The reaction of Mn(O(2)CPh)(2) . 2H(2)O and PhCO(2)H in EtOH/MeCN with NBu(4)(n)MnO(4) gives (NBu(4)(n))[Mn4O2(O(2)CPh)(9)-(H2O)] (4) in high yield (85-95%). Complex 4 crystallizes in monoclinic space group P2(1)/c with the following unit cell parameters at -129 degrees C: a = 17.394(3) Angstrom, b = 19.040(3) Angstrom, c = 25.660(5) Angstrom, beta = 103.51(1)degrees, V = 8262.7 Angstrom(3), Z = 4; the structure was refined on F to R (R(w)) = 9.11% (9.26%) using 4590 unique reflections with F > 2.33 sigma(F). The anion of 4 consists of a [Mn-4(mu(3)-O)(2)](8+) core with a ''butterfly'' disposition of four Mn-III atoms. In addition to seven bridging PhCO(2)(-) groups, there is a chelating PhCO(2)(-) group at one ''wingtip'' Mn atom and terminal PhCO(2)(-) and H2O groups at the other. Complex 4 is an excellent steppingstone to other [Mn4O2]-containing species. Treatment of 4 with 2,2-diethylmalonate (2 equiv) leads to isolation of (NBu(4)(n))(2)[Mn8O4(O(2)CPh)(12)(Et(2)mal)(2)(H2O)(2)] (5) in 45% yield after recrystallization. Complex 5 is mixed-valent (2Mn(II),6Mn(III)) and contains an [Mn8O4](14+) core that consists of two [Mn4O2](7+) (Mn-II,3Mn(III)) butterfly units linked together by one of the mu(3)-O2- ions in each unit bridging to one of the body Mn atoms in the other unit, and thus converting to mu(4)-O2- modes. The Mn-II ions are in wingtip positions. The Et(2)mal(2-) groups each bridge two wingtip Mn atoms from different butterfly units, providing additional linkage between the halves of the molecule. Complex 5 . 4CH(2)Cl(2) crystallizes in monoclinic space group P2(1)/c with the following unit cell parameters at -165 degrees C: a = 16.247(5) Angstrom, b = 27.190(8) Angstrom, c = 17.715(5) Angstrom, beta = 113.95(1)degrees, V = 7152.0 Angstrom(3), Z = 4; the structure was refined on F to R (R(w)) = 8.36 (8.61%) using 4133 unique reflections with F > 3 sigma(F). The reaction of 4 with 2 equiv of bpy or picolinic acid (picH) yields the known complex Mn4O2(O(2)CPh)(7)(bpy)(2) (2), containing Mn-II,3Mn(III), or (NBu(4)(n))[Mn4O2(O(2)CPh)(7)(pic)(2)] (6), containing 4Mn(III). Treatment of 4 with dibenzoylmethane (dbmH, 2 equiv) gives the mono-chelate product (NBu(4)(n))[Mn4O2(O(2)CPh)(8)(dbm)] (7); ligation of a second chelate group requires treatment of 7 with Na(dbm), which yields (NBu(4)(n))[Mn4O2(O(2)CPh)(7)(dbm)(2)] (8). Complexes 7 and 8 both contain a [Mn4O2](8+) (4Mn(III)) butterfly unit. Complex 7 contains chelating dbm(-) and chelating PhCO(2)(-) at the two wingtip positions, whereas 8 contains two chelating dbm(-) groups at these positions, as in 2 and 6. Complex 7 . 2CH(2)Cl(2) crystallizes in monoclinic space group P2(1) with the following unit cell parameters at -170 degrees C: a = 18. 169(3) Angstrom, b = 19.678(4) Angstrom, c = 25.036(4) Angstrom, beta = 101.49(1)degrees, V = 8771.7 Angstrom(3), Z = 4; the structure was refined on F to R (R(w)) = 7.36% (7.59%) using 10 782 unique reflections with F > 3 sigma(F). Variable-temperature magnetic susceptibility studies have been carried out on powdered samples of complexes 2 and 5 in a 10.0 kG field in the 5.0-320.0 K range. The effective magnetic moment (mu(eff)) for 2 gradually decreases from 8.61 mu(B) per molecule at 320.0 K to 5.71 mu(B) at 13.0 K and then increases slightly to 5.91 mu(B) at 5.0 K. For 5, mu(eff) gradually decreases from 10.54 mu(B) per molecule at 320.0 K to 8.42 mu(B) at 40.0 K, followed by a more rapid decrease to 6.02 mu(B) at 5.0 K. On the basis of the crystal structure of 5 showing the single Mn-II ion in each [Mn4O2](7+) subcore to be at a wingtip position, the Mn-II ion in 2 was concluded to be at a wingtip position also. Employing the reasonable approximation that J(wb)(Mn-II/Mn-III) = J(wb)(Mn-III/M(III)), where J(wb) is the magnetic exchange interaction between wingtip (w) and body (b) Mn ions of the indicated oxidation state, a theoretical chi(M) vs T expression was derived and used to fit the experimental molar magnetic susceptibility (chi(M)) vs T data. The obtained fitting parameters were J(wb) = -3.9 cm(-1), J(bb) = -9.2 cm(-1), and g = 1.80. These values suggest a S-T = 5/2 ground state spin for 2, which was confirmed by magnetization vs field measurements in the 0.5-50.0 kG magnetic field range and 2.0-30.0 K temperature range. For complex 5, since the two bonds connecting the two [Mn4O2](7+) units are Jahn-Teller elongated and weak, it was assumed that complex 5 could be treated, to a first approximation, as consisting of weakly-interacting halves; the magnetic susceptibility data for 5 at temperatures greater than or equal to 40 K were therefore fit to the same theoretical expression as used for 2, and the fitting parameters were J(wb) = -14.0 cm(-1) and J(bb) = -30.5 cm(-1), with g = 1.93 (held constant). These values suggest an S-T = 5/2 ground state spin for each [Mn4O2](7+) unit of 5, as found for 2. The interactions between the subunits are difficult to incorporate into this model, and the true ground state spin value of the entire Mn-8 anion was therefore determined by magnetization vs field studies, which showed the ground state of 5 to be S-T = 3. The results of the studies on 2 and 5 are considered with respect to spin frustration effects within the [Mn4O2](7+) units. Complexes 2 and 5 are EPR-active and -silent, respectively, consistent with their S-T = 5/2 and Sr = 3 ground states, respectively.
