Killing two birds with one stone: 2D+2D→3D parallel stacking and 3D self-penetrating structures in one reaction and their crystal-to-crystal transformation

Abstract

Reaction of the flexible phenolic carboxylate ligand 2-(3,5-dicarboxylbenzyloxy)benzoic acid (H3 L) with nickel salts in the presence of 1,2-bis(pyridin-4-yl)ethylene (bpe) leads to the generation of a mixture of the two complexes under solvolthermal conditions, namely poly[[aqua[μ-1,2-bis(pyridin-4-yl)ethylene-κ2 N:N′]{μ-5-[(2-carboxyphenoxy)methyl]benzene-1,3-dicarboxylato-κ3 O 1,O 1′:O 3}nickel(II)] dimethylformamide hemisolvate monohydrate], {[Ni(C16H10O7)(C12H10N2)(H2O)]·0.5C3H7NO·H2O} n or {[Ni(HL)(bpe)(H2O)]·0.5DMF·H2O} n , 1, and poly[[diaquatris[μ-1,2-bis(pyridin-4-yl)ethylene-κ2 N:N′]bis{μ-5-[(2-carboxyphenoxy)methyl]benzene-1,3-dicarboxylato-κ2 O 1:O 5}nickel(II)] dimethylformamide disolvate hexahydrate], {[Ni2(C16H10O7)2(C12H10N2)3(H2O)2]·2C3H7NO·6H2O} n or {[Ni2(HL)2(bpe)3(H2O)2]·2DMF·6H2O} n , 2. In complex 1, the NiII centres are connected by the carboxylate and bpe ligands to form two-dimensional (2D) 4-connected (4,4) layers, which are extended into a 2D+2D→3D (3D is three-dimensional) supramolecular framework. In complex 2, bpe ligands connect to NiII centres to form 2D layers with Ni6(bpe)6 metallmacrocycles. Interestingly, 2D+2D→3D inclined polycatenation was observed between these layers. The final 5-connected 3D self-penetrating structure was generated through further connection of Ni–carboxylate chains with these inclined motifs. Both complexes were fully characterized by single-crystal analysis, powder X-ray diffraction analysis, FT–IR spectra, elemental analyses, thermal analysis and UV–Vis spectra. Notably, an interesting metal/ligand-induced crystal-to-crystal transformation was observed between the two complexes.