Crystal Structures of Magnesium and Calcium Pivalate Hydrates: Mg_2Piv_4 center dot 4HPiv center dot H_2O and CaPiv_2 center dot 5H_2O

摘要

Single crystals of magnesium and calcium pivalate hydrates, Mg_2(mu-H_2O)(mu-Piv)_2(Piv)_2(HPiv)_4 (I) and {[Ca(mu.-H_2O)(H_2O)(mu_2-O,O',eta~2-Piv)Piv]}_n center dot {3H_2O}_n (II), [HPiv = (CH_3)_3CCOOH], were synthesized and studied by X-ray diffraction. Compound I crystallizes in the orthorhombic system, a = 12.199(2) A, b = 19.199(3) A, c = 48.705(7) A, Z = 8, space group Pbca, R_1 - 0.1371. The crystal structure of compound II (a = 11.448(3) A, b = 24.185(6) A, c = 6.537(1) A, (3 =106.41(3) deg, Z = 4) is monoclinic, space group P2_1/c, R_1 = 0.0512. In the molecular structure of I, the magnesium atoms are linked in pairs by a bridging water molecule and by two Piv anions to form dimers in which the Mg coordination environment is a distorted [MgO_6] tetrahedron with Mg-O distances of 2.02-2.11 A. The pivalic acid molecules coordinated to the metal atoms are involved in intramolecular hydrogen bonds with monodentate pivalate groups. In the layered structure of II, the calcium atoms with C.N. = 8 and Ca-O distances of 2.347(3)-2.591(3) A are linked by tetradentate chelat-ing-and-bibridging Piv groups to form polymeric cation ribbons, which alternate with the ribbons of noncoor-dinated Piv anions, thus forming layers due to multiple hydrogen bonds.