The first vanadium selenoiodide V 4 O(Se 2 ) 4 I 6 •I 2 was synthesized at a moderate temperature of 220 °C from V, Se, I 2 , and water. Its crystal structure (tetragonal space group P4 2 /nbc, a = 11.838(1) Å, c = 18.689(1) Åwhere the edges of the distorted tetrahedron V 4 are bridged by four diselenide (Se 2 ) 2− and two iodide ligands; four terminal iodides coordinate V atoms additionally. This type of complex is known for Ti, Nb, and Ta but is new for vanadium. Magnetic susceptibility measurements of V 4 O(Se 2 ) 4 I 6 •I 2 showed four unpaired electrons on vanadium atoms at room temperature and drop of the effective magnetic moment at cool down, presumably due to partial electron pairing. Probability of this transition to the diamagnetic state is in accord with the calculated electronic structure.

The paper is related to an interesting case of revision of X-ray crystal structure with a lack of experimental data. Complexes V4OSe8I6·X (X = I2 or 3,5-dimethylpyrazole) with O-centered complex molecules [V4O(μ-Se2)4I4(μ-I)2] were synthesized in our group. In the further search for new relative compounds in the V-Se-I-O system, we obtained several crystals with different structures, including “V4OSe6I3”, with incredibly complicated connectivity of {V4O(Se2)4I6} units bridged via both diselenide and iodide ligands. Due to the absence of phase-pure products and the possible instability of some of the phases under ambient conditions, we were mainly guided by the single-crystal X-ray diffraction data. However, seeing a very complex coordination mode in the “V4OSe6I3” structure, we have carefully analyzed the structure from the positions of symmetry and chemical synthesis in this system. The “new structure” was recognized as the complex superposition of the structure of another compound with composition “V4OSe6I10” just found in the same experiment. We outlined the course of observations, reasoning and solutions to the symmetry false estimation problem, which we believe to be of interest to readers dealing with X-ray diffraction analysis.

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