Synthesis and Characterization of Two New Copper Tellurites, Ba2Cu4Te4O11Cl4 and BaCu2Te2O6Cl2, in Supercritical H2O

Article abstract of DOI:10.1021/ic971264y

Two new compounds containing tellurite building blocks coordinated to copper and barium atoms have been isolated from hydrothermal solvents. A new layered compound, Ba₂Cu₄Te₄O₁₁Cl₄ (I), has been obtained by reacting BaCl₂·2H₂O, CuO, and Te(OH)₆ in NH₄Cl solution at 375°C for 4 days. Green, platelike crystals of I crystallize in the centrosymmetric space group, P1?, with a = 9.275(2) A?, b = 12.135(2) A?, c = 9.263(2) A?, ? = 98.23(3)°, β = 108.35(3)°, γ = 110.90(3)°, and Z = 2. The compound contains two types of layers, one based on copper oxides linked by Te₄O₁₁ groups, and the other based on Cu₂Cl₄ units. The tellurium atoms adopt the common TeO₃₊₁ units or TeO₃ pyramids, and the oxygen-coordinated copper atoms adopt a square planar CuO₄ arrangement. Dark green, prismatic crystals of BaCu₂O₆Cl₂ (II) were obtained by reacting BaCl₂·2H₂O, Cu₂O, and Te(OH)₆ in NH₄Cl solution at 375°C for 18 h. Compound II was refined in the acentric monoclinic space group, P2₁ (a = 7.434(2) A?, b = 7.448(2) A?, c = 8,271(2) A?, β = 97.42(3)°, Z = 2), and is based on Te₂O₆ units connected by copper atoms or copper chloride groups. As in I, tellurium atoms are contained within TeO₃₊₁ or TeO₃ units and the connecting copper atoms are nearly square planar. The chloride-coordinated copper atoms group adopt a square pyramidal CuO₃Cl₂ geometry with a chlorine atom occupying the apical position. The formal oxidation states of the copper atoms in compound I are distributed such that the connecting atoms in an oxide environment are 2+ and atoms within a chloride environment are 1+, whereas in compound II, all copper atoms are 2+. Bond valence sums for both compounds and magnetic susceptibility data for I support these assignments. The optical band gap for I was determined by diffuse reflectance spectroscopy and indicate that it is a wide band gap material (E_g = 3.00 eV).

Full text of DOI:10.1021/ic971264y

4046
Inorg. Chem. 1998, 37, 4046-4051
Synthesis and Characterization of Two New Copper Tellurites, Ba2Cu4Te4O11Cl4 and
BaCu2Te2O6Cl2, in Supercritical H2O
Christopher R. Feger and Joseph W. Kolis*
Department of Chemistry, Clemson University, Clemson, South Carolina 29634-1905
ReceiVed October 10, 1997
Two new compounds containing tellurite building blocks coordinated to copper and barium atoms have been
isolated from hydrothermal solvents. A new layered compound, Ba2Cu4Te4O11Cl4 (I), has been obtained by
reacting BaCl2‚2H2O, CuO, and Te(OH)6 in NH4Cl solution at 375 °C for 4 days. Green, platelike crystals of I
crystallize in the centrosymmetric space group, P1h, with a ) 9.275(2) Å, b ) 12.135(2) Å, c ) 9.263(2) Å, R
) 98.23(3)°, â ) 108.35(3)°, γ ) 110.90(3)°, and Z ) 2. The compound contains two types of layers, one based
on copper oxides linked by Te4O11 groups, and the other based on Cu2Cl4 units. The tellurium atoms adopt the
common TeO3+1 units or TeO3 pyramids, and the oxygen-coordinated copper atoms adopt a square planar CuO4
arrangement. Dark green, prismatic crystals of BaCu2Te2O6Cl2 (II) were obtained by reacting BaCl2‚2H2O, Cu2O,
and Te(OH)6 in NH4Cl solution at 375 °C for 18 h. Compound II was refined in the acentric monoclinic space
group, P21 (a ) 7.434(2) Å, b ) 7.448(2) Å, c ) 8.271(2) Å, â ) 97.42(3)°, Z ) 2), and is based on Te2O6 units
connected by copper atoms or copper chloride groups. As in I, tellurium atoms are contained within TeO3+1 or
TeO3 units and the connecting copper atoms are nearly square planar. The chloride-coordinated copper atoms
group adopt a square pyramidal CuO3Cl2 geometry with a chlorine atom occupying the apical position. The
formal oxidation states of the copper atoms in compound I are distributed such that the connecting atoms in an
oxide environment are 2+ and atoms within a chloride environment are 1+, whereas in compound II, all copper
atoms are 2+. Bond valence sums for both compounds and magnetic susceptibility data for I support these
assignments. The optical band gap for I was determined by diffuse reflectance spectroscopy and indicate that it
is a wide band gap material (Eg ) 3.00 eV).
Introduction
unusual coordination environments. In addition to the usual
pyramidal TeO3
2-
fragments8,9 like sulfites and selenites,
Recent research efforts in our group have focused on the
synthesis of new materials in supercritical fluids, based on the
techniques reported by Rabenau.1 Supercritical fluids provide
a number of advantages over conventional solid state systems.
Chemical manipulation is often easier and the relatively low
temperatures lead to the isolation of numerous kinetically
stabilized phases. A large number of chalcogenide compounds,
such as Cs3Ag2Sb3S8,2 Cs2AgMS4 (M ) As, Sb),2 CsCu2SbS3,3
and Cs5Sb8S18(HCO3),4 have been isolated from supercritical
amines in our labs. Recently, we have shown that divalent
transition metal group 15-16 phases such as MnSb2S4 can also
be obtained hydrothermally.5
tellurites also form four-coordinated TeO44- fragments10,11 with
C2V symmetry. In fact they are one of the few sources of a
main group building block with this symmetry. Finally tellurites
also adopt a unique TeO3+14- geometry,6,11-12 whereby one of
the axial sites of the pseudotrigonal bipyramid is much longer
than the other. Thus their coordination chemistry is of interest
since they should be a source of new and interesting solid state
phases. This unusually rich chemistry has recently led us to
investigate the synthesis and chemistry of a series of isostructural
metal tellurites M2Te3O8 (M ) Co, Ni, Cu, Zn).6
We are attempting to expand this chemistry by introducing
alkaline-earth ions to the metal tellurites. Due to its unusual
coordination chemistry, copper was our initial target. Indeed
we were successful in forming a series of novel barium copper
tellurites, but we also found that chloride ions from the
mineralizer became incorporated in the lattice, forming barium
copper tellurium oxyhalides. In this paper we report on two
new phases which contain copper(II) in unusual square planar
coordination environments created by tellurium(IV) oxyanion
ligands.
In an attempt to illustrate the breadth of this technique, we
recently became interested in the use of tellurates and tellurites
as building blocks in extended solid systems.6,7 The tellurites
are especially appealing because they adopt a number of very
(1) Rabenau, A. Angew. Chem., Int. Ed. Engl. 1985, 24, 1026.
(2) Wood, P. T.; Schimek, G. L.; Kolis, J. W. Chem. Mater. 1996, 8,
721.
(3) Jerome, J. E.; Schimek, G. L.; Kolis, J. W. Inorg. Chem. 1994, 33,
1733.
(4) Schimek, G. L.; Kolis, J. W. Inorg. Chem. 1997, 36, 1689.
(5) Kolis, J. W.; Korzenski, M. B. In Materials Research Society
Symposium Proceedings; Davies, P. K., Jacobson, A. J., Torardi, C.
C., Vanderah, T. A., Eds.; Materials Research Society: Pittsburgh,
PA, 1997; Vol. 453, p 35.
(6) Feger, C. R.; Schimek, G. L.; Kolis, J. W. J. Solid State Chem.,
submitted.
(8) Kohn, K.; Inoue, K.; Horie, O.; Akimoto, S.-I. J. Solid State Chem.
1976, 18, 27.
(9) Hanke, K. Naturwissenschaften 1967, 54, 199.
(10) Lindqvist, O. Acta Chem. Scand. 1968, 22, 977.
(11) Hanke, K. Naturwissenschaften, 1966, 53, 273.
(12) Hanke, K.; Kupcik, V.; Lindqvist, O. Acta Crystallogr. 1973, B29,
963.
(7) Feger, C. R.; Kolis, J. W. Acta Crystallogr. 1998, C54, 1055.
S0020-1669(97)01264-0 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/24/1998

Copper Tellurites Ba2Cu4Te4O11Cl4 and BaCu2Te2O6Cl2
Inorganic Chemistry, Vol. 37, No. 16, 1998 4047
Table 1. X-ray Crystallographic Data
space group, P21, was chosen after a refinement in P21/m failed to
yield a satisfactory model for the structure. Both structures were solved
by direct methods (TEXSAN)14 and refined on |F| by full-matrix least-
squares techniques in SHELXTL-PLUS.15 Absorption effects were
compensated for by the use of empirical ψ-scan data.16 All atomic
parameters in I were refined anisotropically, except for O(11), which
was refined isotropically. Due to the enlarged thermal parameters
associated with Cu(3) and Cu(4), a number of alternative refinements
were attempted. In one model, Cu(3) and Cu(4) were each separated
into two sites with half-occupancy 0.2 Å apart. Upon refinement, this
model diverged and the separate sites coalesced to their original single
positions. Alternatively, attempts at refining site occupancies of Cu(3)
and Cu(4) failed to yield improvements in the structural model, residual
peak densities, and refinement parameters. Further details are included
in Results and Discussion. All atomic parameters in II were refined
anisotropically, and a refinement in the opposite chirality was performed
to determine the best fit. The refinement with the lowest R and Rw
was used as the final structural solution. No higher symmetry was
detected for either compound with the MISSYM algorithm within the
PLATON program suite.17,18 Crystallographic details are given in Table
1. The final positional parameters, relevant interatomic distances, and
relevant bond angles for both compounds are given in Tables 2, 3, and
4, respectively. The anisotropic thermal parameters can be obtained
in the Supporting Information.
Physical Characterization. The magnetic susceptibility data were
determined using a Quantum Design SQUID magnetometer. A sample
(∼20 mg) of ground crystals of I was placed in a gelatin pill capsule
which was subsequently held in a standard plastic drinking straw.
Readings of the sample holder showed negligible diamagnetic effects
on the bulk sample. Room-temperature diffuse reflectance measure-
ments from 800 to 200 nm on compound I were made using a Shimadzu
UV3100 spectrophotometer equipped with an integrating sphere at-
tachment. Barium sulfate was used as the reflectance standard. The
reflectance data were converted to absorbance data using the Kubelka-
Monk function.19
empirical formula
space group
a (Å)
b (Å)
c (Å)
Ba2Cu4Te4O11Cl4 (I)
P1h (No. 2)
9.275(2)
12.135(2)
9.263(2)
98.23(3)
108.35(3)
110.90(3)
885.2(3)
2
5.091
162.06
1357.05
room temp
0.71073
0.0458
BaCu2Te2O6Cl2 (II)
P21 (No. 4)
7.434(2)
7.448(2)
8.271(2)
90
97.42(3)
90
454.1(2)
2
5.021
158.02
686.52
room temp
0.71073
0.0388
R (deg)
â (deg)
γ (eg)
V (Å3)
Z
F
calcd (g cm-3
)
µ (cm-1
)
fw (g mol-1
T (°C)
)
λ (Å)
Ra (Fo > 6σ(Fo))
Rwb (Fo > 6σ(Fo))
0.0678
0.0491
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w{|Fo| - |Fc|}2/∑w|Fo| ]1/2
;
2
w ) 1/[σ2{|Fo|} + 0.0025{|Fo|}2.
Experimental Details
Synthesis. The compounds obtained in this study were prepared
using modifications on techniques reported by Rabenau.1 Compound
I, Ba2Cu4Te4O11Cl4, was originally prepared by loading BaCl2‚2H2O
(73 mg, 0.30 mmol, Strem, 99+%), CuO (48 mg, 0.60 mmol, Strem,
99.9%), and Te(OH)6 (138 mg, 0.603 mmol, Strem, 99.9%) into fused
silica tubes (5 mm i.d., 7 mm o.d., ∼1.6 cm3 sealed volume). A 0.7
mL amount (45% fill) of a 2 M NH4Cl solution was added, and the
tubes were flame-sealed after the solvent was frozen in liquid nitrogen.
The tubes were placed in a high-pressure autoclave with 2500 psi of
argon counter-pressure to prevent bursting of the tubes during reaction.
The autoclave was placed in a furnace and heated at 375 °C for 5 days,
after which the autoclave was removed directly from the furnace. After
cooling, I was obtained in ∼30% yield as green plates, with the
remainder of the products being the highly crystalline phases, Cu2Te3O8
(yellow plates)6 and TeO2 (clear prisms). The products were filtered,
washed with distilled water and acetone, and physically separated by
color. Compound I is indefinitely stable in air. It was subsequently
determined that yields of I approaching 50% could be achieved by
reacting BaCl2‚2H2O, CuO, and TeO2 (Strem, 99.9%) in a 1:2:2 ratio
in 5 M NH4Cl at 375 °C for 4 days.
Large, green prismatic crystals of BaCu2Te2O6Cl2 (II) were obtained
by heating a mixture of BaCl2‚2H2O (74 mg, 0.30 mmol), Cu2O (43
mg, 0.30 mmol, Strem, 99.9%), and Te(OH)6 (139 mg, 0.605 mmol)
in 1 M NH4Cl solution at 375 °C for 18 h. This material was obtained
at <10% yield with CuTeO4 as the major phase in the form of a yellow
polycrystalline powder. Longer reaction times with similar amounts
of starting materials yielded varying mixtures of I, Cu2Te3O8, and
CuTeO4.13 Compound II proved to be somewhat air or moisture
sensitive, as the material degraded after several days in air, but showed
no visible indications of decomposition after several weeks in mineral
oil.
Results and Discussion
Structure. Compound I, Ba2Cu4Te4O11Cl4, is a two-
dimensional compound with two types of layers situated in the
ac plane as shown in Figure 1. The structure is made up of
two copper tellurite layers separated by a copper chloride layer.
This arrangement of three layers is separated by a layer of
barium atoms. The copper tellurite layer consists of nearly
square planar CuO4 units, TeO3 pyramids, and TeO3+1 poly-
hedra. The copper chloride layer is made up of CuCl4 tetrahedra
and a CuCl2O unit, which is in essentially a distorted trigonal
planar arrangement.
The copper tellurite layer, shown in Figure 2 as a projection
in the ac plane, can be viewed as having Te4O11 subunits
alternating throughout the layer. These subunits are made by
joining two TeO3+1 polyhedra through an apical oxygen atom
and then adding TeO3 pyramids to the opposite apical atom of
each TeO3+1 polyhedra. These Te4O11 subunits are linked to
one another through copper atoms, which are connected to the
ends of two separate subunits and the center of a third.
All of the coordination polyhedra for copper and tellurium
in this layer are fairly regular and have been observed in other
compounds. The TeO3+1 polyhedra have equatorial Te-O
Qualitative SEM/EDS analyses on crystals of both compounds
verified the presence of Ba, Cu, Te, Cl, and O and the absence of any
impurity elements heavier than F.
Crystallography. Crystals of both phases were mounted onto the
ends of glass fibers using quick-drying epoxy and were studied using
a Rigaku AFC7R four-circle diffractometer equipped with graphite-
monochromated Mo KR (λ ) 0.710 73 Å) radiation. An ω-2θ scan
mode was utilized for room-temperature data collection for both
compounds. Three standard reflections measured after every 97
reflections indicated that the crystals were stable (<2% decay) for both
compounds, and 2θ limits of 52° for I and 55° for II were employed.
The intensity data were corrected for both Lorentz and polarization
effects. Additional data are included in Table 1.
(14) TEXSAN: Single-Crystal Structure Analysis Software, Version 1.6b;
Molecular Structure Corp.: The Woodlands, TX, 1993.
(15) Sheldrick, G. M. SHELXTL-PLUS; Siemens Analytical X-Ray Instru-
ments, Inc.: Madison, WI, 1990.
(16) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(17) LePage, Y. J. Appl. Crystallogr. 1987, 20, 264.
(18) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(19) Wendlandt, W. W.; Hecht, H. G. Reflectance Spectroscopy; Inter-
science Publishers: New York, 1966.
The centrosymmetric space group, P1h, was chosen for I on the basis
of lattice parameters and statistical tests. The systematic absence 0k0,
k ) 2n + 1, indicated that II could be either P21 or P21/m. The acentric
(13) Falck, L.; Lindqvist, O.; Mark, W. Acta Crystallogr. 1978, B34, 1450.

4048 Inorganic Chemistry, Vol. 37, No. 16, 1998
Feger and Kolis
Table 3. Relevant Interatomic Distances with ESD’s (in Å)
Ba2Cu4Te4O11Cl4 (I)
Table 2. Atomic Coordinates and Equivalent Isotropic Thermal
Parameters (Å2)
a
Te(1)-O(1)
2.264(10)
Cu(4)-Cl(2)
-Cl(3)
-Cl(4)
-Cl(4)
Ba(1)-Cl(3)
-O(1)
2.360(5)
2.251(5)
2.398(5)
2.446(3)
3.182(4)
2.905(9)
2.910(11)
2.926(7)
2.944(8)
2.961(9)
2.906(10)
2.919(9)
2.926(7)
2.871(10)
2.858(9)
3.225(4)
2.902(7)
2.866(9)
2.872(8)
2.889(9)
2.882(11)
2.878(7)
2.889(8)
2.875(10)
2.878(9)
2.893(10)
X
Y
Z
Ueq
-O(2)
1.865(10)
2.013(11)
1.869(6)
2.009(10)
1.871(11)
1.865(6)
2.263(9)
1.901(10)
1.857(9)
1.872(7)
1.914(9)
1.867(11)
1.861(6)
2.676(4)
1.953(10)
1.960(8)
1.971(8)
1.958(9)
2.666(3)
1.965(8)
1.963(9)
1.968(11)
1.964(9)
2.192(6)
2.305(5)
2.030(8)
Ba2Cu4Te4O11Cl4 (I)
-O(3)
-O(5)
Ba1
Ba2
Te1
Te2
Te3
Te4
Cu1
Cu2
Cu3
Cu4
Cl1
Cl2
Cl3
Cl4
O1
O2
O3
O4
O5
O6
O7
O8
O9
0.28067(8)
0.78471(8)
-0.02330(8)
0.22106(9)
0.47654(9)
0.74715(9)
0.4002(2)
0.8985(2)
0.0982(3)
0.4448(3)
0.0384(5)
0.5513(6)
0.55869(6)
0.24221(7)
0.24132(7)
0.26492(7)
0.26235(7)
0.3282(1)
0.3280(1)
0.0160(2)
-0.0178(2)
0.1443(3)
0.0882(3)
-0.1553(3)
0.0884(3)
0.3495(7)
0.3524(8)
0.1655(8)
0.3502(8)
0.3496(8)
0.3523(7)
0.3484(8)
0.3622(8)
0.3621(8)
0.3657(8)
0.3596(7)
0.01879(7)
0.52130(7)
0.02612(8)
-0.21702(8)
0.55264(8)
0.27196(8)
0.1872(2)
0.6853(2)
0.2371(3)
0.3042(2)
0.3727(4)
0.1548(4)
0.1260(4)
0.5377(4)
0.1945(8)
-0.0876(8)
-0.1249(9)
-0.2769(9)
0.1666(8)
-0.0216(8)
-0.3075(8)
0.4171(8)
0.2297(9)
0.6703(9)
0.4802(8)
0.0098(3)
0.0098(3)
0.0085(4)
0.0084(3)
0.0090(3)
0.0095(3)
0.0090(5)
0.0092(5)
0.054(1)
0.048(1)
0.028(2)
0.024(1)
0.024(1)
0.024(1)
0.009(3)
0.013(3)
0.017(4)
0.013(3)
0.012(3)
0.011(3)
0.011(3)
0.011(3)
0.014(4)
0.013(3)
0.009(2)
Te(2)-O(3)
-O(4)
-O(6)
-O(7)
-O(2)
-O(2)
Te(3)-O(7)
-O(8)
-O(4)
-O(5)
-O(10)
Te(4)-O(1)
-O(9)
-O(6)
-O(6)
-O(7)
-O(11)
Cu(1)-Cl(2)
-O(5)
-O(9)
0.3155(4)
0.4606(4)
0.7102(4)
-O(10)
Ba(2)-Cl(1)
-O(1)
-O(6)
-0.0905(9)
-0.0558(10)
0.0532(10)
0.1289(9)
0.1964(10)
0.3814(10)
0.4117(10)
0.4540(10)
0.6348(10)
0.7057(10)
0.8840(9)
-O(8)
-O(4)
-O(9)
-O(5)
Cu(2)-Cl(4)
-O(2)
-O(7)
-O(8)
-O(4)
-O(8)
-O(10)
-O(11)
Cu(3)-Cl(1)
-Cl(2)
-O(9)
-O(10)
-O(11)
-O(11)
O10
O11
-O(3)
BaCu2Te2O6Cl2 (II)
BaCu2Te2O6Cl2 (II)
0.84350
0.4694(2)
0.1920(2)
0.3144(2)
0.3410(2)
0.0845(5)
Te(1)-O(2)
-O(4)
1.879(7)
1.877(9)
1.876(10)
1.878(8)
1.920(12)
2.374(9)
1.895(8)
1.941(10)
2.717(4)
2.362(4)
2.011(10)
1.902(8)
Cu(2)-O(1)
1.998(9)
1.936(9)
1.937(9)
1.944(9)
3.062(4)
3.166(4)
2.810(10)
2.777(9)
2.851(8)
3.026(10)
2.867(8)
2.569(9)
Ba1
Te1
Te2
Cu1
Cu2
Cl1
Cl2
O1
O2
O3
O4
O5
0.13612(8)
0.13133(9)
0.3446(1)
0.6901(2)
0.3617(2)
-0.1203(5)
-0.5532(5)
0.2012(11)
0.1551(12)
0.5512(12)
-0.1212(12)
0.1909(13)
0.4743(11)
0.07030(7)
0.39125(8)
0.76730(8)
0.4038(2)
0.0878(2)
0.2347(4)
0.3742(4)
0.0113(2)
0.0089(2)
0.0083(2)
0.0119(4)
0.0104(4)
0.0211(9)
0.0196(8)
0.011(2)
0.013(2)
0.018(2)
0.014(2)
0.012(2)
0.016(3)
-O(2)
-O(5)
-O(3)
-O(6)
Te(2)-O(1)
-O(3)
Ba(1)-Cl(1)
-Cl(1)
-O(1)
-O(4)
-O(6)
0.1081(5)
Cu(1)-O(3)
-Cl(1)
-O(1)
0.1812(13)
0.4518(14)
0.4563(16)
0.5000(14)
0.7142(14)
0.7748(17)
-0.0619(9)
0.1683(9)
0.2346(10)
0.3719(10)
0.3994(9)
0.0672(10)
-O(2)
-Cl(2)
-O(2)
-O(4)
-O(5)
-O(5)
-O(6)
O6
six-membered oxygen plane. The Ba-O distances (2.858(9)-
2.961(9) Å) tend to be slightly shorter than the calculated value
(2.95 Å) using the sum of the Ba and O crystal radii.21
a Ueq ) ∑i∑j(Uijai*aj*ai‚aj).
distances of ranging from 1.865(6) to 1.871(11) Å and axial
distances of 2.009(10) and 2.264(10) Å. This coordination
environment is highly similar to those in M2Te3O86 or CuTe2O5.12
The TeO3 pyramid has Te-O distances ranging from 1.857(9)
to 1.914(9) Å and has been seen in several other tellurite
materials as well. The square planar arrangement of oxygen
atoms around Cu(1) and Cu(2) are both fairly regular with bond
distances ranging from 1.953(10) to 1.971(8) Å, which is similar
to those in CuTe2O512 or CuTeO3.20 However, the copper atom
in both crystallographically distinct square planar arrangements
is slightly out of plane (0.31-0.32 Å) with respect to the oxygen
atoms. This arises due to the linkage with the copper chloride
layer. There are long contacts of 2.676(4) and 2.666(3) Å for
Cu(1)-Cl(2) and Cu(2)-Cl(4), respectively, which contribute
to the binding of the tellurite layer with the chloride layer.
Both crystallographically distinct barium atoms are contained
within virtually identical eleven-membered coordination envi-
ronments, consisting of ten oxygen atoms and one chlorine atom.
The oxygen atoms are grouped in planes, one containing four
oxygen atoms and sitting above the barium atom, and the other
containing the remaining six oxygen atoms and sitting below.
The chlorine atom is a longer contact (3.182(4) Å for Ba(1)-
Cl(3A) and 3.225(4) Å for Ba(2)-Cl(1A)) that lies below the
The copper chloride layer can be broken down into [Cu2OCl4]2
units which are shown in Figure 3. Each unit is made up of
two distorted CuCl4 tetrahedra, related by the inversion operator,
which are then connected to a trigonal planar CuOCl2 unit. The
tetrahedral arrangement of chlorine atoms around Cu(4) is highly
distorted with Cu-Cl distances ranging from 2.251(5) to
2.446(3) Å and Cl-Cu-Cl angles ranging from 92.2(1) to
122.7(2)°. The trigonal planar arrangement around Cu(3) is
relatively close to ideal, with the copper atom only 0.16 Å out
of plane with respect to the oxygen and chlorine atoms. The
L-Cu(3)-L (L ) O, Cl) angles range from 111.7(3) to
125.9(4)° which also indicates a fairly regular trigonal planar
geometry. The oxygen atom in this environment is actually
contained within the copper tellurite layer, and the Cu(3)-O(3)
bond seems to be necessary to stabilize the binding of the copper
chloride layer to the tellurite layer.
In addition, both Cu(3) and Cu(4) are typified by significantly
larger thermal parameters than the copper atoms in the tellurite
layer. A number of alternative refinements (vide supra) suggest
that these atoms are each a single site but have larger thermal
motion. This appears to be the result of the irregular coordina-
tion environments of these atoms. These atoms are coordinated
(20) Pertlik, F. J. Solid State Chem. 1987, 71, 291.
(21) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.

Copper Tellurites Ba2Cu4Te4O11Cl4 and BaCu2Te2O6Cl2
Inorganic Chemistry, Vol. 37, No. 16, 1998 4049
Table 4. Relevant Angles with ESDs (deg)
Ba2Cu4Te4O11Cl4 (I)
O(1)-Te(1)-O(2)
O(1)-Te(1)-O(3)
O(1)-Te(1)-O(5)
O(2)-Te(1)-O(3)
O(2)-Te(1)-O(5)
O(3)-Te(1)-O(5)
O(3)-Te(2)-O(4)
O(3)-Te(2)-O(6)
O(3)-Te(2)-O(7)
O(4)-Te(2)-O(6)
O(4)-Te(2)-O(7)
O(6)-Te(2)-O(7)
O(7)-Te(3)-O(8)
O(7)-Te(3)-O(10)
O(8)-Te(3)-O(10)
O(1)-Te(4)-O(9)
O(1)-Te(4)-O(11)
O(9)-Te(4)-O(11)
O(5)-Cu(1)-O(6)
O(5)-Cu(1)-O(8)
O(5)-Cu(1)-O(9)
82.3(4)
173.5(3)
82.9(4)
92.9(4)
95.4(4)
93.0(4)
92.8(4)
93.2(3)
173.2(4)
94.5(4)
82.2(4)
82.8(3)
92.7(4)
92.9(4)
93.7(4)
92.1(4)
92.2(3)
93.9(4)
91.4(4)
86.8(4)
162.3(4)
O(6)-Cu(1)-O(8)
O(6)-Cu(1)-O(9)
O(8)-Cu(1)-O(9)
O(2)-Cu(2)-O(4)
O(2)-Cu(2)-O(10)
O(2)-Cu(2)-O(11)
O(4)-Cu(2)-O(10)
O(4)-Cu(2)-O(11)
O(10)-Cu(2)-O(11)
Cl(1)-Cu(3)-Cl(2)
Cl(1)-Cu(3)-O(3)
Cl(2)-Cu(3)-O(3)
Cl(2)-Cu(4)-Cl(3)
Cl(2)-Cu(4)-Cl(4)
Cl(2)-Cu(4)-Cl(4)
Cl(3)-Cu(4)-Cl(4)
Cl(3)-Cu(4)-Cl(4)
Cl(4)-Cu(4)-Cl(4)
161.6(4)
86.7(4)
89.5(4)
91.5(4)
85.9(4)
162.2(4)
161.0(4)
86.8(4)
89.9(4)
120.7(2)
125.9(4)
111.7(3)
105.3(2)
106.7(2)
122.7(2)
110.9(2)
119.7(2)
92.2(1)
BaCu2Te2O6Cl2 (II)
O(2)-Te(1)-O(4)
O(2)-Te(1)-O(5)
O(4)-Te(1)-O(5)
O(1)-Te(2)-O(3)
O(1)-Te(2)-O(4)
O(1)-Te(2)-O(6)
O(3)-Te(2)-O(4)
O(3)-Te(2)-O(6)
O(4)-Te(2)-O(6)
Cl(1)-Cu(1)-Cl(2)
98.3(4)
92.9(4)
96.5(4)
103.7(4)
84.8(3)
83.7(4)
72.7(3)
93.1(4)
159.0(4)
88.7(1)
Cl(2)-Cu(1)-O(3)
87.2(3)
166.3(2)
95.7(3)
81.2(4)
167.4(4)
97.3(4)
91.7(4)
168.5(4)
79.4(4)
98.1(4)
158.1(4)
93.3(4)
Figure 2. View of the copper tellurite layer in compound I in the ac
plane. Copper atoms are shaded spheres, tellurium atoms are striped
spheres, and oxygen atoms are small, open spheres.
Cl(2)-Cu(1)-O(4)
Cl(2)-Cu(1)-O(5)
O(3)-Cu(1)-O(4)
O(3)-Cu(1)-O(5)
O(4)-Cu(1)-O(5)
O(1)-Cu(2)-O(2)
O(1)-Cu(2)-O(3)
O(1)-Cu(2)-O(6)
O(2)-Cu(2)-O(3)
O(2)-Cu(2)-O(6)
O(3)-Cu(2)-O(6)
Cl(1)-Cu(1)-O(3) 103.6(3)
Cl(1)-Cu(1)-O(4)
Cl(1)-Cu(1)-O(5)
87.2(3)
88.8(3)
Figure 3. [Cu2OCl4]2 unit in Ba2Cu4Te4O11Cl4 (I). All ellipsoids are
at the 70% probability level.
atom to the general formula. Whereas compound I is highly
ordered, with tetrahedral or trigonal planar copper atoms largely
coordinated to chlorine atoms separated from square planar
copper atoms associated with oxygen atoms, compound II
(Figure 4) appears to contain a considerably lower degree of
organization. The structure of II is best described as being based
on Te2O6 units joined together by copper atoms. These Te2O6
units consist of a TeO3+1 unit joined through an oxygen atom
to a TeO3 pyramid. The Te-O bond distances are fairly typical
for their environments with the TeO3+1 unit having three bonds
at 1.878(8)-1.920(12) Å and a fourth bond at 2.374(9) Å and
the TeO3 unit having bond distances of 1.876(10)-1.879(7) Å.
These units are linked to one another through a copper atom
and, when built up around the 21 screw axis, form an infinite
spiral channel running along the b axis. This channel contains
the barium atoms. The coordination sphere of the copper atom
within the spiral chain is nearly square planar, with the oxygen
atoms having a small distortion of ∼0.2 Å out-of-plane and
Cu-O distances of 1.936(9)-1.998(9) Å. The spiral chains
are held together by the remaining copper atom, which is
contained within a square pyramidal arrangement of three
oxygen atoms and two chlorine atoms. All three oxygen atoms
(Cu-O distance: 1.902(8)-2.011(10) Å) and one of the
chlorine atoms (Cu-Cl distance: 2.362(4) Å) make up the
Figure 1. Unit cell view of Ba2Cu4Te4O11Cl4 (I) parallel to the a axis.
Barium atoms are large open spheres, copper atoms are shaded spheres,
tellurium atoms are striped spheres, chlorine atoms are crosshatched
spheres, and oxygen atoms are small, open spheres.
nearly exclusively by low-coordinate chlorine atoms which also
have somewhat larger thermal ellipsoids due to their low
coordination numbers. This unusual behavior of chlorine atoms
has been observed in other tellurium oxyhalides such as
Te6O11Cl2 and H3Fe2(TeO3)4Cl.23
22
The structure of compound II, BaCu2Te2O6Cl2, differs greatly
from compound I, notwithstanding the addition of an oxygen
(22) Abriel, W. Z. Naturforsch. 1981, 36B, 405.
(23) (a) Dusausoy, Y.; Protas, J. Acta Crystallogr. 1969, B25, 1551. (b)
Feger, C. R.; Kolis, J. W.; Gorny, K.; Pennington, C., J. Solid State
Chem., submitted.

4050 Inorganic Chemistry, Vol. 37, No. 16, 1998
Feger and Kolis
Table 5. Valence Bond Sums for Ba2Cu4Te4O11Cl4 and
a
BaCu2Te2O6Cl2
Ba
Cu
Te
O
Cl
Ba2Cu4Te4O11Cl4 (I)
atom 1
atom 2
atom 3
atom 4
atom 5
atom 6
atom 7
atom 8
atom 9
atom 10
atom 11
2.08(1)
2.21(2)
2.02(2)
2.00(2)
0.882(9)
0.936(6)
4.06(5)
4.06(5)
3.94(5)
3.90(5)
2.02(3)
2.18(4)
2.07(4)
2.17(4)
2.18(3)
2.19(3)
2.06(4)
2.24(4)
2.22(4)
2.20(3)
2.23(3)
0.582(6)
0.653(5)
0.555(5)
0.548(3)
BaCu2Te2O6Cl2 (II)
atom 1
atom 2
atom 3
atom 4
atom 5
atom 6
2.12(2)
1.94(2)
1.91(2)
3.93(5)
4.06(6)
2.14(3)
2.15(3)
2.16(4)
2.06(4)
2.07(4)
2.20(3)
0.728(5)
0.355(4)
Figure 4. Unit cell view of BaCu2Te2O6Cl2 (II) parallel to the b axis.
Barium atoms are large open spheres, copper atoms are shaded spheres,
tellurium atoms are striped spheres, chlorine atoms are crosshatched
spheres, and oxygen atoms are small, open spheres.
square plane, with a long copper-chlorine contact (2.717(4)
Å) completing the coordination environment.
a ∑s(M-L) ) ∑exp[(ro-r)/0.37]; s ) individual bond valences, r
) bond distance in structure, and ro ) empirically derived M-L single-
bond distance (Ba-O )2.285, Ba-Cl ) 2.660, CuI-O ) 1.515,
CuII-O ) 1.679, CuI-Cl ) 1.819, CuII-Cl ) 1.979, Te-O ) 1.977
Å). All distances are either from table or calculated from the formula
found in reference 24.
The barium atom in this structure sits within a highly irregular
coordination sphere, consisting of six oxygen atoms and two
chlorine atoms. To best describe the coordination environ-
ment, a distorted square planar arrangement of three oxygen
atoms and one chlorine atom is defined around the central
barium atom. There are two oxygen and one chlorine atoms
below this plane and a lone oxygen atom above the plane. All
of the Ba-O distances except for Ba(1)-O(6) correspond
reasonably well (2.777(9)-3.026(10) Å) to the calculated value
of 2.78 Å.21 The Ba(1)-O(6) distance (2.569(9) Å) is consider-
ably shorter than the expected value, but it is situated in an
otherwise empty region of the barium coordination sphere and
is also locked in as a member of the TeO3+1 unit and the CuO4
square plane.
Valence Bond Sums. Due to the potentially ambiguous
nature of the oxidation states of the copper atoms in compound
I, the well-known correspondence between bond distance and
bond valence24 was used to help in the determination of the
possible oxidation states of the copper atoms in both structures.
Utilizing the common assignments of +2 for barium, -1 for
chlorine, and -2 for oxygen, and assigning a +4 oxidation state
for all tellurium atoms, which is indicated by the obvious steric
effects of a lone pair in either the TeO3+1 or the TeO3
environment, in compound I, there remain six positive charges
which must be distributed between four copper atoms. By using
the assumption that the copper atoms in an oxide environment
were +2 and that those in a chloride environment were +1,
the valence bond sums were calculated accordingly. The bond
sums (Table 5) confirmed all these assignments and suggest
that the simplest formulation for compound I is correct.
Using similar common assignments for compound II sug-
gested that this material is entirely Cu(II). Valence bond sums
also indicated that these assignments are correct, although the
bond sum for Cl(2) is somewhat low, due to the fact that it
only has a significant contact with Cu(1), and the distant contacts
with Cu(1), Cu(2), and Te(2) (3.111, 2.938, and 3.490 Å,
respectively) have no appreciable effect on the overall bond
sum. Although this low coordination number for Cl(2) seems
somewhat unusual, there are other examples of low-coordinate
to uncoordinated chlorine atoms in tellurium oxyhalides, specif-
Figure 5. Temperature-dependent plot of the inverse of magnetic
susceptibility (ø-1) vs temperature (T) for Ba2Cu4Te4O11Cl4 (I). The
material displays a broad antiferromagnetic transition that begins at
90 K.
Physical Properties of Ba2Cu4Te4O11Cl4. A temperature-
dependent plot of the magnetic susceptibility (Figure 5) was
obtained for compound I and shows that it has a broad
antiferromagnetic transition with TN = 90 K. The plot of ø-1
vs T for the data above TN shows that the material exhibits
Curie-Weiss behavior with constants of C ) 0.708 emu K/mol
and θ ) -142 K. The valence assignments indicate that only
the two Cu(II) atoms have any significant paramagnetic
contribution, with each atom having one unpaired electron.
Using the Curie constant the magnetization is 1.68 µB/Cu(II)
center, which is in good agreement with the theoretical spin-
only value of 1.73 µB. This suggests that the valence assign-
ments are correct. Furthermore, the presence of an antiferro-
magnetic transition suggests the presence of superexchange,
possibly through the square planar copper atoms.
Diffuse reflectance spectroscopy was used to determine the
optical band gap of I. The plot of absorbance vs energy is
shown in Figure 6. The plot of (absorbance)1/2 vs energy at
the absorption edge (2.50-3.20 eV, correlation coefficient
0.995) has a better linear dependence than does the plot of
(absorbance)2 vs energy (correlation coefficient 0.974), which
suggests that the material has an indirect band gap.25 Therefore,
ically in Te6O11Cl2 and H3Fe2(TeO3)4Cl.23
22
(24) Brown, I. D.; Altermatt, D. Acta Crystallogr. 1985, B41, 244.

Copper Tellurites Ba2Cu4Te4O11Cl4 and BaCu2Te2O6Cl2
Inorganic Chemistry, Vol. 37, No. 16, 1998 4051
netic material with tetrahedral or trigonal planar Cu(I) and square
planar Cu(II) sites located in separate chloride and oxide layers,
respectively. The magnetic susceptibility data and valence bond
sums also indicate that the assigned distribution of copper
oxidation states is probably correct. The tellurium atoms in
both compounds are exclusively coordinated by oxygen atoms
and are contained within common TeO3+1 or TeO3 units.
Valence bond sums of II are used to suggest that the structural
model is correct.
Since all attempts to obtain compound II in greater quantity
were unsuccessful, it is theorized that compound II is an
intermediate in the formation of compound I. Any prolonged
heating led to the complete disappearance of II in favor of
increased quantities of I. The relative low yields, lack of
stability, and difficulty in producing large quantities of this
material seem to lend credence to the hypothesis that II is an
intermediate en route to the formation of I. Attempts at the
synthesis of calcium and strontium analogues of either phase
failed to yield the desired products. The presence of NH4Cl is
essential to the formation and crystallization of the title phases.
Reactions that contain only BaCl2 as a mineralizer did not
produce the desired products.
Figure 6. Plot of diffuse reflectance spectrum of Ba2Cu4Te4O11Cl4
(I) in units of absorbance vs eV.
the band gap was obtained by determining the inflection point
of the first-derivative curve of reflectance vs energy. This
results in a band gap of 3.00 eV, indicative of an essentially
insulating material. There is also a peak at 1.7 eV, which is
indicative of a spin-allowed transition at the Cu(II) centers. For
Cu(II) in a square planar D4h environment, three spin-allowed
transitions are possible, which normally occur between 10 000
and 14 000 cm-1 26
The fact that we observe only one broad
.
transition in the region of 13 600 cm-1 is probably due to the
poor resolution of this broad band. Our inability to obtain
compound II in any reasonable quantity or purity precluded
any reliable physical characterization of this compound.
Acknowledgment. C.R.F. thanks George L. Schimek for
many valuable discussions. The authors thank Thomas P. Thrash
at Rice University for the SQUID measurements. This work
was supported by the National Science Foundation.
Conclusion
Only compound I was obtained in sufficient yield for full
physical characterization. It is a wide band gap, antiferromag-
Supporting Information Available: Tables of crystallographic and
refinement details, tables of anisotropic thermal parameters and bond
angles, supplemental figures, and descriptions (14 pages). Ordering
information is given on any current masthead page.
(25) Pankove, J. I. Optical Processes in Semiconductors; Prentice Hall,
Inc.: Englewood Cliffs, NJ, 1971.
(26) Ballhausen, C. J. Introduction to Ligand Field Theory; McGraw-Hill:
NewYork, 1962; p 268.
IC971264Y