Copper monosulfide

Copper monosulfide is a chemical compound of copper and sulfur. It was initially thought to occur in nature as the dark indigo blue mineral covellite. However, it was later shown to be rather a cuprous compound, formula Cu₃S(S₂).^[4] CuS is a moderate conductor of electricity.^[5] A black colloidal precipitate of CuS is formed when hydrogen sulfide, H₂S, is bubbled through solutions of Cu(II) salts.^[6] It is one of a number of binary compounds of copper and sulfur (see copper sulfide for an overview of this subject), and has attracted interest because of its potential uses in catalysis^[7] and photovoltaics.^[8]

Copper monosulfide

Names
IUPAC name Copper sulfide
Other names Covellite Copper(II) sulfide Cupric sulfide
Identifiers
CAS Number	1317-40-4 Y
3D model (JSmol)	Interactive image
ChemSpider	14145 Y
ECHA InfoCard	100.013.884
EC Number	215-271-2
PubChem CID	14831
RTECS number	GL8912000
UNII	KL4YU612X7 Y
CompTox Dashboard (EPA)	DTXSID601316949 DTXSID0061666, DTXSID601316949
InChI InChI=1S/Cu.S Y Key: BWFPGXWASODCHM-UHFFFAOYSA-N Y InChI=1/Cu.S/rCuS/c1-2 Key: BWFPGXWASODCHM-BLKBWTQCAT
SMILES [Cu]=S
Properties
Chemical formula	CuS
Molar mass	95.611 g/mol
Appearance	black powder or lumps
Density	4.76 g/cm3
Melting point	above 500 °C (932 °F; 773 K) (decomposes)[1]
Solubility in water	0.000033 g/100 ml (18 °C)
Solubility product (Ksp)	6 x 10−37[2]
Solubility	soluble in HNO3, NH4OH, KCN insoluble in HCl, H2SO4
Magnetic susceptibility (χ)	−2.0·10−6 cm3/mol
Refractive index (nD)	1.45
Structure
Crystal structure	hexagonal
Hazards
GHS labelling:
Pictograms
Hazard statements	H413
Precautionary statements	P273, P501
NIOSH (US health exposure limits):
PEL (Permissible)	TWA 1 mg/m3 (as Cu)[3]
REL (Recommended)	TWA 1 mg/m3 (as Cu)[3]
IDLH (Immediate danger)	TWA 100 mg/m3 (as Cu)[3]
Related compounds
Other anions	Copper(II) oxide
Other cations	zinc sulfide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Manufacturing

Copper monosulfide can be prepared by passing hydrogen sulfide gas into a solution of copper(II) salt.

Alternatively, it can be prepared by melting an excess of sulfur with copper(I) sulfide or by precipitation with hydrogen sulfide from a solution of anhydrous copper(II) chloride in anhydrous ethanol.

The reaction of copper with molten sulfur followed by boiling sodium hydroxide and the reaction of sodium sulfide with aqueous copper sulfate will also produce copper sulfide.

CuS structure and bonding

Copper sulfide crystallizes in the hexagonal crystal system, and this is the form of the mineral covellite. There is also an amorphous high pressure form^[9] which on the basis of the Raman spectrum has been described as having a distorted covellite structure. An amorphous room temperature semiconducting form produced by the reaction of a Cu(II) ethylenediamine complex with thiourea has been reported, which transforms to the crystalline covellite form at 30 °C.^[10]
The crystal structure of covellite has been reported several times,^[11][12][13] and whilst these studies are in general agreement on assigning the space group P6₃/mmc there are small discrepancies in bond lengths and angles between them. The structure was described as "extraordinary" by Wells^[14] and is quite different from Copper(II) oxide, but similar to Copper(II) selenide (or referred to as Klockmannite). The covellite unit cell contains 6 formula units (12 atoms) in which:

• 4 Cu atoms have tetrahedral coordination (see illustration).
• 2 Cu atoms have trigonal planar coordination (see illustration).
• 2 pairs of S atoms are only 207.1 pm apart^[13] indicating the existence of an S-S bond (a disulfide unit).
• the 2 remaining S atoms form trigonal planar triangles around the copper atoms, and are surrounded by five Cu atoms in a pentagonal bipyramid (see illustration).
• The S atoms at each end of a disulfide unit are tetrahedrally coordinated to 3 tetrahedrally coordinated Cu atoms and the other S atom in the disulfide unit (see illustration).

The formulation of copper sulfide as Cu^IIS (i.e. containing no sulfur-sulfur bond) is clearly incompatible with the crystal structure, and also at variance with the observed diamagnetism^[15] as a Cu(II) compound would have a d⁹ configuration and be expected to be paramagnetic.^[6]
Studies using XPS^{[16][17][18][19]} indicate that all of the copper atoms have an oxidation state of +1. This contradicts a formulation based on the crystal structure and obeying the octet rule that is found in many textbooks (e.g.^[6][20]) describing CuS as containing both Cu^I and Cu^II i.e. (Cu⁺)₂Cu²⁺(S₂)²⁻S²⁻. An alternative formulation as (Cu⁺)₃(S²⁻)(S₂)⁻ was proposed and supported by calculations.^[21] The formulation should not be interpreted as containing radical anion, but rather that there is a delocalized valence "hole".^[21][22] Electron paramagnetic resonance studies on the precipitation of Cu(II) salts indicates that the reduction of Cu(II) to Cu(I) occurs in solution.^[23]

ball-and-stick model of part of the crystal structure of covellite	trigonal planar coordination of copper	tetrahedral coordination of copper	trigonal bipyramidal coordination of sulfur	tetrahedral coordination of sulfur-note disulfide unit

See also

• Copper sulfide for an overview of all copper sulfide phases
• Copper(I) sulfide, Cu₂S
• Covellite