Hydrothermal synthesis, structure and magnetic properties of a new three-dimensional iron arsenate [C 6N 4H 21][Fe III 3(HAsO 4) 6]

A hydrothermal reaction of a mixture of iron oxalate, arsenic pentoxide, hydrofluoric acid and triethylenetetramine (TETA) at 150 °C for 48 h gives rise to a new iron arsenate [C 6N 4H 21][Fe 3(HAsO 4) 6], I. The structure consists of a network of FeO 6 and AsO 4 building units connected through their vertices giving rise to a new secondary building unit, SBU-5. The SBU-5 units are through their corners forming a three-dimensional structure possessing one-dimensional channels bound by 8-T atoms (T = Fe, As). The formation of SBU-5 units is noteworthy. Variable temperature magnetic studies indicate antiferromagnetic interactions between the Fe centers with T N of 21.9 K. Crystal data: M = 1156.36, monoclinic, space group = C2/ c (no. 15), a = 18.422(3) Å, b = 8.8527(13) Å, c = 16.169(2) Å, β = 111.592(2)°, V = 2451.9(6) Å 3, Z = 8, ρ calc = 3.037 g cm −3, μ(Mo Kα) = 9.903 mm −1, R 1 = 0.0358, w R 2 = 0.0763, S = 1.140 for 234 parameters.