Hydrogen atoms are omitted for clarity··· 30 Chapter 3 Figure 3.1 A ball and stick diagram of 4··· 43 Figure 3.2 An perspective view showing the coordination environment around the m
Trang 12006
Trang 2Declaration
This work described in this thesis was carried at the Department of Chemistry, National University of Singapore from 21st July 2002 to 21st July 2006 under the supervision of Associate Professor Jagadese J Vittal
All the work described herein is my own, unless stated to the contrary, and it has not been submitted previously for a degree at this or any other university
Ng Meng Tack
November 2006
Trang 3III
ACKNOWLEDGEMENTS
I would like to express my deepest gratitude to my supervisor, Associate Professor Jagadese J Vittal, for his moral and intellectual support during the course of this project With his guidance, I have really learned a lot from the enlightening discussions during the training period I would like to thank Dr Chris Boothroyd from Institite of Materials Research and Engineering (IMRE) for his valuable discussion on the phase properties of Ag2Se and AgInSe2 NPs
Here, I would like to give special mention to my colleagues for their effort in setting up a comfortable and causative working space in the lab for me
To my friends Sin Yee, Li Hui, Doris, Tze Wee, Wee Leng and Danny:
Sincere thanks for their willingness to share with me Truly, I am also indebted to my beloved parents for their invaluable moral support and patient confidence in me
I greatly appreciate the scholarship from the National University of Singapore during my studies
Last but no least, I would like to extend my appreciation to staff from the TG lab, NMR lab, Microanalytical, TEM and IR lab Your help has been invaluable
Trang 4Chapter 1 Introduction to the Chemistry of Monochalcogenocarboxylate
1.3.1 Neutral Group 12 Metal Thio- and Selenocarboxylates
Containing N-donor Ligands
11
1.4.1 Group 13 Metalloligands Anion, [M(SC{O}Ph)4]– (M =
Ga3+, In3+)
12
Trang 5II
1.4.2 Heterobimetallic Metal Thiocarboxylates 13 1.5 Single-Source Precursors for Metal Sulfides and Selenides 14
1.5.1.1 (Et3NH)[In(SC{O}Ph)4]·H2O, a Precursor for
CuInS2 Thin Film
Trang 6Chapter 3 Hetero-bimetallic and Polymeric Selenocarboxylates Derived from
[M(Se(C{O}Ph) 4 ] – (M = Ga and In) as Molecular Precursors for Ternary
Selenides
3.2.1 Structures of Hetero Bi-metallic and Polymeric
Selenocarboxylates
41 3.2.1.1 Structure of (Et3NH)[In(SeC{O}Ph)4]·H2O 43 3.2.1.2 Structures of [K(MeCN)2{M(SeC{O}Ph)4}] 44 3.2.1.3 Structures of
[(Ph3P)2M′In(SeC{O}Ph)4]·CH2Cl2
46 3.2.2 Thermogravimetry and Pyrolysis Experiments 49
4.2.1 Structure of [(Ph3P)3Ag2(SeC{O}Ph)2] and
[(Ph3P)Ag(SeC{O}Ph)]4
63 4.2.2 Thermogravimetry and Pyrolysis Experiments 66
Trang 75.3.4 Surfactant-controlled Growth in a Hot Organic Solvent(s) 91
5.3.4.1 Single Molecular Precursor Approach 95
Chapter 6 Shape and Size Control of Ag 2 Se NCs from Single Precursor
[(Ph 3 P) 3 Ag 2 (SeC{O}Ph) 2 ]
6.2.1 Formation of Ag2Se NCs from [(Ph3P)3Ag2(SeC{O}Ph)2] 99 6.2.2 Morphology and Characterization of the Ag2Se NCs 101
Trang 86.4 Synthesis and Methodology 108
Chapter 7 Synthesis of Cu 2-x Se NPs and Microflakes from
[(Ph 3 P) 3 Cu 2 (SeC{O}Ph) 2 ]
7.2 Formation and Characterization of Cu2-xSe NPs and Microflakes 111
Chapter 8 Synthesis of ZnSe and CdSe NPs from Neutral Zn(II) and Cd(II)
Selenocarboxylates
8.2.3 Structural Characterization of ZnSe and CdSe NPs 129
8.4.1 Synthesis of [Cd(SeC{O}Ph)2] and
8.4
Trang 9VI
Chapter 9 One-Pot Synthesis of New Orthorhombic Phase AgInSe 2 NRs
9.3 Crystal Structure Characterization of AgInSe2 NRs 141
Chapter 10 Synthesis of CuInSe 2 NPs
10.2.1 CuInSe2 NPs Synthesized from OA and DT Solvents 150 10.2.2 CuInSe2 NPs Synthesized from DT and TOPO Solvents 153
Chapter 11 Summary, Highlight and Possible Extension for Future Work
Chapter 12 Experimental
Trang 11VIII
Abbreviations
AACVD Aerosol Assisted Chemical Vapor Deposition
ALAD 5-Aminolevulinate Dehydratase
FTIR Fourier Transform Infrared
HOMO Highest Occupied Molecular Orbital
HRTEM High Resolution Transmission Electronic Microscope
Iso-Bu Iso-butyl
JCPDS Joint Committee of Powder Diffraction Society
LED Light Emitting Diode
LUMO Lowest Unoccupied Molecular Orbital
Lut 3, 5-Dimethylpyridine
Trang 12Me Methyl
MeCN Acetonitrile
NLO Non-Linear Optical
NMR Nuclear Magnetic Resonance
MOCVD Metal Organic Vapor Deposition
SAED Selective Area Electron Diffraction
SEM Scanning Electron Microscope
TOPO Tri-n-octylphosphine Oxide
TOP Tri-n-octylphosphine
TEM Transmission Electronic Microscope
TGA Thermogravimetric Analysis
TMEDA N, N, N, N’-Tetramethylethylenediamine
Tolyl 4-Methyl-Phenyl
Trang 13X
UV-vis Ultra Violet-Visible
XPS X-Ray Photoelectron Spectroscopy
XRPD X-Ray Powder Diffraction
Trang 14Summary
This PhD thesis describes the synthesis and characterization of a few group
11, 12 and 13 metal selenocarboxylate complexes The objective of the study is to explore the chemistry of these compounds and the suitability of these as single-source precursors to metal selenide bulk materials and NPs This thesis comprises two parts
In the first part (chapter 1 to 3) our discussion is focused on the syntheses and characterization, structures and thermal properties of metal selenocarboxylate complexes In the second part of this thesis, (chapter 4 to 8) we have discussed the syntheses of the various metal selenide NPs obtained from the metal selenocarboxylate single-source precursors
The chemistry of metal thiocarboxylates and the usage of these complexes in preparing metal sulfide bulks, thin films and NPs have been reviewed in chapter 1 In the following chapter, the preparation and characterization of Zn, Cd and Hg metal selenocarboxylates anion, [M(SeC{O}Tol)3]- have been discussed The single-crystal X-ray diffraction techniques confirmed the presence of discrete tetraphenylphosphonium cations and anions in the crystal lattice Trigonal planar MSe3 kernel is observed in these anionic metal selenocarboxylates NMR spectra (113Cd, 199Hg and 77Se, as appropriate) and ESI-MS analysis of these metal selenocarboxylates in solution have shown that the complexes [M(SeC{O}Tol)n(SC{O}Ph)3−n]− (n = 3 – 0) persist in solution
In chapter 3, synthesis and characterization of (Et3NH)[In(SeC{O}Ph)4]·H2O along with hetero-bimetallic and polymeric metal selnocarboxylates, namely [NaGa(SeC{O}Ph)4], [K(MeCN)2{Ga(SeC{O}Ph)4}], [NaIn(SeC{O}Ph)4], [K(MeCN)2{In(SeC{O}Ph)4}], [(Ph3P)2CuIn(SeC{O}Ph)4]·CH2Cl2 and [(Ph3P)2AgIn(SeC{O}Ph)4]·CH2Cl2 have been discussed The thermal decomposition
Trang 15In Chapter 6, the synthesis of Ag2Se NPs from [(Ph3P)2Ag2(SeC{O}Ph)2] has been discussed The Ag2Se NCs are highly monodispersed and they formed interesting morphology e g., faceted NCs and nanocubes The shape and size of these NCs are tunable by changing the reaction conditions The growth mechanism of these NCs has been proposed
In the following chapter, a similar precursor, [(Ph3P)2Cu2(SeC{O}Ph)2] has been employed to prepare the Cu2-xSe Nps Both HDA and DT surfactants induced an anisotropic growth on Cu2-xSe NPs The growth mechanism of Cu2-xSe Nps has been found to be different from Ag2Se NPs although similar molecular precursor was used
in the nanosynthesis
In chapter 8, synthesis and characterization of ZnSe and CdSe Nps have been presented The obtained ZnSe NCs show poor luminescence property which could be due to the deep trap emission In contrast, strong quantum confinement effect and luminescence property has been observed in the CdSe NCs The size of the prepared NPs has been found to be close to monodisperse
In chapter 9, the synthesis of a new phase AgInSe2 nanorods has been discussed The synthesized AgInSe2 nanorods are close to monodispersed and the morphology can be tuned by changing the experimental conditions TEM, XRPD, XPS, EDX have been used to characterize this new phase materials
Trang 16In chapter 10, the synthesis of CuInSe2 NCs will be discussed Pure tetragonal CuInSe2 NPs were synthesized from [(Ph3P)2CuIn(SeC{O}Ph)4] in TOPO/DT solvents The CuInSe2 NPs strongly aggregate on the copper grid An unknown compound was obtained together with tetragonal CuInSe2 NP when the reactions were conducted in OA/DT solvents
Finally the salient features of this investigations have been summarized along with future direction of work in this area
Trang 17Se O
O O
2 (Ph4P)[Cd(SeC{O}Tol)3]
Cd Se Se
Se O
O O
3 (Ph4P)[Hg(SeC{O}Tol)3]
Hg Se Se
Se O
O O
Trang 184 (Et3NH)[In(SeC{O}Ph)4]·H2O
In Se
Se
Se Se
O
O O
Trang 19XVI
9 [(Ph3P)2CuIn(SeC{O}Ph)4]·CH2Cl2
Cu Se
Se In
O
Se
Se
O PPh3
Se In
O
Se
Se
O PPh3
Se Ag
Trang 2011b [(Ph3P)Ag(SeC{O}Ph)]4·CH2Cl2
Se Ag
Se Ag
Se Ag
Se Ag PPh 3
Trang 21XVIII
List of Figures
Chapter 1
Figure 1.1 Ball and stick diagram of [Cu3(µ-dppm)3(µ3-SC{O}Ph-S)(µ3
-SC{O}Ph-S,O)]2+ and [Ag3(dppm)3(µ-SC{O}Ph-S)2]2+ cations·· 6
Figure 1.2 The structures of (Ph4P)[M(SC{O}Me)2] and [(Et3NH)2
Ag2(SC{O}Ph)4]··· 7
Figure 1.3 Ball and stick diagram of [Ni(SC{O}Ph)3]– anion unit··· 8
Figure 1.4 Views of the three crystallographically different anions in
[Cd(SC{O}Ph)3]–, showing the numbering scheme used: (a) anion A; (b) anion B; (c) anion C Atoms are shown as 50% probability thermal ellipsoids Hydrogen atoms have been
omitted for clarity··· 9
Figure 1.5 Ball & stick diagram of [Zn(SC{O}Me)3(H2O)]– as synthetic
mimics of ALAD··· 10
Figure 1.6 Repeating unit of the 1D polymer [Cd2(SC{O}Ph)4(µ-Bpy)]n···· 11
Figure 1.7 A ball and stick diagram of [KIn(SC{O}Ph)4(MeCN)2] and a
segment of its polymeric structure··· 12
[M(H2O)x{In(SC{O}Ph)4}2]·(H2O)y (M = Ca and Mg; x = 0 –
2; y = 0 – 2) Lattice water molecules were removed for clarity· 13
Figure 1.9 Ball & stick diagrams of I-9 and I-11a··· 14
Figure 1.10 Faceted and cubic shaped Ag2S NPs obtained from thermolysis
of [Ag(SC{O}Ph)]··· 18
Figure 1.11 TEM images of PbS a) dendrites and b) NRs··· 19
Figure 1.12 a) Low resolution and b) high resolution TEM images of the
synthesized AgInS2 NPs··· 21
Chapter 2
Figure 2.1 ESI-MS spectra of [M(SeC{O}Tol)n(SC{O}Ph)3–n]– , n = 0, 1, 2
and 3; M = Zn (A), Cd (B) and Hg(C)··· 28
Figure 2.2 Diagram showing the numbering scheme and 50% probability
thermal ellipsoids of the [Zn(SeC{O}Tol)3]– anion in 1 Hydrogen atoms are omitted for clarity··· 30
Figure 2.3 Diagram showing the numbering scheme and 50% probability
thermal ellipsoids of the [Hg(SeC{O}Tol)3]– anion in 3 Hydrogen atoms are omitted for clarity··· 30
Chapter 3
Figure 3.1 A ball and stick diagram of 4··· 43
Figure 3.2 An perspective view showing the coordination environment
around the metal centers in compounds 6 and 8··· 45
Figure 3.3 Segments of the one-dimensional coordination of compounds 6
and 8 The hydrogen atoms and phenyl rings are omitted for clarity··· 45
Figure 3.4 A perspective view of 9 and 10 Hydrogen atoms are removed
for clarity··· 47
Trang 22Figure 3.5 XRPD patterns of 5 and 7··· 48 Figure 3.6 Overlay of thermogravimetric curves of 4 – 10··· 49
Figure 3.7 XRPD patterns of the pyrolyzed products of 6 and 8 along with
the reported XRPD pattern of KInSe2··· 52
Figure 3.8 XRPD patterns of the pyrolyzed product of 6 along with the
reported XRPD pattern of KGaTe2··· 52
Figure 3.9 XRPD patterns of the pyrolyzed product of 5 and 7 along with
the reported XRPD pattern of Na2Ga2Se3··· 53
Figure 3.10 XRPD patterns of the decomposed products of compounds 4, 9
and 10··· 54
Chapter 4
Figure 4.1 Ball and stick diagram of 11 Hydrogen atoms and solvent
molecule were removed for clarity··· 64
Figure 4.2 A view of compound 11a Hydrogen atoms, phenyl groups on
the Ph3P and solvent molecule were deleted for clarity··· 66
Figure 4.3 Thermogravimetric curves of 11··· 67
Figure 4.4 XRPD spectrum of the decomposed products of 11, 12 and 13··· 67 Chapter 5
Figure 5.1 Schematic illustration of the density of states, along with the
changes in the band gap, in semiconductor clusters··· 79
Figure 5.2 Idealized density of states for one band of a semiconductor
structure of 3 – 0 dimensions··· 80
Figure 5.3 Room-temperature emission (left) and absorption (right)
spectra taken from difference sizes CdSe NPs··· 81
Figure 5.4 True color image of CdSe NPs illuminated with UV light
http://ehf.uni-oldenburg.de/pv/nano/index.html)··· 83
Figure 5.5 Polarized emission measurements for lasing in (a) NCs and (b)
NRs··· 84
Figure 5.6 (A) Schematic diagram of a platinum mesowire array-based
hydrogen sensor or switch (B) SEM image [400 mm(h) by 600
mm (w)] of the active area of a platinum mesowire array-based
hydrogen sensor··· 86
Figure 5.7 TEM images of poly(N-vinyl-2-pyrrolidone) capped (a) Au and
(b) Pt NPs··· 88
Figure 5.8 TEM image of rutile (rodlike) and anatase (granulous) TiO2··· 90
Figure 5.9 A near monolayer of 5 nm CdSe NPs showing short-range
hexagonal close packing··· 92
Figure 5.10 HRTEM image of CdSe/ZnS-core/shell NPs··· 93
Figure 5.11 TEMs of CdSe NPs from the single-injection experiments The
surfactant ratio was increased from (a) 8 to (b) 20 to (c) 60% HPA in TOPO For the injection volume experiments (d-f), 20% HPA in TOPO was used, as it was found to provide
optimal rod growth conditions··· 94
Figure 5.12 TEM images of various sizes CdSe NPs··· 95
Trang 23XX
Figure 5.13 TEM images of various shapes CdS (a – b), MnS (c – d) and
PbS (e – f) NPs··· 96
Chapter 6
Figure 6.1 TEM images of Ag2Se nanocubes produced at 125 °C after 60
min with surfactant-to-precursor ratios of a) 25 and b) 50 respectively; c) HRTEM image showing the lattice fringes from
a single nanocube··· 101
Figure 6.2 TEM image of silver selenide nanocubes synthesized under
same conditions as in Fig.1a and 1b, except the growth time
was shortened from 60 min to 15 min··· 102
Figure 6.3 TEM images of Ag2Se NCs prepared at 165 °C for 15 min with
surfactant-to-precursor ratio of, a) 25 and b) 50··· 103
Figure 6.4 TEM images of faceted Ag2Se NCs prepared at 180 °C for 5
min with surfactant-to-precursor ratio of, a) 25 and b) 50··· 103
Figure 6.5 X-ray powder diffraction patterns obtained at room temperature
from Ag2Se NCs synthesized at different temperatures··· 104
Figure 6.6 DSC curve of the prepared Ag2Se NCs··· 105
Figure 6.7 Shapes and sizes of Ag2Se NCs produced under different
conditions after 15 min of heating··· 106
Figure 6.8 TEM images of silver selenide NPs synthesized using an
amine-to-precursor ratio of 50 after 15 min of heating at (a) 95
°C, (b) 125 °C and (c) 145 °C··· 107
Figure 6.9 (a) SEM image of Ag2Se obtained from the pyrolysis of
[(Ph3P)3Ag2(SeC{O}Ph)2] (b) An enlarged portion of the shaped Ag2Se crystal is shown at the right hand lower corner···· 107
cube-Chapter 7
Figure 7.1 (a) Low resolution TEM image of Cu2-xSe NCs (b) Zoom in
TEM image of twinned Cu2-xSe NCs (c) HRTEM image of a twinned crystal (d) SAED spectrum of Cu2-xSe NPs··· 112
Figure 7.2 TEM images of Cu2-xSe NPs isolated after 10 min of heating at
220 ˚C with different DT to precursor molar ratio, (a) 45, (b) 90
and (c) 180··· 114
Figure 7.3 IR spectrum of Cu2-xSe NP··· 115
Figure 7.4 TEM images of Cu2-xSe NPs isolated after 10 min of heating at
(a) 220 ˚C; (b) 250 ˚C and (c) 280 ˚C with
Figure 8.1 UV-absorption spectra of ZnSe NPs taken at different time
intervals (The absorption spectra at 15 and 30 min are identical) 123
Trang 24Figure 8.2 Photoluminescence spectrum of ZnSe NPs at different time
intervals··· 124
Figure 8.3a UV-absorption spectra of ZnSe NPs isolated at various
temperatures after 5 min of heating··· 125
Figure 8.3b UV-absorption spectra of ZnSe NPs isolated at various HDA
concentration after 5 min of heating··· 125
Figure 8.4 Optical absorption spectra of CdSe NPs synthesized
with/without HPA··· 126
Figure 8.5 Uv-absorption spectra of CdSe NPs synthesized at different
HPA concentration··· 127
Figure 8.6a UV-absorption spectra of CdSe NPs isolated at different
temperature after 5 min of heating··· 127
Figure 8.6b UV-absorption spectra of CdSe NPs isolated at different TOPO
concentration after 5 min of heating··· 127
Figure 8.7 Optical spectra of CdSe NPs taken at different time intervals
(250 ºC; 2.6 g of TOPO; 44.7 mg of HPA)··· 128
Figure 8.8 (a) Optical absorption (blue) and (b) photoluminescence (red)
spectra of CdSe NPs (t = 5 min)··· 129
Figure 8.9 XRPD patterns of ZnSe and CdSe NPs··· 130 Figure 8.10 SAED of (a) ZnSe and (b) CdSe··· 130
Figure 8.11 (a) Low resolution and (b) high resolution TEM images of
ZnSe NPs (c) The size distribution of the ZnSe NPs··· 131
Figure 8.12 (a) Low resolution and (b) high resolution TEM images of
CdSe NPs (c) The size distribution of the CdSe NPs··· 132
Figure 8.13 EDX of (a) ZnSe, (b) CdSe NPs··· 132 Figure 8.14 IR spectra of TOPO, ZnSe and CdSe NPs··· 133
Chapter 9
Figure 9.1 Low-magnification TEM images of (a) AgInSe2 NRs, (b)
AgInSe2 NCs (c) HRTEM micrograph showing the crystal lattice of an individual NR (d) SAED pattern of AgInSe2 NR···· 137
Figure 9.2 (A) TEM images of AgInSe2 obtained from pure oleylamine
and (B) XRPD pattern of the corresponding AgInSe2 Peaks labeled in * correspond to the tetragonal phase AgInSe2··· 138
Figure 9.3 IR spectra of AgInSe2 NRs, pure DT, OA and the precursor··· 139
Figure 9.4 EDX and the elemental composition analysis of the synthesized
AgInSe2 NRs The copper and carbon signals are from the TEM copper grid The Si signal is from the detector The oxygen signal is from the oxidized AgInSe2··· 140
Figure 9.5 TEM images of AgInSe2 NRs obtained from (A) mixture of OA
and DT at 185 °C after 1.5 hours of heating (B) Mixture of HDA and DT (The mole ratio of each capping agent to the
precursor is fixed at 100)··· 140
Figure 9.6 (A) XRPD pattern of AgInSe2 NRs obtained from OA and DT
at 185 ˚C (B) Bulk AgInSe2 obtained from pyrolysis of the
precursor··· 141
Figure 9.7 XPS spectra of the as-prepared AgInSe2 NRs··· 143
Trang 25XXII
Figure 9.8 (A) XRPD peak positions for orthorhombic AgInS2 X-ray
spectra from AgInSe2 NRs prepared at the following DT concentrations surfactant-to-precursor ratio = 100 (B); 80 (C);
60 (D); 40 (E); 20 (F)··· 144
Figure 9.9 XRPD patterns of AgInSe2 NCs obtained using various
surfactants (T = tetragonal; O = Orthorhombic; * = impurities) 145
Figure 9.10 XRPD patterns of AgInSe2 NPs prepared at the various
temperatures··· 145
Figure 9.11 (a) Open- and (b) closed-aperture Z-scans of 1-mm-thick
solution of the AgInSe2 NRs measured with 200-fs laser pulses
of 780-nm wavelength The laser irradiance used is in the range from 5 GW/cm2 to 47 GW/cm2 The solid lines are the best-fit curves calculated by using the Z-scan theory The closed-aperture Z-scan curves in (b) are shifted vertically for clear
presentation (c) Irradiance dependence of the nonlinear
absorption coefficient (α2NRs) and nonlinear refractive index
(n2NRs) for the AgInSe2 NR solution··· 146
Chapter 10
Figure 10.1 XRPD patterns of the black precipitate obtained from the
OA/DT solvents Peaks labeled with “T” is correspond to tetragonal CuInSe2··· 151
Figure 10.2 TEM images (a & c) of the NPs that obtained from one-pot
reaction at 185 ºC with [surfactant]/[precursor] = 100, together
with the corresponding SAED images (b & d)··· 152
Figure 10.3 XRPD patterns of NPs obtained from OA/DT
(surfactants-to-precursor ratio = 100) solvents at 250 ˚C after (a) 5 and (b) 15 hours heating (Peaks labeled with “T” are correspond to tetragonal phase CuInSe2)··· 153
Figure 10.4 XRPD patterns of CuInSe2 NP synthesized at 230 ˚C with
molar ratio of 1:50:50 (precursor:TOPO:DT) after 2 hours of
heating··· 154
Figure 10.5 (a) Low resolution and (b) & (c) high resolution TEM images
and (d) SAED spectrum of CuInSe2 NPs obtained from
TOPO/DT solvents at 230 ˚C··· 155
Figure 10.6 XRPD patterns of CuInSe2 NPs synthesized at various
temperature Calculated sizes for CuInSe2 NPs based on their XRPD spectra are 8.0 nm (125 °C), 25.5 nm (180 °C), 12.5 nm
(200 °C) and 14.5 (230 °C)··· 156
Trang 26List of Tables and Schemes
Chapter 1
Table 1.1 Summary on thermal decomposed product of metal
thiocarboxylates and selenocarboxylates··· 15
Chapter 2
Table 2.1 Metal and 77Se NMR Spectral Parameters of [M(SeC{O}Tol)n
(SC{O}Ph)3-n]– in CH2Cl2··· 24
Table 2.2 Table showing the m/z of the products of ligand exchange,
[M(SeC{O}Tol)n(SC{O}Ph)3-n]– , in ESI-MS spectra of mixtures of [M(SC{O}Ph)3]– and [M(SeC{O}Tol)3]– (M = Zn –
Hg) in acetone··· 29
Table 2.3 Crystal data and experimental details of 1 – 3··· 29 Table 2.4 Selected Bond Distances (Å), Angle (°) and Deviations (Å)
from the Se3 and O3 Planes in the Anions of 1 – 3··· 31
Table 2.5 Bond Valences parameters of Zn – Hg in 1 – 3··· 33 Chapter 3
Table 3.1 Crystallographic Data and Refinement Parameter for 4, 6, 8, 9
and 10··· 42
Table 3.2 Selected bond lengths (Å) and angles (°) of 4··· 43
Table 3.3 Selected bond distances (Å) and angles (°) in 6 and 8··· 46
Table 3.4 Selected bond lengths (Å) and angles (°) of 9 and 10··· 48
Table 3.5 Pyrolysis and TGA results for 4 – 10··· 50
Chapter 4
Table 4.1 Table summarized the crystallographic data of 11 and 11a··· 63
Table 4.2 Selected bond lengths (Å) and angles (°) of 11··· 65
Table 4.3 Selected bond lengths (Å) and angles (°) of 11a··· 66
Table 4.4 Pyrolysis and TGA results for 11··· 67
Chapter 6
Table 6.1 Summary of the size and morphology of Ag2Se NCs obtained
under different reaction conditions··· 100
Chapter 9
Table 9.1 Table comparing the calculated d-spacings with the
experimental d-spacings··· 142
Trang 27XXIV
Chapter 1
Scheme 1.1 Reactivity of copper thiocarboxylates with triphenylphosphine· 4
Scheme 1.2 Solvent dependent interconversion of deformational and
conformational isomers of I-6 (R = Me) and I-7 (R = Ph) ··· 5
Scheme 1.3 Views of the ‘claw-like’ [M(SC{O}Ph)3]– ion and its complex
with alkali-metal ions··· 9
Scheme 1.4 Diagram illustrating the deposition of β-In2S3 and AgIn5S8 thin
films from I-14a & I-14b by AACVD··· 16
Scheme 1.5 Diagram illustrating the thin film deposition of CuInS2 from
(Et3NH)[In(SC{O}Ph)4]·H2O··· 17
Scheme 1.6 Water soluble luminescent CdS NCs from [(2,
2’-bipy)Cd(SC{O}Ph)2] ··· 20
Chapter 5
Scheme 5.1 Applications of QDs as multimodal contrast agents in
bioimaging··· 82
Trang 28Commun. 2005, 3820 (Hot Article)
3 Ng, M T.; Boothroyd, C B.; Vittal, J J One-pot Synthesis of New Phase AgInSe2 Nanorods J Am Chem Soc 2006, 128, 1178
4 Vittal, J J and Ng, M T Chemistry of Metal Thio- and Selenocarboxylates: Precursors for Metal Sulfide/Selenide Materials, Thin Films and Nanocrystals
Acc Chem Res. 2006, 39, 869 (Cover page)
5 Ng, M T and Vittal, J J New Hetero-bimetallic and Polymeric Selenocarboxylates Derived from [M(SeC{O}Ph)4]- (M = Ga and In) as
Molecular Precursors for Ternary Selenides Inorg Chem 2006, 45, 10147
6 Hendry, I E.; Wei, J.; Ng, M T.; Vittal, J J AgInSe2 nanorods: A
semiconducting material for saturable absorber Appl Phys Lett 2007, 90,
033106
Trang 30Chapter 1 Introduction to Monochalcogeno Carboxylate
Chapter 1 Introduction to the Chemistry of Monochalcogenocarboxylate
1.1 General Introduction
Monochalcogenocarboxylates (RC{O}E– anion, E = S, Se or Te) are asymmetrical chalcogenide ligands in which one of the oxygen atoms of the carboxylate anion is replaced by a chalcogen atom.1, 2 and normally exist either in the form of acid or alkali-metal salt Historically, the synthesis of thiocarboxylic acid was first reported by Kekulé in 1854.3 Since then, the synthesis and properties of numerous chalcogenocarboxylic acids have been published in the literature.4, 5Recently, a comprehensive review by Kato highlighted the developments in the chemistry of monochalcogenocarboxylates over the last century.3 In recent years, our laboratory has been studying the chemistry of metal thiocarboxylates extensively and remarkable chemistry knowledge for metal thiocarboxylates has been established In contrast, until very recently, little has been known about the chemistry of selenocarboxylic acid and/or the corresponding alkali-metal salts, probably due to their instability and the handling difficulties associated with them.6, 7
Over the years, metal sulfides and metal selenides that include powders, thin films and nanoclusters have generated a great deal of scientific and technological interest for a number of different reasons.8-10 The semiconducting nature of these materials has led to fundamental interest in the synthesis of molecular clusters and NCs to investigate size-dependent structure-property relationships A wide variety of synthetic methods have been developed to synthesize these materials Of these an attractive method is the single molecular source approach where the organic fragments present in the coordination metal complexes of chalcogenide- or chalcogen-
Trang 31Chapter 1 Introduction to Monochalcogeno Carboxylate
2
containing ligands are removed and metal chalcogenides are reassembled relatively at low temperature under mild conditions.11, 12 In single-source approach, one can has the control over the stochiometry of the metal chalcogenides, as the atomic ratio in the precursor molecule can be well defined The absence of hazardous gases likes, H2S and H2Se in the single-source approach also illustrated the advantage of this method
However, single-source approach is somewhat different from chimie douce approach
developed by Rouxel.13 In chimie douce approach the products usually retain the
memory of the precursor geometry Meanwhile in single-source approach, the geometry of the product is determined by the crystal structure of the product itself In
chimie douce approach, two important approaches would be that of redox soft chemistry involving intercalation and deintercalation, and that of acido-basic processes which lead to a structural recombination of pre-existing blocks The preparation of new materials often proceeds in the former via an elimination of guest species assembled in layers in a lamellar host (or in rows in a tunnel structure) which reduces the initial dimensionality (or creates empty channels); in the latter, a typical reaction would yield a three-dimensional edifice assembled from two-dimensional precursor units
Hampden-smith et al have shown that the metal thiocarboxylates can be used
as single moleculars precursors for metal sulfide since they undergo thiocarboxylic anhydride elimination reaction, as shown in Equation (1) & (2) to form “MS.14
2M(SOCR)2L2 [(RCOS)M - S - M(SOCR)]L2 + S(COR)2
[(RCOS)M - S - M(SOCR)]L2 2MS + (RCO)2S + 2L
(1)(2)
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Using this strategy they synthesized various group 12 metal sulfide NPs using the corresponding metal thiocarboxylates precursors, M(SC{O}R)2L2 ( M = Zn, Cd, R
= alkyl, aryl; L = Lewis base).14 They also demonstrated that various metal sulfide thin films can be deposited using metal thiocarboxylates precursors using AACVD technique.15-18 Recently Chin et al discovered that the silver thiocarboxylate can take
a different decomposition pathway to form Ag2S in the presence of an amine in solution They claimed Ag2S, RN{H}C{O}Ph and H2S gas were produced during the decomposition process.19 In this chapter, the interesting structural chemistry of metal thio- and selenocarboxylates developed in our laboratory and how some of these compounds have been used as precursors for metal sulfides and selenides will be reviewed
1.2 Group 11 Metal Thio- and Selenocarboxylates
1.2.1 Copper Thio- and Selenocarboxylates
Reactions of triphenylphosphine with copper(I) thioacetate or thiobenzoate led
to the formation of five different products depending on the stoichiometry of the reactants as illustrated in Scheme 1.1.20 In these neutral compounds, remarkable structural diversity with variable bonding modes including µ3-S and µ 3-S2,O, were exhibited20 along with a µ2 bridging mode of sulfur atom which is ubiquitous in the thiolate chemistry.21, 22 In [Cu4(SC{O}Me)4(Ph3P)4] (I-1), the Cu and S atoms are alternatively bonded to form an eight-membered Cu4S4 ring similar to the copper(I) thiolate tetramer, [(SPh)4Cu4(Ph3P)4]23 and two sulfur atoms further bridge two copper atoms to form a highly distorted ‘stepladder’ arrangement with a Cu···Cu separation of 2.748(1) Å Under similar experimental conditions thiobenzoate anion yielded a highly distorted cubane-like neutral cluster [Cu4(SC{O}Ph)4(Ph3P)3] (I-2)
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This reflects the influence of R group of the thiocarboxylate ion on the solid-state structure When the stoichiometric ratio of CuCl : NaSC{O}R : Ph3P is 1:1:2,
thioacetate furnished a dimer, I-3 while thiobenzoate ligand yielded a monomer, I-4
Many phosphine adducts of neutral copper halides and copper mono- and dithiocarbamate compounds are known to associate and/or dissociate in solution 31P NMR of these triphenylphosphine copper thiocarboxylates in CDCl3 and CD2Cl2shows fast exchange between the phosphines and copper ions at all the temperature studied
The selenocarboxylate chemistry is not necessarily similar to that of thiocarboxylate, and this indeed is found to be the case for Cu(I) The unsymmetrical triphenylphosphine dimers, [(Ph3P)3Cu2(SeC{O}R)2] were isolated irrespective of the experimental conditions employed.24 31P NMR studies show the dissociation of these copper selenocarboxylates in solution
Scheme 1.1 Reactivity of copper thiocarboxylates with triphenylphosphine
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1.2.2 Silver Thiocarboxylates
The chemistry of the neutral triphenylphosphine adducts of silver thiocarboxylates is quite different from that of their copper analogues Only monomeric ([Ag(SC{O}R)(Ph3P)2] (R = Me, Ph)) and tetrameric [(AgPh3P)4(µ-SC{O}R)4] (R = Me (I-6), Ph (I-7))] have been isolated by varying the metal to ligand ratio and experimental conditions.25 The solid-state structures of the tetramers depend on the solvents used for preparation or recrystallization as shown in Scheme 1.2 When crystallized from CH2Cl2 compounds I-6 and I-7 have eight-membered
Ag4S4 rings in the solid-state In toluene, I-6 forms another conformational isomer with an Ag···Ag separation of 3.146(1) Å, whereas I-7 gave a ladder structure similar
to I-1 The ability of sulfur atom in PhC{O}S– ligand to form µ2-S and µ3-S bridging, and the nature of Ag(I) to display variable coordination geometries aided formation of two deformational isomers for silver(I) thiobenzoates The size and coordinating ability of the solvents play a role in these systems during and/or nucleation The solvent CH2Cl2 being smaller in size with more coordinating ability, keeps the atoms
in the Ag4S4 ring away from each other preventing formation of any bonds across the eight-membered rings, whereas the atoms in the Ag4S4 tetramer are pushed across the ring to interact with each other due to the poor coordinating ability and relatively larger size of toluene The solvent dependent structures are depicted in Scheme 1.2
Scheme 1.2 Solvent dependent interconversion of deformational and conformational
isomers of I-6 (R = Me) and I-7 (R = Ph)
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1.2.3 Dppm Compounds of Copper and Silver Thiocarboxylates
While exploring the versatile bonding ability of the thiocarboxylate ligand, the triphenylphosphine was replaced by dppm, and a range of tri-nuclear compounds, [M3(µ-dppm)3(SC{O}R)2][X] (For M = Cu or Ag, R = Me or Ph, X = PF6, ClO4, NO3 or PF6) have been isolated.26 In the solid-state structures the thiocarboxylate anions have µ3-S, µ3-S2,O and µ2-S bonding modes, thereby stabilizing the trinuclear core and C–H···O hydrogen bonding is present between one of the methylene hydrogen atoms and the carbonyl oxygen of the thiocarboxylate ligand as shown in Figure 1.1 The 31P NMR studies show that the trinuclear anions retain their solid-state structures in solution unlike the Ph3P compounds It is interesting to note that the ability of the capping ligand to bind to the three metals was preciously thought to be responsible for the stability of the [M3(µ-dppm)3] core since in the absence of a suitable triply briding ligand only dimeric compounds resulted However, our studies show that two µ2-S bonds of thiocarnoxylates are sufficient to stabilize the Ag3(dppm)3 core
Figure 1.1 Ball and stick diagram of
[Cu3(µ-dppm)3(µ3-SC{O}Ph-S)(µ3-SC{O}Ph-S ,O)]2+ and [Ag3(dppm)3(µ-SC{O}Ph-S)2]2+ cations
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1.2.4 Homoleptic Copper and Silver Thiocarboxylates
In the absence of Ph3P homoleptic Cu(I) and Ag(I) thiocarboxylates, (Ph4P)[M(SC{O}Me)2] (M = Cu or Ag) and [(Et3NH)2[Ag2(SC{O}Ph)4] have been isolated.27 Their anions were found to associate in the solid-state, forming an ion-pair dimer when Et3NH+ cation was used, as shown in Figure 1.2 Such ion-pairs exist in (Et3NH)[Cd(SC{O}Ph)3] also.28 It implies that the metal-sulfur bonds can be manipulated in the solid-state by the use of appropriate counter ions Further these compounds thermally decompose to the corresponding metal sulfides in the solid-state and the inception temperature of the thermal decomposition could be manipulated by changing the counter ion
Figure 1.2 The structures of (Ph4P)[M(SC{O}Me)2] and [(Et3NH)2Ag2(SC{O}Ph)4]
1.3 Group 12 Metal Thio- and Selenocarboxylates
Monochalcogenocarboxylate anions, RC{O}E– (E = S or Se), are an interesting class of ligands due to the presence of both soft and hard bonding sites and can exhibit diverse bonding modes as discussed in the previous section In the homoleptic transition- metal complex anions [M(SC{O}Ph)3]– (M = Mn, Co, Ni, Pb), the thiobenzoate ligands are bonded to the central metal atom in a bidentate fashion resulted a distorted octahedral geometry at the metal center as illustrated in Figure
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1.3.29, 30 On the other hand, trigonal pyramidal geometry with a SnS3 core has been observed in [Sn(SC{O}Ph)3]– ion.31 In contrast, Cd(II) and Hg(II) atoms in [A{M(SC{O}Ph)3}2]– anions (A = Na or K, M = Cd or Hg) have trigonal planar geometry with respect to the sulphur atoms.32, 33 In these trinuclear anions, the planarity of the MS3 core has been attributed to the presence of the alkali-metal ions, which bind to the oxygen atoms of the carbonyl groups as illustrated in Scheme 1.3, thereby reducing their bonding to Cd(II) and Hg(II) Multi-NMR studies shows concentration-dependent dissociation of the alkali-metal ions in solution
A similar trigonal planar MS3 geometry, supported by one or more intramolecular M···O interactions, was observed in [M(SC{O}Ph)3]– (M = Group 12 metal ions) even when the alkali-metal ion was absent.34, 35 It may be noted that the trigonal planar MS3 geometry is generally found only in complexes with hindered thiolate ligands for group 12 metal ions.36, 37
Figure 1.3 Ball and stick diagram of [Ni(SC{O}Ph)3]– anion unit
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Scheme 1.3 Views of the ‘claw-like’ [M(SC{O}Ph)3]– ion and its complex with alkali-metal ions
The occurrence of different geometries for a compound in the same unit cell is termed as polytopal isomerism Polymorphism is a general observed phenomenon in various pyridine adducts of nickel thioacetate compounds.38 For the first time, Vittal and his co-workers have reported the compound (Ph4P)[Cd(SC{O}Ph)3] exhibits polymorphism and crystallizes in monoclinic and rhombohedral crystal systems as shown in Figure 1.4 Of these the rhombohedral modification has a unique structure
containing both planar and pyramidal CdS3 cores.34
Figure 1.4 Views of the three crystallographically different anions in [Cd(SC{O}Ph)3]–, showing the numbering scheme used: (a) anion A; (b) anion B; (c) anion C Atoms are shown as 50% probability thermal ellipsoids Hydrogen atoms have been omitted for clarity
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The structure of the thioacetate complexes are completely different in contrast
to thiobenzoates.39 For instance, in [Zn(SC{O}Me)3(H2O)]– anion the hydrogen atoms
of the aqua ligand are hydrogen bonded to adjacent carbonyl oxygen atoms, gives rise
to approximate mirror symmetry in the tetrahedral Zn(II) complex as shown in Figure 1.5 Incidentally this anion represents the only synthetic structural mimic for the unusual active Zn(II) site [(cys)3Zn(OH2)] (ALAD).40 On the other hand, CdS3 core adapted a pyramidal geometry in the [Cd(SC{O}Me)3]– anion rather than a trigonal planar geometry observed in the corresponding thiobenzoate compounds Further, these results indicate that it is possible to isolate [M(SC{O}Me)4]2– anionic compounds (M = Zn, Cd & Hg), unlike those with PhC{O}S– ligand Structural studies of compounds containing MS4 tetrahedral moieties are interesting due to their relevance to bioinorganic chemistry.41, 42 In addition, mixed ligand complexes with chloro ligands can be prepared from [M(SC{O}Me)3]– with Ph4PCl Attempts to prepare [Cd(SC{O}Me)2Cl2]2– resulted in the formation of (Ph4P)2[Cd2(µ-Cl)2(SC{O}Me)4].43 In the salt of [Hg2Cl4(SC{O}Ph)2]2– the neutral Hg(SC{O}Ph)2 is weakly bridged by two chlorine atoms of [HgCl4]2–.44 On the other hand, in [Hg2Cl2(SC{O}Ph)4]2– two Hg(SC{O}Ph)2 moieties are bridged by two chloride ions.45
Figure 1.5 Ball & stick diagram of [Zn(SC{O}Me)3(H2O)]– as synthetic mimics of ALAD
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1.3.1 Neutral Group 12 Metal Thio- and Selenocarboxylates Containing
N-donor Ligands
Reaction between M(SC{O}R)2 with Bpy in 1:1 ratio gives four new 1D polymers, [{M(SC{O}R)2(µ-Bpy)}n] (R = Me, Ph; M = Zn, Cd).46 Polymer [Cd2(SC{O}Ph)4(µ-Bpy)]n, obtained from Cd(SC{O}Ph)2 and Bpy in the ratio 2:1 has
a unique structure in which two Cd(II) are bridged by S atoms of the two PhC{O}S–ligands and each oxygen atom of the bridging ligand is bonded to a Cd(II) atom so that the two PhC{O}S– anions have S2 ,O bonding mode as shown in Figure 1.6 The bridging nature of the thiobenzoate anion observed in this coordination polymer is hitherto unknown for Group 12 metal compounds
The coordination geometry at the metal centers of the neutral [(2, bipy)Cd(SC{O}Ph)2]47 and [(2, 2’-bipy)M(SeC{O}R)2] (M = Zn, Cd; R = Ph, CH3-p-C6H5, Cl-p-C6H5, NO3-C6H5)48 chelated by 2, 2’-bipy is similar to [M(SC{O}R)2(Lut)2] (M = Cd, Zn; R = CH3, C(CH3)3; Lut = 3, 5-dimethylpyridine)
2’-reported by Hampden-Smith et al.14
Figure 1.6 Repeating unit of the 1D polymer [Cd2(SC{O}Ph)4(µ-Bpy)]n