Unusual saddle-like structure of (2-MeOC6H4CS) 2S: Theoretical studies and comparison with its oxygen isologues

Article abstract of DOI:10.1002/zaac.201200357

Compound (2-MeOC₆H₄CS)₂S (1) showed an unusual saddle structure in which the -C(=S)-S-C(=S)- moiety is planar and two benzene rings lie a face-to-face and the distances (3.07 A) between the central sulfur atom and two 2-methoxy oxygen atoms are within the sum of van der Waals radii of the both atoms. However, the results of MO calculation at the B3LYP/6-311+G(2d, p) level showed no orbital interaction between both atoms. From the results of the calculations at the MP2 level, it was deduced that the crystal packing effect is important for such densely packed crystal, due to its less effective volume. On the other hand, the para-methoxy derivative (4-MeOC₆H₄CS)₂S (2) in which the two methoxy oxygen atoms are not able to contact with the central sulfur atom shows an L-shaped structure in which the -C(=S)-S-C(=S)- moiety is not planar. The -C(=O)-S-C(=S)- moiety in compound (2-MeOC₆H₄CO)(2- MeOC₆H₄CS)S (3b) shows an L-shaped structure, though the two methoxy oxygen atoms are in intramolecular contact with the central sulfur atom. The deep blue to green colors of compounds 1 and 2 and the deep violet color of compound 3b are due to transitions of the lone-pair electrons in the HOMO (ψ₈₇) of the thiocarbonyl sulfur atom to the LUMO (ψ₈₉)and of those in the HOMO (ψ₈₃) of the thiocarbonyl sulfur atom to the LUMO (ψ₈₅), respectively. Copyright

Full text of DOI:10.1002/zaac.201200357

ARTICLE
DOI: 10.1002/zaac.201200357
Unusual Saddle-like Structure of (2-MeOC6H4CS)2S: Theoretical Studies
and Comparison with its Oxygen Isologues
Osamu Niyomura,[a] Yuka Kito,[a] Shinzi Kato,*[b] Masaru Ishida,[a] Masahiro Ebihara,[a]
Satoko Hayashi,[c] and Waro Nakanishi*[c]
Keywords: Acyl thioacyl sulfides; Bis(thioacyl) sulfides; MO calculation; Molecular structure; X-ray diffraction
Abstract. Compound (2-MeOC6H4CS)2S (1) showed an unusual sad-
with the central sulfur atom shows an l-shaped structure in which the
dle structure in which the –C(=S)–S–C(=S)– moiety is planar and two –C(=S)–S–C(=S)– moiety is not planar. The –C(=O)–S–C(=S)– moi-
benzene rings lie a face-to-face and the distances (3.07 Å) between the ety in compound (2-MeOC6H4CO)(2-MeOC6H4CS)S (3b) shows an
central sulfur atom and two 2-methoxy oxygen atoms are within the
sum of van der Waals radii of the both atoms. However, the results of molecular contact with the central sulfur atom. The deep blue to green
MO calculation at the B3LYP/6-311+G(2d,p) level showed no orbital colors of compounds 1 and 2 and the deep violet color of compound
interaction between both atoms. From the results of the calculations at 3b are due to transitions of the lone-pair electrons in the HOMO (ψ87)
the MP2 level, it was deduced that the crystal packing effect is impor- of the thiocarbonyl sulfur atom to the LUMO (ψ89) and of those in
tant for such densely packed crystal, due to its less effective volume. the HOMO (ψ83) of the thiocarbonyl sulfur atom to the LUMO (ψ85),
l-shaped structure, though the two methoxy oxygen atoms are in intra-
On the other hand, the para-methoxy derivative (4-MeOC6H4CS)2S
(2) in which the two methoxy oxygen atoms are not able to contact
respectively.
saddle structure of bis(2-methoxybenezenecarbothioyl) sulfide
and theoretical studies for a series of the corresponding acyl
thioacyl and diacyl sulfides and acid anhydride RC(E2)E1C(E3)
R (R = 2-MeOC6H4, 4-MeOC6H4; E2, E1, E3 = O, S).
Introduction
In a previous paper, we stated that bis(2-methoxybenzoyl)
telluride, which is a tellurium isologue of acid anhydrides, is
nearly planar with intramolecular interactions between the
two methoxy oxygen atoms and the central tellurium and be-
tween the two carbonyl oxygen atoms[1] (Scheme 1). Although
we reported the syntheses of a series of acyl thioacyl[2] and
bis(thioacyl) sulfides,[3] X-ray molecular structure analyses
have not yet been performed. To the best of our knowledge,
only the structures of cyclic acyl thioacyl and bis(thioacyl)
sulfides[4,5] and an acyclic sulfide (4-MeC6H4CS)2S[6] have
been described in the literature. We describe here an unusual
Scheme 1. (2-MeOC6H4CO)2Te.
Results and Discussion
* Prof. S. Kato
Fax: +81-52-222-2442
E-mail: kshinzi@nifty.com
* Prof. W. Nakanishi
Preparation of Acyl Thioacyl Sulfides (3)
E-Mail: nakanisi@sys.wakayama-u.ac.jp
[a] Department of Chemistry
Faculty of Engineering
Gifu University
For the preparation of compounds of type 3, the previous
method[2] using acyl chloride with sodium carbodithioates is
disadvantageous with regard to purification of the products due
to the difficulty of removing unreacted acyl chlorides and by-
product NaCl. We found that the use of potassium carbodi-
thioates instead of the sodium salts leads to the complete reac-
tion of acyl chlorides, a shorter reaction time and easy removal
of by-product KCl. (Scheme 2)
Gifu 501–1193, Japan
#
Present address: Maruno-uchi 2–14–32,
Lions-City Maruno-uchi 1105
Naka-ku, Nagoya 460–0002, Japan
[b] Department of Applied Chemistry
College of Engineering
Chubu University
Kasugai 487–8501, Japan
[c] Department of Material Science
Faculty of Systems Engineering and Chemistry
Wakayama University
Molecular Structures
Wakayama, 650–8510, Japan
The molecular structure of bis(2-methoxybenezenecar-
bothioyl) sulfide (1) is shown in Figure 1 along with that of
bis(4-methoxybenezenecarbothioyl) sulfide (2)[2] for compari-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201200357 or from the au-
thor.
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Unusual Saddle-like Structure of (2-MeOC6H4CS)2S
(b)), which suggests that there may be weak intramolecular
π–π interaction between the carbon atoms. Presumably, a
twisted conformation associated with the benzene ring and di-
thiocarboxyl group may allow for this face-to-face approach
of the benzene rings. To the best of our knowledge, such an
unusual saddle-like structure in which two benzene rings show
a face-to-face approach is the first example among carbochal-
cogenoic anhydrides [RC(E’)–E–C(E’)–R, E = O, S, Se, Te;
E’ = O, S].
In the para-methoxy derivative 2, which does not show any
intramolecular interaction between the methoxy oxygen and
the thiocarbonyl or central sulfur atoms, the interplanar angle
S(12)–C(11)···C(21)–S(21) is 84.7(2)°, which reflects an L-
shaped structure (Figure 1 (b), right). The S(12)–C(11)–C(12)–
C(13) and S(11)–C(21)–C(22)–C(23) torsion angles are
14.7(3)° and –18.9(3)°, respectively, which indicates that there
is a small twist between the benzene ring and dithiocarboxyl
groups.
The X-ray molecular structure of compound 3b, in which
one of the two thiocarbonyl sulfur atoms of 1 is replaced by
an oxygen atom, is shown in Figure 3 along with those of
bis(2-methoxybenzoyl) sulfides (4)[1] and 2-methoxybenzoic
anhydride (5)[1,7] for comparison.
Scheme 2.
son. Their crystal data and data-collection parameters as well
as selected bond lengths and angles are summarized in Table 1
and Table 2, respectively.
In compound 3b, the two benzene-ring planes are consider-
ably twisted from the planes of the associated –C(O)S– or
–C(S)S– groups (C(21)–S(11)–C(11)–C(12)
= 32.8(2)°;
S(11)–C(11)–C(12)–C(13) 53.3(3)°, respectively). The
=
O(11)···S(11) and O(12)···S(11) distances are 2.663(2) Å and
3.117(2) Å, respectively, which are shorter than the sum of the
van der Waals radii of both atoms (3.32 Å), though the dis-
tances are significantly different. Such interaction is consid-
ered to reflect an intermediate structure between compound 1,
in which both ortho-methoxy oxygen atoms are in intramolec-
ularly contact with the central sulfur atom and compound 4,
in which neither of the ortho-methoxy oxygen atoms are in
intramolecular contact with the central atom. The
O(12)···S(11)–C(21) linkage in compound 3b is nearly linear
(175.8°), suggesting that the strength of the O(12)···S(11) inter-
actions may be enhanced. Moreover, the S(11)–C(11)/S(11)–
C(21) distances are apparently different, 1.830(2) Å and
1.758(4) Å, respectively (see below: ab initio calculations).
Compound 4 has a –C(O)SC(O)– moiety in which the two
C=O groups point in the same direction. The benzene ring
planes are appreciably twisted from the plane of the associ-
ated –C(O)S– group [O(11)–C(11)–C(12)–C(13)/O(21)–
C(21)–C(22)–C(23) = 22.1(1)°/–56.5(2)°], respectively. The
O(11)=C(11)···C(21)=O(21) interplanar angle is 30.6°. One
of the two ortho-methoxy oxygen atoms (O(12)) is in intramo-
lecular contacts with the central sulfur atom S(11), while the
other (O(22)) is in contact with the carbonyl oxygen atom
O(21). The O(12)···S(11) and O(22)···O(21) distances are
2.719 Å and 2.761 Å, respectively, which are significantly
shorter than the sum of the van der Waals radii of both atoms
(O···S = 3.32 Å and O···O = 3.04 Å, respectively[1,7]). The
O(21)···O(11) distance (2.761 Å) also suggests weak non-
Figure 1. Molecular structures of (2-MeOC6H4CS)2S (1) (a) and (2-
MeOC6H4CS)2S (2) (b). All hydrogen atoms have been omitted for
clarity. The thermal ellipsoid plots represent 50% probability.
Compound 1 has a C2 symmetry axis through the central
sulfur atom S(11), where the [–C(11)=S(12)–S(11)–
C(21)=S(21)–] moiety is planar and the two methoxy groups
are situated opposite each other across the C(11)–S(11)–C(21)
plane (Figure 1 (a)). The C(11)–S(11)–C(21) and
O(11)···S(11)···O(21) planes cross each other at nearly a right
angle on the central sulfur atom S(11). The O(11)···S(11) and
O(21)···S(11) distances are both almost 3.07 Å, which is signif-
icantly shorter than the sum of the van der Waals radii of the
two atoms (3.32 Å) (Figure 2, (a)). Moreover, the two benzene
rings with a dihedral angle of approx. 27° are situated very
close together to give a nearest plane-to-plane distance of
3.18 Å (C(13)···C(22)), which is comparable to the sum of the bonding interaction.[1] The linearity of both the O(12)···S(11)–
van der Waals radii of both carbon atoms (3.42 Å) (Figure 2, C(21) (173.5°) and O(11)···O(21)···O(22) linkages (143.5°)
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Table 1. Crystal data and data collection of (2-MeOC6H4CS)2S (1), (4-MeOC6H4CS)2S (2), and (2-MeOC6H4CO)(2-MeOC6H4CS)S (3b).
Table 2. Selected bond lengths /Å, angles /° and torsion angles /° of (2-MeOC6H4CS)2S (1), (4-MeOC6H4CS)2S (2),
and (2-MeOC6H4CO)(2-MeOC6H4CS)S (3b).
suggests that the orbital interactions between O(12)···S(11) and angle: O(21)–C(21)–C(22)–C(23) = –142.3(1)°), while the
between O(21)···O(22) may be enhanced.
other and the plane of the other associated –C(O)O– group are
On the other hand, the corresponding acid anhydride (2-Me- almost coplanar (torsion angle O(11)–C(11)–C(12)–C(13) =
OC6H4CO)2O (5) assumes an L-shaped structure in contrast to 6.5(2)°). Both the O(11)···O(13) and O(21)···O(22) distances
compound 4 (O(13)···O(11)···C(22) angle is 76.4(2)°) (Figure 3 are short at 2.691(2) Å and 2.651(3) Å, respectively, and the
(c), right). One of the benzene ring planes is considerably O(13)···C(11) and O(22)···C(21) distances are 2.842(2) Å and
twisted from the plane of the associated –COO– group (torsion 2.780(2) Å, respectively. These are significantly shorter than
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Unusual Saddle-like Structure of (2-MeOC6H4CS)2S
determined according to the values of θ1 and θ2 as synperi-
planar (sp), synclinal (sc), anticlinal (ac), or antiperiplanar (ap)
[8]. Table 3 shows the conformations of compounds 1, 2, 3b,
4, and 5 along with the torsion angles (θ1 and θ2) The angles
θ1 and θ2 vary remarkably (9° Ͻ θ1/θ2 Ͻ 172°) according
the number of sulfur atoms replaced by a –C(E2)E1C(E3)–
moiety, so that compounds 1, 2, 3b, 4, and 5 adopt various
conformations (ap/ap, ac/sp, sc/ap, sp/sp and sp/ac, respec-
tively). For compounds 1, 3b, 4, and 5, which have o-methoxy
groups, the ap conformation is preferable for the carbothioate
(–COS–) or carbodithioate groups (–CSS–), while the sp con-
formation is more advantageous than ap for the carbothioate
group (–COS–). Moreover, the conformations of bis(thioaroyl)
sulfides (1 and 2) are influenced by the position of the substitu-
ents on the benzene ring, i.e., an ortho-substituent leads to an
[ap/ap] conformation, whereas a para-substituent leads to an
[sp/ac] conformation.
Figure 2. Top (a) and side views (b) of compound 1 (distances in Å).
Scheme 3.
Intermolecular Short Contacts and Molecular Arrangement
The arrangements of compounds 1 and 2, 3b, 4, and 5
formed by S···H and O···H hydrogen bonding interactions and
S···S, S···C, O···C, C···C and C···H short contacts are shown in
Figure 4 and in the Supporting Information Figure S1, respec-
tively.
For compound 1, intermolecular S···H hydrogen bonding
and C–C/π interactions are observed between the thiocarbonyl
sulfur and benzene-ring hydrogen atoms, and between the
benzene ring-carbon atoms, respectively (Figure 4, (a)). The
molecules are arranged linearly by the CC/π interactions be-
tween the benzene-ring carbon atoms (Figure 4, (b)). The lin-
early arranged molecules have intermolecular contacts be-
tween the thiocarbonyl sulfur and benzene-ring hydrogen
atoms, to give a molecular sheet as shown in Figure 4, (c).
Moreover, these sheets are stacked vertically with respect to
Figure 3. Molecular structures of (a) (2-MeOC6H4CO)(2-Me-
OC6H4CS)S (3b), (b) (2-MeOC6H4CO)2S (4), and (c) (2-Me-
OC6H4CO)2O (5). All hydrogen atoms have been omitted for clarity.
Black dotted lines show intramolecular short contacts. Distances are each other to form 3D networks by intermolecular contacts, in
given in Å. The thermal ellipsoid plots represent 50% probability.
which columns such as A (9.7 ϫ 7.6 Å) are formed (Figure 4,
(d)).
the sum of the van der Waals radii of both atoms (3.04 Å),
For the para-methoxy derivative 2, intermolecular S···H and
which suggests intramolecular interactions between the meth- O···H hydrogen bonds between the thiocarbonyl sulfur and
oxy oxygen atom and the carbonyl group. Thus, one of the methoxy-methyl hydrogen atoms and between the methoxy
two ortho-methoxy oxygen atoms is in contact with the central oxygen and methoxy-methyl hydrogen atoms, respectively, and
oxygen atom, while the O(22) is in contact with the carbonyl weak S···S, S···C and O···C short contacts between the thiocar-
oxygen O(21) (Figure 3 (c), left).[7]
bonyl sulfur atoms, between the thiocarbonyl sulfur and benz-
Regarding the conformers of acid anhydrides, the torsion ene-ring carbon atoms and between the methoxy oxygen and
angles θ1 and θ2 in the –C(E2)E1C(E3)– moiety (E1, E2, E3 = methoxy-methyl carbon atoms, respectively, are observed
O, S) were defined (Scheme 3), and their conformation were along with weak CH/π interactions both between the methoxy-
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Table 3. Conformations and torsion angles of compounds 1–5.
Figure 4. Intermolecular short contacts and molecular arrangement of (2-MeOC6H4CS)2S (1). Dotted lines in (b)–(d) show intermolecular short
contacts. (a) The atoms denoted with a prime show neighboring molecules. (b) The one-dimensional linear chain formed by short contacts
between benzene-ring carbon atoms. (c) Two-dimensional sheet formed by the S···H hydrogen bonding between the thiocarbonyl sulfur and
benzene-ring hydrogen atoms and the C···C short contacts between benzene-ring carbon atoms. (d) 3D networks formed by stacking of these
sheets.
methyl hydrogen and the benzene-ring carbon atoms and be- which rectangular columns such as A (10.2 ϫ 4.4 Å) are
tween the benzene-ring hydrogen and carbon atoms[9] (Figure formed (Figure 5, (c)).
S1 (a)).
In the case of (acyl)(thioacyl) sulfide 3b, intermolecular
The molecules of para-methoxy derivative 2 are arranged O···H hydrogen bonds between the carbonyl oxygen and both
linearly by both hydrogen bonding between the methoxy oxy- methoxy-methyl and benzene-ring hydrogen atoms and be-
gen and methoxy-methyl hydrogen atoms and weak O···C short tween the methoxy oxygen and methoxy-methyl hydrogen
contacts between the methoxy oxygen and the methoxy-methyl atoms, respectively, and weak S···C short contacts between the
carbon atoms (Figure 5, (a)). The linearly arranged molecules thiocarbonyl sulfur and benzene-ring carbon atoms are ob-
have intermolecular contacts between the methoxy oxygen and served along with weak CH/π interactions between the meth-
methoxy-methyl hydrogen atoms and weak O···C short con- oxy-methyl hydrogen and benzene-ring carbon atoms[9] (Fig-
tacts between the methoxy oxygen and methoxy-methyl carbon ure S1 (b)). The molecules are arranged linearly by hydrogen
atoms, to form a ladder and sheet as shown in (Figure 5, (b)). bonds between the carbonyl oxygen and benzene-ring hydro-
Moreover, these sheets are stacked vertically with respect to gen atoms (Figure 6, (a)). Short intermolecular contacts be-
each other to form 3D networks by intermolecular contacts, in tween the methoxy-methyl hydrogen and the benzene-ring car-
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Unusual Saddle-like Structure of (2-MeOC6H4CS)2S
Figure 5. Molecular arrangement of (4-MeOC6H4CS)2S (2). Dotted lines show intermolecular short contacts. a) One-dimensional linear chain
formed by short contacts between methoxy oxygen and hydrogen and/or carbon atoms. (b) Two-dimensional sheet formed by the S···S short
contacts between the thiocarbonyl sulfur atoms. (c) 3D Networks formed by stacking of these sheets.
Figure 6. Molecular arrangement of (2-MeOC6H4CO)(2-MeOC6H4CS)S (3b). Dotted lines show intermolecular short contacts. (a) One-dimen-
sional linear chain formed by hydrogen bonding between benzene ring hydrogen and carbonyl oxygen atoms. (b) Two-dimensional sheet formed
by the above hydrogen bonding and the S···H hydrogen bonding between the thiocarbonyl sulfur and benzene-ring hydrogen atoms. (c) 3D
Networks formed by stacking of these sheets.
bon atoms form a planar sheet (Figure 6, (b)). Moreover, these
On the other hand, for the acid anhydride 5, intermolecular
sheets are stacked vertically with respect to each other to form O···H hydrogen bonds between the carbonyl oxygen and both
3D networks by intermolecular contacts, in which rectangular methoxy-methyl and benzene-ring hydrogen atoms are ob-
channels such as A (7.8 ϫ 4.5 Å) are formed (Figure 6, (c)).
served along with weak CH/π interactions between the benz-
For diacyl sulfide (4), O···H hydrogen bonds between the ene-ring carbon and the methoxy-methyl hydrogen atoms[9]
carbonyl oxygen and methoxy-methyl and benzene-ring hydro- (Figure S1 (d)). The molecules are arranged linearly by hydro-
gen atoms are observed along with weak CH/π interactions gen bonds between the carbonyl oxygen and methoxy-methyl
between the methoxy-methyl hydrogen and the benzene-ring hydrogen atoms (Figure 8, (a)). These molecular chains form
carbon atoms[9] (Figure S1 (c)). The molecules are arranged intermolecular O···H hydrogen bonds between the carbonyl
linearly by hydrogen bonding between the carbonyl oxygen oxygen and methoxy-methyl hydrogen atoms to give a ladder
and benzene-ring hydrogen atoms (Figure 7, (a)). The linearly and sheet (Figure 8, (b)). Moreover, through stacking, these
arranged molecules have intermolecular O···H hydrogen bonds sheets form 3D networks, in which columns such as A (6.5 ϫ
between the carbonyl oxygen and methoxy-methyl hydrogen 3.3 Å) are formed (Figure 8, (c)).
atoms to form a planar sheet (Figure 7, (b)). Moreover, these
sheets are stacked vertically with respect to each other to form
Ab initio Calculations
3D networks by intermolecular contacts, in which rectangular
To elucidate the nature of the nonbonding interactions for
channels such as A (10.5 ϫ 4.2 Å) are formed (Figure 7, (c)). compounds (2-MeOC6H4CS)2S (1), (4-MeOC6H4CS)2S (2),
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Figure 7. Molecular arrangement of (2-MeOC6H4CO)2S (4). Dotted lines show intermolecular short contacts. (a) One-dimensional linear chain
formed by C=O···H hydrogen bond between benzene ring hydrogen carbonyl oxygen atoms. (b) Two-dimensional sheet formed by the O···H
hydrogen bonds between the carbonyl oxygen and methoxy-methyl and benzene-ring hydrogen atoms. (c) 3D Networks formed by stacking of
these sheets.
Figure 8. Molecular arrangement of (2-MeOC6H4CO)2O (5). Dotted lines show intermolecular short contacts. (a) One-dimensional linear chain
formed by C=O···H3C hydrogen bond between carbonyl oxygen and methoxy methyl hydrogen atoms. (b) Two-dimensional sheet formed by
the O···H hydrogen bonds between the carbonyl oxygen and methoxy methyl and benzene ring hydrogen atoms. (c) 3D Networks formed by
stacking of these sheets.
(2-MeOC6H4CO)(2-MeOC6H4CS)S (3b) and (2-MeOC6- agreement with the experimental observation that the
H4CO)2S (4), a natural bond orbital (NBO) analysis was per- S(11)–C(11) bond length is significantly longer than that of
formed at the B3LYP/6-311+G(2d,p) level with Gaussian 03 S(11)–C(21). For diacyl sulfide (4), there are both nonbonding
using X-ray structures.[10–12] The geometries of compounds (2- intramolecular interactions n(O12)Ǟσ*S(11)–C(21) along
MeOC6H4CO)2O (5) and (4-MeOC6H4CO)2O (6)[1] were opti- with delocalization of the lone-pair electrons on the central
mized at the B3LYP/6-311+G(2d,p) level with Gaussian 03. sulfur atom S(11) to the π* orbitals of thiocarbonyl groups
The structural optimizations reproduced well the observed (nS(11)Ǟπ*O(11)=C(11) and nS(11)Ǟπ*O(21)=C(21)). For
structures in crystals, although the calculated structures corre- acid anhydride (5), intramolecular interactions of
spond to those of monomers in vacuo (Supporting Information nO(12)Ǟσ*O(11)–C(21) and nO(22)Ǟπ*O(21)–C(21) are
Table S1). The results of NBO calculations for compounds 1, present along with the expected localization of the lone-pair
2, 3b, 4, 5, and 6 are shown in Table 4.
The results for compounds 3b–5 are discussed first, a de- (nO(11)Ǟπ*O(12)=C(11) and nO(11)Ǟπ*O(21)=C(21)).
tailed examination of the results for 1 and 2 follows. NBO On the other hand, orbital interactions spread over the C(11)
electron on the central oxygen atom to the C=O π* orbitals
calculations for 3b show three types of appreciable nonbonding (=S(12))S(11)C(21)(=S(21)) moiety in 1, which indicates delo-
orbital interactions, nS(21)Ǟσ*S(11)–C(11), nO(12)Ǟσ*S(11)– calization of the lone-pair electrons on the thiocarbonyl sulfur
C(21) and nO(21)Ǟπ*S(21)=C(21), along with nS(11)Ǟ atoms to the S–C σ* orbitals (nS(12)Ǟσ*S(11)–C(11) and
π*C(11)=O(11) and nS(11)Ǟπ*C(21)=S(21). The delocaliza- nS(21)Ǟσ*S(11)–C(21)) along with those on the central sulfur
tion of the lone-pair electrons on the thiocarbonyl and methoxy atom S(11) to the π* orbitals of thiocarbonyl groups
oxygen atoms to the S(11)–C(11) anti-bonding orbital is in (nS(11)Ǟπ*C(11)=S(12) and nS(11)Ǟπ*C(21)=S(21)). How-
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Unusual Saddle-like Structure of (2-MeOC6H4CS)2S
Table 4. NBO analyses of (2-MeOC6H4CS)2S (1), (4-MeOC6H4CS)2S (2), (2-MeOC6H4CO)(2-MeOC6H4CS)S (3b), (2-MeOC6H4CO)2S (4),
(2-MeOC6H4CO)2O (5), and (4-MeOC6H4CO)2O (6).
ever, there is no orbital interaction between the methoxy oxy- also apply for compound 2. What factors operate to control the
gen (O(11), O(21)) and central sulfur atoms (S(11)), although structures of 1 and 2? The energy profile of 1 and 2 were
the O(11)–S(11) and O(21)–S(11) distances of 3.07 Å are sig- investigated, together with the fragment, S(CSPh)2 (I). Struc-
nificantly short. In the case of para-methoxy derivative 2, the tures were optimized with the 6-311+G(2d,p) basis sets at the
stabilization effects due to delocalization of the lone-pair elec- B3LYP level. The optimized structures were confirmed to be
trons on the thiocarbonyl sulfur atoms (S(12) and S(21)) to the minimal by the frequency analysis. The results are collected in
anti-bonding orbital of the sulfur–carbon bonds (S(11)–C(11) Table 5, together with the relative energies of the conformers.
and S(11)–C(21)) are similar at both sites of the central sulfur Four conformers are detected in I, which are called A, B, C,
atom. However, the stabilization energy due to and D.
nS(11)Ǟπ*C(21)=S(21) seems small, presumably due to the
substantial twisting of the π-planes of the central sulfur atom atoms. However, it is unlikely to exist as a stable conformer,
and thiocarbonyl group. since the relative energy is too high, relative to I (A). As a
Conformer I (C) contains a five-membered cycle of SCSCS
The results remind us that some factors other than the intra- result, conformers I (A) and I (D) should be considered as the
molecular CT interactions, which can be evaluated by the NBO partial structures of 1 and 2, respectively, since I (B) is quite
analysis, would operate to control the crystal structure of 1, different from 1 and 2. The results are shown in Figure 9
Z. Anorg. Allg. Chem. 2012, 2508–2520
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
2515

O. Niyomura, Y. Kito, S. Kato, M. Ishida, M. Ebihara, S. Hayashi, W. Nakanishi
Table 5. Structures and energies optimized for 1, 2, and the fragment, S(CSPh)2 (I).
ARTICLE
Compound
(Conformer)
r(2S3S)
/Å
Є1C1S2C
/°
φ(2S1C1S2C)
/°
φ(1C1S2CiC)
/°
φ(1S2CiCoC)
/°
Erel
/kJ·mol–1
B3LYP/6-311+G(2d,p)
I (A: C2)
I (B: C2)
I (C: C2)
I (D: C1)
5.7677
3.4433
2.1045
4.5718
110.68
110.17
103.80
107.81
150.57
–30.90
–17.53
–29.22
126.05
162.61
158.05
7.52
–36.42
153.73
170.70
–177.92
–60.47
–21.14
–30.46
–172.28
–77.65
–31.90
–39.30
–0.66
0.0a)
1.5
98.3
2.3
37.38
–24.72
–45.35
–49.03
30.93
1 (C2)
1’ (C2)
2 (C1)
5.7037
5.7629
4.2725
114.87
112.04
105.57
0.0b)
6.3
–34.8
107.33
–7.54
MP2/Gen (the 6-311+G(3d) basis set for S and O with the 6-311G(d) basis set for C and H)
I (A: C2)
5.7492
4.5640
103.69
105.69
150.36
–8.47
–33.84
172.87
–50.54
–13.83
176.77
–54.92
–41.58
41.41
–32.21
–54.95
37.82
0.0c)
24.8
I (D: C1)
135.39
167.78
–4.39
1 (C2)
2 (C1)
5.6964
4.4977
113.51
105.30
0.0d)
24.4
129.83
–28.03
a) E = –1734.2873 au. b) E = –1963.3984 au. c) E = –1730.9682 au. d) E = –1959.5051 au.
Figure 9. Formation of 1, 1Ј, and 2 through substitution of the hydrogen atoms of I by OMe groups. Compounds 1 and 2 are observed but not
1’ in the crystals.
The observed structure of 1 apparently forms through the a small change was observed in the optimization process of 2
substitution of hydrogen atoms at the o,o’-positions of I (A) with the methoxy groups, which was predicted to be more
by the methoxy groups. Only a slight change was observed in stable than 1. The results are supported by the calculations at
the structure of 1 in the optimization process with the methoxy the MP2 level employing the 6-311+G(3d) basis set for sulfur
groups, relative to the case of I (A). Another topological con- and oxygen with the 6-311G(d) basis set for carbon and hydro-
former of 1 (1’) could also exist as a stable conformer, where gen. On the other hand, the observed structure of 2 forms
methoxy groups were introduced in place of the hydrogen through the substitution of the hydrogen atoms at the p,p’-
atoms at the other o,o’-positions in I (A). A slight change was positions in I (D) by the methoxy groups. A small change was
also detected in the optimization process for 1’. 1’ is predicted observed in the structure of 2 in the optimization process with
to be less stable than 1 by 6.3 kJ·mol–1, relative to 1. Similarly, the methoxy groups. Compound 2 is predicted to be less stable
2516
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© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2012, 2508–2520

Unusual Saddle-like Structure of (2-MeOC6H4CS)2S
than 1. Weak interactions such as π–π interactions are not well
evaluated at the B3LYP level but they would be overestimated
at the MP2 level, which must be responsible for the results of
calculations at the two levels. Why 1 is observed, while the
relative energy of 1’ is almost the same that of 1? The structure
in crystals must be stabilized or destabilized by the crystal
packing effect. The effective volume of 1 is expected to be
smaller than that of 1’, since 1’ seems more extended form
relative to 1. The more densely packed crystals of 1, due to its
less effective volume, would also be advantageous to be ob-
served in crystals.
UV/Vis Spectroscopy
The bis(arenecarbothioyl) sulfides and aromatic acyl
thioacyl sulfides show quite characteristic colors of deep blue
to green. In general, the nǞπ* transitions of dithio esters ap-
pear in the range of 510–580 nm for aromatic dithioesters
(RCSSR’, R = aryl) with a small extinction coefficient due to
the forbidden transition.[13] Table 6 shows the electron spectra
of compounds 1, 2, and 3b along with their calculated values.
Table 6. Electron spectra of compounds 1, 2, and 3b.
Figure 10. Molecular orbital presentation of the excited state 1 (f =
0.017) for syn-(2-MeOC6H4CS)2S (1) (ψ87 = HOMO); the coefficient
for the wavefunctions of each transition given by a.
As shown in Table 6, the electron spectra of compounds 1
(ap/ap-conformer) and 2 (sp/ac-conformer) had absorption
maxima at ca. 600 nm and 620 nm, respectively, which are
assignable to nǞπ* transitions on the thiocarbonyl sulfur atom
based on the magnitude of the extinction coefficient. Such ba-
thochromic shifts of the nǞπ* transitions of 1 and 2 may be
explained in terms of the orbital interactions of the lone-
pair electrons on the central sulfur atom with anti-bonding
orbital nǞπ* transitions (see Table 4: nS(11)Ǟπ*S(12)=C(11)
S(11)Ǟπ*S(21)=C(11)). On the other hand, the corresponding
,
n
nǞπ* transitions of compound 3b (sc/ap-conformer) appeared
at 552 nm. Such a hypsochromic shift for 3b may also be
explained in terms of the orbital interactions of the lone-pair
electrons on the central sulfur atom with the anti-bonding or-
bital nǞπ* transitions (see Table 4: nS(11)Ǟπ*S(21)=C(21) and
Figure 11. Molecular orbital presentation of the excited state 2 (f =
0.003) for syn-(4-MeOC6H4CS)2S (2) (ψ87 = HOMO); the coefficient
for the wavefunctions of each transition given by a.
Figure 10, Figure 11, and Figure 12 show the molecular or-
bital diagrams of excited state 1 (f = 0.017) for (2-MeOC6-
n
S(21)Ǟσ*S(11)–C(21)).
Z. Anorg. Allg. Chem. 2012, 2508–2520
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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O. Niyomura, Y. Kito, S. Kato, M. Ishida, M. Ebihara, S. Hayashi, W. Nakanishi
ARTICLE
H4CS)2S (1; ap/ap) (ψ87 = HOMO), excited state 2 (f = 0.003)
These results may help us to understand the physical proper-
for (4-MeOC6H4CS)2S (2; ac/sp) (ψ87 = HOMO) and excited ties of other unstable sulfur, selenium and tellurium isologues
state 1 (f = 0.003) for (2-MeOC6H4CO)(2-MeOC6H4CS)S (3b; of acid anhydride [RC(= E1)E2C(= E3)R’, (E1, E2, E3 = O, S,
sp/ap) (ψ83 = HOMO), respectively, where the ψ86Ǟψ89, Se, Te; R, R’ = alkyl, aryl)], which could not be synthesized
ψ87Ǟψ89 and ψ83Ǟψ85 transitions correspond to the symmet- so far.
ric-to-symmetric transitions of the s- and p-types are added,
respectively.
Experimental Section
The melting points were measured by a Yanagimoto micromelting
point apparatus and uncorrected. The IR spectra were measured with
a PERKIN ELMER FT-IR 1640 and a JASCO grating IR spectropho-
tometer IR-G. The 1H-NMR and 13C-NMR spectra were recorded with
JNM-α400 instruments at 399.7 and 100.4 MHz, respectively with tet-
ramethylsilane as an internal standard. Electron spectra were measured
with a JASCO U-Best 55. Mass spectra were recorded with a Shim-
adzu GC–MS QP1000 (A) (EI/CI, model) mass spectrometer. The high
resolution mass spectroscopy (H.R. MS) was taken with a Shimadzu
GC–MS 9020DF high resolution mass spectrometer. Elemental analy-
ses were performed by the Elemental Analysis Center of Kyoto Uni-
versity.
Materials
4-Chlorobenzoyl, 4-methylbenzoyl, 2-methoxybenzoyl and 4-meth-
oxybenzoyl chlorides were prepared according to the literature.[14] Po-
tassium arenecarbodithioates were prepared by the reaction of the cor-
responding carbodithioic acids with potassium hydrides as described
in the literature.[15] Bis(2-methoxybenzoyl) sulfide and bis(2-meth-
oxybenzoic) anhydride were synthesized according to the litera-
ture.[16,17]
X-ray Diffraction
Figure 12. Molecular orbital presentation of the excited state 1 (f =
0.0028) for syn-(2-MeOC6H4CO)(2-MeOC6H4CS)S (3b) (ψ83
HOMO); the coefficient for the wavefunctions of each transition given
by a.
=
The measurement was carried out with a Rigaku AFC7R four-circle
diffractometer with graphite-monochromated Mo-Kα radiation (λ =
0.71069 Å). All of the structures were solved and refined using the
teXsan crystallographic software package on an IRIS Indigo com-
puter.[18] X-ray quality crystals of 1, 2, and 3b were obtained by
recrystallization from ether/petroleum ether. These crystals were cut
and coated with an epoxy resin and mounted on a glass fiber. The cell
dimensions were determined from a least-squares refinement of the
setting diffract-meter angles for 25 automatically centered reflections.
Lorentz and polarization corrections were applied to the data, and em-
pirical absorption corrections (ψ-scans[19]) were also applied. The
structures were solved by direct method using SHELX-97[20] and ex-
panded using DIRDIF92.[21] Scattering factors for neutral atoms were
adapted according to Cromer and Waber[22] and anomalous disper-
sion[23] was used. The function minimized was Σw(|Fo|–|Fc|)2, and the
weighting Scheme employed was w = [σ2(Fo)+p2(Fo)2/4]–1. A full-
matrix least-squares refinement was executed with non-hydrogen
atoms being anisotropic. The final least-square cycle included fixed
hydrogen atoms at calculated positions of which each isotropic thermal
parameter was set to 1.2 times of that of the connecting atom.
Concluding Remarks
The crystal structures of a series of (2-MeOC6H4CS)2S (1),
(4-MeOC6H4CS)2S (2) and (2-MeOC6H4CO)(2-MeOC6H4CS)
S (3b) were compared with those of the corresponding oxygen
derivatives (2-MeOC6H4CO)2S (4), (2-MeOC6H4CO)2O (5),
(4-MeOC6H4CO)2O (6). Compound 1 was an unusual saddle
structure in which the –C(=S)–S–C(=S)– moiety is planar and
two benzene rings lie a face-to-face and in addition, no orbital
interactions between the both atoms between the central sulfur
atom and the 2-methoxy oxygen atoms, in spite of substantially
short (3.07 Å). Such unusual structure of 1 was considered to
be stabilized by the crystal packing effect, due to its less effec-
tive volume, rather than intramolcular interaction.
The deep blue to green colors of compounds 1 and 2 and
the deep violet color of compound 3b reflect the transitions of
the lone-pair electrons in the HOMO (ψ87) of the thiocarbonyl
sulfur atom to the LUMO (ψ89) and of the lone-pair electrons
in the ψ83 (HOMO) of the thiocarbonyl sulfur atom to the
LUMO (ψ85).
Bis(2-methoxybenzenecarbothioyl) sulfide (1): Yield: 77%. Mp
(dec.): 102–104 °C. IR (KBr): 1245 (C=S), 1281 (C=S) cm–1. 1H
NMR (400 MHz, CDCl3): δ = 3.72 (s, 6 H, CH3O), 6.54 (d, J = 7.8 Hz,
2 H, arom), 6.76 (t, J = 7.8 Hz, 2 H, arom), 7.20 (t, J = 7.8 Hz, 2 H,
arom) 7.28 (d, J = 7.8 Hz, 2 H, arom). 13C NMR (100 MHz, CDCl3):
δ = 55.5 (CH3O), 110.7, 120.4, 130.3, 132.8, 135.8, 154.1 (arom),
229.0 (C = S). The IR spectrum was in good agreement with that of
2518
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© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2012, 2508–2520

Unusual Saddle-like Structure of (2-MeOC6H4CS)2S
the authentic sample which was prepared from the condensation reac-
tion of the corresponding carbodithioic acid with dicyclohexylcarbodi-
imide.[3c]
Supporting Information (see footnote on the first page of this article):
Experimental part, Figure S1, Table S1, and Table S2.
Acknowledgments
Bis(4-methoxybenzenecarbothioyl) sulfide (2): Yield: 68%. Mp
(dec.): 65–66 °C (65–66 °C[3c]). IR (KBr): 1250, 1265 (C=S) cm–1. 1H
NMR (400 MHz, CDCl3): δ = 3.85 (s, 6 H, CH3O), 6.83 (d, J = 9.0 Hz,
4 H, arom), 8.05 (t, J = 9.0 Hz, 4 H, arom). 13C NMR (100 MHz,
CDCl3): δ = 55.6 (CH3O), 113.8, 130.3, 138.7, 164.5 (arom), 221.3 (C
= S).
This research was by a Grant-in-Aid for Scientific Research on Priority
Areas and by a Grant-in-Aid for Scientific Research from the Ministry
of Education, Science, Sports and Culture of Japan. We thank Emeritus
Prof. Takashi Kawamura of Gifu University for invaluable advices
with X-ray crystallography. We also thank Prof. Mao Minoura for
valuable advices with the depictions of the molecular structures.
The spectroscopic data and physical properties were in good agreement
with that of the authentic sample which was prepared from the conden-
sation reaction of the corresponding carbodithioic acid with dicyclo-
hexylcarbodiimide.[3b]
References
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3h are shown in the supporting information (Table S2).
[3] a) S. Kato, T. Katada, M. Mizuta, Angew. Chem. Int. Ed. Engl.
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(2-Methoxybenzoyl)(2-methoxybenzenecarbothioyl) sulfide (3b): A
solution of 2-methoxybenzoyl chloride (0.144 g, 0.842 mmol) in
dichloromethane (4 mL) was added to a suspension of potassium
2-methylbenezenecarbodithioate (0.197 g, 0.886 mmol) in the same
solvent (20 mL) at 0 °C under argon atmosphere. The color of the
solution gradually changed from red to reddish purple. The mixture
was stirred at the same temperature for 2 h. The white precipitates
(KCl) were filtered off. Removal of the solvent from the filtrate under
reduced pressure (21 °C/3 Torr) gave a dark blue solid. Recrystalli-
zation from Et2O (0.5 mL)/hexane (15 mL) yielded 3b as dark blue
crystals.
[5] S. Yoneda, K. Okazaki, K. Yanagi, M. Minobe, J. Chem. Soc.,
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[6] F. Iwasaki, M. Sakuratani, M. Yasui, N. Kamiya, H. Iwasaki, Bull.
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[7] CCDC Data Base search for aromatic acid anhydrides (ArCO)2O
resulted in 6 hits: (2-MeOC6H4CO)2O (refcorde: ASPRIN); (4-
Yield: 0.217 g (81%). Mp (dec.): 94–100 °C. IR (KBr): 1677 (C=O),
1250 (C=S) cm–1. 1H NMR (400 MHz, CDCl3): δ = 3.74 (s, 3 H)
(CH3O), 3.90 (s, 3 H, CH3O), 6.83 (d, J = 7.8 Hz, 1 H, arom-CS),
6.97 (d, J = 7.8 Hz, 1 H, arom-CO), 6.99 (t, J = 7.8 Hz, 1 H, arom-
CO), 7.00 (t, J = 7.8 Hz, 1 H, arom-CO), 7.42 (t, J = 7.8 Hz, 1 H,
arom-CS), 7.50 (d, J = 7.8 Hz, 1 H, arom-CS), 7.60 (t, J = 7.8 Hz, 1
H, arom-CO), 7.74 (d, J = 7.8 Hz, 1 H, arom-CO). 13C NMR
(100 MHz, CDCl3): δ = 55.7 (CH3O), 55.8 (CH3O), 110.7, 112.0,
120.6, 120.7, 125.2, 130.3, 130.4, 132.6, 134.7, 137.6, 154.0, 158.4
(arom), 185.4 (C=O), 229.5 (C = S). UV/Vis: λmax (lg ε) (CH2Cl2):
222 nm (4.53), 269 (4.00), 340 (4.03), 552 (2.34). C16H14O3S2
(318.40): found C 59.90 (calc 60.35), H 4.55 (4.43)%.
BrC6H4CO)2O
(refcorde:
BBENAN
and BBENAN01); (4-ClC6H4CO)2O (refcorde: CLBNAH):
(4-NO2C6H4CO)2O (refcorde: VIFBAN); (4-Me2NC6H4CO)2O
(refcorde: YENKEH); (9-anthroyl)2O (refcorde: YUYEK). The
interplaner-angle O1=C1–C2=O2 of these compounds are in the
range of 17.5–77.4°.
[8] IUPAC, Compendium of Chemical Terminology, 2nd ed.
Blackwell Scientific Publication, Oxford, UK, 1997; Basic Termi-
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[9] M. Nishio, The CH/π Interaction. Evidence, Nature and Conse-
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[11] C. Lee, W. Yang, R. G. Parr, Phys. Rev. Sect. B 1988, 37, 785–
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[12] Gaussian 2003, 2004, M. J. Frisch, G. W. Trucks, H. B. Schlegel,
G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
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Bis(2-Methoxybenzoyl) sulfide (4). Yield: 0.165 g (62%). Mp (dec.):
66–69 °C (Ref. [16] 65–67 °C).
IR (KBr): 1732 (C=O), 1662 (C=O) cm–1.1H NMR (400 MHz,
CDCl3): δ = 3.87 (s, 6 H, CH3O), 6.96 (d, J = 7.9 Hz, 2 H, arom),
7.00 (t, J = 7.9 Hz, 2 H, arom), 7.48 (t, J = 7.71 (d, 7.9 Hz, 2 H,
arom). 13C NMR (100 MHz, CDCl3): δ = 55.8 (CH3O), 112.0, 120.4,
127.4, 130.2, 134.2, 157.8 (arom), 186.4 (C=O).
2-Methoxybenzoic anhydride (5):[17] Yield: 0.165 g (62%). Mp
(dec.): 70–73 °C. IR (KBr): 1733 (C=O) cm–1. 1H NMR (400 Hz,
CDCl3): δ = 3.85 (s, 6 H, CH3O), 7.00 (d, J = 8.0 Hz, 2 H, arom),
7.03 (t, J = 8.0 Hz, 2 H, arom), 7.55 (t, J = 8.0 Hz, 2 H, arom), 8.01
(t, J = 8.0 Hz, 2 H, arom). 13C NMR (100 Hz, CDCl3): δ = 55.9
(CH3O), 112.1, 118.1, 120.3, 133.0, 135.2, 160.1 (arom), 161.9 (C=O).
Z. Anorg. Allg. Chem. 2012, 2508–2520
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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O. Niyomura, Y. Kito, S. Kato, M. Ishida, M. Ebihara, S. Hayashi, W. Nakanishi
ARTICLE
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