Three new phases in the K/Cu/Th/S system: KCuThS3, K 2Cu2ThS4, and K3Cu 3Th2S7

Article abstract of DOI:10.1021/ic050561x

Synthetic exploration of K/Cu/Th/S quaternary phase space has yielded three new compounds: KCuThS₃ (I), K₂Cu₂ThS ₄ (II), and K₃Cu₃Th₂S₇ (III). All three phases are semiconductors with optical band gaps of 2.95, 2.17, and 2.49 eV(I-III). Compound I crystallizes in the orthorhombic space group Cmcm with a = 4.076(1) A, b = 13.864-(4) A, and c = 10.541(3) A. Compound II crystallizes in the monoclinic space group C2/m with a = 14.522(1) A, b = 4.026(3) A, and c = 7.566(6) A; β = 109.949(1)°. Compound III crystallizes in orthorhombic space group Pbcn with a = 4.051(2) A, b = 14.023(8) A, and c = 24.633(13) A. The compounds are all layered materials, with each layer composed of threads of edge-sharing ThS₆ octahedra bridged by CuS₄ tetrahedral threads of varying dimension. The layers are separated by well-ordered potassium ions. The relatively wide range of optical band gaps is attributed to the extent of the CuS₄ motifs. As the dimension of the CuS₄ chains increases, band gaps decrease in the series. All materials were characterized by single-crystal X-ray diffraction, microprobe chemical analysis, and diffuse reflectance spectroscopy (NIR-UV).

Full text of DOI:10.1021/ic050561x

Inorg. Chem. 2005, 44, 6463−6469
Three New Phases in the K/Cu/Th/S System: KCuThS3, K2Cu2ThS4, and
K3Cu3Th2S7
Hugh D. Selby,†,‡ Benny C. Chan,† Ryan F. Hess,§ Kent D. Abney,§ and Peter K. Dorhout*,†
Department of Chemistry, Colorado State UniVersity, Fort Collins, Colorado 80523-1872,
Chemistry DiVision, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, and
Nuclear Materials and Technology DiVision, Los Alamos National Laboratory,
Los Alamos, New Mexico 87545
Received April 11, 2005
Synthetic exploration of K/Cu/Th/S quaternary phase space has yielded three new compounds: KCuThS3 (I), K2-
Cu2ThS4 (II), and K3Cu3Th2S7 (III). All three phases are semiconductors with optical band gaps of 2.95, 2.17, and
2.49 eV(I
(4) Å, and c
4.026(3) Å, and c
Pbcn with a 4.051(2) Å, b
−
III). Compound I crystallizes in the orthorhombic space group Cmcm with a
10.541(3) Å. Compound II crystallizes in the monoclinic space group C2/m with a
7.566(6) Å; â ) 109.949(1) . Compound III crystallizes in orthorhombic space group
14.023(8) Å, and c 24.633(13) Å. The compounds are all layered materials, with
)
4.076(1) Å, b
) 13.864-
)
)
14.522(1) Å,
b
)
)
°
)
)
)
each layer composed of threads of edge-sharing ThS6 octahedra bridged by CuS4 tetrahedral threads of varying
dimension. The layers are separated by well-ordered potassium ions. The relatively wide range of optical band
gaps is attributed to the extent of the CuS4 motifs. As the dimension of the CuS4 chains increases, band gaps
decrease in the series. All materials were characterized by single-crystal X-ray diffraction, microprobe chemical
analysis, and diffuse reflectance spectroscopy (NIR−UV).
Introduction
the oxides. The bulk of the exploration thus far has focused
on the 4f-nd Ln-transition metal materials, notably the series
CsZnLnSe3 (Ln ) Sm, Gd-Yb), CsCdLnSe3 (Ln ) La-
Nd, Sm, Gd-Y), and CsHgLnSe3 (Ln ) La-Nd, Sm, Gd-
Y), possessing the layered structure type KCuZrS3.5-8 Many
other examples of quaternary Ln-transition metal com-
pounds are known with familiar 2-dimensional layered or
pseudo-1-dimensional structures that have incorporated
magnetically silent d10 coinage metals as the transition metal
element.9-11
Recent efforts have been made to explore the solid-state
chemistry and physics of materials containing mixed d and
f elements. Studies that combine these elements as either
dopants in known binary phases or stoichiometric compo-
nents of novel ternary and quaternary phases have yielded
compounds with interesting properties, including heavy
fermion behavior, unique magnetic coupling and ordering
phenomena, and sensitization and tuning of optical ma-
terials.1-4 Of particular interest are the quaternary lanthanide
(Ln) and actinide (An) chalcogenide phases, as the softer
chalcogenide (S-Te) components offer diverse bonding
modes and a corresponding range of properties not seen in
Frequently studied concurrently with the Ln-based materi-
als, the large body of reported early-An-containing analogues
(5) Yao, J.; Deng, B.; Sherry, L. J.; McFarland, A. D.; Ellis, D. E.; Van
Duyne, R. P.; Ibers, J. A. Inorg. Chem. 2004, 43, 7735-7740.
(6) Mitchell, K.; Huang F. Q.; McFarland, A. D.; Haynes, C. L.; Somers
R., C.; Van Duyne R., P.; Ibers J. A. Inorg. Chem. 2003, 42, 4109-
4116.
* To whom correspondence should be addressed. E-mail:
Peter.Dorhout@colostate.edu. Phone: 970-491-0629. Fax: 970-491-1801.
† Colorado State University.
‡ Chemistry Division, Los Alamos National Laboratory.
§ Nuclear Materials and Technology Division, Los Alamos National
Laboratory.
(7) Mitchell, K.; Haynes, C. L.; McFarland, A. D.; Van Duyne, R. P.;
Ibers, J. A. Inorg. Chem. 2002, 41, 1199-1204.
(8) Mansuetto, M. F.; Keane, P. M.; Ibers, J. A. J. Solid State Chem.
1992, 101, 257-264.
(1) Stewart, G. R. ReV. Mod. Phys. 1984, 56, 755-787.
(2) Cho, N.; Kikkawa, S.; Kanamaru, F.; Takeda, Y.; Yamamoto, O.; Kido,
H.; Hoshikawa, T. Solid State Ionics 1993, 63-65, 696-701.
(3) Murugesan, T.; Ramesh, S.; Gopalakrishnan, J.; Rao, C. N. R. J. Solid
State Chem. 1981, 38, 165-72.
(9) Patschke, R.; Heising, J.; Brazis, P.; Kannewurf, C. R.; Kanatzidis,
M. Chem. Mater. 1998, 10, 695-697.
(10) Huang, F. Q.; Choe, W.; Lee, S.; Chu, J. Chem. Mater. 1998, 10,
1320-1326.
(4) Kageyama, Y.; Oseto, S. Thin-film electroluminescent devices. U.S.
Patent 3,712,855, 1988.
(11) Sutorik, A. C.; Albritton-Thomas, J.; Kannewurf, C. R.; Kanatzidis
M. G., J. Am. Chem. Soc. 1994, 116, 7706-7713.
10.1021/ic050561x CCC: $30.25
Published on Web 08/05/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 18, 2005 6463

Selby et al.
is growing, albeit at a less consistent rate.12 The introduction
of the 5f orbitals has resulted in materials with magnetic
behavior not seen in the Ln materials, new structure types,
and optical/electronic properties that are consistent with
more-diffuse f electrons.13,14 Because of the special handling
requirements associated with the elements Ac, Pa, Np, and
Pu, most of the reported materials feature Th and U as the
An component, with U by far the most thoroughly explored.
Thorium has been neglected largely because of its strong
thermodynamic preference for the Th(IV) f 0 state, which is
less interesting from the perspective of magnetic or electronic
studies than the U(IV) f 2 equivalent. Moreover, Th(IV)
compounds are often isostructural with their U(IV) analogues.
We wish to report here three new Th-containing quaternary
phases which, to the best of our knowledge, have no
compositional U analogues. The phases KCuThS3 (I), K2-
Cu2ThS4 (II), and K3Cu3Th2S7 (III) are semiconductors with
striking variations in color and range of measured band gaps,
despite quite similar compositions and closely related
structures.
phase of the mineral CuS (both identified by single-crystal cell
parameters).16,17 Compound I was the minor component of the
mixture, at approximately 25% of the bulk. EDS analysis of selected
single crystals of I revealed the following composition normalized
to Th: K0.833Cu1.05ThS2.37
.
Compound II was synthesized by reacting 86.9 mg (0.375 mmol)
of Th, 24.7 mg (0.389 mmol) of Cu, 24.0 mg (0.748 mmol) of S,
and 71.3 mg (0.501 mmol) of K2S2. Thorough DMF washing left
a mixture of a small amount of unreacted Th metal, a passivating
layer of II on the Th metal, and a few fibrous, green crystals of
KCu3S2 (identified by single-crystal unit cell parameters).18 The
major product comprised red, irregularly shaped crystals of II,
forming approximately 80% of the bulk. Atomic composition of
II was found by EDS to be K2.45Cu2.45ThS5.14, normalized to Th.
Crystals of II were intimately mixed with small amounts of
elemental S, which likely contributed to the relative abundance of
S in the chemical analysis.
Compound III was synthesized by reacting 29.3 mg (0.126
mmol) of Th, 47.3 mg (0.744 mmol) of Cu, 128.7 mg (4.013 mmol)
of S, and 283.0 mg (1.987 mmol) of K2S2. Repeated DMF washing
revealed a mixture that, by visual inspection, was approximately
60% III and 40% KCu4S3 (determined by single-crystal cell
parameters).16 No other products were observed. Compound III
crystallized as very thin, yellow plates that grew in clusters. A few
of these clusters were analyzed by EDS to yield the atomic
composition K1.59Cu1.59ThS3.84, normalized to Th.
It is of note that compound I could be prepared in near
quantitative yield by stoichiometric combination using K2S2 as the
sulfur source under otherwise identical conditions. However, II and
III could not be made pure via the low-temperature route;
significant quantities of binary and ternary thiocuprate phases were
always present. Even lower temperatures (480 °C, K2S2; 270 °C,
K2S5) served only to enhance the amount of the thiocuprate phases
formed. This observation suggests that the mobility of the Cu(I)
ion couples with the high relative stability of the binary and ternary
phases to create a readily accessible thermodynamic sink. Elevated-
temperature experiments are in progress to determine if II and III
may be isolated as pure phases.
Single-Crystal X-Ray Diffraction. Suitable single crystals of
I, II, and III were coated with epoxy and mounted to glass fibers
in random orientations. The crystals were then mounted on a Bruker
SMART 1000 CCD-equipped diffractometer. Intensity data were
collected at room temperature using the graphite-monochromated
Mo KR line collimated to 0.5 mm. Three sets of 606 0.3°-wide
frames were obtained at three settings of æ (0°, 120°, 240°) as
ω-scans. An additional set of 50 frames collected at the initial æ,ω
settings revealed no measurable decay. Exposure times for I and
II were 20 s; they were 30 s for III. Additional data for III were
collected on a Bruker APEXII diffractometer using an identical
scan program but with 15 s frames. The data for III indicated that
the sample was cracked or composed of closely aligned crystallites
(several reflections broader than 1° in ω; an additional weak lattice
that could be indexed to that of III). Constraining the integration
to the dominant lattice afforded intensity data of quality sufficient
for reasonable structural solution. Cell parameters for integration
were determined from the full data sets, and integration was
performed using SAINT.19 Structures were solved with direct
Experimental Section
Caution: 232Th is a naturally occurring radioisotope which
decays by R-emission (t1/2 ) 1.4 × 1010 years) and should be
handled only in radiological areas.
Synthesis. All reagents were used as received and stored in an
inert (N2)-atmosphere glovebox: Th (metal foil, c.a. 99.9%, Los
Alamos National Laboratory), S (99.999%, Johnson-Mathey), K
(99.999%, Aldrich), and Cu (99.99% Fisher Scientific). All reactions
were performed in a K2S2 molten flux, which was prepared by
stoichiometric reaction of the elements in liquid ammonia per
literature methods.15 Reagents were loaded into fused silica ampules
inside the storage glovebox. The ampules were removed from the
glovebox, flame-sealed under vacuum, and placed in a temperature-
controlled tube furnace. The furnace was then heated to 500 °C at
35°/h and held at that temperature for 288 h. Reactions were slowly
cooled to ambient temperature at 5°/h. Products of interest were
separated from the unreacted salt flux by repeatedly washing the
sample with N,N′-dimethylformamide (DMF) until the supernatant
was clear (the excess solvated KxSy flux is an intense blue color).
All products were air stable indefinitely. Randomly selected crystals
diffracted with comparable intensity and quality to the originals
after exposure to air for periods of weeks to months. In all cases,
the compounds were not targeted by stoichiometric combination
but were discovered as a part of the exploration of quaternary phase
space (K/Th/Cu/S). Compositions of the title compounds, as
determined by energy-dispersive X-ray analyses (EDS) on a JEOL
6300 SEM, were therefore not necessarily related to the stoichi-
ometry of the reactions. Errors in this method are ca. (5%.
Compound I was synthesized by reacting 58.3 mg (0.251 mmol)
of Th, 129.3 mg (2.030 mmol) of Cu, 65.1 mg (2.03 mmol) of S,
and 34.3 mg (0.241 mmol) of K2S2. Following washing by DMF,
the sample contained a mixture of colorless rod/plate crystals of I,
the metallic green ternary KCu4S3, and the metallic purple covellite
(12) Narducci, A. A.; Ibers, J. A. Chem. Mater. 1998, 10, 2811-2823.
(13) Choi, K.-S.; Iordanidis, L.; Chondroudis, K.; Kanatzidis, M. G. Inorg.
Chem. 1997, 36, 3804-3805.
(14) Choi, K.-S.; Patschke, R.; Billinge, S. J. L.; Waner, M. J.; Dantus,
M.; Kanatzidis, M. G. J. Am. Chem. Soc. 1998, 120, 10706-10714.
(15) Sunshine, S. A.; Kang, D.; Ibers, J. A. J. Am. Chem. Soc. 1987, 109,
6202-4.
(16) Ruedorff, W.; Schwarz, H. G.; Walter, M. Z. Anorg. Allg. Chem. 1952,
269, 141-152.
(17) Roberts, H. S.; Ksanda, C. J. Am. J. Sci. 1929, 17, 489-503.
(18) Burschka, C.; Bronger, W. Z. Naturforsch. B 1977, 32, 11-14.
(19) SAINT.; Data processing software for the SMART system; Bruker
Analytical X-ray Instruments, Inc.: Madison, WI, 1995.
6464 Inorganic Chemistry, Vol. 44, No. 18, 2005

Three New Phases in the K/Cu/Th/S System
Table 1. Crystallographic Data for I, II, and III
treated with the Kubelka-Munk function, and the extrapolation
method was used to determine the band gaps.22, 23
empirical
formula
fw
a, Å
b, Å
KCuThS3
(I)
K2Cu2ThS4
(II)
565.56
14.522(1)
4.026(3)
7.566(6)
90.00
109.949(1)
90.00
K3Cu3Th2S7
(III)
430.86
4.076(1)
13.864(4)
10.541(3)
90.00
90.00
90.00
595.7(3)
4
996.42
4.051(2)
14.023(8)
24.633(1)
90.00
Results and Discussion
Structural Results. Compound I crystallized in the
orthorhombic space group Cmcm. Likely the result of its
remarkable stability, excellent quality crystals of I could be
obtained in high purity from a range of compositions.24
Consequently, the structural model was straightforward. All
atoms were given anisotropic thermal parameters, and a full
matrix, least-squares refinement converged to a final R1 of
2.36%. No evidence of disorder or twinning was discovered.
Compound I has two crystallographically unique sulfur atoms
with S-Th and S-Cu distances of 2.7872(2)-2.7838(5) Å
and of 2.334(2)-2.455(2) Å, respectively. These distances
are consonant with the formal oxidation states of Th(IV),
Cu(I), and S2- making I electron precise and a likely insulator
or semiconductor. Compound I is a member of the large
family of quaternary phases, AMRQ3 (A ) alkaline metal;
M ) transition metal; R ) Ln, An metal; Q ) chalcogenide),
with the KCuZrS3 structure type. The structure consists of
sheets that stack in the [010] direction, separated by well-
ordered potassium cations. To use a textile analogy, the
sheets are woven from alternating threads of ThS6 octahedra
and CuS4 tetrahedra which run in the [100] direction. ThS6
threads are formed by equatorial sulfur atoms that are edge
sharing and linked to the CuS4 tetrahedra by one axial and
one equatorial S atom. The CuS4 threads are formed by
corner-sharing of an apical sulfur atom contributed by the
ThS6 octahedra. The sheets are corrugated by virtue of glide
symmetry, making the sense of every other CuS4 tetrahedral
threads opposed. The Cu sites from thread to thread are
alternating above and below the plane of thorium atoms. The
ThS6 octahedra are likewise opposed within a given sheet.
The sheets are anionic and may be described in the shorthand
c, Å
R, deg
â, deg
γ, deg
V, Å3
90.00
90.00
415.8(5)
2
1399.4(1)
4
0.71073
Pbcn (No.60)
298(2)
4.729
0.0785
0.2169
Z
λ(Mo KR), Å
space group
temp., K
0.71073
Cmcm (No.63)
298(2)
4.804
0.0236
0.0495
0.71073
C2/m (No.12)
298(2)
4.517
0.0337
F
calc., Mg/m3
R1%a
wR2%a
0.0708
a R1 ) ∑(|Fo| - |Fc|)/∑|Fo|; wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
2
2
2
Table 2. Selected Bond Distances (Å) for KCuThS3 (I)
bond
distance (Å)
Th(1)-S(1) (2 eqiv)
Th(1)-S(2) (4 eqiv)
Cu(1)-S(1) (2 eqiv)
Cu(1)-S(2) (2 eqiv)
K(1)-S(1) (2 eqiv)
K(1)-S(2) (4 eqiv)
K(1)-S(2)a (2 eqiv)
2.7872(2)
2.7838(5)
2.455(2)
2.334(2)
3.197(3)
3.338(3)
3.700(6)
Table 3. Selected Bond Distances (Å) for K2Cu2ThS4 (II)
bond
distance (Å)
Th(1)-S(1) (4 eqiv)
Th(1)-S(2) (2 eqiv)
Cu(1)-S(1)
Cu(1)-S(2)
Cu(1)-S(2)a
K(1)-S(1) (2eqiv)
K(1)-S(1)a (2eqiv)
K(1)-S(2) (2eqiv)
K(1)-S(2)a
2.794(2)
2.781(3)
2.378(3)
2.425(2)
2.429(3)
3.401(3)
3.296(4)
3.185(3)
3.364(5)
Table 4. Selected Bond Distances (Å) for K3Cu3Th2S7 (III)
2
-
empirical form as ∞[CuThS3 ]. Figure 1 shows the sheets
with their charge-balancing potassium cations in the inter-
layer gallery.
bond
distance (Å)
bond
distance (Å)
Th(1)-S(1)
Th(1)-S(2)
Th(1)-S(3)
Th(1)-S(4)
Th(1)-S(1)a
Th(1)-S(2)a
Cu(1)-S(1)
Cu(1)-S(3)
Cu(1)-S(3)a
Cu(1)-S(3)b
2.79(2)
2.75(2)
2.793(6)
2.803(3)
2.76(2)
2.82(2)
2.351(7)
2.43(3)
2.472(7)
2.47(3)
Cu(2)-S(2) (2 eqiv)
Cu(2)-S(4) (2 eqiv)
K(1)-S(1) (2 eqiv)
K(1)-S(2) (2 eqiv)
K(1)-S(2)a (2 eqiv)
K(1)-S(4) (2 eqiv)
K(2)-S(1)
2.333(6)
2.422(5)
3.546(7)
3.35(2)
3.40(2)
3.185(8)
3.11(2)
3.13(2)
3.139(8)
3.31(3)
As previously noted, this structure is related to a number
of ternary compounds: MAnQ3, including FeUS3 and the
more compositionally relevant MnThSe3.25,26 These two
ternary phases feature distinct sheets with the same parent
MQ6 octahedral threads forming the sheets as in I. However,
in these other phases, sites that would be equivalent to our
Cu Td sites are empty and the transition elements exert their
strong size and electronic preferences for the octahedral sites.
In the MAnQ3 phases, the An element occupies what would
be the larger ‘A’ sites in I and create an overall structure
that is an extended 3D array. Consideration of the anionic
K(1)-S(1)a
K(1)-S(2)
K(1)-S(3)
methods and refined using the XS and XL components of the
SHELXTL software suite.20 A SADABS absorption correction was
applied to all data sets.21 Additional details are reported for I, II,
and III in Table 1, and CIF files for all three are available as
Supporting Information. Selected bond lengths are included in
Tables 2-4.
-
sheet formulation 2∞[CuThS3 ] leads one to the NaLnQ3 class
UV-Visible Spectroscopy. Samples were manually separated
from their mixtures and gently ground to uniform microcrystalline
powders. These samples were analyzed using a Varian Cary 500
Scan UV-vis-NIR spectrophotometer fitted with a Praying Mantis
accessory. A Teflon standard was used as a reference. Data were
(22) McCarthy, T.; Ngeyi, S.-P.; Liao, J.-H.; DeGroot, D. C.; Hogan, T.;
Kannewurf, C. R.; Kanatzidis, M. G. Chem. Mater. 1993, 5, 331-
340.
(23) Wilkinson, F.; Kelly, G. In CRC Handbook of Organic Photochemistry;
Scaiano, J. C. CRC Press: Boca Raton, FL, 1989; Vol. 1, 293-314.
(24) Sutorik, A. C.; Albritton-Thomas, J.; Hogan, T.; Kannewurf, C. R.;
Kanatzidis, M. G. Chem. Mater. 1996, 8, 751-761.
(25) Noel, H.; Padiou, J. Acta Crystallogr. B 1976, 32, 1593-1595.
(26) Narducci, A. A.; Ibers, J. A. Inorg. Chem. 2000, 39, 688-691.
(20) SHELXTL 6.10; Brukers AXS, Inc.: Madison, WI, 2000.
(21) Sheldrick, G. M. SADABS; University of Gottingen: Gottingen,
Germany, 1997.
Inorganic Chemistry, Vol. 44, No. 18, 2005 6465

Selby et al.
an extra Oh site filled with respect to I), it becomes
isostructural with the anionic layers in MnThSe3. Indeed,
the imaginary stoichiometry is maintained in dianionic sheets
that may be written as ∞[ZrSe32-]. Void-filling and charge
2
balance are then trivial matters of placing the appropriate
atoms in the correct sites to re-create a structure related to
compound I. If ZrSe3 is not considered the parent structure,
one may consider it to be a “close uncle” structure, and this
suggests a range of unexplored variations within the three
canonical structure types ZrSe3, MAnQ3, and AMRQ3.
Compound II crystallized in the space group C2/m. The
final R1 value for a full matrix, least-squares refinement with
all atoms treated anisotropically converged at 3.337%. A
rendering of II can be seen in Figure 3.
Compound II also features a layered structure with a close
relationship to I. In II, the sheets are similarly composed of
alternating threads of edge-sharing ThS6 octahedra and CuS4
tetrahedra with potassium cations in the interlayer gallery.
However, the ThS6 threads are separated completely from
each other in the sheet by a double thread of edge-sharing
CuS4 tetrahedra as shown in Figure 3. In contrast, the threads
of ThS6 in I share vertexes in the direction normal to their
direction of propagation. At first glance, the sheets in I and
II appear to be virtually identical, save for the extra CuS4
thread in II. Upon examination of the layers in II, one finds
that the edge-sharing CuS4 tetrahedra are related by a pseudo-
inversion center. This has the effect of orienting the octahedra
in the same direction within the sheet, eliminating the
corrugation observed in I.
Figure 1. Packing diagram of I, showing corrugated sheets consisting of
ThS6 octahedra and CuS4 tetrahedra: crosshatched spheres ) K+; black
spheres ) Th(IV); gray spheres ) Cu(I); hollow spheres ) S2-
.
of compounds which, with the parent ZrSe3 structure, are
not obviously related to I.27 Yet, with some manipulation of
the subtle interplay of redox chemistry and the thermody-
namic need to minimize structural voids, a relationship can
be developed.
For example, to make the charge balance in ZrSe3, some
2-
of the selenides are oxidized to form Se2 anions. These
diselenide units form the alternating tops and bottoms of the
ZrSe3 sheets, with the Zr atoms in distorted bicapped trigonal
prismatic sites. The Se22- units are considerably larger than
a single selenide anion and serve to take up the large void
volume that would result from such a charge-allowed
substitution. Like the ThS6 octahedra of I, the Zr prisms form
threads, in this instance by face sharing. Each of the
diselenide units bridges the Zr atoms in a given thread and
are bound normal to the thread direction in a µ-η2 fashion.
Because of the bridging interaction, the diselenide units are
shared between neighboring Zr atoms and are equivalent by
stoichiometry to two single-selenide anions per Zr atom.
Alternatively, one could consider the η2 binding mode as
occupying a single large coordination site (akin to an olefin
complex) and one would still arrive at a single selenide anion
equivalent per Zr atom. From either perspective, the coor-
dination number of Zr could be argued to be 6, not 8. Such
an argument suggests the trigonal prismatic coordination in
ZrSe3 hides an octahedron and creates a link to the MQ6
octahedra in MnThSe3 and I.
With this notion in mind, one may perform the gedanken
experiment shown in Figure 2. If the two diselenide units
are simply condensed to a single site at the Se-Se centroid,
the Zr coordination environment becomes a grossly distorted
octahedron with large voids in the lattice. Note that the
bridging interaction of the new artificial monoselenide
interaction is maintained and the distorted octahedra are now
edge sharing as in I. The distortion is now contained in the
axial Se-M-Se bend. If this imaginary structure is allowed
to relax and 1 equiv of ZrSe2 per cell is removed (the top or
bottom half of the ZrSe3 sheet may be thought of as having
The structure of II is remarkably rare, with only one
known Ce-containing analogue, K2Cu2CeS4.24 This Ce
structure and that of compound II are closely related to the
magnesium-silicate mineral olivine and share an interesting
relationship with FeTaTe3.28,29 In the latter material, each
sheet is composed of a 2 (octahedra):1 (tetraheda) thread
pattern ratio. This is the opposite ratio of that observed in
II, with the TaTe6 octahedral threads being doubled with
only single FeTe4 tetrahedral threads separating them. It is
also possible to relate compound II to CdI2 when considering
the distorted hcp lattice of sulfur atoms in a given layer of
II. Instead of every octahedral hole being filled, as in CdI2,
every third octahedral hole is filled in II. Like compound I,
bond lengths lead to an assignment of formal oxidation states,
Th(IV), Cu(I), and S2-, and precise electron count.
Unfortunately, only single crystals of moderate to poor
quality (R1 ) 7.85%) could be found for III. However, a
dataset did provide enough information to confidently assign
atomic positions on the basis of relative peak heights and
reasonable bond length and angle measurements. The
structure could be solved in several space groups; each gave
the same model. Also, crystal morphology and color were
distinct from compounds I and II and the absorption edge
is shifted significantly from I and II. Finally, the microprobe
analysis was in excellent agreement with the composition
(28) Carpenter, J. D.; Hwu, S. J. Chem. Mater. 1992, 4, 1368-1372.
(29) Liu, S.-X.; Cai, G.-L.; Huang, J.-L. Acta Crystallogr. C 1993, 49,
4-7.
(27) Sutorik, A. C.; Kanatzidis, M. G. Chem. Mater. 1997, 9, 387-398.
6466 Inorganic Chemistry, Vol. 44, No. 18, 2005

Three New Phases in the K/Cu/Th/S System
Figure 2. The pseudo-synthetic relationship between ZrSe3 and I.
Figure 3. Packing diagram of II, formed from sheets of ThS6 octahedra
and doubled CuS4 tetrahedra: crosshatched spheres ) K+; black spheres
) Th(IV); gray spheres ) Cu(I); hollow spheres ) S2-
.
Figure 4. Packing diagram of III, featuring a sinusoidal distortion of the
sheets as a result of the combination of both single and double CuS4 threads
linking the ThS6 octahedra: crosshatched spheres ) K+; black spheres )
derived from the structure. These three observations led us
to conclude that the reported model is reasonable and correct.
The final structure was solved by direct methods in the space
group Pbcn. This was the most reasonable choice on the basis
of systematic absences, manual examination of reciprocal
space symmetry, and quality of refinement. Atomic positions
were readily located, but high residual electron density
remained near S1. This peak was also close to Cu1 and K2
and modeled reasonably well as a partially occupied S site.
Th(IV); gray spheres ) Cu(I); hollow spheres ) S2-
.
However, the proximity to the other sites was chemically
unreasonable in addition to violating the logical as-found
stoichiometry. Efforts to refine the structure as a simple twin
did not improve the situation, and the data were insufficient
to model with confidence nonmerohedral twins. Analysis of
Inorganic Chemistry, Vol. 44, No. 18, 2005 6467

Selby et al.
Figure 5. A comparison of the three sheet types and progression of the CuS4 dimensionality for I-III: a ) I, b ) III, c ) II; octahedra ) Th(IV), gray
spheres ) Cu(I); colorless spheres ) S2-
.
the raw data revealed a number of weak reflections that did
not fit the cell well, which suggested the presence of closely
aligned crystallites or cracking. This was corroborated by
the observation of striations along the major axis of the
macroscopic crystal. Despite constraints placed on the
integration, the resultant data did not allow for reliable
application of sophisticated disorder/twin models. We there-
fore concluded that the high residual density was an artifact
of poor data. All other sites were refined isotropically.
Compound III has a layered structure much like those of
I and II. In fact, the structure is an interesting hybrid of
compounds I and II. Like I and II, the sheets are composed
of alternating threads of ThS6 octahedra linked by CuS4
tetrahedra, with potassium ions between the sheets. Again,
single threads of ThS6 octahedra are formed by edge sharing,
extending in the [100] direction. Instead of only single or
only double CuS4 threads joining the ThS6 threads, compound
III features both. On one side of the ThS6 octahedral thread
is a single CuS4 thread like those found in compound I, on
the other, a double thread similar to compound II. This
combined pattern results in the sheets exhibiting a sinusoidal
distortion from planarity that propagates along [001] as
shown in Figure 4. Figure 5 shows a comparison of the thread
patterns in compounds I-III. This comparison reveals the
relationship between the three structures: The structure of
III may be considered to be an intermediate between the
1:1 octahedron/tetrahedron ratio of I and the 1:2 ratio found
in II. This interpretation is supported by the analysis of the
empirical formulas of the three compounds. Compound I has
a 1:1:1:3 ratio of K, Cu, Th, and S, respectively. Compound
II has the ratio 2:2:1:4, and III’s ratio is 3:3:2:7 or 1.5:1.5:
1:3.5. This fractional composition is exactly between I and
II. Like I and II, the empirical formula and reasonable bond
lengths make III electron precise with formal oxidation states
of Th(IV), Cu(I), and S2-. To the best of our knowledge,
III is a new structure type.
Figure 6. Diffuse reflectance spectra of I-III {s (I), ‚‚‚‚‚ (II), - - - -
(III)}.
ferences in structure. The other difference is appearance of
complicated structure at the onset of absorption for II and
III, in contrast with the very sharp absorption edge for I.
Several recent papers have discussed the nature of the
observed band gaps in layered materials similar to the title
compounds.5,7,30-32 The conclusion reached by the authors
of these articles was that the band gap was primarily a
function of 1) the distance between the layers and the
corresponding degree of interlayer van der Waals contact
and 2) the dimensionality of features within a layer and their
relative covalency. Since the title compounds all have
potassium cations in the interlayer gallery, there is no true
van der Waals gap and the distance between layers is not
likely a factor in determing the optical band gap. The second
effect, however, is quite likely to have a strong influence on
the value of the optical gap. Extensive calculations on Ln/
d10 compounds isostructural with I have shown that the
materials are direct band gap semiconductors with narrow
bands due to the primarily ionic interactions between the
metals and the chalcogenide anions.6 Since the title com-
pounds contain f 0 Th(IV), we propose that the Th frontier
orbitals are noninteracting and high-lying components of the
conduction band, leaving the Cu 3d and S 3p states
Optical Band Gap Measurements. The diffuse reflec-
tance data for I-III are shown in Figure 6. The band gaps
were 2.95, 2.17, and 2.49 eV for I, II, and III, respectively.
As expected from the precisely determined oxidation states,
the measured band gaps for all three phases fall in the normal
range for semiconductors. However, two significant differ-
ences exist between the three samples. The most obvious
difference is the relatively wide spread of band gaps within
the seriessnearly an electronvolt for seemingly small dif-
(30) Huang, F. Q.; Ibers, J. A. Inorg. Chem. 2001, 40, 2602-2607.
(31) Axtell, E. A., III.; Park, Y.; Chondroudis, K.; Kanatzidis, M. G. J.
Am. Chem. Soc. 1998, 120, 124-136.
(32) Brown, D. B.; Zubieta, J. A.; Vella, P. A.; Wrobleski, J. T.; Watt, T.;
Hatfield, W.; Day, P. Inorg. Chem. 1980, 19, 1945-1950.
6468 Inorganic Chemistry, Vol. 44, No. 18, 2005

Three New Phases in the K/Cu/Th/S System
contributing most to the direct band gap, akin to the
aforementioned Ln materials and the A2TiM2S4 (A ) Rb,
Cs; M ) Cu, Ag) series.30 The presence of Th sites in the
otherwise contiguous CuS4 framework serves to break up
the extended Cu-S interactions, reducing them to pseudo-
1D and narrow 2D interactions in the title compounds. As
discussed in other systems, this reduction in dimensionality
decreases the number of close-lying Cu-S states and narrows
and separates the bands.31 Applying this logic allows us to
explain the shifts in absorption across the series I-III.
Compound I has only a single thread of CuS4 tetrahedra and
therefore the least diffuse bands and largest band gap.
Compound II features double CuS4 threads with more
extended Cu-S interaction leading to the most diffuse bands
and the narrowest band gap. Since III has both types of
threads in isolation, its absorbance profile would appear to
be the superposition of I and II. Further theoretical inves-
tigation is required to confirm this hypothesis.
The second feature of the spectra, the complicated structure
observed in II and III, is less easily rationalized. Compound
I is a direct analogue for the CsMLnSe3 materials and, like
them, is clearly a simple direct band gap semiconductor. The
pre-gap structure in II and III could be the result of impurity,
but the impurities in both compounds do not have bands in
the region in question.32-34 It is more likely that the features
are intrinsic to the materials and suggests indirect transitions
and complex band structure. It is imprudent to speculate what
gives rise to these bands without the benefit of theoretical
computation. However, II and III both have larger numbers
of crystallographically unique S and Cu atoms and/or lower
symmetry than I and may consequently have larger numbers
of energetically discrete states close to the Fermi level.
Conclusion
The successful synthesis and characterization of KCuThS3,
K2Cu2ThS4, and K3Cu3Th2S7 marks the first entry in the
K/Cu/Th/S phase diagram. Although the first two compounds
do have analogues in other compositions, none are known
in the present system.24,35 The third compound, K3Cu3Th2S7,
appears to be a structural and spectroscopic hybrid of the
first two and may represent a new structure type. More
significantly, each of these materials exhibits characteristic
optical band gaps that are quite well separated from each
other. This observation is related to the extent of the CuS4
network featured in each structure, suggesting that Th
concentration is the synthetic handle for tuning the optical
properties of related materials. To date, these materials have
no reported U analogues, although work in this direction is
proceeding. Even though the U analogues are all likely
isolable, the title compounds remain important because they
provide understanding of electronic structure in the absence
of complicating f electrons. Such a basis will allow for a
more certain structure/function relationship to be developed
once the magnetic U analogues are in hand.
Acknowledgment. The authors thank Ms. Susie Miller
and Dr. Brian Scott for the use of their X-ray diffractometers
and Dr. Sandeep Kholi for training on the diffuse reflectance
instruments. Funding for this work was provided by the
Department of Energy, Heavy Element Chemistry-ER15351
and the NMT division of Los Alamos National Laboratory
(H.D.S.).
Supporting Information Available: Additional crystallographic
details in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
(33) Folmer, J. C. W.; Jellinek, F. J. Less-Common Met. 1980, 76, 153-
IC050561X
162.
(34) Peplinski, Z.; Brown, D. B.; Watt, T.; Hatfield, W.; Day, P. Inorg.
Chem. 1982, 21, 1752-1755.
(35) Cody, J. A.; Ibers, J. A. Inorg. Chem. 1995, 34, 3165-3172.
Inorganic Chemistry, Vol. 44, No. 18, 2005 6469