Polar Symmetry and Intercalation of New Multilayered Hybrid Molybdates: [M<sub>2</sub>(pzc)<sub>2</sub>(H<sub>2</sub>O)<i><sub>x</sub></i>][Mo<sub>5</sub>O<sub>16</sub>] (M = Co, Ni)
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The layered molybdate [M2(pzc)2(H2O)x][Mo5O16] (I: M = Ni, x = 5.0; II: M = Co, x = 4.0; pzc = pyrazinecarboxylate) hybrid solids were synthesized via hydrothermal reactions at 160−165 °C. The structures were determined by single-crystal X-ray diffraction data for I (Cc, Z = 4; a = 33.217(4) Å, b = 5.6416(8) Å, c = 13.982(2) Å, β = 99.407(8)°, and V = 2585.0(6) Å3) and powder X-ray diffraction data for II (C2/c, Z = 4; a = 35.42(6) Å, b = 5.697(9) Å, c = 14.28(2) Å, β = 114.95(4)°, and V = 2614(12) Å3). The polar structure of I contains new [Ni2(pzc)2(H2O)5]2+ double layers that form an asymmetric pattern of hydrogen bonds and covalent bonds to stair-stepped [Mo5O16]2- sheets, inducing a net dipole moment in the latter. In II, however, the [Co2(pzc)2(H2O)4]2+ double layers have one less coordinated water and subsequently exhibit a symmetric pattern of covalent and hydrogen bonding to the [Mo5O16]2- sheets, leading to a centrosymmetric structure. Thermogravimetric analyses and powder X-ray diffraction data reveal that I can be dehydrated and rehydrated with from 0 to 6.5 water molecules per formula unit, which is coupled with a corresponding contraction/expansion of the interlayer distances. Also, the dehydrated form of I can be intercalated by ∼4.3 H2S molecules per formula unit, but the intercalation by pyridine or methanol is limited to less than one molecule per formula unit.
