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The guest-host chemistry of the Pd3(dppm)3C02+ cluster (dppm = ( ( C~H S )~P ) ~C H~) has been investigated in some detail for a series of inorganic and organic substrates by X-ray crystallography (in two cases), UV-visible (and IR) spectroscopy, and molecular mechanics. The two X-ray crystallography characterized complexes are the [Pd3(dppm)3-CO](PF6)y(CH3)2CO and [Pd3(dppm)3CO](CF3C02)(PF6).2(CH3)2CO, which have been used to obtain model structures of the empty cavity (formed by the six upper dppm-phenyl groups) and filled cavity (by the CF3CO2anion), respectively. The latter was also used as a starting structure for the computations. The binding constants ( K 1 were measured spectroscopically using the Benesi-Hildebrand (B.-H.), Scatchard (Scat), and Scott (Scot) methods for about 20 different substrates. The stoichiometry of the association is found to be 1:l where the K I I values range from 0.07 to 10 000 M-I. The substrate-cluster associations are competitive and reversible for most studied systems. In some cases (nitro, cyano, and diazonium derivatives), very slow thermal reactions have been observed. Further molecular mechanic calculations on the cluster-aromatic associated complexes showed that agostic interactions are possible at the minimum computed energy configuration for the aromatic compounds. Overall, these studies show that the binding strength of a substrate (both organic and inorganic) into the bifunctional cavity (metallic center and hydrophobic section) is found to be related to a combination of parameters. These properties are the substrate charge and ligand strength, and the size and hydrophobic properties of the substrates. Crystal data: [Pd3(dppm)3CO](PF6)2, 173 K, triclinic (PI), a = 13.640(4) A, b = 14.0639(17) A, c = 22.4835(15) A, a = 104.291(7)', 0 = 105.143(17)', y = 99.301(18)', V = 3914.7(13) A3, Z = 2, R = 0.039, R, = 0.037; [Pd3(dppm)3CO](CF3C02)(PF6),293 K,monoclinic(P21),a= 11.0189(10)A,b= 26.6515(19)A,c= 14.4746(14) A, 0 = 99.786(9)', V = 4188.9(6) A3, Z = 2, R = 0.057, R, = 0.053. organic molecules and ions within the cavity of the P d 3 ( d~p m )~-COz+ cluster in a variety of solvents at 298 K. During the course of this work, the X-ray structures of [Pt3(dppm)3CO](X)-(Y).n(CH3)2CO ( x = Y = PF6-, n = 1; x = CF3C02-, Y = PFs-,

The [Cu(3)(dppm)(3)OH](BF(4))(2) cyclic cluster host is found to be luminescent at 298 K (lambda(max) = 540 nm; tau(e) = 89 +/- 9 &mgr;s; Phi(e) = 0.14 +/- 0.01) in degassed ethanol solutions and at 77 K (lambda(max) = 480 nm; tau(e) = 170 +/- 40 &mgr;s; Phi = 0.73 +/- 0.07) also in ethanol. The nature of the lowest energy excited states has been addressed theoretically using density functional theory and experimentally using UV-visible, luminescence, and polarized luminescence spectroscopy and is found to be (1,3)A(2) arising from the.(18e)(4)(7a(2))(1)(13a(1))(1) electronic configuration. The excited state geometry optimization for the model Cu(3)(PH(3))(6)OH(2+) compound in its T(1) state ((3)A(2)) has been performed using density functional theory and compared to its ground state structure. The Cu.Cu bond length is expected to decrease greatly in the excited state (calculated DeltaQ approximately 0.47 Å), in agreement with the d(10) electronic configuration. The perturbation of the photophysical properties by the addition of two guest carboxylate anions has been investigated. From the Stern-Volmer plots, the quenching constants, k(q), are 1.65 x 10(8) and 5.10 x 10(8) M(-)(1) s(-)(1) for acetate and 4-aminobenzoate, respectively, which are also proportional to the relative binding strengths of the substrates with Cu(3)(dppm)(3)OH(2+) (i.e., acetate < 4-aminobenzoate).

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Raman spectra of the one-dimensional ZrS3-ZrSe3 solid solutions are reported. A mixed one-mode and two-mode phonon behavior is observed. The study of the phonon width indicates a higher sensitivity to disorder in the case of the one-mode phonons compared to the case of the two-mode phonons.Lattice vibrations of one-dimensional transitionmetal trichalcogenides MX3 have been intensively studied. ' ZrS3 and ZrSe3 belong to the MX3 class. They grow having the metal ions in the center of distorted trigonal prisms which share trigonal faces forming isolated chains. ' They both have a monoclinic unit cell (C2q space group) which contains eight atoms associated with two chains. The 24 normal modes at the center I of the Brillouin zone are represented by the irreducible representations of the C2p point group as I' 8A 8 48 8 4A"S 88" V) D 200 400 (c)The 12 even-parity modes 8Ag and 48g are Raman active and have already been studied. ' " As Brattas and Kjekshus showed, 9 the two one-dimensional trichalcogenides ZrS3 and ZrSe3 form a continuous series of solid solutions ZrS3 "Se"with the same C2q point group symmetry. We used chemical transport with iodine to grow single crystals of ZrS3 "Se"solutions typically 1 cm long, 2.5 mm wide, and 0.3 mm thick. Their composition was verified by x rays and gravimetric analysis, the latter method indicated nonstochiometry and Se deficiency only for x = 2.In this Brief Report we present Raman scattering of these one-dimensional mixed compounds following the evolution of the modes frequencies and of the width of two typical phonons as a function of x.The 4880and 51454 lines of a spectra-physics argon-ion laser were used for excitation. Less than 150-mW power was incident on the crystal and Brewster angle geometry together with right-angle scattering were used throughout the work. The scattered light was spectrally analyzed with a Jobin-Yvon HG2S double monochromator and detected with a standard photon-counting technique. Typical room-temperature Raman spectra of ZrS3 "Se"mixed compounds for x =1.5 are presented in Figs.