Tetranuclear manganese carboxylate complexes with a trigonal pyramidal metal topology via controlled potential electrolysis

Controlled potential electrolysis (CPE) procedures are described that provide access to complexes with a [Mn-4(mu(3)-O)(3)(mu(3)-O2CR)](6+) core (3Mn(III),Mn-IV) and a trigonal pyramidal metal topology, starting from species containing the [Mn-4(mu(3)-O)(2)](8+) core (4Mn(III)). [Mn4O2(O2CMe)(6)(py)(2)(dbm)(2)] (6): triclinic, P (1) over bar, a = 10.868(3) Angstrom, b = 13.864(3) Angstrom, c = 10.625(3) Angstrom, alpha = 108.62(1)degrees, beta = 118.98(1)degrees, gamma = 89.34(2)degrees, V= 1307 Angstrom(3), Z = 1, T = -131 degrees C, R (R-w) = 3.24 (3.70%)%. [Mn4O2(O2CPh)(6)(py)(dbm)(2)] (8): monoclinic, P2(1)/c, a = 14.743(6) Angstrom, b = 15.536(8) Angstrom, c = 30.006(13) Angstrom, beta = 102.79(1)degrees, V = 6702 Angstrom(3), Z = 4, T = -155 degrees C, R(R-w) = 4.32 (4.44)%. Both 6 and 8 contain a [Mn4O2](8+) core; 8 only has one py group, the fourth Mn-III site being five-coordinate. (NBu4II)[Mn4O2(O2CPh)(7)(dbm)(2)] (10) is available from two related procedures. CPE of 10 at 0.65 V vs ferrocene 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). Complier 11: monoclinic, P2(1)/n, a = 15.161(3) Angstrom, b = 21.577(4) Angstrom, c = 22.683(5) Angstrom, beta = 108.04(3)degrees, V = 7056 Angstrom(3), Z = 4, T = -100 degrees C, R (wR2) = 8.63 (21.80)%. Complex 12: monoclinic, P2(1)/n, a = 13.549(2) Angstrom, b = 22.338(4) Angstrom, c = 16.618(2) Angstrom, beta = 103.74(1)degrees, V = 4885 Angstrom(3), Z = 4, T = -171 degrees C, R (R-w) = 4.63 (4.45)%. Both 11 and 12 contain a [Mn-4(mu(3)-O)(3)(mu-O2CR)] core with a Mn-4 trigonal pyramid (Mn-IV at the apex) and the RCO2- bridging the Mn-3(III) base. However, in 11, the carboxylate is eta(2),mu(3) with one O atom terminal to one Mn-III and the other O atom bridging the other two Mn-III ions, whereas in 12 the carboxylate is eta(1),mu(3), a single O atom bridging three Mn-III ions. Variable-temperature, solid-state magnetic susceptibility studies on 11 and 12 show that, for both complexes, there are antiferromagnetic exchange interactions between Mn-III/Mn-IV pairs, and ferromagnetic interactions between Mn-III/Mn-III pairs. In both cases, the resultant ground state 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.