Polar derivatives of the [closo-1-CB9H10]− cluster as positive Δε additives to nematic hosts

Abstract

Polar (m z 16 D) and UV transparent >250 nm quinuclidinium (1) and sulfonium (2) zwitterionic derivatives of the [closo-1-CB 9 H 10 ] À anion were synthesized and studied as additives to nematic hosts. The molecular and crystal structures for 1 [C 19 H 44 B 9 N triclinic, P-1, a ¼ 9.766(2) A ˚, b ¼ 10.481(3) A ˚, c ¼ 12.098(3) A ˚, a ¼ 93.804( 9) , b ¼ 90.249(10) , g ¼102.587(10) , Z ¼ 2] were determined by X-ray crystallography and compared with the results of HF/6-31G(d) calculations. Low concentration solutions (<10 mol%) of 1 and 2 in ClEster host (D3 ¼ À0.59) were investigated using thermal and dielectric methods. The results for 1 and 2 showed virtual [T NI ] values of 139 C and 92 C, and D3 extrapolated to infinite dilution of 70 AE 1 and 61 AE 2, respectively. Dielectric results were analyzed using the Maier-Meier relationship and calculated molecular parameters. The apparent order parameter S app was found to be 0.63 and 0.50 for 1 and 2, respectively, which is smaller than that for the pure host (S ¼ 0.66). Analysis of the Kirkwood factors g obtained for each concentration gave an association constant K of 63 AE 2 and 37 AE 1 (model 1) for the assumed dimerization of molecules (2M # M 2 ) of 1 and 2, respectively, in solutions of ClEster.

A nematic to nematic transformation exhibited by a rod-like liquid crystal

“…This provides a semi-empirical value of g at both temperatures studied and thereby giving insight into the antiparallel (or parallel) correlations that exist in the bulk liquid crystal phase (see eqn (1)-(3) below and the ESI † for a more detailed discussion). [14][15][16][17][18][19] …”

Synthesis and Characterization of 12-Pyridinium Derivatives of the [closo-1-CB11H12]− Anion

“…The organic layers were combined and dried (Na 2 SO 4 ), and the solvents were evaporated giving 90 mg (40% yield) of an offwhite solid: { 1 H} 11 B NMR (128 MHz, CD 3 CN) δ major isomer [closo-1-CB 11 H 11 -12-(4-CH 3 OC 5 H 4 N)] (2b, 100 mg, 0.40 mmol) was dissolved in dry DMF (5 mL), LiCl (50 mg, 1.2 mmol) was added, and the resulting mixture was stirred at 80°C for 16 h. The reaction mixture was cooled to rt, DMF was removed in vacuo, water (5 mL) containing [NMe 4 ] + Cl − (130 mg, 1.2 mmol) and CH 2 Cl 2 (5 mL) was added, and the resulting biphasic system was stirred for 2 h. The organic layer was separated and dried (Na 2 SO 4 ), and the solvents were removed. The oily yellow residue was washed with Et 2 O (3 × 5 mL) and dried to give 122 mg (99% yield) of 5b[NMe 4 ] as a white crystalline solid, which was recrystallized twice from a toluene/ CH 3 …”

“…2 In this context, we initially investigated 1-sulfonium derivatives of type IA, 3,4 and later we developed a convenient method for access to 1-pyridinium zwitterions of anions A and B. 5 Although materials of type IA and IB are effective additives that increase dielectric anisotropy Δε of a nematic liquid crystal host, these polar materials rarely exhibit liquid crystalline properties themselves, have high melting points, and display limited solubility in nematic hosts.…”

“…In the B(12) isomer 2b, the pyridine−{CB 11 } bonding distance Table 1. Selected Electronic Parameters for 2b and 3b (4) 1406.47(7) Z 4 4 ρ (calcd), g/cm 3 1.179…”

Boron clusters as structural elements of novel liquid crystalline materials

“…The carboxylic acids can be converted to esters [51,52] or an amino group [53] using standard organic synthetic methods. The amino group at either the carbon or boron atom is particularly useful since it can be transformed into a quinuclidine ring [55] or synthetically valuable dinitrogen derivatives [53,54]. The dinitrogen derivatives can be further transformed into azo groups via diazo couplings, sulphonium rings, or pyridinium rings with relative ease [53,54].…”