A series of ionic 4-(4'-pyridylthio)-1-methylpyridinium salts with different counteranions (1, I(-); 2, BF(4)(-); 3, PF(6)(-); and 4, OTf(-), where OTf = trifluoromethanesulfonate) have been prepared. Structural analysis reveals that the cation exhibits a variety of stacking structures dependent on the anion. Compound 1 crystallizes in space group P2(1/n) (#14), with a = 10.764(3) Angstrom b = 9.601(5) Angstrom, c = 13.105(3) Angstrom, beta = 108.35(2), V = 1285.4(8) A 3, and Z = 4. In this compound, each cation moiety is stacked in a helical arrangement along the c-axis. Compound 2, which is isomorphous to 1, has space group 2(1/n) (#14), with a = 11.647(2) b = 9.203(3) Angstrom, c = 13.232(2) Angstrom, beta = 108.42(2), V = 1345.6(5) Angstrom(3), and Z = 4. Compound 3 crystallizes in space group P2(1/n). (#14), with a = 8.06(1) Angstrom, b=17.43(1) Angstrom, c = 10.30(1) Angstrom, beta = 103.0(1), V = 1410(3) Angstrom(3), and Z = 4. In this salt, the cation molecules assume a head-to-tail stacking arrangement, forming a polar pseudo I-D chain. Compound 4 crystallizes in space group P (1) over bar (#2), with a = 7.585(4) Angstrom, b = 15.443(7) Angstrom, c=6.775 (4) Angstrom, alpha = 99.33(4), beta = 108.35(2)degrees, gamma = 98.37(4), V = 756.6(7) Angstrom(3), and Z = 2. The structure of 4 consists of a columnar stacking of pyridine moieties, with the cation moieties surrounded by the counteranions. Calculations show that the 4-(4'-pyridylthio)-1-methylpyridinium cation may be a good building block for second harmonic generation (SHG) materials, even though salts 1-4 crystaltized in centrosymmetric structures and were SHG inactive. (C) 2002 Elsevier Science (USA).
