Transition metal iodates. II. Crystallographic, magnetic, and nonlinear optic survey of the 3 d iodates

The anhydrous iodates of Cr, Mn, Fe, Co and β-Ni form a single isomorphous family, crystallizing in space group P6 ₃ or P6 ₃22 with lattice constants typified by Mn(IO ₃) ₂ of a = 11.178 ± 0.002, c = 5.035 ± 0.001 Å and four formulas per unit cell; in addition, α-Ni(IO ₃) ₂ forms as a second phase. Mn(IO ₃) ₂, Fe(IO ₃) ₃, α-Ni(IO ₃) ₂ and β-Ni(IO ₃) ₂ order antiferromagnetically at 6.5, 17.0, 3.5 and 5.0 K, respectively; Cr(IO ₃) ₃ and Co(IO ₃) ₂ remain paramagnetic to 1.5 K. Below Θ_N, a weak ferromagnetic moment develops in the Mn, α-Ni and β-Ni iodates. All the anhydrous iodates generate second harmonics. Co(IO ₃) ₂ · 4H ₂O and β-Ni(IO ₃) ₂ · 4H ₂O crystallize isomorphously in space group {P2 ₁}/{c}, with lattice constants a = 8.370 ± 0.005, b = 6.572 ± 0.007, c = 8.514 ± 0.008 Å, β = 99.8 ± 0.1° for the Co compound. Co(IO ₃) ₂ · 2H ₂O is triclinic, with a = 6.666 ± 0.015, b = 10.991 ± 0.025, c = 4.913 ± 0.011 Å, α = 93.1 ± 0.1, β = 92.1 ± 0.1, γ = 98.9 ± 0.1°, space group P overline1, and Ni(IO ₃) ₂ · 2H ₂O is orthorhombic, a = 9.14986 ± 0.00008, b = 12.20896 ± 0.00022, c = 6.58353 ± 0.00013Å at 298 K, space group Pbca. The Co iodate hydrates are paramagnetic to 1.5 K; both Ni hydrates are antiferromagnetic, the dihydrate also developing a weak ferromagnetic moment. The lattice spacings of all 11 compounds are presented, 9 with indexing.