Molybdenum dithiolene complexes as structural models for the active sites of molybdenum(IV) sulfide hydrodesulfurization catalysts

Article abstract of DOI:10.1002/ejic.201000269

The removal of sulfur (as H₂S) from organosulfur species in petroleum feedstocks (hydrodesulfurization, HDS) is carried out on an enormous scale by using heterogeneous catalysts based on MoS₂ (usually doped with Co). Partially hydrogenated thiophenes are postulated intermediates in the MoS₂-catalyzed hydrodesulfurization of thiophene. The present contribution describes new molecular models for the proposed active sites in HDS catalysis. The models are derived from a mixed-ligand (push-pull) molybdenum trisdithiolene {[Mo(tfd)₂(bdt)]; tfd = S₂C ₂(CF₃)₂, bdt = S₂C₆H ₄}: selective intraligand alkyne binding converts the bdt group to a labile Mo-chelating benzodithiin, which can be substituted with a variety of weak donor ligands. The complexes [Mo(tfd)₂-(dht)₂] and [Mo(tfd)₂(tht)₂] (dht = 2,5-dihydrothiophene; tht =tetrahydrothiophene) were synthesized and crystallographically characterized. The Mo(tfd)₂ substructures closely resemble the presumed active site in MoS₂ HDS catalysts. The coordination geometries at molybdenum are approximately trigonal prismatic, and the metal bears two strongly bound dithiolene (tfd) groups and two comparatively weakly bound thioether ligands (dht or tht). Competitive binding experiments establish that tht binds more strongly to the Mo center than dht (K_eq = 6.5±0.5). Preliminary reactivity studies reveal that [Mo(tfd)₂(dht) ₂] decomposes to [Mo(tfd)₃], thiophene, and unidentified species upon heating. Further, [Mo(tfd)₂(tht)2] induces the isomerization of 1,4-cyclohexadiene to 1,3-cyclohexadiene at elevated temperatures.

Full text of DOI:10.1002/ejic.201000269

FULL PAPER
DOI: 10.1002/ejic.201000269
Molybdenum Dithiolene Complexes as Structural Models for the Active Sites
of Molybdenum(IV) Sulfide Hydrodesulfurization Catalysts
[a]
[a]
[b]
[a]
Neilson Nguyen, Daniel J. Harrison, Alan J. Lough, Antonio G. De Crisci, and
Ulrich Fekl*[
a]
Keywords: Molybdenum / Sulfur / Desulfurization / Heterogeneous catalysis
The removal of sulfur (as H
petroleum feedstocks (hydrodesulfurization, HDS) is carried
out on an enormous scale by using heterogeneous catalysts
2
S) from organosulfur species in
tetrahydrothiophene) were synthesized and crystallographi-
cally characterized. The Mo(tfd) substructures closely re-
semble the presumed active site in MoS HDS catalysts. The
2
2
based on MoS
nated thiophenes are postulated intermediates in the MoS
catalyzed hydrodesulfurization of thiophene. The present
2
(usually doped with Co). Partially hydroge-
coordination geometries at molybdenum are approximately
trigonal prismatic, and the metal bears two strongly bound
dithiolene (tfd) groups and two comparatively weakly bound
2
-
contribution describes new molecular models for the pro- thioether ligands (dht or tht). Competitive binding experi-
posed active sites in HDS catalysis. The models are derived
from a mixed-ligand (push–pull) molybdenum trisdithiolene
ments establish that tht binds more strongly to the Mo center
than dht (Keq = 6.5Ϯ0.5). Preliminary reactivity studies re-
{
[Mo(tfd)
2
(bdt)]; tfd = S
2
C
2
(CF
3
)
2
, bdt = S
2
C
6
H
4
}: selective in-
veal that [Mo(tfd)
phene, and unidentified species upon heating. Further,
[Mo(tfd) (tht) ] induces the isomerization of 1,4-cyclohexa-
2 2 3
(dht) ] decomposes to [Mo(tfd) ], thio-
traligand alkyne binding converts the bdt group to a labile
Mo-chelating benzodithiin, which can be substituted with a
2
2
variety of weak donor ligands. The complexes [Mo(tfd)
2
-
diene to 1,3-cyclohexadiene at elevated temperatures.
(
dht) ] and [Mo(tfd) (tht) ] (dht = 2,5-dihydrothiophene; tht =
2
2
2
lent activity in deep desulfurization,[4] the high activity of
those metals is offset by their cost. Developing increasingly
active Mo-based catalysts is thus a worthwhile goal, and we
focus here on molecular coordination compounds of mo-
Introduction
As high-grade petroleum reserves dwindle, lower and
lower grades of petroleum resources must be brought into
service to meet the continually growing energy demands.
Environmental concerns require that the sulfur content of
lybdenum. Heterogeneous MoS -based HDS catalysis has
2
been investigated by experimental surface techniques as well
as by computational (DFT) studies on cluster models.[
However, small molecular (soluble) models mimicking the
active sites in molybdenite HDS catalysts are rare.[ Small
molecule models should be useful for understanding the
mechanism of HDS catalysis and could lead to the develop-
5–7]
low-grade petroleum be reduced before use.[1] Hydrodesul-
furization (HDS) processes – the removal of sulfur from
8]
organosulfur species as H S – utilize catalysts based on mo-
lybdenum(IV) sulfide (MoS ; most commonly encountered
2
2
as the hexagonal molybdenite, usually modified with cobalt
for HDS applications) and hydrogen gas as a feedstock. As
a greater and greater efficiency is being demanded of hydro-
desulfurization techniques, the search for better catalysts
has intensified. Of special interest is the desulfurization of
[
6]
ment of better catalysts. It is thought that exposed (coor-
dinatively unsaturated) edges of MoS sheets are the active
2
[
9]
sites and that the internal centers are inactive. A fragment
of the molybdenite structure is shown in Figure 1, which
shows internal sites, edge sites, and key metric parameters.
As shown in Figure 1, the molybdenum edge sites possess
thiophenes, which are less reactive in HDS than noncyclic
thioethers and much-less reactive than thiols.[
2,3]
Thus, the
removal of sulfur from thiophenes and related “stubborn” pyramidal structures, with molybdenum at the apex of a
refractory) compounds (deep desulfurization) is a formida- square pyramid and four sulfur atoms forming the base of
(
ble challenge. While some noble metal catalysts show excel- the pyramid. Current evidence suggests that thiophene co-
ordinates to the molybdenum edge sites. The coordinated
thiophene then undergoes hydrogenation to 2,5-dihydro-
thiophene and, finally, desulfurization (through cyclorever-
[
[
a] University of Toronto,
3
359 Mississauga Road N, Mississauga, Ontario L5L 1C6,
Canada
Fax: +1-905-828-5425
sion) of the organic moiety produces 1,3-butadiene and a
[13]
terminal metal sulfide (Scheme 1).
Reduction of the
E-mail: ulrich.fekl@utoronto.ca
b] X-ray Crystallography Lab, University of Toronto,
metal sulfide with H releases H S and regenerates the un-
2
2
8
0 St. George St., Toronto, Ontario M5S 3H6, Canada
saturated Mo center.
Eur. J. Inorg. Chem. 2010, 3577–3585
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3577

N. Nguyen, D. J. Harrison, A. J. Lough, A. G. De Crisci, U. Fekl
vide here an alternative approach to the opening up of two
FULL PAPER
labile sites at “S Mo”.
4
The first coordination sphere of neutral molybdenum
trisdithiolenes resembles the environment of the internal
(non-edge sites) molybdenum atoms in molybdenite – in
both cases, the metal geometry is approximately trigonal
prismatic with six sulfur-donor ligands. Our group has pre-
viously reported that mixed-ligand molybdenum trisdithiol-
enes {[Mo(tfd) (bdt)] and [Mo(bdt) (tfd)] with tfd =
2
2
S C (CF ) , bdt = S C H } react with ethylene through the
2
2
3 2
2
6
4
sulfur atoms of one bdt ligand (i.e. intraligand alkene ad-
dition) to form a metal-chelating dihydrobenzodithiin moi-
[
24]
ety.
The weakly bound dihydrobenzodithiin can be sub-
Figure 1. Views of exposed molybdenum sites in hexagonal MoS
2
;
stituted with a variety of nucleophiles, which allows access
(
a) standard orientation, in which the hexagonal layers are oriented to new molybdenum bis- and trisdithiolene complexes. In
[10]
horizontally; (b) rotated to highlight the geometry
sites. The picture was generated with ORTEP,
of the edge
this paper we extend this versatile method to create molyb-
denum bisdithiolenes with thioether ligands (partially hy-
drogenated thiophenes), which provide structural models
[11]
by using MoS
2
[
12]
coordinates from the literature.
for postulated intermediates in MoS -based HDS catalysis.
2
Results and Discussion
The syntheses of our structural models exploits the li-
Scheme 1. Desulfurization of thiophene at a MoS
2
edge site.
gand-based reactivity of [Mo(tfd) (bdt)]: treatment of the
2
trisdithiolene with bis(trimethylsilyl)acetylene (btmsa)[
25]
gave [Mo(tfd) {bdt(btmsa)}], which was subjected to ligand
substitution with excess dht or tht (dht = 2,5-dihydrothio-
phene; tht = tetrahydrothiophene) to yield [Mo(tfd)2-
2
Accurate structural models of MoS -based HDS cata-
2
lysts should have the square-pyramidal structure (with Mo
at the apex and four sulfur donors forming the basal plane)
as seen for the edge sites in molybdenite. Additionally, the
model should incorporate vacant (or labile) sites to bind
organosulfur substrates (e.g. thiophene derivatives). While
(
dht) ] or [Mo(tfd) (tht) ], respectively, upon loss of the
2 2 2
metal-coordinated benzodithiin (Scheme 2, see experimen-
tal section for details). The resulting complexes were char-
acterized by multinuclear NMR spectroscopy, elemental
analysis, and X-ray crystallography. However, this approach
failed to produce any complexes with thiophene ligand.
many examples of molybdenum[
14–18]
[19]
(or tungsten ) com-
plexes bearing four sulfur donors are known, they usually
contain additional strongly bound ligands, such as thiolates
or phosphanes, which cannot be displaced by thioether
groups or other weakly coordinating sulfur donors. How-
ever, they do show catalytic activity toward nitrate and for-
mate reduction, and in that area, are showing promise as
models for enzymes. On the other hand, the few truly four-
coordinate MoS complexes {e.g. [Mo(SR) ], R = 2,4,6-
4
4
triisopropylbenzene} are extremely electrophilic toward
small donor molecules and form a variety of MoS L com-
4
[
20]
plexes, where L = (e.g.) alkyne, MeCN, tBuNC, CO.
However, these four-coordinate MoS complexes have tetra-
4
hedral rather than pyramidal geometry at the metal, which
makes them less desirable as model complexes for the mol-
[21]
ybdenite edge sites. Monosulfided molybdenum or tung-
[
19]
sten
species with dithiolene ligands [“SM(S C R ) ”]
2 2 2 2
have also been produced, and they may be regarded to be
excellent models for the intermediate obtained after butadi-
ene loss (right-hand side of Scheme 1). Schrauzer et al. pro-
duced thioether complexes on tungsten-based dithiolenes
by methylation of one of the dithiete ligands.[ [Mo(CO)2-
Scheme 2. Syntheses of [Mo(tfd)
Mo(tfd) (bdt)].
2 2 2 2
(dht) ] and [Mo(tfd) (tht) ] from
[
2
22]
(
S C Me ) ] complexes are known and offer both the
2 2 2 2
square-pyramidal MoS structure as well as labile CO
Figure 2 shows the crystallographically determined struc-
4
[
19,23]
groups.
as we also confirmed experimentally, see below), we pro- graphic data are summarized in the Exp. Sect. (Table 3).
While CO is a labile ligand in such complexes tures of [Mo(tfd) (dht) ] and [Mo(tfd) (tht) ]. Crystallo-
2
2
2
2
(
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 3577–3585

Mo Dithiolene Complexes as Models for Hydrodesulfurization Catalysts
The structures of [Mo(tfd) (dht) ] and [Mo(tfd) (tht) ] (Fig-
2
2
2
2
ure 2) are, expectedly, quite similar. In each case, the molyb-
denum centers are coordinated by six sulfur atoms. Two
adjacent (cis) coordination sites are occupied by thioether
ligands (dht or tht); these labile sites will possibly allow
access to mechanisms utilizing two coordination sites on
the same Mo atom. In [Mo(tfd) (dht) ], the π bonds of the
2
2
dht ligands do not interact with the metal (i.e. dht binds in
1
an η -S fashion), consistent with experimental (NEXAFS)
data for dht adsorbed on a sulfided molybdenum surface.[
26]
The “locked” conformation of the thioether ligands is likely
19
enforced by crystal packing. NMR spectroscopy ( F) indi-
cates apparent C2v symmetry for [Mo(tfd) (dht) ] and
2
2
[
Mo(tfd) (tht) ], which indicates interconversion between
2 2
ring conformers in solution. The crystal structure determi-
nations for [Mo(tfd) (dht) ] and [Mo(tfd) (tht) ] have
2
2
2
2
yielded detailed information on the sulfur environment in
such species, which is very consistent across the two struc-
tures. Key structural data are summarized in Table 1. The
Figure 2. Top: structure of [Mo(tfd)
2 2
2 2
(dht) ]. Bottom: structure of Mo–S(tfd) bond lengths (Table 1) for [Mo(tfd) (dht) ] and
[
Mo(tfd) (tht) ]. Non-hydrogen atoms are displayed by using 30%
thermal ellipsoids.
2
2
[
Mo(tfd) (tht) ] [average 2.335(1) Å and 2.333(1) Å, respec-
2 2
tively] are marginally shorter than the analogous Mo–S(tfd)
Table 1. Selected structural data for [Mo(tfd)
2
(dht)
2 2 2
] and [Mo(tfd) (tht) ].
[
Mo(tfd)
2
(dht)
2
]
2 2
[Mo(tfd) (tht) ]
Bond lengths (Å)
Mo–S(tfd)
Mo1–S1
Mo1–S2
Mo1–S3
Mo1–S4
Mo1–S5
Mo1–S6
2.336(2)
2.329(2)
2.337(2)
2.337(2)
2.520(2)
2.520(2)
Mo1–S1
Mo1–S2
Mo1–S3
Mo1–S4
Mo1–S5
Mo1–S6
2.331(1)
2.336(1)
2.324(1)
2.343(1)
2.513(1)
2.523(1)
Mo–S(thioether)
Bond angles [°]
S–Mo–S (tfd)
S1–Mo1–S2
S3–Mo1–S4
S5–Mo1–S6
S1–Mo1–S4
S1–Mo1–S5
S3–Mo1–S2
S3–Mo1–S5
S6–Mo1–S2
S6–Mo1–S4
81.28(6)
81.76(6)
75.20(6)
142.11(6)
127.77(6)
137.21(6)
136.69(6)
134.27(6)
129.85(6)
S1–Mo1–S2
S3–Mo1–S4
S5–Mo1–S6
S3–Mo1–S2
S1–Mo1–S4
S3–Mo1–S5
S1–Mo1–S5
S2–Mo1–S6
S4–Mo1–S6
81.50(5)
81.55(5)
73.85(4)
139.92(5)
138.83(5)
130.58(5)
133.30(5)
128.73(5)
135.44(5)
S–Mo–S (thioether)
S–Mo–S (trans S)
Nonbonded distances [Å]
S–S (trigonal face)
inter-tfd
S1–S3
S2–S4
S3–S6
S1–S6
S2–S5
S4–S5
3.170(2)
3.132(2)
3.239(2)
3.233(2)
3.150(2)
3.242(2)
S1–S3
S2–S4
S3–S6
S1–S6
S2–S5
S4–S5
3.117(2)
3.167(2)
3.277(2)
3.151(2)
3.268(2)
3.232(2)
tfd–thioether
S–S (prism edge)
inter-tfd
S1–S2
S3–S4
S5–S6
3.038(2)
3.059(2)
3.075(2)
S1–S2
S3–S4
S5–S6
3.047(2)
3.048(2)
3.026(2)
inter-thioether
Nonbonded angles (trigonal face) [°]
S–S–S
S3–S1–S6
60.77(6)
60.58(6)
58.65(6)
62.14(6)
59.21(6)
58.64(6)
0.59(11)
S3–S1–S6
S1–S3–S6
S1–S6–S3
S4–S2–S5
S2–S4–S5
S2–S5–S4
63.04(5)
58.99(5)
57.97(5)
60.29(5)
61.4(5)
58.3(5)
0.57(8)
S1–S3–S6
S1–S6–S3
S4–S2–S5
S2–S4–S5
S2–S5–S4
interplanar angle
S1–S3–S6 to S2–S4–S5
S1–S3–S6 to S2–S4–S5
Eur. J. Inorg. Chem. 2010, 3577–3585
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3579

N. Nguyen, D. J. Harrison, A. J. Lough, A. G. De Crisci, U. Fekl
FULL PAPER
bonds in [Mo(bdt) (tfd)][
24]
and [Mo(tfd)3][27] [average more octahedral character[27] (70% trigonal prismatic).[32]
2
2
.367(1) Å and 2.355(4) Å, respectively]. Particularly strik- In general, trigonal-prismatic structures are more likely for
n
[34]
ing is the fact that the thioether ligands are apparently very complexes with low d electron counts (i.e. d , n Յ 2).
weakly bonded, with Mo–S bond lengths that are much This has been explicitly discussed for MoS by using crystal
longer, by almost 0.2 Å, than the Mo–S(tfd) bonds. Indeed, field theory. Analogous effects have been shown compu-
2
[
35]
the Mo–S(thioether) bond lengths (thioether = dht or tht, tationally and experimentally for [Mo(butadiene) ] com-
3
[
36]
2
.51–2.52 Å) are among the longest molybdenum–sulfur plexes and computationally for M(CH3)6n complexes (M
bonds known.
= Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re, Ru, Os; n = –2,
[
37]
There are few examples of structurally characterized –1, 0, +1). The two complexes synthesized for the present
Mo–thioether complexes available for comparison. The study – [Mo(tfd) (dht) ] and [Mo(tfd) (tht) ] – are charge
2
2
2
2
IV
2
most similar one is the ethylene adduct [Mo(tfd)2- neutral and formally Mo (d ) species, with two ene–di-
bdt(CH CH )}], with an average distance of 2.523 Å to thiolate donors and two neutral thioether ligands. Similarly,
{
2
2
[
24]
the sulfur atoms on the dihydrobenzodithiin ligand. The neutral group VI metal trisdithiolenes, such as [Mo(tfd) ],
closest non-dithiolene-based Mo system is an octahedral can be reasonably formulated as a d species, with two dian-
3
IV
2
molybdenum “S -crown” thioether complex, with slightly ionic dithiolene ligands and one neutral, weakly donating
4
[
28]
[38]
shorter Mo–S(thioether) distances (2.469–2.498 Å).
dithioketone ligand.
The trigonal-prismatic geometries
Computed Mo–S distances for dht and tht bound to a observed at the metals in [Mo(tfd) (dht) ] and [Mo(tfd) -
2
2
2
Mo3S9 catalyst model fragment are 2.53 Å and 2.50 Å, (tht) ] can, therefore, be rationalized on the basis of low d
2
[
29]
respectively.
can be regarded as being structurally very similar to the plexes, with analogy to group VI metal trisdithiolenes. The
active sites they are modelling. observed trigonal prismatic geometries mimic the environ-
In both compounds, the coordination geometry at mo- ment of the Mo centers in molybdenum(IV) sulfide.
lybdenum is very close to trigonal prismatic. Figure 3 shows The S–Mo–S angles involving the thioether ligands are
the bond angles used to corroborate this statement. By very acute {75.2° for [Mo(tfd) (dht) ] and 73.9° for
Thus, [Mo(tfd) (dht) ] and [Mo(tfd) (tht) ] electron counts and neutral charge states for both com-
2 2 2 2
2
2
using the three largest S–M–Strans angles (Figure 3a) to po- [Mo(tfd) (tht) ]}. The S–Mo–S angles in the dithiolene che-
2
2
sition the structures on the scale ranging from perfect octa- late rings are much wider (ca. 82°) for both complexes.
hedron (0%) to perfect trigonal prism (100%),[
30]
[Mo- Interestingly, there are many examples in the literature of
(
tfd) (dht) ] and [Mo(tfd) (tht) ] were found to have 92% Mo (or W) bisdithiolene complexes with various non-di-
2
2
2
2
[
31]
and 94% trigonal-prismatic character, respectively.
The thiolene ligands that also exhibit this acute non-dithiolene
largest deviations in the SMStrans angles were ca. 14° {for ligand angle and wider dithiolene ligand bite angles. Rel-
Mo(tfd) (dht) ]} and ca. 11° {for [Mo(tfd) (tht) ]}. The tri- evant examples are summarized in Table 2. Despite a large
[
32]
[
2
2
2
2
angular faces of the trigonal prisms contain S–S–S (for- variation in non-dithiolene ligands (which are of variable
mally nonbonded) angles very close to 60° (Figure 3b) – steric demand), the non-dithiolene and the dithiolene bite
the largest deviation is ca. 3° in both cases (Table 1). This angles remain remarkably consistent.
observation is surprising insofar as the large difference be-
This narrow non-dithiolene ligand angle is intriguing. A
tween the Mo–S(tfd) and Mo–S(thioether) bond lengths similar observation was made by Holm and co-workers[
39]
could be expected to lead to a more distorted MoS sub- when narrow C–M–C bond angles for M(CO) (S C Me )
6
2
2 2
2 2
structure.
were observed: 83.5° for M = Mo and 84.1° for M = W.
These bond angles became smaller even more upon step-
wise reduction (monoanion, dianion), down to 72.3° for the
dianions. CO is, of course, a very special ligand because of
its π-acceptor properties, and Fomitchev, Lim and Holm[
concluded that the observed effect is “suggestive of a weak
bonding interaction between the carbonyl ligands”. For
those ligands that are not π acceptors, ligands such as dht
and tht in this work, alternative explanations are needed.
39]
Figure 3. Bond angles used for analysis; (a) example for S–M–Strans
angle, (b) example for S–S–S (nonbonding) angle.
The lowest-lying empty orbitals of the Mo(tfd) fragment
2
points toward an explanation. Using density functional
Trigonal-prismatic geometry, which maximizes ligand– theory (DFT), we found that both a pseudo-tetrahedral
metal and interligand π interactions,[ is quite common structure and the pyramidal structure that is relevant here
33]
for high-valent (oxidized) metal trisdithiolenes (e.g. neutral are minima on the hypersurface for Mo(tfd) , as confirmed
2
group six trisdithiolenes). Reduced analogues, on the other by geometry optimization and subsequent frequency analy-
hand, usually exhibit distortion toward octahedral geome- sis (no imaginary frequency). The pyramidal structure (up-
tries, thereby relieving ligand–ligand repulsion in these hill relative to the pseudo-tetrahedral structure by 12.3 kcal/
comparatively electron-rich systems. To illustrate, the metal mol) has two low-lying empty orbitals (LUMO and
geometry in neutral [Mo(tfd) ] is very close to trigonal pris- NLUMO), shown in Figure 4, that contain some p-orbital
3
[
27]
matic
(99% by using the S–M–Strans angle criterion, see contribution from the sulfur atoms but are largely metal-
while dianionic [Mo(tfd)3] has considerably based and correspond roughly to d
[
31]
2–
above),
x2–y2
(LUMO) and dyz
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 3577–3585

Mo Dithiolene Complexes as Models for Hydrodesulfurization Catalysts
2 2 2
Table 2. A comparative sampling of bite angles (°) in bisdithiolenes with various ligands [mnt = S C (CN) ].
Non-dithiolene bite
angle [°]
Dithiolene bite
angle (av.) [°]
Trigonal-prismatic Deviation[32] [°]
character [%]
Ref.
[31]
[
15]
15]
15]
15]
15]
15]
15]
15]
16]
15]
16]
16]
16]
17]
18]
18]
18]
24]
[
Et
4
4
N]
N]
N]
N]
N]
N]
N]
N]
N]
P]
2
[Mo
[Mo
2
(SCH
2
CH
(mnt)
4
Ph) (mnt) ]
2
OH)
4
]
2
(mnt)
4
]
68
67
68
67
68
66
67
68
66
72
76
77
76
77
76
77
78
72
75
74
83
82
83
82
83
82
83
82
86
82
83
82
82
82
83
81
83
82
82
82
82
96
95
87
92
93
91
86
88
98
83
93
73
90
74
94
81
86
92
94
25
12
10
21
18
14
20
22
23
7
21
10
29
17
28
14
23
20
14
11
[
[Et
2
2
(SPh)
2
[
[Et
4
2
[W
[W
[W
[W
2
(SCH
(SCH
(SCH
2
2
2
2
[
[Et
4
2
2
CH
CH
3
)
2
(mnt)
4
]
[
[Et
4
2
2
2
OH) (mnt) ]
2
4
[
[Et
4
2
2
(SPh)
2
(mnt)
(SCH Ph)
(SCH CH
(mnt)
(mnt) ]·0.5(CH
)(NCS)(mnt)
)(SC -4-Me)(mnt)
)(SC -2-COOH)(mnt)
)(mnt) ]·CH Cl
) (mnt) ]·CH
Ph)(mnt)
4
]
[
[Et
4
2
[Mo
[Mo
2
2
2 4
(mnt) ]
[
[Et
4
2
2
2
3 2
) (mnt) ]
4
[
[Et
4
2
[Mo(NCS)
[W(SPh)
2
2
]
[
[Ph
4
2
2
2
3 2
) CHOH
[
[Et
4
N][Mo(PPh
N][Mo(PPh
3
2
]
[
[Et
4
3
H
6 4
2
]
[
[
[
[
[
[
[
[
Ph
Et
PPh
PPh
Et
Mo(tfd)
Mo(tfd)
3
PNPPh
3
][Mo(PPh
3
6
H
4
2
]
[
4
N][Mo(SPh)(PPh
3
2
2
2
[
4
][Mo(PPh
][Mo(PPh
3
)(SCH
)(SCH
2
CH
3
2
2 2
Cl
[
4
3
2
2
]
[
4
N][Mo(PPh
3
)(Br)(mnt)
{bdt(CH CH )}]
(dht)
(tht)
2
]
[
2
2
2
2
2
2
]
this work
this work
[Mo(tfd)
2
]
(NLUMO), where the labeling assumes that we define the symmetrical arrangement of closest-packed sulfur atoms
paper plane to be the xy plane with y being vertical and x (Figure 5A) is striking, which is quantitatively re-enforced
horizontal. The system will be “frustrated” every time a by the very consistent nonbonded distances (Table 1).
Lewis acid/Lewis base adduct is formed with two added
lone-pair donors L: an L–Mo–L bond angle close to 90°
would optimize overlap with the NLUMO, which, however,
leads to poor overlap with the LUMO. Good overlap with
the orbital that is the LUMO in Mo(tfd) necessitates a
2
narrow L–Mo–L bond angle.
2 2
Figure 5. View of the sulfur environment of [Mo(tfd) (dht) ], by
using the van der Waals radii for the sulfur atoms; A: view perpen-
dicular to S2–3–S6 “close-packed” plane; B: view onto S5–S6 edge.
Figure 4. DFT-computed (B3LYP/SDD, see Experimental Section)
low-lying molecular orbitals (Kohn–Sham orbitals; left: LUMO,
While the preference for trigonal-prismatic (instead of
octahedral) geometry is electronic in origin (as is the acute-
ness of one S–Mo–S angle), the resulting structure is sur-
prisingly consistent with a closest-packing model in which
–
0.205 eV; right: NLUMO, –0.185 eV; plotted at 0.06 isovalue) of
geometry-optimized (local minimum but not global minimum) py-
ramidal Mo(tfd) . Note the similarity of the free pyramidal frag-
ment to the Mo(tfd) substructure in [Mo(tfd) (dht) ] and [Mo(tfd)
tht) ], shown in Figure 2 in a similar orientation.
2
2
2
2
2
-
(
2
the two closest-packed “S ” triangles are stacked on top of
3
another and in which the central Mo is dislocated from the
center toward the more donating sulfur atoms. In both
While the narrow bite angle described above is a devia-
[
Mo(tfd) (dht) ] and [Mo(tfd) (tht) ], the sulfur atoms are
2 2 2 2
tion from a perfect trigonal-prismatic geometry, the “trigo-
nal” planes in [Mo(tfd) (dht) ] and [Mo(tfd) (tht) ] are al-
found in a geometric arrangement very similar to that ob-
2
2
2
2
served for molybdenum inside solid MoS , including the
2
most perfectly parallel.
overlapping Van der Waals radii for adjacent sulfur centers.
If the S1–S3–S6 and S2–S4–S5 faces of both complexes
are taken to define planes, the angle between the two planes
is 0.59° and 0.57° for [Mo(tfd) (dht) ] and [Mo(tfd) (tht) ],
2
2
2
2
Reactivity
respectively (i.e. essentially parallel as in a true triangular
prism). In each triangular face, the sulfur atoms are essen-
The new complexes show some interesting and promising
tially closest packed. A diagram showing the van der Waals reactivity at slightly elevated temperatures (60–120 °C),
spheres for the sulfur atoms of [Mo(tfd) (dht) ] is shown in which, unfortunately, is accompanied by decomposition.
2
2
Figure 5 (the structure of the tht complex leads to a vir- [Mo(tfd) (dht) ] and [Mo(tfd) (tht) ] are stable for days at
2
2
2
2
tually identical picture). Visually, the impression of a very room temperature in nonpolar/noncoordinating solvents
Eur. J. Inorg. Chem. 2010, 3577–3585
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3581

N. Nguyen, D. J. Harrison, A. J. Lough, A. G. De Crisci, U. Fekl
9
FULL PAPER
(
e.g. C D ), but rapidly react with coordinating solvents an equilibrium constant (at 22 °C) of 3.7ϫ10 in favor of
6 6
such as thf and acetonitrile (color change to green or red, dht binding and thus explains the inability of thiophene to
respectively, observed immediately upon dissolution). Both displace dht.
complexes are somewhat unstable in chloroform, decaying
When [Mo(tfd) (dht) ] was heated in deuterated chloro-
2 2
within a few days at room temperature, and within 1 h at form (60 °C, 1 h), thiophene (12%, relative to original con-
1
6
0 °C. The decomposition products were identified by 19F/ centration) was identified by H NMR spectroscopy as one
1
H NMR as [Mo(tfd) ] and free thioethers (dht or tht). Pre- of the decomposition products. [Mo(tfd) ] was also ob-
3
3
sumably molybdenum metal is also deposited, as a faint served, as well as a smaller percentage of unidentified de-
darkening of the NMR tubes can be observed; this film is composition products (by 19F NMR spectroscopy). It there-
insoluble in organic solvents but dissolves in inorganic ac- fore appears that the dht ligands in the [Mo(tfd) (dht) ]
2
2
ids. The complexes are considerably more stable in C D : complex are dehydrogenated to thiophene, although free hy-
6
6
1
only minor decomposition was observed after heating either drogen gas was not observed in the H NMR spectrum.
complex to 60 °C for 1 d. These reactions were not catalytic when excess dht was
The complexes are sufficiently stable (in CDCl ) to deter- present. At the temperatures accessible to this system (be-
3
mine the relative binding constant of dht vs. tht with respect fore decomposition occurs), we have not been able to repro-
to coordination to the Mo(tfd) fragment. We found that ducibly demonstrate desulfurization. Butadiene, which
2
tht binds more strongly by a factor of 6.5(5) at a tempera- would be expected to form upon desulfurization of dht
ture of ca. 22 °C (Figure 6). The lesser binding affinity for (Scheme 1), was not observed in any of the reactions we
dht, relative to that for tht, is likely because of the electron- screened. Performing of the same reaction after an atmo-
withdrawing alkene group in dht, which can be expected to sphere of hydrogen was sealed into the tubes produced no
decrease the σ-donor ability of the thioether ligand. Substi- change in the product type or distribution. All hydrogen
tution of dht with thiophene was not observed at any con- reactions where done under a pressure of 1 atm; greater
centration of thiophene in CDCl or with neat thiophene. pressures may be needed to observe any reactivity. Many
3
These results can be compared to a recent computational proposed HDS mechanisms invoke the action of the sur-
[
41,42]
paper by Joshi et al. in which the adsorption energies of rounding sulfur atoms,
and/or multiple metal cen-
[
43,44]
various sulfur-containing molecules onto MoS is re- ters,
in MoS to facilitate the hydrodesulfurization of
The lowest binding energies for an unsaturated thiophene. Such pathways may not be accessible at the rela-
2
2
[
40]
ported.
molybdenum edge structure with tht and dht were found to tively low temperatures we tried (60–120 °C, as necessitated
be –1.67 eV and –1.60 eV, respectively, which corresponds by the temperature-sensitivity of our model complexes; cf.
[
2]
to an energy difference of –6.75 kJ/mol. Our experimentally 300–400 °C for industrial HDS processes ). It will be the
determined equilibrium constant corresponds to a differ- goal of future studies (with more temperature-stable ana-
ence in binding free energy of –4.6(2) kJ/mol (for tht vs. logs) to investigate whether a HDS cycle can be achieved
dht), quite consistent with the calculated value. Joshi et al. with a single molybdenum center or whether the participa-
[
44]
also calculated the binding energy of thiophene to be tion of more than one metal is required.
–1.04 eV, compared with –1.60 eV for dht (difference:
However, we observed the isomerization of 1,4-cyclo-
–
0.56 eV or –54 kJ/mol). This energy difference would yield hexadiene to 1,3-cyclohexadiene at 110 °C in [D ]cyclohex-
12
ane in the presence of [Mo(tfd) (tht) ]. Performing of the
2
2
same reaction with [Mo(tfd) (bdt)] did not yield any iso-
2
merized diene.
Finally, we would like to address the question of how the
lability of carbon monoxide (which binds weakly to molyb-
denum bisdithiolenes, see Introduction) relates to the la-
bility of thioethers. When a slow stream of carbon mon-
oxide is bubbled through a solution of [Mo(tfd) (dht) ] in
2
2
1
C D for a total of 4 h, a new complex is observed by H
6
6
and 19F NMR spectroscopy [ca. 70–90% conversion, as de-
19
termined by F NMR spectroscopy, with 3,5-bis(trifluoro-
methyl)bromobenzene internal standard]. The new species
is assigned as [Mo(tfd) (dht)(CO)]: NMR integration of the
2
dht protons yields that only one dht molecule is bound per
molybdenum. In addition, the amount of free dht observed
matches the dht bound to the new complex, in accord with
Figure 6. Determination of the equilibrium constant for the bind-
ing of tht vs. dht at 22 °C in CDCl , according to the equation:
3
Mo–dht + tht i Mo–tht + dht. The model, predicting a linear expectations from mass balance. When a large excess of dht
dependence of the ratio [Mo–tht]/[Mo–dht] vs. the ratio of free was added, the equilibrium shifted back to [Mo(tfd)2-
thioethers ([tht]/[dht]), fits the data very well (R2 = 0.9991). No
(
dht) ]. Thus, carbon monoxide and thioethers have a sim-
2
cooperativity is observed, and the two labile sites behave indepen-
dently in this process. The slope yields Keq = 6.5Ϯ0.5 (tht binds
more strongly, by a factor of close to seven, than dht). See Experi-
mental Section for details.
ilar binding strength when coordination to Mo(tfd) frag-
ments is involved. Some metal bisdithiolene complexes con-
taining carbonyls are already known,
2
[
19,23]
and it may be-
3582
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 3577–3585

Mo Dithiolene Complexes as Models for Hydrodesulfurization Catalysts
come useful knowledge for future syntheses that CO and NMR (100 MHz, CDCl
thioethers can be of comparable lability in such systems.
3
): δ = 30.109 (s, C
(724.59): calcd. C 26.52, H 2.23, S 26.55;
found C 26.82, H 1.97, S 26.23.
β α
, tht), δ = 42.31 (s, C ,
16 6
tht) ppm. C16H F12MoS
Synthesis of 2,5-Dihydrothiophene: Grubbs’ second generation
catalyst, 1,3-bis(2,4,6-trimethylphenyl)-2-(imidazolidinylidene)(di-
chlorophenylmethylene)(tricyclohexylphosphane)ruthenium,
Conclusions
Themolecularcompounds[Mo(tfd) (dht) ]and[Mo(tfd) -
2
2
2
(
tht) ] were synthesized and characterized as structural (75 mg, 88.3 µmol) was added to diallyl sulfide (75 mL of a 0.1 
2
models for the hydrodesulfurization catalyst molybdenum solution) in dry chloroform (7.5 mmol). The solution was stirred
disulfide. X-ray crystallography shows that they are excel- under a stream of argon for 24 h. The volatiles were vacuum trans-
ferred to a new container and heated to 70 °C until the volume was
lent models for the proposed active site of molybdenum di-
reduced to ca. 1 mL. The solution was vacuum-distilled a second
sulfide. Preliminary investigations show some intriguing re-
time to a new container and stored under nitrogen. NMR spec-
activity consistent with transfer dehydrogenation, yet tem-
troscopy showed the sample to consist of ca. 70% 2,5-dihydrothio-
perature-sensitivity hampers full exploration of this avenue.
phene and ca. 30% chloroform. Volumes used were adjusted for
It may be anticipated that molecular compounds for actual
HDS catalysis will have to be designed to be more robust
actual 2,5-dihydrothiophene content.
Synthesis of [Mo(tfd)
was repeated but with [Mo(tfd)
dihydrothiophene solution (50 µL), and btmsa (50 µL, 224 µmol).
The crystals were dried in vacuo to give [Mo(tfd) (dht) ] (24.4 mg,
3.8 µmol, or 44%). The crystals were stored under an inert atmo-
sphere and were stable at room temperature. X-ray quality crystals
2
(dht)
2
]: The procedure for [Mo(tfd)
2 2
(tht) ]
at high-temperature conditions, which will likely necessitate
departure from a close structural model. Additionally, it
may be necessary to consider models containing more than
one metal site (e.g. homo- or heterodimetallic complexes of
Mo). The new complexes are useful, however, to test equi-
2
(bdt)] (52.4 mg, 76.1 µmol), 2,5-
2
2
3
1
libria at room temperature, as demonstrated with a dht/tht were obtained directly from the hexane solution. H NMR
IV
competition on a sulfur-ligated Mo center.
(400 MHz, CDCl
3
): δ = 4.35 [m, 8 H, (CH
2
)ϫ4], 5.99 [m, 4 H,
): δ = –54.96 [s, 12 F,
): δ = 48.78 (s, CH ),
(720.56): calcd. C 26.67,
H 1.68, S 26.70; found C 26.89, H 1.49, S 26.04.
1
9
(
CH)ϫ4] ppm. F NMR (376 MHz, CDCl
3
1
3
(CF
3
)
2
ϫ2] ppm. C NMR (100 MHz, CDCl
12MoS
3
2
Experimental Section
δ = 126.62 (s, CH) ppm. C16
H
16
F
6
24]
[
Mo(tfd)
ond generation catalyst, tetrahydrothiophene (tht) (99%) and bis-
trimethylsilyl)acetylene (btmsa) (99%) were obtained from Sigma
2
(bdt)] was prepared by literature methods.[ Grubbs’ sec-
Attempted Synthesis of [Mo(tfd) (thiophene) ]: [Mo(tfd)
2 mg) was placed into an NMR tube with C (500 µL), btmsa
ca. 10 µL), and thiophene (ca. 5uL), and 3,5-bis(trifluoromethyl)-
2
2
2
(bdt)]
(
(
(
6 6
D
Aldrich. Tetrahydrothiophene was redistilled and dried with molec-
ular sieves (3 Å) before use. Bis(trimethylsilyl)acetylene was used
directly. Solvents were dried on a MBraun Solvent Purification Sys-
tem (MB-SPS). NMR spectroscopic data were collected on a
bromobenzene (ca. 3 µL) as an internal standard. After 2 h only
unreacted [Mo(tfd) (bdt)] and btmsa along with a smaller quantity
of the [Mo(tfd) {bdt(btmsa)}] adduct {20% yield relative to unre-
acted [Mo(tfd) (bdt)]} were identified by NMR spectroscopy and
integration. No new products could be detected. The procedure
for [Mo(tfd) (tht) ] was also repeated but by substituting tht with
2
1
13
1
2
Bruker Avance III 400 MHz spectrometer. H and C{ H} spectra
were referenced to the CDCl solvent peaks, (δ =7.26 ppm and
7.23 ppm, respectively). 1H spectra were also referenced to the
solvent peaks where applicable (δ = 7.16 ppm). 19F was refer-
enced to an external capillary of neat trifluoroacetic acid (δ =
78.5 ppm). Elemental analysis was performed by Chemisar
2
3
7
2
2
6 6
C D
thiophene. After 24 h, the solution remained green and no crystals
were observed.
–
Laboratories, Guelph, Ontario, Canada. DFT calculations were
performed on a Desktop PC by using Gaussian 03W Rev D.01[
on closed-shell singlets (charge-neutral molecules) with the
Thermal Decomposition of [Mo(tfd)
(2.5 mg, 3.5 µmol) was placed in an NMR tube with CDCl
(600 µL), and 3,5-bis(trifluoromethyl)bromobenzene (ca. 5 µ L) as
an internal standard. The mixture was heated to 60 °C for 20 h.
2
(dht)
2
]: [Mo(tfd)
2
(dht)
2
]
45]
3
[
46]
B3LYP
functional and SDD basis set (ECP) for molybdenum.
The SDD basis set is the combination of the Dunning/Huzinaga
2 2
Thiophene {12 % yield relative to starting [Mo(tfd) (dht) ]} was
identified in the products by using NMR spectroscopy and integra-
tion.
double-ζ basis set[47] on lighter elements with the Stuttgart–
[
48]
Dresden relativistic effective core potential
(RECP) on heavier
[
49]
elements. To improve the accuracy of the calculation, d functions
were added to all sulfur atoms [as polarization functions; d coeffi-
cients from the 6-311G(d,p) basis set]. No symmetry restrictions
were used, and default convergence criteria were employed.
NoncatalyticDehydrogenation ofdhtwith[Mo(tfd)
2
(dht)
] (0.7 mg, 0.967 µmol) was placed in an NMR tube with dht
600 µL of a 0.062  solution) in CDCl along with 3,5-bis(tri-
2 2
]:[Mo(tfd) -
(
(
dht)
2
3
fluoromethyl)bromobenzene (ca. 5 µL) as an internal standard. The
tube was heated to 60 °C for 24 h and then to 120 °C for 5 h. Thio-
phene was identified by NMR spectroscopy in a 43% yield based
Synthesis of [Mo(tfd)
4.5 µmol) was dissolved in dry hexanes (10 mL) along with tetra-
hydrothiophene (63.4 µL, 719 µmol) and btmsa (80.4 µL,
60 µmol), and the mixture was left to stand. Brown crystals slowly
2 2 2
(tht) ]: In air: [Mo(tfd) (bdt)] (51.3 mg,
7
2 2
on the reagent Mo (tfd) (dht) .
3
Hydrogen Reactivity: Both the thermal decomposition and the non-
catalytic dehydrogenation experiments were repeated, but before
heating, the NMR tubes were thoroughly degassed by freeze-pump-
thaw cycling. Hydrogen at atmospheric pressure was admitted to
the tubes (ca. 1 mL) and then sealed. Heating proceeded as de-
scribed previously. No new products or significant changes in prod-
uct distribution were observed by NMR spectroscopy.
came out of solution over ca. 1 h, and the solution turned red–
purple. After 18 h, the crystals were recovered by filtration and
washed three times with 5 mL portions of hexane. The crystals were
dried in vacuo to give [Mo(tfd) (tht) ] (39 mg, 54 µmol, 72%). The
2 2
crystals were stored under inert atmosphere and were found to be
stable at room temperature. X-ray quality crystals were obtained
directly from the hexane reaction mixture. 1H NMR (400 MHz,
1
9
CDCl
3
): δ = 2.28 (m, 8 H, tht), 3.54 (m, 8 H, tht) ppm. F NMR Isomerization of 1,4-Cyclohexadiene: [Mo(tfd)
2
(tht)
2
] (0.5 mg,
1
3
1
(
376 MHz, CDCl ): δ = –54.9 [s, 12 F, (CF ) ϫ2] ppm. C{ H}
3 3 2
0.69 µmol) and 1,4-cyclohexadiene (5 µL, 52.9 µmol) were added
Eur. J. Inorg. Chem. 2010, 3577–3585
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3583

N. Nguyen, D. J. Harrison, A. J. Lough, A. G. De Crisci, U. Fekl
FULL PAPER
to C
6
D
12 (500 µL) in an NMR tube and sealed. The contents were
integration. An excellent fit was obtained for the simple model Mo–
dht + tht i Mo–tht + dht, which demonstrates that the two labile
sites at Mo have a very similar preference for binding tht vs. dht,
i.e. no cooperativity is observed. The equilibrium constant (for the
reaction as written, Mo–tht as the product of the reaction) is equal
to ([Mo–tht]/[Mo–dht])([tht]/[dht]) , and a straight line was indeed
obtained from plotting the ratio [Mo-tht]/[Mo-dht] against the ra-
tio [tht]/[dht] (Figure 5). The slope yields Keq = 6.5(5); tht binds
more strongly than dht by that factor. A similar experiment was
performed with thiophene (NMR, 20 °C). No substitution was ob-
served at any concentration including neat thiophene.
1
heated to 110 °C for 24 h. H NMR spectroscopy revealed isomer-
ization to 1,3-cyclohexadiene (35% by NMR integration).
Reaction with Carbon Monoxide to Produce [Mo(tfd)
Mo(tfd) (dht) ] (2 mg, 2.77 µmol) was added to C
an NMR tube along with 3,5-bis(trifluoromethyl)bromobenzene
ca. 5 µL) as an internal standard. Carbon monoxide gas was gently
2
(dht)(CO)]:
[
2
2
6 6
D (400 µL) in
–
1
(
bubbled into the solution for a total of 4 h with occasional refilling
of the solvent to make up for evaporation losses. The yellowish-
brown solution turned bright orange, and a new complex was iden-
tified by 19F NMR spectroscopy and integration {70–90% yield
1
relative to [Mo(tfd)
2
(dht)
2
]}. H NMR spectroscopy and integra-
2 2
CCDC-762433 and CCDC-762434 for [Mo(tfd) (tht) ] and [Mo-
tion showed an equal amount of free dht and bound dht on this
complex {excluding dht bound to known [Mo(tfd) (dht) ]}. The
sample was degassed by freeze-pump-thaw cycling, and dht (300 µL
of a 0.067  solution) in C (20 µmol) was added, followed by
shaking. After 2 h, NMR integration revealed 85% [Mo(tfd)
dht) ] and 15% [Mo(tfd) (dht)(CO)], which indicates that the equi-
librium shifted back to the starting materials. H NMR (400 MHz,
): δ = 2.66 [m, 8 H, (CH )ϫ4], 4.60 [m, 4 H, (CH)ϫ4] ppm.
F NMR (376 MHz, C ): δ = –54.92 [s, 12 F, (CF ϫ2] ppm.
(
tfd) (dht) ] (Table 3), respectively, contain the supplementary crys-
2
2
2
2
tallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
6
D
6
2
-
(
2
2
1
Acknowledgments
C
6
9
D
6
2
1
6
D
6
3 2
)
Funding by the Natural Science and Engineering Research Council
Determination of Keq (Preferred Binding of tht Over dht): A stock
solution of dht in CDCl was prepared by adding diallyl sulfide
200 µL ) to CDCl (16 mL) and Grubb’s catalyst (10 mg). After
4 h, the reaction was checked for completion by NMR spec-
(
NSERC) of Canada is gratefully acknowledged, along with an
3
Early Researcher Award (Province of Ontario) to U. F.
(
2
3
troscopy, and the volatiles were purified by vacuum transfer. The
concentration of the stock solution was approximately 0.097 . The
method used for the determination of the equilibrium constant is
based on relative ratios (by NMR integration) and not on absolute
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[
[
3] I. V. Babich, J. A. Moulijn, Fuel 2003, 82, 607–631.
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Matter 2008, 20, 064236–064244.
amounts. [Mo(tfd)
an NMR tube. The NMR spectra were recorded at 22 °C. After
each spectrum, a small amount of dht in CDCl was added. The
2 2 3
(tht) ] (2 mg) was added to CDCl (400 µL) in
3
[
[
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(dht)
2
]
[10] This simple picture is based on the structure of bulk material
and neglects surface reconstruction.
and [Mo(tfd) (tht) ].
2
2
[
Mo(tfd)
2
(dht)
2
]
[Mo(tfd)
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(tht)
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Empirical formula
Formula mass
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C
720.56
0.08ϫ0.06ϫ0.02
triclinic
16 12
H F
12Mo
1
S
6
16 16 1 6
C H F12Mo S
724.59
0.24ϫ0.16ϫ0.10
monoclinic
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[
[
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12.1554(8)
12.9245(9)
76.092(3)
90.074(4)
69.878(3)
1186.03(12)
2
150(2)
0.71073
708
4826/0/317
2.018
1.181
12.0316(5)
25.0104(6)
8.4960(4)
90
109.275(1)
90
2413.27(16)
4
150(1)
0.71073
1432
5440/0/316
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1.161
13879
5440
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7732
4826
1.164
0.0553
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3584
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 3577–3585

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[
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[
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31] The degree of trigonal prismatic character by the S–M–Strans
criterion is determined by first taking the individual “corner”
sulfur atoms on one triangular face of a trigonal prism and
then measuring the S–M–S angles to all the sulfur atoms on
the opposite triangular face. Nine angles are obtained this way.
The average of the three largest angles is used to determine the
degree of octahedral vs. trigonal prismatic character using S–
M–Strans. The S–M–Strans values for a perfect octahedron and
a perfect trigonal prism are 180° and 136°, respectively. Small
chelate bite angles may constrain S–M–Strans from reaching the
octahedral limit, so a correction is applied (εcorr). εcorr is found
by εcorr = 90° + S–M–Sintra, where S–M–Sintra is the average of
the three smallest angles S–M–S angles that correspond to the
sulfur atoms on the same chelating ligand (chelate “bite”). Fi-
nally the degree of prismatic character on the scale ranging
from perfect octahedron (0%) to perfect trigonal prism (100%
TP) is found by using %TP = [1 – (S–M–Strans – 136°)/(εcorr
1
–
36°)] ϫ100%. This criterion is paraphrased from ref.[ but
30]
inversely scaled so that trigonal prismatic character is 100%
while octahedral is 0%.
[
32] For some sense of distortion, the largest deviation is found by
removing the S–M–Sintra angles from the previous set of nine
angles found in ref.[ and by taking the difference between the
smallest and largest angles in the remaining six.
31]
[
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n
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[
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Received: March 8, 2010
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Published Online: July 6, 2010
Eur. J. Inorg. Chem. 2010, 3577–3585
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3585