One-pot synthesis of two pillar-layer frameworks: coordination polymorphs deriving from different linking modes of 1,3,5-benzenetricarboxylate

Abstract

In this work, the aromatic polycarboxylic acid, 1,3,5-benzenetricarboxylate (H₃btc), has been utilized as a variable building block to perform an intensive study on the structure diversity of coordination polymorphs. The one-pot solvothermal reaction of Ni(NO₃)₂ with H₃btc and 1,4-bis(imidazolyl)benzene (bib) ligands affords two novel polymorphous coordination polymers, {[Ni₂(Hbtc)₂(bib)₃]·(H₂O)}_∞ (1) and {[Ni₃(btc)₂(bib)₃(H₂O)₂]·(CH₃OH)(H₂O)₄}_∞ (2). In polymorphs 1 and 2, the aromatic acid adopts different bridging modes (κ¹)-(κ¹)-(κ¹)-μ₃ and (κ¹)-(κ²)-(κ¹-κ¹)-μ₄ to connect nickel ions into 2D (6,3) and (4,4) layers, which are further pillared by the bib ligand to form two binodal pillar-layer frameworks with Schäfli symbols of [6³]·[6¹⁴.8] and [4⁴.6²]·[4⁸.6⁷], respectively. The two polymorphs both exhibit a nickel–bib matrix, but the carboxylic acid ligand takes various coordination modes, finally leading to diverse topological structures. Furthermore, the deprotonation style of 1,3,5-benzenetricarboxylate steers the number of coordination mode around the metal ion, specifically the partially deprotonated Hbtc²⁻ relating to one geometry-independent metal ion, and the fully deprotonated btc³⁻ associating with two crystallographically independent metal ions. The variety of topological structure and metal composition indicates that the ligand H₃btc plays an essential role in the assembly of the coordination polymorph. Magnetic studies reveal the weak ferromagnetic interaction within the binuclear cluster of polymorph 2.