Benzoate substituents effects on the structure of Zn(II) complexes and 1D 4, 4′-bipyridine derived coordination polymers

The aim of this work is to study the influence of different substituents in two closely related ligands, 3,5-dihydroxybenzoate (3,5-(HO)(2)Bz) and 3,5-dimethoxybenzoate (3,5-(MeO)(2)Bz), in the structure of zinc complexes. The compound [Zn(3,5-(MeO)(2)Bz)(2)(CH3OH)](2) (2) has been synthesized, characterized and its crystal structure elucidated, showing a paddle wheel type dinuclear molecule, with four bridging carboxylate ligands in a syn-syn coordination mode and methanol molecules in the apical positions. This discrete structural array is different than the polymeric structure observed in {[Zn(mu-3,5-(HO)(2)Bz)(mu-OH2)(H2O)(2)]center dot 3,5-(HO)(2)Bz center dot 4H(2)O}(n), previously reported in our group. These two zinc complexes were used as precursor for the synthesis of coordination polymers (CPs) with the 4,4'-bipyridine (4,4'-bpy) linker. The solvent used in their synthesis influences the chemical composition of this CPs. Thus, {[Zn(3,5-(HO)(2)Bz)(2)(mu-4,4'-bpy)]center dot 2DMSO}(n) (3) was achieved in dimethylsulfoxide (DMSO) while {[Zn(3,5-(HO)(2)Bz)(2)(mu-4,4'-bpy)]center dot 4,4'-bpy center dot 1/2CH(3)OH}(n) (4) was formed in methanol (MeOH) as solvent. The reaction of 2 with 4,4'-bpy yielded [Zn-2(mu-3,5-(MeO)(2)Bz)4(mu-4,4'-bpy)](n) (5) in methanol, while after recrystallization in boiling water, complex {[Zn(3,5-(MeO)(2)Bz)(2)(mu-4,4'-bpy)]center dot H2O}(n) (6) was isolated in low yield. This compound 6 can also be synthesized by a mechanochemical approach, using water in a liquid assisted grinding. The crystal structures of complexes 3, 4 and 6 were elucidated, all three showing zigzag polymeric arrays. Both polymers containing 3,5-(MeO)(2)Bz (5 and 6), showed solid state luminescence.