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De, ev Cu3 (linear) 2.3 2.84 Cus (triangular) 2.3 2.24Cu,i (square planar) 2.3 (adjacent atoms) 3.11 Cue (octahedral) 2.4 (from center of inversion) 3.6Clementi and Raimondi16 or by Slater's20 rules, were found to be inadequate.21The traditional transition metal basis set of 3d, 4s, and 4p orbitals proved to be optimum for the description of the Cu2 molecule. The lowest filled molecular orbitals, which are largely 3d in character, were important in accounting for the core repulsions at short distances and were extremely important for the calculation of the stretching frequency, coe. The inclusion of the higher lying 4p orbitals in the basis set was important for the calculation of the spectral transition, , since the 4s-4ps mixing effectively lowers the energy of the * orbital. The 4s orbitals were the most important ones since all molecular properties of Cu2 are largely dependent upon them.The energy and core repulsion in the Cusachs approximation varies as S2/(l + S) at short internuclear distances. This dependence approximates the core repulsions of Cu2 and gives the best reproduction of the (20) J. C. Slater, Phys. Rev., 36, 57 (1930). ( 21) We have found that calculations using double valence orbital basis sets yield results that are nearly identical with those using single orbital exponents; hence, only the latter were used here.

CURREST intensive interest in theoretical and structural aspects of metal-metal bonded compounds prompts LZS to report the synthesis of two new trinuclear metal carbonyls.The irradiation (G. E. AH-6 lamp) of an nhexane solution 0 . 0 0 5 ~ in both Fe(CO), and Re,(CO),, for 1 hr. was found to yield Re,Fe(CO),, (I) and the anion [ReFe,(CO),,]-( 11). (I), a stable yellow solid (m.p. 163" decomp.), was isolated by means of silica gel chromatography followed by fractional sublimation of Re,(CO),, from the product. The inolecular formula was determined

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