Crystal structures of mixed-ligand oxocyano complexes of molybdenum(IV) and tungsten(IV) and their reactivity towards molecular oxygen studied by IR spectroscopy

Article abstract of DOI:10.1039/b202654f

The series of compounds, (PPh₄)₂[M(CN)₄O(L)]·xH₂O [M = Mo, W; L = pyrazine (pz), pyridine (py); = phenyl group; x = 0, 2, 3], (PPh₄)₃[Mo(CN)₅O]·7H₂O and K(PPh₄)₂[Mo(CN)₅O]·5H₂O, which are able to bind molecular oxygen giving peroxo complexes (PPh₄)₂[M(CN)₄O(O₂)], have been synthesised. The substrates were characterised by thermogravimetric analysis, vibrational and UV-VIS spectroscopy and the crystal structure determination of (PPh₄)₂[M(CN)₄O(pz)]·3H₂O. The latter salts are isomorphous and consist of anions of approximat octahedral geometry, forming a three-dimensional hydrogen-bonded network with channels that enable the penetration of dioxygen. The solid state reactions of all the salts with O₂ have been studied by measuring their infrared spectra. The integrated intensities of the O-O, pz or py, MO and C≡N bands change with time according to pseudo-first-order kinetics. The rate constants k_obs range from 0.37 × 10^-4 to 1.04 × 10^-4 s^-1 at 323 K. A detailed study of the function of temperature has been undertaken for (PPh₄)₂[W(CN)₄O(pz)]·3H₂O. The activation parameters, ΔH^# = 68 ± 13 kJ mol^-1 and ΔS^# = -117 ± 39 J K^-1 mol^-1, were determined and an associative mechanism of dioxygen uptake was assumed.

Full text of DOI:10.1039/b202654f

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Crystal structures of mixed-ligand oxocyano complexes of
molybdenum(IV) and tungsten(IV) and their reactivity towards
molecular oxygen studied by IR spectroscopy
Dariusz Matoga, Janusz Szklarzewicz, Alina Samotus* and Krzysztof Lewin´ski
Faculty of Chemistry, Jagiellonian University, R. Ingardena 3, 30-060 Kraków, Poland.
E-mail: Samotus@chemia.uj.edu.pl
Received 15th March 2002, Accepted 22nd July 2002
First published as an Advance Article on the web 27th August 2002
The series of compounds, (PPh4)2[M(CN)4O(L)]ؒxH2O [M = Mo, W; L = pyrazine (pz), pyridine (py); Ph = phenyl
group; x = 0, 2, 3], (PPh4)3[Mo(CN)5O]ؒ7H2O and K(PPh4)2[Mo(CN)5O]ؒ5H2O, which are able to bind molecular
oxygen giving peroxo complexes (PPh4)2[M(CN)4O(O2)], have been synthesised. The substrates were characterised
by thermogravimetric analysis, vibrational and UV-VIS spectroscopy and the crystal structure determination of
(PPh4)2[M(CN)4O(pz)]ؒ3H2O. The latter salts are isomorphous and consist of anions of approximately octahedral
geometry, forming a three-dimensional hydrogen-bonded network with channels that enable the penetration of
dioxygen. The solid state reactions of all the salts with O2 have been studied by measuring their infrared spectra. The
᎐
integrated intensities of the O–O, pz or py, MO and C᎐N bands change with time according to pseudo-first-order
᎐
kinetics. The rate constants kobs range from 0.37 × 10Ϫ4 to 1.04 × 10Ϫ4 sϪ1 at 323 K. A detailed study of the function
of temperature has been undertaken for (PPh4)2[W(CN)4O(pz)]ؒ3H2O. The activation parameters, ∆H# = 68 13 kJ
molϪ1 and ∆S# = Ϫ117 39 J KϪ1 molϪ1, were determined and an associative mechanism of dioxygen uptake was
assumed.
Introduction
Results and discussion
The reactions of transition metal complexes with molecular
oxygen have been widely investigated for various metals,1 e.g.
Co, Fe, Mn, Cu, Ni, Ru, Rh, Pd, V, Cr, Ir, Mo, W, for over a
hundred years. Such processes have been mainly studied in solu-
tion, but there are also reports on reactions carried out in the
solid state,2 especially with polymer and silica supported
complexes.
It is characteristic that complexes of M() or M() (M = Mo,
W) have a tendency to react with H2O2 whereas those of M()
undergo reaction with molecular oxygen giving in both cases
peroxo complexes.3,4 In recent years the mixed-ligand tetra-
cyanooxo complexes of molybdenum() and tungsten() of
general formula [M(CN)4O(L)]nϪ, where L is a monodentate
ligand such as CNϪ, CH3CN, pz (pyrazine), have been found
useful in the activation of molecular oxygen.5–8 In aerated polar
organic solvents e.g. dichloromethane and acetonitrile they
react with O2 giving the same final product, (PPh4)2[M(CN)4-
O(O2)] (Ph = phenyl group). The molybdenum complex has
been structurally characterised5,7 confirming the presence of a
κ2-peroxo ligand in cis position to the MoO bond. We have
previously found that (PPh4)2[M(CN)4O(pz)]ؒ3H2O, (PPh4)3-
[W(CN)5O]ؒ7H2O and (PPh4)3[W(CN)5O] reacted with di-
oxygen in the solid state7,8 but a detailed study on the reaction
kinetics was only done for (PPh4)3[W(CN)5O].8
In this work we have explored the use of molybdenum
and tungsten oxocyano complexes as the solid substrates for
reaction with molecular oxygen. We report here the crystal
structures of two substrates that are the first structurally char-
acterised examples of hydrated tetracyanooxo complexes of
Mo and W with the ability to react with dioxygen. We have also
studied the kinetics of the solid-state reactions with O2 for all
salts as well as the influence of various ligands, cation types,
structural properties and the presence of water molecules on
this process with the aim of facilitating the attachment of O2 in
the solid state.
Characterisation of complexes
To study the influence of various factors on the solid-state
reactions with dioxygen we have obtained a series of [M(CN)4-
O(L)]nϪ type complexes (M = Mo or W) with different
monodentate ligands L = pyrazine (pz), pyridine (py) or CNϪ,
using as cations either tetraphenylphosphonium ions alone
(1–3, 6–9, 11) or the mixed cations: Kϩ and PPh4ϩ (4), Csϩ and
Naϩ (5), Kϩ and [(CH3)4N]ϩ (10) (see the Experimental section
for formulae details and numbering). We also compared the
reactivity of hydrated (6, 11) and anhydrous (8, 9) salts.
The results of the thermogravimetric analyses are gathered in
Table 1. They indicate that the dehydration of 1, 3 and 11 takes
place in two steps whereas in the other salts all of the water
molecules are liberated in one step. The weight-loss measure-
ments also show that the ligands L are released in the order:
py > pz > CNϪ and molybdenum complexes are slightly more
stable than their tungsten analogues.
UV-VIS reflectance spectra have been measured for the
molybdenum (1–3) and tungsten (6–11) salts. Each spectrum in
the VIS/near UV part consists of a low-energy asymmetric
band and a high-energy shoulder-like broad band. The second
derivative analyses indicate that there are four bands in this
region. The deconvolution of spectra into Gaussian curves
gives the maxima which are listed in Table 2. The relatively low
intensity of the four bands indicates that they correspond to
spin-allowed d–d transitions, and their number is in agreement
with the low symmetry of the complex anions (approximately
C2v for tetracyanides and C4v for pentacyanides). The highest-
energy d–d transition is taken as a measure of the ligand-field
stabilization energy; it is biggest for 10, which does not react
with dioxygen.
In the UV region for all salts (excluding 10) there are
bands at approximately 273 and 237 nm corresponding to the
tetraphenylphosphonium cation.9 Additionally for pyrazine
DOI: 10.1039/b202654f
J. Chem. Soc., Dalton Trans., 2002, 3587–3592
This journal is © The Royal Society of Chemistry 2002
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Table 1 Results of the thermogravimetric measurements
Salt
T max/K
Liberated molecules
∆m(%) Found (calc)
Decomposition temperature T /K
1
(PPh4)2[Mo(CN)4O(pz)]ؒ3H2O
359
388
428–458
348
358
332
368
338
378
330
363
328
353
2H2O
1H2O
pz
2H2O
py
5H2O
2H2O
5H2O
3H2O, pz
2H2O
py
4.2 (3.5)
1.8 (1.8)
7.9 (7.8)
3.6 (3.6)
6.6 (7.8)
6.7 (6.5)
1.9 (2.6)
9.1 (8.6)
11.1 (12.0)
3.2 (3.2)
7.2 (7.2)
–
473
2
3
(PPh4)2[Mo(CN)4O(py)]ؒ2H2O
(PPh4)3[Mo(CN)5O]ؒ7H2O
493
453
4
6
7
K(PPh4)2[Mo(CN)5O]ؒ5H2O
(PPh4)2[W(CN)4O(pz)]ؒ3H2O
(PPh4)2[W(CN)4O(py)]ؒ2H2O
453
453
463
11
(PPh4)3[W(CN)5O]ؒ7H2Oa
5H2O
2H2O
433
2.2 (2.4)
a Data obtained in the measurement with a heating rate of 5 K per minute (from ref. 6).
Table 2 Results of the second derivative analysis and deconvolution
into Gaussian curves of the reflectance spectra
face-to-face and face-to-edge geometry of interactions involv-
ing one phenyl ring of the first PPh4 and two phenyl rings of
ϩ
the second cation. These chains are separated in the structure
by layers of [M(CN)4O(pz)]2Ϫ anions parallel to the (010) plane
and layers parallel to the (001) plane occupied by water
molecules. Pairs of tetracyanides related by a centre of sym-
metry are bonded through a network of hydrogen-bonds in
which all of the water molecules are involved (Fig. 2). Water
Energy of d–d transitions
E/cmϪ1 Gaussian
Salt
deconvolution results
1
2
(PPh4)2[Mo(CN)4O(pz)]ؒ3H2O
(PPh4)2[Mo(CN)4O(py)]ؒ2H2O
(PPh4)3[Mo(CN)5O]ؒ7H2O
(PPh4)2[W(CN)4O(pz)]ؒ3H2O
(PPh4)2[W(CN)4O(py)]ؒ2H2O
(PPh4)2[W(CN)4O(pz)]
(PPh4)3[W(CN)5O]
K(Me4N)2[W(CN)5O]
(PPh4)3[W(CN)5O]ؒ7H2O
25800, 22820, 17070, 14660
30410, 28520, 16830, 14670
25990, 23200, 16250, 13330
24750, 21770, 17840, 15510
28590, 23410, 16380, 13130
24360, 20680, 16730, 14080
25380, 21230, 17760, 14510
32860, 29570, 18300, 15370
24960, 21210, 16700, 14490
3
6
7
8
9
10
11
tetracyanides there is one more band in this region at about
310 nm which can be ascribed to the electronic transitions in
pyrazine itself.9 Pyridine also absorbs around 305 nm but its
molar absorption coefficient is about 10 times smaller than that
for pyrazine10 and the band is not observed in the spectra.
Description of the structures of 1 and 6
Both salts, 1 and 6 were found to be isomorphous with only
slightly different bond distances and angles. The crystal struc-
ture consists of [M(CN)4O(pz)]2Ϫ anions, two tetraphenyl-
phosphonium cations and three water molecules in the
asymmetric part of the unit cell (Fig. 1). The structure com-
prises infinite chains of tetraphenylphosphonium cations
propagating along the a direction which are stabilized by π
stacking. They form two antiparallel strands of alternating
Fig. 2 Partial projection of the structure of (PPh4)2[W(CN)4O(pz)]ؒ
3H2O (6) onto the (100) plane showing the hydrogen-bond network
(dashed lines) connecting anions and water molecules.
molecules play two distinct roles in the structure. Molecules O2
and O3 form a four-membered ring around a centre of
symmetry and make hydrogen-bonds to cyano ligands of
molecules from different layers. The third water molecule forms
a bridge between one of the cyano ligands and a CH group of
the pyrazine ring in the neighbouring anion. The position of
this water molecule is close to the crossing of layers that separ-
ate chains of tetraphenylphosphonium cations and is not
stabilised by strong hydrogen-bonds. The refinement of the
crystal structure of 1 and 6 showed that multiple alternative
positions for this O4 water molecule are possible. Two types of
water molecules were also distinguished for 1 in the thermo-
gravimetric measurement (Table 1).
Fig. 1 Partial view of the structure of (PPh4)2[W(CN)4O(pz)]ؒ3H2O
(6) along the a direction. H atoms are omitted for clarity.
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Table 3 Selected bond lengths (Å) and angles (Њ) for (PPh4)2[M(CN)4-
The partial projection with the phenyl rings along the a direc-
tion (Fig. 1) permits the observation of the channel between
two adjacent tetracyanides and the O4 water molecules. Such
channels enable the penetration of molecular oxygen into the
structures making the sites along them susceptible to attack by
dioxygen.
O(pz)]ؒ3H2O (M = Mo 1, M = W 6) with estimated standard deviations
in parentheses
1 (M = Mo)
1.662(2)
2.156(3)
2.155(3)
2.171(3)
2.169(3)
2.569(3)
1.137(4)
1.144(4)
1.139(4)
1.132(4)
1.325(4)
1.333(5)
1.396(6)
1.295(6)
1.316(6)
1.381(6)
6 (M = W)
1.686(2)
2.142(3)
2.148(3)
2.142(3)
2.144(3)
2.521(3)
1.145(4)
1.139(4)
1.153(4)
1.148(4)
1.328(4)
1.334(5)
1.385(5)
1.298(6)
1.328(6)
1.376(6)
M–O1
M–C1
M–C2
M–C3
M–C4
M–N5
C1–N1
C2–N2
C3–N3
C4–N4
N5–C5
N5–C8
C5–C6
N6–C6
N6–C7
C7–C8
The crystal structures of 1 and 6 showing the atomic number-
ing of the anions are represented by the example of 6 in Fig. 3.
O1–Mo–C1
O1–Mo–C2
O1–Mo–C3
O1–Mo–C4
O1–Mo–N5
C1–Mo–C2
C1–Mo–C3
C1–Mo–C4
C2–Mo–C3
C2–Mo–C4
C3–Mo–C4
N1–C1–Mo
N2–C2–Mo
N3–C3–Mo
N4–C4–Mo
N5–Mo–C1
N5–Mo–C2
N5–Mo–C3
N5–Mo–C4
99.66(12)
99.13(12)
100.68(12)
100.59(12)
175.65(10)
89.78(11)
159.61(12)
88.10(11)
88.44(11)
160.25(12)
86.76(11)
177.9(3)
176.6(3)
179.7(4)
173.7(3)
79.51(10)
76.63(10)
80.32(10)
83.68(10)
99.26(12)
99.16(12)
100.75(12)
100.48(12)
175.97(9)
89.55(11)
159.93(12)
88.41(11)
88.82(11)
160.33(12)
86.44(11)
177.9(3)
177.1(3)
179.5(3)
174.1(3)
79.69(10)
76.98(10)
80.46(11)
83.41(10)
Fig. 3 Structure of the anion [W(CN)4O(pz)]2Ϫ in the salt 6, showing
the atomic numbering. The atomic numbering in the anion of 1 is
identical.
The complex anions exhibit distorted octahedral geometries
and their symmetry is approximately C2v.The oxo ligand and
pyrazine occupy axial positions, and the four cyanides are
equatorial. Central atoms are displaced towards the oxo ligand
and the average O1–M–C angles are 100.0Њ for 1 and 99.9Њ for 6.
Selected bond lengths and angles are summarised in Table 3.
The Mo–O1 bond distance in 1 (1.662 Å) is shorter than the
corresponding bond in the tungsten salt (1.686 Å). All these
bonds are relatively short and can be treated according to the
classification of Cotton11 as being almost triple ones (MO ≈
1.65 Å). The M–C bond distances are almost the same within
the structure for 6 and the average value is 2.144 Å whereas for
1 two pairs of M–C bond lengths are observed with averages of
2.156 Å and 2.170 Å. For the ligand in trans position to the
M–O1 bond (pyrazine) the Mo–N5 distance in 1 is 2.569 Å and
is longer than the W–N5 distance in 6 (2.521 Å). It is also the
longest bond of this type yet observed among all the character-
ized tetracyanooxo complexes with monodentate ligands.12
Typical IR spectral changes occurring in air are exemplified
for salt 6 in Fig. 4. They show the decrease in intensity of the
substrate bands corresponding to metal–oxygen [νmax(WO)s]
vibrations at 969 cmϪ1 and those of the ligand in trans position
to WO [νmax(pz) at 1037 cmϪ1], which is accompanied by an
increase in intensity of the product bands ascribed to (WO)p at
933 cmϪ1 and O–O vibrations at 871 cmϪ1, characteristic for
(PPh4)2[W(CN)4O(O2)].7,8 While the reaction is proceeding the
᎐
intensities of the C᎐N bands of the substrates decrease which is
᎐
typical for complexes with formal oxidation states  and . The
C᎐N signal in the product is very weak (see the inset in Fig. 4)
and so is not observed in the spectra recorded for thin layers.
During the reaction of salts 1–4, 6–8 and 11 with dioxygen the
integrated intensities of (MO)s, (MO)p, O–O, pz or py (L) and
C᎐N bands change with time according to pseudo-first-order
᎐
᎐
᎐
᎐
kinetics. Their changes are exemplified for salt 6 in Fig. 5. The
values of the pseudo-first-order rate constants, kobs obtained
from the exponential fits (eqn. (4)) are given in Table 4.
The rate constants of the hydrated molybdenum salts are
similar with a tendency to decrease in the order L: py > pz >
CNϪ. In the case of the hydrated tungsten salts the order
according to the decreasing value of kobs is: pz > py. The salt
with L = CNϪ (11) undergoes dehydration at the measurement
temperature and thus is not included in the tungsten series. The
fastest incorporation of dioxygen occurs for 9 and the reaction
proceeds two times faster for 6 than for 7 and 8 which have
approximately the same rate constants (Table 4). The relatively
weak dependence of rate constants on various leaving groups is
favourable for an associative mechanism with dioxygen uptake
as a rate-limiting step.
Solid-state kinetics with molecular oxygen
We have found that all tetraphenylphosphonium salts 1–4, 6–9,
11 react in the solid state with dioxygen according to the overall
stoichiometry illustrated by eqn. (1)–(3):
(PPh4)2[MIV(CN)4O(L)]ؒxH2O ϩ O2
(PPh4)2[MVI(CN)4O(O2)] ϩ L ϩ xH2O (1)
where L = pz or py; x = 0, 2 or 3
(PPh4)3[MIV(CN)5O]ؒxH2O ϩ O2
(PPh4)2[MVI(CN)4O(O2)] ϩ (PPh4)CN ϩ xH2O (2)
where x = 0 or 7
We have observed that dicaesium sodium pentacyanomolyb-
date(), 5 and bis(tetramethylammonium) potassium penta-
cyanooxotungstate(), 10 do not react with molecular oxygen.
K(PPh4)2[MoIV(CN)5O]ؒ5H2O ϩ O2
(PPh4)2[MVI(CN)4O(O2)] ϩ KCN ϩ 5H2O (3)
J. Chem. Soc., Dalton Trans., 2002, 3587–3592
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Fig. 4 The selected IR bands of (PPh4)2[W(CN)4O(pz)]ؒ3H2O (6) kept in air at 313 K. Curve 1: initial spectrum. Curves 2–6: IR spectra recorded
after 1 h 43 min, 3 h 43 min, 24 h 9 min, 45 h 56 min and 117 h 26 min of reaction with dioxygen, respectively. The inset in the top left corner presents
the 2060–2150 cmϪ1 range. For comparison the IR spectrum of the product, (PPh4)2[W(CN)4O(O2)] is given in the bottom left corner. Numbers
indicate the band positions, ν/cmϪ1
.
Table 4 The kinetic data for the reaction with molecular oxygen in the
solid state at 323 K monitored by the IR technique
Table 5 Kinetic data for the reaction of (PPh4)2[W(CN)4O(pz)]ؒ3H2O
(6) with molecular oxygen in the solid state
Salt
kobs × 104/sϪ1
T /K
kobs × 105/sϪ1
Thermodynamic parameters
1
2
3
4
5
6
7
8
(PPh4)2[Mo(CN)4O(pz)]ؒ3H2O
(PPh4)2[Mo(CN)4O(py)]ؒ2H2O
(PPh4)3[Mo(CN)5O]ؒ7H2O
K(PPh4)2[Mo(CN)5O]ؒ5H2O
Cs2Na[Mo(CN)5O]
(PPh4)2[W(CN)4O(pz)]ؒ3H2O
(PPh4)2[W(CN)4O(py)]ؒ2H2O
(PPh4)2[W(CN)4O(pz)]
0.54 0.04
0.65 0.08
0.37 0.09
0.48 0.12
does not react
1.04 0.13
0.49 0.08
0.45 0.05
0.035 0.016a
1.62 0.24
does not react
295
301
308
313
317
320
323
0.20 0.08
0.80 0.06
1.27 0.12
1.7 0.1
3.1 0.2
3.0 0.2
∆H# = 68 13 (kJ molϪ1
∆S# = Ϫ117 39 (J KϪ1 molϪ1
)
)
10.4 1.3
this reaction in the solid state needs a bulky aromatic cation, e.g.
the tetraphenylphosphonium one. Such cations seem to form
loose structures with channels that enable the penetration of
dioxygen into the crystals as was found for 1 and 6.
9
10
(PPh4)3[W(CN)5O]
K(Me4N)2[W(CN)5O]
a Measured at 293 K.
To study the influence of water molecules on the reaction
rate, we have compared the kinetics of the pair of anhydrous 8
and hydrated 6 tungsten salts with pyrazine. At room temper-
ature the rate constant is bigger for the anhydrous salt (kobs
=
0.35 × 10Ϫ5 sϪ1 at 293 K) than for hydrated one (kobs = 0.20 ×
10Ϫ5 sϪ1 at 295 K). At 323 K the opposite relation is observed
(Tables 4 and 5). Thus, at room temperature the lack of water
molecules facilitates the reaction. At higher temperatures, how-
ever, it seems that the rate for the anhydrous salt is limited by
the diffusion of O2 into the crystal. It may be due to structure
collapse after dehydration (it proved to be irreversible for
6) with decay of the channels used for the penetration of
dioxygen. Reversible dehydration was previously reported8 for
salt 11 and the rate constant of its dehydrated salt 9 is the
biggest of all the salts (Table 4). Thus, we suggest that dehydra-
tion favours the reaction with molecular oxygen unless it is
accompanied by structural collapse. The collapse hinders the
reaction with O2 which can be particularly seen at higher
temperatures when diffusion takes control over the process.
In the case of salt 6 the reaction with dioxygen was moni-
tored at various temperatures and the values of the rate con-
stants together with the thermodynamic parameters, ∆H# and
∆S#, obtained by plotting ln(kobs/T ) versus 1/T (Fig. 6) and
Fig. 5 The changes in the peak areas of selected bands in the IR
spectrum of (PPh4)2[W(CN)4O(pz)]ؒ3H2O (6), reacting in the solid state
with molecular oxygen at 313 K, versus time.
We have also found that all salts with tetraphenylphosphonium
cations as well as salt 4 with mixed cations, Kϩ and PPh4ϩ, are
reactive towards O2. These results indicate that the substrate for
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I0 is the integrated intensity at time t = 0. The final pseudo-first-
order rate constants, kobs for each salt were averaged over three
values of ki.
Syntheses
All salts: (PPh4)2[Mo(CN)4O(pz)]ؒ3H2O (1);7 Cs2Na[Mo-
(CN)5O] (5);15 (PPh4)2[W(CN)4O(pz)]ؒ3H2O (6);7 (PPh4)3-
[W(CN)5O] (9)8 and (PPh4)3[W(CN)5O]ؒ7H2O (11)8 were
synthesised according to the methods described by us earlier.
Their purity was confirmed by IR spectroscopy.
Bis(tetraphenylphosphonium)
tetracyanooxopyridinemolyb-
date(IV) dihydrate, (PPh4)2[Mo(CN)4O(py)]ؒ2H2O (2). The
anhydrous salt, (PPh4)2[Mo(CN)4O(py)] has been previously
mentioned by Arzoumanian et al. as being obtained from
(PPh4)3[Mo(CN)5O].16 The salt 2 was prepared by dissolving
K3Na[Mo(CN)4O2]ؒ6H2O (0.42 g, 0.87 mmol) in water (7 cm3).
The pH of the solution was adjusted to ca. 9.0 with HCl (3 M)
and then pyridine (1 cm3, 14.8 mmol) was added followed by
(PPh4)Cl (0.75 g, 2 mmol). The resulting green crystals of 2
(0.37 g, 43%) were filtered off, washed two times with a small
amount of water and dried in air (Found: C, 67.5; H, 4.9;
N, 7.5. C57H49MoN5O3P2 requires C, 67.8; H, 4.9; N, 6.9%);
λmax/nm (CH2Cl2 under N2) 647 (εmax/dm3 molϪ1 cmϪ1 49);
νmax/cmϪ1 (MoO) 963vs and (CN) 2089m, 2098m and 2111vw
(KBr). The salt is insoluble in water and acetone but soluble in
such polar organic solvents as C2H5OH, CH3CN and CH2Cl2.
Fig. 6 The plot of ln(kobs/T ) versus 1/T for (PPh4)2[W(CN)4O(pz)]ؒ
3H2O (6).
calculating the values of the slope and the intercept by linear
regression, are summarised in Table 5. The negative value of the
entropy of activation implies the associative mechanism of O2
incorporation. Thus, the first stage of the reaction seems to
involve nucleophilic attack of O2 and electron transfer from
MIV to O2, which is responsible for the rapid decrease in the
intensity of the cyanide bands in all of the salts (Fig. 5). In the
next step the ligand in trans position to the MO bond is released
which is followed by rearrangement of the coordination sphere
and the formation of a side-on peroxo ligand at the metal
centre. However, the comparison of these data with solution
kinetic measurements, carried out for (PPh4)3[W(CN)5O]ؒ7H2O
reacting with O2 in ethanol–acetone under pseudo-first-order
conditions,8 shows that the reaction may proceed according to
the more complicated mechanism proposed for the reaction in
solution.
Tris(tetraphenylphosphonium) pentacyanooxomolybdate(IV)
heptahydrate, (PPh4)3[Mo(CN)5O]ؒ7H2O (3). We modified the
method of synthesis described by Wieghardt et al.17 using
Cs2Na[Mo(CN)5O] and KCN as starting materials. The reac-
tion temperature was also lowered from 313 K to ca. 293 K. The
salt 3 was prepared by dissolving Cs2Na[Mo(CN)5O] (5) (0.16 g,
0.29 mmol) and KCN (0.42 g, 8.6 mmol) in water (10 cm3).
Then a solution of (PPh4)Cl (0.34 g, 0.91 mmol) in water
(5 cm3) was added. The mixture was left for two days at room
temperature in air for crystallization. The resulting green
crystals of 3 (0.3 g, 76%) were filtered off, washed several times
with water and dried in air (Found: C, 66.3; H, 5.5; N, 5.0.
C77H74MoN5O8P3 requires C, 66.7; H, 5.4; N, 5.0%); νmax/cmϪ1
(MoO) 933s and (CN) 2079s and 2102vw (KBr).
Experimental
Starting materials and general procedures
The starting materials for the syntheses, K3Na[M(CN)4O2]ؒ
6H2O (M = Mo, W) were prepared as described in the liter-
ature.13,14 All ligands, other reagents and solvents were of ana-
lytical grade (Sigma-Aldrich or POCh) and used as supplied.
Carbon, hydrogen and nitrogen were determined by con-
ventional organic microanalysis. UV-VIS absorption spectra
were recorded on a Shimadzu UV 2101PC or on a Varian Cary
50 Conc spectrophotometers. Reflectance spectra were meas-
ured in BaSO4 pellets versus BaSO4 as reference (Shimadzu UV
2101PC with ISR-260 attachment). IR spectra were measured
as KBr pellets on a Bruker IFS 48 spectrometer. Thermogravi-
metric analysis was performed on a Mettler thermoanalyser
TGA/SDTA 851, under argon with a heating rate of 2 K per
minute. The solid-state kinetics was studied by measuring
IR spectra at 323 K ( 1 K) using NaCl plates covered with
thin layers of the salts 1–10 which under these conditions
transformed to the peroxo salts, (PPh4)2[Mo(CN)4O(O2)] or
(PPh4)2[W(CN)4O(O2)]. For salt 6 the monitoring was carried
out additionally at 295, 301, 313, 317 and 320 K ( 1 K) and for
salt 8 at 293 K. The spectra (measured in absorbance mode)
were collected in time t and the integrated intensities It of the
decreasing MO band ((MO)s) of the substrate as well as the
increase of both the O–O and MO ((MO)p) bands of the prod-
uct formed were taken for kinetic calculations for each salt. The
Bis(tetraphenylphosphonium) potassium pentacyanooxomolyb-
date(IV) pentahydrate, K(PPh4)2[Mo(CN)5O]ؒ5H2O (4). The salt
was prepared by dissolving K3Na[Mo(CN)4O2]ؒ6H2O (0.5 g,
1 mmol) and KCN (0.1 g, 2 mmol) in water (10 cm3). The pH of
the solution was adjusted to ca. 9.0 with HCl (3 M) and then
(PPh4)Cl (1.2 g, 3.2 mmol) was added. The resulting green crys-
tals of 4 (0.56 g, 53%) were filtered off, washed several times
with water and dried in air (Found: C, 61.3; H, 4.6; N, 6.5.
C53H50KMoN5O6P2 requires C, 60.6; H, 4.8; N, 6.7%); νmax
/
cmϪ1 (MoO) 937s and (CN) 2079s, 2094vw and 2104vw (KBr).
Bis(tetraphenylphosphonium)
tetracyanooxopyridinetung-
state(IV) dihydrate, (PPh4)2[W(CN)4O(py)]ؒ2H2O (7). The salt
was prepared by changing the proportions of substrates in the
synthesis described by Roodt et al.18 who obtained (PPh4)2-
[W(CN)4O(py)]ؒ8H2O. The salt 7 was prepared by dissolving
K3Na[W(CN)4O2]ؒ6H2O (0.34 g, 0.59 mmol) in water (7 cm3).
The pH of the solution was adjusted to ca. 7.0 with HCl (3 M)
and then pyridine (1 cm3, 14.8 mmol) was added followed by
(PPh4)Cl (0.5 g, 1.47 mmol). The resulting green crystals of 7
(0.33 g, 51%) were filtered off, washed two times with a small
amount of water and dried in air (Found: C, 62.4; H, 4.5; N,
6.5. C57H49N5O3P2W requires C, 62.4; H, 4.5; N, 6.4%); λmax/nm
(CH2Cl2 under N2) 614 (εmax/dm3 molϪ1 cmϪ1 69); νmax/cmϪ1
(WO) 960vs and (CN) 2076m and 2083m (KBr). The salt is
insoluble in water and acetone but soluble in such polar organic
solvents as C2H5OH, CH3CN and CH2Cl2.
ϩ
strong band of PPh4 at 1106 cmϪ1 was used as an internal
intensity standard. The time dependence of It for each band i
was fitted to eqn. (4).
It = I∞ ϩ (I0 Ϫ I∞)exp(Ϫkit)
(4)
The adjustable parameters were I0, I∞ and the pseudo-first-
order rate constants, ki. I∞ is the integrated intensity at t = ∞ and
J. Chem. Soc., Dalton Trans., 2002, 3587–3592
3591

View Article Online
Table 6 Selected crystallographic data for (PPh4)2[Mo(CN)4O(pz)]ؒ
3H2O (1) and (PPh4)2[W(CN)4O(pz)]ؒ3H2O (6)
O4 is positionally disordered with multiple alternative positions
of low occupancy not included in the refinement. In the final
refinement cycle all non-hydrogen atoms except for O4 were
refined anisotropically. The largest peaks in the final difference
maps were located near the Mo and W atoms. All calculations
were performed using SHELXL; scattering factors and anom-
alous dispersion factors were those given in SHELXL.19 The
molecular structure drawings were made with the ORTEP-III
program.20
1
6
Empirical formula
M
C56H50MoN6O4P2
1028.90
C56H50N6O4P2W
1116.81
T /K
Crystal system
Space group
293(2)
293(2)
Triclinic
Triclinic
¯
¯
P1
P1
a/Å
b/Å
c/Å
α/Њ
13.5730(2)
13.6890(2)
16.9070(3)
69.3040(7)
89.2790(6)
62.1020(6)
2552.37(7)
2
13.6050(2)
13.68400(10)
16.8940(3)
69.2620(5)
89.2020(5)
61.8950(5)
2549.61(6)
2
CCDC reference numbers 181899 and 181900.
See http://www.rsc.org/suppdata/dt/b2/b202654f/ for crystal-
lographic data in CIF or other electronic format.
β/Њ
γ/Њ
Acknowledgements
V/Å3
Z
This work was supported in part by the Polish Research
Committee, KBN, Grant no. 3T09A 057 17.
ρcalc/Mg mϪ3
1.339
0.372
1.455
2.380
µ/mmϪ1
Reflections collected
Independent reflections
Rint
20030
11650
0.0212
1.076
19887
11621
0.0211
1.006
References
Goodness of fit on F 2
Final R indices [I>2σ(I)]
R1
1 (a) M. L. Tobe and J. Burgess, Inorganic Reaction Mechanisms,
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Chem., 1977, 39, 423.
0.0506
0.1355
0.0279
0.0669
wR2
Bis(tetraphenylphosphonium)
tetracyanooxopyridinetung-
state(IV), (PPh4)2[W(CN)4O(pz)] (8). The anhydrous salt was
obtained by dehydration of (PPh4)2[W(CN)4O(pz)]ؒ3H2O (6) in
a desiccator over P4O10 under anaerobic conditions. After four
days of dehydration a mass loss of 4.89% was observed which
corresponds to the release of three water molecules (4.84%);
νmax/cmϪ1 (WO) 969vs and (CN) 2069m, 2078w and 2085vw
(KBr).
3 M. H. Dickman and M. T. Pope, Chem. Rev., 1994, 94, 569.
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12 A. Samotus, J. Szklarzewicz and D. Matoga, Bull. Pol. Acad. Sci.,
Chem., 2002, 50, 145, and refs. therein.
Bis(tetramethylammonium) potassium pentacyanooxotung-
state(IV), K[(CH3)4N]2[W(CN)5O] (10). The salt was prepared
by dissolving K3Na[W(CN)4O2]ؒ6H2O (1.5 g, 2.64 mmol) and
KCN (0.34 g, 5.22 mmol) in water (10 cm3). The pH of the
mixture was adjusted to ca. 8.7 with HCl (3 M) and then
[(CH3)4N]Br (1.4 g, 9.08 mmol) was added. The resulting blue
precipitate of 10 (0.13 g, 11%) was filtered off, washed several
times with ethanol and dried in air (Found: C, 30.1; H, 4.9;
N, 18.4. C13H24KN7OW requires C, 30.2; H, 4.6; N, 19.0%);
νmax/cmϪ1 (WO) 935s and (CN) 2077vs and 2108vw (sh) (KBr).
The salt is insoluble in C2H5OH, CH3CN, acetone and CH2Cl2
but soluble in water.
13 A. Samotus, M. Dudek and A. Kanas, J. Inorg. Nucl. Chem., 1975,
37, 943.
X-Ray structure determination
14 A. Roodt, S. S. Basson and J. G. Leipoldt, Polyhedron, 1994, 13, 599.
15 M. Dudek and A. Samotus, Transition Met. Chem., 1985, 10, 271.
16 H. Arzoumanian, A. Bouraoui, V. Lazzeri, M. Rajzmann and
H. Teruel, New J. Chem., 1992, 16, 965.
17 K. Wieghardt, G. Backes-Dahmann, W. Holzbach and W. J.
Swiridoff, Z. Anorg. Allg. Chem., 1983, 499, 44.
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Met. Chem., 1988, 13, 336.
19 G. M. Sheldrick, SHELXL97, University of Göttingen, Germany,
1997.
Crystal data for these salts, and a summary of data collection
and structure refinement parameters, are given in Table 6.
The position of the Mo, W and P atoms was determined by
Patterson methods; the remaining non-hydrogen atoms were
located in successive difference Fourier syntheses. The hydrogen
atoms of the pyrazine and phenyl rings were included in the
structure factor calculations at idealised positions and were not
refined. The hydrogen atoms of water molecule O2 were located
from a difference Fourier map and included at fixed positions,
and those of O3 and O4 could not be located. Water molecule
20 M. N. Burnett and C. K. Johnson, ORTEP-III, Report ORNL-6895,
Oak Ridge National Laboratory, TN, USA, 1996.
3592
J. Chem. Soc., Dalton Trans., 2002, 3587–3592