DOUBLY-HYDRATED HEXAFLUOROACETYLACETONE AS A TETRADENTATE LIGAND - SYNTHESIS, MAGNETOCHEMISTRY, AND THERMAL TRANSFORMATIONS OF A MN(III)2 COMPLEX

A convenient synthesis of the doubly-hydrated form of hexafluoroacetylacetone (hfacH) is reported, viz. 1,1,1,5,5,5-hexafluoropentane-2,2,4,4-tetraol (hfptH4; 1), together with the initial employment of the latter as a ligand. A reaction system in CH2Cl2 comprising [Mn3O(OAc)6(py)3](ClO4), hfacH, hfptH4, and py (py = pyridine) in a 1:6:1.5:9 ratio leads to a 58% yield of (pyH)2[Mn2(hfpt)(hfac)4] (2). Crystal data for 1 at -171-degrees-C: monoclinic, P2(1)/n, a = 11.108(6) angstrom, b = 5.104(3) angstrom, c = 14.736(8) angstrom, beta = 90.30(2)degrees, Z = 4, V = 835.44 angstrom3, R (R(w)) = 6.58% (7.42%). Crystal data for 2 at -130-degrees-C: monoclinic, C2/c, a = 17.884(5) angstrom, b = 12.573(3) angstrom, c = 23.715(7) angstrom, beta = 107.77(1)degrees, Z = 4, V = 5077.62 angstrom3, R (R(w)) = 9.80% (9.37%). The structure of 1 confirms a bis(gem-diol) structure with an extended-chain conformation. The anion of 2 consists of two Mn(hfac)2 fragments bridged by the hfpt4- group; the latter functions as a bidentate chelate ligand to each Mn(III), employing one alkoxide oxygen atom from each gem-diolate pair. Variable-temperature magnetochemical studies have been performed on powdered samples of 2 in the range 5-320 K. The Mn(III) centers are weakly interacting; the exchange interaction is ferromagnetic, and fitting of the data leads to the following values for the variables: J = +0.21 cm-1 (employing the -2JS1.S2 convention), D = 0.9 cm-1, g = 1.99. Vacuum thermolysis of 2 in the range 111-150-degrees-C yields (py)Mn(hfac)3 (3) and lesser amounts of cis-Mn(py)2(hfac)2 (5), Mn(hfac)3 (4), the tetraol (1), and a manganese(greater-than-or-equal-to IV) oxide. All but the oxide are volatile and have been characterized in part by single-crystal X-ray diffraction. The mechanism of thermolysis is proposed to be initiated by proton transfer from pyH+ to the tetraolate oxygen to which it is hydrogen bonded; this process facilitates the electrophilic cleavage of C/O bonds, which furnishes hfac- as well as oxide for the manganese oxide product. Crystal data for 3 (-175-degrees-C): a = 10.487(2) angstrom, b = 15.790(4) angstrom, c = 9.356(2) angstrom, alpha = 101.78(1)degrees, beta = 106.58(1)degrees, gamma = 108.50(1)degrees with Z = 2 in space group P1BAR. Crystal data for 4 (-159-degrees-C): a = 8.879(0) angstrom, b = 12.941(1) angstrom, c = 18.748(1) angstrom, beta = 91.35(0)degrees with Z = 4 in space group P2(1)/n. Crystal data for 5: a = 9.112(3) angstrom, b = 16.821(6) angstrom, c = 16.315(5) angstrom, beta = 105.34(5)degrees with Z = 4 in space group C2/c.