Inclusion of dihydroxyaromatics by a lanthanum(III) 2,6-dipicolinate complex

Abstract

Lanthanum complexes possessing dihydroxyaromatic guests namely, (H2bpy)1.5[La(26pdc)3]·2(cat)·4H2O, (H2bpy)3[La(26pdc)3]2·3(23dhn)·19H2O, (H2bpy)1.5 [La(26pdc)3]·3(27dhn)·10H2O [26pdc=2,6-pyridinedicarboxylate, bpy=4,4′-bipyridine, cat=1,2-dihydroxybenzene, 23dhn=2,3-dihydroxynaphthalene, 27dhn=2,7-dihydroxynaphthalene] are synthesized from 4,4′-bipyridinium lanthanum(III) tris-pyridinedicarboxylate and structurally characterized. Two different types of templates to accommodate hosts are found in these host–guest complexes. 1,2-Dihydroxybenzene molecules are held by template formed by interactions of a [tris-2,6-dipicolinate lanthanum(III)] anion with a 4,4′-bipyridinium cation; whereas dihydroxynaphthalene molecules are held by templates formed between two complex anions interacting with one 4,4′-bipyridinium cation. Complexes 1 and 2 without guest molecules are fluorescent in solid state; whereas dihydroxyaromatic guest included complexes 3–5 are non-fluorescent in solid state. However, in solution, complex 1 causes increase in fluorescence emission intensity of 1,2-hydroxyaromatic compounds and recognition of 1,2-dihydroxybenzene by complex 1 is significant.