Novel Organometallic Building Blocks for Molecular Crystal Engineering. 2. Synthesis and Characterization of Pyridyl and Pyrimidyl Derivatives of Diboronic Acid, [Fe(η⁵-C₅H₄-B(OH)₂)₂], and of Pyridyl Boronic Acid, [Fe(η⁵-C₅H₄-4-C₅H₄N)(η⁵-C₅H₄-B(OH)₂)]

Abstract

The synthesis and structural characterization of the ferrocenyl diboronic acid complex [Fe(η5-C5H4-B(OH)2)2] (1) and of its products of monosubstitution, [Fe(η5-C5H4-4-C5H4N)(η5-C5H4-B(OH)2)] (2 in three polymorphic modifications, 2a−c), and of disubstitution, [Fe(η5-C5H4-4-C5H4N)2] (4), [Fe(η5-C5H4-C6H4-4-C5H4N)2] (6), and [Fe(η5-C5H4-5-C4H3N2)2] (7), are reported together with an investigation of the mode of supramolecular bonding in the solid state. The competition between the hydrogen-bonding interactions of the (B)O−H···O(B) and (B)O−H···N types in the cases of crystalline 1 and 2 has been investigated. The B(OH)2 group provides two hydrogen bonding donor groups and two acceptors, forming mainly cyclic hydrogen-bonded systems in topological analogy with a primary amido group. Compounds 4, 6, and 7 are examples of neutral disubstituted pyridyl and pyrimidyl ferrocenyl complexes with potentials as supramolecular ligands. The compounds [Fe(η5-C5H4-4-C5H4NH)(η5-C5H4-B(OH)2)][NO3] (3a), [Fe(η5-C5H4-4-C5H4NH)(η5-C5H4-B(OH)2)][SO4]·3H2O (3b), and [Fe(η5-C5H4-4-C5H4NH)2][Cl]2·4H2O (5) have been obtained by treatment with acids of compounds 2 and 4, respectively. The interionic hydrogen bonds have also been investigated.