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2145schematically shown in Figure 3, a simple reorientation of the copper square-pyramidal moieties might suffice, in principle, to bring about the dimer -+ uniform-chain transformation without any dramatic change in the geometry of the first coordination sphere around the metal centers or in the occupancy of space. An arrangement of dimers similar to that depicted in Figure 3 exists along the c axis of the title compound, and we also note that competition between neighboring copper atoms for bonding to apical chlorine atoms has been shown to be a relevant factor in determining the crystal chemistry of chloride-bridged chain compounds of copper(II).i6i8 In any event, the precise nature of the low-temperature phase of the present compound and the mechanism or reason for the postulated transition are interesting problems that remain open to further studies, particularly lowtemperature X-ray studies.In conclusion, the results presented in this paper confirm the utility of synthesizing new halide-bridged copper(I1) compounds with heterocyclic ligands as appropriate candidates for studying the impact of structural phase transitions on the magnetic int e r a c t i o n~.~~ As more of these types of systems are prepared and studied, it will hopefully be possible to provide some insight into the mechanisms that underlie the structural changes in them. This problem, of course, is also relevant to the family of distortion models typified by the spin-Peierls instability, Le., those in which changes in lattice energy and changes in exchange energy are of comparable magnitude.Registry No. Cu2L2CI2.2CH3OH, 120232-12-4; 8-aminoquinoline, 578-66-5; salicylaldehyde, 90-02-8. Supplementary Material Available:Tables SI-SIII, listing angles and distances associated with the aromatic rings, thermal parameters, and the derived hydrogen positions (3 pages); a table of calculated and observed structure factors (1 1 pages). Ordering information is given on any current masthead page. (35) See paper by L. J. de Jongh in ref 2a.[Au(dppm)],(BF,), is phosphorescent in solution ( A, , , = 593 nm, T = 21 ps, = 0.31). An SCF-Xa-SW molecular orbital calculation carried out on the model compound [Au(H2PCH2PH2)]?+ found the Au-Au u* HOMO to have 78% Au character. Of this, 41% is from the 6s orbital and 41% is from the 5d,z orbital. The metal-metal interactions are discussed. The 293-nm (e 21 OOO M-' cm-I) absorption band is attributed to a u(p,) -a*(s,dg) transition. The A d 2 emissive state appears to be "Ju*)(a) (C2h symmetry). The binuclear Ad2 compounds [A~(dppm)]~Cl~, [ A u ( C H~)~P P~~]~, [~-Bu,N],[Au(S,C=C(CN)~)],, [Au-(CH,P(S)Ph2)]2, and [AU(S~CNE~,)]~ are luminescent in the solid state at room temperature with A,, ranging from 465 to 593 nm and excited-state lifetimes ranging from 1 to 24 1 s . (Ph3PAu),(S2C=C(CN),) is luminescent at 77 K but not at room temperature. Mononuclear Ph3PAuCI luminesces in the solid state ( A, , , = 491 nm, 7 = 3 ps).

Solutions of K[Au(CN)(2)] and K[Ag(CN)(2)] in water and methanol exhibit strong photoluminescence. Aqueous solutions of K[Au(CN)(2)] at ambient temperature exhibit luminescence at concentration levels of > or =10(-2) M, while frozen methanol glasses (77 K) exhibit strong luminescence with concentrations as low as 10(-5) M. The corresponding concentration limits for K[Ag(CN)(2)] solutions are 10(-1) M at ambient temperature and 10(-4) M at 77 K. Systematic variations in concentration, solvent, temperature, and excitation wavelength tune the luminescence energy of both K[Au(CN)(2)] and K[Ag(CN)(2)] solutions by >15 x 10(3) cm(-1) in the UV-visible region. The luminescence bands have been individually assigned to *[Au(CN)(2)(-)](n) and *[Ag(CN)(2)(-)](n) excimers and exciplexes that differ in "n" and geometry. The luminescence of Au(I) compounds is related for the first time to Au-Au bonded excimers and exciplexes similar to those reported earlier for Ag(I) compounds. Fully optimized unrestricted open-shell MP2 calculations for the lowest-energy triplet excited state of staggered [Au(CN)(2)(-)](2) show the formation of a Au-Au sigma single bond (2.66 A) in the triplet excimer, compared to a weaker ground-state aurophilic bond (2.96 A). The corresponding frequency calculations revealed Au-Au Raman-active stretching frequencies at 89.8 and 165.7 cm(-1) associated with the ground state and lowest triplet excited state, respectively. The experimental evidence of the exciplex assignment includes the extremely large Stokes shifts and the structureless feature of the luminescence bands, which suggest very distorted excited states. Extended Hückel (EH) calculations for [M(CN)(2)(-)](n) and *[M(CN)(2)(-)](n) models (M = Au, Ag; n = 2, 3) indicate the formation of M-M bonds in the first excited electronic states. From the average EH values for staggered dimers and trimers, the excited-state Au-Au and Ag-Ag bond energies are predicted to be 104 and 112 kJ/mol, respectively. The corresponding bond energies in the ground state are 32 and 25 kJ/mol, respectively.

The structures and temperature-dependent photoluminescence properties of the one-dimensional compounds [(TPA)(2)Au][Au(CN)(2)], 1, and (TPA)AuCl, 2, are reported. An extended linear chain with weak Au.Au interactions along the c-axis is evident in the structure of 1, and a helical chain with a pitch of 3.271 A is seen for 2. The intrachain Au...Au separation is 3.457(1) and 3.396(2) A in 1 and 2, respectively. As a result of this weak Au...Au interaction, the physical properties of these compounds are anisotropic. Scanning electron microscopy (SEM) studies indicate that single crystals of both compounds are noninsulating. Single crystals of 1 do not luminesce visibly, but grinding the crystals finely initiates a strong green emission under UV irradiation at room temperature. Further interesting optical properties include the dependence of the emission profile of the powder on the exciting wavelength and luminescence thermochromism. When excited at wavelengths < 360 nm, the powder exhibits a blue emission at 425 nm while excitation with longer wavelengths leads to a green emission near 500 nm. While the green emission dominates at ambient temperature, cooling to cryogenic temperatures leads to the dominance of the blue emission. Fibers of 2 are luminescent at 78 K with an emission band centered at 580 nm. Compound 1 crystallizes in the orthorhombic space group Cccm (No. 66), with Z = 2, a = 6.011(1) A, b = 23.877(6) A, c = 6.914(1) A, V = 992.3(3) A(3), and R = 0.0337. Compound 2 crystallizes in the trigonal space group R3 (No. 148), with Z = 18, a = 22.587(2) A, b = 22.587(2) A, c = 9.814(2) A, V = 4336 A(3), and R = 0.0283.

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The X-ray structure of (Tl[Au(C(6)Cl(5))(2)])(n), 1, consists of 1-D linear polymer chains parallel to the crystallographic z axis. The crystal structure of 1 has channels that run parallel to these chains with interatom distances in the range 3.231-4.076 A. There are holes in these channels with diameters as large as 10.471 A, which can accommodate a variety of solvents. Complex 1 displays reversible vapochromic emission and absorption spectral behavior when the solid is exposed to a variety of organic vapors such as acetone, acetonitrile, triethylamine, acetylacetone, tetrahydrothiophene, 2-fluoropyridine, tetrahydrofuran, and pyridine. Complex 1 is luminescent at room temperature and at 77 K in the solid state. UV excitation at 495 nm leads to an emission at 531 nm.

A correlation is found between the activity of Au clusters for the catalytic oxidation of CO and the concentration of F-centers in the surface of a MgO support. These results are consistent with recent theoretical results showing that F-centers in MgO serve to anchor Au clusters and control their charge state by partial transfer of charge from the substrate F-center to the Au cluster.