Structural Design Parameters for Highly Birefringent Coordination Polymers

Abstract

A series of coordination polymer materials incorporating the highly anisotropic 2-(2-pyridyl)-1,10-phenanthroline (phenpy) building block have been synthesized and structurally characterized. M(phenpy)[Au(CN)2]2 (M = Cd, Mn) are isostructural and form a 1-D chain through bridging [Au(CN)2](-) units and extend into a 2-D sheet through aurophilic interactions. M(phenpy)(H2O)[Au(CN)2]2·2H2O (M = Cd, Mn, and Zn) are also isostructural but differ from the first set via the inclusion of a water molecule into the coordination sphere, resulting in a 1-D topology through aurophilic interactions. In(phenpy)(Cl)2[Au(CN)2]·0.5H2O forms a dimer through bridging chlorides and contains a free [Au(CN)2](-) unit. In the plane of the primary crystal growth direction, the birefringence values (Δn) of 0.37(2) (Cd(phenpy)[Au(CN)2]2), 0.50(3) (In(phenpy)(Cl)2[Au(CN)2]·0.5H2O), 0.56(3) and 0.59(6) (M(phenpy)(H2O)[Au(CN)2]2·2H2O M = Cd and Zn, respectively) were determined. β, a structural parameter defined by phenpy units rotated in the A-C plane relative to the light propagation (C) direction, was found to correlate to Δn magnitudes. The addition of a carbon-carbon double bond to terpy has increased the molecular polarizability anisotropy of the building block, and all structures have reduced deviation from planarity in comparison to terpy and terpy derivative structures, leading to these higher Δn values, which are among the highest reported for crystalline solids.

Correlating Structural Features and 207Pb NMR Parameters with the Stereochemical Activity of PbII Lone Pairs in Birefringent Pb[2,6‐bis(benzimidazol‐2‐yl)pyridine] Complexes

“…Birefringence (Δ n ) arises when the refractive index varies depending on the direction of light propagation through a crystal, and can be traced to the anisotropic arrangement of the atoms and molecules within the material , . The magnitude of birefringence depends on a number of factors, including the polarizability anisotropy of the building blocks (which is high for bbp), the orientation of these components within the lattice and the crystal‐growth habit , . The magnitude of Δ n was determined by optical microscopy for all compounds at 546 nm; the results are summarized in Table .…”

“…This wide range of observed Δ n values reflects differences in the orientation of the bbp ligands and the viewing direction during the experiment. In the case of [Pb(bbp)Br 2 ] · 2H 2 O, which is amongst the most birefringent compounds known, bbp ligands adopt a favourable parallel alignment and are oriented in a near optimal direction with respect to the viewing direction , …”

“…The targeted series of Pb II complexes feature the tridentate 2,6‐bis(benzimidazol‐2‐yl)pyridine ligand (bbp); the Pb II /bbp combination is of particular interest, because previous reports have shown that non‐Pb II ‐based bbp materials and Pb II systems with other planar aromatic capping ligands, can be highly birefringent by virtue of aligning the highly polarizable anisotropic components. Thus, a merging of these two components in the quest for highly birefringent coordination polymer materials is a logical progression.…”

Amorphization of a Ru‐Ru‐Cd‐Coordination Polymer at Low Pressure

“…Furthermore, the back‐bone inorganic polymer described here opens up possibilities for liquid casting and shaping heterometal inorganic polymers into a variety of different solid forms, promising to be an extremely exciting step forward in producing chemically functionalizable hybrid glass materials. The characterization of the structures derived from 1 under pressure and temperature are in progress as well as the study of their possible properties such as sensors and tuneable by pressure absorbent …”

Polymorphism and Supramolecular Isomerism: The Impasse of Coordination Polymers

“…Evidence of polymorphism can also be confirmed by nanoindentation or by optical properties as refractive index (n) or the identification of an interference figure caused by birefringence, which is the presence of different n and mainly depends on crystallographic orientations [91]. Once polymorphism has been identified and characterized, the proper conditions to isolate or to only reach one polymorphic form are to be established, avoiding the presence of mixtures and undesired products.…”