Phenyl substituted ditelluro-imidodiphosphinate complexes of iron, nickel, palladium and platinum, and their pyrolysis studies generating metal tellurides

Article abstract of DOI:10.1016/j.poly.2018.12.038

The tellurium complexes M[N(PPh₂Te)₂]_n (M = Fe (1), Ni (2), Pd (3), Pt (4) and n = 2 or 3) have been prepared using the ditellurido anions [N(PPh₂Te)₂]^? and their ability to generate tellur

Full text of DOI:10.1016/j.poly.2018.12.038

Polyhedron 160 (2019) 157–162
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Phenyl substituted ditelluro-imidodiphosphinate complexes of iron,
nickel, palladium and platinum, and their pyrolysis studies generating
metal tellurides
b,1
Temidayo Oyetunde a,b, Mohammad Afzaal c, , Paul O’Brien
⇑
a Centre for Chemical and Biochemical Research (CCBR), Redeemer’s University, Ede, P.M.B. 230, Osun State 232102. Nigeria
b School of Chemistry and School of Materials, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
c Maths and Natural Sciences Division, Higher Colleges of Technology, P.O. Box: 7947, Sharjah, United Arab Emirates
a r t i c l e i n f o
a b s t r a c t
Article history:
The tellurium complexes M[N(PPh2Te)2]n (M = Fe (1), Ni (2), Pd (3), Pt (4) and n = 2 or 3) have been pre-
pared using the ditellurido anions [N(PPh2Te)2]ꢀ and their ability to generate tellurides was investigated
by pyrolysis in a quartz glass tube, under vacuum at 500 °C for 90 min. The products were characterised
by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-
rays (EDAX) and X-ray photoelectron spectroscopy (XPS). The XRD revealed an orthorhombic phase for
the metal telluride from 1, while the hexagonal phase was observed for tellurides from 2, 3 and 4 respec-
tively. Magnetic measurements on FeTe2 (from 1) indicated an antiferromagnetic sample with a transi-
tion temperature at 75 K.
Received 13 November 2018
Accepted 14 December 2018
Available online 28 December 2018
Keywords:
Single-source precursors
Metal tellurides
Antiferromagnetic
Imidodiphosphinate ligands
X-ray photoelectron spectroscopy
Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction
Nickel telluride is an important intermetallic compound of the
3d transition metal chalcogenides series, for which various proper-
Dichalcogenoimidodiphosphinates, [N(PR2E)2]ꢀ (R = alkyl, aryl;
E = S, Se) are chelating ligands that readily form cyclic complexes
with main group, transition, lanthanides and actinides [1] metals.
The useful synthesis of [N(PPh2Te)2]ꢀ was developed by Chivers
et al. [2] using the anion [N(PPh2)2]ꢀ. The sodium salts of the ditel-
lurido ligands [N(PR2Te)2]ꢀ were obtained in good yields (R = iPr,
Ph, tBu) [2,5,6]. Metal complexes of the ditellurido ligands [N(PR2-
Te)2]ꢀ have shown novel structures and new reaction chemistry in
which the tellurium donor sites exhibit greater flexibility than sul-
fur or selenium, having a tellurium-centered ligand bridging two
metal centres. Metal tellurides have potential applications as low
band gap semiconductor materials in solar cells, thermoelectric
devices and telecommunications. [3,4] This is because the peculiar
and valuable properties of tellurium have resulted in its extensive
research as an important p-type narrow band gap semiconductor.
These properties include photoconductivity, piezoelectricity, ther-
moelectricity, non-linear optical responses and photoelectricity
[7–9]. Metal complexes of the isopropyl derivative anion [N(PiPr2-
Te)2]ꢀ have been shown to serve as efficient single-source precur-
sors for pure metal telluride thin films or nanomaterials, e.g. CdTe,
PbTe, In2Te3 [10–12].
ties have been previously studied [13–16]. Some of these are elec-
tric, magnetic, crystallographic (helical chain conformation) and
thermodynamic properties. The nickel-telluride system consists
of two ordered compounds: NiTe and NiTe2, with a range of contin-
uous solid solutions between them [17]. Oftedal [18] reported that
NiTe has a hexagonal structure of the NiAs-(B8)-type, while
Tengnér [19] reported NiTe2 to have the hexagonal Cd(OH)2-(C6)-
type structure. In a crystal of nickel telluride, the Ni2+ ions occupy
a simple hexagonal lattice, while the Te2ꢀ ions occupy a close-
packed hexagonal lattice, with both lattices penetrating each other
[13]. Also, NiTe can be used as an ohmic contacting layer of II–VI
semiconductors because of their distinctive electrical transport
property [16]. For reports on the deposition of nickel telluride,
there are only a few, such as flash evaporation [20], AACVD [21]
and electrodeposition [22].
The early synthesis of palladium ditelluride was reported by
Thomassen [22] and Wöhler et al. [23] by preparing it as the only
compound from the reaction of the constituent elements. Also,
Groeneveld [24] prepared the compound by fusing the elements
in the correct atomic proportions. Palladium monotelluride was
also prepared by Thomassen by dry fusion of the elements in
evacuated tubes [22]. About nine binary phases of the
palladium-tellurium system are known, which include Pd17Te4,
Pd3Te, Pd20Te7, Pd8Te3, Pd7Te3, Pd9Te4, Pd3Te2, PdTe and PdTe2
[25]. However, the most important of these seems to be PdTe
⇑
Corresponding author.
E-mail address: mafzaal@hct.ac.ae (M. Afzaal).
1
Deceased.
https://doi.org/10.1016/j.poly.2018.12.038
0277-5387/Ó 2018 Elsevier Ltd. All rights reserved.

158
T. Oyetunde et al. / Polyhedron 160 (2019) 157–162
and PdTe2 because of their similar structural type with NiAs and
CdI2 respectively [24,25]. As a nanocrystal, palladium telluride
can be applied as a catalyst for methanol electro-oxidation and it
also behave as a strongly coupled superconductor [26]. The early
synthesis of platinum telluride involved both wet and dry proce-
dures as the main synthetic routes [24]. The wet method involved
the reaction of hydrogen telluride with a solution of platinum
metal salt, while the dry route was based on the direct fusion of
the weighed constituents. In the platinum-tellurium system, the
most important phases are PtTe and PtTe2 [27]. According to
Groeneveld [24], PtTe2 has a CdI2 structural type while PtTe con-
sists of an orthorhombic structure [27].
FeTe2 is an example of crystalline transition metal ditellurides
in the 3d series known to exhibit 3D magnetic ordering and semi-
conductivity [28]. FeTe2 is a marcasite, containing a narrow 3d
band (about 1 eV), and is known to exhibit good magnetic proper-
ties [28], semiconductivity [29], high electrical conductivity [30]
and high thermoelectric powder values [30]. Traditionally, FeTe2
had been prepared by the direct contact of the elements in sealed
tubes [31], while new synthetic routes involved OMVPE and
MOCVD [32,33]. Through a solution-based solvothermal reduction,
FeTe2 nanoparticles were obtained [28,31]. From the precursor [Fe
{tBu2P(Te)NR}2] using gas-phase deposition, thin films of FeTe2
were obtained by Song and Bochmann [34].
TMEDA (10.40 ml, 69.09 mmol) was added to the suspension,
which was heated to 100 °C for 6 h. The resulting suspension was
allowed to settle and the yellow mother liquor decanted. The crude
solid was suspended in hexane, washed with hexane (3 ꢁ 20 ml)
and dried under vacuum to give a creamy white powder. Yield:
9.00 g, 65%.
2.3. Synthesis of (TMEDA)Na[(TePPh2)2N] [11]
Toluene (20 ml) was added to solid [NaN(PPh2)2] (4.13 g,
10.14 mmol) and tellurium powder (2.64 g, 20.67 mmol). The
ligand TMEDA (1.52 ml, 10.14 mmol) was added to the suspension,
which was heated at 80 °C for 3 h. The resulting mixture was fil-
tered at room temperature through a sintered glass to give a clear
deep red solution. This was decanted and the residue washed with
hexane (3 ꢁ 15 ml), followed by drying under vacuum to give a
yellow polycrystalline powder. Yield: 2.00 g, 24%.
2.3.1. Synthesis of the complexes
All the complexes were prepared by modifying the procedures
reported in the literature. Also, all attempts to grow quality crys-
tals from solutions of these complexes were unsuccessful. Concen-
trated solutions of the complexes in THF layered with hexane at
room temperature were prepared, but no growth was observed
after several weeks. The reason(s) for this remained unclear.
In this work, telluride complexes of iron (1), nickel (2), palla-
dium (3) and platinum (4) have been prepared and characterized,
using the phenyl substituted anionic [N(PPh2Te)2]ꢀ ligand. Sam-
ples were pyrolysed under vacuum in a quartz glass reactor. This
yielded black deposits which were analysed by X-ray powder
diffraction (XRD), scanning electron microscopy (SEM) and energy
dispersive analysis of X-rays (EDAX) studies. Magnetic and conduc-
tivity measurements were attempted on various resulting materi-
als to determine their properties.
2.4. Synthesis of [Fe{(TePPh2)2N}3] (1)
A solution of (TMEDA)Na[(TePPh2)2N] (1.50 g, 1.86 mmol) in
THF (25 ml) was added via cannula to a solution of FeCl3 (0.10 g,
0.62 mmol) in THF (15 ml) at room temperature. The resulting
brown solution was stirred for 2 h, followed by solvent removal
under reduced pressure. Fresh THF (25 ml) was added, filtered
and concentrated under vacuo. Hexane (25 ml) was added and
the obtained solution was refrigerated overnight, followed by sol-
vent removal under vacuum. A brown powder was obtained. Yield:
0.90 g, 74%. Elemental analysis calculated for C72H60FeN3P6Te6: C,
43.77; H, 3.06; N, 2.13; P, 9.42%. Found: C, 45.80; H, 4.10; N,
2.84; P, 10.27%.
2. Experimental
2.1. Materials and methods
All synthetic procedures were done under an inert atmosphere
using a double manifold Schlenk-line, attached to an Edwards
E2M8 vacuum pump and a dry nitrogen cylinder. Solid air-
sensitive compounds were handled in a glove box under an inert
atmosphere of dry nitrogen. Chemicals were purchased from
Sigma-Aldrich and Fischer Chemicals and were used as received.
Dry solvents were used throughout the syntheses, either distilled
over standard drying agents (Na/benzophenone, CaH2 etc.) or pur-
chased and stored in flasks over molecular sieves. Elemental anal-
yses were performed by the microanalysis section of the School of
Chemistry, University of Manchester. TGA measurements were
performed using a Seiko SSC5200/S220TG/DTA model with a heat-
ing rate of 10 °C minꢀ1 under nitrogen. NMR spectra were recorded
using a Bruker Avance (III) 400 MHz FT-NMR spectrometer, using
CDCl3 or d8-toluene as the solvent. 1H NMR spectra were refer-
enced to the solvent signal and the chemical shifts were reported
relative to Me4Si. 31P NMR spectra were referenced externally to
an 85% solution of H3PO4 and the chemical shifts were reported
relative to H3PO4. Conductivity studies on NiTe and PdTe involved
wire connection to a Keithley 2400 source meter. Electricity of
0–2 V was applied and the I-V curve was obtained to determine
the flow of current or otherwise.
2.5. Synthesis of [Ni{(TePPh2)2N}2] [35] (2)
A solution of (TMEDA)Na[(TePPh2)2N] (0.80 g, 0.992 mmol) in
THF (20 ml) was added via cannula to a solution of Ni(OAc)2
(0.12 g, 0.50 mmol) in THF (15 ml) at room temperature. A colour
change from green to brown occurred and the solution was stirred
for 2 h, followed by solvent removal under vacuo. Fresh THF
(20 ml) was added and the solution filtered. Hexane (25 ml) was
added and the resulting solution was left overnight, after which
the solvent was removed to give a brown powder. Yield: 0.41 g,
65%. Elemental analysis calculated for C48H40NiN2P4Te4: C, 43.07;
H, 3.01; N, 2.09; P, 9.26%. Found: C, 45.25; H, 4.11; N, 2.64; P,
11.89%. 1H NMR, (d, ppm, CDCl3, 400 MHz): 6.5–8.3 (m, ArH); 31P
{1H} NMR (d, ppm, CDCl3): 10.29.
2.6. Synthesis of [Pd{(TePPh2)2N}2] [36] (3)
A solution of (TMEDA)Na[(TePPh2)2N] (0.80 g, 0.99 mmol) in
THF (25 ml) was added via cannula to a solution of Pd(OAc)2
(0.11 g, 0.50 mmol) in THF (20 ml) at room temperature. The
resulting dark orange solution was stirred for 2 h, followed by sol-
vent removal under reduced pressure. Fresh THF (25 ml) was
added and the solution filtered. The clear filtrate was left over-
night, giving an orange deposit from which solvent was removed
to give a dark orange powder. Yield: 0.5 g, 74%. Elemental analysis
calculated for C48H40PdN2P4Te4: C, 41.59; H, 2.91; N, 2.02; P, 8.95%.
2.2. Synthesis of [NaN(PPh2)2] [2]
Toluene (75 ml) was added to a mixture of solid [HN(PPh2)2]
(13.30 g, 34.45 mmol) and NaH (0.84 g, 34.84 mmol). The amine

T. Oyetunde et al. / Polyhedron 160 (2019) 157–162
159
Found: C, 43.77; H, 3.08; N, 2.54; P, 10.34%. 1H NMR (d, ppm, CDCl3,
400 MHz): 6.8–7.9 (m, ArH); 31P {1H} NMR (d, ppm, CDCl3): 22.4.
was reacted with sodium hydride yielding the sodium amide [NaN
(PPh2)2], as previously reported without detailed characterization
[6]. Oxidation of the amide with elemental tellurium in the pres-
ence of N,N,N0,N0-tetramethylethylenediamine (TMEDA) produced
the ditellurido ligand (TMEDA)Na[(TePPh2)2N] (Scheme 1). The
complexes were prepared by the addition of the corresponding
metal salt to a solution of ligand in THF at room temperature
(Scheme 2). All the complexes were highly unstable in air, which
may have contributed to the marginally higher than expected val-
ues for the microanalytical results.
Complexes 2, 3 and 4 were characterised by NMR spectroscopy
(1H and 31P {1H} NMR in CDCl3). The 1H NMR spectrum for complex
2 displayed multiplets between d 6.5 and 8.3 ppm for the aromatic
protons. For complex 3, the multiplets for the aromatic protons
were seen between d 6.8 and 7.9 ppm. In the spectrum of complex
4, the aromatic protons were observed between d 6.8 and 8.0 ppm.
Also, for these complexes, other singlet peaks were shown for pro-
tons in different environments, which indicated coupling with
other spin-active nuclei, e.g. ArH-ArH and ArH-P. For the 31P {1H}
NMR spectra, a singlet peak was observed for complex 2 at d
10.29 ppm, while that of complex 3 occurred at d 22.4 ppm. For
complex 4, the singlet peak was at d 27.27 ppm. For 1, no NMR
studies were conducted due to its paramagnetic nature.
2.7. Synthesis of [Pt{(TePPh2)2N}2] [36] (4)
A solution of (TMEDA)Na[(TePPh2)2N] (0.80 g, 0.99 mmol) in
THF (25 ml) was added via cannula to a solution of PtCl2 (0.13 g,
0.50 mmol) in THF (15 ml) at room temperature. The solution
turned brown immediately and was stirred for 2 h, followed by sol-
vent removal under reduced pressure. Fresh THF (25 ml) was
added and the solution filtered. The clear yellow filtrate was con-
centrated under vacuum and hexane (30 ml) was added. This
was refrigerated, after which the solvent was removed to give a
yellow powder. Yield: 0.30 g, 42%. Elemental analysis calculated
for C48H40PtN2P4Te4: C, 39.09; H, 2.74; N, 1.90; P, 8.41%. Found:
C, 40.93; H, 3.45; N, 2.54; P, 9.85%. 1H NMR (d, ppm, CDCl3,
400 MHz): 6.8–8.0 (m, ArH); 31P {1H} NMR (d, ppm, CDCl3): 27.27.
2.8. Pyrolysis of the precursors
The pyrolysis experiments were carried out in a quartz glass
tube reactor using a Carbolite heating furnace. Samples were
heated at 500 °C under vacuum for 90 min and subsequently
cooled to room temperature for 1 h under nitrogen. 500 mg of
the sample was used for each experiment. Black deposits were
obtained and pulverized afterwards, prior to subsequent character-
isation methods.
3.1. Thermogravimetric analysis
The physical properties of complexes 1–4, probed by thermo-
gravimetry analysis (TGA), showed a single-step decomposition
with a rapid weight loss (Fig. S1 ESI). However, [Fe{(TePPh2)2N}3]
(1) was an exception to this, having two decomposition steps.
Although its decomposition occurred in two steps, the observed
residue value of 25% is close to the calculated value of 22% for a
residue containing FeTe2 and elemental tellurium. [Ni{(TePPh2)2-
N}2] (2) decomposed between 280 and 370 °C with a final residue
of about 20%, which is higher than the calculated value of 14% for
NiTe from the precursor. The rapid weight loss of [Pd{(TePPh2)2-
N}2] (3) occurred between 270 and 363 °C, with a residue amount
of 20%, which is close to the 17% calculated value for PdTe in the
precursor. The decomposition of [Pt{(TePPh2)2N}2] (4) was
between 274 and 348 °C, with 18% final residue, which is also
almost in agreement with the calculated value of 22% for PtTe.
2.9. Characterisation of the black deposits
X-ray diffraction studies were performed on a Bruker AXS D8
diffractometer using monochromated Cu-Ka radiation. The sam-
ples were mounted flat and scanned from 10 to 80° in a step size
of 0.05 with a count rate of 9 s. The diffraction patterns were then
compared to the documented patterns in the ICDD index. SEM was
performed using a Philips XL30 FEG SEM. All deposits were coated
with carbon to avoid charging of the sample by the electron beam,
using Edward’s coating system E306A before scanning electron
microscopy (SEM) was carried out. Energy dispersive X-ray (EDX)
analyses were done using a DX4 instrument. The XPS spectra were
recorded using a Kratos Axis Ultra spectrometer, employing a
monochromated Al K
a X-ray source and an analyser pass energy
of 80 eV (wide scans) or 20 eV (narrow scans), resulting in a total
energy resolution of ca. 1.2 and 0.6 eV, respectively. Uniform
charge neutralisation of the photoemitting surface was achieved
by exposing the surface to low energy electrons in a magnetic
immersion lens system (Kratos Ltd). The system base pressure
was 5 ꢁ 10ꢀ10 mBar. Spectra were analysed by first subtracting a
Shirley background and then obtaining accurate peak positions
by fitting peaks using a mixed Gaussian/Lorenzian (30/70) line
shape. During fitting, spin orbit split components were constrained
to have identical line widths, elemental spin orbit energy separa-
tions and theoretical spin orbital area ratios. Quantitative analysis
was achieved using theoretical Scofield elemental sensitivities and
recorded spectrometer transmission functions. All photoelectron
binding energies (BE) were referenced to C1s adventitious contam-
ination peaks set at 285 eV BE. The analyser was calibrated using
elemental references; Au 4f7/2 (83.98 eV BE), Ag3d5/2 (368.26 eV
BE) and Cu2p3/2 (932.67 eV BE).
3.2. Pyrolysis of the complexes
Complex 1 was pyrolyzed at 500 °C and black deposits were
obtained, pulverized and analysed by XRD. The sample formed
-
N
H
N
-
+
2 Te
TMEDA
PPh
PPh
2
N Na
2
NaH
PPh
PPh
PPh2
PPh
2
2
2
Te
Te
Na(TMEDA)
Scheme 1. Synthesis of the ditelluroimidodiphosphinate ligand.
MX2
THF
+ 2 TMEDA + 2 NaX
(M = Fe, Ni, Pd, Pt; X = Cl)
2
3. Results and discussion
The ligand [HN(PPh2)2] was prepared from (Me3Si)2NH and
PPh2Cl, which were commercially available. This amine is a reagent
with limited isolation and characterization [37,38]. The compound
Scheme 2. Synthesis of the ditelluroimidodiphosphinate complexes.

160
T. Oyetunde et al. / Polyhedron 160 (2019) 157–162
was orthorhombic iron telluride FeTe2 (ICDD 04-003-2015) and
hexagonal tellurium (ICDD 01-079-0736) (Fig. 1a). Tellurium
gave peaks from the primary reflections of 2-theta at 23.02°,
corresponding to the (1 0 0) plane, and additional reflections
of 2-theta at 27.56, 38.28, 43.35, 45.94 and 62.85° for the
(0 1 1), (0 1 2), (1 1 1), (0 0 3) and (1 1 3) planes, respectively.
The lattice parameter of a = 5.290(8) Å is a close match with
the literature value (Table S1, ESI). The deposited material
consists of crisp flakes, as revealed by the SEM (Fig. 2a). EDX
analysis showed the iron to tellurium ratio as 29.8:59.7%
respectively,
together
with
phosphorus
contamination
(ca 10%). The deposition of a metal telluride and tellurium
might be expected since this had been previously reported
[12,21]. It might be explained that the high ratio of Te:M in
the precursor could be responsible for the deposition of
elemental tellurium [1].
(b)
(a)
10
20
30
40
50
60
70
80
10
20
30
40
50
60
70
80
2-Theta (degrees)
2-Theta (degrees)
(c)
(d)
10
8 0
10
20
30
40
50
60
70
8 0
10
20
30
40
50
60
70
2-Theta (degrees)
2-Theta (degrees)
Fig. 1. XRD patterns of (a) orthorhombic FeTe2 and hexagonal tellurium from 1. * indicates tellurium, (b) hexagonal nickel telluride from 2, (c) hexagonal palladium telluride
deposited from 3 and (d) hexagonal PtTe2 and rhombohedral PtTe from 4. All depositions were at 500 °C.
Fig. 2. SEM images of: (a) iron telluride and tellurium from 1, (b) nickel telluride from 2, (c) palladium telluride from 3 and (d) platinum telluride from 4. All depositions
occurred at 500 °C. Scale size = 1 mm.

T. Oyetunde et al. / Polyhedron 160 (2019) 157–162
161
Complex 2 was pyrolysed at 500 °C under a constant flow of
nitrogen, which gave a black deposit that was later pulverized prior
to XRD analysis. XRD of the pyrolysed sample confirmed the depo-
sition of hexagonal nickel telluride NiTe (ICDD 00-038-1393), hav-
ing the preferred orientation along the (1 0 1) plane (Fig. 1b). SEM
studies to determine the morphology of the material revealed
them to be tiny fused crystallites of nickel telluride (Fig. 2b). The
obtained lattice parameters of a = 3.930(3) Å, and c = 5.367(4) Å
are in agreement with reported values in the literature (Table S1,
ESI). EDX analysis on the hexagonal crystallites showed a high
nickel content, with nickel and tellurium having 43.9 and 26.3%,
respectively, together with phosphorus contamination (29.8%). In
a previous study, hexagonal nickel telluride Ni0.51Te was also
deposited from [Ni{(SePiPr2)(TePiPr2)N}2] [21a].
The pyrolysis of complex 4 at 500 °C also deposited a black resi-
due, which was analysed by XRD. The X-ray diffraction pattern
revealed a mixture of both rhombohedral platinum telluride PtTe
(ICDD 01-088-2262) and hexagonal platinum telluride PtTe2 (ICDD
04-003-1897) (Fig. 1d). Traces of PtTe were observed at 2-theta
values of 26.32, 31.60, 41.10, 44.84, 55.11 and 56.66°. These corre-
spond to the (1 0 1), (1 0 4), (1 0 7), (0 1 8), (0 0 1 2) and (0 2 4)
planes, respectively. The lattice parameters indicated values of
4.027 and 5.223 Å for a and c, respectively. SEM analysis of the
deposited powder showed the morphology to be uniformly
arranged flat flakes of platinum telluride (Fig. 2d). EDX analysis
on the deposited sample indicated the values for platinum and tel-
lurium to be 32.8 and 40.3% respectively, with phosphorus as
26.9%.
The pyrolysis of complex 3 at 500 °C also produced a black resi-
due, which was analysed by XRD. The sample formed was hexago-
nal palladium telluride PdTe (ICDD 00-029-0971) (Fig. 1c). The
obtained lattice parameters match closely with the reported val-
ues, a = 4.132 Å (Table S1, ESI). The deposited material consists of
globular crystallites of palladium telluride, as indicated by SEM
(Fig. 2c). EDX analysis on the sample revealed a high tellurium con-
tent with a Pd:Te ratio of 30.1:56.8% respectively, together with
phosphorus (13.2%).
3.3. Magnetic measurements and XPS analysis on iron telluride
Iron tellurides are antiferromagnetic materials whose magnetic
properties depend on the temperature between 2.5 and 300 K
[28,41,42]. From the magnetic measurements, it should be possible
to evaluate phase relationships which exist in iron telluride
systems.
DC magnetization plots of FeTe2 powders deposited from [Fe
{(TePPh2)2N}3] (1) are shown in Fig. 3. Magnetization versus tem-
perature for ZFC and FC experiments at 100 Oe magnetic fields
are given in Fig. 3, which shows the superimposition of the ZFC
and FC curves on each other and their values increased with
decreasing temperature. Hence, this might indicate the antiferro-
magnetic behaviour of the sample.
In the amorphous state, FeTe2 displays a strong antiferromag-
netic coupling between localized moments, though without a
long-range magnetic ordering, and transits to a spin-glass state
at 6 K [28,43]. However, the crystalline state shows 3D antiferro-
magnetic ordering at ꢂ83 K [44]. From Fig. 3 shown above, we
can assume that the antiferromagnetic transition temperature,
TN, occurs at around 75 K. Previously, the magnetic properties of
various iron and tellurium having integral stoichiometric ratios
have been studied. An example is FeTe as an antiferromagnetic
material with a transition temperature of 70 K [45], while FeTe2
transits as an antiferromagnetic material at 100 K [28].
0.025
0.020
0.015
FC
0.010
0.005
0.000
ZFC
The surface atomic coverage and surface chemistry of the pow-
der obtained from 1 were determined by XPS. The Fe 2p peak
appeared at 714 and 728 eV for 2p3/2 and 2p1/2, respectively
(Fig. S2, ESI). This indicates iron oxide/hydroxide, suggesting the
probable surface oxidation of the sample prior to XPS analysis. Iron
0
50
100
150
200
250
300
Temperature (K)
Fig. 3. Zero field-cooled (ZFC) and field-cooled (FC) curves of hexagonal iron
telluride deposited from [Fe{(TePPh2)2N}3] (1) at 100 0e.
(b)
(a)
500 nm
500 nm
Fig. 4. TEM images of (a) palladium telluride and (b) nickel telluride.

162
T. Oyetunde et al. / Polyhedron 160 (2019) 157–162
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4. Conclusions
Ditelluridoimidodiphosphinate complexes [M{(TePPh2)2N}2]
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
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T.O. acknowledges the School of Chemistry, the University of
Manchester for funding. The authors will like to thank Prof.
Jonathan Coleman for assistance on the conductivity studies of
some samples. We are grateful to Dr. Paul Wincott and Dr. Floriana
Tuna for XPS and SQUID measurements, respectively.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.poly.2018.12.038.
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