title: Tetranuclear manganese carboxylate complexes with a trigonal pyramidal metal topology via controlled potential electrolysis.
abstract: Controlled potential electrolysis (CPE) procedures are described that provide access to complexes with a [Mn4(mu 3-O)3(mu 3-O2CR)]6+ core (3MnIII,MnIV) and a trigonal pyramidal metal topology, starting from species containing the [Mn4(mu 3-O)2]8+ core (4MnIII). [Mn4O2(O2CMe)6(py)2(dbm)2] (6): triclinic, P1, a = 10.868(3) A, b = 13.864(3) A, c = 10.625(3) A, alpha = 108.62(1) degrees, beta = 118.98(1) degrees, gamma = 89.34(2) degrees, V = 1307 A3, Z = 1, T = -131 degrees C, R (Rw) = 3.24 (3.70)%. [Mn4O2(O2CPh)6(py)(dbm)2] (8): monoclinic, P2(1)/c, a = 14.743(6) A, b = 15.536(8) A, c = 30.006(13) A, beta = 102.79(1) degrees, V = 6702 A3, Z = 4, T = -155 degrees C, R (Rw) = 4.32 (4.44)%. Both 6 and 8 contain a [Mn4O2]8+ core; 8 only has one py group, the fourth MnIII site being five-coordinate. (NBun4)[Mn4O2(O2CPh)7(dbm)2] (10) is available from two related procedures. CPE of 10 at 0.65 V vs ferocene in MeCN leads to precipitation of [Mn4O3(O2CPh)4(dbm)3] (11); similarly, CPE of 6 at 0.84 V in MeCN/CH2Cl2 (3:1 v/v) gives [Mn4O3(O2CMe)4(dbm)3] (12). Complex 11: monoclinic, P2(1)/n, a = 15.161(3) A, b = 21.577(4) A, c = 22.683(5) A, beta = 108.04(3) degrees, V = 7056 A3, Z = 4, T = -100 degrees C, R (wR2) = 8.63 (21.80)%. Complex 12: monoclinic, P2(1)/n, a = 13.549(2) A, b = 22.338(4) A, c = 16.618(2) A, beta = 103.74(1) degrees, V = 4885 A3, Z = 4, T = -171 degrees C, R (Rw) = 4.63 (4.45)%. Both 11 and 12 contain a [Mn4(mu 3-O)3(mu-O2CR)] core with a Mn4 trigonal pyramid (MnIV at the apex) and the RCO2- bridging the MnIII3 base. However, in 11, the carboxylate is eta 2,mu 3 with one O atom terminal to one MnIII and the other O atom bridging the other two MnIII ions, whereas in 12 the carboxylate is eta 1,mu 3, a single O atom bridging three MnIII ions. Variable-temperature, solid-state magnetic susceptibility studies on 11 and 12 show that, for both complexes, there are antiferromagnetic exchange interactions between MnIII/MnIV pairs, and ferromagnetic interactions between MnIII/MnIII pairs. In both cases, the resultant ground states of the complex is S = 9/2, confirmed by magnetization vs field studies in the 2.00-30.0 K and 0.50-50 kG temperature and field ranges, respectively.
authors.affiliation: Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, Indiana 47405-7102, USA.
authors.forename: S
authors.initials: S
authors.lastname: Wang
authors.forename: M S
authors.initials: MS
authors.lastname: Wemple
authors.forename: J
authors.initials: J
authors.lastname: Yoo
authors.forename: K
authors.initials: K
authors.lastname: Folting
authors.forename: J C
authors.initials: JC
authors.lastname: Huffman
authors.forename: K S
authors.initials: KS
authors.lastname: Hagen
authors.forename: D N
authors.initials: DN
authors.lastname: Hendrickson
authors.forename: G
authors.initials: G
authors.lastname: Christou
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D055598:Chemical Phenomena; D015392:Chemistry, Inorganic / Q000379:methods; D002627:Chemistry, Physical; D004572:Electrolysis; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry*; D017895:Manganese Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D009566:Nitrates / Q000737:chemistry*; D010084:Oxidation-Reduction; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D002264:Carboxylic Acids; D017895:Manganese Compounds; D009566:Nitrates; D014867:Water; D008345:Manganese