Synthesis, Characterization, and Crystal Structures of New Dications Bearing the −Se−Se− Bridge

Abstract

Starting from 1,3-dimethyl-4-imidazoline-2-selone (1), 1,2-bis(2-selenoxo-3-methyl-4-imidazolinyl-2-)ethane (3) and 1,3-dimethylimidazolidine-2-selone (4), the following six compounds, [(C(5)H(8)N(2)Se-)(2)](2+).2Br(-) (I), [(C(5)H(8)N(2)Se-)(2)](2+).2I(-) (II), [(C(5)H(8)N(2)Se-)(2)](2+).Cl(-).I(3)(-) (III) [(C(5)H(10)N(2)Se-)(2)](2+).Br(-).IBr(2)(-) (IV), [(C(5)H(7)N(2)Se-)(2)](2+).I(3)(-).(1)/(2)I(4)(-) (V) and [(C(5)H(7)N(2)Se-)(2)](2+).2I(-).CH(3)CN (VI), in which the selenium compounds are oxidized to dications bearing the uncommon -Se-Se- bridge, have been prepared, and I-V crystallographically characterized. I and III were obtained by reacting 1 with IBr and ICl respectively, while II was obtained by reduction of previously described hypervalent selenium compound of 1 (5) bearing the I-Se-I group with elemental tellurium. These three compounds contain the same [(C(5)H(8)N(2)Se-)(2)](2+) dication balanced by two bromides in I, two iodides in II, and Cl(-) and I(3)(-) in III. However, on the basis of the Se-Cl bond length of 2.778(5) Å, III can also be considered as formed by the [(C(5)H(8)N(2)Se-)(2)Cl](+) cation, with I(3)(-) as counterion. Similarly to III, compound IV, which was obtained by reacting 4 with IBr, can be considered as formed by [(C(5)H(10)N(2)Se-)(2)Br](+) cations and IBr(2)(-) anions. As in II, compound V has been prepared by reduction of the hypervalent selenium compound of 3 (6) bearing two I-Se-I groups with elemental tellurium. In V, the [(C(5)H(7)N(2)Se-)(2)](2+) cation is balanced by I(3)(-) and half I(4)(2-) anions. The structural data show that all the cations are very similar, with Se-Se bond lengths ranging from 2.409(2) to 2.440(2) Å. FT-IR and FT-Raman spectra of I-VI allow one to identify two bands around 230 +/- 10 and 193 +/- 5 cm(-1) that are common to all compounds. These bands are generally strong in the FT-Raman and weak in the FT-IR spectra and should contain a contribution of the nu(Se-Se) stretching vibration. The spectra are also in good agreement with the structural features of the polyhalide anions present in the crystals. Crystallographic data are as follows: I is monoclinic, space group P2(1), with a = 9.849(6) Å, b = 11.298(5) Å, c = 7.862(6) Å, beta = 106.44(2) degrees, Z = 2, and R = 0.0362; II is monoclinic, space group P2(1), with a = 8.063(6) Å, b = 11.535(5) Å, c = 10.280(5) Å, beta = 107.13(2) degrees, Z = 2, and R = 0.0429, III is monoclinic, space group P2(1)/n, with a = 10.431(7) Å, b = 18.073(5) Å, c = 11.223(6) Å, beta = 100.76(2) degrees, Z = 4, and R = 0.0490; IV is monoclinic, space group P2(1)/n, with a = 10.298(5) Å, b = 18.428(7) Å, c = 11.475(6) Å, beta = 104.10(4) degrees, Z = 4, and R = 0.0300; V is triclinic, space group P&onemacr;, with a = 7.456(6) Å, b = 11.988(5) Å, c = 12.508(5) Å, alpha = 79.32(2) degrees, beta = 85.49(2) degrees, gamma = 80.62(2) degrees, Z = 2, and R = 0.0340.

First ICN Adduct with a Selenium Donor (R = Se): Is It an Ionic [RSeCN]+I− or a “T‐Shaped” R(I)SeCN Hypervalent Compound?

“…[11] DFT calculations have greatly enabled deeper insight into the nature of the chemical bond in some CT and tbp adducts between halogens or inter-halogens and some S-or Se-donors, including 2. [11,12] In particular, for 2·I 2 , [12] 2·Br 2 , [12] and 2·IBr, [11] the calculated geometries of the organic frameworks are in very good agreement with the experimental data for 2·I 2 , [7] 3·2I 2 , [7] 3·2Br 2 , [14] and 3·2IBr, [11] though in general the SeϪX bond lengths were slightly overestimated. Hence, we performed calculations at the same level of theory on 2·ICN (both in the tbp and in the CT type arrangements), on the dimer (2·ICN) 2 and on the [2·CN] ϩ cation.…”

Recent Advances in the Field of Main‐Group Mono‐ and Diatomic “Allotropes” Stabilised by Neutral Ligands

“…We consider this an unlikely achievement, and an examination of the electronic structure of the crystallographically characterised [NHC-Se-Se-NHC] 2 + (27) suggests why. [51] The LUMO for this tailor-made precursor is a s-symmetric antibonding orbital associated with the Ch À Ch bond-reduction would simply lead to cleavage and formation of two neutral chalcoureas (e.g., selenourea 28), a well-established class of compound. Canonically, these can be represented with an NHC!Ch bonding situation, and thus be considered "molecular allotropes".…”

Complexes of Bidentate Phosphane Selenide Ligands with Mesitylenetellurenyl Iodide and with Tellurium Diiodide

“…In a previous paper we described the self-assembly of iodophosphane selenides RRЈP(=Se)I as bifunctional donor-acceptor molecules (selenium donor, iodine acceptor). [8] The bifunctional selenocarbonyl ligand 1,2-bis(3-methyl-4-imidazolin-2-selone)ethane was recently shown to undergo Br 2 [13] and IBr [14] oxidative addition at the Se atom of the ϾC=Se group, exhibiting a subtle interplay of soft-soft and hydrogen-bonding interactions in the solid.…”