Terephthalate salts: salts of monopositive cations

Abstract

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) Å, β = 93.1552 (4)°, V = 363.451 (3) Å3, Z = 2. The Li anions are tetrahedrally coordinated and the packing of the terephthalate anions resembles the γ-packing of aromatic hydrocarbons. Na2C8H4O4 crystallizes in Pbc2 1, with a = 3.54804 (5), b = 10.81604 (16), c = 18.99430 (20) Å, V = 728.92 (2) Å3, Z = 4. The coordination of the two independent Na is trigonal prismatic and the terephthalate packing resembles the β packing of hydrocarbons. (NH4)2C8H4O4 also crystallizes in Pbc21, with a = 4.0053 (5), b = 11.8136 (21), c = 20.1857 (24) Å, V = 955.1 (2) Å3, Z = 4. The cations and planar anions are linked by hydrogen bonds and the packing is a looser version of the β packing. K2C8H4O2 crystallizes in P21/c, with a = 10.561 (4), b = 3.9440 (12), c = 11.535 (5) Å, β = 113.08 (3)°, V = 442.0 (3) Å3, Z = 2. The K is trigonal prismatic and the packing is also β. 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) Å, β = 98.04 (3) and 94.56 (5)°, V = 816.8 (3) and 790.9 (3) Å3, respectively, and Z = 4. The packing in the hydrogen-bonded acid salts is also β. Electrostatic interactions among the terephthalate anions appear to be important in determining the crystal packing.