Abstract The monomeric SeOCl3- ion, which can be prepared as the tetraphenylarsonium salt from SeOCl2 and As(C6H5)4Cl, was structurally characterized by a low-temperature single crystal X-ray diffraction analysis. [As(C6H5)4]SeOCl3 is monoclinic, space group P21/c, with a = 9,332(3), b = 13,761(4), c = 18,985(6) Å, β = 110,97(3)° (at -135 °C), Z = 4; it contains a novel type of ψ-trigonal bipyramidal oxotrichloroselenate(IV) anion which is not associated to dimers or polymer chains as in known structures. The equatorial positions are occupied by doubly bonded oxygen (Se-O 1,601(3) Å) and by one Cl(Se-Cl 2,234(1) Å), the axial Se-Cl bonds (2,430(1) and 2,475(1) Å) being significantly longer. [N(C2H5)4]SeOCl3, which was obtained as crystals by oxidation of trichloroselenate(II), is triclinic, space group P1̄, with a = 10,607(3), b = 8,950(2), c = 8,862(2) Å, α = 119,79(2)°, β = 101,07(2)°, γ = 96,28(2)°, Z = 2. The X-ray structure analysis shows the anions to be present as centrosymmetric dimers Se2O2Cl6 2- like in the [P(C6H5)4]+ salt, with two tetragonal SeOCl4 pyramids linked through a Cl···Cl edge and the lone pairs trans to the axial Se-O bonds (1,589(4) Å). Se-Cl bond lengths are 2.270(1) and 2,351(2) Å (terminal); 2,698(1) and 2,920(1) Å (bridging). The results show that the nature of the reaction products of the Lewis acid SeOCl2 with halogenides as bases changes very sensitively with small variations in cations and environment. The vibrational spectra are discussed.

Krebs, B., Hucke, M., Hein, M., & Schäffer, A. (1983). Monomere und dimere Oxotrihalogenoselenate(IV): Darstellung, Struktur und Eigenschaften von [As(C6H5)4]SeOCl3 und [N(C2H5)4]SeOCl3 / Monomerie and Dimeric Oxotrihalogenoselenates(IV): Preparation, Structure and Properties of [As(C6H5)4]SeOCl3 and [N(C2H5)4]SeOCl3. Zeitschrift Für Naturforschung B, 38(1), 20–29.