Tetrasulfur tetranitride
Encyclopedia
Tetrasulfur tetranitride is an inorganic compound
with the formula
S4N4. This gold-poppy coloured solid is the most important binary sulfur nitride
, which are compounds that contain only the elements
sulfur
and nitrogen
. It is a precursor to many S-N compounds and has attracted wide interest for its unusual structure and bonding.
Nitrogen and sulfur have similar electronegativities
. When atoms are so evenly matched, they often form extensive families of covalently bonded structures. Indeed, a large number of S-N and S-NH compounds are known with S4N4 as their parent.
. It can be viewed as a derivative of a hypothetical eight-membered ring of alternating sulfur and nitrogen atoms. The pairs of sulfur atoms across the ring are separated by 2.586 Å, resulting in a cage-like structure as determined by single crystal X-Ray diffraction. The nature of the "transannular" S–S interactions remains a matter of investigation because it is significantly shorter than the sum of the van der Waal's distances but has been explained in the context of molecular orbital theory
. The bonding in S4N4 is considered to be delocalized, which is indicated by the fact that the bond distances between neighboring sulfur and nitrogen atoms are almost the same.
enthalpy of formation anticipates its inherent instability, and originates in the difference in energy of S4N4 compared to its highly stable decomposition products:
Although many complex molecules are unstable in a thermodynamic sense yet stable kinetically, this is uncommon for very simple compositions, such as sulfur nitride.
Because one of its decomposition products is a gas, S4N4 is an explosive. Purer samples tend to be more explosive. Small samples can be detonated by striking with a hammer.
S4N4 is thermochromic, changing from pale yellow below −30 °C to orange at room temperature to deep red above 100 °C.
with ammonia
.
Until recently, S4N4 was prepared by the reaction of ammonia with SCl2
in carbon tetrachloride
followed by extraction into dioxane, producing sulfur and ammonium chloride
as side-products:
A related synthesis employs sulfur monochloride and NH4Cl instead:
A more recent synthesis entails the use of [(Me3Si)2N]2S as a precursor with pre-formed S–N bonds. [(Me3Si)2N]2S is prepared by the reaction of lithium bis(trimethylsilyl)amide
and SCl2
.
The [((CH3)3Si)2N]2S reacts with the combination of SCl2 and SO2Cl2
to form S4N4, trimethylsilyl chloride
, and sulfur dioxide
:
ic compounds such as SbCl5
and SO3
. The cage is distorted in these adducts, thus delocalization of electron
s may be disrupted.
The reaction of [Pt2Cl4(PMe2Ph)2] with S4N4 is reported to form a complex where a sulfur forms a dative bond to the metal. This compound upon standing is isomerised to a complex in which a nitrogen atom forms the additional bond to the metal centre.
It is protonated by HBF4 to form a tetrafluoroborate
salt:
The soft Lewis acid CuCl
forms a polymer containing intact S4N4 rings as the bridging ligands:
S4N4 is sensitive to hydrolysis
in the presence of base
. Dilute NaOH hydrolyzes S4N4 as follows, yielding thiosulfate
and trithionate:
More concentrated base
yields sulfite
:
([Ir(Cl)(CO)(PPh3)2] in an oxidative addition
reaction to form a six coordinate iridium
complex where the S4N4 binds through two sulfur atoms and one nitrogen atom. This compound arises by the formal breaking of one S-N bond in the oxidative addition, followed by the coordination of the lone pair on another sulfur atom to form a dative bond. A related Pt(IV) compound arises from Zeise's salt
.
generates [S4N5]−:
It is indicative of the richness of this area that a related cation is also known, i.e. [S4N5]+.
Treatment with tetramethylammonium
azide
produces the heterocycle [S3N3]−:
In the language of electron counting
, [S3N3]− has 10 pi-electrons: 2e−/S plus 1e−/N plus 1e− for the negative charge.
In an apparently related reaction, the use of PPN
+N3 gives a salt containing the blue [NS4]− anion:
The anion NS4− has a chain structure described using the resonance [S=S=N-S-S]− ↔ [S–S–N=S=S]−.
.
metal yields the low temperature superconductor polythiazyl
or polysulfurnitride (transition temperature (0.26±0.03) K), often simply called "(SN)x". In the conversion, the silver
first becomes sulfided, and the resulting Ag2S
catalyzes the conversion of the S4N4 into the four-membered ring S2N2, which readily polymer
izes.
and the C60
molecule.
compound Se4N4 is known and has been the subject of some research. In addition, adducts of aluminium chloride
with Se2N2 have been isolated, this is formed from Se4N4.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
S4N4. This gold-poppy coloured solid is the most important binary sulfur nitride
Sulfur nitride
Sulfur nitride can refer to a number of sulfur nitrogen compounds:* tetrasulfur tetranitride, S4N4* disulfur dinitride, S2N2* polythiazyl, xAdditionally, some unstable species are known:*mononitrogen monosulfide, SN, analogous to nitrogen monoxide, NO...
, which are compounds that contain only the elements
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
. It is a precursor to many S-N compounds and has attracted wide interest for its unusual structure and bonding.
Nitrogen and sulfur have similar electronegativities
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...
. When atoms are so evenly matched, they often form extensive families of covalently bonded structures. Indeed, a large number of S-N and S-NH compounds are known with S4N4 as their parent.
Structure
S4N4 adopts an unusual “extreme cradle” structure, with D2d point group symmetrySymmetry group
The symmetry group of an object is the group of all isometries under which it is invariant with composition as the operation...
. It can be viewed as a derivative of a hypothetical eight-membered ring of alternating sulfur and nitrogen atoms. The pairs of sulfur atoms across the ring are separated by 2.586 Å, resulting in a cage-like structure as determined by single crystal X-Ray diffraction. The nature of the "transannular" S–S interactions remains a matter of investigation because it is significantly shorter than the sum of the van der Waal's distances but has been explained in the context of molecular orbital theory
Molecular orbital theory
In chemistry, molecular orbital theory is a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule...
. The bonding in S4N4 is considered to be delocalized, which is indicated by the fact that the bond distances between neighboring sulfur and nitrogen atoms are almost the same.
Properties
S4N4 is stable to air. It is, however, unstable in the thermodynamic sense with a positive enthalpy of formation of +460 kJ mol−1. This endothermicEndothermic
In thermodynamics, the word endothermic describes a process or reaction in which the system absorbs energy from the surroundings in the form of heat. Its etymology stems from the prefix endo- and the Greek word thermasi,...
enthalpy of formation anticipates its inherent instability, and originates in the difference in energy of S4N4 compared to its highly stable decomposition products:
- 2 S4N4 → 4 N2 + S8
Although many complex molecules are unstable in a thermodynamic sense yet stable kinetically, this is uncommon for very simple compositions, such as sulfur nitride.
Because one of its decomposition products is a gas, S4N4 is an explosive. Purer samples tend to be more explosive. Small samples can be detonated by striking with a hammer.
S4N4 is thermochromic, changing from pale yellow below −30 °C to orange at room temperature to deep red above 100 °C.
Synthesis
was first prepared in 1835 by W. Gregory, by the reaction of sulfur monochlorideDisulfur dichloride
Disulfur dichloride is the chemical compound with the formula S2Cl2 . Some alternative names for this compound are sulfur monochloride , disulphur dichloride and sulphur monochloride...
with ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
.
Until recently, S4N4 was prepared by the reaction of ammonia with SCl2
Sulfur dichloride
Sulfur dichloride is the chemical compound with the formula SCl2. This cherry-red liquid is the simplest sulfur chloride and one of the most common. It is used as a precursor to organosulfur compounds.-Chlorination of sulfur:...
in carbon tetrachloride
Carbon tetrachloride
Carbon tetrachloride, also known by many other names is the organic compound with the formula CCl4. It was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent...
followed by extraction into dioxane, producing sulfur and ammonium chloride
Ammonium chloride
Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride...
as side-products:
- 24 SCl2 + 64 NH3 → 4 S4N4 + S8 + 48 NH4Cl
A related synthesis employs sulfur monochloride and NH4Cl instead:
- 4 NH4Cl + 6 S2Cl2 → S4N4 + 16 HCl + S8
A more recent synthesis entails the use of [(Me3Si)2N]2S as a precursor with pre-formed S–N bonds. [(Me3Si)2N]2S is prepared by the reaction of lithium bis(trimethylsilyl)amide
Lithium bis(trimethylsilyl)amide
Lithium bisamide is the organosilicon compound with the formula [3Si]2NLi. This colourless solid is a strong non-nucleophilic base used for deprotonation reactions and as a ligand...
and SCl2
Sulfur dichloride
Sulfur dichloride is the chemical compound with the formula SCl2. This cherry-red liquid is the simplest sulfur chloride and one of the most common. It is used as a precursor to organosulfur compounds.-Chlorination of sulfur:...
.
- 2 [(CH3)3Si]2NLi + SCl2 → [((CH3)3Si)2N]2S + 2 LiCl
The [((CH3)3Si)2N]2S reacts with the combination of SCl2 and SO2Cl2
Sulfuryl chloride
Sulfuryl chloride is an inorganic compound with the formula SO2Cl2. At room temperature, it is a colorless liquid with a pungent odor. Sulfuryl chloride is not found in nature, as can be inferred from its rapid hydrolysis....
to form S4N4, trimethylsilyl chloride
Trimethylsilyl chloride
Trimethylsilyl chloride, also known as chlorotrimethylsilane is a silyl halide, with a variety of different uses in chemistry. It has the formula 3SiCl, and under standard conditions it is a colourless liquid, which is stable in the absence of water...
, and sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
:
- [((CH3)3Si)2N]2S + SCl2 + SO2Cl2 → S4N4 + 4 (CH3)3SiCl + SO2
Acid-base reactions
S4N4 serves as a Lewis base by binding through nitrogen to strongly Lewis acidLewis acid
]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
ic compounds such as SbCl5
Antimony pentachloride
Antimony pentachloride is a the chemical compound with the formula SbCl5. It is a colourless oil, but typical samples are yellowish due to impurities...
and SO3
Sulfur trioxide
Sulfur trioxide is the chemical compound with the formula SO3. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain. It is prepared on massive scales as a precursor to sulfuric acid.-Structure and bonding:Gaseous SO3 is a trigonal planar molecule of...
. The cage is distorted in these adducts, thus delocalization of electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s may be disrupted.
- S4N4 + SbCl5 → S4N4·SbCl5
- S4N4 + SO3 → S4N4·SO3
The reaction of [Pt2Cl4(PMe2Ph)2] with S4N4 is reported to form a complex where a sulfur forms a dative bond to the metal. This compound upon standing is isomerised to a complex in which a nitrogen atom forms the additional bond to the metal centre.
It is protonated by HBF4 to form a tetrafluoroborate
Tetrafluoroborate
Tetrafluoroborate is the anion BF4−. This tetrahedral species is isoelectronic with tetrafluoromethane, CF4 and tetrafluoroammonium NF4+, and is valence isoelectronic with many stable and important species including the closely related anion perchlorate, ClO4−...
salt:
- S4N4 + HBF4 → [S4N4H+]
[ BF]
The soft Lewis acid CuCl
Copper(I) chloride
Copper chloride, commonly called cuprous chloride, is the lower chloride of copper, with the formula CuCl. The substance is a white solid sparingly soluble in water, but very soluble in concentrated hydrochloric acid...
forms a polymer containing intact S4N4 rings as the bridging ligands:
- n S4N4 + n CuCl → (S4N4)n-μ-(-Cu-Cl-)n
S4N4 is sensitive to hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
in the presence of base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
. Dilute NaOH hydrolyzes S4N4 as follows, yielding thiosulfate
Thiosulfate
Thiosulfate is an oxyanion of sulfur. The prefix thio indicates that thiosulfate ion is a sulfate ion with one oxygen replaced by a sulfur. Thiosulfate occurs naturally and is produced by certain biochemical processes...
and trithionate:
- 2 S4N4 + 6 OH− + 9 H2O → S2O + 2 S3O + 8 NH3
More concentrated base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
yields sulfite
Sulfite
Sulfites are compounds that contain the sulfite ion SO. The sulfite ion is the conjugate base of bisulfite. Although the acid itself is elusive, its salts are widely used.-Structure:...
:
- S4N4 + 6 OH− + 3 H2O → S2O + 2 SO + 4 NH3
Reactions of S4N4 where the ring remains intact
S4N4 reacts with Vaska's complexVaska's complex
Vaska's complex is the trivial name for the chemical compound trans-chlorocarbonylbisiridium, which has the formula IrCl[P3]2. This square planar diamagnetic organometallic complex consists of a central iridium atom bound to two mutually trans triphenylphosphine ligands, carbon monoxide, and a...
([Ir(Cl)(CO)(PPh3)2] in an oxidative addition
Oxidative addition
Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre...
reaction to form a six coordinate iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
complex where the S4N4 binds through two sulfur atoms and one nitrogen atom. This compound arises by the formal breaking of one S-N bond in the oxidative addition, followed by the coordination of the lone pair on another sulfur atom to form a dative bond. A related Pt(IV) compound arises from Zeise's salt
Zeise's salt
Zeise's salt, potassium trichloroplatinate, is the chemical compound with the formula KPtCl3]·H2O. The anion of this air-stable, yellow, coordination complex contains an η2-ethylene ligand. The anion features a platinum atom with a square planar geometry.-Preparation:This compound is commercially...
.
Reactions of S4N4 where the ring does not remain intact
The reaction of S4N4 with the [Pd2Cl6]2− anion forms a series of three palladium complexes in which the S4N4 ring has been fragmented.S4N4 as a precursor to other S-N compounds
Many important S-N compounds are prepared from S4N4. Reaction with piperidinePiperidine
Piperidine is an organic compound with the molecular formula 5NH. This heterocyclic amine consists of a six-membered ring containing five methylene units and one nitrogen atom...
generates [S4N5]−:
- 3 S4N4 + 4 C5H10NH → (C5H10NH2)+[S4N5]− + (C5H10N)2S + ⅜ S8 + N2
It is indicative of the richness of this area that a related cation is also known, i.e. [S4N5]+.
Treatment with tetramethylammonium
Quaternary ammonium cation
Quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR4+, R being an alkyl group or an aryl group. Unlike the ammonium ion and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged,...
azide
Azide
Azide is the anion with the formula N3−. It is the conjugate base of hydrazoic acid. N3− is a linear anion that is isoelectronic with CO2 and N2O. Per valence bond theory, azide can be described by several resonance structures, an important one being N−=N+=N−...
produces the heterocycle [S3N3]−:
- S4N4 + NMe4N3 → NMe4[S3N3] + ⅛ S8 + 2 N2
In the language of electron counting
Pi bond
In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital...
, [S3N3]− has 10 pi-electrons: 2e−/S plus 1e−/N plus 1e− for the negative charge.
In an apparently related reaction, the use of PPN
Bis(triphenylphosphine)iminium chloride
Bisiminium chloride is the chemical compound with the formula [3P)2N]Cl, often written [2N]Cl and abbreviated PPNCl. This colorless salt is a source of the PPN+ cation, which is used to isolate reactive anions...
+N3 gives a salt containing the blue [NS4]− anion:
- 2 S4N4 + PPN(N3) → PPN[NS4] + ½ S8 + 5 N2
The anion NS4− has a chain structure described using the resonance [S=S=N-S-S]− ↔ [S–S–N=S=S]−.
Reaction with acetylenes
S4N4 reacts with electron poor acetylenesAlkyne
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...
.
Polythiazyl
Passing gaseous S4N4 over silverSilver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
metal yields the low temperature superconductor polythiazyl
Polythiazyl
Polythiazyl , x, was the first conducting inorganic polymer. In addition to being an electrical conductor, it was also found to be a superconductor at very low temperatures .-Structure and bonding:...
or polysulfurnitride (transition temperature (0.26±0.03) K), often simply called "(SN)x". In the conversion, the silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
first becomes sulfided, and the resulting Ag2S
Silver sulfide
Silver sulfide, Ag2S, is the sulfide of silver. This dense black solid constitutes the tarnish that forms over time on silverware and other silver objects. Silver sulfide is insoluble in all solvents, but is degraded by strong acids. Silver sulfide features a covalent bond, as it is made up of...
catalyzes the conversion of the S4N4 into the four-membered ring S2N2, which readily polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
izes.
- S4N4 + 8 Ag → 4 Ag2S + 2 N2
- S4N4 → (SN)x
Miscellaneous facts
S4N4 has been shown to co-crystallize with benzeneBenzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
and the C60
Fullerene
A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and they resemble the balls used in association football. Cylindrical ones are called carbon nanotubes or buckytubes...
molecule.
Se4N4
The seleniumSelenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...
compound Se4N4 is known and has been the subject of some research. In addition, adducts of aluminium chloride
Aluminium chloride
Aluminium chloride is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron trichloride, giving it a yellow colour. The solid has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large...
with Se2N2 have been isolated, this is formed from Se4N4.