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''''Neon compounds''' are [[chemical compound]]s containing the [[chemical element|element]] [[neon]] (Ne) with other [[molecules]] or elements from the [[periodic table]]. Compounds of the [[noble gas]] neon were believed not to exist, but there are now known to be [[molecular ion]]s containing [[neon]], as well as temporary excited neon-containing molecules called [[excimer]]s. Several neutral neon molecules have also been predicted to be stable, but are yet to be discovered in nature. Neon has been shown to crystallize with other substances and form [[clathrate]]s or [[Van der Waals molecule|Van der Waals solid]]s. Neon has a high first ionization potential of 21.564 eV, which is only exceeded by that of helium (24.587&nbsp;eV), requiring too much energy to make stable ionic compounds. Neon's polarisability of 0.395&nbsp;ų is the second lowest of any element (only helium's is more extreme). Low polarisability means there will be little tendency to link to other atoms.<ref>{{cite journal|last1=Frenking|first1=Gernot|last2=Cremer|first2=Dieter|title=The chemistry of the noble gas elements helium, neon, and argon — Experimental facts and theoretical predictions|journal=Structure and Bonding|date=1 March 2005|volume=73|issue=Noble Gas and High Temperature Chemistry|pages=17–95|doi=10.1007/3-540-52124-0_2}}</ref> Neon has a Lewis basicity or proton affinity of 2.06&nbsp;eV.<ref name=gro>{{cite journal |last1=Grochala |first1=Wojciech |title=On the position of helium and neon in the Periodic Table of Elements |journal=Foundations of Chemistry |volume=20 |issue=3 |pages=191–207 |date=1 November 2017 |doi=10.1007/s10698-017-9302-7}}</ref> ==Van der Waals molecules== Van der Waals molecules are those where neon is held onto other components by London dispersion forces. The forces are very weak, so the bonds will be disrupted if there is too much molecular vibration, which happens if the temperature is too high (above that of solid neon). Neon atoms themselves can be linked together to make clusters of atoms. The dimer Ne₂, trimer Ne₃ and neon tetramer Ne₄ have all been characterised by [[Coulomb explosion imaging]]. The molecules are made by an expanding supersonic jet of neon gas. The neon dimer has an average distance of 3.3&nbsp;Å between atoms. The neon trimer is shaped approximately like an equilateral triangle with sides 3.3&nbsp;Å long. However the shape is floppy and isosceles triangle shapes are also common. The first excited state of the neon trimer is 2&nbsp;meV above the ground state. The neon tetramer takes the form of a tetrahedron with sides around 3.2&nbsp;Å.<ref>{{cite journal|last1=Ulrich|first1=B.|last2=Vredenborg|first2=A.|last3=Malakzadeh|first3=A.|last4=Schmidt|first4=L. Ph. H.|last5=Havermeier|first5=T.|last6=Meckel|first6=M.|last7=Cole|first7=K.|last8=Smolarski|first8=M.|last9=Chang|first9=Z.|last10=Jahnke|first10=T.|last11=Dörner|first11=R.|title=Imaging of the Structure of the Argon and Neon Dimer, Trimer, and Tetramer|journal=The Journal of Physical Chemistry A|date=30 June 2011|volume=115|issue=25|pages=6936–6941|doi=10.1021/jp1121245|pmid=21413773|bibcode=2011JPCA..115.6936U}}</ref> Van der Waals molecules with metals include LiNe.<ref>{{cite thesis|last1=Lee|first1=Chang Jae|title=Rotationally Resolved Laser Spectroscopy of the 3s ²Σ⁺ → 2p ²Π Transition in Lithium-6 Neon and Lithium Neon Van Der Waals Molecules|type=Ph.D.|date=1 January 1991|bibcode=1991PhDT.......128L}}</ref> More Van der Waals molecules include CF₄Ne and CCl₄Ne, Ne₂Cl₂, Ne₃Cl₂,<ref>{{cite journal|last1=Hair|first1=Sally R.|last2=Cline|first2=Joseph I.|last3=Bieler|first3=Craig R.|last4=Janda|first4=Kenneth C.|title=The structure and dissociation dynamics of the Ne₂Cl₂ Van der Waals complex|journal=The Journal of Chemical Physics|date=1989|volume=90|issue=6|pages=2935|doi=10.1063/1.455893|bibcode=1989JChPh..90.2935H}}</ref> I₂Ne, I₂Ne₂, I₂Ne₃, I₂Ne₄, I₂Ne_xHe_y (x=1-5, y=1-4).<ref>{{cite journal|last1=Kenny|first1=Jonathan E.|last2=Johnson|first2=Kenneth E.|last3=Sharfin|first3=Wayne|last4=Levy|first4=Donald H.|title=The photodissociation of van der Waals molecules: Complexes of iodine, neon, and helium|journal=The Journal of Chemical Physics|date=1980|volume=72|issue=2|pages=1109|doi=10.1063/1.439252|bibcode=1980JChPh..72.1109K}}</ref> Van der Waals molecules formed with organic molecules in gas include [[aniline]],<ref>{{cite journal|last1=Becucci|first1=M.|last2=Pietraperzia|first2=G.|last3=Castellucci|first3=E.|last4=Bréchignac|first4=Ph.|title=Dynamics of vibronically excited states of the aniline–neon van der Waals complex: vibrational predissociation versus intramolecular vibrational redistribution|journal=Chemical Physics Letters|date=May 2004|volume=390|issue=1–3|pages=29–34|doi=10.1016/j.cplett.2004.03.138|bibcode=2004CPL...390...29B}}</ref> [[dimethyl ether]],<ref>{{cite journal|last1=Maris|first1=Assimo|last2=Caminati|first2=Walther|title=Rotational spectrum, dynamics, and bond energy of the floppy dimethylether⋯neon van der Waals complex|journal=The Journal of Chemical Physics|date=2003|volume=118|issue=4|pages=1649|doi=10.1063/1.1533012|bibcode=2003JChPh.118.1649M}}</ref> [[1,1-difluoroethylene]],<ref>{{cite journal|last1=Dell’Erba|first1=Adele|last2=Melandri|first2=Sonia|last3=Millemaggi|first3=Aldo|last4=Caminati|first4=Walther|last5=Favero|first5=Paolo G.|title=Rotational spectra and dynamics of the van der Waals adducts of neon and argon with 1,1-difluoroethylene|journal=The Journal of Chemical Physics|date=2000|volume=112|issue=5|pages=2204|doi=10.1063/1.480786|bibcode=2000JChPh.112.2204D}}</ref> [[pyrimidine]],<ref>{{cite journal|last1=Caminati|first1=Walther|last2=Favero|first2=Paolo G.|title=Chemistry at Low Pressure and Low Temperature: Rotational Spectrum and Dynamics of Pyrimidine-Neon|journal=Chemistry: A European Journal|date=1 February 1999|volume=5|issue=2|pages=811–814|doi=10.1002/(SICI)1521-3765(19990201)5:2<811::AID-CHEM811>3.0.CO;2-1}}</ref> [[chlorobenzene]],<ref>{{cite journal|last1=Oh|first1=Jung-Jin|last2=Park|first2=Inhee|last3=Peebles|first3=Sean A.|last4=Kuczkowski|first4=Robert L.|title=The rotational spectrum and structure of the chlorobenzene–neon van der Waals dimer|journal=Journal of Molecular Structure|date=December 2001|volume=599|issue=1–3|pages=15–22|doi=10.1016/S0022-2860(01)00833-X|bibcode=2001JMoSt.599...15O}}</ref> [[cyclopentanone]],<ref>{{cite document|last1=Lin|first1=Wei|title=Determination of the structure of the argon cyclopentanone and neon Van der Waals complexes|hdl=1811/49680}}</ref> [[cyanocyclobutane]],<ref>{{cite journal|last1=Pringle|first1=Wallace C.|last2=Frohman|first2=Daniel J.|last3=Ndugire|first3=William|last4=Novick|first4=Stewart E.|title=The FT Microwave Spectra and Structure of the Argon and Neon Van Der Waals Complexes of Cyanocyclobutane|date=1 June 2010|url=https://molspect.chemistry.ohio-state.edu/symposium_65/symposium/Program/TH.html#TH05}}</ref> and [[cyclopentadienyl]].<ref>{{cite journal|last1=Yu|first1=Lian|last2=Williamson|first2=James|last3=Foster|first3=Stephen C.|last4=Miller|first4=Terry A.|title=High resolution laser spectroscopy of free radical-inert gas complexes: C₅H₅·He, C₅H₅·He₂, C₅H₅·Ne, and CH₃–C₅H₄·He₂|journal=The Journal of Chemical Physics|date=1992|volume=97|issue=8|pages=5273|doi=10.1063/1.463788|bibcode=1992JChPh..97.5273Y}}</ref> ==Ligands== Neon can form a very weak bond to a transition metal atom as a [[ligand]], for example Cr(CO)₅Ne,<ref>{{cite journal|last1=Perutz|first1=Robin N.|last2=Turner|first2=James J.|title=Photochemistry of the Group 6 hexacarbonyls in low-temperature matrices. III. Interaction of the pentacarbonyls with noble gases and other matrices|journal=Journal of the American Chemical Society|date=August 1975|volume=97|issue=17|pages=4791–4800|doi=10.1021/ja00850a001}}</ref> Mo(CO)₅Ne, and W(CO)₅Ne.<ref name=zhangf/> NeNiCO is predicted to have a binding energy of 2.16&nbsp;kcal/mol. The presence of neon changes the bending frequency of Ni−C−O by 36&nbsp;cm⁻¹.<ref>{{cite journal|last1=Taketsugu|first1=Yuriko|last2=Noro|first2=Takeshi|last3=Taketsugu|first3=Tetsuya|title=Identification of the Matrix Shift: A Fingerprint for Neutral Neon Complex?|journal=The Journal of Physical Chemistry A|date=February 2008|volume=112|issue=5|pages=1018–1023|doi=10.1021/jp710792c|bibcode=2008JPCA..112.1018T}}</ref><ref>{{cite journal|last1=Manceron|first1=L|last2=Alikhani|first2=M.E|last3=Joly|first3=H.A|title=Infrared matrix isolation and DFT study of NiN₂|journal=Chemical Physics|date=March 1998|volume=228|issue=1–3|pages=73–80|doi=10.1016/S0301-0104(97)00339-X|bibcode=1998CP....228...73M}}</ref> NeAuF<ref name="neauf">{{cite journal|last1=Wang|first1=Xuefeng|last2=Andrews|first2=Lester|last3=Brosi|first3=Felix|last4=Riedel|first4=Sebastian|title=Matrix Infrared Spectroscopy and Quantum-Chemical Calculations for the Coinage-Metal Fluorides: Comparisons of Ar-AuF, Ne-AuF, and Molecules MF₂ and MF₃|journal=Chemistry: A European Journal|date=21 January 2013|volume=19|issue=4|pages=1397–1409|doi=10.1002/chem.201203306}}</ref> and NeBeS<ref name="nebes">{{cite journal|last1=Wang|first1=Qiang|last2=Wang|first2=Xuefeng|title=Infrared Spectra of NgBeS (Ng = Ne, Ar, Kr, Xe) and BeS₂ in Noble-Gas Matrices|journal=The Journal of Physical Chemistry A|date=21 February 2013|volume=117|issue=7|pages=1508–1513|doi=10.1021/jp311901a|pmid=23327099|bibcode=2013JPCA..117.1508W}}</ref> have been isolated in [[noble gas matrix]]es.<ref>{{cite journal|last1=Cappelletti|first1=David|last2=Bartocci|first2=Alessio|last3=Grandinetti|first3=Felice|last4=Falcinelli|first4=Stefano|last5=Belpassi|first5=Leonardo|last6=Tarantelli|first6=Francesco|last7=Pirani|first7=Fernando|title=Experimental Evidence of Chemical Components in the Bonding of Helium and Neon with Neutral Molecules|journal=Chemistry: A European Journal|date=13 April 2015|volume=21|issue=16|pages=6234–6240|doi=10.1002/chem.201406103|pmid=25755007}}</ref> NeBeCO₃ has been detected by infrared spectroscopy in a solid neon matrix. It was made from beryllium gas, dioxygen and carbon monoxide.<ref name=zhangf>{{cite journal|last1=Zhang|first1=Qingnan|last2=Chen|first2=Mohua|last3=Zhou|first3=Mingfei|last4=Andrada|first4=Diego M.|last5=Frenking|first5=Gernot|title=Experimental and Theoretical Studies of the Infrared Spectra and Bonding Properties of NgBeCO₃ and a Comparison with NgBeO (Ng = He, Ne, Ar, Kr, Xe)|journal=The Journal of Physical Chemistry A|date=19 March 2015|volume=119|issue=11|pages=2543–2552|doi=10.1021/jp509006u|pmid=25321412|bibcode=2015JPCA..119.2543Z}}</ref> The cyclic molecule Be₂O₂ can be made by evaporating Be with a laser with oxygen and an excess of inert gas. It coordinates two noble gas atoms and has had spectra measured in solid neon matrices. Known neon containing molecules are the homoleptic Ne.Be₂O₂.Ne, and heteroleptic Ne.Be₂O₂.Ar and Ne.Be₂O₂.Kr. The neon atoms are attracted to the beryllium atoms as they have a positive charge in this molecule.<ref>{{cite journal |last1=Zhang |first1=Qingnan |last2=Li |first2=Wan-Lu |last3=Zhao |first3=Lili |last4=Chen |first4=Mohua |last5=Zhou |first5=Mingfei |last6=Li |first6=Jun |last7=Frenking |first7=Gernot |title=A Very Short Be-Be Distance but No Bond: Synthesis and Bonding Analysis of Ng-Be2O2-Ng′ (Ng, Ng′=Ne, Ar, Kr, Xe) |journal=Chemistry - A European Journal |date=10 February 2017 |volume=23 |issue=9 |pages=2035–2039 |doi=10.1002/chem.201605994|pmid=28009065 }}</ref> Beryllium sulfite molecules BeO₂S, can also coordinate neon onto the beryllium atom. The dissociation energy for neon is 0.9 kcal/mol. When neon is added to the cyclic molecule, the ∠O-Be-O decreases and the O-Be bond lengths increase.<ref>{{cite journal |last1=Yu |first1=Wenjie |last2=Liu |first2=Xing |last3=Xu |first3=Bing |last4=Xing |first4=Xiaopeng |last5=Wang |first5=Xuefeng |title=Infrared Spectra of Novel NgBeSO2 Complexes (Ng = Ne, Ar, Kr, Xe) in Low Temperature Matrixes |journal=The Journal of Physical Chemistry A |date=21 October 2016 |volume=120 |issue=43 |pages=8590–8598 |doi=10.1021/acs.jpca.6b08799|pmid=27723974 }}</ref> ==Solids== High pressure Van der Waals solids include (N₂)₆Ne₇.<ref>{{cite journal|last1=Plisson|first1=Thomas|last2=Weck|first2=Gunnar|last3=Loubeyre|first3=Paul|title=A High Pressure van der Waals Insertion Compound|journal=Physical Review Letters|date=11 July 2014|volume=113|issue=2|page=025702|doi=10.1103/PhysRevLett.113.025702|bibcode=2014PhRvL.113b5702P|pmid=25062210}}</ref> pp '''Neon hydrate''' or '''neon clathrate''', a [[clathrate]], can form in [[ice II]] at 480&nbsp;MPa pressure between 70&nbsp;K and 260&nbsp;K.<ref name=teer>{{cite journal|last1=Teeratchanan|first1=Pattanasak|last2=Hermann|first2=Andreas|title=Computational phase diagrams of noble gas hydrates under pressure|journal=The Journal of Chemical Physics|date=21 October 2015|volume=143|issue=15|pages=154507|doi=10.1063/1.4933371|pmid=26493915|bibcode=2015JChPh.143o4507T|url=https://www.pure.ed.ac.uk/ws/files/21882419/JChemPhys_143_154507_2015.pdf}}<!--https://www.pure.ed.ac.uk/ws/files/21882419/JChemPhys_143_154507_2015.pdf}}--></ref> Other neon hydrates are also predicted resembling [[hydrogen clathrate]], and those clathrates of [[Helium compounds#Clathrate|helium]]. These include the C₀, ice I_''h'' and ice I_''c'' forms.<ref name=teer/> Neon atoms can be trapped inside my butthole.[[fullerenes]] such as [[Buckminsterfullerene|C₆₀]] and [[C70 fullerene|C₇₀]]. The isotope [[Neon-22|²²Ne]] is strongly enriched in [[carbonaceous chondrite]] meteorites, by more than 1,000 times its occurrence on Earth. This neon is given off when a meteorite is heated.<ref>{{cite journal|last1=Jungck|first1=M. H. A.|last2=Eberhardt|first2=P.|title=Neon-E in Orgueil Density Separates|journal=Meteoritics|date=1979|volume=14|pages=439–440|bibcode=1979Metic..14R.439J}}</ref> An explanation for this is that originally when carbon was condensing from the aftermath of a supernova explosion, cages of carbon form that preferentially trap sodium atoms, including ²²Na. Forming fullerenes trap sodium orders of magnitude more often than neon, so Na@C₆₀ is formed. rather than the more common ²⁰Ne@C₆₀. The ²²Na@C₆₀ then decays radioactively to ²²Ne@C₆₀, without any other neon isotopes.<ref>{{cite journal|last1=Dunk|first1=P. W.|last2=Adjizian|first2=J.-J.|last3=Kaiser|first3=N. K.|last4=Quinn|first4=J. P.|last5=Blakney|first5=G. T.|last6=Ewels|first6=C. P.|last7=Marshall|first7=A. G.|last8=Kroto|first8=H. W.|title=Metallofullerene and fullerene formation from condensing carbon gas under conditions of stellar outflows and implication to stardust|journal=Proceedings of the National Academy of Sciences|date=21 October 2013|volume=110|issue=45|pages=18081–18086|doi=10.1073/pnas.1315928110|pmid=24145444|pmc=3831496|bibcode=2013PNAS..11018081D}}</ref> To make buckyballs with neon inside, buckminsterfullerene can be heated to 600&nbsp;°C with neon under pressure. With three atmospheres for one hour, about 1 in 8,500,000 molecules end up with Ne@C₆₀. The concentration inside the buckyballs is about the same as in the surrounding gas. This neon comes back out when heated to 900&nbsp;°C.<ref>{{cite journal|last1=Saunders|first1=M.|last2=Jimenez-Vazquez|first2=H. A.|last3=Cross|first3=R. J.|last4=Poreda|first4=R. J.|title=Stable Compounds of Helium and Neon: He@C₆₀ and Ne@C₆₀|journal=Science|date=5 March 1993|volume=259|issue=5100|pages=1428–1430|doi=10.1126/science.259.5100.1428|pmid=17801275|bibcode=1993Sci...259.1428S}}</ref> [[Dodecahedrane]] can trap neon from a neon ion beam to yield Ne@C₂₀H₂₀.<ref>{{cite journal |last1=Jiménez-Vázquez |first1=Hugo A. |last2=Tamariz |first2=Joaquín |last3=Cross |first3=R. James |title=Binding Energy in and Equilibrium Constant of Formation for the Dodecahedrane Compounds He@C12H12 and Ne@C12H12 |journal=The Journal of Physical Chemistry A |date=March 2001 |volume=105 |issue=8 |pages=1315–1319 |doi=10.1021/jp0027243}}</ref> Neon also forms an intercalation compound (or alloy) with fullerenes like C₆₀. In this the Ne atom is not inside the ball, but packs into the spaces in a crystal made from the balls. It intercalates under pressure, but is unstable at standard conditions, and degases in under 24 hours.<ref>{{cite journal |last1=Schirber |first1=J. E. |last2=Kwei |first2=G. H. |last3=Jorgensen |first3=J. D. |last4=Hitterman |first4=R. L. |last5=Morosin |first5=B. |title=Room-temperature compressibility of C60 : Intercalation effects with He, Ne, and Ar |journal=Physical Review B |date=1 May 1995 |volume=51 |issue=17 |pages=12014–12017 |doi=10.1103/PhysRevB.51.12014|pmid=9977961 }}</ref> However at low temperatures Ne•C₆₀ is stable.<ref>{{cite journal |last1=Aleksandrovskii |first1=A. N. |last2=Gavrilko |first2=V. G. |last3=Esel’son |first3=V. B. |last4=Manzhelii |first4=V. G. |last5=Udovidchenko |first5=B. G. |last6=Maletskiy |first6=V. P. |last7=Sundqvist |first7=B. |title=Low-temperature thermal expansion of fullerite C60 alloyed with argon and neon |journal=Low Temperature Physics |date=December 2001 |volume=27 |issue=12 |pages=1033–1036 |doi=10.1063/1.1430848|url=http://dspace.nbuv.gov.ua/handle/123456789/129143}}<!--http://dspace.nbuv.gov.ua/handle/123456789/129143 }}--></ref> Neon can be trapped inside some [[metal-organic framework]] compounds. In [[NiMOF-74]] neon can be absorbed at 100&nbsp;K at pressures up to 100&nbsp;bars, and shows hysteresis, being retained till lower pressures. The pores easily take up six atoms per unit cell, as a hexagonal arrangement in the pores, with each neon atom close to a nickel atom. A seventh neon atom can be forced under pressure at the centre of the neon hexagons.<ref>{{cite journal|last1=Wood|first1=Peter A.|last2=Sarjeant|first2=Amy A.|last3=Yakovenko|first3=Andrey A.|last4=Ward|first4=Suzanna C.|last5=Groom|first5=Colin R.|title=Capturing neon – the first experimental structure of neon trapped within a metal–organic environment|journal=Chem. Commun.|date=2016|volume=52|issue=65|pages=10048–10051|doi=10.1039/C6CC04808K|pmid=27452474}}</ref> Neon is pushed into crystals of [[ammonium iron formate]] (NH₄Fe(HCOO)₃) and [[ammonium nickel formate]] (NH₄Ni(HCOO)₃) at 1.5&nbsp;GPa to yield Ne•NH₄Fe(HCOO)₃ and Ne•NH₄Ni(HCOO)₃. The neon atoms become trapped in a cage of five metal triformate units. The windows in the cages are blocked by ammonium ions. Argon does not undergo this, probably as its atoms are too big.<ref>{{cite journal |last1=Collings |first1=Ines E. |last2=Bykova |first2=Elena |last3=Bykov |first3=Maxim |last4=Petitgirard |first4=Sylvain |last5=Hanfland |first5=Michael |last6=Paliwoda |first6=Damian |last7=Dubrovinsky |first7=Leonid |last8=Dubrovinskaia |first8=Natalia |title=Neon-Bearing Ammonium Metal Formates: Formation and Behaviour under Pressure |journal=ChemPhysChem |date=4 November 2016 |volume=17 |issue=21 |pages=3369–3372 |doi=10.1002/cphc.201600854|pmid=27500946 }}</ref> Neon can penetrate TON [[zeolite]] under pressure. Each unit cell contains up to 12 neon atoms in the ''Cmc''2₁ structure below 600 MPa. This is double the number of argon atoms that can be inserted into that zeolite. At 270&nbsp;MPa occupancy is around 20% Over 600&nbsp;MPa this neon penetrated phase transforms to a ''Pbn''2₁ structure, which can be brought back to zero pressure. However all the neon escapes as it is depressurized.<ref name=thib>{{cite journal |last1=Thibaud |first1=Jean-Marc |last2=Rouquette |first2=Jérôme |last3=Dziubek |first3=Kamil |last4=Gorelli |first4=Federico A. |last5=Santoro |first5=Mario |last6=Garbarino |first6=Gaston |last7=Clément |first7=Sébastien |last8=Cambon |first8=Olivier |last9=van der Lee |first9=Arie |last10=Di Renzo |first10=Francesco |last11=Coasne |first11=Benoît |last12=Haines |first12=Julien |title=Saturation of the Siliceous Zeolite TON with Neon at High Pressure |journal=The Journal of Physical Chemistry C |date=3 April 2018 |volume=122 |issue=15 |pages=8455–8460 |doi=10.1021/acs.jpcc.8b01827}}</ref> Neon causes the zeolite to remain crystalline, otherwise at pressure of 20&nbsp;GPa it would have collapsed and become amorphous.<ref name=thib/> [[Silica glass]] also absorbs neon under pressure. At 4&nbsp;GPa there are 7 atoms of neon per nm³.<ref name=thib/> ==Ions== Ionic molecules can include neon, such as the clusters {{chem|Ne|''m''|He|''n''|+}} where ''m'' goes from 1 to 7 and ''n'' from 1 to over 20.<ref>{{cite journal|last1=Bartl|first1=Peter|last2=Denifl|first2=Stephan|last3=Scheier|first3=Paul|last4=Echt|first4=Olof|title=On the stability of cationic complexes of neon with helium – solving an experimental discrepancy|journal=Physical Chemistry Chemical Physics|date=2013|volume=15|issue=39|pages=16599–604|doi=10.1039/C3CP52550C|pmid=23958826|bibcode=2013PCCP...1516599B}}</ref> HeNe⁺ (helium neide) has a relatively strong covalent bond. The charge is distributed across both atoms.<ref>{{cite journal|last1=Bieske|first1=E. J.|last2=Soliva|first2=A. M.|last3=Friedmann|first3=A.|last4=Maier|first4=J. P.|title=Photoinitiated charge transfer in N2O+–Ar|journal=The Journal of Chemical Physics|date=1992|volume=96|issue=10|pages=7535|doi=10.1063/1.462405|bibcode=1992JChPh..96.7535B}}</ref> When metals are evaporated into a thin gas of hydrogen and neon in a strong electric field, ions are formed that are called '''neides'''. Ions observed include TiNe⁺, TiH₂Ne⁺, ZnNe²⁺, ZrNe²⁺, NbNe²⁺, NbHNe²⁺, MoNe²⁺, RhNe²⁺, PdNe⁺, TaNe³⁺, WNe²⁺, WNe³⁺, ReNe³⁺, IrNe²⁺, AuNe⁺ (possible).<ref>{{cite journal|last1=Kapur|first1=Shukla|last2=Müller|first2=Erwin W.|title=Metal–neon compound ions in slow field evaporation|journal=Surface Science|date=February 1977|volume=62|issue=2|pages=610–620|doi=10.1016/0039-6028(77)90104-2|bibcode=1977SurSc..62..610K}}</ref> SiF₂Ne²⁺ can be made from neon and {{chem|SiF|3|2+}} using mass spectrometer technology. SiF₂Ne²⁺ has a bond from neon to silicon. {{chem|SiF|3|2+}} has a very weak bond to fluorine and a high electron affinity.<ref>{{cite journal|last1=Roithová|first1=Jana|last2=Schröder|first2=Detlef|title=Silicon Compounds of Neon and Argon|journal=Angewandte Chemie International Edition|date=2 November 2009|volume=48|issue=46|pages=8788–8790|doi=10.1002/anie.200903706}}</ref> NeCCH⁺, a substituted acetylene, is predicted to be energetically stable by 5.9&nbsp;kcal/mol, one of the most stable organic ions.<ref>{{cite journal|last1=Frenking|first1=Gernot|last2=Koch|first2=Wolfram|last3=Reichel|first3=Felix|last4=Cremer|first4=Dieter|title=Light noble gas chemistry: structures, stabilities, and bonding of helium, neon, and argon compounds|journal=Journal of the American Chemical Society|date=May 1990|volume=112|issue=11|pages=4240–4256|doi=10.1021/ja00167a020}}</ref> ===Ionic clusters=== Metal ions can attract multiple neon atoms to form clusters. The shape of the cluster molecules is determined by repulsion between neon atoms and d-orbital electrons from the metal atom. For copper, neonides are known with numbers of neon atoms up to 24, Cu⁺Ne_1-24. Cu⁺Ne₄ and Cu⁺Ne₁₂ have much greater numbers than those with higher number of neon atoms. Cu⁺Ne₂ is predicted to be linear. Cu⁺Ne₃ is predicted to be planar T shaped with an Ne-Cu-Ne angle of 91°. Cu⁺Ne₄ is predicted to be square planar (not tetrahedral) with D_4h symmetry. For alkali and alkaline earth metals the M⁺Ne₄ cluster is tetrahedral. Cu⁺Ne₅ is predicted to have a square pyramid shape. Cu⁺Ne₆ has a seriously distorted octahedral shape. Cu⁺Ne₁₂ has an icosahedral shape. Anything beyond that is less stable, with extra neon atoms having to make an extra shell of atoms around an icosahedral core.<ref name="Frou">{{cite journal|last1=Froudakis|first1=George E.|last2=Muhlhauser|first2=Max|last3=Farantos|first3=Stavros C.|last4=Sfounis|first4=Antonis|last5=Velegrakis|first5=Michalis|title=Mass spectra and structures of Cu+Rgn clusters (Rg=Ne, Ar)|journal=Chemical Physics|date=June 2002|volume=280|issue=1–2|pages=43–51|doi=10.1016/S0301-0104(02)00512-8|bibcode=2002CP....280...43F}}</ref> ==Neonium== The ion NeH⁺ formed by protonating neon, is called neonium. It is produced in an AC electric discharge through a mixture of neon and hydrogen with more produced when neon outnumbers hydrogen molecules by 36:1.<ref name="mats"/> The dipole moment is 3.004&nbsp;D.<ref name="mats">{{cite journal|last1=Matsushima|first1=Fusakazu|last2=Ohtaki|first2=Yuichiro|last3=Torige|first3=Osamu|last4=Takagi|first4=Kojiro|title=Rotational spectra of [sup 20]NeH[sup +], [sup 20]NeD[sup +], [sup 22]NeH[sup +], and [sup 22]NeD[sup +]|journal=The Journal of Chemical Physics|date=1998|volume=109|issue=6|pages=2242|doi=10.1063/1.476791|bibcode=1998JChPh.109.2242M}}</ref> Neonium is also formed by excited [[dihydrogen cation]] reacting with neon: Ne + H₂^+* → NeH⁺ + H<ref>{{cite journal|doi=10.1039/F29726800259|title=Ion-Molecule Reactions of the Rare Gases with Hydrogen Part 1.-Diatomics-in-Molecules Potential Energy Surface for ArH2+|authors=P. J. Kuntz AND A. C. Roach|volume=68|journal=J. Chem. Soc., Faraday Trans. 2|pages=259–280|year=1972}}</ref> {|class="wikitable" |colspan=2|Far infrared spectrum of ²⁰Ne¹H⁺<ref name="mats"/> |²⁰NeD⁺ |²²NeH⁺ |²²NeD⁺ |- !Transition !colspan=4|observed frequency |- !J !colspan=4|GHz |- |1←0 |1 039.255 | | | |- |2←1 |2 076.573 | |2 067.667 | |- |3←2 |3 110.022 |1 647.026 |3 096.706 | |- |4←3 |4 137.673 |2 193.549 |4 119.997 |2 175.551 |- |5←4 |5 157.607 |2 737.943 | |2 715.512 |- |6←5 | |3 279.679 | |3 252.860 |- |7←6 | |3 818.232 | |3 787.075 |- |8←7 | |4 353.075 | |4 317.643 |- |9←8 | |4 883.686 | | |} The infrared spectrum around 3μm has also been measured.<ref>{{cite journal|last1=Wong|first1=M.|title=Observation of the infrared absorption spectra of 20NeH+ and 22NeH+ with a difference frequency laser|journal=The Journal of Chemical Physics|date=1982|volume=77|issue=2|pages=693–696|doi=10.1063/1.443883|bibcode=1982JChPh..77..693W}}</ref> ==Excimers== The {{chem|Ne|2|*}} molecule exists in an excited state in an [[excimer lamp]] using a microhollow cathode. This emits strongly in the [[vacuum ultraviolet]] between 75 and 90&nbsp;nm with a peak at 83&nbsp;nm. There is a problem in that there is no window material suitable to transmit these short wavelengths, so it must be used in a vacuum. If about one part in a thousand of hydrogen gas is included, most of the {{chem|Ne|2|*}} energy is transferred to hydrogen atoms and there is a strong monochromatic [[Lyman alpha]] emission at 121.567&nbsp;nm.<ref>{{cite journal|last1=Kogelschatz|first1=Ulrich|title=Excimer lamps: history, discharge physics, and industrial applications|journal=Proc. SPIE|date=3 May 2004|volume=5483|issue=Atomic and Molecular Pulsed Lasers V|page=272|doi=10.1117/12.563006|series=SPIE Proceedings|bibcode=2004SPIE.5483..272K}}</ref> Cesium can form excimer molecules with neon CsNe^*.<ref>{{cite journal|last1=Novak|first1=R.|last2=Bhaskar|first2=N. D.|last3=Happer|first3=W.|title=Infrared emission bands from transitions between excited states of cesium–noble gas molecules|journal=The Journal of Chemical Physics|date=1979|volume=71|issue=10|pages=4052|doi=10.1063/1.438174|bibcode=1979JChPh..71.4052N}}</ref> A hydrogen-neon [[excimer]] is known to exist. Fluorescence was observed by Möller due to bound free transition in a Rydberg molecule of NeH^*. NeH is metastable and its existence was proved by mass spectroscopy in which the NeH⁺ ion is neutralized and then reionized.<ref name=parker>{{cite journal|title=Electron Propagator Calculations on the Discrete Spectra OF ArH AND NeH|authors=Eric P. Parker and J.V. Ortiz|journal=Chemical Physics Letters|volume=163|issue=4|date=17 November 1989|pages=366–370|bibcode=1989CPL...163..366P|doi=10.1016/0009-2614(89)85151-6}}</ref> The spectrum of NeH includes lines at 1.81, 1.60 and I .46&nbsp;eV, with a small band at 1.57&nbsp;eV<ref>{{cite journal|last1=Ketterle|first1=W.|last2=Walther|first2=H.|title=A discrete spectrum of neon hydride|journal=Chemical Physics Letters|date=May 1988|volume=146|issue=3–4|pages=180–183|doi=10.1016/0009-2614(88)87427-X|bibcode=1988CPL...146..180K}}</ref> The bondlength in NeH is calculated as 1.003&nbsp;Å.<ref name=parker/> A helium neon excimer can be found in a mixed plasma or helium and neon.<ref>{{cite journal|last1=Tanaka|first1=Y.|title=Absorption Spectra of Ne₂ and HeNe Molecules in the Vacuum-UV Region|journal=The Journal of Chemical Physics|date=1972|volume=57|issue=7|pages=2964–2976|doi=10.1063/1.1678691|bibcode=1972JChPh..57.2964T}}</ref> Some other excimers can be found in solid neon, including {{chem|Ne|2|+|O|−}} which has a luminescence peaking around 11.65&nbsp;eV, or {{chem|Ne|2|+|F|−}} luminescing around 10.16–10.37&nbsp;eV and 8.55&nbsp;eV.<ref>{{cite journal|last1=Belov|first1=A. G.|last2=Fugol|first2=I. Ya.|last3=Yurtaeva|first3=E. M.|last4=Bazhan|first4=O. V.|title=Luminescence of oxygen–rare gas exciplex compounds in rare gas matrices|journal=Journal of Luminescence|date=1 September 2000|volume=91|issue=1–2|pages=107–120|doi=10.1016/S0022-2313(99)00623-7|bibcode=2000JLum...91..107B}}</ref> ==Minerals== Bokiy's crystallochemical classification of minerals included "compounds of neon" as type 82. However, no such minerals were known.<ref>{{cite book|last1=Bokiy|first1=G. B.|editor1-last=Marfunin|editor1-first=Arnold S.|title=Advanced Mineralogy: Volume 1 Composition, Structure, and Properties of mineral Matter Concepts, Results, and Problems|date=1994|publisher=Springer Science & Business Media|page=155|url=https://books.google.com/?id=6PHvCAAAQBAJ&pg=PA155|isbn=978-3-642-78525-2}}</ref> ==Predicted compounds== Analogously to the known ArBeO and the predicted HeBeO (beryllium oxide noble gas adducts), NeBeO is expected to exist, albeit with a very weak bond dissociation energy of 9&nbsp;kJ/mol. The bond is enhanced by a dipole-induced positive charge on beryllium, and a vacancy in the σ orbital on beryllium where it faces the neon.<ref name=Kobayashi12>{{cite journal|last1=Kobayashi|first1=Takanori|last2=Kohno|first2=Yuji|last3=Takayanagi|first3=Toshiyuki|last4=Seki|first4=Kanekazu|last5=Ueda|first5=Kazuyoshi|title=Rare gas bond property of Rg–Be2O2 and Rg–Be2O2–Rg (Rg=He, Ne, Ar, Kr and Xe) as a comparison with Rg–BeO|journal=Computational and Theoretical Chemistry|date=July 2012|volume=991|pages=48–55|doi=10.1016/j.comptc.2012.03.020}}</ref> ==References== {{Reflist|30em}} {{Noble gas compounds}} [[Category:Neon compounds| ]]'