This investigation focuses on a series of pseudotetrahedral complexes of the form Cu(NN)2 +, where NN denotes a 1,10-phenanthroline ligand with alkyl substituents in the 2 and 9 positions and the counterion is PF6 -. In these copper(I) systems, steric effects are of considerable interest because the electronic configuration predisposes the reactive charge-transfer excited state to undergo a flattening distortion or to add a fifth ligand. Both effects lead to emission quenching and a shorter excited-state lifetime. Bulky substituents inhibit these processes, but the spatial distribution of the atoms involved is more important than the total molecular volume in determining the influence of a substituent. According to the results of this study, the effective size decreases in the following order:  sec-butyl > neopentyl > n-octyl ≈ n-butyl > methyl. In conjunction with the electrochemical data, the absorption and the emission spectra reveal three kinds of steric effects:  (1) Clashes between substituents on opposite phenanthroline ligands hinder D 2 flattening distortions in the oxidized form of the complex and in the charge-transfer excited state of the Cu(NN)2 + system itself. (2) Steric interactions connected with a highly branched substituent, like the neopentyl group, destabilize the Cu(NN)2 + ground state. (3) Finally, the presence of bulky groups disfavors expansion of the coordination number. The complex with sec-butyl substituents is noteworthy because it exhibits the longest excited-state lifetime (∼400 ns in CH2Cl2) ever measured for a Cu(NN)2 + system in fluid solution. In addition, it exhibits a luminescence lifetime of 130 ns in acetonitrile which is ordinarily a potent quencher of photoexcited Cu(NN)2 + systems.

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A variety of (diphosphine)platinum(II) carbonate complexes, (LL)Pt(CO(3)), are readily prepared from the corresponding (diphosphine)platinum dichlorides by treatment with silver carbonate in dichoromethane solution provided that water is present. This reaction also permits facile preparation of analogous (13)C-labeled complexes. The carbonate ligands in these complexes have been characterized by IR and (13)C NMR spectroscopy. Alternative preparative routes involve conversion of the precursor dichlorides to the corresponding dialkoxides or diphenoxides, followed by treatment with water and carbon dioxide. Various reaction intermediates have been spectroscopically observed in the latter syntheses. Two crystalline modifications of (Ph(2)PCH(2)CH(2)CH(2)PPh(2))Pt(CO(3)), one with and one without a dichloromethane of solvation, have been studied by single-crystal X-ray diffraction. Crystal data for PtP(2)O(3)C(28)H(26): P2(1)/c, Z = 4, T = 200 K, a = 10.362(8) Å, b = 14.743(6) Å, c = 19.183(10) Å, beta = 122.69(6) degrees. Crystal data for PtP(2)O(3)C(28)H(26).CH(2)Cl(2): P2(1)/c, Z = 4, T approximately 298 K, a = 11.744(2) Å, b = 15.526(3) Å, c = 15.866(3) Å, beta = 101.58(1) degrees.