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)]

The synthesis and structural characterization of the ferrocenyl diboronic acid complex [Fe(eta(5)-C5H4-B(OH)(2))(2)] (1) and of its products of monosubstitution, [Fe(eta(5)-C5H4-4-C5H4N)(eta(5)-C5H4-B(OH)(2))] (2 in three polymorphic modifications, 2a-c), and of disubstitution, [Fe(eta(5)- C5H4-4-C5H4N)(2)] (4), [Fe(eta(5)-C5H4-C6H4-4-C5H4N)(2)] (6), and [Fe(eta(5)-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(eta(5)-C5H4-4-C5H4NH)(eta(5)-C5H4-B(OH)(2))] [NO3] (3a), [Fe(eta(5)-C5H4-4-C5H4NH)(eta(5)-C5H4-B(OH)(2))][SO4].3H(2)O (3b), and [Fe(eta(5)-C5H4-4-C5H4NH)(2)][Cl](2).4H(2)O (5) have been obtained by treatment with acids of compounds 2 and 4, respectively. The interionic hydrogen bonds have also been investigated.