Cadmium amido alkoxide and alkoxide precursors for the synthesis of nanocrystalline CdE (E = S, Se, Te)

Article abstract of DOI:10.1021/ic0485155

The synthesis and characterization of a family of alternative precursors for the production of CdE nanoparticles (E = S, Se, and Te) is reported. The reaction of Cd(NR₂)₂ where NR₂ = N(SiMe ₃)₂ with n HOR led to the isolation of the following: n = 1 [Cd(μ-OCH₂CMe₃)(NR₂)(py)]₂ (1, py = pyridine), Cd[(μ-OC₆H₃(Me)₂-2,6) ₂Cd(NR₂)(py)]₂ (2), [Cd(μ-OC ₆H₃(CHMe₂)₂-2,6)(NR ₂)(py)]₂ (3), [Cd(μ-OC₆H ₃(CMe₃)₂-2,6)(NR₂)(py)]₂ (4), [Cd(μ-OC₆H₂(NH₂)₃-2,4,6) (NR₂)-(py)]₂ (5), and n = 2 [Cd(μ-OC₆H ₃(Me)₂-2,6)(OC₆H₃(Me) ₂-2,6)(py)₂]₂ (6), and [Cd(μ-OC ₆H₃(CMe₃)₂-2,6)(OC₆H ₃-(CMe₃)₂-2,6)(THF)]₂ (7). For all but 2, the X-ray crystal structures were solved as discrete dinuclear units bridged by alkoxide ligands and either terminal -NR₂ or -OR ligands depending on the stoichiometry of the initial reaction. For 2, a trinuclear species was isolated using four μ-OR and two terminal -NR₂ ligands. The coordination of the Cd metal center varied from 3 to 5 where the higher coordination numbers were achieved by binding Lewis basic solvents for the less sterically demanding ligands. These complexes were further characterized in solution by ¹H, ¹³C, and ¹¹³Cd NMR along with solid-state ¹¹³Cd NMR spectroscopy. The utility of these complexes as alternative precursors for the controlled preparation of nanocrystalline CdS, CdSe, and CdTe was explored. To synthesize CdE nanocrystals, select species from this family of compounds were individually heated in a coordinating solvent (trioctylphosphine oxide) and then injected with the appropriate chalcogenide stock solution. Transmission electron spectroscopy and UV-vis spectroscopy were used to characterize the resultant particles.

Full text of DOI:10.1021/ic0485155

Inorg. Chem. 2005, 44, 1309−1318
Cadmium Amido Alkoxide and Alkoxide Precursors for the Synthesis of
Nanocrystalline CdE (E S, Se, Te)
)
Timothy J. Boyle,* Scott D. Bunge, Todd M. Alam, Gregory P. Holland, Thomas J. Headley, and
Gabriel Avilucea
AdVanced Materials Laboratory, Sandia National Laboratories, 1001 UniVersity BouleVard SE,
Albuquerque, New Mexico 87105
Received October 22, 2004
The synthesis and characterization of a family of alternative precursors for the production of CdE nanoparticles (E
S, Se, and Te) is reported. The reaction of Cd(NR2)2 where NR2 N(SiMe3)2 with n HOR led to the isolation
of the following: n 1 [Cd( -OCH2CMe3)(NR2)(py)]2 (1, py pyridine), Cd[( -OC6H3(Me)2-2,6)2Cd(NR2)(py)]2 (2),
[Cd( -OC6H3(CHMe2)2-2,6)(NR2)(py)]2 (3), [Cd( -OC6H3(CMe3)2-2,6)(NR2)(py)]2 (4), [Cd( -OC6H2(NH2)3-2,4,6)(NR2)-
(py)]2 (5), and n 2 [Cd( -OC6H3(Me)2-2,6)(OC6H3(Me)2-2,6)(py)2]2 (6), and [Cd( -OC6H3(CMe3)2-2,6)(OC6H3-
(CMe3)2-2,6)(THF)]2 (7). For all but 2, the X-ray crystal structures were solved as discrete dinuclear units bridged
by alkoxide ligands and either terminal NR2 or OR ligands depending on the stoichiometry of the initial reaction.
For 2, a trinuclear species was isolated using four -OR and two terminal NR2 ligands. The coordination of the
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)
)
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)
µ
µ
µ
µ
)
µ
µ
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−
µ
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Cd metal center varied from 3 to 5 where the higher coordination numbers were achieved by binding Lewis basic
solvents for the less sterically demanding ligands. These complexes were further characterized in solution by 1H,
13C, and 113Cd NMR along with solid-state 113Cd NMR spectroscopy. The utility of these complexes as “alternative
precursors” for the controlled preparation of nanocrystalline CdS, CdSe, and CdTe was explored. To synthesize
CdE nanocrystals, select species from this family of compounds were individually heated in a coordinating solvent
(trioctylphosphine oxide) and then injected with the appropriate chalcogenide stock solution. Transmission electron
spectroscopy and UV−vis spectroscopy were used to characterize the resultant particles.
Introduction
more flexible precursors will be necessary to generate tailor-
made, high-quality quantum dots with specific properties. It
was recently reported that the toxic, pyrophoric, and unstable
Me2Cd typically used to synthesize CdE materials, could be
replaced by “green precursors” such as the acetate, oxide,
and carbonate derivatives with significant improvements in
the final CdE materials.9 Metalorganic species, such as
alkoxides or amides, may yield even greater improvements
due to the control that can be introduced by the readily
accessible varied ligand sets.
Nanomaterials are of increased interest based on the
promise of novel physical behavior related to surface
phenomena that dominate on this length scale. Examples of
this would include photoluminescent quantum dots (i.e., CdE
where E ) S, Se, Te) that demonstrate different color
emissions based on the size of the nanoparticle. The strong
size and shape dependent optical properties of these materials
have led to their use in optoelectronic devices1-3 and as
biological tags.4-8 As the application of CdE materials grows,
Currently there is a dearth of structural information
involving cadmium alkoxides (Cd(OR)2).10-14 This can be
* To whom correspondence should be addressed. E-mail: tjboyle@
Sandia.gov. Phone: (505) 272-7625. Fax: (505) 272-7336.
(1) Romanov, S. G.; Chigrin, D. N.; Torres, C. M. S.; Gaponik, N.;
Eychmuller, A.; Rogach, A. L. Phys. ReV. E: Stat., Nonlinear, Soft
Matter Phys. 2004, 69, 46606.
(2) Gaponik, N.; Eychmuller, A.; Rogach, A. L.; Solovyev, V. G.; Torres,
C. M. S.; Romanov, S. G. J. Appl. Phys. 2004, 95, 1029.
(3) Yu, A. M.; Meiser, F.; Cassagneau, T.; Caruso, F. Nano Lett. 2004,
4, 177.
(5) Nisman, R.; Dellaire, G.; Ren, Y.; Li, R.; Bazett-Jones, D. P. J.
Histochem. Cytochem. 2004, 52, 13.
(6) Mansson, A.; Sundberg, M.; Balaz, M.; Bunk, R.; Nicholls, I. A.;
Omling, P.; Tagerud, S.; Montelius, L. Biochem. Biophys. Res.
Commun. 2004, 314, 529.
(7) Sukhanova, A.; Devy, M.; Venteo, L.; Kaplan, H.; Artemyev, M.;
Oleinikov, V.; Klinov, D.; Pluot, M.; Cohen, J. H. M.; Nabiev, I. Anal.
Biochem. 2004, 324, 60.
(4) Pinaud, F.; King, D.; Moore, H. P.; Weiss, S. J. Am. Chem. Soc. 2004,
126, 6115.
(8) Derfus, A. M.; Chan, W. C. W.; Bhatia, S. N. Nano Lett. 2004, 4, 11.
(9) Qu, L. H.; Peng, Z. A.; Peng, X. G. Nano Lett. 2001, 1, 333.
10.1021/ic0485155 CCC: $30.25
Published on Web 01/25/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 5, 2005 1309

Boyle et al.
rationalized by the relative thermal instability of the com-
bination of a soft metal with a hard alkoxy ligand. If properly
controlled, however, this characteristic instability can be
exploited to fine-tune nanocrystal CdE production. To do
this in a meaningful manner, a family of closely related
precursors must be synthesized and systematically processed
to generate materials under identical conditions. We have
previously shown how this approach worked for ZnO
nanoparticles wherein we synthesized a family of mono-,
di-, tetra-, and heptanuclear zinc alkyl alkoxide precursors
that were then systematically converted to ZnO nanomaterials
using 1-methyl imidazole and water.15 From this study, it
was found that the structure of the Zn-O central core of
the precursors play a pivotal role in the aspect ratio of the
resultant nanorods.
Figure 1. Structure plot of 1. Thermal ellipsoids of heavy atoms drawn
at 30% level. Carbon atoms are drawn as ball-and-stick for clarity.
Using a similar approach, we undertook the synthesis and
characterization of a series of cadmium amido alkoxides [Cd-
(NR2)(OR)], and cadmium(II) alkoxide [Cd(OR)2] com-
pounds which were then used to generate quantum dots.
Since the potentially useful precursor, cadmium bistrimeth-
ylsilylamide [Cd(NR2)2] derivative, is a liquid at room
temperature, it was omitted from consideration in this study.
The alcohols investigated ranged from neo-pentanol (H-
OCH2CMe3, HONep), 2,6-di-methyl phenol (H-OC6H3-
(Me)2-2,6, H-DMP), 2,6-di-iso-propyl phenol (H-OC6H3-
(CHMe2)2-2,6, H-DIP), 2,6-di-tert-butyl phenol (H-OC6H3-
(CMe3)2-2,6, H-DBP), and 2,4,6-tris(dimethyl amino methyl
phenol (H-OC6H2(CH2NMe2)3-2,4,6, H-TMAP). This family
of compounds was synthesized through the alkoxy amide
exchange shown in eq 1 in toluene (tol), tetrahydrofuran
(THF) and/or pyridine (py).
Figure 2. Structure plot of 2. Thermal ellipsoids of heavy atoms drawn
at 30% level. Carbon atoms are drawn as ball-and-stick for clarity.
Cd(NR2)2 + nHOR f Cd(NR2)2-n(OR)n(solv) (1)
n ) 1, 2
The following heteroligated compounds were identified
as [Cd(µ-ONep)(NR2)(py)]2 (1); Cd[(µ-DMP)2Cd(NR2)(py)]2
(2); [(py)2(DMP)Cd(µ-DMP)2Cd(NR2)(py)] (2a); [Cd(µ-
OAr)(NR2)]2, OAr ) DIP (3), DBP (4), and TMAP (5). Plots
of 1, 2, 2a, 4, and 5 are shown in Figures 1-5, respectively.
Note that a plot of 3 can be found in the Supporting
Information. The homoligated compounds were identified
as [Cd(µ-DMP)(DMP)(py)2]2 (6) and [Cd(µ-DIP)(DIP)-
(THF)]2 (7). Plots of 6 and 7 are shown in Figures 6 and 7,
respectively. This report is an effort to shed light into the
structural chemistry of cadmium aryloxides and examine their
potential use as precursors for semiconductor nanocrystals.
Experimental Section
All compounds described below were handled with rigorous
exclusion of air and water using standard Schlenk line and glovebox
Figure 3. Structure plot of 2a. Thermal ellipsoids of heavy atoms drawn
at 30% level. Carbon atoms are drawn as ball-and-stick for clarity.
(10) Darensbourg, D. J.; Niezgoda, S. A.; Draper, J. D.; Reibenspies, J. H.
J. Am. Chem. Soc. 1998, 120, 4690.
techniques. Diethyl ether, THF, and py were stored under argon
and used as received (Aldrich) in sure seal bottles. The following
chemicals were used as received (Aldrich): CdBr2, Li(NR2),
H-ONep, H-DMP, H-DIP, H-DBP, H-TMAP, Se (-100 mesh,
99.5+ %), Te (-40 mesh, 99.997%), S(SiMe3)2, technical grade
(90%) trioctylphosphine oxide (TOPO), 99% TOPO, and technical
grade trioctylphosphine (TOP, 90%). Tetradecylphosphonic acid
(TDPA) and octadecylphosphonic acid (ODPA) were purchased
(11) Darensbourg, D. J.; Niezgoda, S. A.; Reibenspies, J. H.; Draper, J. D.
Inorg. Chem. 1997, 36, 5686.
(12) Boulmaaz, S.; Papiernik, R.; Hubert-Pfalzgraf, L. G.; Vaissermann,
J.; Daran, J.-C. Polyhedron 1992, 11, 1331.
(13) Herrmann, W. A.; Huber, N. W.; Priermeier, T. Angew. Chem., Int.
Ed. Engl. 1994, 33, 105.
(14) Goel, S. C.; Chiang, M. Y.; Buhro, W. E. J. Am. Chem. Soc. 1990,
112, 6724.
(15) Boyle, T. J.; Bunge, S. D.; Andrews, N. L.; Matzen, L. E.; Sieg, K.;
Rodriguez, M. A.; Headley, T. J. Chem. Mater. 2004, 16, 3279.
1310 Inorganic Chemistry, Vol. 44, No. 5, 2005

Precursors for Nanocrystalline CdE
Figure 7. Structure plot of 7. Thermal ellipsoids of heavy atoms drawn
at 30% level. Carbon atoms are drawn as ball-and-stick for clarity.
Elemental analysis was performed on a Perkin-Elmer 2400 CHN-
S/O elemental analyzer. All NMR samples were prepared from dried
crystalline materials that were handled and stored under an argon
atmosphere and redissolved in the appropriate deuterated solvent
(toluene-d8) at saturated solution concentrations. All solution spectra
were obtained on a Bruker DRX400 spectrometer at 399.8 and 100.5
MHz for 1H and 13C experiments, respectively. A 5 mm broadband
probe was used for all experiments. 1H NMR spectra were obtained
using a direct single pulse excitation, with a 10 s recycle delay
and 8 scan average. The 13Cd NMR spectra were obtained using a
Figure 4. Structure plot of 4. Thermal ellipsoids of heavy atoms drawn
at 30% level. Carbon atoms are drawn as ball-and-stick for clairity.
1
WALTZ-16 composite pulse H decoupling, a 5 s recycle delay,
and a π/4 pulse excitation.
Rotors of dry crystalline materials of 1-4 were packed under
an inert atmosphere, and 113Cd NMR spectra were collected. The
chemical shift was referenced against a 1.0 M (aq) Cd(ClO4)2
solution (0.0 ppm) using solid CdCl2 as a secondary standard (183
ppm).17 The 113Cd solid-state spectra were collected under magic
angle spinning (MAS) conditions at a rotor spinning frequency of
5 kHz. A single π/2 pulse of 2 µs was applied with a 60 s recycle
delay, and 2048 scan averages were obtained for each sample.
Multiple MAS frequencies were attempted to discern the isotropic
chemical shift. The spinning sideband manifold was fit with the
DMFIT software package18 to extract both the chemical shift
anisotropy (CSA) and asymmetry parameter (η).
Figure 5. Structure plot of 5. Thermal ellipsoids of heavy atoms drawn
at 30% level. Carbon atoms are drawn as ball-and-stick for clarity.
General Synthesis. The 1 or 2 equiv of the appropriate alcohol
were slowly added to a vial containing Cd(NR2)2 in toluene to
generate the respective hetero- or homoligated species. Upon
addition, the initial yellow tinged reaction mixture remained clear
and was allowed to stir for 12 h. After this time, a precipitate formed
for most of the samples. For these reactions, pyridine was added
and the reaction mixture was warmed until clear. Crystals were
grown either by transferring the mixture to a freezer (-37 °C) or
allowing them to sit uncapped in the glovebox until crystals formed.
Yields were not optimized. Note! Extreme care must be taken in
the handling and storage of cadmium containing compounds, as
well as the subsequent waste due to the extreme toxicity associated
with this metal.
Figure 6. Structure plot of 6. Thermal ellipsoids of heavy atoms drawn
at 30% level. Carbon atoms are drawn as ball-and-stick for clarity.
[Cd(µ-ONep)(NR2)(py)]2 (1). Cd(NR2)2 (1.00 g, 2.31 mmol) and
HONep (0.203 g, 2.31 mmol) in ∼5 mL toluene were used. Yield
46.5% (0.47 g). FTIR (KBr, cm-1) 2950(s), 2932(s), 284(s), 2778-
(w), 2741(w), 2706(w), 147(m), 1461(m), 1395(w), 1363(m), 1334-
from Alfa Aesar. Methanol (99.9%) and acetone (99.7%) were
purchased from Fisher and used as received. Cd(NR2)2 was
synthesized with minor modification from literature reports using
CdBr2 and 2 equiv of Li(NR2).16
FT-IR data were obtained on a Bruker Vector 22 Instrument
using KBr pellets under an atmosphere of flowing nitrogen.
(17) Sakida, S.; Shojiya, M.; Kawamoto, Y. Solid State Commun. 2000,
115, 553.
(18) Massiot, D.; Fayon, F.; Capron, M.; King, I.; LeCalve´, S.; Alonso,
B.; Durand, J.-O.; Bujoli, B.; Gan, Z.; Hoatson, G. Magn. Reson.
Chem. 2002, 40, 70.
(16) Burger, H.; Sawodny, W.; Wannagat, U. J. Organomet. Chem. 1965,
3, 113.
Inorganic Chemistry, Vol. 44, No. 5, 2005 1311

Boyle et al.
(w), 1261(m), 1188(m), 1076(s), 1056(s), 1018(s), 958(w), 937(w),
920(w), 901(w), 832(m), 756(m,sh), 679(s), 588(m), 529(sh,m).
113Cd(88.7 MHz, tol-d8) δ 356 (1 Cd), 241 (2.5 Cd), 138, 137 (0.4
Cd). Anal. Calcd for C32H68Cd2N4O2Si4: C, 43.77; H, 7.81; N, 6.38.
Found: C, 43.67; H, 8.09; N, 5.99.
(CH3)2)2). 113Cd NMR (THF-d8): δ 0.944. Anal. Calcd for C56-
Cd2H84O6: C, 62.34; H, 7.79. Found: C, 61.91; H, 7.55.
General Synthesis of CdE Nanoparticles. The general synthesis
follows for the CdE materials produced using the various Cd
precursors. Under flowing argon in a 250 mL three-neck flask
equipped with a septum, a thermometer adapter, and a gas adapter,
TOPO, TDPA, or ODPA, and the desired Cd precursor were mixed.
The Cd solution was then heated to 320 °C with stirring. In a
glovebox, a chalcogenide stock solution was prepared by mixing
TOP, anhydrous toluene (∼0.1 g), and the desired chalcogenide:
(i) S(SiMe3)2, (ii) Se, or (iii) Te. The chalcogenide stock solution
was drawn into a syringe (3 mL) in the glovebox, transferred to
the Schlenk line, and then rapidly injected (∼1.0 s) into the heated
Cd solution. After the appropriate time (15 s to 2 h), the reaction
vessel was placed into a boiling water bath. Once the reaction
mixture reached ∼60 °C, the reaction was quenched via the addition
of a previously prepared 50:50 methanol/acetone solution.
Cd[(µ-DMP)2Cd(NR2)(py)]2 (2). Cd(NR2)2 (1.00 g, 2.31 mmol)
and H-DMP (0.283 g, 2.31 mmol) in ∼ 5 mL toluene were used.
Yield 38.0% (0.380 g). FTIR (KBr, cm-1) 3067(w), 3036(w), 2958-
(s br), 1061(m), 1591(m), 1475(s), 1466(m), 1460(m), 1446(m),
1422(m), 1265(s), 1231(m), 1215(w), 1092(m), 1068(m), 933(m),
877(m, sh), 845(s), 753(m), 701(m). 113Cd(88.7 MHz, tol-d8) δ
213.8 (2 Cd), 90.0 (1 Cd). Anal. Calcd for C54H82Cd3N4O4Si4: C,
49.86, 6.35 H, 4.31 N. Found 49.46 C, 6.73 H, 4.56 N.
[Cd(µ-DIP)(NR2)]2 (3). Cd(NR2)2 (1.00 g, 2.31 mmol) and
H-DIP (0.412 g, 2.31 mmol) in ∼ 5 mL toluene were used. Yield
59.6% (0.62 g). FTIR (KBr, cm-1) 3061(w), 3025(w), 2960(s),
2928(m sh), 2871(m), 1460(m), 1430(s), 1383(m), 1360(m), 1319
(m), 1258(s), 1248(s), 1184(s), 1107(m), 989(m), 932(w), 873(m),
832(s), 756(s), 678(m), 618(m), 569(m), 537(w), 464(w). 113Cd-
(88.7 MHz, tol-d8) δ 250.0 (1 Cd), 157.5 (3.6 Cd), 139.1 (0.5 Cd),
9.0 (0.3 Cd). Anal. Calcd for C18H35CdNOSi2: C, 48.03; H, 7.84;
N, 3.11. Found C, 48.07; H, 7.79; N, 2.95.
(i) CdS Nanoparticles. Compound 2 or 7 (0.38 mmol), TOPO
90% (3.8 g, 9.0 mmol), S(SiMe3)2 (0.10 g, 0.60 mmol), and TOP
(2.0 g, 5.0 mmol) were used in the previously described synthesis.
The reaction time was 4 min.
(ii) CdSe Nanoparticles. Compound 3 or 7 (0.39 mmol), TOPO
90% (3.8 g, 9.0 mmol), TDPA (0.22 g, 7.0 mmol), Se (0.041 g,
0.50 mmol), and TOP (2.0 g, 5.0 mmol) were used in the previously
described synthesis. The reaction time was 2 min.
[Cd(µ-DBP)(NR2)]2 (4). Cd(NR2)2 (1.00 g, 2.31 mmol) and
H-DBP (0.477 g, 2.31 mmol) in ∼5 mL toluene were used. Yield
81.1% (0.90 g). FTIR (KBr, cm-1) 3094(w), 3072(w), 2958(s),
2919(m, sh), 2875(m, sh) 1466(w), 1459(w), 1405(s), 1385(m),
1260(s), 1250(s), 1211(s), 1190(s), 1120(m), 961(s), 872(s), 845-
(m), 825(m), 789(m), 756(m), 721(w), 699(m), 633(w). 113Cd (88.7
MHz, tol-d8) δ 142.1 (1 Cd). Anal. Calcd for C40H78Cd2N2O2Si4:
C, 50.24; H, 8.12; N, 2.93. Found: C, 50.12; H, 8.00; N, 2.86.
(iii) CdTe Nanoparticles. Compound 4 or 7 (0.80 mmol), TOPO
90%(3.2 g, 7.6 mmol), ODPA (0.80 g, 0.30 mmol), Te (0.034 g,
0.30 mmol), and TOP (2.0 g, 5.0 mmol) were used in the previously
described synthesis. The reaction time was 5 min.
General X-ray Crystal Structure Information.17 Each crystal
was mounted onto a thin glass fiber from a pool of Fluorolube and
immediately placed under a liquid N2 stream, on a Bruker AXS
diffractometer. The radiation used was graphite monochromatized
Mo KR radiation (λ ) 0.7107 Å). The lattice parameters were
optimized from a least-squares calculation on carefully centered
reflections. Lattice determination and data collection were carried
out using SMART Version 5.054 software. Data reduction was
performed using SAINT Version 6.01 software. Structure refine-
ment was performed using XSHELL 3.0 software. The data were
corrected for absorption using the SADABS program within the
SAINT software package.
[Cd(µ-TMAP)(NR2)]2 (5). Cd(NR2)2 (0.48 g, 1.1 mmol) and
H-TMAP (0.29 g, 1.1 mmol) in ∼5-mL were used. Yield 59.4%
(0.35 g). FTIR (Nujol, cm-1) 2963(s), 2905(w), 1447(w), 1414-
(w), 118(s), 1007(s), 876(m), 823(s), 787(s), 705(w), 686(w), 443-
(m). 1H NMR (399.8 MHz, CDCl3) δ 7.08, 6.96 (1.0H, s,
OC6H2(CH2N(CH3)2)3), 3.65, 3.31 (6.0H, s, OC6H2(CH2N(CH3)2)3),
2.27, 2.16 (18.0H, s, OC6H2(CH2N(CH3)2)3), 0.06 (18.0H, s, N(Si-
(CH3)3)2). 13C{1H} NMR (100.5 MHz, tol-d8) δ 168.3, 153.5, 131.8,
127.3 (OC6H2(CH2N(CH3)2)3), 71.6, 62.3 (OC6H2(CH2N(CH3)2)3),
47.5, 45.8 (OC6H2(CH2N(CH3)2)3). 29Si{1H} NMR (tol-d8) δ -4.51.
113Cd NMR (py-d5) δ 213.8. Anal. Calcd for C42Cd2H88N8O2Si4:
C, 46.91; H, 8.19; N 10.42. Found: C, 46.82; H, 7.86; N 9.43.
Each structure was solved using direct methods that yielded the
heavy atoms, along with a number of the C, N, and O atoms.
Subsequent Fourier synthesis yielded the remaining atom positions.
The hydrogen atoms were fixed in positions of ideal geometry and
refined within the XSHELL software. The idealized hydrogen atoms
had their isotropic temperature factors fixed at 1.2 or 1.5 times the
equivalent isotropic U of the C atoms to which they were bonded.
The final refinement of each compound included anisotropic thermal
parameters on all non-hydrogen atoms. Additional information
concerning the data collection and final structural solutions of 1-7
can be found in the Supporting Information. Table 1 lists the data
collection parameters for 1-7, respectively.
[Cd(µ-DMP)(DMP)(py)2]2 (6). Cd(NR2)2 (0.48 g, 1.1 mmol)
and H-DMP (0.27 g, 2.2 mmol) in ∼5 mL py were used. Yield
51.0% (0.20 g). FTIR (KBR, cm-1) 2975(s), 2952(m), 2905(w),
1445(m), 1414(m), 1247(s), 1156(s), 989(s), 883(s), 777(m), 754-
1
(m), 707(m), 662(wm), 450(m). H NMR (399.8 MHz, py-d5) δ
7.13 (2.0H, d, OC6H3(CH3)2)), 6.65 (1.0H, m, OC6H3(CH3)2)), 2.50
(6.0H, s, OC6H3(CH3)2)). 13C{1H} NMR (100.5 MHz, py-d5) δ
168.3, 129.1, 126.6, 124.5, 114.3 (OC6H3(CH3)2), 19.1 (OC6H3-
(CH3)2). 113Cd NMR (py-d5) 105.2. Anal. Calcd for C52Cd2-
H56N4O4: C, 60.83; H, 5.46; N, 5.46. Found: C, 61.04; H, 5.53;
N, 5.19.
Optical Characterization. UV-vis absorption spectra were
collected at room temperature on a Varian Carey 400 spectropho-
tometer. Each aliquot was quenched directly in a UV cell containing
toluene. The spectra were collected from 800 to 300 nm with a
scan rate of 0.5 nm per minute.
[Cd(µ-DIP)(DIP)(THF)]2 (7). Cd(NR2)2 (0.48 g, 1.1 mmol) and
H-DIP (0.40 g, 2.2 mmol) in ∼5 mL THF were used. Yield 48.7%
(0.25 g). FTIR (Nujol, cm-1) 2979(s), 2949(m), 1588(w), 1484-
(w), 1415(s), 1244(s), 1172(s), 981(s), 887(m), 774(m), 753(m),
1
684(m), 661(w), 450(m); H NMR (399.8 MHz, THF-d8) δ 6.82
(2.0H, d, OC6H3(CH(CH3)2)2), 6.46 (1.0H, t, OC6H3Me2), 3.38
(2.0H, m, OC6H3(CH(CH3)2)2), 1.16 (12.0H, d, OC6H3(CH(CH3)2)2).
13C{1H} NMR (100.5 MHz, THF-d8) δ 167.8, 131.7, 129.8, 123.1
(OC6H3(CH(CH3)2)2), 28.0 (OC6H3(CH(CH3)2)2), 23.8 (OC6H3(CH-
Transmission Electron Microscopy (TEM). An aliquot of the
desired solution was placed directly onto a carbon coated copper
TEM grid (300 mesh) purchased from Electron Microscopy
Sciences. The aliquot was then allowed to dry overnight. The
1312 Inorganic Chemistry, Vol. 44, No. 5, 2005

Precursors for Nanocrystalline CdE
Table 1. Data Collection Parameters for 1-7
1
2
2a
3
4
5
6
7
chemical formula
fw
temp (K)
C
32H68N4O2Si4
C
108H164N8O8Si8
C
45H60Cd2N4O3Si2
C
72H140Cd4N4O4Si8
C
40H78Cd2N2O2Si4
C
42H88Cd2N8O2Si4
C
52H56Cd2N4O4
C
56H84Cd2O6
878.06
203(2)
2601.59
203(2)
985.95
203(2)
1800.20
203(2)
956.20
168(2)
1074.36
168(2)
1025.81
168(2)
1078.03
168(2)
space group
triclinic
P1
monoclinic
P21/c
monoclinic
P21
monoclinic
P21/c
triclinic
P1
monoclinic
P21/n
monoclinic
C2/c
orthorhombic
P212121
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
9.5720(10)
10.1847(10)
12.5815(12)
98.7510(10)
109.9070(10) 98.717(2)
98.741(12)
1112.09(19)
1
1.311
33.733(4)
17.768(2)
23.015(3)
9.9973(4)
13.6501(6)
17.4569(8)
17.051(2)
17.567(2)
31.225(4)
10.078(2)
11.736(3)
11.869(3)
66.838(3)
88.463(3)
70.341(3)
1206.4(4)
1
1.316
1.012
1.72 (1.81)
4.43 (4.49)
13.871(2)
13.832(2)
14.788(2)
21.819(7)
9.497(3)
22.736(7)
16.026(5)
16.579(5)
20.494(6)
94.7970(10)
90.139(3)
102.302(3)
99.469(5)
13635(3)
4
1.267
1.036
6.77 (9.79)
21.13 (23.64)
2373.90(18)
2
1.379
0.987
2.83 (3.14)
5.88 (6.12)
9353(2)
4
1.278
1.040
12.33 (15.09)
26.43 (27.62)
2772.1(8)
2
1.287
0.892
4.43 (8.11)
8.25 (9.40)
4647(3)
4
1.466
0.964
3.33 (5.37)
6.44 (7.00)
5445(3)
4
1.315
1.040
5.01 (9.49)
8.71 (10.88)
D
calcd(mg/m3)
µ(Mo KR) (mm-1
)
1.093
R1a (%) (all data) 2.96 (3.44)
wR2b (%) (all data) 6.45 (6.80)
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo| × 100. b wR2 ) [∑w(Fo - Fc )2/∑(w|Fo| )2]1/2 × 100.
resultant particles were studied using a Philips CM 30 TEM
operating at 300 kV accelerating voltage.
Cadmium aryloxide derivatives (6, 7) were synthesized
in good yield by treatment of Cd(NR2)2 with 2 equiv of an
appropriate phenol (eq 2). Selected coordinating Lewis basic
solvents were chosen to assist in the dissolution and
crystallization of these compounds. The n ) 2 reaction (eq
1) with DMP in py yielded 6, whereas with DIP in THF, 7
was isolated. Structure plots of 6 and 7 are shown in Figures
6 and 7, respectively.
Crystal Structures. Single-crystal X-ray diffraction stud-
ies were undertaken to determine the structural aspects of
these compounds prior to formation of CdE nanoparticles.
For 1 (Figure 1), each Cd metal center adopts a distorted
tetrahedral (Td) geometry using a terminal NR2, two µ-ONep,
and a coordinated py solvent molecule. A trinuclear species
was isolated for the DMP derivative 2 (Figure 2). The central
Cd was found to adopt a Td arrangement using four µ-DMP.
The Td bound terminal Cd atoms are additionally bound by
a terminal NR2 and a py molecule. An additional structure
was isolated for a reaction mixture that had a slight excess
of H-DMP as 2a, shown in Figure 3. The Cd metal centers
are again Td and possess two µ-DMP. One of the Cd metal
centers binds a DMP ligand and two py molecules, whereas
the other Cd binds the NR2 and one py molecule.
Both 3 (Supporting Information) and 4 (Figure 4) have
similar arrangements where each of the Cd metal centers
adopt a trigonal planar arrangement using one terminal NR2
and two µ-OAr. Neither compound, when isolated from py,
showed any coordinated solvent. The increased steric bulk
of the ortho substituents prevents further coordination by
the Lewis basic solvent.
A plot of 5 reveals that the polydentate TMAP-ligated
compound is dinuclear and solvent-free in the solid state
(Figure 5). Each Td-bound Cd atom is coordinated to one
terminal amido ligand, intramolecularly coordinated to the
nitrogen atom of the dimethylamino substituent, and is linked
to the other Cd atom by two symmetrical bridging TMAP
ligands. The amido aspect of the ligand prevents further
coordination by any solvent molecules.
Results and Discussion
A series of structurally characterized heteroleptic “Cd-
(OR)(NR2)” complexes and homoleptic “Cd(OR)2“ were
evaluated as precursors to CdE nanocrystals to determine
precursor structural effects on the final materials morphol-
ogies. No reports of structurally characterized heteroligated
”Cd(OR)(NR2)” were available in the literature, and until
recently, the existence of Cd(OR)2 as discrete, structurally
characterized, molecular species was limited to a few homo-
and heterometallic compounds.10-14 The synthesis, charac-
terization, and properties of all precursors and the resultant
CdE nanomaterials are discussed below.
Synthesis. The reaction shown in eq 1 was followed for
the synthesis of the family of “Cd(NR2)(OR)” compounds.
For each sample, the Cd(NR2)2 precursor was dissolved in
tol and allowed to react overnight with the desired HOR.
Except for the DBP derivative, a precipitate formed which
would not redissolve even upon heating. Pyridine was added
and the reaction was heated until the reaction mixture turned
clear. Crystals were grown by allowing the reaction mixtures
to cool and slowly evaporate or cooling the reaction mixture
to -37 °C overnight. Plots of 1, 2, and 2a are shown in
Figures 1-3, respectively, where 1 and 2 were found to
possess coordinated py solvent molecules. An additional off
stoichiometric species was also isolated for 2 and crystal-
lographically characterized as Cd2(µ-DMP)2(DMP)(NR2)-
(py)3 (2a) (Figure 3). This was generated when a slight excess
of H-DMP was added to the reaction mixture. No further
attempts were made to synthesize this compound or fully
characterize it; however, its structure demonstrates the
various constructs that are available to tailor the properties
of the final CdE nanoparticles generated in this system. The
DIP (3, Supporting Information) and DBP derivative (4,
Figure 4) were easily crystallized from toluene. The same
structure was also solved for crystals of 4 grown from py.
The TMAP derivative (5), also grown from toluene, is shown
in Figure 5.
Investigation of the full alkoxides led to the isolation of
compounds 6 and 7, shown in Figures 6 and 7, respectively.
Inorganic Chemistry, Vol. 44, No. 5, 2005 1313

Boyle et al.
Table 2. 113Cd NMR Data for 1-7
The solid-state dinuclear structures are similar to the amido
alkoxy species, wherein each trigonal-bipyramidal (TBP) Cd
atom of 6 bridges to the other Cd atom via two µ-DMP
ligands. The TBP coordination is completed by the addition
of one terminal DMP and two py solvent molecules. The
Td Cd atoms of 7 are bound two µ-DIP ligands as well as
one terminal DIP ligand and one molecule of THF.
The bond distances and angles of the “Cd(NR2)(OR)”
species 1-7 are consistent with those of the previously
reported Cd-(OR)10-14 and -(NR2)19-23 species. The ter-
minal aryloxide ligands of 6 and 7 notably exhibit a small
Cd-O-Ar angle, demonstrating the absence of π -donation
from the aryl ring, a feature typically found present in early-
transition metal aryloxide compounds.24,25
nuclearity
Cd CN solv
δ solution -state
δ solid-state
compd
113Cd (integration)
113Cd (integration)
1
dinuclear, 4 py
356(1), 241(2.5),
138, 137(0.4)
213.8(2), 90.0(1)
250.0(1), 157.5(3.6),
139.1(0.5), 9.0(0.3)
142.1(1)
+ 304, 302, 300
2
3
trinuclear, 4 py
dinuclear, 3 tol
+ 202, 200, 198,
196, 192
+ 179, 176, 173
4
5
6
7
dinuclear, 3 tol
dinuclear, 4 tol
dinuclear, 4 py
213.8
105.2
dinuclear, 4 THF 0.944
statements concerning the solution structure were not dis-
cernible. Therefore, 113Cd NMR spectra were collected for
each compound and are metrically listed in Table 2. As
indicated by previous studies, the variation of the 113Cd
chemical shifts is very complex:10,11,27 the ligand set and the
coordination number (CN) dramatically affect both the
isotropic 113Cd chemical shift and shielding anisotropy. In
addition rapid exchange of ligands along with coordination
by Lewis basic solvents is possible in solution and further
complicates the position of the chemical shift.28
In general, for the same ligand type an increase in the Cd
CN results in a decrease in the observed 113Cd isotropic
chemical shift.28 A fully oxygen coordinated Cd species
(either 5 or 6 coordinated) would be predicted to have a 113Cd
NMR chemical shift between -10 and +235 ppm.27-29
Introduction of sulfur in place of oxygen atoms increases
the observed 113Cd chemical shift on the order of +300 to
+400 ppm. In comparison, a similar substitution of nitrogen
for oxygen atoms increases the observed 113Cd chemical shift
by approximately +100 to +200 ppm. For example, the
cadmium(II) maleate dehydrate has 113Cd chemical shifts at
δ -7 and +12 ppm, while the heterometalic alkoxide, [Cd-
{Zr2(OPri)9}] (OPri ) OCHMe2), has a 113Cd shift of +67
ppm (CN ) 5: all O atoms), CdNb2(O2CCH3)2(OPri)10 (CN
) 5: all O atoms) of +34 ppm,30 and [{Cd(OPri)3}Ba{Zr2-
(OPri)9}]2 (CN ) 4: all O atoms) of +235 ppm.29 In
comparison, the octahedrally coordinated Cd with two N
atoms in Na2Cd(EDTA) (CN ) 6: two N and four O atoms)
has a 113Cd shift of approximately +110 to +95 ppm.28 These
shifts and predicted changes can be used to understand the
spectra observed in the characterization of 1-7.
Bulk Properties. To establish that the crystal structures
of 1-7 are representative of the bulk material, Fourier
transformed infrared (FTIR) spectroscopy, elemental analysis
(EA), and additional analytical information were collected.
The data garnered are discussed in the following paragraphs.
The FTIR spectra of 1-7 show no OH peaks around 3000
cm-1 which is consistent with full exchange. For 1-5, the
normally strong M-NR2 amide stretches present around
1400-1450 cm-1 are weaker due to the dominating presence
of the alkyl and solvent stretches, in comparison to the other
family members due to the dominating presence of the alkyl
and solvent stretches. For 2, the NR2 resonances are weaker
in comparison to the other members of this family. This is
consistent with the extended trinuclear structure observed
in the solid state. For the M-O bonds there should be a
stretch present between 800 and 400 cm-1. Each sample also
had a stretch around 755 cm-1 that was tentatively assigned
to Cd-O. For 1, another very broad and strong stretch
associated with py is observed that is not present or is present
at lower levels for the other species. The EAs of the bulk
powders for 1-7 were found to be consistent with the solid-
state structure. This is surprising for a number of the
compounds reported, since molecules with coordinated
solvents often yield inconsistent elemental analyses.26 In
addition, amido species are often volatile and too reactive
to obtain meaningful analysis.
1
NMR Studies: Solution Behavior. 13C and H NMR
spectra were collected for 1-7; however, the data obtained
were not informative with respect to the nuclearity of the
complexes in solution. The appropriate sets of ligand
resonances were observed for each sample but definitive
For compound 1, the 113Cd NMR shifts in solution (δ )
+356 ppm) and in the solid-state (δ approximately +302
ppm) correspond to the retention of the dinuclear solid-state
structure in solution (CN ) 4: two N and two O atoms).
The appearance of additional 113Cd resonance in solution
reveals that there is considerable rearrangement of the
molecule in solution. This dynamic ligand behavior may
statistically generate up to at least 8 types of Cd species (4:
0, 3:1, 2:2, 1:3, 0:4 NR2/OR; for 4 dimers and 4 monomers).
Compound 2a represents an example of the structure that
(19) Bashall, A.; Beswick, M. A.; Harmer, C. N.; McPartlin, M.; Paver,
M. A.; Wright, D. S. J. Chem. Soc., Dalton Trans. 1998, 517.
(20) Beswick, M. A.; Cromhout, N. L.; Harmer, C. N.; Palmer, J. S.;
Raithby, P. R.; Steiner, A.; Verhorevoort, K. L.; Wright, D. S. Chem.
Commun. 1997, 583.
(21) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Organometallics 1991,
10, 3781.
(22) Bailey, P. J.; Mitchell, L. A.; Raithby, P. R.; Rennie, M. A.;
Verhorevoort, K.; Wright, D. S. Chem. Commun. 1996, 1351.
(23) Just, O.; Gaul, D. A.; Rees, W. S. Polyhedron 2001, 20, 815.
(24) Kerschner, J. L.; Fanwick, P. E.; Rothwell, I. P.; Huffman, J. C. Inorg.
Chem. 1989, 28, 780.
(25) Coffindaffer, T. W.; Steffy, B. D.; Rothwell, I. P.; Folting, K.;
Huffman, J. C.; Streib, W. E. J. Am. Chem. Soc. 1989, 111, 4742.
(26) Boyle, T.; Alam, T.; Mechenbier, E.; Scott, B.; Ziller, J. Inorg. Chem.
1997, 36, 3293.
(27) Summers, M. F. Coord. Chem. ReV. 1988, 86, 43.
(28) Wasylishen, R. E.; Fyfe, C. A. High-Resolution NMR of Solids. In
Annual Reports on NMR Spectroscopy; Webb, G. A., Ed.; Academic
Press: New York, 1982; Vol. 12; p 1.
(29) Veith, M.; Mathur, S.; Hunch, V. J. Am. Chem. Soc. 1996, 118, 903.
(30) Boulmaaz, S.; Papiernik, R.; Hubert-Pfalzgraf, L. G.; Septe, B.;
Vassermann, J. J. Mater. Chem. 1997, 7, 2053.
1314 Inorganic Chemistry, Vol. 44, No. 5, 2005

Precursors for Nanocrystalline CdE
could form in solution for a 1:3 arrangement. The observation
of resonances between +241 and +137 ppm suggests that
either an increase in the CN in solution or a substitution of
oxygen-coordinating ligands in place of nitrogen-coordinating
ligands is occurring.
The trinuclear compound 2 shows resonances at δ ) +213
and +90. The down field chemical shift is consistent with
CN ) 5 and suggests coordination by N atoms such as that
observed for the terminal Cd metal centers in 2. The
resonance at +90 suggests a fully O coordinated environment
such as that observed for the central Cd atom in compound
2.
For 3, the 113Cd NMR chemical shift in solution (δ )
+250 ppm) and in the solid-state (δ approximately +200
ppm) is assigned to the trigonally coordinated Cd species
(CN ) 3: one N and two O atoms). Literature values for
trigonal coordinated Cd species are limited, but the chemical
shift observed for 3 is higher than the +77 ppm 113Cd NMR
chemical shift reported for the Cd environment with trigonal
oxygen coordination in cadmium phenoxides,31 but is closer
to a proposed related pyridine adduct of cadmium phen-
oxide.32 The change from an oxygen donating ligand to a
nitrogen donating ligand is expected to increase the observed
113Cd chemical shift by ∼100 ppm, as noted above. The
additional 113Cd resonances observed in solution suggest
significant changes in the coordination environment with
dissolution for this compound.
Due to the simplicity of the observed single 113Cd peaks
recorded for 5-7, it is difficult to state whether the structure
is retained in solution or not. It appears, based on the
chemical shift, that 5 retains its dinculear Td environment;
however, the chemical shifts for 6 and 7 do not agree. Due
to the large sterically bulky ligands, it is assumed that these
species are monomeric in solution with significant shifts
upfield due to change in CN.
Figure 8. Solid-state 113Cd MAS NMR spectra of (i) (a) 3, (b) 1, and (c)
4 and (ii) expansion of the isotropic region of the 113Cd MAS NMR spectra
of (a) 3, (b) 1, and (c) 4.
Solid-state 113Cd NMR data were also collected on select
compounds in an effort to discern additional information
about the local bonding environments of these molecules.
Figure 8 shows the 113Cd MAS NMR spectra of 2, 3, and 4.
Very large spinning sideband manifolds that span hundreds
of ppm resulting from chemical shift anisotropy (CSA) were
observed. The observed CSAs were 960 ppm for 4, 987 ppm
for 3, and 660 ppm for 1. From previous solid-state 113Cd
NMR investigation of sulfur-coordinated Cd species, it was
demonstrated that the magnitude of the CSA anisotropy
reflects the range of bonding distances associated with Cd,
while the CSA asymmetry reflects the local site sym-
metries.33,34 In addition, 113Cd isotropic resonances of similar
chemical shift were experimentally observed (see inset of
Figure 8) for each of these compounds. Due to the extreme
sensitivity of 113Cd NMR chemical shifts to local environ-
Figure 9. Irradiated CdE solutions (a) 2, E ) S, (b) 3, E ) Se, and (c) 4,
E ) Te.
ments, small differences in the isotropic chemical shifts were
attributed to small differences in local crystal packing.
Attempts to draw a correlation between the major peaks
in the solid and in the solution phase did not yield conclusive
evidence for peak assignments concerning nuclearity of the
structures. For 1 and 3, the solid-state resonances of the
dinuclear species fall between the two major peaks observed
in solution. For 4, the solid-state resonance is 30 ppm less
than the solution resonance. If this trend is true, then the
major peaks observed for 1, 3, and 5 are consistent with the
dinuclear species, whereas 6 and 7 would have to represent
mononuclear species. This implies the structures observed
in the solid state are retained in solution.
(31) Darensbourg, D. J.; Wildeson, J. R.; Lewis, S. J.; Yarbrough, J. C. J.
Am. Chem. Soc. 2002, 124, 7075.
(32) Darensbourg, D. J.; Niezgoda, S. A.; Draper, J. D.; Reibenspies, J. H.
J. Am. Chem. Soc. 1998, 120, 4690.
(33) Lee, G. S. H.; Fisher, K. J.; Vassallo, A. M.; Hanna, J. V.; Dance, I.
G. Inorg. Chem. 1993, 32, 2.
(34) Murphy, P. D.; Stevens, W. C.; Cheung, T. T. P.; Lacelle, S.; Gerstein,
B. C.; Kurtz, D. M., Jr. J. Am. Chem. Soc. 1981, 103, 4400.
Inorganic Chemistry, Vol. 44, No. 5, 2005 1315

Boyle et al.
Figure 10. UV-vis spectra for CdE materials generated from (a) 2, E ) S, (b) 3, E ) Se, (c) 4, E ) Te, (d) 7, E ) S, (e) 7, E ) Se, and (f) 7, E ) Te.
Nanoparticle Synthesis. While existing reports indicate
that the choice of precursors has relatively little effect on
the final CdE nanoparticles’ morphology, the presence of a
free amine and alcohol (which would be expected to form
upon decomposition of 2-7) may have a larger effect than
decomposition products from the other Cd precursors
investigated. Further, the lower decomposition temperatures
expected for the compounds reported here in comparison to
the previously reported “green” precursors should allow for
altered growth patterns. CdE nanoparticles, synthesized from
2-7, were prepared by slight modification to a method
recently investigated by Peng and co-workers (i.e., CdS and
CdSe) and also Alivisatos and co-workers (i.e., CdTe).35,36
Experimentally, TOPO, ODPA, or TDPA and the cadmium
precursor were heated until a transparent solution resulted.
A chalcogenide solution was then injected, and the growth
temperature was set to 320 °C. The progress of crystal growth
for each CdE was monitored by UV-vis spectroscopy and
TEM. For all of the reactions, the ratio of cadmium precursor
to surfactants, the moles of chalcogenide injected, and the
temperature of the reaction over a 2 h time period were kept
constant. Under these conditions, it was found that the oxide
(CdO) and acetate (Cd(OAc)2) derivatives yielded nano-
particles of similar sizes and shapes.
A survey of the cadmium chalcogenides was performed
with these novel precursors. A different precursor was used
for each synthesis to determine the general utility of these
compounds in the preparation of CdE nanoparticles. Figure
9 illustrates that all the particles generated were high quality
(35) Peng, Z. A.; Peng, X. G. J. Am. Chem. Soc. 2001, 123, 183.
(36) Manna, L.; Milliron, D. J.; Meisel, A.; Scher, E. C.; Alivisatos, A. P.
Nat. Mater. 2003, 2, 382.
1316 Inorganic Chemistry, Vol. 44, No. 5, 2005

Precursors for Nanocrystalline CdE
Figure 11. TEM images of CdE from (a) 2, E ) S, (b) 3, E ) Se, (c) 4, E ) Te, (d) 5, E ) S, (e) 6, E ) Se, and (f) 7, E ) Te.
luminescent materials. The UV-vis spectra and TEM images
are shown in Figures 10 and 11, respectively. The high
quality of the material isolated indicates the potential utility
of these precursors in controlling the various physical
properties of CdE materials.
Cadmium Sulfide. The reaction systems for both com-
pounds remained pale yellow during the synthesis of the
nanocrystals. The UV-vis spectra of the CdS nanoparticles
from the heteroligated (2) and homoligated (5) species are
shown in Figure 10a,d. These spectra revealed an absorption
at λmax ) 425 and 400 nm, for 2 and 5, respectively. These
emissions are consistent with the literature reports on TOP
capped CdS nanocrystals of 4-5 nm in size.37 TEM images
(Figure 11a,d) confirm the expected 4-5 nm sized nano-
particles with little variation in spherical morphology for
either precursor (Figure 11a,d). From this study, the amine
or alcohol generated upon decomposition of either the homo
or heteroligated species was unable to facilitate anisotropic
wurtzite growth of CdS under the reaction conditions
presented, thus spherical shapes were obtained for both
samples.
Cadmium Selenide. Under identical synthetic conditions
to CdS, the cadmium reaction mixture changed from light
yellow to wine red upon injection of the Se/TOP stock
solution. The UV-vis spectra of the CdSe from 3 or 6
(Figure 10b,e) show a λmax ) 540 nm for the heteroligated
and λmax ) 547 nm for the homoligated species. The UV-
vis spectra indicate 3 nm CdSe were produced. The TEM
images (Figure 11b,d) show ill-defined rods are formed from
both precursors. The width are consistent with the 3 nm
(37) Bunge, S. D.; Krueger, K. M.; Boyle, T. J.; Rodriguez, M. A.; Headley,
T. J.; Colvin, V. L. J. Mater. Chem. 2003, 13, 1705.
Inorganic Chemistry, Vol. 44, No. 5, 2005 1317

Boyle et al.
observed in the UV-vis spectrum (the width is the only
dimension will possess an emission for this shaped material).
As previously described, the presence of TDPA preferentially
poisons the 001 face.37 Surprisingly, in comparison to the
use of CdO or Cd(OAc)2 as precursors, well-defined nano-
rods with uniform aspect ratios were not generated from this
synthesis when the same reaction conditions are used. This
clearly demonstrates that the precursors have a significant
effect on the growth and morphology of the final CdE
materials.
Cadmium Telluride. With respect to the synthesis of
CdTe nanocrystals, the reaction mixture changed from
colorless to dark brown-red upon injection of the Te stock
solution at 320 °C. The UV-vis spectra show a λmax ) 670
and 680 nm (Figure 10c,f) for 4 and 7, respectively, which
are consistent with CdTe nanocrystals 6-7 nm in size. TEM
images confirm the spherical nature and size of the CdTe
nanoparticles (Figure 11c,f). The CdTe morphology gener-
ated under these synthetic conditions is unusual since a
tetrapod morphology is typically observed.36 Apparently
compounds 4 and 7 via decomposition generate conditions
that inhibit the wurtzite growth of the tetrapodal arms.
easily oligomerize reducing their utility. With the mixed
ligand set, not only can we fine-tune the various properties
of interest, we can also use these species to form more
complex heteroleptic alkoxide species in a controlled manner.
Solution-state and solid-state NMR data show the bulk
materials are consistent with the solid-state structures;
however, a great deal of fluxtionality was noted on the basis
of 113Cd NMR data.
Using these specialty precursors, we systematically gener-
ated a series of CdE materials under identical conditions to
explore the effect the hetero- and homoligand sets have on
the final morphology of the CdE material. It was found that
(i) CdS spheres, (ii) CdSe rods, and (iii) CdTe spheres were
isolated for both homo- and heteroligated species. These
morphologies were different from those noted in the literature
using “green precursors” under identical synthesis conditions.
Therefore, the morphological changes must be related to the
influence of the decomposition byproducts of the starting
precursors, poisoning and promoting different growth planes.
Additional work in understanding how to further garner
control over the growth of final materials is underway based
on the fundamental information learned in this study.
Summary and Conclusions
Acknowledgment. For support of this research, the
authors would like to thank the Office of Basic Energy
Sciences of the Department of Energy and the United States
Department of Energy. Sandia is a multiprogram laboratory
operated by Sandia Corporation, a Lockheed Martin Com-
pany, for the United States Department of Energy under
contract DE-AC04-94AL85000.
A family of alternative “Cd(OR)(NR2)” and “Cd(OR)2”
precursors were synthesized and structurally characterized
for production of CdE materials. The change in steric bulk
around the metal center had little effect on the structure of
the majority of species isolated since most were isolated as
a dinuclear species. This is unusual since additional coor-
dination sites were available as evidenced by the ability of
some Cd metal centers to bind solvent molecules. The
presence of additional coordination sites is important because
the homoleptic amides are very sensitive to atmospheric
water and the homoleptic alkoxides, while more stable, can
Supporting Information Available: Crystallographic data in
CIF format and additional figure. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC0485155
1318 Inorganic Chemistry, Vol. 44, No. 5, 2005