Koner Rajesh, Goldberg Israel
School of Chemistry, Sackler Faculty of Exact Sciences, Tel-Aviv University, Ramat-Aviv, 69978 Tel-Aviv, Israel.
Acta Crystallogr C. 2009 Jan;65(Pt 1):m37-41. doi: 10.1107/S0108270108040419. Epub 2008 Dec 23.
1-Benzofuran-2,3-dicarboxylic acid (C(10)H(6)O(5)) is a dicarboxylic acid ligand which can readily engage in organometallic complexes with various metal ions. This ligand is characterized by an intramolecular hydrogen bond between the two carboxyl residues, and, as a monoanionic species, readily forms supramolecular adducts with different organic and inorganic cations. These are a 1:1 adduct with the dimethylammonium cation, namely dimethylammonium 3-carboxy-1-benzofuran-2-carboxylate, C(2)H(8)N(+).C(10)H(5)O(5)(-), (I), a 2:1 complex with Cu(2+) ions in which four neutral imidazole molecules also coordinate the metal atom, namely bis(3-carboxy-1-benzofuran-2-carboxylato-kappaO(3))tetrakis(1H-imidazole-kappaN(3))copper(II), [Cu(C(10)H(5)O(5))(2)(C(3)H(4)N(2))(4)], (II), and a 4:1 adduct with La(H(2)O)(7) ions, namely heptaaquabis(3-carboxy-1-benzofuran-2-carboxylato-kappaO(3))lanthanum 3-carboxy-1-benzofuran-2-carboxylate 1-benzofuran-2,3-dicarboxylic acid solvate tetrahydrate, La(C(10)H(5)O(5))(2)(H(2)O)(7).C(10)H(6)O(5).4H(2)O, (III). In the crystal structure, complex (II) resides on inversion centres, while complex (III) resides on axes of twofold rotation. The crystal packing in all three structures reveals pi-pi stacking interactions between the planar aromatic benzofuran residues, as well as hydrogen bonding between the components. The significance of this study lies in the first crystallographic characterization of the title framework, which consistently exhibits the presence of an intramolecular hydrogen bond and a consequent monoanionic-only nature. It shows further that the anion can coordinate readily to metal cations as a ligand, as well as acting as a monovalent counter-ion. Finally, the aromaticity of the flat benzofuran residue provides an additional supramolecular synthon that directs and facilitates the crystal packing of compounds (I)-(III).
1-苯并呋喃-2,3-二羧酸（C(10)H(6)O(5)）是一种二羧酸配体，它能够很容易地与各种金属离子形成有机金属配合物。该配体的特征在于两个羧基残基之间存在分子内氢键，并且作为单阴离子物种，它很容易与不同的有机和无机阳离子形成超分子加合物。这些加合物包括与二甲基铵阳离子形成的1:1加合物，即3-羧基-1-苯并呋喃-2-羧酸二甲基铵，C(2)H(8)N(+).C(10)H(5)O(5)(-)，（I）；与Cu(2+)离子形成的2:1配合物，其中四个中性咪唑分子也与金属原子配位，即双(3-羧基-1-苯并呋喃-2-羧基-O(3))四(1H-咪唑-N(3))铜(II)，[Cu(C(10)H(5)O(5))(2)(C(3)H(4)N(2))(4)]，（II）；以及与La(H(2)O)(7)离子形成的4:1加合物，即七水双(3-羧基-1-苯并呋喃-2-羧基-O(3))镧3-羧基-1-苯并呋喃-2-羧酸盐1-苯并呋喃-2,3-二羧酸溶剂合物四水合物，La(C(10)H(5)O(5))(2)(H(2)O)(7).C(10)H(6)O(5).4H(2)O，（III）。在晶体结构中，配合物（II）位于对称中心上，而配合物（III）位于二次旋转轴上。所有三种结构中的晶体堆积揭示了平面芳香苯并呋喃残基之间的π-π堆积相互作用以及各组分之间的氢键作用。本研究的意义在于对标题骨架进行了首次晶体学表征，该骨架始终呈现分子内氢键的存在以及随之而来的仅为单阴离子的性质。它进一步表明，该阴离子既可以作为配体与金属阳离子容易地配位，也可以作为单价抗衡离子起作用。最后，扁平苯并呋喃残基的芳香性提供了一种额外的超分子合成子，它指导并促进了化合物（I） - （III）的晶体堆积。
