Event

Current Topics in Noble-Gas Chemistry; from Xenon(II) Oxide Species to

Coordination Compounds of KrF2, XeF6, and XeO3

-Several representative topics in contemporary synthetic and structural noble-gas chemistry will be presented in this seminar:

            The [XeOXeOXe]2+ cation has been synthesized as its [µ-F(ReO2F3)2]– salt by reaction of ReO3F with XeF2 in anhydrous hydrogen fluoride (aHF) solvent at –30 oC [1]. The cation provides the first example of a binary Xe(II) oxide species and a structurally characterized noble-gas dication. The crystal structure of [XeOXeOXe][µ-F(ReO2F3)2]2 consists of a planar, zig-zag-shaped [XeOXeOXe]2+ cation (C2h) that is fluorine bridged through its terminal Xe atoms to two [µ-F(ReO2F3)2]– anions. The [XeOXe]2+ dication was synthesized as its CH3CN adduct-cation, [CH3CNXeOXeNCCH3]2+, by reaction of [FXeOXe---FXeF][AsF6] with CH3CN in aHF and was also structurally characterized [2].

            Acetonitrile and the aggressive oxidative fluorinator, XeF6, react at −40 oC in Freon-114 to form the highly endothermic and shock-sensitive F6XeNCCH3 and F6Xe(NCCH3)2·CH3CN adducts, which provide the first examples of XeVI–N bonds [3]. Their low-temperature (LT) X-ray structures show the XeF6 moieties have local C3v and C2v symmetries, respectively, with a stereo-active Xe valence electron lone pair.

            Many examples of XeF2 molecules coordinated to s- and d-block cations have been structurally characterized, but the coordination chemistry of the potent oxidative fluorinating agent, KrF2, was, until recently, nonexistent. Among the fluorine-coordinated KrF2 adducts that have been synthesized and structurally characterized are [F2OBr(KrF2)2(AsF6)], [4] [Mg(KrF2)4(AsF6)2], [5] F4OMFKrF (M = Cr, Mo, or W), F4OCrFKrFCrOF4, [6] and a series of Hg2+ salts in which as many as eight KrF2 molecules are homoleptically coordinated to Hg2+, e.g., [Hg(KrF2)8][AsF6]2 [7]. Most of these complexes were synthesized at low temperatures in aHF.

            The reaction of KrF2 with [XeF][AsF6] in aHF has yielded the [FXeFKrF]+ cation at low temperatures. The mixed Kr/Xe cation is isovalent with the known and structurally characterized [F(XeF)2]+ and [F(KrF)2]+ cations. The [FXeFKrF][AsF6] salt undergoes redox decomposition at  –40 oC to form XeF4, Kr, and AsF5. The reactions of [XeF5][AsF6] with KrF2 yielded the adduct-cation salts [F5XeFKrF][AsF6] and [F5Xe(FKrF)2][AsF6]. The [FXeFXeF]+, [F5XeFKrF]+, and [F5Xe(FKrF)2]+ cations are presently the only examples of isolable mixed noble-gas species.

            Xenon trioxide, a potent shock-sensitive detonator, exhibits Lewis acid properties towards halide ions. The structures of the cage anions in [N(C2H5)4]3[X3(XeO3)3]∙2CH3CN and [N(CH3)4]4[X4(XeO3)4]  (X = Cl, Br) have been obtained [8]. They provide the first examples of isolable compounds with stable Xe–Br bonds and are room-temperature stable and shock insensitive. Adduct formation between XeO3 and a variety of nitrogen [9] and oxygen [10] donors will also be briefly described. One of the most notable examples is the room-temperature stable 15-crown-5 adduct of XeO3, (CH2CH2O)5XeO3 [11]. The well-isolated XeO3 molecule in this complex is symmetrically coordinated to the five oxygen atoms of the crown ether.

Selected References:

(1)   Ivanova, Mercier, Schrobilgen, J. Am. Chem. Soc. 2015, 137, 13398-13413. 

(2)   DeBackere, Bortolus, Schrobilgen, Angew. Chem. Intl. Ed. 2016, 55, 11917–11920; VIP.

(3)   Matsumoto, Haner, Mercier, Schrobilgen,  Angew. Chem. Intl. Ed. 2015, 54, 14169–14173; VIP.

(4)   Brock, Casalis de Pury, Mercier, Schrobilgen, Silvi, J. Am. Chem. Soc. 2010, 132, 3533–3542.

(5)   Lozinšek, Mercier, Schrobilgen, Žemva, Angew. Chem. Intl. Ed. 2017, 56, 6251–6254; Hot Paper.

(6)   Mercier, Breddemann, Brock, Bortolus, Schrobilgen, Chem. Eur. J. 2019, 25, 12105–12119.

(7)   DeBackere, Schrobilgen, Angew. Chem. Intl. Ed. 2018, 57, 13167–13171.

(8)   Goettel, Haensch, Schrobilgen, J. Am. Chem. Soc. 2017, 139, 8725–8733.

(9)   Goettel, Matsumoto, Mercier, Schrobilgen  Angew. Chem. Intl. Ed. 2016, 55, 13780–13783, VIP

(10) Marczenko, Goettel, Mercier, Schrobilgen, Chem. Eur. J. 2019, 25, 12357–12366, VIP.

(11) Marczenko, Mercier,