Syntheses and crystal structure of first octahedral d-metal complexes containing three and four isocyanato ligands, mer-[Mo(NCO)3py 3]·2py and trans-(py2H)[Mo(NCO)4py 2]

Article abstract of DOI:10.1016/j.inoche.2005.01.013

By refluxing of a mixture of (NH₄)₂[MoCl ₅(H₂O)] and KOCN in pyridine, the neutral mer-[Mo(NCO)₃py₃] and anionic trans-[Mo(NCO) ₄py₂]^- species originated simultaneously at reflux temperature. After a separation of the water-unsoluble neutral and water-soluble ionic species, the single crystals of compounds [Mo(NCO) ₃py₃]·2py (1) and (py₂H)[Mo(NCO) ₄py₂] (2) have been prepared and crystal structures of both were determined by X-ray crystallography.

Full text of DOI:10.1016/j.inoche.2005.01.013

Inorganic Chemistry Communications 8 (2005) 397–400
www.elsevier.com/locate/inoche
Syntheses and crystal structure of first octahedral d-metal
complexes containing three and four isocyanato ligands,
mer-[Mo(NCO)3py3] Æ 2py and trans-(py2H)[Mo(NCO)4py2]
ˇ
Nives Kitanovski, Amalija Golobic, Boris Ceh
*
ˇ
ˇ ˇ
Faculty of Chemistry and Chemical Technology, University of Ljubljana, P.O. Box 537, Askerceva 5, 1000 Ljubljana, Slovenia
Received 4 August 2004; accepted 21 January 2005
Abstract
By refluxing of a mixture of (NH4)2[MoCl5(H2O)] and KOCN in pyridine, the neutral mer-[Mo(NCO)3py3] and anionic trans-
[Mo(NCO)4py2]ꢀ species originated simultaneously at reflux temperature. After a separation of the water-unsoluble neutral and
water-soluble ionic species, the single crystals of compounds [Mo(NCO)3py3] Æ 2py (1) and (py2H)[Mo(NCO)4py2] (2) have been pre-
pared and crystal structures of both were determined by X-ray crystallography.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Molybdenum(III); Isocyanate; Pyridine; Crystal structure
In the last 30 years, numerous transition metal com-
plexes containing a mononuclear octahedral halogeno-
pyridine/picoline species of type mer-[MX3L3] and
trans/cis-[MX4L2]z (M = transition metal; X = Cl, Br,
I; L = pyridine (py), 4-methylpyridine (pic); z =
+1, 0, ꢀ1) were prepared and structurally characterized.
Much more rare are corresponding compounds contain-
ing pseudo halogeno ligands like NCS and NCO, respec-
tively. The crystal structure of only one mer-complex,
crystalline form as mer-[Mo(NCO)3py3] Æ 2py (1) and
trans-(py2H)[Mo(NCO)4py2] (2) [7], the structures of
which were determined by
X-ray diffraction analysis [8].
a
single crystal
The molecular structure of the compound 1 is shown
in Fig. 1 with selected bond distances and angles in the
caption of the figure. The central molybdenum atom is
surrounded by six N-donor ligands, which constitute a
typical distorted octahedral coordination sphere with a
mer ligand arrangement of pyridine molecules and isocy-
anate groups. There is almost no difference between the
Mo and N distances for NCO groups, which are in the
[Os(NCS)3py3] [1], and
a
few trans-compounds,
(picH)2[Mn(NCS)4pic2] Æ 2pic [2] and (picH)2 [Fe(NCS)4
pic2] Æ 2pic [2], Hg[Co(NCS)4py2] [3], and (py2H) [Mo
(NCS)4py2] [4] have been determined but none of the
isocyanate complex of related stoichiometry has been
noticed in the literature. We described here a synthesis
[5], a separation of neutral [Mo(NCO)3py3] and ionic
[Mo(NCO)4py2]ꢀ species [6], subsequently isolated in a
˚
range 2.080(4)–2.092(4) A. Similar differences were
found also for the Mo–N distances for the pyridine mol-
˚
ecules, which are between 2.196(3) and 2.207(3) A. The
N–Mo–N angles range from 88.36(13)ꢁ to 91.98(14)ꢁ
and deviate less than 2ꢁ from the ideal value of 90ꢁ.
The N–C–O ligands are almost perfectly linear, the an-
gles being in the range 178.6(6)–179.9(5)ꢁ. The angle be-
tween the axial pyridine rings is 87.5(3)ꢁ, which means
nearly ideal staggered conformation. The dihedral
*
Corresponding author. Tel.: +386 1 2419 110; fax: +386 1 2419
220.
ˇ
E-mail address: boris.ceh@uni-lj.si (B. Ceh).
1387-7003/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.01.013

398
N. Kitanovski et al. / Inorganic Chemistry Communications 8 (2005) 397–400
Fig. 2. Molecular structure of 2 (labeled atoms from the asymmetric
˚
unit). Selected bond lenghts (A) and angles (ꢁ): Mo–N(1) 2.096(3),
Fig. 1. Molecular structure of 1 (labeled atoms from the asymmetric
˚
Mo–N(2) 2.098(3), Mo–N(3) 2.183(3), Mo–N(4) 2.198(3), O(1)–C(1)
1.198(5), O(2)–C(2) 1.197(5), N(1)–C(1) 1.155(4), N(2)–C(2) 1.152(4),
N(3)–C(3) 1.336(5, N(3)–C(7) 1.349(5), N(4)–C(8) 1.340(4), C(3)–C(4)
1.379(7), C(4)–C(5) 1.362(8), C(5)–C(6) 1.369(8), C(6)–C(7) 1.372(7),
C(8)–C(9) 1.376(5), C(9)–C(10) 1.361(5), N(5)ꢁ ꢁ ꢁN(6) 2.706(6), N(5)–
H(56) 1.04(9), N(6)ꢁ ꢁ ꢁH(56) 1.68(9) and N(1)–Mo–N(2) 178.89(12),
N(1)–Mo–N(3) 89.65(9), N(1)–Mo–N(4) 90.46(9), N(1)–Mo–N(1)
90.72(10), N(1)–Mo–N(2) 89.95(10), N(2)–Mo–N(3) 89.47(9), N(2)–
Mo–N(4) 90.42(9), N(2)–Mo–N(2) 89.36(10), N(3)–Mo–N(4)
179.84(14), Mo–N(1)–C(1) 175.1(3), Mo–N(2)–C(2) 171.3(3), Mo–
N(3)–C(3) 121.4(3), Mo–N(3)–C(7) 121.1(3), C(3)–N(3)–C(7) 117.4(4),
Mo–N(4)–C(8) 120.9(2), C(8)–N(4)–C(8) 118.3(3), O(1)–C(1)–N(1)
179.3(4), O(2)–C(2)–N(2) 178.5(4), N(3)–C(3)–C(4) 122.9(4), C(3)–
C(4)–C(5) 119.0(5), C(4)–C(5)–C(6) 118.9(5), C(5)–C(6)–C(7) 119.6(5),
N(3)–C(7)–C(6) 122.1(4), N(4)–C(8)–C(9) 121.8(3), C(8)–C(9)–C(10)
119.5(4), C(9)–C(10)–C(9) 119.0(5), N(5)–H(56)ꢁ ꢁ ꢁN(6) 169(9).
unit). Selected bond lenghts (A) and angles (ꢁ): Mo(1)–N(1) 2.088(3),
Mo(1)–N(2) 2.080(4), Mo(1)–N(3) 2.092(4), Mo(1)–N(4) 2.197(3),
Mo(1)–N(5) 2.196(3), Mo(1)–N(6) 2.207(3), O(1)–C(1) 1.192(6),
O(2)–C(2) 1.195(8), O(3)–C(3) 1.190(7), N(1)–C(1) 1.159(5), N(2)–
C(2) 1.137(7), N(3)–C(3) 1.141(6) and N(1)–Mo(1)–N(2) 91.98(14),
N(1)–Mo(1)–N(3) 177.02(14), N(1)–Mo(1)–N(4) 90.19(13), N(1)–
Mo(1)–N(5) 90.93(12), N(1)–Mo(1)–N(6) 88.75(13), N(2)–Mo(1)–
N(3) 90.90(14), N(2)–Mo(1)–N(4) 91.02(13), N(2)–Mo(1)–N(5)
89.51(13), N(2)–Mo(1)–N(6) 179.25(14), N(3)–Mo(1)–N(4) 89.02(13),
N(3)–Mo(1)–N(5) 89.83(13), N(3)–Mo(1)–N(6) 88.36(13), N(4)–
Mo(1)–N(5) 178.74(13), N(4)–Mo(1)–N(6) 89.10(12), N(5)–Mo(1)–
N(6) 90.35(12), O(1)–C(1)–N(1) 179.9(5), O(2)–C(2)–N(2) 178.6(6),
O(3)–C(3)–N(3) 179.3(6).
angles between the (least-square) plane Mo–N2–N4–
N5–N6 and the pyridine rings containing N4, N5 and
N6 atoms are 42.9(2)ꢁ, 49.7(2)ꢁ and 53.8(2)ꢁ,
respectively.
The molecular structure of the compound 2 is shown
in Fig. 2 with selected bond distances and angles in the
caption of the figure. Four NCO and two Npy donor
atoms depict an elongated octahedron around molybde-
num atom. In both species, py2H+ and [Mo(N
CO)4py2]ꢀ, only one of the pyridine rings lays in a mir-
ror plane. This requires a perfect staggered conforma-
tion of the pyridine rings in both ions. The Mo–NCO
cis bounded NCO groups are part of the octahedral
coordination sphere, and the Mo–NCO distances are a
bit longer [9].
The results of thermal gravimetric analyses (TGA) of
compounds 1 and 2 are shown in Fig. 3 [10]. The initial
sharp mass-loss step of 23.7% within the range 25–80 ꢁC
in 1 corresponds to the complete removal of two weakly
˚
distances 2.096(3) and 2.098(3) A are slightly longer
and, oppositely, the mean Mo–Npy length of 2.183(3)
˚
and 2.198(3) A is slightly shorter than those in 1. The
N–Mo–N angles deviate less than 0.7ꢁ from the ideal va-
lue of 90ꢁ. The pyridine molecule and pyridinium cation
in py2H+ are held together by the strong hydrogen bond
˚
with the Nꢁ ꢁ ꢁN distance of 2.706(6) A and N–Hꢁ ꢁ ꢁN an-
gle of 169(9)ꢁ. Until now, the X-ray structures of less
than a dozen species have been determinated in which
the NCO group is bounded to the central molybdenum
atom. In all compounds, the oxidation number of the
molybdenum is +2, except in one with +4 where two
Fig. 3. Thermogravimetric analysis of 1 and 2.

N. Kitanovski et al. / Inorganic Chemistry Communications 8 (2005) 397–400
399
[3] A.L. Beauchamp, L. Pazdernik, R. Rivest, Acta Crystallogr. B32
(1976) 650.
bound solvated pyridine molecules (calc. 25.6%). The
temperature range of the loss of one pyridine molecule
from the py2H+ cation in 2 cannot be precisely deter-
mined, it starts at approximately 100 ꢁC and is com-
pleted at about 150 ꢁC. The removal of the
corresponding molecule in an analog isothiocyanate
complex (trans-(py2H)[Mo(NCS)4py2]) occurs at some-
what lower temperature range [4]. The course of both
curves between 250 and 450 ꢁC is very similar finishing
by a complete oxidation of both substances into MoO3
at about 450 ꢁC (calc. 23.3%, found 22.8% for 1, and
calc. 24.8%, found 25.3% for 2).
ˇ
ˇ
[4] N. Kitanovski, A. Golobic, B. Ceh, Croat. Chem. Acta 77 (2004)
593.
[5] Synthesis: All reagents and organic solvents were obtained from
commercial sources and were used without further purification.
All reactions were carried out under an atmosphere of argon or
dinitrogen. Mixture of 2.00 g (6.1 mmol) of (NH4)2 [MoCl5(H2O)],
5.00 g (62 mmol) of KCN and 20 ml of pyridine was refluxed for
10 h and cooled to room temperature. The dark black coloured
mixture was filtrated and the crude product washed with several
portions of cooled degassed water to remove by-products and
remains of the reactants. The yellow solid product was subse-
quently washed with little portion of ethanol, diethyl ether and
dried in vacuo. It was found that by reflux of (py2H)[Mo(N-
CO)4py2] in pyridine the final product is always [Mo(NCO)3py3].
Therefore, the mass ratio of both substances strongly depends on
the reflux-time. With regard to the composition of the mixture, the
total yield is between 50% and 60%.
Because of an insignificant coupling of m(Mo–NCO
)
and m(Mo–Npy) vibrations, and due to the close-to-90ꢁ
geometry of all six N–Mo–N bond angles in both com-
pounds, one obtains an ideal C2v local point group sym-
metry for both Mo(NCO)3 and Mo(Npy)3 frameworks
in 1 (three IR active stretching vibrations, 2A1 + B1),
[6] Separation: To the purified mixture an appropriate portion of
degassed water, warmed up to 60 ꢁC, was added and the
suspension thoroughly stirred. The pale yellow insoluble molec-
ular product was removed by filtration and the soluble ionic one
was precipitated by an excess of pyridinium chloride (pyHCl). The
procedure was repeated several times until both substances were
separated. It was found that approximately 0.6 g of ionic
component of the purified mixture is dissolved in 100 ml of
warmed water (60 ꢁC).
[7] Crystallisation of 1: 0.10 g of [Mo(NCO)3py3] was dissolved in
7 ml of degassed pyridine, the suspension warmed up to 35 ꢁC,
stirred for 15 min, filtrated and slowly cooled down to 10 ꢁC.
Yellowish crystals suitable for X-ray structure determination were
isolated. Anal. Calc. for C28H25MoN8O3: C 54.46, H 4.08, N
18.15. Found: C 54.18, H 3.96, N 17.93. Crystallisation of 2: 0.10 g
of pyH[Mo(NCO)4py2] was dissolved in a warmed (40 ꢁC) mixture
of 3 ml of acetone and 4 ml of pyridine, the suspension was
filtrated and slowly cooled down to room temperature. Yellow
crystals were collected after filtration. Anal. Calc. for
and D4h and D
symmetry for Mo(NCO)4 and Mo
1h
(Npy)2 frameworks in 2 (in both cases, one IR active
stretching vibration, Eu and Rþu ), respectively [11,12].
Because of the real symmetry (C1 in 1 and Cs in 2), more
than one band could usually be expected from the par-
ticular stretching. For m(NC): 2237(s), 2206(s), 2155(s)
in 1, and 2224(sh), 2205(s), 2154(m) in 2. For m(CO):
1367(s), 1342(s), 1305(m) in 1, and 1355(w), 1338(m),
1331(s) in 2. For d (NCO): 607(s), 601(s) in 1, and
605(s), 599(s) in 2. For m(Mo–NCO): 341(sh), 349(s) in
1, and 349(s), 344(sh) in 2. For m(Mo–Npy): 273(s) in
1, and 277(s), in 2 [13].
C24H21MoN8O4: C 49.58, H 3.64, N 19.27. Found: C 49.13, H
3.58, N 19.34.
Supplementary materials
[8] Crystallographic data: For
monoclinic, P21/n, a = 8.305(1), b = 16.763(2), c = 20.884(6) A,
C28H25MoN8O3 (1), Mr = 617.50,
˚
All atoms parameters and other crystallographic data
for both compounds have also been deposited with the
Cambridge Crystallographic Data Centre as supplemen-
tary material with the deposition numbers: CCCD
244698 and 244699, for 1 and 2, respectively. These data
can be obtained free of charge via http://www.ccdc.
cam.ac.uk/const/retrieving.html.
3
b = 90.10(2)ꢁ, V = 2907(1) A , Z = 4, Dc = 1.411 Mg mꢀ3
,
˚
l = 0.49 mmꢀ1
, F(0 0 0) = 1260, yellow prism, 0.84 · 0.48 ·
0.18 mm, T = 293(2) K. Of 15546 collected reflections 6971 were
unique (Rint = 0.0145), 4868 observed [I > 2.5r(I )], which refined
to R = 0.041, wR = 0.044; for C24H21MoN8O4 (2):, Mr = 581.42,
˚
orthorhombic, Pnma, a = 8.188(1), b = 9.889(1), c = 32.034(4) A,
3
V = 2593.8(5) A , Z = 4, Dc = 1.489 Mg mꢀ3
, ,
l = 0.55 mmꢀ1
˚
F(0 0 0) = 1180, yellow prism, 0.74 · 0.36 · 0.28 mm, T =
293(2) K. Of 6751 reflections 3286 were unique (Rint = 0.0143),
2477 observed [I > 2.5r(I)], which refined to R = 0.025,
wR = 0.029. It was found that the freshly prepared crystals of 1
and 2 slowly lost the crystallinity on exposure to the atmosphere
due to the escape of solvated pyridine molecules. Therefore,
prismatic single crystals of 1 and 2 were sealed under argon into
thin-walled glass capillaries together with a drop of mother liquor.
X-ray diffraction studies on 1 and 2 were performed using data
collected on Enraf Nonius CAD-4 diffractometer with graphite-
Acknowledgements
We are thankful for the financial support of the Min-
istry of Education, Science and Sport, Republic of
ˇ
Slovenia, through Grant MSZS PS-511-103. We thank
ˇ
ˇ
Dr. R. Cerc-Korosec for thermogravimetric data.
˚
monochromated MoKa radiation (k = 0.71069 A). The data were
corrected for Lorentz polarisation and absorption. Structures
were solved by direct methods using SIR97 [14]. We employed
References
full-matirx least-squares refinements on
F magnitudes with
anisotropic displacement factors for all non-hydrogen atoms
using Xtal 3.4 [15]. The exceptions were C and N atoms (labelled
as C(24)–C(29) and N(81)–N(86)) from one of the solvate pyridine
molecules in 1 which is disordered. These atoms were refined
[1] S. Kolf, W. Preetz, Z. Naturforsch. B53 (1998) 1335.
[2] J.D. Harris, W.E. Eckles, A.F. Hepp, S.A. Duraj, P.E. Fanwick,
Inorg. Chim. Acta 338 (2002) 99.

400
N. Kitanovski et al. / Inorganic Chemistry Communications 8 (2005) 397–400
isotropically. Since it could not be resolved which of the six atoms
[10] Thermogravimetric curves were recorded by a Perkin–Elmer
Thermogravimetric Analyzer TGA 7. The polycrystalline samples
were heated up in air at pressure of 1 bar with the heating rate of
5 ꢁC/min and within the temperature range 25–600 ꢁC.
[11] K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, fifth ed., Wiley, New York, 1997.
[12] R.J.H. Clark, C.S. Williams, Inorg. Chem. 4 (1965) 351.
[13] Infrared spectra were recorded as nujol suspension using Perkin–
Elmer 1720 X and Perkin–Elmer 2000 FT-IR instruments within
the ranges 4000–400 and 700–100 cmꢀ1, respectively.
from the pyridine ring are N and which are C, each of the six
maxima from the ring was treated as to be occupied partially (1/6)
with N and partially(5/6) with C atom. The positions of H atoms
in both structures were obtained from the difference Fourier maps,
only those from
a disordered solvate pyridine molecule of
compound 1 were not located. For 1 only positional parameters
of H atoms (the exception was H21) and for 2 the positional
parameters of H atoms together with their anisotropic displace-
ment factors were refined. In the final cycle of the refinement, we
used 6121 and 3002 reflections (included were those ‘‘less than’’
reflections for which Fc > Fo) and 388 and 248 parameters for 1
and 2, respectively.
[14] A. Altomare, M.C. Burla, G. Cascarano, C. Giacovazzo, A.
Guagliardi, G. Polidori, R. Spagna, J. Appl. Cryst. 32 (1999) 115.
[15] S.R. Hall, G.S.D. King, J.M. Stewart (Eds.), Xtal 3.4 Userꢀs
Manual, Universities of Western Australia, Lamb and Perth,
1994.
[9] F.A. Cotton, M.D. Diebold, W.J. Roth, Inorg. Chem. 26 (1987)
2848.