Hydrothermal and structural chemistry of the zinc(II)- and cadmium(II)-1,2,4-triazolate systems

Article abstract of DOI:10.1021/ic062269a

Hydrothermal reactions of 1,2,4-triazole with zinc and cadmium salts have yielded 10 structurally unique materials of the M(II)/trz/X^n- system, with M(II) = Zn and Cd and X^n- = F^-, Cl^-, Br^-, I^-, OH^-, NO₃^-, and SO₄^2- (trz = 1,2,4-triazolate). Of the zinc-containing phases, [Zn(trz)₂] (1), [Zn₂(trz)₃(OH)] ·3H₂O (3·3H₂O), and [Zn₂(trz) (SO₄)(OH)] (4) are three-dimensional, while [Zn(trz)Br] (2) is two-dimensional. All six cadmium phases, [Cd₃(trz)₃F ₂(H₂O)]·2.75H₂O (5·2.75H ₂O), [Cd₂(trz)₂Cl₂(H₂O)] (6), [Cd₃(trz)₃Br₃] (7), [Cd ₂(trz)₃I] (8), [Cd₃(trz)₅(NO ₃)(H₂O)]·H₂O (9·H₂O), and [Cd₈(trz)₄(OH)₂(SO₄) ₅(H₂O)] (10), are three-dimensional. In all cases, the anionic components X^n- participate in the framework connectivity as bridging ligands. The structural diversity of these materials is reflected in the variety of coordination poiyhedra displayed by the metal sites: tetrahedral; trigonal bipyramidal; octahedral. Structures 3, 5, and 7-9 exhibit two distinct polyhedral building blocks. The materials are also characterized by a range of substructural components, including trinuclear and tetranuclear clusters, adamantoid cages, chains, layers, and complex frameworks.

Full text of DOI:10.1021/ic062269a

Inorg. Chem. 2007, 46, 4887−4904
Hydrothermal and Structural Chemistry of the Zinc(II)- and
Cadmium(II)-1,2,4-Triazolate Systems
Wayne Ouellette, Bruce S. Hudson, and Jon Zubieta*
Department of Chemistry, Syracuse UniVersity, Syracuse, New York 13244
Received November 29, 2006
Hydrothermal reactions of 1,2,4-triazole with zinc and cadmium salts have yielded 10 structurally unique materials
-
-
2-
of the M(II)/trz/Xn system, with M(II)
1,2,4-triazolate). Of the zinc-containing phases, [Zn(trz)2] (1), [Zn2(trz)3(OH)]
(OH)] (4) are three-dimensional, while [Zn(trz)Br] (2) is two-dimensional. All six cadmium phases, [Cd3(trz)3F2-
)
Zn and Cd and Xn
)
F-, Cl-, Br-, I-, OH-, NO3-, and SO4 (trz
)
‚
3H2O (3 3H2O), and [Zn2(trz)(SO4)-
‚
(H2O)]
(9
‚
2.75H2O (5
‚
2.75H2O), [Cd2(trz)2Cl2(H2O)] (6), [Cd3(trz)3Br3] (7), [Cd2(trz)3I] (8), [Cd3(trz)5(NO3)(H2O)]
‚
H2O
-
‚
H2O), and [Cd8(trz)4(OH)2(SO4)5(H2O)] (10), are three-dimensional. In all cases, the anionic components Xn
participate in the framework connectivity as bridging ligands. The structural diversity of these materials is reflected
in the variety of coordination polyhedra displayed by the metal sites: tetrahedral; trigonal bipyramidal; octahedral.
Structures 3, 5, and 7−9 exhibit two distinct polyhedral building blocks. The materials are also characterized by a
range of substructural components, including trinuclear and tetranuclear clusters, adamantoid cages, chains, layers,
and complex frameworks.
Complex structures,1-6 based on a molecular scale com-
posite of inorganic and organic components, provide the
potential for the design of novel functional materials for
technological applications.7 The inorganic component may
confer useful magnetic or optical properties, mechanical
hardness, and thermal stability, while the organic component
offers processability, a potential for structural diversification,
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Published on Web 05/12/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 12, 2007 4887

Ouellette et al.
Scheme 1
Scheme 2
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synergism between organic and inorganic substructures in
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structural information onto the inorganic substructure, while
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triazolate/anion compounds. Furthermore, triazoles are readily
derivatized, and a large number of functionalized compounds
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4888 Inorganic Chemistry, Vol. 46, No. 12, 2007

Zinc(II)- and Cadmium(II)-1,2,4-Triazolate Systems
yield. IR (KBr pellet, cm-1): 3127 (w), 1510 (s), 1458 (s), 1314
(s), 1276 (m), 1163 (s), 1077 (m), 1033 (m), 1009 (m), 894 (w),
817 (w), 663 (s).
In addition to providing structural diversity and unusual
magnetochemistry, the azolates also allow the design of
materials with interactions between closed-shell d10 metal
cations, providing a route to new luminescent materials. A
number of binary Cu(I)/pyrazolates and Cu(I)/triazolates with
photoluminescent properties have been described.61,73,74 More
recently, we demonstrated that the ternary Cu(I)/trz/anion
system also provided a series of materials with bright
phosphorescence and luminescent thermochromism. As an
extension of this work, the ternary phrases M(II)/trz/anion
for M ) Zn and Cd have been investigated. The three-
dimensional structures of [Zn(trz)2] (1), [Zn2(trz)3(OH)]‚
3H2O (3‚3H2O), [Zn2(trz)(SO4)(OH)] (4), [Cd3(trz)3F2(OH)]‚
3H2O (5‚3H2O), [Cd2(trz)2Cl2(H2O)] (6), [Cd3(trz)3Br3] (7),
[Cd2(trz)3I] (8), [Cd3(trz)5(NO3)(H2O)]‚H2O (9‚H2O), and
[Cd8(trz)4(OH)2(SO4)5(H2O)] (10) are reported, as well as
the two-dimensional structure of [Zn(trz)Br] (2).
Synthesis of [Zn2(trz)(OH)(SO4)] (4). A solution of ZnSO4‚
7H2O (0.462 g, 1.607 mmol), 1,2,4-triazole (0.232 g, 3.359 mmol),
and H2O (10.00 g, 556 mmol) in the mol ratio 0.48:1.00:166 was
stirred briefly before heating to 200 °C for 48 h (initial and final
pH values of 4.5 and 7.5, respectively). Colorless crystals of 4 were
isolated in 85% yield. IR (KBr pellet, cm-1): 3430 (s), 3148 (m),
1560 (m), 1524 (m), 1292 (m), 1208 (m), 1174 (m), 1113 (s), 1077
(s), 1008 (m), 900 (m), 873 (m), 826 (m), 644 (m), 620 (m).
Synthesis of [Cd3(trz)3F2(OH)]‚3H2O (5‚3H2O). A solution of
CdF2 (0.249 g, 1.655 mmol), 1,2,4-triazole (0.234 g, 3.388 mmol),
H2O (10.00 g, 556 mmol), and tetrabutylammonium hydroxide
(40%) (0.250 mL, 0.385 mmol) in the mol ratio 0.49:1.00:164:
0.11 was stirred briefly before heating to 180 °C for 72 h (initial
and final pH values of 5.5 and 3.5, respectively). Colorless crystals
of 5‚3H2O, suitable for X-ray diffraction, were isolated in 90%
yield. IR (KBr pellet, cm-1): 3100 (b), 1751 (m), 1508 (s), 1403
(m), 1325 (m), 1284 (s), 1197 (m), 1155 (s), 1069 (s), 1016 (m),
991 (s), 881 (m), 664 (s).
Experimental Section
General Considerations. All chemicals were used as obtained
without further purification: zinc oxide, zinc nitrate hexahydrate,
zinc sulfate heptahydrate, zinc bromide, cadmium fluoride, cadmium
chloride hemipentahydrate, cadmium bromide, cadmium iodide,
cadmium nitrate tetrahydrate, cadmium sulfate hydrate, 1,2,4-
triazole, and tetrabutylammoniumhydroxide were purchased from
Aldrich. All syntheses were carried out in 23 mL poly(tetrafluo-
roethylene) lined stainless steel containers under autogenous
pressure. The reactants were stirred briefly, and the initial pH was
measured before heating. Water was distilled above 3.0 M Ω in-
house using a Barnstead model 525 Biopure distilled water center.
The reactions’ initial and final pH values were measuered using
Hydrion pH sticks.
Synthesis of [Zn(trz)2] (1). A mixture of ZnO (0.142 g, 1.745
mmol), 1,2,4-triazole (0.234 g, 3.388 mmol), and H2O (10.00 g,
556 mmol) in the mol ratio 0.52:1.00:164 was stirred briefly before
heating to 200 °C for 48 h, with initial and final pH values of of
5.0 and 6.0. Colorless blocks of 1, suitable for X-ray diffraction,
were isolated in 85%. IR (KBr pellet, cm-1): 3139 (m), 1508 (s),
1458 (w), 1346 (w), 1312 (w), 1275 (s), 1205 (w), 1159 (s), 1070
(m), 1004 (m), 883 (w), 664 (s).
Synthesis of [Zn(trz)Br] (2). A mixture of ZnBr2 (0.391 g, 1.736
mmol), 1,2,4-triazole (0.238 g, 3.446 mmol), and H2O (10.00 g,
556 mmol) in the mol ratio 0.50:1.00:161 was stirred briefly before
heating to 200 °C for 48 h. Initial and final pH values of 2.5 and
3.0, respectively, were recorded. Colorless rods of 2 suitable for
X-ray diffraction were isolated in 80% yield. IR (KBr pellet, cm-1):
3129 (w), 3108 (m), 3041 (w), 2943 (w), 1528 (s), 1330 (w),
1302 (s), 1217 (w), 1177 (m), 1096 (s), 1042 (m), 1005 (m), 902
(w), 884 (m), 658 (s).
Synthesis of [Zn2(trz)3(OH)]‚3H2O (3‚3H2O). A solution of
Zn(NO3)2‚6H2O (0.478 g, 1.607 mmol), 1,2,4-triazole (0.233 g,
3.373 mmol), and H2O (10.00 g, 556 mmol) in the mol ratio 0.48:
1.00:165 was stirred briefly before heating to 200 °C for 72 h (initial
and final pH values of 4.0 and 3.0, respectively). Colorless blocks
of 3‚3H2O, suitable for X-ray diffraction, were isolated in 90%
Synthesis of [Cd2(trz)2Cl2(H2O)] (6). A solution of CdCl2‚
2.5H2O (0.290 g, 1.270 mmol), 1,2,4-triazole (0.237 g, 3.431 mmol),
and H2O (10.00 g, 556 mmol) in the mol ratio 0.37:1.00:162 was
stirred for 10 min before heating to 200 °C for 96 h (initial and
final pH values of 5.0 and 4.5, respectively). Colorless plates of 6
were isolated in 65% yield. IR (KBr pellet, cm-1): 3590 (s), 3400
(s), 3132 (w), 1753 (w), 1598 (w), 1560 (w), 1501 (s), 1283 (s),
1190 (w), 1155 (s), 1062 (m), 1010 (w), 992 (m), 881 (m), 662
(m).
Synthesis of [Cd3(trz)3Br3] (7). A mixture of CuBr2 (0.577 g,
1.676 mmol), 1,2,4-triazole (0.233 g, 3.373 mmol), H2O (10.00 g,
556 mmol), and tetrabutylammonium hydroxide (40%) (0.250 mL,
0.385 mmol) in the mol ratio 0.50:1.00:165:0.11 was stirred briefly
before heating to 200 °C for 48 h. Initial and final pH values of
4.5 and 3.0, respectively, were recorded. Colorless plates of 7
suitable for X-ray diffraction were isolated in 75% yield. IR (KBr
pellet, cm-1): 3245 (b), 3123 (w), 2996 (w), 1734 (w), 1638 (w),
1542 (m), 1508 (s), 1409 (m), 1299 (m), 1279 (s), 1159 (s), 1123
(w), 1079 (s), 1045 (m), 998 (w), 988 (m), 968 (w), 875 (m), 699
(m), 666 (m), 653 (m), 623 (s).
Synthesis of [Cd2(trz)3I] (8). A solution of CdI2 (0.613 g, 1.674
mmol), 1,2,4-triazole (0.235 g, 3.402 mmol), and H2O (10.00 g,
556 mmol) in the mol ratio 0.49:1.00:163 was stirred briefly before
heating to 180 °C for 48 h (initial and final pH values of 4.0 and
3.0, respectively). Colorless rods of 8 suitable for X-ray diffraction
were isolated in 70% yield. IR (KBr pellet, cm-1): 3233 (b), 3123
(w), 2994 (w), 2892 (w), 1535 (w), 1502 (s), 1411 (w), 1301 (m),
1275 (m), 1153 (s), 1121 (m), 1069 (m), 1046 (m), 996 (w), 870
(w), 660 (m), 616 (s).
Synthesis of [Cd3(trz)5(NO3)(H2O)]‚H2O (9‚H2O). A solution
of Cd(NO3)2‚4H2O (0.491 g, 1.592 mmol), 1,2,4-triazole (0.233 g,
3.373 mmol), and H2O (10.00 g, 556 mmol) in the mol ratio 0.47:
1.00:165 was heated at 200 °C for 96 h (initial and final pH values
of 4.5 and 4.5, respectively). Colorless blocks of 9‚H2O were
isolated in 85% yield. IR (KBr pellet, cm-1): 3567 (b), 3233 (b),
3123 (w), 2994 (w), 2892 (w), 1535 (w), 1502 (s), 1411 (w), 1301
(m), 1275 (m), 1153 (s), 1121 (m), 1069 (m), 1046 (m), 996 (w),
870 (w), 660 (m), 616 (s).
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Synthesis of [Cd8(trz)4(SO4)5(OH)2(H2O)] (10). A mixture of
CdSO4‚8H2O (0.430 g, 0.559 mmol), 1,2,4-triazole (0.232 g, 3.359
mmol), H2O (10.00 g, 556 mmol), and tetrabutylammonium
hydroxide (40%) (0.075 mL, 0.116 mmol) in the mol ratio 0.17:
Inorganic Chemistry, Vol. 46, No. 12, 2007 4889

Ouellette et al.
1.00:768:0.03 was stirred for 20 min before heating to 200 °C for
48 h. Initial and final pH values of 4.5 and 3.0, respectively, were
recorded. Colorless crystals of 10 suitable for X-ray diffraction were
isolated in 65% yield. IR (KBr pellet, cm-1): 3487 (b), 3141 (w),
1654 (m), 1637 (m), 1508 (s), 1284 (m), 1156 (s), 1117 (s), 1061
(s), 990 (m), 874 (m), 799 (m), 739 (w), 666 (m), 613 (m).
X-ray Crystallography. Structural measurements were per-
formed on a Bruker-AXS SMART-CCD diffractometer at low
temperature (90 K) using graphite-monochromated Mo KR radiation
(λMo KR ) 0.710 73 Å).75 The data were corrected for Lorentz and
polarization effects and absorption using SADABS.76,77 The
structures were solved by direct methods. All non-hydrogen atoms
were refined anisotropically. After all of the non-hydrogen atoms
were located, the model was refined against F2, initially using
isotropic and later anisotropic thermal displacement parameters.
Hydrogen atoms were introduced in calculated positions and refined
isotropically. Neutral atom scattering coefficients and anomalous
dispersion corrections were taken from the International Tables,
Vol. C. All calculations were performed using SHELXTL crystal-
lographic software packages.78
Crystallographic details have been summarized in Table 1.
Atomic positional parameters, full tables of bond lengths and
angles, and anisotropic temperature factors are available in the
Supporting Information. Selected bond lengths and angles are given
in Table 2.
Gas and Vapor Sorption Measurements. All gas and vapor
adsorption measurements were obtained using a Micromeritics
ASAP 2020 volumetric gas adsorption instrument equipped with a
vapor dosing attachment. The crystalline sample of [Zn(trz)F]‚H2O
was evacuated under dynamic vacuum at 160 °C at a heating rate
of 0.1 °C/min until the outgas rate was less than 2 mTorr/min. For
all isotherms, warm and cold free space correction measurements
were taken using ultrahigh-purity helium gas. The H2 and N2
isotherms at 77 K were measured in liquid-nitrogen baths using
UHP grade gas sources. The methanol isotherm measurements at
298 K were performed in a constant temperature bath using triple
distilled and degassed methanol.
insoluble and intractable polycrystalline powders. The ex-
pedient of hydrothermal reaction conditions affords a con-
venient method for the preparation of single crystals,
allowing more routine structural characterization by single-
crystal X-ray diffraction.55 The techniques of hydrothermal,
and more generally solvatothermal synthesis, have been well-
established for the preparation of metal oxides and organic-
inorganic composite materials.80,81 The product composition
may depend on critical factors such as pH of the medium,
temperature, and hence pressure, as well as the presence of
potential charge balancing anions which may also be
incorporated into the product. In the series of materials
described in this contribution, a charge-balancing inorganic
anion is incorporated in all cases, with the exception of the
binary material [Zn(trz)2] (1). In all compounds of this study,
as well as the previously described Cu/trz/X materials,82 the
heterocyclic ligand is present in the deprotonated triazolate
form and functions as a tridentate bridging group.
The hydrothermal chemistry of the zinc and cadmium
triazolates is generally characterized by the incorporation of
anionic component of the metal salt into the final product.
The exceptions are [Zn(trz)2] (1), which was prepared from
ZnO, and [Zn2(trz)3(OH)]‚3H2O (3‚3H2O), which failed to
incorporate the nitrate anion of the starting material Zn-
(NO3)2‚6H2O. Despite repeated attempts, no conditions could
-
be found that provided Zn/trz/NO3 phases. Similarly, we
were unable to prepare crystalline products of the Zn/trz/I-
composition. The use of ZnCl2 resulted in the previously
reported [Zn(trz)Cl],83 while the reaction of ZnF2‚4H2O with
1,2,4-triazole yielded the known phase [Zn(trz)F]‚H2O.84 In
contrast, the cadmium series afforded crystalline materials
-
2-
with X ) F-, Cl-, Br, and I- as well as NO3 and SO4
.
It is also noteworthy that incorporation of coordinated
water and/or hydroxide ligands is quite common, as evident
in compounds 3-6, 9, and 10. However, the hydroxide-
containing phases were uniformly prepared from acidic
solutions.
DFT Calculations. Solid-state density functional theory (DFT)
calculations79 were performed with the program DMol3 to calculate
the electronic band structure of [Zn(trz)Cl]. DMol3 solid-state
calculations were performed with the program option set to “fine”
(corresponding to a k-point separation of 0.04 Å-1) and the energy
convergence of 1 × 10-6 hartree, the dnp (double numerical with
p and d polarization) basis set (comparable to a 6-31G(d,P)
Gaussian-type basis set), and the VWN-BP generalized gradient
approximation (GGA) density functional. Unlike many plane-wave
DFT packages, Dmol3 does not optimize lattice constants, such that
the atoms within the unit cell were optimized with the cell
parameters specified by the 90 K X-ray diffraction study.
The infrared spectra of all compounds 1-10 exhibit a
medium intensity band in the 3100-3160 cm-1 range and a
medium to strong band in the 1200-1290 cm-1 range,
associated with ν(C-H) and ν(C-N) or ν(N-N) of the
triazolate ligand, respectively. The sulfate phases 4 and 10
exhibit characteristic ν(S-O) bands in the 1060-1075 and
(80) (a) Stein, A.; Keller, S. W.; Mallouk, T. E. Science 1993, 259, 1558.
(b) Laudise, R. A. Chem. Eng. News 1987, Sept 28, p 30. (c)
Gopalakrishnan, J. Chem. Mater. 1995, 7, 1265. (d) Whittinghan, M.
S. Curr. Opin. Solid State Mater. Sci. 1996, 1, 227. (e) Weller, M.;
Dann, S. E. Curr. Opin. Solid State Mater. Sci. 1998, 3, 137. (f)
Gopalakrishnan, J.; Bhuvanrh, N. S. P.; Rangan, K. K. Curr. Opin.
Solid State Mater. Sci. 1996, 1, 285. (g) Rabenau, A. Angew. Chem.,
Int. Ed. Engl. 1985, 24, 1026. (h) Lobachev, A. N. Crystallization
processes under hydrothermal conditions; Consultants Bureau: New
York, 1973. (i) Yoshimura, M.; Suchanek, W. L.; Byrappa, K. Mater.
Res. Soc. Bull. 2000, Sept, 17. (j) Fing, S.; Xu, R. Acc. Chem. Res.
2001, 34, 239.
Results and Discussion
Syntheses and Infrared Spectroscopy. Although metal-
triazolate-based materials have excited considerable attention
in recent years, the polymeric phases generally occur as
(75) SMART, Data Collection Software, version 5.630; Bruker-AXS Inc.:
Madison, WI, 1997.
(76) SAINT Plus, Date Reduction Software, version, 6.45A; Bruker-AXS
Inc.: Madison, WI, 1997.
(81) Zubieta, J. Compr. Coord. Chem. 2 2003, 1, 697.
(77) Sheldrick, G. M. SADABS; University of Go¨ttingen: Go¨ttingen,
Germany, 1996.
(78) SHELXTL PC, version 6.12; Bruker-AXS Inc.: Madison, WI, 2002.
(79) (a) Delley, B. J. Chem. Phys. 1990, 92, 508. (b) Delley, B. J. Chem.
Phys. 2000, 113, 7756. (c) DMol3 is available as part of Materials
Studio.
(82) Ouellette, W.; Prosvirin, A. V.; Chieffo, V.; Dunbar, K. R.; Hudson,
B.; Zubieta, J. Inorg. Chem. 2006, 0000.
(83) Kro¨ber, J.; Bkouchi-Waksman, I.; Pascard, C.; Thomann, M.; Kahn,
O. Inorg. Chim. Acta 1995, 230, 159.
(84) Goforth, A. M.; Su, C.-Y.; Mipp, R.; Macquart, R. B.; Smith, M. D.;
Zur Loye, H.-C. J. Solid State Chem. 2005, 178, 2511.
4890 Inorganic Chemistry, Vol. 46, No. 12, 2007

Zinc(II)- and Cadmium(II)-1,2,4-Triazolate Systems
Table 1. Summary of Crystallographic Data for the Structures of [Zn(trz)2] (1), [Zn(trz)Br] (2), [Zn2(trz)3(OH)]‚3H2O (3‚3H2O), [Zn2(trz)(OH)(SO4)]
(4), [Cd3(trz)3F2(OH)]‚3H2O (5‚3H2O), [Cd2(trz)2Cl2(H2O)] (6), [Cd3(trz)3Br3] (7), [Cd2(trz)3I] (8), [Cd3(trz)5(NO3)(H2O)]‚H2O (9‚H2O), and
[Cd8(trz)4(SO4)5(OH)2(H2O)] (10)
param
1
2
3
4
empirical formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V,Å3
C4H4N6Zn
203.52
orthorhombic
Pbca
9.9639(8)
9.7061(8)
14.1313(9)
90
90
90
1366.6(3)
8
1.978
C2H2BrN3Zn
213.35
monoclinic
P21/n
6.3341(6)
9.6687(9)
9.0805(8)
90
102.888(2)
90
542.10(9)
4
C3H6.50N4.50O2Zn
203.00
orthorhombic
Pnma
7.5978(4)
9.9695(5)
17.5058(9)
90
CH1.50N1.50O2.50S0.50 Zn
155.94
orthorhombic
Pnma
7.3183(4)
6.8119(4)
13.7846(7)
90
90
90
687.18(7)
8
3.015
90
90
1326.00(12)
8
2.034
3.651
90
Z
D
calcd, g cm-3
2.614
11.764
90
µ, mm-1
T, K
3.528
90
7.275
90
λ, Å
0.710 73
0.0460
0.1161
0.710 73
0.0185
0.0481
0.710 73
0.0283
0.0704
0.710 73
0.0250
0.0627
R1a
wR2b
param
5
6
7
8
empirical formula
fw
cryst syst
space group
a, Å
C6H13Cd3F2N8O4
652.33
orthorhombic
Ccca
18.0700(6)
18.0766(6)
17.9952(6)
90
90
90
5878.0(3)
16
2.949
C2H3CdClN3O0.50
224.92
orthorhombic
Pnma
7.5186(4)
11.7796(6)
12.3158(6)
90
C6H6Br3Cd3N9
C3H3CdI0.50N4.50
277.95
orthorhombic
Pnma
7.8569(5)
10.3906(6)
18.5780(11)
90
781.13
monoclinic
P21/c
15.6858(11)
12.5013(9)
8.4003(6)
90
103.0910(10)
90
1604.4(2)
4
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
90
90
90
90
1090.76(10)
8
2.739
4.370
90
1516.67(16)
8
2.435
4.837
90
D
calcd, g cm-3
3.234
11.461
90
µ, mm-1
T, K
4.364
90
λ, Å
0.710 73
0.0374
0.0921
0.710 73
0.0186
0.0426
0.710 73
0.0533
0.1411
0.710 73
0.0295
0.0611
R1a
wR2b
param
9
10
empirical formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C10H10Cd3N16O5
771.54
monoclinic
C2/c
19.6945(9)
17.3497(8)
13.8790(7)
90
91.047(2)
90
4741.6(5)
8
C8H12Cd8N12O23S5
1703.80
monoclinic
P21
9.1409(4)
13.5467(7)
13.5525(7)
90
108.4870(10)
90
1591.59(14)
2
Z
D
calcd, g cm-3
2.162
2.723
90
3.555
5.678
90
µ, mm-1
T, K
λ, Å
0.710 73
0.0421
0.1079
0.710 73
0.0164
0.0371
R1a
wR2b
2
2
2
2
2
2
a R1 ) Σ|Fo| - |Fc|/Σ|Fo|. b wR2 ) {Σ[w(Fo - Fc )2]/Σ[w(Fo )2]1/2}; w ) 1/ [σ2(Fo ) + (aP)2 + bP], with P ) [max(Fo ,0) + 2Fc ]/3 for all data.
600-650 cm-1 range. The nitrate material 9 shows ν(N-
As shown in Figure 1b, the structure of the binary
composition [Zn(trz)2] (1) is three-dimensional. The Zn(II)
sites are tetrahedral with {ZnN4} coordination through
bonding to two N1 and two N4 sites of four triazolate ligands.
The triazolate groups bridge two zinc sites, leaving the N2
position of the rings unbound.
O) stretches at 1502 and 1153 cm-1.
X-ray Crystal Structures. Triazole and its derivatives
have been demonstrated to provide a wealth of coordination
polymers with complex and unusual architectures and a range
of physical properties. As anticipated, the hydrothermal
chemistry of 1,2,4-triazolate with Zn(II) and Cd(II) is
characterized by an unusually varied structural chemistry.
The complex three-dimensional structure of 1 is con-
structed from adamantoid {Zn10(trz)12} cages, shown in
Inorganic Chemistry, Vol. 46, No. 12, 2007 4891

Ouellette et al.
Table 2. Summary of the Structural Characteristics of the Compounds of This Study and Related Materials
compd
[Zn(trz)2] (1)
[Zn(trz)F]‚H2O
[Zn(trz)Cl]
dimensionality
coord geometrya
M-N
M-X(X)
substructures
3-D
3-D
2-D
tet, {ZnN4}
trig bipy, {ZnN3F2}
tet, {ZnN3Cl}
1.972(3)-1.996(3)
2.006(3)-2.027(2)
2.003(5)-2.006(5)
{Zn10(trz)12} cages
{Zn(trz)F}n chains
2.054(9), av
2.214(2)
{Zn2Cl2(trz)4}2- clusters
and {Zn4(trz)4}4+ rings
{Zn2Br2(trz)4}2- clusters
and {Zn4(trz)4}4+ rings
{Zn(trz)3}nn- chains
[Zn(trz)Br] (2)
2-D
3-D
tet, {ZnN3Br}
oct, {ZnN6}
2.001(2)-2.006(2)
2.110(3)-2.219(3)
2.3485(3)
[Zn2(trz)3(OH)]‚3H2O
(3‚3H2O)
tet, {ZnN3O}
oct, {ZnN2O4}
1.965(3)-1.984(2)
2.079(2)
2.023(2)
[Zn2(trz)(SO4)(OH)] (4)
3-D
3-D
2.043(1) (OH),
2.245(2) (SO4)
{Zn3(µ3-OH)}5+ clusters
n-
and {Zn2(SO4)(OH)}n
layers
[Cd3(trz)3F2(H2O)]‚2.75H2O
(5‚2.75H2O)
oct, {CdN3F3}
2.252(5)-2.271(5)
2.259(5)-2.273(5)
2.289(3)-2.421(3) (F),
2.238(9) (H2O)
{Cd4F4}4+ clusters,
{Cd6(trz)6F4(H2O)2}2+
clusters
2n+
trig bipy, {CdN3FO}
{Cd6(trz)6F4(H2O)2}n
chains
[Cd2(trz)2Cl2(H2O)] (6)
[Cd3(trz)3Br3] (7)
[Cd2(trz)3I}] (8)
3-D
3-D
oct, {CdN4Cl2} and
{CdN2Cl3O}
2.303(2)-2.306(2),
2.217(2)
2.303(2)-2.306(2) (Cl),
2.7097(8)-2.7406(8) (Cl)
{Cd(trz)2Cl}nn- chains,
2n-
{Cd(trz)2Cl2(H2O)}n
chains
oct, {CdN2Br4} and
{CdN3Br3};
trig bipy, {CuN4Br}
oct, {CdN6}; tet, {CdN3O}
2.194(8)-2.201(9),
2.279(9)-2.319(9);
2.226(9)-2.313(9)
2.296(5)-2.411(5);
2.189(5)-2.210(3)
2.315(5)-2.374(4);
2.203(5)-2.256(7),
2.210(5)-2.337(1)
2.186(3)-2.338(3)
2.798(1)-2.972(1),
2.724(1)-2.981(1);
2.668(1)
{Cd(trz)2Br2}n2n- chains,
{Cd3(trz)2Br3}nn+ layers
3-D
3-D
-; 2.7469(6)
{Cd(trz)I} chains
[Cd3(trz)5(NO3)(H2O)]‚H2O
(9‚H2O)
oct, {CdN6}; 2 × trig bipy,
{CdN3O2} and {CdN4O}
-; 2.493(5) (NO3),
2.531(5) (H2O)
{Cd(trz)3}nn- chains,
{Cd2(trz)7(H2O)2}3-
clusters
[Cd8(trz)4(OH)2(SO4)5(H2O)]
(10)
3-D
oct, {CdN2O4)} (×4)
2.186(2)-2.320(2) (OH)
{Cd3(µ3-OH)}5+ clusters,
{Cd7(trz)4}10n+ chains,
6n+
{Cd8(SO4)5}n
framework
{CdNO5} (×1)
{CdNO5} (×1)
2.148(2)
2.239(3)
2.303(2)-2.446(2) (SO4)
2.288(2)-2.501(3) (SO4),
2.299(3) (H2O)
{CdO6} (×1)
2.272(2)-2.362(2) (SO4),
2.262(2) (OH)
{CdN2O4} (×1)
2.207(3)-2.213(3)
2.296(2)-2.540(3) (SO4)
a Key: tet, tetrahedral; trig bipy, trigonal bipyramidal; oct, octahedral.
Figure 1c, which link to adjacent cages through the zinc
nodes. The volume of the cage pore of ca. 1500 Å allows
interpenetration of the three-dimensional framework by a
second, independent three-dimensional unit. The observation
of such inextricably interpenetrated framework structures is
not unusual in the structural chemistry of metal-organic
frameworks.
The bromide phase [Zn(trz)Br] (2) is the only two-
dimensional structure of this study (Figure 2b). The network
is constructed from tetrahedral {ZnN3Br} sites, with the
coordination geometry at each zinc site defined by nitrogen
donors from three triazolates and a terminal bromine ligand.
The secondary building unit is a binuclear {Zn2Br2(trz)4}2-
cluster, with zinc centers bridged by two triazolates in the
N1,N2-bridging mode, to form a {Zn2N4} heterocycle. Each
zinc atom also bonds to the N4 position of an exocyclic
triazolate ligand. The binuclear units are interlinked through
the remaining sites of the triazolate groups. This connectivity
pattern generates a second ring structure {Zn4(NCN)4}. As
shown in Figure 2b, the bromine atoms project from either
face of the layer and interdigitate with the bromine atoms
from adjacent layers.
lographic c-axis. The coordination geometry at the zinc sites
is defined by three nitrogen donors from three triazolate
ligands in the equatorial plane and two axial fluoride ligands.
The chain substructure reveals zinc centers bridged by two
fluoride ligands and triazolate ligands in the N1,N2-bridging
mode (Figure 3b). In addition, each zinc is coordinated to
the N4 position of a third triazolate. The chains are in turn
interconnected through the remaining triazolate nitrogen
donors into the framework structure of Figure 3a. When
observed along the c-axis direction, it is evident that alternate
triazolate groups project at angles of 120° to produce the
hexagonal grid pattern for the framework, shown in Figure
3a. The framework hexagon is approximately 8 Å on an edge,
resulting in a “free” volume of 43.9%. The channels are
occupied by the water of crystallization. However, the zinc
chloride phase [Zn(trz)Cl] exhibits the same corrugated layer
structure as 2 and is isomorphous with 2.
The three-dimensional structure of [Zn2(trz)3(OH)]‚3H2O
(3‚3H2O) is shown in Figure 4b. The structure is best
n-
described as {Zn(trz)3}n chains, running parallel to the
a-axis, linked through tetrahedral {ZnN3(OH)} sites. As
shown in Figure 4c, the chain is constructed from octahedral
{ZnN6} centers. Each zinc site is bridged to each of two
adjacent zinc sites through three triazolate ligands in the N1,-
N2-bridging mode. Consequently, the triazolate groups
project outward from the Zn‚‚‚Zn axis of a chain so as to
make an angle of 60° between the planes of alternate
triazolate rings when the chain is projected onto the bc-plane.
The structure of 2 is quite distinct from that of the
previously reported zinc(II)/triazolate/fluoride phase. The
open-framework, three-dimensional structure of [Zn(trz)F]‚
H2O is illustrated in Figure 3a. The building blocks of the
structure are chains of trigonal bipyramidal Zn(II) centers
with {ZnN3F2} coordination, running parallel to the crystal-
4892 Inorganic Chemistry, Vol. 46, No. 12, 2007

Zinc(II)- and Cadmium(II)-1,2,4-Triazolate Systems
Figure 2. (a) ORTEP view of the structure of [Zn(trz)Br] (2), showing
the atom-labeling scheme and 50% thermal ellipsoids. (b) Ball and stick
representation of the two-dimensional structure of 2 in the bc-plane.
rhomboid void channels and the regions above and below
the {ZnN3(OH)} sites.
The sulfate phase [Zn2(trz)(SO4)(OH)] (4) also manifests
a complex three-dimensional structure, shown in Figure 5b.
The structure may be described as {Zn2(SO4)(OH)}nn- layers
in the ab plane, shown in Figure 5c, linked in the third
dimension through triazolate ligands. As shown in Figure
5b, the stacking of Zn/S/O layers produces interlamellar
regions populated by the triazolate ligands.
The secondary building units of the structure are trinuclear
{Zn3(µ3-OH)}5+ clusters, which exhibit two distinct Zn(II)
coordination geometries. The first is a distorted octahedral
{ZnN2O4} site, exhibited by two zinc centers of the triad.
The coordination geometry is defined by N1(N2) nitrogen
donors from two triazolate ligands, the µ3-hydroxy group,
and an oxygen donor from each of three sulfate groups. These
six coordinate zinc atoms form a chain substructure linked
through N1,N2-bridging triazolate ligands and bridging
hydroxy groups, running parallel to the b-axis.
The second zinc site exhibits distorted square pyramidal
geometry with the basal plane occupied by a triazolate N4
nitrogen, two sulfate oxygen atoms and the hydroxy group,
and a sulfate oxygen donor in the apical position. The {Zn3-
(OH)}5+ clusters form hydroxy-, triazolate-, and sulfate-
Figure 1. (a) View of the structure of [Zn(trz)2] (1), showing the atom-
labeling scheme and 50% thermal ellipsoids. (b) View of the three-
dimensional structure of 1 in the ac-plane. (c) Adamantoid {Zn10(trz)12}
cage that provides the secondary building unit for 1.
The N4 position of each triazolate ligand bonds to the
tetrahedral zinc sites, each of which bridges to three adjacent
{Zn(trz)3}nn- chains through the three triazolate groups. The
coordination geometry at this second zinc site is completed
by a hydroxy group. The connectivity pattern generates the
centered hexagonal network in projection onto the bc-plane,
as illustrated in Figure 4b. The water molecules of crystal-
lization occupy the volume between chains, both the
Inorganic Chemistry, Vol. 46, No. 12, 2007 4893

Ouellette et al.
Figure 3. (a) View of the structure of [Zn(trz)F]‚1.33H2O in the ab-plane,
showing the large channels that contain the water of crystallization. (b)
{Cd(trz)F} chain substructure of [Zn(trz)F]‚1.33H2O.
bridged chains in the ab-plane. The chains are in turn
connected into a network through bridging sulfate groups.
Each sulfate adopts a η3, µ5 coordination mode, using three
oxygen donors and leaving a single pendant {S-O} group
on each sulfate site. The sulfate moieties bridge two
octahedral and two square pyramidal zinc sites of a chain
and bridge to a square pyramidal zinc of an adjacent chain
to produce the layer substructure of Figure 5c. The layers
stack along the c-direction. Each triazolate ligand adopts the
N1,N2,N4-bridging mode, linking two six coordinate zinc
sites of the chain and a square pyramidal zinc of an adjacent
layer.
Figure 4. (a) Atom-labeling scheme and 50% thermal ellipsoids for the
structure of [Zn2(trz)3(OH)]‚3H2O (3‚3H2O). (b) View of the three-
n-
dimensional structure of 3. (c) {Zn(trz)3}n chain and one set of the
tetrahedral zinc sites that serve to link adjacent chains.
The cadmium fluoride phase [Cd3(trz)3F2(OH)]‚3H2O (5‚
3H2O) adopts the three-dimensional structure of Figure 6b.
There are two distinct cadmium sites: six coordinate
{CdN3F3} centers defined by three triazolate nitrogens, two
µ3-fluoride ligands, and a µ4-fluoride and a distorted trigonal
bipyramidal {CdN3FO} site defined by three triazolate
nitrogen donors, a µ4-fluoride, and a hydroxo ligand.
The secondary building unit is a hexanuclear cadmium
cluster, shown in Figure 6c. The cluster consists of a
central {Cd4F4} core of six coordinate cadmium centers.
The core is linked to two five-coordinate cadmium sites
through the µ4-fluoride donors and through N1,N2-bridging
triazolate groups. Each of two cadmium centers of the
central core participates in two N1,N2-bridging interactions
with a five-coordinate site, while the remaining two cadmium
atoms of the core participate in a single triazolate bridge
with the five coordinate sites. Consequently, two cadmium
centers of the core participate in two N1(N2) interactions
and a single N4 bond to an exo-core triazolate, and the
remaining two metal centers exhibit a single N1(N2) bridge
and two bonds to N4 sites of exo-cluster triazolate groups.
These clusters are linked through triazolate nitrogen donors
into chains, running parallel to the crystallographic a-axis
(Figure 6d).
The connectivity pattern generates intersecting hydrophilic
channels parallel to the a- and c-axes. The aqua ligands
project into these channels which are also occupied by the
water molecules of crystallization.
Multiple coordination modes are also observed for [Cd2(trz)2-
Cl2(H2O)] (6), whose three-dimensional structure is depicted
in Figure 7b. The complex structure may be understood in
terms of two one-dimensional substructures. The first is a
chain of distorted six coordinate {CdN4Cl2} sites. Each
cadmium site of this chain is linked to two adjacent sites
through two N1,N2-bridging triazolate ligands and a bridging
4894 Inorganic Chemistry, Vol. 46, No. 12, 2007

Zinc(II)- and Cadmium(II)-1,2,4-Triazolate Systems
ligand, and a µ3-chloride donor that serves to link the two
types of chain in the ac-plane. Propagation into the third
dimension is achieved through the triazolate nitrogen donors
that are not involved in bonding to cadmium sites in the plane
of Figure 7c. Alternatively, the structure could be described
as {CdCl}nn+ layers, parallel to the ac plane, linked through
triazolate ligands into a framework structure. This description
is revealed in Figure 7b.
A view of the three-dimensional structure of [Cd3(trz)3-
Br3] (7), projected onto the ab-plane, is shown in Figure 8b.
While the connectivity pattern for 8 is unusually complex
and based on the presence of three distinct cadmium
polyhedra, {CdN2Br4}, {CdN3Br3}, and {CdN4Br}, the
structure may be described most simply as Cd/Br/triazolate
layers parallel to the ac-plane, linked through additional
triazolate ligands in the third dimension. A view of the layer
substructure of 7, shown in Figure 8c, illustrates the structural
complexity deriving from the three cadmium environments.
The {CdN2Br4} octahedra (type 1) are defined by four
bromine donors in the equatorial plane and two triazolate
nitrogen donors in the axial positions. These octahedra
engage in opposite edge-sharing through the bromine ligands
to generate {CdBr2}n chains, parallel to the c-axis. This chain
is decorated with {CuN3Br3} sites (type 2), alternating at
either edge of the chain. These second cadmium sites
participate in bonding to µ3-bromine atoms of the chain and
are additionally linked to the chain cadmium sites through
an N1,N2-triazolate bridge. Thus, the{CuN3Br3} centers
exploit their remaining bromine and triazolate groups to
bridge to three Cd sites of the third type {CdN4Br}. Type 2
cadmium bridges to one type 3 site through a µ2-bromine
and an N1,N2-triazolate linkage. In addition, the type 2 sites
bond to the N4 donor of a triazolate group which uses the
remaining N1,N2 positions to bridge two additional type 3
cadmium sites. The distorted trigonal bipyramidal type 3 sites
form binuclear {Cd2(1,2-triazolate)2} subunits, each of which
bridges to four cadmium type 2 sites of the layer and four
type 2 and two type 3 cadmium sites on adjacent layers. In
the ac-plane, the type 2 and type 3 cadmium sites form a
ribbon that propagates parallel to the type 1 chain. The
alternating chains and ribbons connect to form the layer
substructure. The triazolate groups project from either face
of the layer and serve to link the layers in the b-direction.
The three-dimensional structure of [Cd2(trz)3I] (8) is
isomorphous with that of [Zn2(trz)3(OH)] (3). As shown in
Figure 9, compound 8 exhibits the centered hexagonal
projection in the bc-plane. The metrical differences between
8 and 3 reflect the substitution of Cd(II) for Zn(II) and I-
and OH-. Despite a 14% increase in volume of 8 compared
to 3, the crystals of 8 do not contain water of crystallization.
The three-dimensional structure of [Cd3(trz)5(NO3)(H2O)]‚
H2O (9‚H2O), shown in Figure 10b, is constructed from the
{M(II)(trz)3}nn- chains, previously described for compounds
3 and 8. However, the connectivity between chains in 9 is
provided by two unique structural elements, as shown in
Figure 10c, providing an architecture constructed from three
distinct cadmium coordination polyhedra. The first are the
Figure 5. (a) ORTEP view of the atom-labeling scheme and 50% thermal
ellipsoids for [Zn2(trz)(SO4)(OH)] (4). (b) View of the three-dimensional
structure of 4. (c) Layer substructure of 4 in the ab-plane.
chloride to each neighbor. The transoid disposition of the
chloride donors produces a zigzag {CdCl}n core.
The second cadmium coordination geometry {CdN2Cl3O}
participates in a second chain substructure that propagates
parallel to the first chain in the ac-plane (Figure 7c). Each
cadmium of this type bonds to two N4-triazolate nitrogen
donors in a transoid disposition, two cisoid µ2-Cl donors that
bridge exclusively to cadmium sites of this chain, an aqua
n-
{CdN6} sites of the {Cd(trz)3}n chains. These chains are
Inorganic Chemistry, Vol. 46, No. 12, 2007 4895

Ouellette et al.
Figure 6. (a) View of the structure of [Cd3(trz)3F2(OH)]‚3H2O (5‚3H2O), showing the atom-labeling scheme and 50% thermal ellipsoids. (b) View of the
three-dimensional structure of 5 in the ab-plane. (c) Hexanuclear cadmium building block of 5, showing the {Cd4F4} core. (d) Chain of hexanuclear clusters
linked through triazolate bridges.
n-
analogous to the {Zn(trz)3}n chains of 3 and exhibit the
same profile with triazolate rings at 60° angles with respect
to each other about the chain axis. The remaining structural
components are the trigonal bipyramidal {CdN3O2} sites and
binuclear {Cd2(trz)7(H2O)2}3- sites which connect a given
chain to six neighboring chains.
the five-coordinate cadmium sites. The triazolate ligand
bridging the two cadmium centers of this binuclear unit
adopts the N1,N4-bridging mode, leaving the N2 site
uncoordinated.
The connectivity pattern generates a hexagonal grid pattern
in projection, similar to that previously observed for com-
pounds 3 and 8. However, in the latter materials, the metal
siteofthechainlinkingmotif{Zn(trz)3(OH)}2-or{Cd(trz)3Br}2-
occupies the centroid of the virtual hexagons. In the case of
9, the Cd‚‚‚Cd axes of the {Cd2(trz)7}3- and {Cd(trz)3(SO4)2}5-
subunits are displaced ca. 0.4 Å from the centroids of the
hexagons. Consequently, for compounds 3 and 8, the
projected hexagons are divided by the {Zn(trz)3(OH)}2- and
{Cd(trz)3Br}2- subunits into three equivalent rhombs with
edge dimensions of 6.2 and 6.4 Å, respectively. In contrast,
The first five coordinate cadmium site is defined by three
N4 triazolate donors in the equatorial plane and two axial
sulfate oxygen donors. The sulfate ligands are monodentate
with the uncoordinated oxygen atoms aligned parallel to the
b-axis. The triazolate ligand planes of this cadmium site are
disposed at ca. 120° to each other and parallel to the axes of
the {Cd(trz)3}nn- chains. Three adjacent {Cd(trz)3}nn- chains
are linked through these five coordinate cadmium sites.
The cadmium atoms of the binuclear {Cd2(trz)7}3- clusters
exhibit distorted {CdNO4} trigonal bipyramidal geometry.
Each cadmium center of the cluster coordinates to three
triazolate ligands through the N4 positions. The binuclear
site bridges three adjacent {Cd(trz)3}nn- chains through these
triazolate groups. When the structure is viewed down the
chain axis (Figure 10b), it is observed that the planes of the
triazolate groups of the binuclear clusters align parallel to
and are eclipsed by the planes of the triazolate ligands of
2-
the SO4 groups of adjacent virtual chains of {Cd(trz)3-
(SO4)2}5-/{Cd2(trz)7}3- chains of 9 project into one rhomb
and the Cd‚‚‚Cd vectors of adjacent virtual chains are
displaced toward each other from the centroids of the
hexagonal grid. This results in division of the hexagons into
two equivalent rhombs with diagonals of 8.2 and 13.1 Å
and a flattened rhomb with diagonals of 5.8 and 19.7 Å.
The sulfate groups project into the latter rhomb, while the
4896 Inorganic Chemistry, Vol. 46, No. 12, 2007

Zinc(II)- and Cadmium(II)-1,2,4-Triazolate Systems
Figure 8. (a) ORTEP representation of the structure of [Cd3(trz)3Br3] (7),
showing the atom-labeling scheme and 50% thermal ellipsoids. (b) View
of the three-dimensional structure of 7 in the bc-plane. (c)Network
substructure of 7 in the ac-plane showing the three cadmium environments
and their linking through triazolate and bromine bridges.
Figure 11b. The structural complexity is related to the
presence of eight crystallographically unique cadmium sites.
Two {CdN2O4} coordination sites and one {CdN2O5} center
form a µ3-OH-bridged triad, while a second µ3-OH-bridged
triad contains two other {CdN2O4} sites and a unique {CdO6}
polyhedron, as shown in Figure 11c,d, respectively. A second
{CdNO5} site involves aqua ligation, and there is an
additional {CdN2O4} site that does not participate in triad
formation, illustrated in Figure 11e,f, respectively.
Figure 7. (a) Atom-labeling scheme and 50% thermal ellipsoids for the
structure of [Cd2(trz)2Cl2(H2O)] (6). (b) View of the three-dimensional
structure of 6 in the bc-plane. (c) View of the structure of 6 in the ac-
n-
plane, showing the {Cd(trz)2Cl}n chains running parallel to the a-axis.
N1,N4-bridging triazolate groups of the {Cd2(trz)7}3- clusters
project into the former. Apparently, the volume enclosed by
the flattened rhombs is inaccessible to solvent, as the water
of crystallization is found exclusively in the void regions
defined by the former rhombs.
It is noteworthy that the cadmium sulfate substructure of
The complex three-dimensional structure of the cadmium-
sulfate phase [Cd8(trz)4(OH)2(SO4)5(H2O)] (10) is shown in
10, {Cd8(SO4)5}n6n+, is three-dimensional (Figure 11g). When
2-
projected onto the ac-plane, the Cd/SO4 substructure
Inorganic Chemistry, Vol. 46, No. 12, 2007 4897

Ouellette et al.
Figure 9. (a) View of the structure of [Cd2(trz)3I] (8), showing the atom-
labeling scheme and 50% thermal ellipsoids. (b) Three-dimensional structure
of 8 in the bc-plane.
appears as cadmium sulfate layers stacking along the
crystallographic a-axis and connected through sulfate link-
ages.
In contrast, the cadmium-triazolate substructure is one-
dimensional, as illustrated in Figure 11h. The weaving of
these strands through the three-dimensional structure of 10
is highlighted in Figure 11b. The chains propagate parallel
to the a-axis and are constructed from {Cd4(trz)4}4+ rings
linked through exocyclic cadmium sites. The organic ligands
are largely confined to the interlamellar regions between the
cadmium sulfate layers of Figure 11f.
Thermal Analyses. The compounds of this study were
analyzed by TGA under 20 mL min-1 flowing nitrogen,
while ramping the temperature at a rate of 5° min-1 from
25 to 800 °C. The thermal decomposition profile of [Zn-
(trz)2] (1), shown in Figure 12a, is characteristic for the zinc
compounds of this study, 1-4. There is a rapid weight loss
between ca. 375 and 450 °C attributed to the partial or total
loss of the triazole components. This process is followed by
a gradual weight loss in 1 and 3 from the combustion of the
remaining triazole ligands. In the case of compound 4, [Zn2-
(trz)(OH)(SO4)], there is a plateau of stability between 425
and 575 °C, followed by a second sharp weight loss between
575 and 625 °C of ca. 27%, corresponding to the loss of
SO3 (Figure 12b).
Figure 10. (a) ORTEP representation of the structure of [Cd3(trz)5(NO3)-
(H2O)]‚H2O (9‚H2O), showing the atom-labeling scheme and 50% thermal
n-
ellipsoids. (b) View of the three-dimensional structure of 9. (c) {Cd(trz)3}n
chainof9andonesetoftrigonalbipyramidalandbinuclear{Cd2(trz)7(H2O)2}3-
sites that connect the chain to neighboring chains.
products of heating to 300 and 550 °C are shown in Figure
14. The spectrum of the 300 °C product is essentially
identical with that observed at room temperature. However,
the spectrum of the product from heating at 550 °C is
characterized by bands at ca. 2110 and 520 cm-1, consistent
with ν(CtN) and ν(Zn-C) of Zn(CN)2. In addition, a broad
band centered at 1150 cm-1, assigned to ν(S-O) of Zn(SO4).
The product of thermolysis at temperatures above 650 °C
exhibits an infrared spectrum similar to that of Zn(CN)2.
Consequently, the thermal chemistry of 4 is consistent with
the following equations:
The thermodiffraction pattern for compound 4 in the 25-
450 °C temperature range is shown in Figure 13. The
diffraction profile is largely unchanged to 450 °C, indicating
that the zinc-oxo-sulfate framework is thermally robust and
persistent to at least 450 °C. The infrared spectra of the
[Zn2(trz)(OH)(SO4)] 450 °C8 Zn(CN)2 + Zn(SO4)
-SO3
Zn(CN)2 + Zn(SO4)
8 Zn(CN)2 + ZnO
650 °C
4898 Inorganic Chemistry, Vol. 46, No. 12, 2007

Zinc(II)- and Cadmium(II)-1,2,4-Triazolate Systems
Figure 11. (a) Atom-labeling scheme and 50% thermal ellipsoids for the structure of [Cd8(trz)4(OH)2(SO4)5(H2O)] (10). (b) View of the three-dimensional
structure of 10 in the bc-plane. (c, d) Two η3-OH-bridged cadmium triads that are observed as secondary building units of 10. (e) Aqua-ligated {CdNO5}
site of 10. (f) “Isolated” {CdN2O4} site. (g) Three-dimensional cadmium sulfate substructure of 10. (h) One-dimensional cadmium-triazolate substructure
of 10.
Inorganic Chemistry, Vol. 46, No. 12, 2007 4899

Ouellette et al.
and 550 °C and sublimation of the residual cadmium above
600 °C. The thermodiffraction pattern of 7 shows that the
framework is stable to ca. 375 °C, whereupon a new
crystalline phase appears (Supporting Information Figure S8).
Since [Zn(trz)F]‚H2O exhibits an open framework structure
with considerable volume occupied by water molecules of
crystallization, the thermal behavior of this material was
investigated in expectation that the dehydrated [Zn(trz)F]
would exhibit sorptive properties. As shown in Figure 17a,
the thermogravimetric profile of [Zn(trz)F]‚H2O is character-
ized by a weight loss of ca. 10% between room temperature
and 85 °C. This is followed by a plateau to 360 °C,
whereupon ligand thermolysis is observed. The thermodif-
fraction profile for [Zn(trz)F]‚H2O is largely unchanged from
room temperature to 450 °C, suggesting that the framework
structure persists beyond the partial decomposition of the
ligand above 360 °C. (Figure 17b).
Sorptive Properties. While the majority of the materials
of this study exhibit relatively dense frameworks, several
may be characterized as open three-dimensional frameworks
with pores occupied by water molecules of crystallization.
The most prominent of these is [Zn(trz)F]‚H2O, whose
structure reveals large, water-occupied channels running
parallel to the crystallographic c-axis.
The material [Zn(trz)F]‚H2O was desolvated under dy-
namic vacuum at 160 °C until the outgas rate was less than
2 mTorr min-1. The desolvated host showed N2 uptake of
ca. 22 mL/g when P > 0.05 at 77.4 K and type I absorption
behavior according to the IUPAC classification (Figure 18).85
The BET and Langmuir surface areas for [Zn(trz)F] are
calculated as 66 and 108 m2 g-1, respectively. The pore
volume of 0.04 cm3 g-1, calculated from the N2 sorption
data, gives a porosity of 40%, in good agreement with the
estimated value of 43.9% by X-ray crystallography. The
median pore width, calculated by the Horvath-Kawazoe
method, is 5.3 Å.86
The desolvated framework also exhibits modest H2 uptake
with type I absorption behavior (Supporting Information
Figure S9). The uptake is ca. 0.16% by weight at 150 Torr
absolute pressure, with a maximum of 0.21% at 1000 Torr.
The desolvated material [Zn(trz)F] also binds methanol
(Figure 19), exhibiting a characteristic Langmuir isotherm.
The amount of methanol absorbed at a relative pressure of
0.2 atm is ca. 6.5 wt %, rising to ca. 9.2% at 0.8 atm. The
relatively modest sorption exhibited by [Zn(trz)F]‚H2O most
likely reflects the rather narrow channel structure of the
material, as well as the unidimensional nature of the channel
substructure.
Figure 12. Thermogravimetric profiles in the temperature range 30-800
°C for (a) [Zn(trz)2] (1) and (b) [Zn2(trz)(OH)(SO4)] (4).
All four zinc-triazolate phases of this study give Zn(CN)2
as one product of the thermal decomposition, as monitored
by infrared spectroscopy.
The cadmium series is also characterized by rapid weight
loss in the 375-425 °C range, as illustrated in Figure 15a
for [Cd3(trz)3F2(OH)]‚3H2O (5‚3H2O). In this case, there is
a preliminary dehydration process between 40 and 150 °C,
corresponding to the loss of the water of crystallization. The
subsequent step between 370 and 390 °C, associated with
the loss of the organic component, is succeeded by a plateau
of stability between 400 and 600 °C. The infrared spectrum
of the product of thermolysis of 5 at 550 °C exhibits bands
at ca. 2200 and 675 cm-1, consistent with the formation of
Cd(CN)2. Decomposition proceeds above 600 °C with
sublimation of the cadmium products to complete the
thermolysis. The thermodiffraction profile for compound 5
is shown in Figure 16. The pattern is generally unchanged
between 25 and 450 °C, showing once more that partial loss
of the organic component does not result in structural
collapse. The framework of the product of the initial weight
loss 5′ is thermally robust and persists to ca. 600 °C.
The cadmium bromide and cadmium iodide phases,
[Cd3(trz)3Br3] (7) and [Cd2(trz)3I] (8), deviate somewhat from
the pattern adopted by the other members of the series. As
shown in Figure 15b, compound 7 exhibits the loss of triazole
in two steps between 275 and 300 °C and 410 and 430 °C.
These processes are followed by loss of Br2 between 450
Photoluminescence Properties. Polymeric complexes of
metal cations with the d10 configuration, such as Cu(I), Zn-
(II), and Cd(II), and polyazaheterocyclic ligands have been
shown to possess interesting luminescent properties.61,74,87-92
(85) IUPAC. Pure Appl. Chem. 1985, 57, 603.
(86) Horvath, G.; Kawazoe, K. J. Chem. Eng. Jpn. 1983, 16, 470.
(87) Dias, H. V. R.; Diyabalanage, H. V. K.; Eldabaja, M. G.; Elbjeirami,
O.; Rawashdeh-Omary, M. A.; Omary, M. A. J. Am. Chem. Soc. 2005,
127, 7489 and references therein.
(88) Wong, W.-Y.; Liu, L.; Shi, J.-X. Angew. Chem., Int. Ed. 2003, 42,
4064.
4900 Inorganic Chemistry, Vol. 46, No. 12, 2007

Zinc(II)- and Cadmium(II)-1,2,4-Triazolate Systems
Figure 13. Thermodiffraction pattern of 4 in the 30-450 °C temperature range.
Figure 14. Infrared spectra of [Zn(trz)(OH)(SO4)] (4) at room temperature,
300 °C, and 550 °C.
The emissions observed for materials of the Cd(II)/4-pyridyl-
1,2,4-triazole and Zn(II)/tetrazolyl classes were assigned as
originating from intraligand π-π* transitions.
Sodium triazolate exhibits no observable photolumines-
cence, while 1,2,4-triazole itself is characterized in the
solid-state spectrum at room temperature by an excitation at
318 nm, producing an emission at 421 nm (Supporting
Information Figure S10). The photoluminescence of 1,2,4-
triazole has been assigned as originating from π-π* transi-
tions.
Of the materials of this study, only [Zn(trz)Cl] exhibited
luminescence properties. As shown in Figure 20, excitation
at 308 nm at room-temperature results in an emission at 510
nm with a lifetime of 47.2 µs. (Supporting Information
Figure 15. Thermogravimetric patterns in the 30-800 °C range for (a)
[Cd3(trz)3F2(OH)]‚3H2O (5‚3H2O) and (b) [Cd3(trz)3Br3] (7).
Figures S11 and S12). This luminescence behavior of [Zn-
(trzCl)] is tentatively assigned as originating from a ligand
π-π* transition. This assignment is based on the broad and
unstructured emission profile, the long luminescence lifetime,
and comparisons to related Zn(II) and Cd(II) solid-state
materials. The photoluminescence of [Zn(trz)Cl] does not
exhibit significant thermochromism.
(89) Enomoto, M.; Kishimura, A.; Aida, T. J. Am. Chem. Soc. 2001, 123,
5608.
(90) Ding, B.; Yi, L.; Wang, Y.; Cheng, P.; Liao, D.-Z.; Yan, S.-P.; Jiang,
Z.-H.; Song, H.-B.; Wang, H.-G. Dalton Trans. 2006, 665.
(91) Wang, X.-S.; Tang, Y.-Z.; Huang, X.-F.; Qu, Z.-R.; Che, C.-M.; Chan,
P. W. H.; Xiong, R.-G. Inorg. Chem. 2005, 44, 5278.
(92) He, X.; Lu, C.-Z.; Yuan, D.-Q. Inorg. Chem. 2006, 45, 5760.
Inorganic Chemistry, Vol. 46, No. 12, 2007 4901

Ouellette et al.
Figure 16. Thermodiffraction profile for compound 5 in the 30-450 °C temperature range.
Figure 17. (a) Thermogravimetric profile of [Zn(trz)F]‚H2O in the 30-800 °C temperature range. (b) Thermodiffraction pattern of [Zn(trz)F]‚H2O in the
30-450 °C temperature range.
To understand the optical properties of [Zn(trz)Cl], solid-
state density functional theory (DFT) calculations were
performed. The total density of states (DOS) for [Zn(trz)Cl]
is shown in Figure 21, where the partial density of states
(PDOS) for the Zn 3d orbitals are shown as green curves
and the ligand p-orbitals as red curves. The Fermi level is
illustrated as a vertical dashed line. It is noteworthy that the
calculation predicts an energy separation of 2.92 eV between
the HOMO and the LUMO of [Zn(trz)Cl]. This is in good
agreement with the value of 3.03 eV derived from the
4902 Inorganic Chemistry, Vol. 46, No. 12, 2007

Zinc(II)- and Cadmium(II)-1,2,4-Triazolate Systems
Figure 20. Excitation and emission spectra of [Zn(trz)Cl] at room
temperature (solid lines) and 77 K (dashed lines).
Figure 18. BET N2 sorption isotherm for [Zn(trz)F] at 77.4 K.
Figure 21. Electronic band structure of [Zn(trz)Cl]. The unit cell of [Zn-
(trz)Cl] contains 4 formula units.
Figure 19. Binding of host solid [Zn(trz)F] with methanol.
Conclusions
photoluminescence spectrum for the absorption energy. The
calculation also suggests that the Fermi level is largely ligand
p-character and that the LUMO is dominated by ligand
character.
Hydrothermal methods have been exploited in the prepara-
tion of 10 materials of the M(II)-triazolate family, where
M(II) is zinc or cadmium. With the exception of the
homoleptic phase [Zn(trz)2] (1), all compounds of this study
incorporated charge-balancing anions in addition to the
triazolate group to provide materials of the general type
M(II)/triazolate/Xn-, where Xn- may be mononegatively
changed (halide, hydroxide, or nitrate) or dinegatively
charged (sulfate).
The ability of triazolate bridge to three metal centers
contributes to the remarkable structural diversity of the
ternary metal/triazolate/anion materials. The synergism of
the potentially tridentate bridging triazolate and the effective-
ness of the anionic components Xn- in adopting bridging
modes provides complex connectivity patterns and higher
dimensional materials. Thus, of the compounds of this study,
only [Zn(trz)Br] (2) is two-dimensional, while the remainder
are three-dimensional.
The absence of photoluminescence for all materials of the
study with the exception of [Zn(trz)Cl] was unanticipated.
While any explanation of these observations remains tenta-
tive, several rationalizations present themselves. Since all
the materials of the study are three-dimensional with the
exceptions of the two-dimensional and isomorphous [Zn-
(trz)Cl] and [Zn(trz)Br], we speculate that apparently there
is more vibrational coupling for the three-dimensional
structures in comparison to the two-dimensional systems.
Furthermore, the absence of photoluminescence for [Zn(trz)-
Br] suggest that the bromide analogue possesses a greater
vibrational density of states which provides more effective
radiationless relaxation for the bromide material than in the
case of the chloride analogue.
Inorganic Chemistry, Vol. 46, No. 12, 2007 4903

Ouellette et al.
The structural chemistry is complex, with both the identity
of the metal and of the anion Xn- acting as significant
structural determinants. This observation is reinforced by the
range of component substructures revealed by the materials
of this study: clusters, rings, cages, chains, layers, and even
three-dimensional frameworks. While only four zinc-contain-
ing phases are reported, the variability in coordination
polyhedra is demonstrated by the tetrahedral, trigonal bipy-
ramidal, and octahedral sites embedded in the structures. The
anions Xn- can also adopt a variety of bridging or terminal
coordination modes, and the M-X-M and M-O-E (E )
N, S) angles are quite “soft”. While these factors provide a
rich structural chemistry, they also contribute to the absence
of predictability in the design of new materials.
The structural and compositional complexity of the metal-
triazolate system can be further enhanced by the synthetic
conditions exploited in their isolation. The hydrothermal
domain is itself complicated, with variables such as time,
temperature, stoichiometries of reactants, pH, nucleation and
growth rates, starting materials, etc., requiring careful
navigation. However, what is evident from this study and
others in the emerging field of metal-polyazaheterocycle
chemistry is the certainty that huge numbers of materials
with unusual, unprecedented, and inconceivable structures
remain to be discovered. Furthermore, as representative of
the important class of organic/inorganic hybrid materials, the
metal-triazolates exhibit a range of composite physical
properties which may be amenable to tuning for applications
to sorption, optical materials, and magnetism.
As an example of potentially useful physical properties,
the open-framework structure of [Zn(trz)F]‚H2O suggested
potential microporosity. The dehydrated material [Zn(trz)F]
is indeed microporous, exhibiting type I isotherms for
sorption of H2, N2, and MeOH. Furthermore, the photolu-
minescence associated with many d10 complexes encouraged
us to study the optical properties of the materials of this
study. However, only [Zn(trz)Cl] exhibited photolumines-
cence, presumably arising from a ligand π-π* transition.
Acknowledgment. This work was funded by a grant from
the National Science Foundation, CHE-0604527. We thank
Dr. Damian G. Allis for assistance with the DMol3 calcula-
tions. We are also grateful to Prof. Joseph Chaiken for helpful
discussions on the luminescence spectroscopy.
Supporting Information Available: Crystallographic files in
CIF format for compounds 1-10, TGA profiles for compounds 2,
3, 6, and 8-10, thermodiffraction profiles for 3-5 and 7, IR spectra
for 5‚3H2O, a BET H2 isotherm of [Zn(trz)F], excitation and
emission spectra for 1,2,4-triazole, and emission decay traces and
experimental fits for [Zn(trz)Cl] at room temperature and at 77.4
K (Tables S.1-S.15). This material is available free of charge via
the Internet at http://pubs.acs.org.
IC062269A
4904 Inorganic Chemistry, Vol. 46, No. 12, 2007