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Electronic spectra of several square-planar complexes of the type [MX,]! (M = Pd(II), Pt(II), Au(III); X = Cl-, Br-, CN-, NH3) are reported in nonaqueous media at room and liquid nitrogen temperatures. In most cases the spectral resolution is considerably enhanced in the rigid, low-temperature glasses. Detailed assignments of spectra measured under carefully controlled conditions allow a comparison of electronic structures and energy levels in the various square-planar systems. The halide complexes show strong ligand->-metal charge-transfer absorptions, the cyanides show metal-*-ligand bands, whereas the ammine complexes exhibit allowed d -* p transitions. Trends in d-d and charge-transfer energies are discussed.Recent investigations of the electronic structures of x square-planar complexes indicate that the electronic energy levels vary according to the nature of the ligand.2-4 The nature of the variation, however, is(1) Author to whom correspondence should be addressed. not presently clear. In view of the several theoretical (2) . B. Gray and C.

Electronic absorption and magnetic circular dichroism (MCD) spectral measurements are reported for the linear dicyano complexes of Cu(I), Ag(I), Au(I), and Hg(II). In addition to aqueous and nonaqueous measurements at 300°K, some low-temperature absorption measurements are reported for Áu(CN)f and Ag(CN)2in glassy EPA solutions at 77°K and for solid films of [(n-C4H9)4N][Au(CN)J and [(«-C4H9)4N][Ag(CN)2] at 40°K. Spectral resolution is markedly enhanced at low temperature, especially for the gold complex for which 27 bands were resolved between 40,000 and 54,000 cm-1. The intense absorptions observed for the M(CN)2complexes are characterized as metal ligand charge-transfer type from the occupied metal d orbitals to the cyanide * level 2ttu. A semidetailed interpretation of the Au(CN)2-absorption and MCD spectra is given in terms of an energy level scheme which includes metal spin-orbit coupling. Spectral assignments are also given for Ag(CN)2-and Cu(CN)f \ The results are discussed in terms of d orbital participation in bonding and in both -donor and -acceptor bonding with the CN~l igand.

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