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

Two 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)

Polynuclear and polymeric squarato-bridged coordination compounds

“…) independent of the nature of the central metal ions, 85 the alternative CuIJII) complex [Cu 2 IJdpya) 4 IJμ 1,3 -C 4 O 4 )] 2+ (10) yielded μ 1,3 -bonding. 10…”

Synthesis, Structural Characterization and Ligand-Enhanced Photo-Induced Color-Changing Behavior of Two Hydrogen-Bonded Ho(III)-Squarate Supramolecular Compounds

“…The inherent character of lanthanide ions with high affinity for oxygen atoms and high coordination numbers, result in the formation of a number of MOFs with flexible coordination geometry and various structural dimensionality from multi-carboxylate ligands [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]. The squarate, C 4 O 4 2− , has been widely used as a polyfunctional ligand, including (1) acts as a bridging ligand with various coordination modes (μ 2 to μ 6 bridges shown in Scheme 1) to build up many coordination polymers with novel extended networks, including 1D chain, 2D layer, 3D cube- and cage-like frameworks and so forth and (2) behaviors as hydrogen bond donor, acceptor or π−π constructor for the assembly of extended supramolecular architecture [30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63]. In the previous investigation, several 2D and 3D LnMOFs constructed via the bridges of lanthanide and squarate ligand with various coordination modes have been synthesized under hydrothermal or solvothermal conditions [64,65,…”

“…Their thermal behavior, magnetic property and photo-luminescence spectra of 2D and 3D LnMOFs have also been studied. With our continuous effort on the study of metal-squarate coordination polymers (CPs) [58,59,60,61,62,63], we report here the synthesis, structural characterization, thermal stability and light-induced color-changing behavior of two Ho(III)-squarate hydrogen-bonded supramolecular networks, [Ho 2 (C 2 O 4 )(C 4 O 4 ) 2 (H 2 O) 8 ]·4H 2 O ( 1 ) and [Ho(C 4 O 4 ) 1.5 (H 2 O) 3 ] ( 2 ), (C 4 O 4 2− = dianion of squaric acid, C 2 O 4 2− = dianion of oxalic acid), in which the squarate acts as the bridging ligands with μ 1,2 -coordination mode (Scheme 1b) for 1 and combined μ 1,2 -plus μ 1,2,3 -coordination modes (Scheme 1b,c) for 2 to build up 1D ladder-like CP and 2D bi-layered MOF, respectively.…”

pH effect on the assembly of metal–organic architectures

“…12 For this particular class of supramolecular assemblies, the most frequently observed effects caused by changing pH conditions is the different dimension of the resulting metal-organic architectures. 11,[13][14][15][16][17][18][19][20][21][22][23][24] For example, the reaction of cupric acetate with benzoic acid and 4,4 0 -bpy in methanol-water solution at pH ¼ 5.5 produced the mononuclear [Cu(H 2 O)(benzoate) 2 (4,4 0 -bpy) 2 ](benzoic acid) 2 $(4,4 0 -bpy) (1) (Fig. 1), 14 (5) (Fig.…”