Phosphorescence and Structure of a Tetrameric Copper(I)-Amide Cluster

The colorless copper(I) cluster [CuN(Si(CH(3))(3))(2)](4), which contains a square-planar Cu(4)N(4) core, phosphoresces in CH(2)Cl(2) solution (lambda(max), 512 nm; lifetime, 30 &mgr;s) and in the solid state at room temperature. Its electronic absorption spectrum in CH(2)Cl(2) consists of two intense bands at 283 and 246 nm; these transitions, as well as the phosphorescence, are likely to involve population of MOs reflecting substantial Cu.Cu interactions. Solid [CuN(Si(CH(3))(3))(2)](4) luminesces with approximately the same spectrum as that of the CH(2)Cl(2) solutions. At 77 K, the solid-state luminescence red-shifts slightly (lambda(max), 524 nm) and narrows substantially (fwhm, 2400 cm(-)(1); vs 3500 cm(-)(1) at 300 K); the emission lifetime in glassy Et(2)O solution is 690 &mgr;s. X-ray analysis of crystals of [CuN(Si(CH(3))(3))(2)](4) at 130 and 296 K shows that, although the previously reported structure solution (in space group I2/m, with the molecules on 2/m sites; Eur. J. Solid State Inorg. Chem. 1992, 29, 573-583) is approximately correct, the lattice is actually primitive, P2/n, and the only crystallographically required symmetry element for the molecule is a 2-fold axis. C(24)H(72)Cu(4)N(4)Si(8): monoclinic, space group P2/n, Z = 2. At 130 K, a = 9.285(3) Å, b = 13.393(3) Å, c = 17.752(5) Å, and beta = 90.53(2) degrees. [At 296 K, a = 9.3773(4) Å, b = 13.5836(7) Å, c = 17.814(2) Å, and beta = 90.207(7) degrees.] At 130 K, the Cu and N atoms in the cluster are planar within 0.007 Å, and the Cu-N and Cu.Cu distances are 1.917(4)-1.925(4) and 2.6770(7)-2.6937(7) Å, respectively. Despite the low volatility of the compound, it can be used as a precursor for chemical vapor deposition (CVD) of copper metal, under H(2) carrier gas, with both source and substrate at ca. 200 degrees C. Smaller amounts of Cu metal films are also deposited when the substrate temperature is as low as 145 degrees C (in the dark) or 136-138 degrees C (under Pyrex-filtered Xe arc lamp illumination). Thus, Cu CVD with this precursor shows slight photochemical enhancement.