Hydrothermal Synthesis and Structural Characterization of Two pH‐Controlled Cd–Squarate Coordination Frameworks, [Cd2(C4O4)2.5(H2O)4]·(dpaH)·1.5(H2O) and [Cd(C4O4)(dpa)(OH2)] (dpa = 2,2′‐dipyridylamine)

Abstract

AbstractTwo extended coordination frameworks of CdII–squarate complexes with the formulas [Cd2(C4O4)2.5(H2O)4](dpaH)·1.5(H2O) (1) and [Cd(C4O4)(dpa)(H2O)] (2) (dpa = 2,2′‐dipyridylamine) have been synthesized under hydrothermal conditions and characterized by single‐crystal X‐ray diffraction studies. Structural determination reveals that compound 1 consists of a free monoprotonated 2,2′‐dipyridylamine ion (dpaH+) and a two‐dimensional (2D) anionic, layered framework, {[Cd2(C4O4)2.5(H2O)4]–}, which is formed with two antiprismatic square‐boxes as the fundamental building unit through the connection between CdII ions and hybrid μ1,2,3‐, μ1,2,3,4‐squarates. Each square‐box acts as a host for the inclusion of one pyridine ring of dpaH+. Adjacent dpaH+ cations are then self‐assembled by the parallel alignment of the other pyridine ring of dpaH+ to complete a 3D network with one‐dimensional (1D) channels intercalated by water molecules. Compound 2 contains a distorted octahedral CdII center coordinated by two squarates, two waters and one dpa ligand to form a 1D 2‐legged, ladder‐like framework by the connection of a [Cd(dpa)(μ2‐H2O)]24+ dimeric unit and a μ1,2‐squarate. Weak π–π stacking interaction and hydrogen bonds of N–H···O, O–H···O and C–H···O among the squarate, water and dpa ligands provide additional intra‐ and intermolecular interactions on the stabilization of these two polymeric frameworks. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)