Noble-Gas Chemistry More than Half a Century after the First Report of the Noble-Gas Compound

Recent development in the synthesis and characterization of noble-gas compounds is reviewed, i.e., noble-gas chemistry reported in the last five years with emphasis on the publications issued after 2017. XeF(2) is commercially available and has a wider practical application both in the laboratory use and in the industry. As a ligand it can coordinate to metal centers resulting in [M(XeF(2))(x)](n+) salts. With strong Lewis acids, XeF(2) acts as a fluoride ion donor forming [XeF](+) or [Xe(2)F(3)](+) salts. Latest examples are [Xe(2)F(3)][RuF(6)]·XeF(2), [Xe(2)F(3)][RuF(6)] and [Xe(2)F(3)][IrF(6)]. Adducts NgF(2)·CrOF(4) and NgF(2)·2CrOF(4) (Ng = Xe, Kr) were synthesized and structurally characterized at low temperatures. The geometry of XeF(6) was studied in solid argon and neon matrices. Xenon hexafluoride is a well-known fluoride ion donor forming various [XeF(5)](+) and [Xe(2)F(11)](+) salts. A large number of crystal structures of previously known or new [XeF(5)](+) and [Xe(2)F(11)](+) salts were reported, i.e., [Xe(2)F(11)][SbF(6)], [XeF(5)][SbF(6)], [XeF(5)][Sb(2)F(11)], [XeF(5)][BF(4)], [XeF(5)][TiF(5)], [XeF(5)](5)[Ti(10)F(45)], [XeF(5)][Ti(3)F(13)], [XeF(5)](2)[MnF(6)], [XeF(5)][MnF(5)], [XeF(5)](4)[Mn(8)F(36)], [Xe(2)F(11)](2)[SnF(6)], [Xe(2)F(11)](2)[PbF(6)], [XeF(5)](4)[Sn(5)F(24)], [XeF(5)][Xe(2)F(11)][Cr(V)OF(5)]·2Cr(VI)OF(4), [XeF(5)](2)[Cr(IV)F(6)]·2Cr(VI)OF(4), [Xe(2)F(11)](2)[Cr(IV)F(6)], [XeF(5)](2)[Cr(V)(2)O(2)F(8)], [XeF(5)](2)[Cr(V)(2)O(2)F(8)]·2HF, [XeF(5)](2)[Cr(V)(2)O(2)F(8)]·2XeOF(4), A[XeF(5)][SbF(6)](2) (A = Rb, Cs), Cs[XeF(5)][Bi(x)Sb(1-x)F(6)](2) (x = ~0.37–0.39), NO(2)XeF(5)(SbF(6))(2), XeF(5)M(SbF(6))(3) (M = Ni, Mg, Zn, Co, Cu, Mn and Pd) and (XeF(5))(3)[Hg(HF)](2)(SbF(6))(7). Despite its extreme sensitivity, many new XeO(3) adducts were synthesized, i.e., the 15-crown adduct of XeO(3), adducts of XeO(3) with triphenylphosphine oxide, dimethylsulfoxide and pyridine-N-oxide, and adducts between XeO(3) and N-bases (pyridine and 4-dimethylaminopyridine). [Hg(KrF(2))(8)][AsF(6)](2)·2HF is a new example of a compound in which KrF(2) serves as a ligand. Numerous new charged species of noble gases were reported (ArCH(2)(+), ArOH(+), [ArB(3)O(4)](+), [ArB(3)O(5)](+), [ArB(4)O(6)](+), [ArB(5)O(7)](+), [B(12)(CN)(11)Ne](−)). Molecular ion HeH(+) was finally detected in interstellar space. The discoveries of Na(2)He and ArNi at high pressure were reported. Bonding motifs in noble-gas compounds are briefly commented on in the last paragraph of this review.