Influence of substituents in aryl groups on the structure, thermal transitions and electrorheological properties of zinc bis(diarylphosphate) hybrid polymers.

ABSTRACT

The structures and thermal properties of three new hybrid one-dimensional (1D) polymers based on zinc bis(diarylphosphate)s containing p-substituted phenyl rings are reported. The crystal structures of Zn[O2P(p-OC6H4NO2)2]2 (1), Zn[O2P(p-OC6H4OMe)2]2 (2) and Zn[O2P(p-OC6H4CO2Et)2]2 (3) differ from that of their unsubstituted analogue, Zn[O2P(OPh)2]2 (ZnDPhP). Compounds 1 and 3 consist of tetrahedrally coordinated zinc cations connected by double bridges of phosphate groups (2+2 bridging mode) and form polymeric chains that are packed in a distorted hexagonal lattice with six closest neighbours. In compound 2 zinc cations are linked by alternating single and triple phosphate bridges (3+1 bridging mode) and the resulting chains, having only four closest neighbors, are packed in a distorted tetragonal manner. DFT computations revealed that the 2+2 bridging mode, even at the highest energy conformation, is more stable than the 3+1 one. Simultaneous Thermal Analysis, Raman spectroscopy and powder XRD (PXRD) studies show that pyrolysis of the studied hybrid polymers begins above 260 °C, leading to a mixture of zinc condensed phosphates and carbonaceous deposits that may have electron-conducting properties. DSC and PXRD studies provide evidence that crystalline domains in 2 and 3 rearrange and/or disappear at a much lower temperature (ca. 150 °C) leading to an isotropic liquid (in the case of 3) or an amorphous solid material (in the case of 2). Electrorheological measurements indicate that 1-3 are polarized in an external electric field, and the type of electrorheological effect depends on the type of functional group attached to the phenyl ring; this feature can be utilized in designing new electrorheological devices.