CONVERSION OF HYDROGEN-BONDED MANGANESE(II)AND ZINC(II) SQUARATE (C4O42-) MOLECULES, CHAINS AND SHEETS TO 3-DIMENSIONAL CAGE NETWORKS

Very strong hydrogen-bonding interactions,can be utilized to guide the assembly of the molecular building block [Mn(HC4O4)(2)(OH2)(4)] (H2C4O4 = squaric acid, 3,4-dihydroxycyclobut-3-ene-1,2-dione) in the crystal. X-Ray structural analysis of these crystals [triclinic, P $($) over bar$$ 1, a = 5.1910(4), b = 7.4605(7), c = 8.9088(11) Angstrom, alpha = 67.07(1), beta = 77.23(1), gamma = 74.49(1)degrees, Z = 1] revealed the presence of two very short hydrogen-bonding contacts, O-H...O = 2.464(1) and 2.481(1) Angstrom, which are responsible for the formation of chains and sheets of manganese squarates(1-) in the crystal. Additional hydrogen-bonding contacts that are weaker-but numerous are present and they lead to the formation of a strongly associated three-dimensional manganese squarate(1-) network. The complexity of this hydrogen-bonding pattern was simplified by substituting, in the zinc analogue. two water molecules with dmso (dmso = dimethyl sulfoxide) to give [Zn(C4O4)(OH2)(2)(dmso)(2)], which was characterized by single-crystal X-ray diffraction [monoclinic, P2(1)/c, a = 15.697(6), b = 8.116(4). c = 12.211(5) Angstrom, beta = 115.83(3)degrees, Z = 4]. Here, extended chains of zinc squarate are present and found to be linked together by hydrogen bonds to form a layered solid. Further growth of this structure to produce a three-dimensional framework was prevented by virtue of the dmso ligands occupying axial positions at the zinc centre. The ability of the hydrogen bonds to act collectively over a large surface area of these solids adds to their overall crystal stability, as these compounds are insoluble at room temperature in aqueous and non-aqueous media. However, in aqueous media at 25-100 degrees C they undergo conversion reactions leading to the known extended three-dimensional cage network M(C4O4)(OH2)(2)(M = Mn or Zn).