Room temperature synthesis and crystal structure of mer-[MoBr 3Py3], the vibrational spectra of mer-[MoBr 3Py3], mer-[MoI3Py3] and trans,trans-[MoBr2Py4][MoBr4Py2]

Article abstract of DOI:10.1002/zaac.201300122

The reaction of MoBr₃ and pyridine at room temperature provided single crystals of mer-[MoX₃Py₃]. mer-[MoBr ₃Py₃] crystallizes in P2₁/n monoclinic space group with cell dimensions a = 9.2297(5) A, b = 12.911(8) A, c = 15.7022(9) A and β = 90.479(3)°. There are four formula units in a unit cell. Mo-N distances are in the range 2.196(8)-2.214(8) A and Mo-Br distances are 2.573(1) A and 2.574(1) A. Fundamental vibrational frequencies of pyridine molecules are strongly affected upon coordination in all three coordination compounds: mer-[MoBr₃Py₃], mer-[MoI₃Py₃] and trans,trans-[MoBr₂Py ₄][MoBr₄Py₂]. Copyright

Full text of DOI:10.1002/zaac.201300122

ARTICLE
DOI: 10.1002/zaac.201300122
Room Temperature Synthesis and Crystal Structure of mer-[MoBr3Py3], the
Vibrational Spectra of mer-[MoBr3Py3], mer-[MoI3Py3] and trans,trans-
[MoBr2Py4][MoBr4Py2]
Gleb Veryasov,*[a] Evgeny Goreshnik,[a] and Adolf Jesih[a]
Keywords: Molybdenum; Coordination compounds; X-ray diffraction; Vibrational spectroscopy
Abstract. The reaction of MoBr3 and pyridine at room temperature
provided single crystals of mer-[MoX3Py3]. mer-[MoBr3Py3] crys-
range 2.196(8)–2.214(8) Å and Mo–Br distances are 2.573(1) Å and
2.574(1) Å. Fundamental vibrational frequencies of pyridine molecules
tallizes in P21/n monoclinic space group with cell dimensions a = are strongly affected upon coordination in all three coordination com-
9.2297(5) Å, b = 12.911(8) Å, c = 15.7022(9) Å and β = 90.479(3)°.
pounds: mer-[MoBr3Py3], mer-[MoI3Py3] and trans,trans-[MoBr2Py4]-
There are four formula units in a unit cell. Mo–N distances are in the
[MoBr4Py2].
priate quality for X-ray crystal structure determination. In this
paper the room temperature synthesis and the crystal structure
of mer-[MoBr3Py3] is described and tentative assignment of
vibrational data are provided.
Introduction
The first literature on neutral monomeric trihalo-tripyridine
molybdenum(III) coordination compounds dates back to
the year 1931, when Rosenheim described synthesis of
mer-[MoCl3Py3] and mer-[MoBr3Py3] (Py = pyridine)[1] by the
reaction of the corresponding molybdenum trihalides in boiling
pyridine. The use of (NH4)2[MoX5H2O] (X = Cl, Br, I) have
been demonstrated to lead to the same products, while the
presence of methanol in the reaction mixture resulted in the
precipitation of ionic trans,trans-[MoX2Py4][MoX4Py2].[2,3]
The crystal structure of mer-[MoCl3Py3] was determined,
while for mer-[MoBr3Py3] the cell parameters were derived
from powder data and authors expressed believe that mer-
[MoCl3Py3] and mer-[MoBr3Py3] are isostructural.[2] The d3
transition metal coordination compounds were studied for the
photo-initiated two-electron oxidation process which is ex-
pected to be a common feature in second and third row transi-
tion metal coordination compounds. mer-[MoX3Py3] (X = Br,
I), and especially mer-[MoCl3Py3], which was found to phos-
phoresce in solid state were considered for such a study.[4] The
precise crystal structure of mer-[MoBr3Py3] would possibly
also contribute to the knowledge on photochemical processes
associated to this compound. Precipitation of mer-[MoBr3Py3]
as the last step in the synthesis[1] did not provide crystals suit-
able for X-ray measurements. To reduce the crystallization rate
the reaction of molybdenum tribromide and pyridine was con-
ducted at room temperature, which provided crystals of appro-
Results and Discussion
Due to the slight solubility[5] of mer-[MoBr3Py3] in pyridine
it was anticipated, the MoBr3 reaction with pyridine might pro-
ceed at lower temperatures albeit at lower reaction rates. The
reaction between finely divided MoBr3 and pyridine took three
weeks to complete at room temperature yielding almost pure
mer-[MoBr3Py3]. The side product in traces were plate crys-
tals, identified by single-crystal X-ray diffraction as
trans,trans-[MoBr2Py4][MoBr4Py2], which was already re-
ported to appear as the side product in the reaction between
(NH4)2[MoBr5.H2O] and pyridine diluted with methanol.[3]
Crystal Structure
The mer-[MoBr3Py3] crystallizes in the monoclinic space
group P21/n with four formula units in a unit cell, Table 1.
Cell parameters obtained (a = 9.2297(5) Å, b = 12.911(8) Å,
c = 15.7022(9) Å, β = 90.479(3) °) differ from previously re-
ported parameters based on powder diffraction data.[2]
Molybdenum in mer-[MoBr3Py3] has octahedral surroundings
of three bromine atoms and three nitrogen atoms (Figure 1),
angles formed by central molybdenum atom and atoms in trans
and cis positions are close to 180° and 90° with the highest
deviation in angle Br2–Mo1–Br3 at 176.92°, and angle
Br2–Mo1–N1 at 87.33°. The Mo–Br bond lengths at
2.573(1) Å and 2.574(1) Å correspond well with the average
value 2.565(1) Å for bond lengths found in ionic
coordination compounds with pyridine ligands, trans,trans-
[MoBr2Py4][MoBr4Py2][3] and trans-[MoIIIBr2Py4]Br3.[6] The
* Prof. Dr. G. Veryasov
E-Mail: gleb.veryasov@ijs.si
[a] Department of Inorganic Chemistry and Technology
Jozˇef Stefan Institute
Jamova cesta, 39
1000 Ljubljana, Slovenia
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201300122 or from the au-
thor.
Z. Anorg. Allg. Chem. 2013, 639, (6), 939–942
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
939

G. Veryasov, E. Goreshnik, A. Jesih
ARTICLE
three Mo–N bond lengths in mer-[MoBr3Py3] are slightly
different but in a very narrow range from 2.196(8) Å
to 2.214(8) Å, the corresponding Mo–N bond lengths
in
trans,trans-[MoBr2Py4][MoBr4Py2][3]
and
trans-
[6]
[MoIIIBr2Py4]Br3
are in the range from 2.207(4) Å–
2.237(4) Å. The pyridine ring is almost planar; the greatest
torsion angle found is N2–C6–C7–C8 at 2.22°. The average
C–N distance 1.344 Ä, C–C distance 1.374
Ä and
average angles C–N–C 116.78°, N–C–C 123.57°, C–C–C
118.68° in pyridine rings are comparable to corresponding dis-
tances and angles in ionic molybdenum coordination
compounds, trans,trans-[MoBr2Py4][MoBr4Py2] and trans-
[MoIIIBr2Py4]Br3.[3,6] The pyridine molecules are arranged in
a propeller like formation around a plane formed by three ni-
trogen atoms and one bromine atom.
Table 1. Summary on crystal structure of mer-[MoBr3Py3].
Figure 1. mer-[MoBr3Py3] molecular unit; thermal ellipsoids are given
at 30% probability level.
Empirical formula
MoBr3C15N3H15
Formula weight
572.96
Temperature /K
Radiation
Crystal system, space group
Unit cell dimensions /Å
a /Å
b /Å
c /Å
200
spectrum of mer-[MoBr3Py3] is assigned to the Mo–Br stretch-
ing vibration according to the assignment provided for the in-
frared bands at 260 cm–1 and 269 cm–1 for the same type of
vibration.[7,9]
MoKα (0.71069 Å)
Monoclinic, P 21/n
9.2297(5)
12.9112(8)
15.7022(9)
90.48(0)
1871.1(2)
4
2.034
7.106
1192
β /°
V /Å3
Z
Calculated density /g·cm–3
Absorption coeff. /mm–1
F(000)
Color
Orange-yellow
6.09–73.96
–12–8, –16–16, –9–20
Full-matrix on F2
8352
4242
199
0.0692
Theta range for data collection
Limiting indices
Refinement method
Measured reflections
Independent used in refinement
Free parameters
R1
wR2
0.1615
1.056
1.399, –1.339,
Goodness-of-fit on F2
Largest diff. peak and hole /e·Å–3
Figure 2. Raman spectra of mer-[MoBr3Py3], trans,trans-[MoBr2Py4]-
[MoBr4Py2] and mer-[MoI3Py3] in the range 100–500 cm–1.
Accordingly the band at 207 cm–1 in the Raman spectrum
of the mer-[MoI3Py3] originates from the Mo–I stretching vi-
bration. The frequency ratio between the two is 0.80 which
Vibrational Spectroscopy
The study of resonance Raman effect was reported on corresponds well to Mo–I/Mo–Br stretching vibration fre-
mer-[MoBr3Py3] and mer-[MoCl3Py3][7] with laser excitation quency ratio (0.80) in octahedral [Rh(en)2X2]+ (en = ethylendi-
lines in the range from 647.1 to 476.5 nm and the highest amine) cations.[10] The band at 244 cm–1 in the Raman spec-
sevenfold enhancement was observed in the 1606 cm–1 band trum of mer-[MoI3Py3] is assigned to Mo–N stretching vi-
associated with the carbon–carbon stretching vibration of the bration, which is expected to occur in the range from 200 cm–1
pyridine ring. The utilization of He-Ne excitation line at to 287 cm–1. The Mo–N stretching vibrations in general appear
632.8 nm to obtain Raman spectra of mer-[MoBr3Py3], weaker than Mo–X vibrations and are not sensitive to
mer-[MoI3Py3] and trans,trans-[MoBr2Py4][MoBr4Py2] in this the type of halogen.[11] Therefore, in trans,trans-
work is not expected to provide strong pre-resonance enhance- [MoBr2Py4][MoBr4Py2] the weak Raman band at 235 cm–1 is
ment according to electronic spectrum of mer-[MoBr3Py3] assigned to the Mo–N vibration, the corresponding infrared
where principal bands appear at 385 and 310 nm.[5,8] Raman band was found at 242 cm–1.[3] In the Raman spectrum of
spectra of mer-[MoBr3Py3], mer-[MoI3Py3] and trans,trans- mer-[MoBr3Py3] there is no discernible band around
[MoBr2Py4][MoBr4Py2] are shown on Figure 2 and Figure 3. 240 cm–1, but it is possible it is obscured by an uneven back-
The band at 258 cm–1 in the low-frequency part of the Raman ground. Other bands in the low-frequency region of
940
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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 939–942

Room Temperature Synthesis and Crystal Structure of mer-[MoBr3Py3]
Figure 3. Raman spectra of mer-[MoBr3Py3], trans,trans-[MoBr2Py4][MoBr4Py2] and mer-[MoI3Py3] in the range 500–3300 cm–1.
pumped out on a vacuum line and the product mer-[MoBr3Py3] was
collected as orange-yellow needle crystals. Yield: 96%. Mo-
I3C15H15N3: C 31.44; H 2.64; N 7.33 ; found C 31.00; H 2.65; N
7.20%. MoI3 was prepared from Mo(CO)6 and iodine and
mer-[MoI3Py3] was prepared from MoI3 and pyridine according to
published procedures.[14]
mer-[MoBr3Py3] and trans,trans-[MoBr2Py4][MoBr4Py2]
Raman spectra we found uncertain to assign due to the appear-
ance of Mo–X and Mo–N bands in the same region and the
lack of isotopic substitution data, which was already pointed
out by Filippo et al.[7]
The coordination of the pyridine molecule to the metal atom
affects pyridine internal vibrations, which results in split and/
or shifted bands in the vibrational spectra of pyridine coordina-
tion compounds.[5,12]
Raman Spectroscopy: Raman spectra of crystalline samples were
measured with a Horiba Jobin Yvon LabRAM HR spectrometer using
the 632.81 nm excitation line of a He-Ne laser at 1.7 mW power. Scat-
tered light was collected by an Olympus x50 long distance objective
in backscattering configuration and spectra recorded were an average
of 100 scans with an integration time of 5 seconds. The spectrometer
zero-order grating position and the position of the polycrystalline sili-
con 520.6 cm–1 band were checked prior to and after each measure-
ment to maintain the wavenumber accuracy of 0.5 cm–1. Raman spec-
tra were also measured on the same single crystals on which X-ray
diffraction data were obtained.
Conclusions
The mer-[MoBr3Py3] was synthesized at room temperature
from finely divided MoBr3 and anhydrous pyridine in three
weeks. Molybdenum in mer-[MoBr3Py3] has octahedral sur-
roundings of three bromine atoms and three nitrogen atoms
and the pyridine molecules are arranged in a propeller like
formation around a plane formed by three nitrogen atoms and Infrared Spectroscopy: IR spectra were measured with a Perkin–El-
mer GX FTIR spectrometer in the range from 600–4000 cm–1 as Nujol
one bromine atom. Vibrational spectra reveal the fundamental
mulls between NaCl windows and as KBr pellets with 1 cm–1 resolu-
frequencies of pyridine molecules are strongly affected
tion. Continuous flow of nitrogen was kept through the sample cham-
upon coordination in all three coordination compounds:
ber for 20 minutes prior to measurement in order to remove airborne
mer-[MoBr3Py3], mer-[MoI3Py3] and trans,trans-[MoBr2Py4]-
[MoBr4Py2].
carbon dioxide and water vapor.
Chemical Analyses: Analyses for C, H and N were performed with
an Elementar Vario EL cube elemental analyzer.
Experimental Section
Materials and Syntheses: All material transfer and handling was per-
formed on a vacuum line or in a glow box to avoid moisture. Molybd-
enum foil (Sigma–Aldrich, St. Louis, Missouri, USA, Ն 99.9%), bro-
mine (Sigma–Aldrich, St. Louis, Missouri, USA, Ն 99.5%), iodine
(Merck KGaA, Darmstadt, Germany, sublimed) and Mo(CO)6 (Sigma–
Crystal Structure Analysis: Crystal data on orange-yellow needles,
mer-MoBr3Py3 were collected on a Rigaku AFC7 diffractometer
equipped with a Mercury CCD area detector, using graphite monochro-
matized Mo-Kα radiation. Data were treated using the Rigaku Crys-
talClear software suite package.[15] The structure was solved by direct
Aldrich, St. Louis, Missouri, USA, Ն 99.9%) were used as received. methods using the SIR-92[16] program (teXan crystallographic soft-
Anhydrous pyridine (Sigma–Aldrich, St. Louis, Missouri, USA, ware package of Molecular Structure Corporation[17]) and refined on
99.8%) was dried under CaH2 and distilled prior to use. MoBr3 was
prepared by a modified procedure[13] from bromine vapor and molybd- WinGX.[19] Hydrogen atoms were included on idealized positions and
enum foil at 600 K in a quartz ampoule with the attached reservoir refined with geometrical restrictions. The figures were prepared using
F2 with SHELXL-97[18] software implemented in the program package
holding liquid bromine at room temperature. The synthesis of mer-
[MoBr3Py3][1] was carried out at room temperature by the reaction of
pyridine and MoBr3. MoBr3 (28 mg) was placed into a glass flask
containing pyridine (5 mL) and was kept at room temperature. After
DIAMOND 3.1 software.[20] Details of the data collection and struc-
ture elucidation are listed in Table 1 and Table 2. Crystallographic data
for the structure of mer-MoBr3Py3 have been deposited with the Cam-
bridge Crystallographic Data Centre, CCDC, 12 Union Road, Cam-
disappearance of traces of MoBr3 (three weeks) the pyridine was bridge CB21EZ, UK. Copies of the data may be obtained on quoting
Z. Anorg. Allg. Chem. 2013, 939–942
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de 941

G. Veryasov, E. Goreshnik, A. Jesih
ARTICLE
Table 2. Atomic coordinates and isotropic displacement parameters
/ϫ10–2 for mer-[MoBr3Py3].
Acknowledgments
Financial support of the Slovenian Research Agency (ARRS) is
acknowledged.
Atom
x
y
Z
U
Mo1
Br1
Br2
Br3
N1
N2
N3
C1
H1
C2
H2
C3
H3
C4
H4
C5
H5
C6
H6
C7
H7
C8
H8
C9
H9
C10
H10
C11
H11
C12
H12
C13
H13
C14
H14
C15
H15
0.0074(1)
–0.1302(1)
–0.0568(1)
0.0785(1)
0.1230(8)
0.2097(9)
–0.1923(9)
0.104(1)
0.04320
0.170(1)
0.15370
0.262(1)
0.30830
0.286(1)
0.34930
0.213(1)
0.22730
0.334(1)
0.33350
0.462(1)
0.54550
0.469(1)
0.55570
0.342(1)
0.34070
0.217(1)
0.13250
–0.273(1)
–0.24040
–0.401(1)
–0.45320
–0.450(1)
–0.53670
–0.367(1)
–0.39620
–0.242(1)
–0.18740
0.08748(7)
–0.01560(9)
0.25817(9)
–0.07753(9)
0.1820(6)
0.0789(7)
0.1003(7)
0.1639(9)
0.10990
0.223(1)
0.21020
0.3003(9)
0.34110
0.3190(9)
0.37070
0.2578(9)
0.26980
0.049(1)
0.02880
0.047(1)
0.02760
0.072(1)
0.07000
0.102(1)
0.11890
0.105(1)
0.12620
0.0161(9)
–0.04810
0.0196(9)
–0.04040
0.1153(9)
0.12080
0.204(1)
0.26850
0.1920(9)
0.25090
0.25774(6)
0.14245(7)
0.18170(7)
0.34007(7)
0.3543(5)
0.1855(5)
0.3339(5)
0.4383(6)
0.45450
0.5009(7)
0.55830
0.4748(7)
0.51550
0.3892(7)
0.37140
0.3324(7)
0.27470
0.2214(7)
0.27820
0.1797(7)
0.20870
0.0952(8)
0.06580
0.0561(8)
–0.00140
0.1022(7)
0.07480
0.3517(6)
0.33280
0.3963(8)
0.40780
0.4234(8)
0.45230
0.4070(7)
0.42630
0.3618(7)
0.34970
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Supporting Information (see footnote on the first page of this
article): Tables containing band frequencies and tentative assignments.
Received: February 27, 2013
Published Online: April 22, 2013
942
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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 939–942