A uranyl peroxide, Na 5 [(UO 2) 3 (O 2) 4 (OH) 3 ](H 2 O) 13 , with an open sheet of uranyl polyhedra has been synthesized under ambient conditions and structurally characterized. The structure (orthorombic, Cmca, a) 23.632(1) Å, b) 15.886(1) Å, c) 13.952(1) Å, V) 5237.7 Å 3 , and Z) 8) consists of sheets composed of two symmetrically unique uranyl (UO 2) 2+ ions that are coordinated equatorially by two peroxide groups and two OHgroups, forming distorted uranyl hexagonal bipyramids of composition (UO 2)(O 2) 2-(OH) 2 4-. The uranyl bipyramids are connected into sheets with openings with dimensions 13.7 Å along [010] and 15.9 Å along [100]. The shortest dimension of the cavity is 8.08 Å. Sheets of two-dimensionally polymerized uranyl polyhedra are the most common structural type of inorganic uranyl phases; however, such an open topology has never been observed.

Density functional calculations have been performed on the ground and excited states of MnCl(CO) 5 in order to explain the photochemistry of MX(CO) 5 complexes (M ) Mn, Re; X ) Cl, Br, I). As found earlier for Mn 2 -(CO) 10 (Inorg. Chem. 1996, 35, 2886, the e g -type unoccupied 3d orbitals in the pseudooctahedral environment are located rather high in the virtual orbital spectrum, and the corresponding ligand-field (LF) excitations are more than 1 eV above the lowest excitations. Potential energy curves (PECs) nevertheless show that the lowest excited states, which involve transitions to the Mn-Cl σ* orbital at equilibrium geometry, are dissociative for axial and equatorial CO loss. The mechanism is again, as in Mn 2 (CO) 10 , a strongly avoided crossing of the lowest excited state (a 1,3 E) with the higher dissociative LF states (different ones for CO ax and CO eq dissociation) which rapidly descend upon Mn-CO bond lengthening. In spite of the lowest excitation being to the Mn-Cl σ*-orbital, Mn-Cl homolysis cannot occur out of the lowest excited state. The photochemical behavior of Mn 2 -(CO) 10 , MnH(CO) 5 , and MnCl(CO) 5 is compared. The mechanisms of CO loss are found to be very similar, but there is a large difference with respect to the breaking of the σ bond (Mn-Mn, Mn-H, or Mn-Cl). Only in the case of Mn 2 (CO) 10 , the lowest broad absorption band contains the σ f σ* excitation and leads to σ bond breaking.

The photophysical properties of the metal-metal bonded complexes [Ru-(E)(E')(CO),(iPr-DAB)] (E