The colorless copper(I) cluster [CuN(Si(CH3)(3))(2)](4), which contains a square-planar C4N4 core, phosphoresces in CH2Cl2 solution (lambda(max), 512 nm; lifetime, 30 mu s) and in the solid state at room temperature. Its electronic absorption spectrum in CH2Cl2 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(CH3)(3))(2)](4) luminesces with approximately the same spectrum as that of the CH2Cl2 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 Et2O solution is 690 mu s. X-ray analysis of crystals of [CuN(Si-cm (CH3)(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. C24H72Cu4N4Si8 : monoclinic, space group P2/n, Z = 2. At 130 K, a = 9.285(3) Angstrom, b = 13.393(3) Angstrom, c = 17.752(5) Angstrom, and beta =90.53(2)degrees. [At 296 K, a = 9.3773(4) Angstrom, b = 13.5836(7) Angstrom, c = 17.814(2) Angstrom, and beta = 90.207(7)degrees.] At 130 K, the Cu and N atoms in the cluster are planar within 0.007 Angstrom, and the Cu-N and Cu ... Cu distances are 1.917(4)-1,925(4) and 2.6770(7)-2.6937(7) Angstrom, 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 s low as 145 degrees C (in the-dark) or 136-138 degrees C (under Pyrex;filtered Xe are lamp illumination). Thus, Cu CVD with this precursor shows slight photochemical enhancement.