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

Reaction of the flexible phenolic carboxylate ligand 2-(3,5-dicarboxylbenzyloxy)benzoic acid (H 3 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-κ 2 N : N ′]{μ-5-[(2-carboxyphenoxy)methyl]benzene-1,3-dicarboxylato-κ 3 O 1 , O 1′ : O 3 }nickel(II)] dimethylformamide hemisolvate monohydrate], {[Ni(C 16 H 10 O 7 )(C 12 H 10 N 2 )(H 2 O)]·0.5C 3 H 7 NO·H 2 O} n or {[Ni(H L )(bpe)(H 2 O)]·0.5DMF·H 2 O} n , 1 , and poly[[diaquatris[μ-1,2-bis(pyridin-4-yl)ethylene-κ 2 N : N ′]bis{μ-5-[(2-carboxyphenoxy)methyl]benzene-1,3-dicarboxylato-κ 2 O 1 : O 5 }nickel(II)] dimethylformamide disolvate hexahydrate], {[Ni 2 (C 16 H 10 O 7 ) 2 (C 12 H 10 N 2 ) 3 (H 2 O) 2 ]·2C 3 H 7 NO·6H 2 O} n or {[Ni 2 (H L ) 2 (bpe) 3 (H 2 O) 2 ]·2DMF·6H 2 O} n , 2 . In complex 1 , the Ni II 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 Ni II centres to form 2D layers with Ni 6 (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.