INCORPORATION OF A(2)Q INTO HGQ AND DIMENSIONAL REDUCTION TO A(2)HG(3)Q(4) AND A(2)HG(6)Q(7) (A = K, RB, CS, Q = S, SE) - ACCESS OF LI IONSIN A(2)HG(6)Q(7) THROUGH TOPOTACTIC ION-EXCHANGE

The synthesis of the one-dimensional K(2)Hg(3)Q(4) (Q = S, Se) and Cs2 Hg3Se4 and the three-dimensional A(2)Hg(6)S(7) (A = K, Rb, Cs), and A( 2)Hg(6)Se(7) (A = Rb, Cs) in reactive A(2)Q(x) fluxes is reported. Pal e yellow, hexagonal plates of K2Hg3S4 crystallize in space group Pbcn, with a = 10.561(5) Angstrom, b = 6.534(3) Angstrom, and c = 13.706(2) Angstrom, V = 945.8(7) Angstrom(3), d(calc) = 5.68 g/cm(3), and final R = 5.7%, R-W = 6.3%. Red, hexagonal plates of K2Hg3Se4 crystallize i n space group Pbcn, with a = 10.820(2) Angstrom, b = 6.783(1) Angstrom , and c = 14.042(2) Angstrom, V = 1030.6(5) Angstrom(3), d(calc) = 6.4 2 g/cm(3), and final R = 7.7%, R-W = 8.4%. Orange yellow, hexagonal pl ates of Cs2Hg3Se4 crystallize in space group Pbcn, with a = 12.047(4) Angstrom, b = 6.465(2) Angstrom, and c = 14.771(6) Angstrom, V = 1150. 4(7) Angstrom(3), d(calc) = 6.83 g/cm(3), and final R = 5.5%, R, = 6.2 %. Black needles of K2Hg6S7 crystallize in space group <P(4)over bar 2 (1)m>, with a = 13.805(8) Angstrom and c = 4.080(3) Angstrom, V = 778( 1) Angstrom(3), d(calc) = 6.43 g/cm(3), and final R = 3.1%, R-W = 3.6% . Black needles of Rb2Hg6S7 crystallize in space group P4(2)nm, with a = 13.9221(8) Angstrom and c = 4.1204(2) Angstrom, V = 798.6(1) Angstr om(3), d(calc) = 6.65 g/cm(3), and final R = 4.3%, R-W = 5.0%. Black n eedles of Cs2Hg6S7 crystallize in space group P4(2)nm, with a = 13.958 (4) Angstrom and c = 4.159(2) Angstrom, V = 810.2(8) Angstrom(3), d(ca lc) = 6.94 g/cm(3), and final R = 4.3%, R-W = 4.4%. Black needles of C s2Hg6Se7 crystallize in space group P4(2)nm, with a = 14.505(7) Angstr om and c = 4.308(2) Angstrom, V = 906(1) Angstrom(3), d(calc) = 7.41 g /cm(3), and final R 3.6%, R-W = 4.0%. The A(2)Hg(3)Q(4) compounds cont ain linear chains. The A(2)Hg(6)Q(7) compounds display noncentrosymmet ric frameworks with Af cations residing in tunnels formed by both tetr ahedral and linear Hg atoms. K2Hg6S7, Rb2Hg6S7, Cs2Hg6S7, Rb2Hg6Se7, a nd Cs2Hg6Se7 display room-temperature bandgaps of 1.51, 1.55, 1.61, 1. 13, and 1.17 eV, respectively. Bandgap engineering through S/Se solid solutions of the type Rb2Hg6Se7-xSx and Cs2Hg6Se7-xSx is possible in t hese materials. All A(2)Hg(6)Q(7) melt congruently, with melting point s of 556 +/- 10 degrees C, except for Rb2Hg6Se7 which degrades. Rb2Hg6 S7 can undergo ion exchange reactions with LiI to give Li1.8Rb0.2Hg6S7 .