SYNTHESIS, SPECTROSCOPY, AND X-RAY STRUCTURE OF OS2CL(CHP)4 - AN UNUSUAL OS25+ COMPLEX WITH A POLAR ARRANGEMENT OF 6-CHLORO-2-HYDROXYPYRIDINATO LIGANDS AND ONE AXIAL CHLORIDE
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The compound Os2Cl(chp)4has been prepared from the melt reaction of Os2Cl2(O2CCH3)4with 6-chloro-2-hydroxypyridine (Hchp) at 145 C. The neutral Os25+complex contains a polar arrangement of chp ligands and a single axial chloride. This molecule represents the first structurally characterized compound with an Os-Os bond order of 2.5. Another product of the reaction is Os2Cl4(chp)2L where L is either pyridine or water, depending upon the conditions used to crystallize the compound. Details of the characterization of these species are reported in the paper following this one. Dark brown, air-stable crystals of composition Os2Cl(chp)4.2(CH3)2CO were grown from a solution of acetone-diethyl ether (2:1). The crystallographic data are as follows: triclinic, space group P1, a = 9.226 (1) , b = 13.168 (2) , c = 14.396 (2) , = 95.4 (1), = 106.7 (1), = 100.7 (1), V = 1624.9 (4) 3, Z = 2. The structure was refined to R = 0.038 (Rw= 0.059). The Os-Os distance is 2.348 (1) A, Os(1)-Cl(axial)-2.433 (2) A, Os-O(av) = 2.002 [6] , Os-N(av) = 2.088 [6] A. The molecule is twisted from an ideal eclipsed conformation by approximately 15. The two acetone molecules are present as solvent of crystallization and do not interact with the diosmium unit. The title compound was also investigated by a variety of methods including infrared, UV-visible, and ESR spectroscopy. The electrochemistry, as determined by cyclic voltammetry, reveals two reversible processes; E1/2(ox) = +0.90 V and E1/2(red) =-0.60 V vs. Ag/AgCl at room temperature. The low-temperature ESR spectrum (-196 C) is consistent with that reported for other RuIIRuIIIand OsIIOsIIIdinuclear complexes whose magnetic properties are indicative of a triplet contribution to the ground state. A room-temperature measurement (Evans' method) gave a magnetic moment of 2.90 B, also consistent with earlier results. 1986, American Chemical Society. All rights reserved.
