Terephthalate salts: salts of monopositive cations

The crystal structures of dilithium, disodium and diammonium terephthalate (1,4-benzenedicarboxylate) have been solved ab initio using Monte Carlo simulated annealing techniques, and refined using synchrotron powder data. The structures of dipotassium terephthalate, potassium hydrogen terephthalate and ammonium hydrogen terephthalate have been refined using single-crystal techniques. Li2C8H4O4 crystallizes in P2(1)/c, with a = 8.35921 (5), b = 5.13208 (2), c = 8.48490 (5) A, beta = 93.1552 (4) degrees, V = 363.451 (3) A3, Z = 2. The Li anions are tetrahedrally coordinated and the packing of the terephthalate anions resembles the gamma-packing of aromatic hydrocarbons. Na2C8H4O4 crystallizes in Pbc2(1), with a = 3.54804 (5), b = 10.81604 (16), c = 18.99430 (20) A, V = 728.92 (2) A3, Z = 4. The coordination of the two independent Na is trigonal prismatic and the terephthalate packing resembles the beta packing of hydrocarbons. (NH4)2C8H4O4 also crystallizes in Pbc2(1), with a = 4.0053 (5), b = 11.8136 (21), c = 20.1857 (24) A, V = 955.1 (2) A3, Z = 4. The cations and planar anions are linked by hydrogen bonds and the packing is a looser version of the beta packing. K2C8H4O2 crystallizes in P2(1)/c, with a = 10.561 (4), b = 3.9440 (12), c = 11.535 (5) A, beta = 113.08 (3) degrees, V = 442.0 (3) A3, Z = 2. The K is trigonal prismatic and the packing is also beta. Both KHC8H4O4 and (NH4)HC8H4O4 crystallize in C2/c, with a = 18.825 (4) and 18.924 (4), b = 3.770 (2) and 3.7967 (9), c = 11.179 (2) and 11.481 (2) A, beta = 98.04 (3) and 94.56 (5) degrees, V = 816.8 (3) and 790.9 (3) A3, respectively, and Z = 4. The packing in the hydrogen-bonded acid salts is also beta. Electrostatic interactions among the terephthalate anions appear to be important in determining the crystal packing.