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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.