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Home , Chalcocite, Copper sulfide, Covellite, Djurleite

AmericanMineralogist, Volume 66, pages 807-818,l98I

Coppercoordination in low chalcociteand . and other -richsulfides Howeno T. EveNs.Jn. U.S. GeologicalSurvey Reston,Virginia 22092

Abstract

The new structure determinationsof low ,CurS, and djurleite' Cupe3sS, have provided a large number ofobservations ofthe coordination behavior ofcopper vrith in copper-richsulfides. Ranges of Cu-S bond lengths are2.18 to 2.244 in linear CuS, groups; 2.21to 2.60Ain triangular CuS3groups; 2.23 to 2.904 in tetrahedralCuSa groups. Cu-Cu dis- tancesrange from 2.45A upward, the most common around 2.77A. These observationsare comparedwith structural data from other copper-rich ,in which the tetrahedral, tri- angular and linear Cu-S bond configurations frequently show large distortions and wide var- iations in bond lengths.

Introduction atmosphericpressure.) A representationof the phase diagram in the CurS end of this range,adapted from In nature the strategicmetal copperis usually con- Potter (19'17),is shown in Figure l. centrated as a , or sometimesas native metal One major of copper is chalcocite, Cu'S. Its (as in the Michigan deposits).When con- crystal structureis complex,requiring a (pseudo)or- ditions are favorable,copper may be concentratedin thorhombic unit cell senta,ining 96 formula units. or oxysalt systems(for example,in Chile). In Rahlfs (1936)first measuredthis unit cell; later Buer- each of the two chemical systems-sulfide and ger and Buerger(194) made a thorough study of the oxide--+opper behavesin a highly characteristic and orthorhombic crystallography.The existenceof the distinctively different manner. The fully oxidized closeJyingphase Cu, no, rrS was not suspecteduntil it state (+2) in oxide systemshas been continuously was discovered by Djurle (1958). This phase was and intensively studied by inorganic chemists for confirmed and established as a naturally-occurring centuries,and the behavior ofcopper in aqueoussys- speciesby Roseboom(1962) and Morimoto tems is relatively well understood. Less work has (1962); it was appropriately named djurleite. Potter been done on anhydrousoxide (or halide) systemsor (1977) found that the homogeneityrange x in Cu,S on the lower valencestates, and even lesson sulfide for low chalcocite is very narrow (x : 1.997 to systems. 2.000+0.002),but much broader for djurleite (x : The copper-sulfur system itself is very complex, 1.934to 1.965+0.002).The crystallographyof djur- and has been well defined only in the last 15 years. leite is even more complex than that of low chalco- The phasediagram was first adequatelymapped out cite, requiring (accordingto Takeda, Donnay, Rose- by Roseboom (1966). The system has since been boom and Appleman, 1967) an orthorhombic unit thoroughly restudied by Cook (1972) and by Potter cell containing 128 Cu.S. Low chalcociteand djur- (1977),both confirming and refining Roseboom'sre- leite are physically difficult to distinguish and prob- sults. Potter used electrochemicaltechniques which ably equally common. Many samples labelled made it possibleto define both stableand metastable chalcocite are actually mainly djurleite, or an in- phase regions accurately in the low temperature timately intergrown mixture of low chalcocite and ranges down to room temperature, which are not djurleite. readily accessibleto other methods. Earler, Djurle Because of their commercial importance low (1958) used X-ray techniquesto identify and define chalcocite and djurleite have been the focus of inter- the various phasesin the range CurS-CuS. (No other est in the Cu-S system.Our understandingof the na- binary compounds are known outside this range at ture of all phasesin the systemwill depend primarily 0003-004x/8I /0708-0807$02.00 807 EVANS: COPPER COORDINATION, LOW CHALCOCITE AND DII]RLEITE

clinic. Both might be consideredas interstitial com- pounds of copper in a hexagonal-close-packed framework of sulfur. Consequently,both are subject to intensive twinning which tends to mimic the higher hexagonal symmetry. The twinning in djur- leite is obvious and complex, and has been carefully studied by Takeda, Donnay, and Appleman (1967). In low chalcocite a prevalent twin law results in nearly perfect superposition of monoclinic lattices to produce an apparentend-centered orthorhombic lat- tice. In this structure the lower symmetry was real- ized only when the author discovered an untwi-nned X-ray intensity distribution in ths single crystal pat- terns. The structure analyses were carried out on data collected from untwinned crystals, using the sym- bolic addition procedurefor phasedetermination. In low chalcocite,24 Cu and 12 S were found in 25 the monoclinic asymmetric unit in spacn group 72r/ c; in djurleite, 62 Cu and 32 S were found in P2,/n No direct evidence of disorder was Fig. l. Phase diagram for the system Cu-S in the low temperatureregion near Cu2Sadapted from Potter (1977).Single- found, and all atomic sites are fully occupied. A wide phase regions are shaded. The crystallographic CulS ratios in variation of thermal motions becameapparent in the djurleite are indicated by arrows on the abscissa. anisotropic analyses.The sulfur and many of the copper atoms are not severelyelliptical and have rea- on a knowledge of their crystal structures,and the sonable root-mean-square vibration amplitudes: crystal chemical behavior of copper in such systems. -0.12A for S, -0.16A for Cu. Somecopper atoms, When the ratio of Cu to S is much below unity, cop- especially those in ambiguous coordinationo have per generallyis found in more or lessregular tetrahe- much larger and more anisotropic vibrations. With dral coordination,as in .When the CulS appropriate absorption and anomalous dispersion ratio approachesor is greaterthan unity, the coordi- correctionsapplied, in anisotropicmode, the reliabil- nation tends to decrease(as to triangular in , ity index convergedfor low chalcociteto R : 0.086 CuS) and becomeirregular and more complex. The for 5,155 intensity data, and for djurleite to R : author has followed a program of study of the crystal 0.116for 5,686data (Evans, 1979b). structuresof copper-rich sulfidesin order to provide Both structures are based on a fairly regular hex- a broader basis for the interpretation of copper-sul- agonal-close-packed sulfur framework. The copper fur solid state . To the present, this has in- atoms are mainly in triangular, threefold coordina- cluded analysesof covellite (Evans tion. One feature these structureshave in common and Konnert, 1976), low chalcocite (Evans, l97l) with certain other structures (e.g., covellite, stro- and djurleite (Evans, 1979d; Details of the last two meyerite)is a CuS-typesheet in which the triangular structures, which are published elsewhere (Evans, network of sulfur atoms has alternatetriangular sites 1979b), have provided a rich body of information occupiedby copper atoms.This feature is prominent about copper in a sulfur environment. The purpose in high chalcocite, which has a hexagonal unit cell of this paper is to review this bformation and also containing 2 CurS, but according to Clava, Reidin- that provided by other copper-richsulfide structures. ger, and Wuensch(1979) these sites are only 7l per- The emphasisis on coordination geometry, and no cent occupied. Similar sheets are present in low attempt is made here to discussa theoreticalbasis for chalcociteand djurleite, but the continuousCuS net bonding. is intemrpted in an ordered manner by many vacant triangular sites. Figure 2 shows schematicviews of Crystal structuresoflow chalcociteand djurleite the unit cells of low chalcocite and djurleite viewed Low chalcocite and djurleite were originally de- along the monoclinic D axes,to illustrate the distribu- scribed as orthorhombic, but both are actually mono- tion of copper atoms with respect to these sheets, EVANS: COPPER COORDINATION. LOW CHALCOCITE AND DJURLEITE 809

s-l s Cu-l a/z Cu4 v Cu-l s z s-l --v C!-2

Cu-l Cu-3 s Hrzs,Bcu* s-2 Cu-2 -4 ---lOCu Sactlon g Cu Cu-2 ---lOCu Cu-4 s s-2 Cu- | A _-z Sccrlon Gu-3 Cu-l x s z Cu-2 Cu-2 -1 s-l C!-2 Cu- | s Cu-l s-l ab.a.

Fig. 2. Schematicprojections of the crystal structures of (a) low chalcocite and @) djurleite projected along the motroclinic D axes. The hexagonal-close-packedlayers ofsulfur atoms (circles) are shown on edge in these views and the distribution ofthe copper atoms (not shown) is indicated. which appear on edgein theseviews. In low chalco- Bond distributionsin low chalcociteand djurleite cite there is one kind of sheet,S-1, containing within the cell 12 S atomsand 8 Cu atoms;in djurleite there In the structures of low chalcocite and djurleite the are two kinds of sheets,S-1 and S-2, each containing Cu-S bond lengths are between 2.18 and 2.904 16 S atoms,but with 9 Cu in S-1 and ll Cu in S-2. (somewhat arbitrarily ignoring Cu-S distances The remaining copper atoms lie at approximately r/t greater than 2.90A), although most, expecially those and% positionsbetween the sheets(except Cu(62) of clearly associatedwith triangular coordination, are djurleite, which is halfway between).Figure 2 shows less than 2.50A. Among the triangles some have the copper distribution in these different sheets. nearly equal Cu-S distancesof 2.31+0.014 (e.g., In Figure 3 stereoscopicviews of portions of the Cu(2), Cu(9), Cu(13) of low chalcocite;Cu(7), crystal structure of low chalcocite are shown viewed Cu(25), Cu(38) of djurleite), but thesehave S-Cu-S along the c axis in sectionsas indicated in Figure 2; anglesranging from 111.80to 131.6'. The most se- in Figure 4 similar views of djurleite are shown. verely distorted coordination in low chalcocite is These views illustrate the ellipsoids of thermal vibra- shown by Cu(15) and Cu(19), which both have two tion as 50 percent probability envelopes,and also the short (2.18to 2.244) and one long distance(2.87 and numbering system of the atoms as used by Evans 2314), suggestingan approach to linear, twofold (1979b).In Figure 3, the top layer of sulfur atoms in coordination; and Cu(14) (four bonds 2.25 to 2.87L) section A is identical with the bottom layer in section which is grossly displaced from the nearesttriangular B; the bottom layer of section A is the same as the plane. In djurleite, one copper , Cu(62), top layer of sectionB, but inverted by glide symme- unambiguously has twofold coordination (2.18 and try. Figure 4 shows similar stereoscopicprojections 2.194, S-Cu-S angle172.20), whereas 1l othersare of djurleite in 3 sections viewed along the a axis. In notably displaced from triangular planes, approach- Figure 4 the top sulfur layersin sectionA and section ing tetrahedral coordination. In Figure 5, the distri- B are identical with the bottom layers of section B bution of Cu-S bond lengths for all the copper atoms and section C respectively, but the top layer of sec- in thesetwo structuresis shown as dashesjoined by a tion A is the same as the bottom layer of the same bar for eachatom. The wide variation in the averages section, related by symmetry centers;the top layer of for eachCuS, or CuSoconfiguration is striking, but a sectionC is the sameas the bottom of this section,re- line can be drawn through all the bars at 2.30+0.01A. lated by glides and centers. New ways are still being The S-Cu-S anglesfor these have not been shown, sought to illustrate these complex structures. but they rangefrom 97.6" to 150.6'. 810 EVANS: COPPER COORDINATION. LOW CHALCOCITE AND DJURLEITE

LOII CHPLCOCITESECTION F LOI,ICHFLCOCITE SECTIONA

LOh CHFLCOCI TE SECTI ON B LO'.]CHRLCOC I TE SECTI ON 8

Fig. 3. Stereoscopicprojections of the crystal structure of low chalcocite viewed along the c axis, normal to the sulfur layers. The atoms are representedas 50 percent probability thermal ellipsoids, and only the Cu atoms are numbered. The structure is shown in two sections as indicated in Figure 2a.

A major influenceon the actual location of a given The hexagonal-close-packedsulfur framework it- copper atom is imposedby other surrounding copper self is somewhatbut not severelydistorted. The S-S atoms. Each copper atom is surrounded by 2 to 7 distancesrange from 3.9 to 4.24, giving an average other copper atoms at distancesless than 1.0A. the of 3.95A. As an indicator of the amount of distortion nearest approach is 2.524 in low chalcocite and in the framework, the largest displacement of sulfur 2.454 n djurleite (the Cu-Cu distance in metallic from the mean plane of the sulfur sheetsis 0.18A, copper is 2.5564). All of these cu-cu distancesare and the averagedisplacement is 0.09A. Of the 44 dit- shown for each copper atom as circles in Figure 5. ferent sulfur atoms 32 are bonded to 6 copper atoms, All of the 270 Cu-S interatomic distancesless than ll to 7, and I to 5, in a fairly even distribution in 3.0A in low chalcociteand djurleite are collectedto space. produce the population histogram in Figure 6a, The compositionrange measuredby Potter (1977) where the lengths are counted in intervals of 0.05A. for djurleite closely matchesthe span x : 62/32 to A symmslrical peak is formed centered at 2304, 63/32 n Cu,S (see Fig. l). The author's structure which representsthe averagetriangular bond length analysis of djurleite from Sweetwater, Missouri in these structures. A corresponding diagram for 403 (Evans, 1979b)revealed onTy62 copper atoms in the Cu-C\r distances(Fig. 6b) shows a peak at about asymmetric uni1, indicating a composition for that 2.77A, which correspondsto the nearest available crystal at the lower limit of the indicated range. The neighboring triangular site to a given triangular site possibility exists, therefore, that a site is available in in the close-packedsulfur framework. the crystal structure into which one additional copper EVANS: COPPER COORDINATION. LOW CHALCOCITE AND DJURLEITE Ell

DJURLEITE SECIION A DJURLE]TE SECTlONF

DJURLE]TE SECI]ON 8 OJURLE]TE SECTIONB

OJURLEITE SECT]ONC OJURLEITE SECTIONC

Fig. 4. Stereoscopicprojections of the crystal structure of djurleite viewed along tle a axis normal to the sulfur layers, in three sectioilt as indicated in Fig. 2b. Details are shown as in Figure 3. atom can be insertedwithout seriouslydisturbing the Specialfeatures of the structuresof low chalcocite structure.A careful searchfor sucha site showedthat and djurleite no triangular or linear sites are available, but that there are three or four possibletetrahedral sites.No The most unexpectedfeature to appear in these trace of any electrondensity was found at thesesites structuresis the linear, twofold CuS, group in djur- in the structure analysis.Unfortunately, no firm pre- leite (seenas Cu(62) in the lower left region of Sec- diction can be made as to the location of a 63rd Cu tion B of Fig. 4). Only rarely has such a group been atom, and a new crystal structureanalysis on a phase reported for copper in a copper s'lfids solid phase; in equilibrium vrith low chalcocitewill be neededto one is found in the structure of synthetic Bi'Cu'SoCl find this atom. Such a structure analysisis not con- describedby Lewis and Kupcik (1974), and in that templated by the author at this time. compound it is in disorder with a triangular group. 812 EVANS: COPPER COORDINATION. LOW CHALCOCITE AND DJURLEIT:E

3.O

I o-o g b ooo o: o o I unifr 0 .!o 80 oo n oao""a3 vo o oo oo o o o o8 o eo o o eoooo o Cu- Crl o o ooo o o

T I t I TTIITI.II- lr t IiI I I rilltrtt' Cu-S a

t5 Cu otonr

o o o^o oo oo o^ ^o o oo o t^ o^ o O o O o o - ^ ; a ^oO^ ' o o o {8- 8 oooo 6o qo"o o ;^ ^oo o 't o oeoo@o-o o- " e 0 ^o ^O -:3 ^Bo5to!o3.o S63- o o3o^Ro Oe luu : .uX.8e" ;4"-^::. :3o9.8-I. ^uo^ I I 6 e8 Sooo- o I units I o 8o I oo oo .3lo!e 6U o 8 o' o oo oo oo o o Cu-Cu o

2.5 8 T- rIl,rl.ltrl, "lTitr, IIIII,III,I'I I1'I^t ..rtllrI I'ltl I-ttl

Cu-S b

60 62

Cu olon!

Fig. 5. Copper-sulfur bond lengths (marked on vertical bars) and copper-copper distances (open circles) plotted for the 24 different copper atoms in low chalcocite (a) and 62 copper atoms in djurleite (b).

Two copper atoms in low chalcocite show a strong siderable local distortion of the framework. Appre- tendency for linear coordination, each having two ciable local adjustments are also needed to allow the short bonds at an angle of 150". Theseatoms, Cu(I5) Cu-Cu distancesto adopt longer distancesaround and Cu(19), show exaggeratedelongation of their 2.8A. In the two structures,pairs of triangular groups thermal ellipsoids,indicating a disorder betweentri- that share an edge (two sulfur atoms) are rare. Where angular and linear siteshere also, but it was not pos- such a configuration might occur, one of the copper sible to prove this hypothesis conclusively in the atoms is generally forced out of the lfiangle toward a structure analysis (Evans, 1979b). tetrahedralcenter, or toward a linear position as with An octahedron of sulfur atoms may be considered Cu(15) and Cu(19) in low chalcocite.Such atoms al- as an integral element (never isolated) of the struc- ways have large and markedly anisotropic apparent tures of low chalcociteand djurleite. The dimensions thermal motions. In djurleite there is one edge- of the ideal configuration,shown in Figure 7, will be: shared pair of fairly normal triangles adjacent to the edge (S-S distance) 3.95A; Cu-S (triangle), 2.28A; symmetry center at 0, l/2, l/2. Herc the adjacent Cu-S (inear), 1.98A; Cu-Cu (adjacent triangles) (edge-shared)Cu-Cu distanceis 2.54A, the alternate l.36A; Cu-Cu (alternate triangles), 2.$A; Cu-Cu (corner-shared) distance is 2.70A and the opposite (opposite triangles), 3.?3.4.The CuS, triangle is of distances(through the symmetrycenter) arc 3.47 and nearly optinum size in the sulfur framework, but the 3.e44. introduction of a linear CuS, group requires a con- Certainly, low chalcocite and djurleite are very EVANS: COPPER COORDINATION: LOW CHALCOCITE AND DJURLEITE 8r3

Observolions r00

2.O 2.5 3.0 2.O ?.5 3.0 A units Fig. 6. Distribution ofcopper-sulfur bond lengths (a) and copper-copper distances (b) in low chalcocite and djurleite combined. crowded structures, in which the Cu-Cu distances three phases differ only slightly in their free energy averagelittle more than those in the metal. Presum- content, and the high mobility of the copper atoms ably somesort of metal-metal interaction is involved permits the rapid and easy transformation of one in these structures, although they are in fact p-type phaseinto another (Putnis, 1977). (Shuey, 1975).At 103'C for low chalcociteand 93o for djurleite the copperportion of Comparison with other copper-rich sulfides these structures effectively melts while the sulfur por- The trend toward decreasingcopper coordination tion remains intact in the hexagonal high-chalcocite with increasingCulS ratio is well established.Most phase.A heating experinent with the Guinier-Lenne copper compoundsin which CulS ratio is less than heating X-ray powder camerashowed no perceptible 0.5 contain copper in fairly regular tetrahedral coor- changein unit cell volume of low chalcocite up to the dination: for example, chalcopyrite, CuFeS, (Cu-S transition point. At this point the volume expansion distance 23024; Hall and Stewart, 1973).As the ra- of the subcell to the hexagonalhigh chalcocite unit tio passesunity to higher values, triangular coordina- cell is only 0.7 percent.The appearanceof high ionic tion becomesmore and more prevalent, until in low conductivity in high chalcocite (Hirahara, l95l) is chalcociteand djurleite, it predominates.Finally, lin- associatedwith the tenuous and extended electron ear twofold coordination occasionally appears. Fig- density in the sulfur interstices found by Buerger and ure 8 showssome of the speciesin the CulS range of Wuensch (1963) and Sadanaga,et al. (1965).The approximately I to 2, and shows the variation of Cu- S bond lengthsin thesespecies. Figures 9 to 12 illus- trate the cooper coordination in four of these struc- tures. Triangular coordination for copper was first found by Oftedal (1932) in the structure of covellite, which has recently been refined (Evans and Konnert,1976; ,"|)i Kalbskopf, Pertlik and Zeemann, 1975).Of the six \ ,' Lr" copper atoms in the hexagonal unit cell, two are in slightly distorted tetrahedral coordination (apical Cu-S, 23314, basal2.305A) and four are in regular triangular coordination (2.l9lA). The tetrahedron is typical, comparable with that in chalcopyrite, but the triangular bond lenglh is unusually short (seeFigs. 8 and 9). According to Shuey (1975) covellite is a p- Fig. 7. Idealized octahedron of sulfur atoms (open circles), with type metal, and from X-ray photoelectron spectro- 4 copper atoms occupying alternate faces. scopicstudies, while Nakai et al. (1978)have shown EVANS: COPPER COORDINATION. LOW CHALCOCITE AND DIURLEITE

'o Low cholcocite Cu2S ,l*=' l-tt Djurleite Cur.SssS

Tetrogonol CuzS

Stromeyerile AgCuS

Tetrohedrif e Cul2SbaS13

Bornite CusF€Sa

Anilite Cu7S4

Covellile CUS

Cholcopyrite CuFeS2

CsCqS2, NoCu4S4

Bi2Cu3SaCl H I 2.O 2.5 3.O Ronge of Cu-S bond lengths, A Fig. 8. Ranges of copper-sulfur bond lengths in various coppcr-rich sulfide structures, in linear CuS2 groups (crosses); in triangular CuS3 groups (triangles); in tetrahedral CuSa groups (squares). that copper is monovalentin most sulfides,including angular Cu-S bonds result from the reduced size of covellite. From X-ray photoelectron spectroscopic the associatedS- ions. studies Folmer and Jellinek (1980) have concluded Another earlier report of triangular coordination is that the conducting electrons in covellite are drawn in stromeyerite,AgCuS (Frueh, 1955).Here the tri- from the sulfur atoms. and that the shortened tri- angular sheet is the same as that found in covellite, and in intemrpted form in low chalcocite and djur- leite. All of the copper is confined to these sheets, which are joined to each other through linear S-Ag-S links (Fig l0). The Ag-S distanceis 2.40A, whereas

Fig. 9. The crystal structure of covellite. Large open circles are sulfur atoms, small black circles are copper atoms in this and Fig. 10. The crystal structure of stromeyerite.Medium-sized following figures. circles (line shaded) are atoms. EVANS: COPPER COORDINATION, LOW CHALCOCITE AND DJI]RLEITE

the known linear Cu-S distancesare not greaterthan 2.20L. Thus in stromeyerites that aie slightly deficient in silver, it is not likely that copper will en- ter this site in its place. Recently, Cava et al. (1979),using neutron diffrac- tion data, have successfullyrefined the highly dis- ordered structure of high chalcocite at four different temperatures,l20oo 200",260" and 325"C, by as- suming anharmonic thermal motion for the copper atoms. They found that by distributing Cu in two dif- ferent sites,all ofthe copper could be accountedfor and a reliability index of R : 0.071was attained (at 120'C). The alternatetriangular sitesin the hexago- nal close-packedsulfur layers are 7l percent occu- pied in regular coordination. In addition, all (12) of the triangular sitesbetween the layers are populated Fig. 12.The crystalstructure oftetragonal (high pressure)Cu2S. by the remaining Cu atoms, each site occupied 2l The cubic unit of the close-packedsulfur framework is indicated percent of the time. The latter have highly extended by dashed lines. and anharmonic electron-densitydistributions, but clearly in the disordered, high temperature state, cop- per is found mainly in triangular coordination. range from 2.29 to 2524, and the S-Cu-S angles Anilite, CurSo,is a recently describedlow-temper- from 102o to l35o; in the triangles the respective ature phase in the Cu-S sulfur system, which has a ranges are2.24 to 2.35A and l09o to 133o.Cu-Cu unique structure reported by Koto and Morimoto distancesas low as 2.644 are found, and the average (1970).Of 28 copper atoms in the orthortro-6is unit copper atom has 4 copper neighborsat distancesless cell, 8 are in tetrahedral coordination and 20 are in than 3.0A, compared with 4.7 neighbors for low triangular coordination (Fig. I l). As the cation popu- chalcociteand djurleite. For comparison,the nearest lation becomesmore crowded, these configurations Cu-Cu distancein covelliteis 3.199A. exhibit more distortion than is found in covellite or The structureof the tetragonal,high-pressure form stromeyerite.The Cu-S bonds in the tetrahedra of CurS (Janosi, 1964)is interestingin its simplicity; it containsonly one kind ef sepper atom in a regular triangle with Cu-S bond length 2314, and S-Cu-S angle 120o.(Fig. l2). This form is stableabove about 2 kbars, and has a specfficcell volume about 1.3 per- cent smaller than that of low chalcocite. Cu-Cu dis- tances are all greater than 2.64A. The reason why this seemingly simple and satisfactory structure should revert to the very complex low-chalcocite structure at atmospheric pressureis at present wholly unknown. The structure of , CurFeSo,is usually ob- scured by intense pseudocubictwinning, but Koto and Morimoto (1975) have evolved details of an or- thorhombic superstructure in which the cations are divided into two groups, one tetrahedral and the other triangular in coordination.The structureof tet- rahedrite, Cu,2SboS,r,(Wuensch, 1964) also contains both triangular and tetrahedral groups. As mentioned above, in all sulfide structures known at presenthaving CulS < 0.5, the copperis in Fig. ll. The crystal structure of anilite. CuS3 and CuSa tetrahedral coordination. This coordination can be coordination groups are shown as triangles and t€trahedra. seenalso in structuresthat have a high Cu/S ratio, 816 EVANS: COPPER COORDINATION. LOW CHALCOCITE AND DJURLEITE

ab

Fig. 13. Structuresof (a) the (CuaSa)o"-chain in Na3CuaSa,and (b) the (Cu3S2)'"- sheetin CsCu3S2. but always in highly distorted form. In fact, in the 0.001)A; in gladite, PbCuBi,S, (Kohatsu and clearly triangular groups, the Cu atom is often more Wuensch,1976) they arc2.29,2.34,2.34,and 2.55(+ or lessdisplaced out of the triangular S, plane, and is 0.03)4. On the whole, however, it is difficult to find sometimes described as approaching tetrahedral any systematic tendencies in the wide variations in coordination. This configuration in which three Cu- copper coordination in sulfides. Nevertheless,the tet- S bonds are short (- 2.25-2.44) and one is long (2.4- rahedral coordination is quire regular in some struc- 2.94) seemsto be characteristicfor copper in sul- tures, such as chalcopyrite,CUFeS' (Hall and Stew- fides, and can be seen even in structures that have a art, 1973);covellite CurS(S') (Evans and Konnert, low CulS ratio. For example,in aikinite, PbCuBiS, 1976);and tetrahedrite,Cu,rSboS,, (Wuensch, 1964), (Kohatsu and Wuensch,l97l), the Cu-S distancesin in all of which the Cu-S bond lengths are within the the tetrahedronare 2.31, 2.37, 2.37, and 2.43 (+ range2.30-2344.

ab

Fig. 14. Molecular stnrctures of the thiourea-copp€r complexes (a) [Cua(SCN2II+)"]a*, (b) [Cuo(SCNTIIo)g]o*. EVANS: COPPER COORDINATI ON. LOW CHALCOCITE AND DJURLEITE 817

A rich group of synthetic alkali copper sulfides has shown to contain this same configuration. One ex- long been known, and has been recently investigated ample is the thiourea (NHTCSNHT, tu) complex in terms of their crystal chemistry. In NarCuoSoiso- [Cu.tu.](NO,)o.4H,O (Grimth et a1.,1976).The mo- lated tubelike chains are made up of CuS, lfiangles lecular cation is shown in Figure l4a. The group is (Burschka, 1980).These chains may condenselater- somewhatdistorted in terms of bond lengthsQ.l9 to ally to form layer structures as found in KCurS, and 23lA), S-Cu-S angles(106' to 126') and warping of KrCurSu,the latter also incorporating copper in tet- the triangular planes. Cu-Cu distancesvary from rahedral coordination (Burschka, 1979). Similar 2.83 to 3.094. These authors also report that when complex layers have also been found in BaCuoS,by the concentration of thiourea in the acidic aqueous Iglesiasand Steinfink (1975).In CsCurS,two layers solutions is increased, the complex adds on three of sulfur in close packing are joined by copper atoms more thiourea molecules by converting tlree of the in linear, twofold coordination (Burschka,1980). The CuS3triangles to tetrahedra,to form [Cu.tu"] (NOr)o ' chain and sheetmotifs are shownin Figure 13.In the 4HrO (Fig. l4b). In the new compound the remain- triangles the Cu-S distanceaverages 2304, and the ing triangle is regular with a Cu-S bond length of linear Cu-S distance is 2.17A. In all these com- 2.244. pounds many Cu-Cu distanceslie in the range 2.55- Other monovalent copper complexes that have 2.7s4. been reported are of interest in that they contain lin- ear CuS, groups. Dance (1976a\ has prepared from Organometallic cluster model complexes ethanol solutionsa thiophenol (C6H,SH) complex of The octahedral group in which the octahedron has composition[(n-C.HJN]r[Cur(SCuHr),] in which the all four alternate octahedral faces occupied occurs pentanuclear copper anion cluster contains four tri- twice in low chalcocite[Cu(1,7,8,9), Cu(4,10,11,12)] angular CuS, groups and one linear CuS, group, as and twice in djurleite lCru(1,22,25,26),Cu(18,57, shown in Figure l5a. The molecule may be derived 58,60)1.It is not suggestedthat the presenceof these from the octahedral CuoSucomplex by replacing one CuoSugroups imparts any molecular characterto the S atom by a linear S-Cu-S link. The triangular Cu-S structures. Nevertheless, it is inter- bond lengths average 2.27A and the linear bond $fing to find several organometallic monovalent lengths arc 2.164.. From similar systemsDance copper complexes that have been slmthesized and (1976b)has also prepared the compound [(CrHr)N]

ab

Fig. 15. Molecular structuresof the thiol-copper complexes(a) [Cu5(SC5H5)r]2-,and (b) [Cu5(SCaHe)6]-. 818 EVANS: COPPER COORDINATION, LOW CHALCOCITE AND DJURLEITE

which has a pentanuclear cluster Hall, S. R. and Stewart,J. M' (1973)The crystal structure refine- [Cur(S-t-CoHr).], B29' containing two triangular groups and three linear ment of chalcopyrite, CuFeS2' Acta Crystallogaphica' groups (Fig. l5b). Here the triangular Cu-S bond 579-585. Hirahara, E. (1951) The electrical conductivity and isothermal leneth ii Z.ZlA and the linear bond length is 2.17A. Hall effect in cuprous sulfide . Journal of the In this molecule, which has D, symmetry, the three Physical Society of Japan, 6, 428437 . linear S-Cu-S groups are bent inward to 170" and Iglesias,J. E. and Steinnng H. (1975)The crystal structuresand Matcrials ResearchBulle- thus three copper atoms appear to be somewhatat- phasetransition of c and B BaCuaS3' triangular atoms, which are at tirr.7,1247-1258. tracted to the capping Janosi, A. (1964) La structure du sulfure cuivreux quadratique. a distanceof 2.724. This phenomenonsupports the Acta Crystallographica,17, 3ll-312- suggestion that copper atoms positively interact in Kalbskopf, R., Pertlik, F., and Zeem'nn' J. (1975) Verfeinerung the sulfur environment. der Kristallstruktur des Covellins, CuS, mit Einkristalldaten' Petrologische Mitteilungen, Perhapsby studying model Cu-S clustersof this Tschermak's Mineralogische und gained into the behavior 22,242-249. type, further insight can be Kohatsu. L and Wuensch, B. J. (1971) The crystal structure of of copper in the copper-rich sulfides. aikinite, PbCuBiSr. Acta Crystallographica, 827, 1245-1252' Kohatsu, L and Wuensch,B. J. (1976)The crystalstructure of gla- References dite PbCuBisSe, a superstructure intermediate in the series Acta Crystallogra- Buerger,M. J. and Buerger,N. W. (1944)Low chalcociteand high Bi2S3-PbCuBiS3(bismuthinite-aikinite). chalcocite.American Mineralogist, 29, 55-65. phica, B32, 2401-2409. (1970) structure of anilite. Buerger,M. J. and Wuensch,B. J., (1963)Distribution of atoms in Koto. K. and Morimoto, N. The crystal high shfsssils, CuzS. Science,l4l, 276-277. Acta Crystallographica, 826, 915-924. investigationof Burschka,C. (1979) Na3CuaSa-einThiocuprate mit imverknupf- Koto, K. and Morinoto, N. (1975)Superstructure bornite, Cu5FeSa,by the modified partial Patterson function. ten [Cu4S4]-Ketten. Zeitschrift fur Naturforschung' 34b' 39G - 397. Acta Crystallographica, B3l, 2268-2273 (1974) The crystal structure of Burschka, C. (1980) CsCuaS3und CsCu3S2:Sulfide mit tetrae- Lewis, J., Jr. and Kupcik, V. B30' 848-852. drische und linear koordinierten Kupfer. Zeitschrift fiir anorga- Bi2Cu3SaCl.Acta Crystallographica, a new copper . nischeund allgemeineChemie, 463,65-71. Morimoto, N. (1962), Djurleite, 338-344. Cava,R. J., Reidinger,F. and Wuensch,B. J. (1979)A single-crys- Mineralogical Journal (Tokyo) 3, Niwa, Y' (1978)X-ray tal neutron-difraction study of the mobile Cu ions in the fast- Nakai, I', Sugitani,Y., Nagashima,K. and spectroscopic study of copper . Journal ion conductor B-Cu2S (high chalcocite). American Crystallogra- photoelectron phic Association Program and Abstracts, vol. 6, no. 2' 87. of tnorganic and Nuclear Chemistry' 40,789-791. of covellite. Zeitschrift for Cook, W. R., Jr. (1972) Phasechanges in Cu2S as a function of Oftedal, l. (1932), The crystal structure temperature. National Bureau of Standards Special Pubtcation Kristallographie,83, 9-25. investigationof the sys- 364, Solid State Chemistry,703-7 ll. Potter,R. W. il (1977)An electrochemical Dance,I. G. (I976a) Formation and x-ray structureof the hexa-(t' tem copper-sulfur. , 72, 152+1542. of phase transforma- butylthiolato) pentacuprate (f) monoanion. Chemical Commu- Putnis, A. (1977) Electron diffraction study 62' lO7-114. nications, 1976,6849. tions in copper sulfrdes. American Mineralogist' Dance, I. G. (1976b)The hepta (p2-benzenethioliato)-pentacuprateRahlfs, P. (1936) Uber die kubischen Hochtemperaturmodifika- Silbers und des (I) dianion; x-ray crystal and molecular structur€' Chemical tionen der Sulfide, Selenide und Telluride des Physikalische Chemie, B3l' Communications,1976, 103-104. einwertigen Kupters. Zeitschrift Iiir Djurle, S. (1953)An x-ray study on the systemCu-S. Acta Chen- 157-r94. a new mineral. ica Scandinavica,12, 1415-1426. Roseboom,E. H., Jr. (1962) Djurleite, Cur scS, Evans,H. T., Jr (19?l) Crystal structureof low chalcocite.Nature American Mineralogist 47, I I 8l-l I 84. of the systemCu-S Physical Science, 232, 69-70. Roseboom,E. H., Jr. (1966)An investigation 25o anLd700"C. Eco- Evans, H. T., h. (1919a)Djurleite (Curg+S)and low chalcocite and some natural copper sulfidcs between (Cu2S):new crystal structue studies.Science, 203' 35G358. nomic Geology, 61, 641-672' N. (1965)On the sta- Evans, H. T., Jr. (19?9b) The crystal structures of low chalcocite Sadanaga,R., Ohmasa,M', and Morimoto, structure of and djurleite. Zeitschrift fiir Kristallographie, 150, 299-320. tistical distribution of copper ions in the B-chalco- 275-290. Evans, H. T., Jr. and Konnert, J. A. (1976) Crystal structure re- cite. Mineralogical Journal (Tokyo) 4, minerals.Elsevier Scien- finement of covellite. American Mineralogist 6l' 996-1000. Shuey,R. T. (1975)Semiconducting ore Folmer, J. C. W. and Jellinek, F' (1980)The valenceof copper in tific Publishing Co., New York. D. E. (1967)Djur- sulfides and selenides: an x-ray photoelectron spectroscopy Takeda, H., Donnay, J. D. H. and Appleman, 125, 41U22. study. Journal of the LessCommon Metals, 76, 153-162' leite twimning. Zeitschrift fff Kristallographie, E. H'' and Appleman' Frueh, A. J., Jr. (1955) The crystal structure of stromeyerite, Takeda, H., Donnay, J. D. H., Roseboom, Cu1 Zeitschr- AgCuS: a possible def€ct structure. Zeitschrift fiir Kristallo- D. E. (1967)The crystallographyof djurleite, e7S. graphie,106,299-301. ift fiir Kristallographie, 125, 404413. Grifrth, E. H., Hunt, G. W., and Amma, E. L. (1976)The ada- Wuensch, B. J. (1964) Thc crystal structur€ of tetrahedrite' 437453' mantane structure in polynuclear Cu+Secores: The crystal and Cul2SbaSI 3. Zeitschrift fiir Kristallographie' I 19' molecular structures of Cua[SC(NHz)z]c(NOr)o'4H2O and Cua[SC(NHr)2]s(NOr)o'4H2O. Chemical Communications' Manuscript received,Febntary 10, I98l; 1976.432433. acceptedforpublication, March 4, 1981.