Cu+…Cu+metallophilic (‘cuprophilic’) interactions are significantly weaker in Cu3[Co(CN)6]than Ag+…Ag+interactions in Ag3[Co(CN)6], but that this lowering of energy scale counterintuitively translatesto a more moderate—rather than enhanced—degree of structural flexibility. The same conclusion is drawn fromconsideration of a simple GULP model, which we also present here. Our results demonstrate that stronginteractions can actually be exploited in the design of ultra-responsive materials if those interactions are set upto act in tension

Gas-phase synthesis and reactivity of binuclear gold hydride cations, (R3PAu)(2)H+ (R = Me and Ph)

© Royal Society of Chemistry 2006Electrospray ionization of a mixture of the two gold phosphine chlorides, R3PAuCl (R = Ph and Me), silver nitrate and the amino acid N,N-dimethylglycine (DMG) yields a range of gold containing cluster ions including: (R3P)Au(PR'3)+; (R3PAu)(R'3PAu)Cl+ and (R3PAu)(R'3PAu)(DMG-H)+ (where R = R' = Ph; R = R' = Me; R = Me and R' = Ph). Collision induced dissociation (CID) of the (R3PAu)(R'3PAu)(DMG-H)+ precursor ions yielded the hitherto unknown gold hydride dimers (R3PAu)(R'3PAu)H+. The gas-phase chemistry of these dimers was studied using ion-molecule reactions, collision induced dissociation, electronic excitation dissociation (EED) and DFT calculations on the (H3PAu)2H+ model system. A novel phosphine ligand migration was found to occur prior to fragmentation under CID conditions and this was supported by DFT calculations, which revealed a transition state with a bridging phosphine ligand.George N. Khairallah, Richard A. J. O'Hair and Michael I. Bruce