Extent of protonation of 4,4′-bipyridinium cations and nature of host influences the amount of guest intake by cobalt(II) 2,6-pyridinedicarboxylate

Abstract

4,4′-Bipyridinium cobalt(II) 2,6-pyridinedicarboxylate hexahydrate forms host–guest complexes with hydroxy-aromatic compounds 2,3- or 2,7-dihydroxynaphthalene and phloroglucinol. Impressive aspect of the complex is the modification of protonated species in different ways while forming host–guest complexes with hydroxyaromatics. Complex with 2,3-dihydroxynaphthalene has 4,4′-bipyridinium monocation and dication as counter-ions, whereas 2,7-dihydroxynaphthalene complex has only 4,4′-bipyridinium dication. Host-guest complex with phloroglucinol has two 4,4′-bipyridinium monocations. Guest dependent templates are formed in each case. In the case of 2,3-dihydroxynaphthalene, interactions among amine-water-naphthalenediol resulted in chain-like structures within the self-assembly; whereas host–guest complex having 2,7-dihydroxynaphthalene holds water clusters within self-assembly. Substrate dependent host–guest complexes with variations on amounts of guest intake per unit cell was observed; for example with 1, 3, 5-trihydroxybenzene as guest molar ratio of cobalt ion with respect to guest is unity, whereas three equivalents of 2, 3- or 2, 7-dihydroxynaphthalene molecules per cobalt complex were observed.