A phosphine complex of copper (I) bromide as single-source precursor for the aerosol-assisted chemical vapour deposition of phosphide

Article abstract of DOI:10.1016/j.ica.2009.01.031

A new homobimetallic complex [Cu₂(tpp)₂(dppm)Br₂] (1) of copper(I) bromide with triphenylphosphine (tpp) and bis-diphenylphosphinomethane (dppm) has been synthesized and charaterized by m.p., elemental analysis, FT-IR,

Full text of DOI:10.1016/j.ica.2009.01.031

Inorganica Chimica Acta 362 (2009) 3069–3072
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
A phosphine complex of copper (I) bromide as single-source precursor
for the aerosol-assisted chemical vapour deposition of phosphide
b
Muhammad Shahid a, Imtiaz-ud-Din a, Muhammad Mazhar a, , Kieran C. Molloy
*
a Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan
b Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A new homobimetallic complex [Cu2(tpp)2(dppm)Br2] (1) of copper(I) bromide with triphenylphosphine
(tpp) and bis-diphenylphosphinomethane (dppm) has been synthesized and charaterized by m.p., ele-
mental analysis, FT-IR, 1H NMR, mass spectrometry, thermal studies and single crystal X-ray analysis.
The solid-state molecular structure of 1, belonging to the monoclinic crystal system with space group
P21/n, describes it as a neutral dinuclear species in which two copper atoms are bridged together through
two bromides and a dppm ligand and each copper atom possesses a distorted tetrahedral geometry. Com-
plex 1 was studied as a single-source precursor for the fabrication of phase pure thin films of Cu3P by aer-
osol-assisted chemical vapour deposition. The films have been characterized by PXRD, SEM and ED-XRF
analyses and found to exhibit the particles size range 200ꢀ400 nm with high purity and surface
uniformity.
Received 23 October 2008
Accepted 30 January 2009
Available online 6 February 2009
Keywords:
Copper phosphide
X-ray structure
Thin film
CVD
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
single-source precursor for the growth of Cu3P thin films by AACVD
on glass and ceramic substrates.
Copper phosphides, existing in a variety of compositions includ-
ing Cu3P, CuP2 and Cu2P7 are potentially important materials in di-
verse technological applications. The phosphorus-rich phases are
thermally and chemically unstable whereas metal-rich and mono-
phosphides are usually hard refracting materials with relatively
high electrical conductivities [1]. The use of nanoparticles of Cu3P
in photonic crystals, filters, catalysts [2–5], bio-encapsulation
[6,7], drug delivery [8,9], potential negative electrodes [10], solder
and alloying additives [11,12] has been well established. The for-
mation of complexes of increased solution stability is a pre-requi-
site for the preparation of films by CVD method as revealed from
our earlier reports [13,14].
Although several routes to the synthesis of Cu3P and fabrication
of thin films by soft chemistry approaches have been reported,
there are only limited reports for the deposition of Cu3P by sin-
gle-source chemical vapour deposition methods [15]. Aitkin re-
cently reported synthesis of Cu3P from red phosphorus and a
variety of copper sources by solvothermal treatment [16].
Although transition metal phosphine derivatives are well explored
class of coordination complexes, their use as precursors to solid-
state phosphide materials is rather under exploited.
2. Experimental
2.1. General considerations
All manipulations were carried out under an atmosphere of dry
argon using Schlenk and glovebox techniques. All the chemicals
used were purchased from Aldrich and the solvents were rigor-
ously dried over sodium benzophenoate.
Elemental analysis was performed using a CHN Analyzer LECO
model CHNS-932. Melting point was determined in a capillary tube
using an electrothermal melting point apparatus, model MP.D
Mitamura Riken Kogyo (Japan) and is uncorrected. The IR spectrum
was recorded as KBr pellets on a Bio-Rad Excaliber, model FTS 300
MX spectrometer (USA), in the frequency range 4000–400 cmꢀ1. 1H
NMR spectrum was recorded on a Bruker 300 MHz NMR spectrom-
eter in CDCl3 at room temperature. Mass spectrum was recorded
on a MAT 312 Finnigan (Germany).
2.2. Synthesis of Cu2(tpp)2(dppm)Br2 (1)
To further explore the routes to grow copper phosphide thin
films, we report here the simple synthesis and characterization of
the dinuclear complex [Cu2(tpp)2(dppm)Br2] (1) and its use as a
The stoichiometric amounts of dppm 0.33 g (0.87 mmol) and
tpp 0.46 g (1.74 mmol) were added to the suspension of copper
(I) bromide (0.25 g; 1.74 mmol) in 20 ml THF under inert atmo-
sphere at 25 °C and stirred the mixture for 2 h. The reaction mix-
ture was filtered through cannula and the colourless filterate was
* Corresponding author. Tel.: +92 3005193859.
E-mail address: mazhar42pk@yahoo.com (M. Mazhar).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.01.031

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M. Shahid et al. / Inorganica Chimica Acta 362 (2009) 3069–3072
evaporated to dryness under reduced pressure. The solid, thus, ob-
tained was redissolved in a minimum quantity of THF and crystal-
lized in THF/CHCl3 mixture (3:1) to give white crystals, suitable for
X-ray crystallography, on slow evaporation at room temperature.
Yield: 85%. m.p. 270 °C. Anal. Calc. for Cu2C61H52Br2P4: C, 60.97;
H, 4.26. Found: C, 60.86; H, 4.92%. 1H NMR (300 MHz, CDCl3,
ppm): 3.77 (m, 2H, CH2-dppm) 6.97–7.48 (m, 50H, Ph-dppm and
tpp). FT-IR(KBr, cmꢀ1): 3049w, 1585w, 1570w, 1481m, 1431m,
1095m, 781m, 694s, 515m, 413m. EI-MS (positive mode): m/z
calc. (found) 384(383.7) [dppm]+, 356(354.7) [CuP(tpp)]+,
279.5(280.8) [Cu(PPh)2]+, 262(261.7) [tpp]+, 223.5(220.9) [CuBr2]+,
202.5(198.9) [CuP2Ph]+, 185(182.9) [PPh2]+, 125(120.9) [CuP2]+,
107.9 [PPh]+, 94.5(91) [CuP]+, 77 [C6H5]+, 51 [C4H3]+. TGA: 103–
251 °C (7.6 wt% loss), 251–383 °C (67.8 wt% loss), 383–530 °C (res-
idue 12.0%).
of the precursor (1) in 15 ml THF in a two neck round bottomed
flask. On one side, the flask was connected via tubing to a quartz
reactor loaded with 2.5 ꢁ 1 cm glass substrates inside a carbolite
tube furnace and a flow of argon gas was regulated using a platon
flow gauge on the other. The flask was set in an ultrasonic humid-
ifier equipped with a piezoelectric transducer which generated
droplets of the precursor solution which were then transferred
by the carrier gas into reactor chamber. Glass substrates were
washed in concentrated nitric acid, subsequently washed with
deionized water several times and then oven dried. Deposition
was carried out at 450 °C with a flow rate of 130 ml/min on glass
substrates for 2 h.
Powder X-ray diffraction (PXRD) studies of films were carried
out by means of a Bruker AXS D8 diffractometer using monochro-
matic Cu Ka radiation. The morphology of films was determined by
a FEG-SEM Philips XL30 scanning electron microscope. Samples
were carbon coated before observation and Horiba XRF Analyzer
Mensa Bio100, Japan, was used to calculate the composition (ele-
mental ratio) of copper phosphide material.
2.3. X-ray crystallography
Single crystal X-ray data were collected on a Nonius Kappa im-
age plate diffractometer using monochromatic Mo Ka. Using phi
and omega scans 406 1.5° images were collected [17]. The unit cell
was determined, the reflections were integrated and scaled with
the HKL Denzo-Scalepack suite of programs [18] and the data were
corrected for absorption using Sortav [19]. The structure of 1 was
solved by direct method using SIR97 [20] and refined by full-matrix
least-squares against F2 using SHELXL97 [21]. All non-hydrogen
atoms were refined anisotropically. Additional crystal data and
structure refinement details are listed in Table 1.
3. Results and discussion
3.1. Synthesis and characterization
The complex 1 was prepared by simple mixing of the reactants
in the appropriate mole ratios as shown in chemical Eq. (1)
THF
2CuBr þ 2tpp þ dppm ! Cu2ðtppÞ2ðdppmÞBr2
ð1Þ
r:temp
The compound is soluble in common organic solvents such as
dichloromethane, chloroform and tetrahydrofuran (THF) and is sta-
ble in air under normal conditions. In FT-IR spectrum, the copper-
phosphorus stretching vibrational bands appear around 500 cmꢀ1
which support the existence of a link between phosphorus and
the metal but a copper–bromide stretching mode could not be re-
solved [22,23]. The 1H NMR spectral data for 1 explicitly show the
resonance of methylene protons of dppm at chemical shift
3.77 ppm and broad multiplets in the range 6.92–7.48 ppm for aro-
matic protons [24,25], thus all the protons in the compound were
identified by their intensity and multiplicity pattern and the total
number of protons calculated from the integration curve are in
agreement with the proposed molecular formula.
2.4. Materials chemistry
The controlled thermal analysis of the complex was carried out
using a Seiko SSC/S200 thermal analyzer at a heating rate of 10 °C/
min under N2 flow.
Thin film deposition was performed via Ultrasonic Aerosol As-
sisted Chemical Vapour Deposition (UAACVD) by dissolving 0.1 g
Table 1
Crystallographic and structure refinement data for complex 1.
Empirical formula
Formula weight
Crystal habit, colour
T (K)
Cu2C61H52Br2P4
1195.81
block, colourless
423 (2)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
monoclinic
P21/n
14.5900(1)
17.8560(1)
21.0700(2)
104.368(1)
5317.44(7)
4
1.494
2.462
2424
b (Å)
c (Å)
b (°)
Volume (Å3)
Z
Density (calculated) (Mg mꢀ3
)
)
Absorption coefficient (mmꢀ1
F(000)
Crystal size (mm)
h range for data collection (°)
Index ranges
0.30 ꢁ 0.20 ꢁ 0.20
3.56–30.03
ꢀ20 6 h 6 20; ꢀ25 6 k 6 25;
ꢀ29 6 l 6 29
112448
Reflections collected
Independent reflections [R(int)
]
15522 [0.0657]
Maximum and minimum transmission 0.83 and 0.63
Refinement method
full-matrix least-squares on F2
1.023
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0344 and wR2 = 0.0716
R1 = 0.0544 and wR2 = 0.0791
0.505 and ꢀ0.577
Largest difference peak and hole
(e Åꢀ3
)
Fig. 1. ORTEP drawing showing the molecular structure of complex 1.

M. Shahid et al. / Inorganica Chimica Acta 362 (2009) 3069–3072
3071
The electron impact mass spectrum of 1 does not show molec-
ular ion peak. The fragmentation pattern show various ions of low
m/z ratios as given in experimental section. The base peak at m/z
261.8 corresponds to triphenylphosphine moiety of the complex.
geometry around each metal center is distorted tetrahedral. The
0
Cu–Br bond lengths fall in the range 2.4882(3)–2.5695(3) ÅA, which
0
are longer than the reported values (ꢂ2.393 ÅA) [26], describing
weaker coordination of the bromide to Cu(1). The copper–phos-
0
phorus distances are 2.2513(5) and 2.556(5) ÅA owing to the pres-
ence of two different phosphine ligands. The values are close to
the expected range for four coordinate Cu(1) systems [22,27].
The P–Cu–P and P–Cu–Br angles (Table 2) support distorted tetra-
hedral environment around each copper (I) atom as evident from
the data. The P(1)–Cu(1)–P(3) and P(2)–Cu(2)–P(4) angles 120.47
and 121.01°, respectively in 1 are larger than the ideal tetrahedral
value and show deviation which may be attributed to the strain
imposed by the phenyl rings of dppm and tpp ligands [28].
3.2. Structural analysis of 1
The solid-state structure of [Cu2(dppm)(tpp)2Br2] (1) (Fig. 1),
belonging to the monoclinic system with space group P21/n, con-
sists of a dinuclear Cu2P4Br2 core (Table 1). The coordination envi-
ronment around the two copper atoms is similar. Each copper
atom is coordinated to one phosphorus atom of each of the dppm
and tpp ligands whereas the bromo-ligands are bridging the two
copper centers in
l2-fashion. The bridging dppm ligand between
the two metal centers behave in
l2-fashion and the coordination
3.3. Pyrolysis studies, thin film deposition and characterization
The thermal behaviour of the complex was studied by TG anal-
ysis over a range of 25–550 °C under nitrogen atmosphere. TGA
curve of complex 1, as delineated in Fig. 2, shows three steps
weight loss. The first, occurring at 103–251 °C, is associated with
a 7.6% weight loss. The second step, which starts at 251 °C and is
completed at 383 °C, is associated with the largest weight loss of
67.8%, followed by the last stage ranging from 383 to 530 °C,
resulting in a residue amounting to 12.0% of the initial weight, cor-
responding to copper phosphide (12.01%) as shown in Eq. (2)
Table 2
Selected bond distances (Å) and angles (°) for complex 1.
Bond distances (Å)
Cu(1)–Br(2)
Cu(1)–P(3)
Cu(1)–Br(1)
Cu(1)–P(1)
2.5555(3)
2.2435(5)
2.5033(3)
2.2556(5)
Cu(2)–Br(1)
Cu(2)–P(2)
Cu(2)–Br(2)
Cu(2)–P(4)
2.4882(3)
2.2448(5)
2.5695(3)
2.2513(5)
Bond angles (°)
Cu(2)–Br(1)–Cu(1)
P(3)–Cu(1)–P(1)
P(1)–Cu(1)–Br(1)
P(1)–Cu(1)–Br(2)
P(3)–Cu(1)–Br(1)
P(3)–Cu(1)–Br(2)
C(7)–P(1)–Cu(1)
72.568(9)
120.47(2)
C(7)–P(1)–C(61)
C(7)–P(1)–C(1)
105.66(9)
103.21(9)
101.32(9)
112.523(16)
107.925(17)
70.392(9)
3Cu2ðtppÞ ðdppmÞ Br2 AꢀA!CVD 2Cu3P þ Volatiles
ð2Þ
109.791(16)
103.055(16)
110.401(17)
110.956(17)
115.77(7)
C(1)–P(1)-C(61)
P(4)–Cu(2)–Br(1)
P(4)–Cu(2)–Br(2)
Cu(1)–Br(2)–Cu(2)
P(2)–Cu(2)–Br(1)
2
2
450 ꢃC
Eq. (2) demonstrated the decomposition of complex 1 to target
material, Cu3P, and volatiles, subsequent studies provide an evi-
dence for the clean deposition of the target material.
112.396(16)
The films deposited (black) from complex 1 exhibit a good adhe-
sion to the substrate which pass the ‘‘Scotch tape test” and are
stable toward air and moisture. They reflect light in multi-shaded
colours depending on the particle size and thickness of the depos-
ited film. The low resolution scanning electron microscopic (SEM)
image (Fig. 3a) of the copper phosphide thin film shows the forma-
tion of crystalline material with smooth, porous and homogenously
dispersed morphology. The SEM image (Fig. 3b) at high magnifica-
tion shows that the particles in the size range 200–400 nm, having
irregular shaped structures, are present in the form of clusters on
the films with loss of perfect orientation.
The crystalline nature of the material was further strengthened
by PXRD of copper phosphide films. The fingerprints of the powder
X-ray diffractogram (Fig. 4) of the copper phosphide obtained from
the decomposition of complex 1 are in good agreement with the
reported data for Cu3P [29,30] [JPCDS card no. 71-2261]. The
deposition of copper phosphide thin films by using complex 1
as a single-source precursor for AACVD was found to be more
Fig. 2. Thermogram of the complex 1, showing loss in weight with rise in
temperature.
Fig. 3. SEM micrograph of films deposited from complex 1 at 450 °C on soda glass (a) at 800 magnification and (b) at 12800 magnification.

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M. Shahid et al. / Inorganica Chimica Acta 362 (2009) 3069–3072
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.
2009.01.031.
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Acknowledgements
M.S. and M.M. would like to thank Higher Education Commis-
sion, Islamabad and Pakistan Science Foundation for financial sup-
port and I.D. is grateful to Punjab Education department for
granting study leave and to QAU for providing financial support.
Appendix A. Supplementary material
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CCDC 649743 contains the supplementary crystallographic data
for 1. These data can be obtained free of charge from The Cam-