A NEW BRIDGING LIGAND FOR THE [MO-2](4- SYNTHESES AND X-RAY CRYSTAL-STRUCTURES OF THE REDOX PAIR [MO-2(MU-ETA(2)-(NPH)(2)CNHPH)(4)](0() DIMER )+)/

The quadruply bonded molybdenum dimer [Mo-2{mu-eta(2)-(NPh)(2)CNHPh}(4 )] (1), bridged by four triphenylguanidine anion (guanidino) ligands, has been synthesized and structurally characterized. The guanidino lig ands greatly stabilize the oxidized forms of this complex, and it is r eversibly oxidized to the red monocation and the blue dication at read ily accessible potentials (E(1/2) = -0.05 and +0.85 V vs Ag/AgCl, resp ectively). The [Mo-2{mu-eta(2)-(NPh)(2)CNHPh}(4)](+) cation (2) has al so been structurally characterized as its [BF4](-) salt showing that t he Mo-Mo distance increases from 2.0839(9) to 2.2902(12) Angstrom on o xidation, an unprecedented increase for such systems and almost 4 time s that previously observed for a [Mo-2](4+/5+) pair. The N-Mo-Mo-N tor sion angle is also found to increase from 4.5 to 7.6 degrees on oxidat ion. The crystallographic data are as follows. 1 . 2.2Et(2)O: C84.8H86 Mo2N12O2.2, monoclinic, P2/n, a = 13.127(3) Angstrom, b = 14.335(3) An gstrom, c = 22.752(3) Angstrom, beta = 90.434(13)degrees, Z = 2. 2[BF4 ](-). 3CH(2)Cl(2): C79H70BCl6F4Mo2N12, monoclinic, P2(1)/c, a = 13.426 (3) Angstrom, b = 23.693(7) Angstrom, c = 23.573(7)Angstrom, beta = 92 .93(2)degrees, Z = 4.