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

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](I3)2 (1), where phen = 1,10-phenanthroline, crystallizes in the hexagonal space group R3̄ 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 R1 (wR2) values of 0.0365 (0.0782) based on 1981 (F ≥ 4σF) observed independent reflections. The structure of the [Mn(phen)3]2+ cation is unexceptional, whereas there are two types of symmetric I3- ions with I-I distances of 2.828(1) and 2.912(1) Å. The longer I3- ions and the trischelate cations form layers of hexagonal network, while the shorter I3- ions are present as linkages between the layers in the crystal. The complex, [Mn(bpy)3](I3)1.5(I8)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 R1 (wR2) values of 0.0536 (0.1310) based on 4192 (F ≥ 4σF) observed independent reflections. The structure consists of [Mn(bpy)3]2+ cations, two types of I3- ions, and infinite linear polyiodide chains of the composition, (I82-)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 I3- ions. Room temperature magnetic susceptibility measurements gave the magnetic moments of 5.85 and 6.05 μB for 1 and 2, respectively; the values are consistent with the expected spin-only magnetic moment for high-spin d5 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.