Neon compounds are chemical compounds containing the 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 ions containing neon, as well as temporary excited neon-containing molecules called excimers. 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 clathrates or Van der Waals solids.
Neon has a high first ionization potential of 21.564 eV, which is only exceeded by that of helium (24.587 eV), requiring too much energy to make stable ionic compounds. Neon's polarisability of 0.395 Å3 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. [1] Neon has a Lewis basicity or proton affinity of 2.06 eV. [2] Neon is theoretically less reactive than helium, making it the least reactive of all the elements. [3]
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 Å between atoms. The neon trimer is shaped approximately like an equilateral triangle with sides 3.3 Å long. However the shape is floppy and isosceles triangle shapes are also common. The first excited state of the neon trimer is 2 meV above the ground state. The neon tetramer takes the form of a tetrahedron with sides around 3.2 Å. [4]
Van der Waals molecules with metals include LiNe. [5]
More Van der Waals molecules include CF4Ne and CCl4Ne, Ne2Cl2, Ne3Cl2, [6] I2Ne, I2Ne2, I2Ne3, I2Ne4, I2NexHey (x=1-5, y=1-4). [7]
Van der Waals molecules formed with organic molecules in gas include aniline, [8] dimethyl ether, [9] 1,1-difluoroethylene, [10] pyrimidine, [11] chlorobenzene, [12] cyclopentanone, [13] cyanocyclobutane, [14] and cyclopentadienyl. [15]
Neon can form a very weak bond to a transition metal atom as a ligand, for example Cr(CO)5Ne, [16] Mo(CO)5Ne, and W(CO)5Ne. [17]
NeNiCO is predicted to have a binding energy of 2.16 kcal/mol. The presence of neon changes the bending frequency of Ni−C−O by 36 cm−1. [18] [19]
NeAuF [20] and NeBeS [21] have been isolated in noble gas matrixes. [22] NeBeCO3 has been detected by infrared spectroscopy in a solid neon matrix. It was made from beryllium gas, dioxygen and carbon monoxide. [17]
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. [23]
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. [24]
High pressure Van der Waals solids include (N2)6Ne7. [25]
Neon hydrate or neon clathrate, a clathrate, can form in ice II at 480 MPa pressure between 70 K and 260 K. [26] Other neon hydrates are also predicted resembling hydrogen clathrate, and those clathrates of helium. These include the C0, ice Ih and ice Ic forms. [26]
Neon atoms can be trapped inside fullerenes such as C60 and C70. The isotope 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. [27] 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. [28] To make buckyballs with neon inside, buckminsterfullerene can be heated to 600 °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 °C. [29]
Dodecahedrane can trap neon from a neon ion beam to yield Ne@C20H20. [30]
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. [31] However at low temperatures Ne•C60 is stable. [32]
Neon can be trapped inside some metal-organic framework compounds. In NiMOF-74 neon can be absorbed at 100 K at pressures up to 100 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. [33]
Neon is pushed into crystals of ammonium iron formate (NH4Fe(HCOO)3) and ammonium nickel formate (NH4Ni(HCOO)3) at 1.5 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. [34]
Neon can penetrate TON zeolite under pressure. Each unit cell contains up to 12 neon atoms in the Cmc21 structure below 600 MPa. This is double the number of argon atoms that can be inserted into that zeolite. At 270 MPa occupancy is around 20% Over 600 MPa this neon penetrated phase transforms to a Pbn21 structure, which can be brought back to zero pressure. However all the neon escapes as it is depressurized. [35] Neon causes the zeolite to remain crystalline, otherwise at pressure of 20 GPa it would have collapsed and become amorphous. [35]
Silica glass also absorbs neon under pressure. At 4 GPa there are 7 atoms of neon per nm3. [35]
Ionic molecules can include neon, such as the clusters Ne
mHe+
n where m goes from 1 to 7 and n from 1 to over 20. [36] HeNe+ (helium neonide cation) has a relatively strong covalent bond. The charge is distributed across both atoms. [37]
When metals are evaporated into a thin gas of hydrogen and neon in a strong electric field, ions are formed that are called neonides or neides. Ions observed include TiNe+, TiH2Ne+, ZnNe2+, ZrNe2+, NbNe2+, NbHNe2+, MoNe2+, RhNe2+, PdNe+, TaNe3+, WNe2+, WNe3+, ReNe3+, IrNe2+, AuNe+ (possible). [38]
SiF2Ne2+ can be made from neon and SiF2+
3 using mass spectrometer technology. SiF2Ne2+ has a bond from neon to silicon. SiF2+
3 has a very weak bond to fluorine and a high electron affinity. [39]
NeCCH+, a substituted acetylene, is predicted to be energetically stable by 5.9 kcal/mol, one of the most stable organic ions. [40]
A neon containing molecular anion was unknown for a long time. In 2020 the observation of the molecular anion [B12(CN)11Ne]− was reported. The vacant boron in the anions [B12(CN)11]− is very electrophilic and is able to bind the neon. [B12(CN)11Ne]− was found to be stable up to 50 K and lies significantly above the Ne condensation temperature of 25 K. This temperature is remarkably high and indicates a weak chemical interaction. [41]
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+Ne1-24. 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 D4h 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. [42]
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. [43] The dipole moment is 3.004 D. [43]
Neonium is also formed by excited dihydrogen cation reacting with neon: Ne + H2+* → NeH+ + H [44]
Far infrared spectrum of 20Ne1H+ [43] | 20NeD+ | 22NeH+ | 22NeD+ | |
Transition | observed frequency | |||
---|---|---|---|---|
J | 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. [45]
The 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 nm with a peak at 83 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 Ne*
2 energy is transferred to hydrogen atoms and there is a strong monochromatic Lyman alpha emission at 121.567 nm. [46]
Cesium can form excimer molecules with neon CsNe*. [47]
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. [48] The spectrum of NeH includes lines at 1.81, 1.60 and 1.46 eV, with a small band at 1.57 eV [49] The bondlength in NeH is calculated as 1.003 Å. [48]
A helium neon excimer can be found in a mixed plasma or helium and neon. [50]
Some other excimers can be found in solid neon, including Ne+
2O−
which has a luminescence peaking around 11.65 eV, or Ne+
2F−
luminescing around 10.16–10.37 eV and 8.55 eV. [51]
Bokiy's crystallochemical classification of minerals included "compounds of neon" as type 82. However, no such minerals were known. [52]
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 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. [53]
Diatomic molecules are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen or oxygen, then it is said to be homonuclear. Otherwise, if a diatomic molecule consists of two different atoms, such as carbon monoxide or nitric oxide, the molecule is said to be heteronuclear. The bond in a homonuclear diatomic molecule is non-polar.
Helium is a chemical element; it has symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements, and it does not have a melting point at standard pressures. It is the second-lightest and second most abundant element in the observable universe, after hydrogen. It is present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined. Its abundance is similar to this in both the Sun and Jupiter, because of the very high nuclear binding energy of helium-4, with respect to the next three elements after helium. This helium-4 binding energy also accounts for why it is a product of both nuclear fusion and radioactive decay. The most common isotope of helium in the universe is helium-4, the vast majority of which was formed during the Big Bang. Large amounts of new helium are created by nuclear fusion of hydrogen in stars.
The noble gases are the naturally occurring members of group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Under standard conditions, these elements are odorless, colorless, monatomic gases with very low chemical reactivity and cryogenic boiling points.
Xenon is a chemical element; it has symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized.
Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) made of twenty hexagons and twelve pentagons, and resembles a football. Each of its 60 carbon atoms is bonded to its three neighbors.
In chemistry, noble gas compounds are chemical compounds that include an element from the noble gases, group 18 of the periodic table. Although the noble gases are generally unreactive elements, many such compounds have been observed, particularly involving the element xenon.
Endohedral fullerenes, also called endofullerenes, are fullerenes that have additional atoms, ions, or clusters enclosed within their inner spheres. The first lanthanum C60 complex called La@C60 was synthesized in 1985. The @ (at sign) in the name reflects the notion of a small molecule trapped inside a shell. Two types of endohedral complexes exist: endohedral metallofullerenes and non-metal doped fullerenes.
Krypton is a chemical element; it has symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often used with other rare gases in fluorescent lamps. Krypton is chemically inert.
The helium hydride ion, hydridohelium(1+) ion, or helonium is a cation (positively charged ion) with chemical formula HeH+. It consists of a helium atom bonded to a hydrogen atom, with one electron removed. It can also be viewed as protonated helium. It is the lightest heteronuclear ion, and is believed to be the first compound formed in the Universe after the Big Bang.
Giacinto Scoles is a European and North American chemist and physicist who is best known for his pioneering development of molecular beam methods for the study of weak van der Waals forces between atoms, molecules, and surfaces. He developed the cryogenic bolometer as a universal detector of atomic and molecule beams that not only can detect a small flux of molecules, but also responds to the internal energy of the molecules. This is the basis for the optothermal spectroscopy technique which Scoles and others have used to obtain very high signal-to noise and high resolution ro-vibrational spectra.
Binary compounds of hydrogen are binary chemical compounds containing just hydrogen and one other chemical element. By convention all binary hydrogen compounds are called hydrides even when the hydrogen atom in it is not an anion. These hydrogen compounds can be grouped into several types.
In physics and chemistry, "monatomic" is a combination of the words "mono" and "atomic", and means "single atom". It is usually applied to gases: a monatomic gas is a gas in which atoms are not bound to each other. Examples at standard conditions of temperature and pressure include all the noble gases, though all chemical elements will be monatomic in the gas phase at sufficiently high temperature. The thermodynamic behavior of a monatomic gas is much simpler when compared to polyatomic gases because it is free of any rotational or vibrational energy.
Xenon monochloride (XeCl) is an exciplex which is used in excimer lasers and excimer lamps emitting near ultraviolet light at 308 nm. It is most commonly used in medicine. Xenon monochloride was first synthesized in the 1960s. Its kinetic scheme is very complex and its state changes occur on a nanosecond timescale. In the gaseous state, at least two kinds of xenon monochloride are known: XeCl and Xe
2Cl, whereas complex aggregates form in the solid state in noble gas matrices. The excited state of xenon resembles halogens and it reacts with them to form excited molecular compounds.
Chromium(I) hydride, systematically named chromium hydride, is an inorganic compound with the chemical formula (CrH)
n. It occurs naturally in some kinds of stars where it has been detected by its spectrum. However, molecular chromium(I) hydride with the formula CrH has been isolated in solid gas matrices. The molecular hydride is very reactive. As such the compound is not well characterised, although many of its properties have been calculated via computational chemistry.
The helium dimer is a van der Waals molecule with formula He2 consisting of two helium atoms. This chemical is the largest diatomic molecule—a molecule consisting of two atoms bonded together. The bond that holds this dimer together is so weak that it will break if the molecule rotates, or vibrates too much. It can only exist at very low cryogenic temperatures.
Helium is the smallest and the lightest noble gas and one of the most unreactive elements, so it was commonly considered that helium compounds cannot exist at all, or at least under normal conditions. Helium's first ionization energy of 24.57 eV is the highest of any element. Helium has a complete shell of electrons, and in this form the atom does not readily accept any extra electrons nor join with anything to make covalent compounds. The electron affinity is 0.080 eV, which is very close to zero. The helium atom is small with the radius of the outer electron shell at 0.29 Å. Helium is a very hard atom with a Pearson hardness of 12.3 eV. It has the lowest polarizability of any kind of atom, however, very weak van der Waals forces exist between helium and other atoms. This force may exceed repulsive forces, so at extremely low temperatures helium may form van der Waals molecules. Helium has the lowest boiling point of any known substance.
Solid nitrogen is a number of solid forms of the element nitrogen, first observed in 1884. Solid nitrogen is mainly the subject of academic research, but low-temperature, low-pressure solid nitrogen is a substantial component of bodies in the outer Solar System and high-temperature, high-pressure solid nitrogen is a powerful explosive, with higher energy density than any other non-nuclear material.
Argon compounds, the chemical compounds that contain the element argon, are rarely encountered due to the inertness of the argon atom. However, compounds of argon have been detected in inert gas matrix isolation, cold gases, and plasmas, and molecular ions containing argon have been made and also detected in space. One solid interstitial compound of argon, Ar1C60 is stable at room temperature. Ar1C60 was discovered by the CSIRO.
The magnesium argide ion, MgAr+ is an ion composed of one ionised magnesium atom, Mg+ and an argon atom. It is important in inductively coupled plasma mass spectrometry and in the study of the field around the magnesium ion. The ionization potential of magnesium is lower than the first excitation state of argon, so the positive charge in MgAr+ will reside on the magnesium atom. Neutral MgAr molecules can also exist in an excited state.
Diargon or the argon dimer is a molecule containing two argon atoms. Normally, this is only very weakly bound together by van der Waals forces. However, in an excited state, or ionised state, the two atoms can be more tightly bound together, with significant spectral features. At cryogenic temperatures, argon gas can have a few percent of diargon molecules.