The effects, assessed by electrochemical techniques and single crystal structures, of ortho substitution on benzoate ligands supporting the quadruply-bonded dimolybdenum bond

Article abstract of DOI:10.1016/S0020-1693(02)01095-2

The syntheses, electrochemistry and structures of Mo₂(O₂C-o-C₆H₄Cl)₄, 1·4THF, Mo₂(O₂C-o-C₆H₄Br)₄, 2·2THF, Mo₂(O₂C-o-C₆H₄I)₄, 3·2THF, and Mo₂(O₂C-o-C₆H₄NO₂) ₄ (4), as determined by single-crystal X-ray diffraction, are reported. Molecules 1, 2, and 3 co-crystallized each with two axially coordinated THF molecules; complex 1 contained two more THF molecules within the unit cell. The Mo-Mo distances in 1-4 are 2.1029(10), 2.1014(13), 2.1055(7), and 2.0942(12) A?, respectively. The oxidation potentials for 1-3 were similar at 674, 655, and 647 mV, but that for 4 at an E_1/2(ox) of 792 mV was higher.

Full text of DOI:10.1016/S0020-1693(02)01095-2

Inorganica Chimica Acta 340 (2002) 147ꢀ154
/
www.elsevier.com/locate/ica
The effects, assessed by electrochemical techniques and single crystal
structures, of ortho substitution on benzoate ligands supporting the
quadruply-bonded dimolybdenum bond
Teerayuth Liwporncharoenvong, Rudy L. Luck *
Department of Chemistry, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA
Received 20 February 2002; accepted 7 May 2002
Abstract
The syntheses, electrochemistry and structures of Mo2(O2C-o-C6H4Cl)4, 1×
C6H4I)4, 3×2THF, and Mo2(O2C-o-C6H4NO2)4 (4), as determined by single-crystal X-ray diffraction, are reported. Molecules 1, 2,
and 3 co-crystallized each with two axially coordinated THF molecules; complex 1 contained two more THF molecules within the
/
4THF, Mo2(O2C-o-C6H4Br)4, 2×/2THF, Mo2(O2C-o-
/
˚
unit cell. The Moꢀ
/
Mo distances in 1ꢀ4 are 2.1029(10), 2.1014(13), 2.1055(7), and 2.0942(12) A, respectively. The oxidation
/
potentials for 1ꢀ3 were similar at 674, 655, and 647 mV, but that for 4 at an E1/2(ox) of 792 mV was higher.
/
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Electrochemical techniques; Benzoate ligands; Quadruply-bonded dimolybdenum
1. Introduction
of interest to see if the interplanar angles between the
benzene and carboxylate groups would change upon
coordination to the Mo2 core and if there would be
any relationship between the degree of twist and the
4ꢁ
The tetracarboxylato dimolybdenum(II) unit is well
established [1] and various carboxylate ligands have
4ꢁ
Moꢀ
/
Mo atom interaction as assessed through crystal-
been employed to stabilize the Mo2
Mo2(O2CCF3)4 [2],
[Mo2(O2CCH2NH3)4]Cl4×
(NCCH3)(DMSO)×
core unit, e.g.
[3],
lographic and electrochemical measurements.
Mo2(O2CC6H5)4
/
3H2O [4] and Mo2(FCA)4-
/
2DMSO [5] (FCAHꢂferrocenemo-
/
2. Experimental
nocarboxylic acid). An examination [3] consisting of
variance on axial coordination and inductive effects of
the ligand, found that the Moꢀ
not sensitive and compared with the Cr2
resisted change.
/
Mo quadruple bond was
4ꢁ
2.1. General data
core [6]
Oxygen was excluded during all operations by using
vacuum lines or a glovebox supplied with purified
nitrogen. All solvents except methanol and water were
dried over and distilled from sodium benzophenone
ketyl. Methanol was dried over Magnesium metal.
Water and all solvents were degassed before use. IR
spectra were recorded by using a Mattson Galaxy Series
FTIR 3000. NMR spectra were recorded on a Varian
Unity Inova 400 mHz. Visible absorption spectra were
recorded by using a Hewlett Packard 8452A diode array
spectrophotometer. The preparation of K4Mo2Cl8 was
reported elsewhere [9]. Elemental analyses were ob-
tained at Galbraith Laboratories, Inc., Knoxville, TN.
We were interested in a consideration of both ligand-
4ꢁ
inductive effects and Mo2
consequence by use of o-
substituted benzoic acid derivatives. There appears to be
only two such compounds established structurally, i.e.
Mo2(O2CC6H4-o-C6H5)4 [7] and Mo2(O2CC6H4-o-
OH)4 [8]. The ligands employed in this study were o-
chloro, o-bromo, o-iodo, o-nitro-benzoic acids. It was
* Corresponding author. Tel.: ꢁ
2061
E-mail address: rluck@mtu.edu (R.L. Luck).
/
1-906-487 2309; fax: ꢁ1-906-487
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 0 9 5 - 2

148
T. Liwporncharoenvong, R.L. Luck / Inorganica Chimica Acta 340 (2002) 147ꢀ154
/
The electrochemical measurements were accom-
nm (in THF). Anal. Calc. for Mo2C28H16O8I: C, 28.50;
H, 1.37. Found: C, 28.15; H, 1.61%.
plished with a Bioanalytical Systems CV-50W work-
station controlled by a 366 MHz Pentium based
Gateway PC. The cyclic voltammetric experiments
were performed in a 5.0 ml cell equipped with a glassy
carbon working electrode (0.071 cm2), a platinum wire
auxiliary electrode, and a Ag/AgCl reference electrode.
The electroactive compounds were dissolved (0.001 mol
lꢃ1) in dried benzonitrile also containing tetrabutylam-
2.2.4. Preparation of Mo2(C7H4NO4)4 (4)
A solution of K4Mo2Cl8 (200 mg, 0.317 mmol) in 10
ml of distilled water was added to a solution of o-
nitrobenzoic acid (220 mg, 1.317 mmol) in 20 ml
methanol. The solution was stirred under N2 for at least
30 min. The powdery red product was filtered through a
sintered-glass frit, and vacuum dried. Subsequent re-
monium hexafluorophosphate (Fluka, ꢀ99%) as the
/
supporting electrolyte (0.10 mol lꢃ1). An argon atmo-
sphere was maintained over the solutions throughout
the electrochemical experiments. Ferrocene oxidized at
0.51 V under these conditions.
crystallization with THFꢀhexanes resulted in com-
/
pound 4. Yield 250 mg, 91.95%; IR 1605 m, 1519
1
versus, and 1400 s cmꢃ1; H NMR (CDCl3) d 7.59 (t,
Jꢂ
/
2 Hz, 4H), 7.73 (t, Jꢂ
/
2 Hz, 4H), 7.85 (d, Jꢂ2 Hz,
/
4H), 8.32 (d, Jꢂ
/
2 Hz, 4H); UV 464 and 362 nm (in
THF). Anal. Calc. for Mo2C28H16N4O16: C, 39.27; H,
2.2. Synthesis
1.88. Found: C, 38.43; H, 1.94%.
2.2.1. Preparation of Mo2(C7H4O2Cl)4 (1)
A solution of K4Mo2Cl8 (200 mg, 0.317 mmol) in 10
ml of distilled water was added to a solution of o-
chlorobenzoic acid (210 mg, 1.342 mmol) in 20 ml
methanol. The yellow product was isolated by filtration
and vacuum dried. Subsequent recrystallization with
2.3. Crystallography
In all cases, crystals were removed from the mother
liquor, coated with epoxy resin and placed on the head
of a thin glass fiber, which was anchored in a goini-
ometer mounting pin. The pin-mounted crystal was then
inserted into the goniometer head of the X-ray diffract-
ometer and centered in the beam path. Standard CAD4
centering, indexing, and data collection programs were
utilized [10]. About 25 reflections between 10 and 158 in
u were located by a random search pattern, centered
and used in indexing. Final cell constants and orienta-
tion matrix were obtained by collecting appropriate
preliminary data and refined by a least-squares fit.
During data collection, three intensity standards and
three orientation standards were measured at regular
intervals to measure the rate of decay of the crystal and
to accommodate for crystal movement.
THFꢀ
85.60%; IR 1569 m, and 1506 versus cmꢃ1; H NMR
(CDCl3) d 7.32ꢀ7.40 (m, 8H), 7.46ꢀ7.49 (m, 4H), 8.16ꢀ
/
hexanes resulted in compound 1. Yield 220 mg,
1
/
/
/
8.19 (m, 4H); UV 424 nm (in THF). Anal. Calc. for
Mo2C28H16O8Cl4: C, 41.31; H, 1.98. Found C, 40.68; H,
2.05%.
2.2.2. Preparation of Mo2(C7H4O2Br)4 (2)
A solution of K4Mo2Cl8 (200 mg, 0.317 mmol) in 10
ml of distilled water was added to a solution of o-
bromobenzoic acid (270 mg, 1.344 mmol) in 20 ml
methanol. The solution was stirred under N2 for at least
30 min. The resulting yellow product was isolated by
filtration and vacuum dried. Subsequent recrystalliza-
tion with THFꢀ
270 mg, 86.04%; IR 1567 m, and 1513 s cmꢃ1; 1H NMR
(CDCl3) d 7.27 (t, Jꢂ2 Hz, 4H), 7.38 (t, Jꢂ2 Hz, 4H),
7.68 (d, Jꢂ2 Hz, 4H), 8.14 (d, Jꢂ2 Hz, 4H); UV 424
C4H8O:
/
hexanes resulted in compound 2. Yield
Data were first reduced and corrected for absorption
using psi-scans [11] and then solved using the program
SIR-97 [12], which afforded nearly complete solutions for
the non-H atoms in all cases. These programs were
utilized using the WINGX interface [13]. The models were
then refined using SHELXL-97 [14] first with isotropic and
then anisotropic thermal parameters to convergence.
The positions and isotropic thermal parameters of H-
atoms were constrained and set to 1.5 times the isotropic
equivalent of the atoms they were attached to, respec-
tively. This constituted the final model for both com-
pounds and appropriate crystallographic data is listed in
Table 1. In 1 there were disorder in one of the THF
molecules of solvation and in 4, one of the oxygen atoms
on the nitro groups on each unique molecule was
disordered. Attempts to model Cl atoms at the same
site as the Br atoms in 2 or constrained at separate
distances were not successful as no significant deviation
away from unity for the Br occupancy was observed in
/
/
/
/
nm (in THF). Anal. Calc. for Mo2C28H16O8Br4×
/
C, 36.12; H, 2.27. Found C, 37.26; H, 2.64%.
2.2.3. Preparation of Mo2(C7H4O2I)4 (3)
A solution of K4Mo2Cl8 (200 mg, 0.317 mmol) in 10
ml of distilled water was added to a solution of o-
iodobenzoic acid (330 mg, 1.331 mmol) in 20 ml
methanol. The solution was stirred under N2 for at least
30 min. The powdery yellow product, which precipitated
almost immediately, was filtered through a sintered-
glass frit, and vacuum dried. Subsequent recrystalliza-
tion with THFꢀ
337 mg, 90.27%; IR 1560 m, and 1497 s cmꢃ1; 1H NMR
(CDCl3) d 7.11 (t, Jꢂ2 Hz, 4H), 7.44 (t, Jꢂ2 Hz, 4H),
8.02 (d, Jꢂ2 Hz, 4H), 8.16 (d, Jꢂ2 Hz, 4H); UV 424
/hexanes resulted in compound 3. Yield
/
/
/
/

T. Liwporncharoenvong, R.L. Luck / Inorganica Chimica Acta 340 (2002) 147ꢀ
/
154
149
Table 1
Crystal data and structure refinement details for 1ꢀ
/4
1×4THF
2×2THF
3×2THF
4
Formula
Mr
C28H16Mo2O8Cl4×4C4H8O C28H16Mo2O8Br4×2C4H8O C28H16Mo2O8I4×2C4H8O C56H32Mo4O32N8
1102.55
yellow prism
orthorhombic
Pbca
1136.14
yellow prism
triclinic
1324.14
yellow prism
monoclinic
P21/c
856.33
red prism
triclinic
Habit
Crystal system
¯
¯
Space group
˚
P/
1
/
P/
1
/
a (A)
˚
9.4383(16)
21.520(4)
23.624(7)
90
8.128(2)
11.000(2)
11.5170(15)
101.499(13)
97.904(18)
100.275(19)
976.7(4)
0.71069
293
9.5680(11)
14.4670(14)
14.8480(15)
90
11.018(3)
11.800(2)
13.1884(18)
109.069(13)
99.291(16)
103.092(18)
1525.9(5)
0.71069
293
b (A)
˚
c (A)
a (8)
b (8)
g (8)
90
90
98.828(9)
90
3
˚
V (A )
4798.3(18)
0.71069
293
2030.9(4)
0.71069
293
l (Mo Ka radiation)
Temperature (K)
Z
4
1.53
1
1.93
2
2.17
2
1.86
Dcalc (g cmꢃ3
)
Number of reflctionns measured
3127
2644
1798
3582
3084
5350
3035
Number of observed data jIjꢀ2s(I) 2215
Number of parameters
Rint
277
236
0.096
235
0.038
471
0.113
0.078
0.041
0.113
0.946
0.005
a
R(F)
0.040
0.072
0.030
0.073
0.039
0.072
b
c
d
c
d
wR(F2)
Goodness-of-fit
Max. (D/s)
0.978
0.001
1.045
0.001
0.956
0.001
ꢃ3
˚
Residual max/min (DQ) (e A
)
0.66/ꢃ0.34
0.57/ꢃ0.57
1.73/ꢃ1.33
0.80/ꢃ0.38
Scattering factors from international tables for crystallography (vol. C).
a
Rꢂa(FoꢃFc)/a(Fo).
b
Rwꢂ[a[w(Fo2ꢃFc2)2]/a[w(Fo2)2]]1/2
.
wꢂ1/[s2(Fo2)ꢁ(0.0434P)2ꢁ0.5955P], where Pꢂ(max(Fo2, 0)ꢁ2Fc2)/3.
c
wꢂ1/[s2(Fo2)ꢁ(0.0246P)2ꢁ0.4445P], where Pꢂ(max(Fo2, 0)ꢁ2Fc2)/3.
d
the refinements. Selected bond distance and angles for
1ꢀ4 are given in Table 2.
the voltammograms obtained at various scan rates using
a glassy carbon electrode for 1ꢀ4, with the data from
these listed in Table 3. Compounds 1ꢀ3 appear to
/
/
/
exhibit reversible voltammograms as evidenced by the
fact that the ipc/ipa ratio is ‘close’ to unity. However,
under the measurement conditions, 4 exhibits quasi-
reversible voltammograms as the ipc/ipa deviates signifi-
3. Results and discussion
3.1. Synthetic and electrochemical details
cantly from unity and with an E1/2(ox)ꢂ
/
780 mV is the
most difficult complex to oxidize.
Complexes 1ꢀ4 were prepared using slight adapta-
/
tions to well established procedures [15] and their IR, 1H
NMR and visible spectra are listed in the experimental
section. These measurements confirmed the presence of
the ligand, that the samples were diamagnetic and
possessed an absorption in the visible previously as-
Table 4 lists data for various dimolybdenum tetra-
benzoate systems. There is a trend between pKa values
and the oxidation potentials, i.e. the lower the pKa
value, the higher the oxidation potential as we reported
before [20]. The lower pKa values for the carboxylate
ligands suggest that these ligands would donate less
4ꢁ
signed to a d0d* transition [1].
/
electron density to the Mo2
core rendering this unit
Electrochemical studies on these compounds are of
interest. The reversibility and quasi-reversibility of the
harder to oxidize. It remains for additional studies in
different solvents to determine the relationship between
oxidation potentials and axial ligation.
4ꢁ
Mo2 core in different solvents were previously noted
[16]. Recently benzonitrile was used for electrochemical
studies on dimolybdenum systems due to its high
dielectric constant [17]. In this solvent, Mo2(acetate)4
3.2. Structural details
exhibited a reversible oxidation at E1/2
(DEpꢂ66 mV) [18].
In this electrochemistry study, all four dimolybdenum
ꢂ448 mV
/
/
ORTEP3 for WINDOWS [22] representations of 1ꢀ
displayed in Figs. 2ꢀ5, respectively. In all cases, the
molecules, including the two comprising 4, see Fig. 5,
/
4 are
/
complexes were measured in benzonitrile. Fig. 1 displays

150
T. Liwporncharoenvong, R.L. Luck / Inorganica Chimica Acta 340 (2002) 147ꢀ154
/
Table 2
˚
Selected bond distance (A) and angles (8) for 1ꢀ4
/
a
1
2
3
4
Bond distances
b
Mo1ꢀMo1
2.1029(10)
2.107(4)
2.110(4)
2.111(4)
2.119(4)
1.264(7)
1.271(7)
1.275(7)
1.262(7)
2.1014(13)
2.115(4)
2.105(4)
2.1055(7)
2.106(3)
2.115(3)
2.0942(12)
2.099(4)
2.093(4)
Mo1ꢀO11
Mo1ꢀO12
b
Mo1ꢀO21
Mo1ꢀO22
O11ꢀC10
O12ꢀC10
O21ꢀC20
2.122(4)
2.105(4)
2.103(3)
2.113(3)
2.134(3)
2.101(3)
1.270(8)
1.278(7)
1.274(5)
1.272(5)
1.271(6)
1.257(6)
1.260(8)
1.276(7)
1.278(5)
1.273(5)
1.271(6)
1.261(6)
b
O22ꢀC20
X1ꢀC16
X2ꢀC26
1.726(7) (XꢂCl)
1.725(8) (XꢂCl)
1.911(8) (XꢂBr)
1.868(9) (XꢂBr)
2.101(4) (XꢂI)
2.102(5) (XꢂI)
1.483(8) (XꢂN)
1.461(8) (XꢂN)
Bond angles
b
b
b
b
Mo1ꢀMo1ꢀO11
Mo1ꢀMo1ꢀO12
Mo1ꢀMo1ꢀO21
Mo1ꢀMo1ꢀO22
O11ꢀMo1ꢀO21
O11ꢀMo1ꢀO22
O12ꢀMo1ꢀO21
O12ꢀMo1ꢀO22
O11ꢀMo1ꢀO12
O21ꢀMo1ꢀO22
Mo1ꢀO11ꢀC10
Mo1ꢀO12ꢀC10
Mo1ꢀO21ꢀC20
Mo1ꢀO22ꢀC20
O12ꢀC10ꢀC11
O11ꢀC10ꢀO12
O11ꢀC10ꢀC11
O22ꢀC20ꢀO21
C10ꢀC11ꢀC16
C20ꢀC21ꢀC26
X1ꢀC16ꢀC11
91.73(11)
91.56(11)
92.30(11)
90.84(11)
88.76(16)
90.59(15)
90.96(16)
89.50(15)
176.71(15)
176.81(15)
117.1(4)
91.83(14)
91.55(12)
90.77(13)
92.18(13)
89.21(17)
90.59(17)
90.65(17)
89.37(17)
176.62(18)
177.05(18)
117.1(4)
91.14(7)
91.10(8)
92.39(7)
91.58(11)
92.05(11)
91.50(10)
92.21(10)
90.71(14)
90.53(14)
89.42(14)
89.11(14)
176.36(14)
176.05(14)
116.3(4)
91.02(7)
91.14(11)
88.52(11)
88.62(11)
91.52(11)
176.53(10)
176.58(10)
116.5(2)
b
b
b
b
b
116.9(4)
116.8(4)
117.7(5)
118.3(4)
117.3(2)
116.8(3)
116.4(3)
115.5(3)
118.0(4)
116.9(6)
117.4(4)
117.1(7)
117.7(2)
119.6(4)
116.8(4)
119.3(5)
122.6(6)
120.4(6)
121.7(6)
121.2(6)
122.6(4)
117.8(4)
123.5(5)
117.1(5)
120.2(6)
123.8(6)
117.9(7)
125.8(8)
122.0(4)
124.5(4)
123.6(5)
122.8(5)
124.7(6)
122.7(5) (XꢂCl)
121.2(6) (XꢂCl)
125.5(7)
123.1(6) (XꢂBr)
124.6(6) (XꢂBr)
125.0(4)
123.2(3) (XꢂI)
123.8(3) (XꢂI)
121.0(5) (XꢂN)
119.7(5) (XꢂN)
119.7(6) (XꢂN)
X2ꢀC26ꢀC21
a
Distances and angles listed for only one molecule of 4.
Symmetry transformations used to generate equivalent atoms: ꢃxꢁ1, ꢃy, ꢃzꢁ1.
b
were arranged around inversion points with one Mo
atom and two complete ligands constituting the asym-
metric unit, as is normally the case for similar molecules
substituent increased from F, Cl to Br, there was an
increase in this angle assessed at 6.7, 13.7 and 18.38,
respectively [24]. This trend was not maintained with o-
iodobenzoic acid which had an interplanar angle of
16.5(4)8, see Table 5. The reason for this, as the data in
[23]. Compounds 1ꢀ3 each co-crystallized with two
/
axially bound THF molecules and 1 contained two
more THF molecules packed in a disordered arrange-
ment (atoms refined with isotropic thermal parameters
with restraints on the distances) in the void between the
molecules in the unit cell. This resulted in the formula-
tions given in Table 1. The fact that 4 does not possess
Table 5 illustrate, is that the dipoleꢀdipole interactions
/
between the halogen and carbonyl oxygen atoms are
minimized both by increasing this interplanar angle as
well as by the increase in the halogenꢀ
/
carbon atom
bond distance (see Table 5), from Cl to I. Further, upon
4ꢁ
any ligands bonded axially is the reason why the Moꢀ
/
coordination of the acid ligands to the Mo2 core, we
˚
Mo atom distances at 2.0943(10) and 2.0963(10) A for
find the ligand maintains the same trend regarding the
distances labeled as f and g in the diagram in Table 5, i.e.
these distances increase from Cl to I. However, the
corresponding interplanar angles for the Cl derivative 1
is more than twice that for the Br compound 2 and
identical to that for the iodo 3.
the two molecules is significantly shorter than the
at 2.1029(10),
corresponding distance in 1ꢀ
/
3
˚
2.1014(13) and 2.1055(7) A, respectively.
Table 5 lists the data for the interplanar carboxyꢀ
benzene angles for the free ligand and that of the
corresponding dimolybdenum complex. It was pre-
viously established that as the size of the o-halogen
/
It is noteworthy that within compounds 1, 3 and 4,
there were great differences in the same interplanar

T. Liwporncharoenvong, R.L. Luck / Inorganica Chimica Acta 340 (2002) 147ꢀ
/
154
151
Table 3
Visible spectra and electrochemical data for 1ꢀ
/
4
b
c
a
Complex
MW
UVꢀ/Vis
SR
Epc (mV)
Epa (mV)
E1/2 (mV)
DEp (mV)
ipc (mA)
ipa (mA)
(ipc/ipa)
1
2
3
4
813.88
424
424
424
100
100
100
100
631
611
606
739
706
690
686
821
674
654
646
780
75
79
80
82
6.68
7.95
9.99
4.28
8.88
10.25
11.49
8.08
0.75, 0.85, 0.88
0.76, 0.83, 0.88
0.87, 0.89, 0.91
0.53, 0.58, 0.49
991.48
1179.48
859.88
362, 464
Values for all complexes are listed at scan rates of 100, 500, and 1000 mV sꢃ1, respectively.
a
Electrochemical data are listed using notation in reference [19].
nm, THF.
b
c
BAS CV 50 electrochemical analyzer, SR, scan rate, glassy carbon working electrode, a platinum wire auxiliary electrode, a Ag/AgCl reference
electrode, 0.001 mol lꢃ1 tetrabutylammonium hexafluorophosphate in dried benzonitrile as supporting electrolyte (0.10 mol lꢃ1), ferrocene oxidized
at 510 mV under these conditions.
Table 4
Listing of oxidative potentials and MoꢀMo distance for various Mo2(O2CR)4 compounds and the pKa values for the corresponding acids
a
˚
R
pKa
E1/2 (ox) (mV)
MoꢀMo distance (A)
Working electrode, solvent
b
2-(NO2)C6H4
2-BrC6H4
2-IC6H4
2.18
2.85
2.86
2.88
3.44
3.36
792
647
655
674
610
570
2.0942(7)
2.1014(13)
2.1055(12)
2.1029(10)
GCE, benzonitrile
GCE, benzonitrile
b
b
GCE, benzonitrile
GCE, benzonitrile
b
2-ClC6H4
2,4,6-(CH3)3C6H2
2,6-(CH3)2C6H3
c
GCE, benzonitrile
GCE, benzonitrile
c
a
These are the pKa values for the corresponding carboxylic acids in water at 25 8C [21].
E1/2 measured in this study.
All data obtained from reference [17].
b
c
Fig. 1. Cyclic voltammogram plots at varying scan rates for 1
outer-; 0.500 middle-; and 1.000 inner-trace in V sꢃ1
/
top left, 2
/
bottom left, 3
/
top right, and, 4
/
bottom right. Scan rates: 0.100
*
*
*
*
.

152
T. Liwporncharoenvong, R.L. Luck / Inorganica Chimica Acta 340 (2002) 147ꢀ154
/
Fig. 4. ORTEP3 [22] representation of 3 displaying the atomic labeling
scheme. THF molecules and H atoms were omitted for clarity.
Thermal ellipsoids are drawn at the 50% probability level.
Fig. 2. ORTEP3 [22] representation of 1 displaying the atomic labeling
scheme. THF molecules and H atoms were omitted for clarity.
Thermal ellipsoids are drawn at the 50% probability level.
with an earlier study which established the Moꢀ
/
Mo
atom bond as insensitive [3].
carboxyꢀ
/
benzene angle as the data in Table 5 illustrates.
It was only in the bromo-derivative 2 that these angles at
13.8(6) and 15.1(4)8 were not significantly different. In
the case of o-nitrobenzene, the presence of a proton on
the carboxy group resulted in a change in this angle
from 30.26(3) (COOH) to 53.88(4)8 (COOꢃ), see Table
5. Clearly if just the protonation of the carboxy group
results in such a large change in the angle, crystal
packing forces present in 1 and 4 may be enough to
account for the variances therein. Therefore, this inter-
planar angle, while sensitive (i.e. near co-planarity) to
the size of the substituent, does not appear restricted in
any other way. Finally, the degree of twist does not
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 179597ꢀ
/
179601 for com-
pounds 1ꢀ5, respectively, with 5 representing a redeter-
/
mination of o-iodobenzoic acid. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
cause any change in the Moꢀ
Mo bond
distance, see Table 2, a conclusion which is consistent
/
Mo atom interaction
1EZ, UK (fax: ꢁ44-1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
/
judging from the similarities in the Moꢀ
/
Fig. 3. ORTEP3 [22] representation of 2 displaying the atomic labeling
scheme. THF molecules and H atoms were omitted for clarity.
Thermal ellipsoids are drawn at the 50% probability level.
Fig. 5. ORTEP3 [22] representation of two molecules that constitute 4
displaying the atomic labeling scheme. H atoms were omitted for
clarity and thermal ellipsoids are drawn at the 20% probability level.

T. Liwporncharoenvong, R.L. Luck / Inorganica Chimica Acta 340 (2002) 147ꢀ
/
154
153
Table 5
Comparison of selected carboxy-benzene interplanar angles and distances between o-halobenzoic acids and compounds 1ꢀ
/4
c
Selected distances
˚
(A)
o-Cl-benzoic
a
acid
o-Br-benzoic
b
acid
o-I-benzoic acid
1
2
3
Cl1
Cl2
Br1
Br2
I1
I2
A
1.346
1.202
1.521
1.405
1.737
3.217
2.892
1.295
1.208
1.487
1.362
1.885
3.275
3.004
1.304(5)
1.220(5)
1.488(5)
1.394(5)
2.104(4)
3.469(4)
1.271(7) 1.275(7) 1.278(7) 1.276(7) 1.274(5) 1.278(5)
1.264(7) 1.262(7) 1.270(8) 1.260(8) 1.272(5) 1.273(5)
1.482(9) 1.479(9) 1.482(9) 1.488(9) 1.489(6) 1.485(6)
1.416(9) 1.389(9) 1.408(9) 1.392(9) 1.390(6) 1.395(6)
1.726(7) 1.725(8) 1.911(8) 1.868(9) 2.101(4) 2.102(5)
3.180(6) 3.138(7) 3.343(7) 3.333(7) 3.428(4) 3.461(4)
2.918(5) 2.978(5) 2.967(4) 2.963(4) 3.193(3) 3.114(3)
B
C
D
E
F
G
Interplanar angles
3.105(3)
a
b
e
c
13.7
18.3
15.36(1) , 16.5(4) 27.5(4)
36.4(6)
13.8(6)
15.1(4)
27.9(4)
39.4(3)
d
(8)
a
Ref. [25].
Ref. [26].
Ref. [27,28].
b
c
d
For NO2, interplanar angles in the free ligand are 30.26(3)8 (COOH) and 53.88(4)8 (COOꢃ) [29], and in 4, 42.4(5), 64.0(5) and 52.6(5), 62.7(5)8.
Ref. [28].
e
[12] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C.
Acknowledgements
Giacovazzo, A. Gugliardi, A.G.G. Moliterni, G. Polidori, R.J.
Spagna, Appl. Crystallogr. 32 (1999) 115.
[13] L.J. Farrugia, Appl. Crystallogr. 32 (1999) 837.
We thank the Royal Thai government scholarship
program (to T.L.), Michigan Technological University
and the NSF (CHE-0079158) for generous support.
[14] G.M. Sheldrick, SHELXL97, Program for Crystal Structure Re-
finement, University of Gottingen, Gottingen, Germany, 1997.
¨ ¨
[15] (a) J.V. Brencic, F.A. Cotton, Inorg. Chem. 9 (1970) 351;
(b) A. Bino, F.A. Cotton, P.E. Fanwick, Inorg. Chem. 18 (1979)
1719;
(c) F.A. Cotton, L.R. Falvello, C.A. Murillo, Inorg. Chem. 22
(1983) 382.
References
[16] A. Carvill, P. Higgins, G.M. McCann, H. Ryan, A.J. Shiels, J.
Chem. Soc., Dalton Trans., (1989) 2435.
[1] F.A. Cotton, R.A. Walton, Multiple Bonds Between Metal
Atoms, second ed., Oxford, New York, 1993.
[17] M.H. Chisholm, K.C. Glasgow, L.J. Klein, A.M. Macintosh,
D.G. Peters, Inorg. Chem. 39 (2000) 4354.
[2] F.A. Cotton, J.G. Norman, J. Coord. Chem. 1 (1971) 161.
[3] F.A. Cotton, M. Extine, L.D. Gage, Inorg. Chem. 17 (1978) 172.
[4] A. Bino, F.A. Cotton, P.E. Fanwick, Inorg. Chem. 18 (1979)
1719.
[18] T. Liwporncharoenvong, R.L. Luck, J. Am. Chem. Soc. 123
(2001) 3615.
[19] D.T. Sawyer, A. Sobkowiak, Jr., J.L. Roberts, Electrochemistry
for Chemists (Chapter 3), Wiley Interscience, New York, 1995.
[20] T. Liwporncharoenvong, T.B. Lu, R.L. Luck, Inorg. Chim. Acta
329 (2002) 51.
[5] F.A. Cotton, L.R. Falvello, A.H. Reid, Jr., J.H. Tocher, J.
Organomet. Chem. 319 (1987) 87.
[6] F.A. Cotton, M.W. Extine, G.W. Rice, Inorg. Chem. 17 (1978)
176.
[21] J.A. Dean (Ed.), Lange’s Handbook of Chemistry, 13th ed.,
McGraw Hill, New York, 1979.
[7] F.A. Cotton, J.L. Thompson, Inorg. Chem. 20 (1981) 3887.
[8] F.A. Cotton, G.N. Mott, Inorg. Chim. Acta 70 (1983) 159.
[9] J.V. Brencic, F.A. Cotton, Inorg. Chem. 9 (1970) 351.
[22] L.T. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[23] Reference [1], p. 145.
[10] Enrafꢀ
/
Nonius (1994). CAD4 express software. EnrafꢀNonius,
/
[24] G. Ferguson, K.M.S. Islam, Acta Crystallogr. 21 (1966) 1000.
[25] (a) Data in table taken from G. Ferguson, G.A. Sim, Acta
Crystallogr. 14 (1961) 1262;
Delft, The Nethelands.
[11] A.C.T. North, D.C. Phillips, F.S. Mathews, Appl. Crystallogr., A
24 (1968) 351.

154
T. Liwporncharoenvong, R.L. Luck / Inorganica Chimica Acta 340 (2002) 147ꢀ154
/
(b) L. Golic, J.C. Speakman, Izv. Jug. Cent. Krist., Ser. A 10
(1975) 72.
[28] J.Z. Gougoutas, Cryst. Struct. Commun. 6 (1977) 703. Inter-
planar angle calculated using the program PARST (M. Nardelli, J.
Appl. Crystallogr. 28 (1995) 659) with data from the Cambridge
Data Base (CDB) (F.H. Allen, O. Kennard, R. Taylor, Acc.
Chem. Res. 16 (1983) 146).
[26] G. Ferguson, G.A. Sim, Acta Crystallogr. 15 (1962) 346.
[27] The structure of o-iodobenzoic acid was reported in Ref. [28].
However, this was with an R value of 8%. We have redetermined
this structure (R value of 2%, submitted as supplementary
material) for the purpose of getting more accurate bond lengths
and angles and this is where the data reported was obtained.
[29] G. Smith, J.M. Gentner, D.E. Lynch, K.A. Byriel, C.H.L.
Kennard, Aust. J. Chem. 48 (1995) 1151. PARST [28] used to
calculate angle with data from the CDB [28].