Polyiodides of transition metal trischelate cations: syntheses, structures, and spectral and electrical conductivity studies of [Mn(phen) 3](I 3) 2 and [Mn(bpy) 3](I 3) 1.5(I 8) 0.25

Abstract

Two structurally significant polyiodides have been synthesized as salts of manganese(II) trischelates and characterized by three-dimensional X-ray crystallographic data. The complex, [Mn(phen) 3](I 3) 2 ( 1), where phen = 1,10-phenanthroline, crystallizes in the hexagonal space group R 3 ̄ with 6 mononuclear cations in a cell of dimensions, a = b = 16.456(3) Å; c = 25.864(4) Å. The structure has been refined to the final R 1 ( wR 2) values of 0.0365 (0.0782) based on 1981 ( F ≥ 4 σF) observed independent reflections. The structure of the [Mn(phen) 3] 2+ cation is unexceptional, whereas there are two types of symmetric I 3 − ions with I–I distances of 2.828(1) and 2.912(1) Å. The longer I 3 − ions and the trischelate cations form layers of hexagonal network, while the shorter I 3 − ions are present as linkages between the layers in the crystal. The complex, [Mn(bpy) 3](I 3) 1.5(I 8) 0.25 ( 2), where bpy = 2,2′-bipyridine, crystallizes in the monoclinic space group C2/c with 8 mononuclear cations in a cell of dimensions, a = 29.321(1) Å; b = 12.9177(4) Å; c = 23.2863(8) Å; β = 120.950(2)°. The structure has been refined to the final R 1 ( wR 2) values of 0.0536 (0.1310) based on 4192 ( F ≥ 4 σF) observed independent reflections. The structure consists of [Mn(bpy) 3] 2+ cations, two types of I 3 − ions, and infinite linear polyiodide chains of the composition, (I 8 2−) n . Powder diffuse reflectance spectra measured for the complexes are similar exhibiting features at 23.0, 20.8, 18.5 and 17.2 kK, and are characteristic of the presence of I 3 − ions. Room temperature magnetic susceptibility measurements gave the magnetic moments of 5.85 and 6.05 μ B for 1 and 2, respectively; the values are consistent with the expected spin-only magnetic moment for high-spin d 5 manganese(II) complexes. Single crystal EPR spectral measurements with the applied field aligned parallel to the trigonal or pseudo-trigonal symmetry axis of the molecules gave zero-field splitting ( D) values of 0.154 cm −1 ( g = 2.06) and 0.066 cm −1 ( g = 2.03) for 1 and 2, respectively. A comparison of the conductivities of the complexes in a single crystal form reveals a higher anisotropic conductivity for 2, which is attributed to the presence of linear polyiodide chains.