Bis(l-methyIimidazolyl)diselenide and l-methylimidazole-2-selenolate complexes of zinc, cadmium, and mercury: Synthesis, characterization, and their conversion to metal selenide quantum dots

Article abstract of DOI:10.1246/bcsj.81.489

Treatment of a methanolic solution of metal acetate with bis(l-methylimidazolyl)diselenide, [(MelmSe)₂], yields complexes of composition [M(OAc)₂{(MeImSe)₂}] (M = Zn, Cd, or Hg) whereas reactions of [MX₂(M₂NCH₂CH ₂-NMe2)] (X = CI or OAc) with sodium 1 -methylimidazole-2-selenolate gave selenolate complexes of the general formula [M(MeImSe)₂] (M = Zn or Cd). The complexes were characterized by elemental analysis, IR, UV-vis, NMR (¹H, ¹³C, and ⁷⁷Se) data. The crystal structure of [Cd(OAc)₂{(MeImSe)2}] was established by single-crystal X-ray diffraction. The cadmium atom adopts a distorted octahedral configuration defined by asymmetrically chelated acetate groups and chelating diselenide ligand. Thermal behavior of adducts was studied by thermogravimetric analysis. Pyrolysis in hexadecylamine/tri-n-octylphosphine oxide gave MSe quantum dots, which were characterized by UV-vis, photolumi-nescence, XRD, EDAX, SAED, and TEM.

Full text of DOI:10.1246/bcsj.81.489

Ó 2008 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 81, No. 4, 489–494 (2008)
489
Bis(1-methylimidazolyl)diselenide and 1-Methylimidazole-2-selenolate
Complexes of Zinc, Cadmium, and Mercury: Synthesis, Characteriza-
tion, and Their Conversion to Metal Selenide Quantum Dots
ꢀ1
Gotluru Kedarnath,1 Liladhar Baburao Kumbhare,1 Vimal Kumar Jain, Amey Wadawale,1
Gautam Kumar Dey,2 Chidamabaranathan Thinaharan,3 Shivalingegowda Naveen,4
Mandayam Anandalwar Sridhar,4 and Javaregowda Shashidhara Prasad4
1Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India
2Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400085, India
3Technical Physics & Prototype Engineering Division, Bhabha Atomic Research Centre, Mumbai 400085, India
4Department of Studies in Physics, Manasagangotri, University of Mysore, Mysore 570006, India
Received November 1, 2007; E-mail: jainvk@barc.gov.in
Treatment of a methanolic solution of metal acetate with bis(1-methylimidazolyl)diselenide, [(MeImSe)2], yields
complexes of composition [M(OAc)2{(MeImSe)2}] (M = Zn, Cd, or Hg) whereas reactions of [MX2(Me2NCH2CH2-
NMe2)] (X = Cl or OAc) with sodium 1-methylimidazole-2-selenolate gave selenolate complexes of the general for-
mula [M(MeImSe)2] (M = Zn or Cd). The complexes were characterized by elemental analysis, IR, UV–vis, NMR (1H,
13C, and 77Se) data. The crystal structure of [Cd(OAc)2{(MeImSe)2}] was established by single-crystal X-ray diffrac-
tion. The cadmium atom adopts a distorted octahedral configuration defined by asymmetrically chelated acetate groups
and chelating diselenide ligand. Thermal behavior of adducts was studied by thermogravimetric analysis. Pyrolysis in
hexadecylamine/tri-n-octylphosphine oxide gave MSe quantum dots, which were characterized by UV–vis, photolumi-
nescence, XRD, EDAX, SAED, and TEM.
The compound semiconductor nanoparticles of II–VI mate-
rials have received considerable attention in the past 15 years
or so. This is primarily due to their shape and size-dependent
optoelectronic properties which can be and have been used for
a variety of optoelectronic and bioengineering applications.1–5
To meet these objectives, a convenient synthesis of nanoparti-
cles with desirable shape and composition is of paramount im-
portance. A wide variety of synthetic routes for amine/thiols/
phosphates capped and uncapped II–VI nanomaterials have
been developed.6–22 These include reactions of group II source
(e.g., metal oxides, metal alkyls (Et2Zn and R2Cd), or metalo-
organic derivatives such as Cd(OAc)2) with a group VI carrier
(e.g., organophosphine chalcogenide (R3PE) or bis(trimethyl-
silyl)chalcogenide) in an appropriate coordinating solvent,6–8
controlled precipitation method involving treatment of a metal
salt (MO and M(OAc)2) with ammonium/sodium sulfide,
H2S;9,10 reduction of sulfur/selenium with KBH4 and the cor-
responding metal salt at room temperature,11,12 ultrasonic syn-
thesis from Zn(OAc)2 and selenourea,13 biological methods
using yeasts,14 and pyrolysis of single source precursors.19–21
The later technique has been quite successful and straight
forward in terms of synthesis of both the precursors as well as
high quality nanoparticles on a gram scale. The chemistry of
numerous homo- and heteroleptic single source precursors,
such as [M(SeCOAr)2(tmen)], [M(SeCH2CH2CH2NMe2)2],
[M(S2CAr)2(tmen)] (M = Zn, Cd, and Hg; tmen = Me2-
NCH2CH2NMe2), etc. derived from simple and internally
functionalized chalcogenolate ligands has been explored.19–24
Cadmium complexes with simple chalcogenolate ligands tend
to polymerize25,26 whereas mercury complexes quite often lead
to the formation of dichalcogenide and mercury metal.27 As in
other preparative routes where the metal and chalcogen sour-
ces are independently brought together during the course of
reaction, it was of interest to design single source precursor
molecules without M–E linkages and evaluate their suitability
for the preparation ME nanoparticles.
Experimental
Materials and Methods. Zinc, cadmium, and mercury ace-
tates, N,N,N0,N0-tetramethylethylenediamine (tmen), hexadecyl-
amine (HDA), and tri-n-octylphosphine oxide (TOPO) were ob-
tained from commercial sources. The compounds [M(OAc)2-
(tmen)], [MCl2(tmen)] (M = Zn and Cd),19 and bis(1-methylimi-
dazolyl)diselenide, [(MeImSe)2], [mp 144 ꢁC, UV–vis (CH3OH)
ꢀ
max: 216, 295 nm, 1H NMR (CDCl3) ꢁ 3.58 (s, Me), 6.99 and 7.09
(each s, CH=CH); 13C{1H} NMR (CDCl3) ꢁ 34.8 (s, Me), 124.0,
129.9 (s), and 133.6 (each s, ring carbons); 77Se{1H} NMR (in
CDCl3) ꢁ 380]28 were prepared according to the literature method.
1H, 13C{1H}, and 77Se{1H} NMR spectra were recorded on a
Bruker DPX-300 NMR spectrometer operating at 300, 75.47,
and 57.23 MHz, respectively. Chemical shifts are relative to inter-
1
nal chloroform peaks at ꢁ 7.26 for H and ꢁ 77.0 for 13C{1H} or
methanol peaks (1H ꢁ 4.78 (OH); 13C ꢁ 49.0) and external Ph2Se2
(ꢁ 463 relative to Me2Se) in CDCl3 for 77Se{1H}. IR spectra were
recorded as Nujol mulls between CsI plates on a Bomem MB-102
FT-IR spectrometer. Electronic spectra were recorded in methanol
on a Chemito Spectrascan UV 2600 double beam UV–vis spectro-
Published on the web April 10, 2008; doi:10.1246/bcsj.81.489

490 Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
Bis(1-methylimidazolyl)diselenide
77Se{1H} NMR (CD3OD) ꢁ 428.
Table 1. Crystallographic and Structural Determination
Data for [Cd(OAc)2{(MeImSe)}2] 2H2O
Preparation of [Cd(OAc)2{(MeImSe)2}] (1b): Prepared sim-
ilar to 1a and recrystallized from dichloromethane as orange nee-
dle-shaped crystals in 94%: mp 169 ꢁC; Anal. Calcd for C12H16-
CdN4O4Se2: C, 26.2; H, 2.9; N, 10.2%. Found: C, 25.2; H, 2.9;
N, 9.8%. UV–vis ꢀmax (CH3OH): 219, 292 nm; IR: 1560 cmꢂ1 (ꢄ
C=O); 1H NMR (CD3OD) ꢁ 1.99 (s, OAc), 3.81 (s, Me), 7.34 and
7.40 (each d, J ¼ 1:3 Hz); 13C{1H} NMR (CD3OD) ꢁ 20.5 (s,
OAc), 35.2 (s, Me), 125.2, 131.1, and 135.7 (each s, ring carbons),
180.2 (s, C=O); 77Se{1H} NMR (CD3OD) ꢁ 425.
CCDC-636598 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge, CB2
1EZ, UK (Fax: +44 1223 336033; E-mail: deposit@ccdc.cam.
ac.uk).
Preparation of [Hg(OAc)2{(MeImSe)2}] (1c): Prepared sim-
ilarly to the zinc adduct and recrystallized in dichloromethane–
hexane mixture to obtain light green product in 71% (260 mg);
mp 125 ꢁC; Anal. Calcd for C12H16HgN4O4Se2: C, 22.6; H, 2.5;
N, 8.8%. Found: C, 21.6; H, 2.5; N, 8.6%. IR: 1661, 1576 cmꢂ1
(C=O); UV–vis ꢀmax (CH3OH): 224 nm; 1H NMR (CD3OD) ꢁ
1.95 (s, OAc), 3.64 (s, Me), 6.61, 7.00 (s); 13C{1H} NMR (CD3-
OD) ꢁ 20.4 (s, OAc), 35.7 (s, Me), 123.8, 126.6, and 137.2 (each
s, ring carbons), 175.1 (s, C=O).
ꢃ
Chemical formula
Formula weight
Crystal size/mm3
Temperature/K
C12H20CdN4O6Se2
586.64
0:30 ꢄ 0:25 ꢄ 0:20
298(2)
0.71073
Orthorhombic/Pbca
30.464(10)
14.870(7)
˚
Wavelength/A
Crystal system/space group
˚
Unit cell dimensions a/A
˚
b/A
˚
c/A
8.420(6)
3814(3)
3
˚
Volume/A
Z
8
2.043
4.997
2272
Dcalcd/g cmꢂ3
ꢅ/mmꢂ1
Fð000Þ
Limiting indices
0 ꢅ h ꢅ 39; ꢂ10 ꢅ k ꢅ 19;
ꢂ6 ꢅ l ꢅ 10
No. of reflections collected/unique 6335/4368
No. of data/restraints/parameters
4368/7/245
Final R1, !R2 indices [I > 2ꢆðIÞ] 0.0363, 0.0692
R1, !R2 (all data)
0.1077, 0.0851
1.000
Goodness of fit on F2
3
˚
Largest diff. peak and hole (e/A ) 0.5900 and ꢂ0:8600
Preparation of [Zn(MeImSe)2]n (2a): To a freshly prepared
NaMeImSe (from [(MeImSe)2] (236 mg, 0.74 mmol) and NaBH4
(62 mg, 1.63 mmol) in methanol) was added a toluene suspension
of [ZnCl2(tmen)] (182 mg, 0.72 mmol). The whole was stirred at
room temperature for 3 h and the solvents were evaporated under
vacuum. The residue was extracted with toluene and filtered. The
filtrate was concentrated under reduced pressure to yield a cream
solid (200 mg, 72%), mp >250 ꢁC; Anal. Calcd for C8H10N4Se2-
Zn: C, 24.9; H, 2.6; N, 14.5%. Found: C, 25.9; H, 2.4; N, 14.0%.
photometer. Fluorescence spectra were recorded using a Hitachi
F-4500 FL spectrofluorometer.
Thermogravimetric analyses (TGA) were performed on a
Nitzsch STA PC-Luxx TG-DTA instrument. TG curves were re-
corded at a heating rate of 5 ꢁC minꢂ1 under a flowing nitrogen at-
mosphere. X-ray powder diffraction patterns were obtained on a
Philips PW-1820 powder diffractometer using Cu Kꢂ radiation.
EDAX measurements were carried out on a Tescan Vega
2300T/40 instrument. A JEOL-2000FX transmission electron mi-
croscope operating at accelerating voltages up to 200 kV was used
for TEM studies. The samples for TEM and SAED were prepared
by placing a drop of sample dispersed in acetone on a carbon-coat-
ed copper grid.
Intensity data for [Cd(OAc)2{(MeImSe)2}], which crystallizes
as a hydrate, were measured on a Rigaku AFC7S diffractometer
fitted with Mo Kꢂ radiation so that ꢃmax ¼ 27:5ꢁ. The structure
was solved by direct methods29 and refinement was on F2 29 using
data that had been corrected for absorption effects with an empir-
ical procedure,30 with non-hydrogen atoms modeled with aniso-
tropic displacement parameters, with hydrogen atoms in their cal-
culated positions. Molecular structure was drawn using ORTEP.31
Crystallographic and structural determination data are listed in
Table 1.
1
UV–vis ꢀmax (CH3OH): 231 nm; H NMR (CDCl3) ꢁ 3.52, 3.56,
3.59, 3.64, 3.68, and 3.75 (Me), 6.48–6.82 (m), 7.36 (s) (ring pro-
tons); 13C{1H} NMR (CDCl3) ꢁ 35.8 (s, Me), 120.4, 120.8, 126.7,
127.1, 145.3 (s).
Preparation of [Cd(MeImSe)2]n (2b): To a freshly prepared
methanolic solution of NaMeImSe (from (MeImSe)2 (150 mg,
0.47 mmol) and NaBH4 (39 mg, 1.03 mmol)) was added a meth-
anolic solution of [Cd(OAc)2(tmen)] (159 mg, 0.46 mmol) and the
whole was stirred for 3 h at room temperature. The solvent was
evaporated under vacuum and the white residue was washed with
several portions of distilled water followed by acetone and again
dried in vacuo (131 mg, 66%), mp >350 ꢁC; Anal. Calcd for C8-
H10CdN4Se2: C, 22.2; H, 2.3; N, 12.9%. Found: C, 22.4; H, 2.1;
N, 12.7%. Product is insoluble in all common organic solvents,
and hence could not be characterized further.
Synthesis of Complexes.
{(MeImSe)2}] (1a):
[(MeImSe)2] (150 mg, 0.47 mmol), a solution of Zn(OAc)2 2H2O
Preparation of [Zn(OAc)2-
To a methanolic solution (10 cm3) of
Preparation of Metal Selenide Nanoparticles Using 1: To a
pre-heated (210 ꢁC) mixture of HDA (4 g) and TOPO (800 mg) in
a three-necked flask, a solution of [Zn(OAc)2{(MeImSe)2}] (150
mg, 0.3 mmol) in a mixture of CHCl3 (1.5 cm3)/CH3OH (1 cm3)
and TOPO (200 mg) was injected rapidly with vigorous stirring
under flowing argon. The temperature dropped to 170 ꢁC and
was raised to and maintained at 200 ꢁC for 30 min. The hot solu-
tion was cooled down rapidly to 70 ꢁC and methanol (20 cm3) was
added so as to get a cream flocculent precipitate of ZnSe which
was washed thoroughly with methanol, followed by centrifuging
and drying under vacuum. Similarly, red CdSe quantum dots were
prepared by injecting [Cd(OAc)2{(MeImSe)2}] at 190 ꢁC and sta-
bilizing at 178 ꢁC for 20 min. The mercury complex was pyrolysed
ꢃ
(101 mg, 0.47 mmol) in the same solvent (10 cm3) was added with
stirring which continued for 2 h. The solvent was evaporated un-
der vacuum and the yellow residue was recrystallized from meth-
anol–ethyl acetate as yellow needle-shaped crystalline solid (yield
180 mg, 78%): mp 170 ꢁC; Anal. Calcd for C12H16N4O4Se2Zn: C,
28.6; H, 3.2; N, 11.1%. Found: C, 27.5; H, 3.2; N, 10.6%. UV–vis
ꢀmax (CH3OH): 219, 284 nm; IR: 1620, 1581 cmꢂ1 (ꢄ C=O);
1H NMR (CD3OD) ꢁ 1.95 (s, OAc), 3.83 (s, Me-), 7.41 and 7.45
(each d, J ¼ 1:3 Hz); 13C{1H} NMR (CD3OD) ꢁ 21.6 (OAc), 35.2
(s, Me), 124.9, 130.7, and 136.4 (ring carbons), 179.0 (C=O);

G. Kedarnath et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
491
.
[M(OAc)2 nH2O] + (MeImSe)2
[M(OAc)2{(MeImSe)2}] + nH2O
(1)
[MX2(tmen)] + 2NaMeImSe
[M(MeImSe)2] + tmen + 2NaX
(2)
(M = Zn or Cd; X = Cl or OAc)
Scheme 1.
in an HDA (1 g) and toluene (5 cm3) mixture at 95 ꢁC for 20 min
and processed in a manner similar to ZnSe preparation.
Results and Discussion
Synthesis and Spectroscopy. Treatment of a methanolic
solution of metal acetate with bis(1-methylimidazolyl)disele-
nide afforded readily 1:1 addition complexes of composition
[M(OAc)2{(MeImSe)2}] (1) (M = Zn (1a), Cd (1b), or
Hg (1c)). Reaction of MX2(tmen) (X = Cl or OAc) with
NaMeImSe gave selenolate complexes of composition
[M(MeImSe)2] (2) (Scheme 1).
1
The H and 13C{1H} NMR spectra displayed expected res-
onances. The ring proton and carbon resonances appeared at
lower field for 1a and 1b from the corresponding signals for
the free ligand. The coordination of ring nitrogen (N-3) to the
metal atom can be inferred from the chemical shift of C-4
resonance. The signal appeared at lower field (135.7–137.2
ppm) than its position for the free ligand (133.6 ppm). The ace-
tate groups showed single absorptions in the 1H and 13C NMR
spectra suggesting their magnetic equivalence. The 77Se-
{1H} NMR spectra of 1a and 1c showed a singlet which was
deshielded by ꢆ45 ppm from its position in free ligand. The
nitrogen coordination to metal center may be inducting elec-
tron density from the selenium atom consequently resulting
Figure 1. Crystal structure of [Cd(OAc)2{(MeImSe)2}]
2H2O with atomic numbering scheme. The ellipsoids were
drawn at the 25% probability level.
ꢃ
ꢁ
˚
Table 2. Bond Lengths (A) and Angles ( ) for [Cd(OAc)2-
{(MeImSe)2}] 2H2O
ꢃ
Cd1–N1
Cd1–N3
Cd1–O1
Cd1–O2
Cd1–O3
Cd1–O4
Se1–C5
Se2–C9
Se2–Se1
2.267(4)
2.230(4)
2.289(4)
2.521(4)
2.435(4)
2.335(4)
1.904(5)
1.904(5)
2.336(1)
N1–C5
N2–C5
N3–C9
N4–C9
O1–C1
O2–C1
O3–C3
O4–C3
1.323(6)
1.358(6)
1.314(6)
1.352(6)
1.242(6)
1.255(6)
1.240(6)
1.265(6)
1
in deshielding.32 The H NMR spectrum of 2a showed a com-
plex pattern which may be due to magnetically different ligand
moieties in an associated structure.
X-ray Crystallography.
The molecular structure of
[Cd(OAc)2{(MeImSe)2}] (1b), which crystallized as a hydrate,
is shown in Figure 1 and the selected bond lengths and angles
are given in Table 2. The coordination environment around the
central cadmium atom is distorted octahedral defined by the
O4N2 core of two asymmetrically chelated acetate groups and
the chelating diselenide. The degree of asymmetry of the ace-
tate group in the Cd–O bond distances is slightly different
with the difference between the Cd–O bond distances being
N3–Cd1–N1
N3–Cd1–O1
N1–Cd1–O1
N3–Cd1–O4
N1–Cd1–O4
O1–Cd1–O4
N3–Cd1–O3
N1–Cd1–O3
O1–Cd1–O3
O4–Cd1–O3
N3–Cd1–O2
N1–Cd1–O2
O1–Cd1–O2
O4–Cd1–O2
107.57(15)
117.36(14)
91.23(14)
92.37(13)
105.02(14)
140.21(13)
145.42(14)
91.80(14)
89.76(13)
54.35(13)
87.54(14)
144.78(13)
53.90(13)
105.94(13)
O3–Cd1–O2
C5–Se1–Se2
C9–Se2–Se1
C5–N1–C6
C5–N1–Cd1
C6–N1–Cd1
C9–N3–Cd1
C10–N3–Cd1
O1–C1–O2
O3–C3–O4
N1–C5–Se1
N2–C5–Se1
N3–C9–Se2
N4–C9–Se2
92.75(13)
99.09(15)
99.81(15)
106.3(4)
134.3(3)
119.2(3)
129.2(3)
124.3(4)
122.6(5)
121.1(5)
127.2(4)
122.4(4)
125.7(4)
123.1(4)
˚
˚
0.10–0.23 A. The Cd–O distances (2.289 and 2.521 A) are
well in agreement with those reported in several cadmium
complexes.33–35
The diselenide ligand forms a seven-membered chelate ring
and binds the metal atom through imidazole nitrogen atoms.
There is a marked change in the geometry of the diselenide
˚
on coordination. The Se–Se distance (2.336(1) A) is reduced
28
˚
on complexation (free ligand 2.3568(15) A); whereas the
C–N distances in one of the imidazole rings are marginally
reduced while the same in other ring are little affected. The
N–C–Se angles (127.2(4) and 125.7(4)ꢁ) open up marginally
on coordination (free ligand 122.8(3)ꢁ).28 The Cd–N distances
The water molecules are associated with [Cd(OAc2)-
{(MeImSe)2}] through hydrogen bonding, a view showing
such contacts is given in Figure 2. The water molecule forms
˚
are considerably shorter than those reported (2.33–2.44 A) in
long O–H O hydrogen bonds with the oxygen atoms of two
acetate groups of neighboring molecules involving O5–H50
ꢃꢃꢃ
[Cd(SeCOPh)2(tmen)],19 [Cd(Sepy)2]n,11 and [Cd(S2COEt)2-
(phen)].36
ꢃꢃꢃ
00
˚
O2 (2.006 A) and O5–H5 O4 (2.087 A) contacts. Additional
˚
ꢃꢃꢃ

492 Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
Bis(1-methylimidazolyl)diselenide
a
60
30
20
40
50
2θ
/degree
b
Figure 2. Line diagram of [Cd(OAc)2{(MeImSe)2}]
2H2O showing intermolecular hydrogen bondings.
ꢃ
contacts of this water molecule involve bonds with two other
free water molecules in the lattice (O6–H60 O5 = 2.1912 A)
˚
ꢃꢃꢃ
and (O6–H600 O5 = 2.194 A).
˚
ꢃꢃꢃ
Thermal Studies. TG analyses of 1 were carried out to as-
sess their suitability as precursors for the preparation of metal
selenides. These complexes underwent two–three step decom-
position with onset temperatures of 165 (1a), 170 (1b), and
105 ꢁC (1c). The decomposition led to the formation of metal
selenides as inferred from % weight loss and confirmed from
the XRD patterns of the residues. The XRD patterns of the res-
60
10
40
50
20
30
2θ
/degree
Figure 3. a) XRD pattern of the TG residue of [Cd(OAc)2-
{(MeImSe)2}] (hexagonal CdSe), b) XRD pattern of CdSe
obtained from solvothermal decomposition of the precur-
sor in HDA/TOPO mixture (4:1) at 178 ꢁC for 20 min.
˚
idues from 1a (XRD d values (A) 3.27, 2.00, and 1.706) and 1c
˚
(XRD d values (A) 3.51, 2.15, and 1.83) have been interpreted
in terms of cubic MSe (M = Zn37 or Hg38) while the pattern of
the residue from 1b was in conformity with the hexagonal
determined from XRD and SAED patterns were in agreement
with each other.
˚
CdSe (XRD d values (A) 3.71, 3.49, 3.28, 2.54, 2.14, 1.97,
and 1.83) (Figure 3).39
Semiconducting materials show quantum confinement effect
when their particle size becomes equal or less than the Bohr’s
radius of that material. The quantum confinement effect is
manifested in the absorption spectra where absorption, de-
pending on the size of the particle, is blue shifted from the
bulk material value.43,44 The electronic spectra in methanol
(Figures 5 and 6) of metal selenide nanoparticles prepared
during this study displayed absorptions at 377 (ZnSe), 608
(CdSe), and 588 (HgSe) nm, which were blue shifted with re-
spect to the absorptions for bulk materials [480 (ZnSe), 713
(CdSe), and 12400 (HgSe) nm]. This suggests that the particles
are quantum confined. Absorption spectrum of HgSe particles
showed a broad absorption edge tailing into the infrared end of
the spectrum. Excitation profiles of these dots displayed max-
ima at 358 (1a), 603 (1b), and 582 (1c) nm whereas emission
profiles showed an emission maxima at 433 (ZnSe), 694
(CdSe), and 674 (HgSe) nm. The narrow fwhm (full width at
half maxima) of the emission peaks of ZnSe and CdSe nano-
particles shows their narrow size distribution.
Having assessed the suitability of 1 as precursors for metal
selenide synthesis, it was considered worth exploring their de-
composition in coordinating solvents. Thus, solvothermal de-
composition of 1a and 1c in HDA/TOPO mixture gave cubic
MSe (M = Zn or Hg) quantum dots while 1b yielded hex-
agonal CdSe nanoparticles (from XRD). The EDAX analyses
(ZnSe: Found: Zn, 46.4; Se, 53.7%. Calcd for ZnSe: Zn, 45.3;
Se, 54.7%. CdSe: Found: Cd, 61.1; Se, 38.9%. Calcd for CdSe:
Cd, 58.7; Se, 41.3%) was consistent with the MSe composi-
tion. The particle sizes estimated from Scherrer formula40,41
are 1.6 (ZnSe), 6.6 (CdSe), and 4.6 (HgSe) nm. The TEM im-
ages of these particles show that they are spherical in shape
(Figure 4) with an average diameter of 6 (ZnSe), 10 (CdSe),
and 8 (HgSe) nm. The mismatch between the sizes estimated
by XRD and obtained by TEM is because particle size does
not determine the line width directly in XRD.42 The particles
obtained were crystalline as determined by SAED. SAED pat-
terns of nanoparticles revealed that the formation of cubic MSe
(M = Zn and Hg) or hexagonal CdSe with diffraction rings
corresponding to lattice planes: (111), (220), (311), (400),
(331), and (422) (ZnSe); (100), (220), and (311) (HgSe); and
(100), (002), (101), (110), and (112) (CdSe). The phases
Conclusion
The Group 12 complexes, devoid of any M–Se linkage, of
an internally functionalized diselenide have been isolated as

G. Kedarnath et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
493
a
a
b
c
35 nm
b
400
500
600
800
700
Wavelength/nm
Figure 6. a) Absorption spectrum, b) excitation, and c)
emission profiles of CdSe quantum dots obtained by the
thermolysis of [Cd(OAc)2{(MeImSe)2}].
400 nm
ature (95 ꢁC) and reaction time of synthesis, the HgSe quantum
dots obtained were crystalline in nature.
We thank Drs. T. Mukherjee and D. Das for encouragement
of this work. The authors are grateful to Dr. S. K. Gupta and
his group for EDAX measurements and Dr. V. K. Manchanda
and his group for providing microanalysis of these complexes.
The authors would like to express their thanks to DST, Gov-
ernment of India for financial assistance under the project
SP/I2/FOO/93.
c
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