Varying the coinage metal in cyclic trinuclear pyrazolate complexes is found to significantly affect the solid-state packing, photophysics, and acid−base properties. The three isoleptic compounds used in this study are {[3,5-(CF 3 ) 2 Pz]M} 3 with M ) Cu, Ag, and Au (i.e., Cu 3 , Ag 3 , and Au 3 , respectively). They form isomorphous crystals and exist as trimers featuring nine-membered M 3 N 6 rings with linear two-coordinate metal sites. On the basis of the M−N distances, the covalent radii of two-coordinate Cu I , Ag I , and Au I were estimated as 1.11, 1.34, and 1.25 Å, respectively. The cyclic {[3,5-(CF 3 ) 2 Pz]M} 3 complexes pack as infinite chains of trimers with a greater number of pairwise intertrimer M‚‚‚M interactions upon proceeding to heavier coinage metals. However, the intertrimer distances are conspicuously short in Ag 3 (3.204 Å) versus Au 3 (3.885 Å) or Cu 3 (3.813 Å) despite the significantly larger covalent radius of Ag I . Remarkable luminescence properties are found for the three M 3 complexes, as manifested by the appearance of multiple unstructured phosphorescence bands whose colors and lifetimes change qualitatively upon varying the coinage metal and temperature. The multiple emissions are assigned to different phosphorescent excimeric states that exhibit enhanced M‚‚‚M bonding relative to the ground state. The startling luminescence thermochromic changes in crystals of each compound are related to relaxation between the different phosphorescent excimers. The trend in the lowest energy phosphorescence band follows the relative triplet energy of the three M I atomic ions. DFT calculations indicate that {[3,5-(R) 2 Pz]M} 3 trimers with R ) H or Me are bases with the relative basicity order Ag , Cu < Au while fluorination (R ) CF 3 ) renders even the Au trimer acidic. These predictions were substantiated experimentally by the isolation of the first acid−base adduct, {[Au 3 ] 2 :toluene} ∞ , in which a trinuclear Au I complex acts as an acid.

Synthetic details, solid-state structures, and photophysical properties of a group of trimeric copper(I) complexes containing pyrazolate ligands are described. The reaction of copper(I) oxide and the fluorinated pyrazoles [3-(CF(3))Pz]H, [3-(CF(3)),5-(Me)Pz]H, and [3-(CF(3)),5-(Ph)Pz]H leads to the corresponding trinuclear copper(I) pyrazolates, {[3-(CF(3))Pz]Cu}(3), {[3-(CF(3)),5-(Me)Pz]Cu}(3), and {[3-(CF(3)),5-(Ph)Pz]Cu}(3), respectively, in high yield. The {[3,5-(i-Pr)(2)Pz]Cu}(3) compound was obtained by a reaction between [Cu(CH(3)CN)(4)][BF(4)], [3,5-(i-Pr)(2)Pz]H, and NEt(3). These compounds as well as {[3,5-(Me)(2)Pz]Cu}(3) and {[3,5-(CF(3))(2)Pz]Cu}(3) adopt trimeric structures with nine-membered Cu(3)N(6) metallacycles. There are varying degrees and types of intertrimer Cu...Cu interactions. These contacts give rise to zigzag chains in the fluorinated complexes, {[3-(CF(3))Pz]Cu}(3), {[3-(CF(3)),5-(Me)Pz]Cu}(3), {[3-(CF(3)),5-(Ph)Pz]Cu}(3), and {[3,5-(CF(3))(2)Pz]Cu}(3), whereas the nonfluorinated complexes, {[3,5-(Me)(2)Pz]Cu}(3) and {[3,5-(i-Pr)(2)Pz]Cu}(3) form dimers of trimers. Out of all the compounds examined in this study, {[3-(CF(3)),5-(Ph)Pz]Cu}(3) has the longest (3.848 Angstroms) and {[3,5-(Me)(2)Pz]Cu}(3) has the shortest (2.946 Angstroms) next-neighbor intertrimer Cu...Cu distance. The Cu...Cu separations within the trimer units do not vary significantly (typically 3.20-3.26 Angstroms). All of these trinuclear copper(I) pyrazolates show bright luminescence upon exposure to UV radiation. The luminescence bands are hugely red-shifted from the corresponding lowest-energy excitations, rather broad, and unstructured even at low temperatures, suggesting metal-centered emissions owing to intertrimer Cu...Cu interactions that are strengthened in the phosphorescent state. The {[3-(CF(3)),5-(Ph)Pz]Cu}(3) compound exhibits an additional highly structured phosphorescence with a vibronic structure corresponding to the pyrazolyl (Pz) ring. The luminescence properties of solids and solutions of the trimeric compounds in this study show fascinating trends with dramatic sensitivities to temperature, solvent, concentration, and excitation wavelengths.

The interaction of the trinuclear mercury(II) complex [(o-C(6)F(4)Hg)(3)] (1) and pyrene leads to the formation of the 1:1 adduct 1.pyrene. The crystal structure of this adduct reveals the existence of supramolecular stacks in which molecules of 1 and molecules of pyrene alternate along the infinite chains. Steady-state and time-resolved photoluminescence measurements indicate the occurrence of a heavy atom effect which results in red, green, and blue (RGB) phosphorescent emissions for 1.pyrene, 1.naphthalene, and 1.biphenyl, respectively.

{[3,5-(CF(3))(2)Pz]Ag}(3) (1) films exhibit selective/reversible sensing of small-organic-molecule (SAM) vapors, which readily switch-on bright-green (benzene or toluene) or bright-blue (mesitylene) luminescence that switches-off upon vapor removal. Vapors of electron-deficient SAMs or non-aromatic solvents did not attain luminescence switching and were not adsorbed.

The preparation of three isonitrile complexes (CyNC)Au(I)Cl, (CyNC)Au(I)Br, and (CyNC)Au(I)I, along with their structural and spectral characterization, are reported. X-ray crystal structures reveal that these crystallize in the same space group and have closely related structures. The structures involve pleated chains of linear, two-coordinate monomers that are arranged in a head-tail fashion. However, these chains vary significantly in the degree of aurophilic interactions among the individual molecules. Thus, (CyNC)Au(I)Cl forms infinite chains with alternating Au...Au distances of 3.3894(7) and 3.5816(7) A. Within the chains of (CyNC)Au(I)Br, however, the alternation of Au.Au distances is more pronounced so that there are dimers, with an Au.Au distance of 3.4864(9) A, and neighboring gold centers at 3.7036(9) A. In (CyNC)Au(I)I, the gold-gold contacts do not lie within the range of significant aurophilic bonding. The closest Au...Au distance is 3.7182(11) A while every other Au...Au distance is 3.9304(12) A. The steric factor of the X ligand and dipole-dipole interactions between the antiparallel complexes is much more significant than aurophilic interactions in governing the self-association of the complexes in this series. The colorless crystals of each solid display an orange luminescence band with a strikingly large Stokes' shift ( approximately 21000 cm(-)(1), 2.6 eV). However, considerable care had to be taken to ensure that the crystals used for the study of the luminescence were free of a surface impurity that produced a turquoise-green luminescence in (CyNC)Au(I)Cl. The diffuse reflectance spectra for the solids show a similar three-band pattern in the 200-330 nm range.

This work represents a synergistic experimental/computational study of the molecular spectroscopy and bonding in Au(CO)Cl in solution and the solid state. The luminescence behavior for crystalline solids is similar for Au(CO)Cl and related (RNC)AuCl complexes that likewise stack in infinite chains, and both exhibit orange-red unstructured phosphorescence bands with extremely large Stokes shifts ((15−20) × 103 cm-1). The long aurophilic distances computed for the ground state (∼3.2 Å) are contracted in the phosphorescent excited state (∼2.6 Å), demonstrating excimeric Au−Au covalent bonds. The spectral data suggest phosphorescent species in which the excimeric Au−Au bonding is extended beyond two adjacent molecules in the solid state. Controlling the concentration in frozen solutions attains phosphorescent bands due to dimeric species for which the emission energies are higher (in the blue region) than those for crystalline solids and are reproduced by ab initio calculations. The spectral findings herein suggest that predictive information about the supramolecular structure may be obtained by the luminescnce behavior. This is exemplified by crystals of (1,1,3,3-Me4BuNC)AuCl, whose red-orange luminsecence anticipated an extended-chain supramolecular structure, which was later verified crystallographically, as the molecules were found to pack in zigzag chains with alternating short (3.418 Å) and long (4.433 Å) aurophilic distances. Solutions of Au(CO)Cl exhibit negative deviation from Beer's law for, higher-energy monomer bands with the appearance of lower-energy bands at high concentrations due to the dimerization of molecules. Time-dependent density-functional theory (TD-DFT) calculations for monomer and dimer models show good agreement with the experimental spectra and account for the major absorption bands. Ab initio calculations (CCSD(T)/cc-pVTZ) show a blue shift of ∼23 cm-1 in the νC ⋮ O frequency upon complexation, thus providing the first computational evidence of this anomalous blue shift known experimentally for Au(CO)Cl.

As part of our efforts to discover simple routes to room-temperature phosphors, we have investigated the interaction of bis(pentafluorophenyl)mercury (1) or trimeric perfluoro-o-phenylene mercury (2) with selected arenes (naphthalene, biphenyl, and fluorene). Solution studies indicate that 2, unlike 1, quenches the fluorescence of naphthalene. When compared to 1, the high quenching efficiency of 2 may be correlated to the higher affinity that 2 displays for arenes as well as to more acute external heavy-atom effects caused by the three mercury atoms. In the crystal, the adducts [1.naphthalene], [1.biphenyl], [1.fluorene], and [2.fluorene] form supramolecular binary stacks in which the arene approaches the mercury centers of 1 or 2 to form Hg-C pi-interactions. Analysis of the electrostatic potential surfaces of the individual components supports the involvement of electrostatic interactions. The luminescence spectra of the adducts show complete quenching of the fluorescence and display heavy-atom-induced emission whose energies and vibronic progressions correspond to the phosphorescence of the respective pure arene. The phosphorescence lifetimes are shortened by 3 or 4 orders of magnitude when compared with those of the free arenes. Taken collectively, the structural, photophysical, and computational results herein suggest that the proximity of the three mercury centers serves to enhance the Lewis acidity of 2, which becomes a better acceptor and a more effective heavy-atom effect inducer than 1.

The interaction of water with two transition metal carbides, titanium carbide (TiC) and vanadium carbide (VC), has been investigated. The adsorption, reaction, and desorption of water on the (100) face of singlecrystal samples of these materials have been studied as a function of substrate temperature over the range 100-600 K. The adsorption state of water on these surfaces has been probed with high resolution electron energy loss spectroscopy (HREELS). The reactivity of water has been directly measured with HREELS and X-ray photoelectron spectroscopy (XPS). The desorption of molecular water and the products of surface reactions has been followed with temperature programmed desorption. Collectively, these measurements indicate that water adsorbs both molecularly and dissociatively on TiC and VC; however, a greater degree of reactivity at cryogenic temperatures is observed on TiC. Dissociation of water produces surface bound hydrogen and hydroxyl groups on both surfaces and a fully dissociated surface oxide on TiC. Furthermore, a greater participation of the surface carbon atoms is observed at the TiC surface through the evolution of CO x species at elevated temperatures. The differences in surface bonding and desorption profiles are discussed in terms of differences in electronic structure of the two metal carbides. Some possible implications of these studies for the use of TiC and VC as tribological materials are also discussed.