Abstract
The influence of weak hydrogen bonds on the crystal packing of a series of heavy and transition metal coordination polymers synthesized using the ligand 5-ethynyl-1,3-benzenedicarboxylic acid (H2ebdc) has been evaluated. Five coordination polymers were prepared and crystallographically characterized. These comprise two 1D chains, [Pb(ebdc)(DMSO)2] (1) and [Pb(ebdc)(DMF)] (2), two 2D nets, [Cu3(ebdc)(H2O)1.5(MeOH)0.5]·6H2O (3) and [Pb2(ebdc)2(DMF)4]·H2O (4), and a single 3D framework, [HNEt3][Zn3(μ3-OH)(μ2-H2O)(ebdc)3(MeOH)0.67(H2O)0.33]·MeOH·1.33H2O (5). The crystal structure of the free acid ligand form, H2ebdc·H2O, is also reported. Within the lead(II) coordination structures, ethynyl-derived C–H···O interactions are consistently found to provide the dominant influence over the crystal packing, as determined by solid-state structural analysis in combination with vibrational spectroscopy. The influence of weak hydrogen-bonding effects on the crystal packing of the transition metal coordination polymers that contain lattice water and methanol molecules was found to be far less prominent, which is interpreted in terms of the greater prevalence of strong hydrogen-bond donors and acceptors forming O–H···O interactions within these crystalline lattices.
Highlights
The design of crystalline architectures employing an understanding of the intermolecular interactions available to molecular subunits is the basis for crystal engineering, a key field straddling solid-state molecular assembly and structural analysis, whose importance lies in its capability for allowing control of crystal properties and functions as well as its structure
Nontarget interactions that are allowed by this ligand include π−π stacking derived from the central aromatic ring as well as strong hydrogen bonding from either the carboxylic acid or carboxylate functionality
While gaining control over weak hydrogen-bond interactions during the self-assembly of coordination polymers remains a distant goal at the present time, this study has identified lead(II) and its corresponding coordination polymers as interesting species for study using ligands containing weak hydrogen-bond donors, in which the resulting weak hydrogen bonds are influential in forming the solid state-structures
Summary
A weak hydrogen bond can broadly be defined as an electrostatic interaction formed by a hydrogen atom between two structural moieties of moderate to low electronegativity, of which C−H···X (X = O/N) interactions are a key example The study of these interactions began with the discovery of increased polarization of haloforms with ketones, pyridines, and ethers.. This observation was linked by spectroscopic interpretations to hydrogen bonding, to account for large bathochromic shifts observed in the infrared (IR) spectra of such species.7 While assignment of these interactions by crystallography were initially resisted in the wake of strong criticisms by Donohue toward a study by Sutor, in recent years, advancements in the field of crystallography and in computational power have demonstrated and confirmed the fundamental importance of these interactions to supramolecular self-assembly. ASelected bond lengths and angles for the coordination polymers 1−5 are available as Supporting Information
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