Highly quadrupolar derivatives of the [closo-B10H10]2- anion: Investigation of liquid crystalline polymorphism in an homologous series of 1,10-bis(4-alkoxypyridinium) zwitterions

A series of pyridinium bis-zwitterions [closo-B10H8-1,10-2 (4-ROC5H4N)] (1[n]) was obtained in 55–60% yield by reacting [closo-B10H8-1,10-2(IPh)] (3) with 4-alkoxypyridines and the resulting derivatives were analyzed for their liquid crystalline properties. Optical, thermal and XRD analyses revealed the formation of a nematic and rare lamellar phases, LamCr, driven by dipolar interactions. Upon elongation of the terminal alkoxy chain, the nematic phase is gradually replaced by the lamellar polymorphism. The solid-state structures of 1[8], 1[12] and 1[16] were established by single crystal XRD: 1[8] P21/c, Z = 4, a = 12.6009 (2) Å, b = 20.7889 (2) Å, c = 12.61150 (10) Å, β = 103.9910 (10)°; 1[12] P-1, Z = 2, a = 9.6262 (2) Å, b = 12.0464 (2) Å, c = 17.9226 (3) Å, α = 80.5940 (10)°, β = 83.0700 (10)°, γ = 74.9860 (10)°; 1[16] P-1, Z = 2, a = 9.6827 (3) Å, b = 11.6711 (5) Å, c = 22.8486 (7) Å, α = 77.416 (3)°, β = 86.925 (2)°, γ = 66.202 (4)°. © 2018 Elsevier B.V.