Synthesis of phosphinochalcogenoic amidato complexes of divalent transition metals and their thermolysis to metal selenide and telluride phases

Article abstract of DOI:10.1039/a702460f

Protolysis of the transition-metal diamides [M{N(SiMe₃)₂}₂(thf)_n] (M = Cr, Mn, Fe or Co) with 2 equivalents of phosphinochalcogenoic amides Bu^t₂P(E)NHR (E = Se or Te, R = Prⁱ or cyclo-C₆H₁₁) gave a series of thermally stable metal-selenium and -tellurium complexes [M{Bu^t₂P(E)NR}₂]. The complex [Ni{Bu^t₂P(Se)NR}₂] was obtained from Li[Bu^t₂(Se)NR] and [NiCl₂(PMe₃)₂]. The compounds sublime readily under reduced pressure and are suitable for the gas-phase deposition of metal chalcogenide films. The selenium precursors lead to MSe (M = Cr, Mn, Fe or Ni), while tellurium complexes afford MTe₂ (M = Fe, Mn or Co). By contrast, [Co{Bu^t₂P(Se)NR}₂] gives Co₃Se₄, while [Ni{Bu^t₂P(Se)NR}₂] generates NiSe or Ni₆Se₅, depending on the deposition conditions.

Full text of DOI:10.1039/a702460f

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Synthesis of phosphinochalcogenoic amidato complexes of divalent
transition metals and their thermolysis to metal selenide and telluride
phases†
Xuejing Song and Manfred Bochmann*
School of Chemistry, University of Leeds, Leeds, UK LS2 9JT
Protolysis of the transition-metal diamides [M{N(SiMe3)2}2(thf)n] (M = Cr, Mn, Fe or Co) with 2 equivalents of
phosphinochalcogenoic amides But2P(E)NHR (E = Se or Te, R = Pri or cyclo-C6H11) gave a series of thermally
stable metal–selenium and –tellurium complexes [M{But2P(E)NR}2]. The complex [Ni{But2P(Se)NR}2] was
obtained from Li[But2(Se)NR] and [NiCl2(PMe3)2]. The compounds sublime readily under reduced pressure
and are suitable for the gas-phase deposition of metal chalcogenide films. The selenium precursors lead to
MSe (M = Cr, Mn, Fe or Ni), while tellurium complexes afford MTe2 (M = Fe, Mn or Co). By contrast,
[Co{But2P(Se)NR}2] gives Co3Se4, while [Ni{But2P(Se)NR}2] generates NiSe or Ni6Se5, depending on the
deposition conditions.
Phosphinochalcogenoic amidato anions [R2P(E)NRЈ]Ϫ (E = O
E
or Se) are known to give stable chelate complexes with a variety
P
P
(i )
of metals.1 For example, the sulfur compounds form a series of
monomeric complexes of CoII and NiII, [M{R2P(S)NRЈ}2],
with square-planar or tetrahedral structures, depending on the
size of R and RЈ.2 We have recently prepared related phosphino-
selenoic and -telluroic amides3 and shown that the zinc and
cadmium complexes [M{But2P(E)NR}2] (M = Zn, or Cd,
E = Se or Te)4 are very suitable as precursors for the deposition
of ME films by low-pressure MOCVD (metal-organic chemical
vapour deposition) methods.5 Single-source precursors for metal
chalcogenide materials have attracted considerable interest.6
Those suitable for the gas-phase deposition of films must be
sufficiently volatile and combine the right degree of thermal
stability with the ability to decompose cleanly at moderate tem-
peratures, preferably between 200 and 400 ЊC. The thermal
stability of the tellurium derivatives described here is particu-
larly noteworthy in this context since few tellurium complexes
possess the properties required for gas-phase deposition pro-
cesses. For example, a number of complexes of Cr, Mn, Fe and
Co with the silyltellurolato ligand [TeSi(SiMe3)3]Ϫ have been
reported. Contrary to expectation, none of these proved suf-
ficiently volatile and stable to allow sublimation under reduced
pressure and metal telluride film growth.7
Various approaches have recently been explored to generate
transition-metal chalcogenides by the thermolysis of well
defined precursor complexes, usually in solution or in the solid
state. For example, heating dithiocarbamato complexes of FeII,
NiII and CoII leads to a number of metal sulfide phases, depend-
ing on the reaction conditions.8 The thermolysis of [Mn(CO)3-
(PEt3)2(TeCH2Ph)]9 or of the ditelluride [{(Et3P)2(OC)3-
MnTe}2]10 at 300 ЊC leaves a residue of polycrystalline MnTe,
and the sealed-tube pyrolysis of the iron telluride complexes
[{Fe(cp)(CO)(PEt3)}2Te] (cp = η-C5H5) and [Fe4Te4(PEt3)4]
gives FeTe powders.11 Manganese selenide and telluride are
important because of their optoelectronic properties and as
magnetic dopants for Group – semiconductors.12 We report
here the synthesis of a series of selenium and tellurium com-
plexes of the type [M{But2P(E)NR}2] and their behaviour as
precursors for the gas-phase deposition of metal chalcogenide
films.
R
N
N H
R
E
M
P
P
E
N
R
E
–
(ii )
Li+
a, R = Pri; b, R = C6H11
N
R
E =
M
Se Te
1
3
5
7
9
Cr
2
4
6
8
Mn
Fe
Co
Ni
Scheme 1 (i) [M{N(SiMe3)2}2], light petroleum, room temperature
(r.t.); (ii) CrCl2, FeCl2 or [NiCl2(PMe3)2], thf, r.t.
Results and Discussion
The reaction of a series of bis(amido) complexes of divalent
transition metals [M{N(SiMe3)2}2(thf)n] (M = Cr, Mn, Fe or
Co; thf = tetrahydrofuran) with the di-tert-butylphosphino-
chalcogenoic amides But2P(E)NHR (E = Se or Te) in light
petroleum at room temperature leads to the isolation of the
corresponding complexes [M{But2P(E)NR}2] 1–9 in high yields
(R = Pri a or cyclo-C6H11 b) (Scheme 1). All complexes are
moderately soluble in light petroleum but are isolated by re-
crystallisation from toluene as well shaped crystals. The chrom-
ium and iron complexes 1a and 5a were also made from the
reaction of Li[Bu2 P(Se)NPri] with MCl2 in thf, while the nickel
2
derivatives 9a and 9b were obtained from Li[But2P(Se)NR]
and [NiCl2(PMe3)2]. Attempts to isolate the analogous nickel–
tellurium complexes failed, however; these compounds appear
to be thermally unstable. The analytical data of the new
complexes are collected in Table 1.
Numerous attempts were made to grow X-ray-quality crys-
tals. Unfortunately all samples proved to be twinned. Mass
spectrometric data, the solubility behaviour and the volatility
of these compounds suggest, however, that like the sulfur com-
plexes [M{But2P(S)NR}2] (M = Co or Ni)2a all these complexes
are monomeric, with a distorted tetrahedral structure, analo-
gous to the structurally characterised zinc complex [Zn{But2P-
(Se)NPri}2].4
† Non-SI units employed: bar = 101 325 Pa, µB ≈ 9.27 × 10Ϫ24 J TϪ1
.
J. Chem. Soc., Dalton Trans., 1997, Pages 2689–2692
2689

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Table 1 Analytical data of phosphinochalcogenoic amido complexes
Analysis (%)a
C
Yield
(%)
Compound
Colour
M.p./ЊC
µ/µB
H
N
1a [Cr{But2P(Se)NPri}2]
1b [Cr{But2P(Se)NC6H11}2]
2a [Cr{But2P(Te)NPri}2]
2b [Cr{But2(Te)NC6H11}2]
3a [Mn{But2P(Se)NPri}2]
3b [Mn{But2P(Se)NC6H11}2]
4a [Mn{But2P(Te)NPri}2]
4b [Mn{But2P(Te)NC6H11}2]
5a [Fe{But2P(Se)NPri}2]
5b [Fe{But2P(Se)NC6H11}2]
6a [Fe{But2P(Te)NPri}2]
6b Fe{But2P(Te)NC6H11}2]
7a [Co{But2P(Se)NPri}2]
7b [Co{But2P(Se)NC6H11}2]
8a [Co{But2P(Te)NPri}2]
8b [Co{But2P(Te)NC6H11}2]
9a [Ni{But2P(Se)NPri}2]
9b [Ni{But2P(Se)NC6H11}2]
Light blue
Light blue
Light green
Light turquoise
White
36
41
75
57
79
74
70
76
65
46
67
67
89
91
86
45
43
50
>220b
>220b
228b
>115b
220
>220
>230b
>230b
>220
>220
206
42.6 (43.0)
48.2 (48.4)
42.7 (42.5)
36.7 (37.1)
42.9 (42.8)
48.8 (48.2)
37.0 (37.0)
42.4 (42.3)
43.4 (42.7)
48.4 (48.2)
36.9 (36.9)
42.5 (42.3)
42.6 (42.5)
48.0 (47.9)
36.9 (36.8)
42.4 (42.1)
42.6 (42.5)
48.2 (48.0)
8.2 (8.1)
8.2 (8.4)
7.1 (7.3)
7.0 (7.0)
7.8 (8.1)
8.5 (8.5)
6.9 (7.0)
7.3 (7.3)
8.5 (8.1)
8.3 (8.3)
6.9 (7.0)
7.4 (7.3)
7.9 (8.0)
8.2 (8.3)
6.8 (7.0)
7.1 (7.3)
8.1 (8.1)
8.4 (8.3)
4.6 (4.6)
3.9 (4.0)
3.4 (3.5)
3.8 (3.9)
4.9 (4.5)
3.8 (4.0)
4.2 (3.9)
3.3 (3.5)
4.2 (4.5)
3.8 (4.0)
3.7 (3.9)
3.5 (3.5)
4.2 (4.0)
3.8 (4.0)
3.7 (3.9)
3.4 (3.5)
4.3 (4.5)
3.9 (4.0)
White
5.8
5.0
Off-white
Off-white
White
White
Yellow
Yellow
Violet
Violet-blue
Dark green
Dark green
Green
>220
240
4.8
5.4
>220
236b
220
5.0
3.0
3.0
224b
>260
Green
a
Calculated values in parentheses. b With decomposition.
Table 2 Formation of metal chalcogenide films by gas-phase thermolysis of [M{But2P(E)NR}2] complexesa
T/ЊC
Compound
Reactor
Substrate
t/min
Metal chalcogenide phase
JCPDS referenceb
21-0241
1a
1b
3a
3b
4a
210
400
40
30
120–240
60–180
60
120
120
20–50
20
120
15
Cr0.68Sec
200–220
190–220
190–220
170
220
200
200–210
170–180
150
170
180
380–420
370–450
340–460
380
350
350
400–420
400
400
400
320
Cr0.68Sec
α-MnSe (cubic)c
α-MnSe
11-683
18-813
MnTe2 (cubic)
MnTe2
4b
MnTe2
18-813
26-795
14-0419
15-0463
(9-234)
15-0463
5a, 5b
6a, 6b
7a
FeSe (hexagonal)c
c
FeTe2
Co3Se4
Co3Se4 (ϩCoSe2)
Co3Se4
7b
60
200
150–200
180
350
30
120
60
Co3Se4
8a
8b
9a
320–350
320–350
300
CoTe2 c (orthorhombic)
CoTe2
11-553
210
10
Ni6Se5
29-0934
210
270
15
Ni6Se5
29-0934
220
300
60
NiSe
02-0892
9b
210
260
25
Ni6Se5
29-0934
200
400
10
NiSe ϩ NiSe2
02-0892/41-1495
a
Reactor pressure (1.6–5.4) × 10Ϫ6 mbar. b Joint Committee on Powder Diffraction Standards, International Center of Diffraction Data, Swarth-
more, PA. c Film with strong preferential orientation. MnSe, [200]; FeTe2, [011]; CoTe2, [120].
The magnetic moments indicate high-spin configurations in
the solid state. As Kuchen and co-workers2 showed, the mag-
netism of the nickel complexes [Ni{R2P(S)NRЈ}2] can be very
variable, and diamagnetic as well as paramagnetic complexes
are known. The nickel complexes 9a and 9b closely resemble in
this respect the sulfur analogues with R = But and RЈ = Pri or
cyclo-C6H11.2a
thermally slightly more stable. The results are shown in Table
2. The solid state products were assigned by their X-ray
diffraction patterns in comparison with the Joint Committee
on Powder Diffraction Standards (JCPDS) data of authentic
samples. As is common for gas-phase deposited films, the metal
chalcogenide products showed strong preferential orientation
in almost all cases.
The driving force for the preparation of these complexes was
to explore their potential as single-source precursors for the
gas-phase deposition of metal chalcogenide films, particularly
for metal tellurides for which sufficiently volatile and thermally
stable precursor complexes were, until now, rare or non-
existent. The phosphinochalcogenoic amidato complexes
described here fulfil these requirements and have proved
superior to bulky arene chalcogenolato complexes.13,14 All new
complexes (with the exception of 2a and 2b) sublime under
reduced pressure between 150 and 220 ЊC and deposit metal
chalcogenide films on glass substrates heated to 320–400 ЊC.
There was little difference in the volatility of the isopropropyl
(a) and cyclohexyl (b) derivatives, although the latter appeared
In contrast to the thermolysis of the zinc and cadmium
phosphinochalcogenoic amidato complexes described earlier,
which leads exclusively to films with a 1:1 metal:chalcogenide
ratio, transition-metal chalcogenides can form a large number
of compounds with different M :E stoichiometries and different
metal oxidation states. In general, selenium precursors give
films with lower chalcogenide:metal ratios than does tellur-
ium. For example, 3a and 3b give strongly oriented films of
cubic α-MnSe (rock salt structure, a = 5.462 Å), while 5a and 5b
generate hexagonal FeSe (achavalite-type). The behaviour of
the cobalt complexes 7a and 7b is more complex; they generally
lead to mixtures of Co3Se4 together with CoSe2 as a minor
component, although for shorter reaction times (30 min) and
2690
J. Chem. Soc., Dalton Trans., 1997, Pages 2689–2692

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Experimental
ME + But2P
NR
ME2 + But2P PBut2
E
PBut2
NR
Heat
[M{But2P(E)(NR)}2]
General procedures
All reactions were carried out under dry nitrogen using stand-
ard vacuum-line techniques. Solvents were distilled under
nitrogen from sodium–benzophenone [diethyl ether, thf, light
petroleum (b.p. 40–60 ЊC)], sodium (toluene) or calcium hydride
(dichloromethane). Magnetic moments were measured on
powdered samples under nitrogen, using a Johnson-Matthey
magnetic balance. Powder X-ray diffraction data were recorded
using a Phillips PW 1710 diffractometer. The compounds
[Cr{N(SiMe3)2}2(thf)2],19 [{Mn[N(SiMe3)2]2(thf)}2],20 [Fe{N-
(SiMe3)2}2],21 [Co{N(SiMe3)2}2(thf)],22 But2P(E)NHR (E = Se
or Te, R = Pri or cyclo-C6H11)3 were prepared according to
literature methods.
NR NR
Scheme 2
lower reactor and substrate temperatures (180 and 320 ЊC,
respectively) only Co3Se4 could be detected. By contrast, the
bulk pyrolysis of the selenide cluster [Co6Se8(PEt3)6] above
325 ЊC is reported to give µ-CoSe.15 On the other hand, selenid-
ation of cobalt foil at 550–700 ЊC has been reported to give
Co3Se4 films with a thin surface layer of CoSe2.16
The decomposition of complexes 9a and 9b depended to
some extent on the reaction conditions. At thermolysis tem-
peratures of 260–300 ЊC Ni6Se5 was formed, while at у300 ЊC
NiSe was produced, sometimes as a mixture with some NiSe2.
The chromium complexes 1a and 1b gave films which showed
an X-ray diffraction pattern very close to that of Cr0.68Se.
The thermolysis of the tellurium complexes 4, 6 and 8 pro-
ceeded more straightforwardly to give films of the metal ditel-
lurides MTe2 (M = Mn, Fe or Co). The chromium complexes 2a
and 2b decompose appreciably above 115 ЊC, before an
adequate sublimation rate could be reached, and attempts at
growing chromium telluride films proved unsuccessful. All
the metal chalcogenide films were checked by energy-dispersive
X-ray fluorescence (EDAX) analysis for trace impurities. There
was no evidence for phosphorus incorporation within the
detection limits of this technique.
Preparation of complexes
Most complexes were prepared from the metal amides follow-
ing closely similar procedures. Alternatively, metathesis of
MCl2 with Li[But2P(E)NR] can be used in some cases, although
yields tend to be lower. Representative methods are given below.
Method A, [Cr{But2P(Te)NC6H11}2] 2b. To a solution of
[Cr{N(SiMe3)2}2(thf)2] (1.60 g, 3.10 mmol) in light petroleum
(15 cm3) at room temperature was added But2P(Te)NHC6H11
(2.30 g, 6.20 mmol) in light petroleum (15 cm3). The dark mix-
ture was stirred for 3 h. A precipitate formed which was filtered
off and recrystallised from toluene to afford light turquoise
crystals of complex 2b (1.40 g, 57%).
The deposition of MnTe2 films from complex 4 contrasts
with the formation of MnTe from the bulk pyrolysis of pre-
cursors such as [{(Et3P)2(CO)3MnTe}2] for which no MnTe2 was
detected.10 Formation of MTe2 phases is expected on the basis
of the M :Te stoichiometry, at least at lower reaction temper-
atures where the rate of tellurium loss due to evaporation is
limited. The stoichiometries of iron tellurides were found pre-
viously to depend on the Fe:Te ratio of the precursor, with
[{Fe(cp)(CO)(PEt3)}2Te] (Fe:Te = 2:1) leading to FeTe, while
[{(Et3P)(OC)(cp)FeTe}2] (Fe:Te = 1:1) resulted in FeTe2.11a On
the other hand, another precursor with a 1:1 Fe:Te ratio,
[Fe4Te4(PEt3)4], generates FeTe.11b Both FeTe and FeTe2 are of
interest, for example, as catalysts for the oxychlorination of
propene.17
The compounds 2, 3, 4, 6, 7 and 8 were obtained similarly.
Method B, [Cr{But2P(Se)NPri}2] 1a. A solution of But2P-
(Se)NHPri (2.54 g, 9.0 mmol) in thf (100 cm3) was treated with
a 2.5  solution (3.6 cm3) of LiBun (9.0 mmol) in hexanes at
0 ЊC. The yellow solution formed was allowed to warm to room
temperature and stirred for 1 h. To this was added CrCl2 (0.55 g,
4.5 mmol) in thf (20 cm3). The reaction mixture was stirred for
4 h. After evaporation of the solvent in vacuo the residue was
extracted with toluene to give light blue crystals of complex 1a
(1.0 g, 36%).
The compounds 1b, 5a and 5b were prepared similarly. The
iron–tellurium complexes 6a and 6b can however only be
obtained using method A.
There are numerous phases Co1-xTe. Steigerweld et al.18
showed that the telluride cluster [Co6Te8(PEt3)6] is thermolysed
at 300 ЊC to give β-CoTe. This contrasts with the formation of
orthorhombic CoTe2 from complex 8 at similar temperatures
but under reduced pressure.
Method C, [Ni{But2P(Se)NPri}2] 9a. A solution of But2P-
(Se)NHPri (2.55 g, 9.0 mmol) in thf (100 cm3) was treated with
LiBun (2.5 , 3.6 cm3, 9.0 mmol) in hexanes at 0 ЊC and allowed
to warm to room temperature. To this was added a solution of
[NiCl2(PMe3)2] (1.26 g, 4.5 mmol) in thf (20 cm3) at room tem-
perature. The dark green solution was stirred for 4 h, the solvent
was removed in vacuo, and the residue extracted with toluene.
Cooling of the filtrate to Ϫ16 ЊC gave green crystals of complex
9a (1.20 g, 43%).
The thermolysis reactions of complexes 1–9 to give mono- or
di-chalcogenide solid-state products can in a simplified manner
be described as shown in Scheme 2, i.e. leading to selenium-
containing by-products where metal monoselenides are formed,
while the deposition of MTe2 phases results in tellurium-free
organic residues. The organic by-products of the thermolysis
reactions were monitored by mass spectrometry and 31P NMR
spectroscopy. The deposition of metal selenides was accom-
panied by a product mixture which was identified mainly as
But2P(Se)NHR. Similar thermolysis fragments had previously
been identified as by-products of the growth of zinc and cad-
mium chalcogenide films.5 By contrast, the deposition of MTe2
phases gave rise to tellurium-free products such as (But2P)2NHϩ
(m/z 305).
The results show that sterically hindered phosphinochalco-
genoic amides are highly suitable ligands for the synthesis of
a series of transition-metal selenium and thermally com-
paratively stable tellurium complexes which, due to their
monomeric structure and volatility, are suitable as precursors
for the gas-phase deposition of ordered transition-metal
selenide and telluride films.
Compound 9b was obtained similarly. No nickel products
could be isolated using Li[But2P(Te)NR].
Thermolysis reactions
Gas-phase depositions of metal chalcogenide films were carried
out in a horizontal reactor described earlier,14 evacuated to ca.
2 × 10Ϫ6 mbar. Glass substrates were degreased in boiling tri-
chloroethane, cleaned by a H2O2/H2SO4 treatment and washed
repeatedly with deionised water. Films were grown by placing
the precursor complex (ca. 50 mg) in a glass boat inside the all-
glass reactor which was evacuated to ca. (1–6) × 10Ϫ6 mbar
and heated in a thermostatted oven to the given sublimation
temperature of 170–230 ± 1 ЊC (cf. Table 2), while the glass
substrate was mounted on a hot-finger and kept at a higher
deposition temperature. Highly oriented specular polycrystal-
J. Chem. Soc., Dalton Trans., 1997, Pages 2689–2692
2691

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9 A. P. Coleman, R. S. Dickson, G. B. Deacon, G. D. Fallon, M. Ke,
line films were obtained, typically of 1–1.5 µm thickness after a
growth period of 1–2 h. The phases were identified by their
X-ray patterns using either Co-Kα (λ = 1.7902 Å) or Cu-Kα
(λ = 1.542 Å) radiation; either X-ray source showed the films to
be strongly oriented. The elemental composition and the
absence of phosphorus impurities was confirmed by EDAX
analysis (typical detection limit ca. 0.01% w/w).
K. McGregor and B. O. West, Polyhedron, 1994, 13, 1277.
10 M. L. Steigerwald and C. E. Rice, J. Am. Chem. Soc., 1988, 110,
4228.
11 (a) M. L. Steigerwald, Chem. Mater., 1989, 1, 52; (b) M. L.
Steigerwald, T. Siegrist and S. M. Stuczynski, Chem. Mater., 1992,
114, 3155.
12 See, for example, W. Heimbrodt, L. Gridnera, M. Happ,
F. Neugebauer, D. Suisky, N. Hoffmann and J. Griesche, J. Cryst.
Growth, 1996, 159, 1005; R. H. Mauch and K. O. Velthaus, Ger. Pat.,
DE 4 435 016 (Chem. Abstr., 1996, 124, 30 1976u); V. Nunez,
T. M. Giebultowicz, W. Faschinger, G. Bauer, H. Sitter and
J. K. Furdyna, Mater. Res. Soc. Symp. Proc., 1995, 376, 589;
J. M. Hartmann, G. Feuillet, M. Charleux and H. Mariette, J. Appl.
Phys., 1996, 79, 3035.
13 M. Bochmann, K. Webb, M. Harman and M. B. Hursthouse,
Angew. Chem., Int. Ed. Engl., 1990, 29, 638; M. Bochmann and
K. J. Webb, Mater. Res. Soc. Symp. Proc., 1991, 204, 149;
M. Bochmann, A. P. Coleman, K. J. Webb, M. B. Hursthouse
and M. Mazid, Angew. Chem., Int. Ed. Engl., 1991, 30, 973;
M. Bochmann, A. K. Powell and X. Song, J. Chem. Soc., Dalton
Trans., 1995, 1645; M. Bochmann, X. Song, M. B. Hursthouse
and A. Karaulov, J. Chem. Soc., Dalton Trans., 1995, 1649;
M. Bochmann, G. C. Bwembya, A. K. Powell and X. Song,
Polyhedron, 1995, 14, 3495.
Acknowledgements
This work was supported by the Engineering and Physical
Sciences Research Council. We are grateful to Mr S. Bennett,
University of East Anglia, for powder X-ray and EDAX
measurements.
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Received 10th April 1997; Paper 7/02460F
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