A BINUCLEAR MANGANESE SYSTEM WITH 3 ISOLATED OXIDATION-STATES - SYNTHESIS, STRUCTURES, AND PROPERTIES OF MOLECULES WITH A MN2(OR)2 BRIDGE UNIT CONTAINING MN-IIIMN-III, MN-IIIMN-II, AND MN-IIMN-II

The Mn(III) complex of the pentadentate ligand 2-(bis(salicylideneamino)methyl)phenolate(3-) (salmp), first prepared in 1935, has been reinvestigated in order to determine if it possesses the binuclear structure and unusual magnetic properties, and is a member of an electron-transfer series related to that, of the corresponding Fe(III) complex. The latter is part of the series [Fe2(salmp)2]0,-2-, whose preparation and properties have been recently reported. The complex Mn2(salmp)2.2MeCN (1.2MeCN) crystallizes in triclinic space group P1BAR with a = 9.841 (2) angstrom, b = 10.615 (2) angstrom, c = 11.261 (2) angstrom, alpha = 71.00 (2)-degrees, beta = 65.58 (2)-degrees, gamma = 88.25 (2)-degrees, and Z = 1. The molecule is composed of two trans-MnN2O4 distorted octahedra bridged by two phenolate oxygen atoms. The salmp ligand acts as a bridging and terminal ligand to each Mn atom. Reaction of 1 with 1 equiv of NaSEt in the presence of Ph4PBr in acetonitrile affords (Ph4P)[Mn2(salmp)2] (3). The compound 3.3.5DMF crystallizes in space group P1BAR with a = 12.852 (2) angstrom, b = 13.811 (2) angstrom, c = 19.900 (2) angstrom, alpha = 92.84 (1)-degrees, beta = 94.92 (1)-degrees, gamma = 91.60 (1)-degrees, and Z = 2. Reaction of 1 with 2 equiv of NaSEt in the presence of Et4NCl in acetonitrile gives (Et4N)2[Mn2(salmp)2] (4). The compound 4.4MeCN was obtained in monoclinic space group P2(1)/c with a = 11.216 (4) angstrom, b = 17.445 (5) angstrom, c = 17.388 (5) angstrom, beta = 104.86 (2)-degrees, and Z = 2. The conformations of the three complexes [Mn2(salmp)2]0,-,2- are essentially identical with one another and with those in the analogous series [Fe2(salmp)2]0,-,2-. These complexes are part of a five-membered electron-transfer series [Mn2(salmp)2]z, with z = 2-, 1-, 0, 1+, and 2+; the cationic species were not isolated. Mn2(salmp)2 is centrosymmetric and exhibits a Jahn-Teller distortion, and [Mn2(salmp)2]2- is also centrosymmetric. [Mn2(salmp)2]- has a noncentrosymmetric, trapped-valence structure, which, from the presence of an intervalence band at 1170 nm (acetonitrile), is retained in solution. Angular distortions suggest that the structure of [Mn2(salmp)2]2- is strained by the large size of the high-spin Mn(II) ion. The complex is sensitive to hydrolysis. The apparent yellow hydrolysis product has been separately prepared from Mn(II), salicylaldehyde, and a base in methanol. The compound [Mn2(sal)4(MeOH)2].MeOH crystallizes in space group P2(1)/c with a = 11.893 (3) angstrom, b = 20.290 (4) angstrom, c = 13.491 (2) angstrom, beta = 104.14 (2)-degrees, and Z = 4. It has an idealized centrosymmetric structure with two distorted Mn(II)O6 octahedra bridged by two phenolate oxygen atoms. Two salicylaldehyde anions are terminal ligands, and the methanol molecules are bound trans to their phenolate oxygen atoms. The ferromagnetism exhibited by the [Fe2(salmp)2]0,-,2- series is not shown by [Mn2(salmp)2]0,-,2-. These complexes contain high-spin Mn(II,III) and are weakly antiferromagnetically coupled. For 1.2DMF, J = 6.5 (2) cm-1 in H(ex) = JS1.S2. The complexes [Mn2(salmp)2]0,-,2- comprise the only series in which the oxidation states Mn(III)Mn(III), Mn(III)Mn(II), and Mn(II)Mn(II), supported by invariant ligands, have been structurally characterized.