Noncovalent Z...Z (Z = O, S, Se, and Te) interactions: How do they operate to control fine structures of 1,8-dichalcogene-substituted naphthalenes?

Article abstract of DOI:10.1246/bcsj.81.1605

Homonuelear Z...Z (Z = O, S, Se, and Te) interactions are investigated employing naphthalene 1,8-positions in l,8-(MeZ)₂C ₁₀H₆ (la-ld: Z = O (a), S (b), Se (c), and Te (d)), l-MeZ-8-PhZe₁₀H₆ (2a-2c). and l,8-(PhZ)₂C ₁₀H₆ (3a-3d). Three types of structures are detected for la-3d: BB for la, CC for lb, lc, 2c, and 3d, and AB for 2a, 2b, and 3a-3c, in our definition, by X-ray crystallographic analysis, although some have already been reported. Quantum chemical calculations are performed on la-1d and 3c, together with model c, Me(H)Se...Se(H)Me, to elucidate how the fine structures are controlled by the interactions. AB are stabilized by the n _p(Z)... σ*(Z-C) 3c-4e interactions for Z = S, Se, and Te. While CC are substantially stabilized by the n(Z) ...σ*(Z-C) interactions, they are well summarized as the disappearance of the nodal plane in π* (Z...z.). Factors to control the fine structures are clarified and visualized using the HOMO or HOMO-1 of model c. The energy profile of model c helps us to imagine the whole picture of the noncovalent Se...Se interactions.

Full text of DOI:10.1246/bcsj.81.1605

Ó 2008 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 81, No. 12, 1605–1615 (2008) 1605
Noncovalent ZꢀꢀꢀZ (Z ¼ O, S, Se, and Te) Interactions:
How Do They Operate to Control Fine Structures
of 1,8-Dichalcogene-Substituted Naphthalenes?
ꢀ
Satoko Hayashi and Waro Nakanishi
Department of Material Science and Chemistry, Faculty of Systems Engineering,
Wakayama University, 930 Sakaedani, Wakayama 640-8510
Received April 11, 2008; E-mail: nakanisi@sys.wakayama-u.ac.jp
Homonuclear Z Z (Z ¼ O, S, Se, and Te) interactions are investigated employing naphthalene 1,8-positions in
ꢁꢁꢁ
1,8-(MeZ)2C10H6 (1a–1d: Z ¼ O (a), S (b), Se (c), and Te (d)), 1-MeZ-8-PhZC10H6 (2a–2c), and 1,8-(PhZ)2C10H6
(3a–3d). Three types of structures are detected for 1a–3d: BB for 1a, CC for 1b, 1c, 2c, and 3d, and AB for 2a, 2b,
and 3a–3c, in our definition, by X-ray crystallographic analysis, although some have already been reported. Quantum
chemical calculations are performed on 1a–1d and 3c, together with model c, Me(H)Se Se(H)Me, to elucidate how
ꢀ
ꢁꢁꢁ
the fine structures are controlled by the interactions. AB are stabilized by the n (Z) ꢀ (Z–C) 3c–4e interactions for
ꢁꢁꢁ
p
ꢀ
Z ¼ S, Se, and Te. While CC are substantially stabilized by the n(Z) ꢀ (Z–C) interactions, they are well summarized
ꢁꢁꢁ
ꢀ
as the disappearance of the nodal plane in ꢁ (Z Z). Factors to control the fine structures are clarified and visualized
ꢁꢁꢁ
using the HOMO or HOMOꢂ1 of model c. The energy profile of model c helps us to imagine the whole picture of
the noncovalent Se Se interactions.
ꢁꢁꢁ
Much attention has been paid to weak interactions1–13 be-
Z
Z
Z
Z
Z
Z
cause they determine fine structures of compounds and create
high functionalities of materials. The interactions play an im-
portant role in structure, biological activity,14 regulation of en-
zymatic functions,15 stabilization of folded protein struc-
tures,16 in supramolecular chemistry,17 and in donor–acceptor
complexes for electronic material.18 They are also utilized as
tools in crystal engineering for material development.19 How-
ever, difficulty is often encountered in the detection of weak
interactions and in demonstrating a cause and effect relation
with phenomena arising from them because they are literally
weak. Superficial factors can be mistaken for meaningful inter-
actions, because they usually work behind other factors of su-
perficial contribution. Each phenomenon in question should be
analyzed as a result of the weak interaction, if it is the real
cause. It is inevitable to set up a system for the establishment
of the factors controlling the fine structures. It is also important
to strengthen weak interactions for effective detection.
I
II
C
Z
Z
Z
Z
III
IV
Scheme 1. Noncovalent interactions caused by direct
orbital overlaps. I: ꢀ(2c–4e), II: ꢁ(2c–4e), III: distorted
ꢁ(2c–4e), and IV: ꢀ(3c–4e).
Naphthalene 1,8-positions provide a good system to study
noncovalent interactions,2–4,8,23,25 since the distances between
the nonbonded heteroatoms at these positions are close to
Several cases of orbital overlap in noncovalent Z Z interac-
ꢁꢁꢁ
˚
tions of group 16 elements are shown in Scheme 1. Direct
orbital overlap between nonbonded atoms will increase as
the distance between the atoms in question become shorter.
Therefore, close location and appropriate orientation of the
orbitals are necessary for effective interactions.4,8,20 Lone pair
orbitals of group 16 elements cause versatile reactivities and
give structurally interesting compounds.21 To detect the weak
interactions, the nonbonded atoms must be fixed within the
sum of van der Waals radii22 in an organic compound of rigid
structure.4,3a,23 Although severe exchange repulsions usually
accompany the interactions,4c–4f,23 they can be substantially
decreased by placing the atoms at suitable positions and direc-
tions in a molecule.4g,24
van der Waals radii minus one A for main group ele-
ments.4b,4d–4g,4i,8,25 Weak noncovalent interactions gain cova-
lent nature as the nonbonded distances decrease relative to
the sum of van der Waals radii. Interactions between nonbond-
ed atoms at naphthalene 1,8-positions may contain both char-
acteristics depending on Z. Noncovalent homonuclear Z Z
ꢁꢁꢁ
(Z ¼ O, S, Se, and Te) interactions are thoroughly investigat-
ed, aiming to clarify the whole picture of the noncovalent in-
teractions at naphthalene 1,8-positions. To clarify the cause-
and-effect in weak interactions is another purpose of our inves-
tigations.10
1,8-Dichalcogene-substituted naphthalenes, 1,8-(MeZ)2-
C10H6 (1a–1d: Z ¼ O (a), S (b), Se (c), and Te (d)), 1-MeZ-
Published on the web December 12, 2008; doi:10.1246/bcsj.81.1605

1606 Bull. Chem. Soc. Jpn. Vol. 81, No. 12 (2008)
Noncovalent Z Z Interactions
ꢁꢁꢁ
Me
Z
Z Me
Me
Z
Z Ph
Ph
Z
Z Ph
C12
C10
C9
C1
Se2
1
2
3
Se1
C11
(Z = O (a), S (b), Se (c), and Te (d))
Chart 1. 1,8-Dichalcogene-substituted naphthalenes 1–3.
Figure 1. ORTEP drawing of 1cA with atomic numbering
scheme for selected atoms (50% probability thermal
level).
R'
Z
Z
Z
Z
Z
Z
R'
C11
R
R
AA-t
AB
CC
R'
C1
S1
C10
C9
S2
R
R'
Z
Z
C12
R
BB
Scheme 2. Typical structures in 1–3.
8-PhZC10H6 (2a–2c), and 1,8-(PhZ)2C10H6 (3a–3d) are em-
ployed for the investigations (Chart 1): 1d and 2d were not
prepared successfully, which may be due to the facile cleavage
of the Te–CMe bonds in the compounds. Structures of 1a–1c,
2a–2c, and 3a–3d (1a–3d) were determined by X-ray crystal-
lographic analysis, although 1a,26 1b,2b 2c,4e,4g 3b,27 and 3d3a
have already been reported.
Figure 2. ORTEP drawing of 2b with atomic numbering
scheme for selected atoms (50% probability thermal
level).
The structures around Z in 8-G-1-RZC10H6 are well de-
scribed as three types, A (A), B, and C, where the Z–CR bond
is perpendicular to the naphthyl plane in A, it is on the plane
in B, and C is intermediate between A and B.4c,4d,4f–4i,5b
Scheme 2 illustrates typical structures for 1-RZ-8-R0ZC10H6,
AA-t (AA pairing of the trans conformation), BB, AB, and
CC.4g The BB structure was reported for 1a26 by Sternhell
et al., CC for 1b2b by Glass et al., and for 3d3a by Furukawa
et al. We investigated the structure of 2c, which was also
CC and a successive change was observed by changing the
substituent at the phenyl p position in 2c.4e–4g
Se2
C9
C10
C1
C11
Se1
C12
Figure 3. ORTEP drawing of 3c with atomic numbering
scheme for selected atoms (50% probability thermal
level).
Fine structures of 1a–3d were analyzed to understand how
they are controlled by weak interactions and how the weak
interactions operate to determine the fine structures. They were
analyzed from the viewpoint of noncovalent homonuclear
(Z ¼ O, S, Se, and Te) are the main factors, together with
Z Z interactions at the naphthalene 1,8-positions, together
with the p–ꢁ conjugations of p(Z) ꢁ(Nap) and/or p(Z)
p(Z) ꢁ(Nap/Ph) conjugations, although the crystal packing
ꢁꢁꢁ
ꢁꢁꢁ
effect must also be considered.
ꢁꢁꢁ
ꢁꢁꢁ
ꢁ(Ph) (p(Z) ꢁ(Nap/Ph)). Results of quantum chemical
ꢁꢁꢁ
Results and Discussion
(QC) calculations are reported for donor–acceptor interactions
in Me Z Z0RMe (Z, Z0 ¼ O, S, Se, and Te; R ¼ Me and
Structures of 1–3. Single crystals were obtained for 1b–3c
via slow evaporation of hexane solutions. The X-ray crystallo-
graphic analyses were carried out for a suitable crystal of each
compound. Although the structures of 1a,26 1b,2b 2c,4e,4g 3b,27
and 3d3a have already been reported, that of 3b was reex-
amined to improve refinement. While one structure corre-
sponds to 2b and 3a–3c, two correspond to 1a–1c, 2a, and
2c in the crystals. Figures 1–3 show the structures of 1cA,
2b, and 3c, respectively. Those of 1cB, 2aA, 2aB, 3a, and 3b
are shown in the Supporting Information (SI) (Figures S1–
S4, respectively). Table 1 displays selected interatomic dis-
tances, angles, and torsional angles, necessary for discussion.
ꢁꢁꢁ
2
CN).28 However, it is also important to clarify the factors that
control the fine structure in the real compounds, 1a–3d. QC
calculations were performed on 1a–1d and 3c to analyze the
results and elucidate the mechanisms to control the fine struc-
tures. QC calculations were also performed on model c
(Me(H)Se Se(H)Me), devised based on the observed struc-
tures of 1c to visualize the factors and to imagine the whole
picture of the interactions.
ꢁꢁꢁ
Here, we report the structures of 1a–3d, although some have
already been reported. Factors controlling fine structures are
clarified. The noncovalent homonuclear Z Z interactions
ꢁꢁꢁ

S. Hayashi et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 12 (2008) 1607
Table 1. Nonbonded Z Z Distances, Angles, and Torsional Angles around Z, Observed in 1–3
ꢁꢁꢁ
Z ¼ O
a)
a)
1aA
1aB
2aA
2aB
103 K
3a
103 K
2.616(9)
ꢂ0:42
Tempb)
RT
RT
103 K
2.590(3)
ꢂ0:45
c)
˚
r/A
ꢀr/A
2.543
ꢂ0:50
2.547
ꢂ0:49
2.604(3)
ꢂ0:44
d)
˚
ꢂ1/ꢃ e)
117.23
117.23
152.65
152.65
ꢂ179:85
ꢂ179:85
BB
117.26
117.26
152.70
152.70
ꢂ179:34
ꢂ179:34
BB
115.7(3)
118.0(3)
151.4(3)
93.2(3)
174.5(3)
94.0(4)
AB
116.8(4)
117.7(3)
151.0(3)
93.4(3)
118.05(12)
117.76(13)
148.26(12)
83.91(12)
169.28(13)
ꢂ82:92ð19Þ
AB
ꢂ2/ꢃ f)
ꢂ3/ꢃ g)
ꢂ4/ꢃ h)
ꢃ1/ꢃ i)
ꢃ2/ꢃ j)
Structure
ꢂ174:8ð3Þ
ꢂ93:8ð4Þ
AB
Z ¼ S
k)
k)
1bA
1bB
2b
3bl)
3bm)
Tempb)
RT
2.918
ꢂ0:68
103.9
103.6
155.4
168.3
ꢂ143:2
ꢂ158:3
CC
RT
2.936
ꢂ0:66
101.5
103.3
151.9
162.6
ꢂ142:1
ꢂ153:0
CC
RT
3.047(2)
ꢂ0:55
RT
3.004
RT
3.021(2)
ꢂ0:58
c)
˚
r/A
ꢀr/A
d)
˚
ꢂ0:60
102.46
102.67
168.52
105.07
ꢂ159:99
ꢂ95:25
AB
ꢂ1/ꢃ e)
103.1(2)
104.9(2)
172.8(2)
80.7(1)
171.9(3)
69.5(4)
AB
102.4(2)
104.2(2)
165.0(2)
91.9(1)
ꢂ2/ꢃ f)
ꢂ3/ꢃ g)
ꢂ4/ꢃ h)
ꢃ1/ꢃ i)
ꢃ2/ꢃ j)
Structure
ꢂ152:1ð4Þ
101.7(4)
AB
Z ¼ Se
n)
n)
1cA
1cB
2cA
2cB
3c
Tempb)
103 K
3.051(4)
ꢂ0:75
103 K
3.064(4)
ꢂ0:74
RT
3.091(1)
ꢂ0:71
RT
3.048(1)
ꢂ0:75
103 K
3.135(2)
ꢂ0:67
c)
˚
r/A
ꢀr/A
d)
˚
ꢂ1/ꢃ e)
99.29(16)
99.27(16)
164.47(3)
150.34(3)
ꢂ154:1ð3Þ
ꢂ138:8ð3Þ
CC
98.41(16)
98.50(16)
146.46(3)
159.73(3)
136.8(3)
148.0(3)
CC
98.2(4)
98.1(3)
140.2(3)
156.5(3)
122.4(3)
141.8(3)
CC
97.8(4)
97.80(8)
99.15(9)
171.32(9)
95.87(8)
ꢂ154:74ð16Þ
109.70(16)
AB
ꢂ2/ꢃ f)
98.4(3)
ꢂ3/ꢃ g)
ꢂ4/ꢃ h)
ꢃ1/ꢃ i)
ꢃ2/ꢃ j)
Structure
148.6(4)
157.6(2)
ꢂ133:0ð7Þ
ꢂ143:2ð6Þ
CC
a) Ref. 26. b) Temperature for measurements. c) r(Z1, Z2). d) rðZ1; Z2Þ ꢂ ꢁrvdWðZÞ. e) = C1Z1C11. f)
À
= C9Z2C12. g) = Z2Z1C11. h) = Z1Z2C12. i) = C10C1Z1C11. j) = C10C9Z2C12. k) Ref. 2b. l) Ref. 27.
m) Reexamined data in this work. n) Refs. 4e and 4g.
À
À
À
À
À
Scheme 3 summarizes the structures of 1a–3c determined in
this work, together with those reported in the literature.
The CC structure of 3d3a is also contained in Scheme 3. Three
structures are observed for 1a–3d: BB for 1a, CC for 1b,
1c, 2c, and 3d, and AB29 for 2a, 2b, and 3a–3c, as shown in
Figures 1–3 and Scheme 3. The structures of 1d and 2d are
yet unknown, since they have not been prepared successfully
perhaps due to facile cleavage of the Te–CMe bonds during
preparation.30 The CC structure is strongly suggested for 1d
by QC calculations: 1d (CC) is optimized even starting from
1d (AB), which will be discussed latter (Table 2). The struc-
ture of 1d (CC) is displayed in Scheme 3. Scheme 3 demon-
strates that the three types of structures distribute systematical-
ly along with the feature size of molecules, if the structure of
1d and 2d are supposed to the both CC.
Table 1 displays selected interatomic distances, angles, and
torsional angles, necessary for discussion. Differences between
the observed O O distances and the sum of the van der Waals
radii22a in 1a (BB) (ꢀrðO; OÞ ¼ robsdðO; OÞ ꢂ 2rvdWðOÞ) are
ꢁꢁꢁ
˚
ꢂ0:50 to ꢂ0:49 A. The magnitudes seem to have little affect
on the structure of 1a, although the p lone pair orbitals
(np(O)) would overlap to some extent at those distances. In-
stead, the p–ꢁ conjugation of p(O)–ꢁ(Nap) must be much
stronger than the n (O) n (O) interaction in 1a (BB). The
ꢁꢁꢁ
p
p
p(O)–ꢁ(Nap) conjugation places the O–CMe bonds on the
naphthyl plane, which must be the main factor controlling
the structure of 1a (BB). The ꢀr values in 2a (AB) and 3a
˚
(AB) are ꢂ0:45 and ꢂ0:42 A, respectively. One may suppose
ꢀ
an important role to determine AB in 2a and 3a, at first glance.
that the noncovalent n (O) ꢀ (O–C) 3c–4e interaction plays
ꢁꢁꢁ
p

1608 Bull. Chem. Soc. Jpn. Vol. 81, No. 12 (2008)
Noncovalent Z Z Interactions
ꢁꢁꢁ
O (a)
S (b)
Se (c)
Te (d)
Z
1
BBa)
CCb)
CC
CC
Me Te Te Ph
2
CCc)
AB
AB
AB
3
CCf)
ABd),e)
AB
a) Ref. 26. b) Ref. 2b. c) Refs. 4e and 4g. d) Ref. 27. e) Reexamined. f) Ref. 3a.
Scheme 3. Observed structures in 1a–3d.
However, AB appears without the noncovalent O O interac-
Why are such systematic distributions observed in 1a–3d as
shown in Scheme 3? QC calculations were performed to ana-
lyze the factors controlling the fine structures, although the
crystal packing effect must also play an important role to de-
termine the structures.
ꢁꢁꢁ
tion. The p(O)–ꢁ(Ph) conjugation may control AB of 2a and
3a,31 in addition to the p(O)–ꢁ(Nap) conjugation. Namely,
the structures of 2a (AB) and 3a (AB) are determined mainly
by the p(O)–ꢁ(Nap/Ph) conjugations.
The importance of the noncovalent Z Z interaction be-
comes larger as Z ¼ O goes to S then to Se and further to
QC Calculations. QC calculations were performed on
1a–1d and 3c.33,34 Calculations were performed both at the
density functional theory (DFT) level of the Becke three pa-
rameter hybrid functionals with the Lee–Yang–Parr correlation
functional (B3LYP)35–37 and the Møller–Plesset second order
energy correlation (MP2) method.38–40 The 6-311+G(2d,p)
basis sets of Gaussian 0341 were employed for the calculations
of 1a–1c at the DFT (B3LYP) level. The DGDZVP basis sets42
were employed for Te with the 6-311+G(2d,p) basis sets for C
and H in the calculations of 1d at DFT (B3LYP) level. The
6-311+G(d) basis sets were employed for O, S, and Se with
the 6-31G(d) basis sets for C and H in the calculations of
1a–1c and the DGDZVP basis sets42 were employed for
all nuclei in 1d at the MP2. Frequency analysis was carried
out on all optimized structures of 1a–1d. The B3LYP/
6-311+G(2d,p) method was applied to the calculations of
3c. Similarly, 6-311+G(d) basis sets were employed for Se
with the 4-31G(d) basis sets for C and H in the calculations
of 3c at the MP2 level. Frequency analysis was not performed
on 3c.
ꢁꢁꢁ
Te, whereas the p(Z)–ꢁ(Nap/Ph) conjugations decrease in
the order Z ¼ O ꢄ S > Se > Te. The noncovalent S S inter-
ꢁꢁꢁ
action has greater effect on the structure of 1b (CC) with
˚
ꢀr(S, S) of ꢂ0:67 A. CC forms when BB is distorted, where
ꢁ(2c–4e) is also distorted in CC. Namely, the distorted
ꢁ(2c–4e) interaction must operate to determine the structure
of 1b (CC). The ꢀr(S, S) values of 2b (AB) and 3b (AB)
˚
are ꢂ0:55 and ꢂ0:59 A, respectively, which are smaller than
˚
that in 1b (CC) by ca. 0.10 A. The noncovalent n (S)
ꢁꢁꢁ
p
ꢀ
ꢀ (S–C) 3c–4e interaction must play an important role in
stabilizing the structures of 2b (AB) and 3b (AB), with the
assistance of the p(S)–ꢁ(Nap/Ph) conjugations.
In the case of Z ¼ Se, ꢀr(Se, Se) of 1c (CC) and 2c (CC)
˚
are ꢂ0:75 and ꢂ0:73 A, respectively, and that of 3c (AB) is
˚
ꢂ0:67 A. The values in CC are smaller than those in AB by
˚
0.06–0.08 A. Distorted ꢁ(2c–4e) interaction operates to deter-
mine the structures of 1c (CC) and 2c (CC) as in 1b (CC). The
structure of 3c (AB) must be the result of noncovalent
ꢀ
n (Se) ꢀ (Se–C) 3c–4e interaction, together with the p(Se)–
Scheme 4 shows model c (Me(H)Se Se(H)Me) devised
ꢁꢁꢁ
ꢁꢁꢁ
p
ꢁ(Nap/Ph) conjugations. The Te Te distance in 3d (CC) is
based on the structure of 1c.43 The energy profile for model
c is examined to visualize the factors controlling the fine struc-
tures and to imagine the whole picture of the noncovalent
ꢁꢁꢁ
˚
˚
reported to be 3.135 A, where ꢀrðTe; TeÞ ¼ ꢂ0:67 A for 3d
(CC). However, we must be careful when the ꢀr(Z, Z) values
are discussed, since they are not determined mainly by the
Se Se interactions. Calculations were performed with the
ꢁꢁꢁ
MP2/6-311+G(3d,2p) method.
magnitude of the Z Z interactions.32
ꢁꢁꢁ

S. Hayashi et al.
Table 2. Results of QC Calculations on 1a–1da)
Bull. Chem. Soc. Jpn. Vol. 81, No. 12 (2008) 1609
AA-t (C2)
At the DFT (B3LYP) levelb)
1a
AB (C1)
BB (C2v)
CC (C2)
c)
˚
r(O O)/A
E(F)/au
ꢀE(F)/kJ molꢂ1
2.7576
ꢂ614:9307
2.6525
ꢂ614:9332
ꢂ6:6
2.5492
ꢂ614:9350
ꢂ11:3
—
—
ꢁꢁꢁ
c)
0.0d)
—
c)
1b
r(S S)/A
E(F)/au
(2.9374)e)
(ꢂ1260:8973)e)
(6.8)e)
2.9374f)
ꢂ1260:9012
ꢂ3:4
˚
3.2684
ꢂ1260:8999
3.0316
ꢂ1260:9038
ꢂ10:2
ꢁꢁꢁ
ꢀE(F)/kJ molꢂ1
0.0d)
1c
r(Se Se)/A
E(F)/au
(3.0747)e)
(ꢂ5267:5568)e)
(5.5)e)
3.1038
ꢂ5267:5657
ꢂ17:9
˚
3.4364
ꢂ5267:5589
3.1553
ꢂ5267:5647
ꢂ15:2
ꢁꢁꢁ
ꢀE(F)/kJ molꢂ1
0.0d)
1d
r(Te Te)/A
E(F)/au
g)
(3.3541)e)
(ꢂ13691:6394)e)
(9.7)e)
3.3724
ꢂ13691:6511
ꢂ21:0
˚
3.6936
ꢂ13691:6431
—
—
ꢁꢁꢁ
g)
g)
ꢀE(F)/kJ molꢂ1
0.0d)
—
At the MP2 levelh)
1a
r(O O)/A
E(F)/au
i)
i)
i)
c)
˚
—
—
—
2.6508
ꢂ612:8726
2.5296
ꢂ612:8730
ꢂ1:1
—
—
ꢁꢁꢁ
c)
c)
ꢀE(F)/kJ molꢂ1
0.0d)
—
1b
r(S S)/A
E(F)/au
i)
i)
i)
i)
˚
—
—
—
3.0592
ꢂ1258:0809
—
—
3.0601
ꢂ1258:0806
0.8
ꢁꢁꢁ
i)
i)
ꢀE(F)/kJ molꢂ1
0.0c)
—
1c
r(Se Se)/A
E(F)/au
i)
i)
i)
i)
˚
—
—
—
3.1664
ꢂ5262:8721
—
—
3.1587
ꢂ5262:8729
ꢂ2:1
ꢁꢁꢁ
i)
i)
ꢀE(F)/kJ molꢂ1
0.0d)
—
1d
r(Te Te)/A
E(F)/au
g)
g)
g)
i)
˚
3.6828
ꢂ13684:8452
—
—
—
—
—
3.4022
ꢂ13685:8528
ꢂ20:0
ꢁꢁꢁ
i)
i)
ꢀE(F)/kJ molꢂ1
0.0d)
—
a) Energies containing the sum of electronic and thermal Gibbs free energies at 298.15 K are given by
E(F) (and ꢀE(F)). b) The 6-311+G(2d,p) basis sets are employed for 1a–1c and the DGDZVP basis
sets for Te with the 6-311+G(2d,p) basis sets in the calculations of 1d. c) Optimized to be BB, when
starting from CC. d) Taken as the standard. e) Corresponding to the species with two imaginary fre-
quencies. f) CC (C1) with all positive frequencies which are very close to CC (C2) with only one neg-
ative (imaginary) frequency for each. See also Ref. 44. g) Optimized to be CC when starting from AB.
h) The 6-311+G(d) basis sets are employed for O, S, and Se with the 6-31G(d) basis sets for C and H
in the calculations of 1a–1c and the DGDZVP basis sets42 are employed for all nuclei in 1d. i) Not
calculated.
Indeed, structures and energies evaluated on the basis of QC
calculations essentially correspond to those in the gas phase,
but the factors controlling and stabilizing structures in the
gas phase must also operate in solid state. Other factors such
as the crystal packing effect in crystals are stronger than those
predicted by QC calculations for molecules. However, it is ex-
pected that such structures would be preferentially observed
that are substantially stabilized in the gas phase even if the
crystal packing effect operates. Therefore, it is instructive to
examine those predicted by QC calculations as incentive fac-
tors to control fine structures while they are not so predomi-
nant.
Results of Calculations on 1a–1d and 3c. Table 2 shows
the energies containing thermal corrections to Gibbs free ener-
gy at 298.15 K (E(F)) for 1a–1d, together with the energy dif-
ferences (ꢀE(F)). Table 2 also contains the optimized Z Z
distances for 1a–1d. Table 3 shows the energies on the poten-
tial energy surface (E) for 3c, together with the energy differ-
ꢁꢁꢁ

1610 Bull. Chem. Soc. Jpn. Vol. 81, No. 12 (2008)
Noncovalent Z Z Interactions
ꢁꢁꢁ
ences (ꢀE). Table 2 (3) also contains the optimized Z Z dis-
ꢁꢁꢁ
On the other hand, AA-t (C2), AB (C1), and CC (C2)44 are
energy minima, whereas BB (C2v) is not for 1b and 1c45 (see
also Tables S2 and S3 in the SI). CC and AB would be in equi-
librium in solutions for 1b and 1c. 1c (CC) is predicted to be
the global minimum, which explains well the observed re-
sults.46 While 1b (AB) is calculated to be more stable than
1b (CC), the energy difference is very small when calculated
at the MP2 level (ꢀE ¼ EðCCÞ ꢂ EðABÞ ¼ 0:8 kJ molꢂ1). The
crystal packing effect controls the subtle energy balance for
the structures of 1b in crystals. In the case of 1d, AA-t (C2)
and CC (C2)44 are optimized to be stable (see also Table S4
in the SI). 1d (CC) must be the global minimum, since 1d
(AB) converges to 1d (CC), starting from 1d (AB), and 1d
(CC) is substantially more stable than 1d (AA). Results of
MP2 calculations well support the observed structures, al-
though the calculations are limited to the important conformers
of AB (C1) and BB (C2v) for 1a, AB (C1) and CC (C2) for 1b
and 1c, and AA (C2) and CC (C2) for 1d.47
While 1c (AB) is calculated to be more stable than 1c (CC)
by 1.1 kJ molꢂ1, 3c (AB) is predicted to be more stable than 3c
(CC) by 5.8 kJ molꢂ1 on the potential energy surface at the
MP2 level. Therefore, the energy difference between 3c
(AB) and 3c (CC) is predicted to be larger than the case of
1c (AB)/1c (CC) by 4.7 kJ molꢂ1 at the MP2 level. The energy
difference between 3c (AB)/3c (CC) is also predicted to be
smaller than 1c (AB)/1c (CC) at the B3LYP level, although
CC are predicted to more stable in this case. These results
explain well the preferential AB conformer in 3c relative to
the case of 1c.
tances for 3a. Table 3 also contains the data of 1c for conven-
ience of comparison.
For 1a, AA-t (C2), AB (C1), and BB (C2v) are optimized to
be stable, while BB is optimized even when starting from CC,
based on DFT calculations. The three structures are demon-
strated to be the energy minima by the frequency analysis of
1a (see also Table S1 in the SI). BB is a global minimum con-
taining a thermal correction to Gibbs free energy at 298.15 K
(and on the potential energy surface). The observed 1a (BB)
is well explained by the QC calculations.
1Me
2Me
1Se 2Se
θ1
θ2
1H
1: ∠1H1Se1C,
2H
θ
θ
2: ∠2H2Se2C
z
1Me
φ1
y
x
1Se 2Se
φ2
2Me
φ
1: ∠2Se1H1Se1C, 2: ∠1Se2H2Se2C
φ
Scheme 4. Model c.
Table 3. Results of QC Calculations on 1c and 3ca)
AA-t (C2)
AB (C1)
BB (C2v)
CC (C2)
B3LYP
1cb),c)
3.4364
ꢂ5267:7173
3.1553
ꢂ5267:7219
ꢂ12:1
(3.0747)d)
3.1038
ꢂ5267:7211
ꢂ10:0
˚
r(Se Se)/A
ꢁꢁꢁ
E/au
(ꢂ5267:7182)d)
ꢀE/kJ molꢂ1
0.0e)
(ꢂ2:4)d)
3cb)
r(Se Se)/A
E/au
(3.0798)f)
(ꢂ5651:2882)f)
(ꢂ5:0)f)
3.1104
ꢂ5651:2922
ꢂ15:5
˚
3.4129
ꢂ5651:2863
3.1568
ꢂ5651:2917
ꢂ14:3
ꢁꢁꢁ
ꢀE/kJ molꢂ1
0.0e)
MP2
1cc),g)
h)
h)
h)
h)
˚
r(Se Se)/A
—
—
—
3.1664
ꢂ5263:0316
—
—
3.1587
ꢂ5263:0312
1.1
ꢁꢁꢁ
h)
E/au
ꢀE/kJ molꢂ1
0.0e)
—
h)
3ci)
r(Se Se)/A
E/au
h)
h)
h)
h)
˚
—
—
—
3.1670
ꢂ5643:2775
—
—
3.1222
ꢂ5643:2753
5.8
ꢁꢁꢁ
h)
h)
ꢀE/kJ molꢂ1
0.0e)
—
a) Energies on the potential energy surface are given by E. b) The 6-311+G(2d,p) basis sets being
employed. c) The same structures shown in Table 2. d) Corresponding to the species with two imag-
inary frequencies. e) Taken as the standard. f) Should correspond to the species with two imaginary
frequencies, although frequency analysis was not performed. g) The 6-311+G(d) basis sets employed
for Se with the 6-31G(d) basis sets for C and H. h) Not calculated. i) The 6-311+G(d) basis sets
employed for Se with the 4-31G(d) basis sets for C and H.

S. Hayashi et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 12 (2008) 1611
After observation of the fine structures caused by the nonco-
valent Z Z interactions in the naphthalene system, together
with analysis based on QC calculations, the next extension is
to exhibit the whole picture of the interactions and visualize
the factors.
dicted to be the global minimum and AB is the next global
minimum. They are on the same energy surface. AA-t (C2)
with ðꢃ1; ꢃ2Þ ¼ ð87:5ꢃ; 87:5ꢃÞ is predicted to be a local mini-
mum on another energy surface. AA-t becomes less stable
as the structure is deformed then it assimilates into the
energy surface leading to AB and CC at around ðꢃ1; ꢃ2Þ ¼
ð60:0ꢃ; 177:5ꢃÞ and (140.0ꢃ, 164.3ꢃ).
ꢁꢁꢁ
Energy Profile for Model c. To imagine the whole picture
of the noncovalent Se Se interactions, the energy profile for
ꢁꢁꢁ
model c (Z ¼ Se) is examined. The potential energy surfaces
are calculated by optimizing model c with ꢃ1 fixed suitably.
The ðꢃ1; ꢃ2Þ values of AA-t, AB, BB, and CC are employed
as the starting values. Figure 4 draws the energy profile for
model c calculated with the MP2/6-311+G(3d,2p) method,
Factors to Control the Structures. Factors controlling
the fine structures are visualized exemplified by model c.
Scheme 5 draws the HOMO and HOMOꢂ1 of AA-t, AB,
BB, and CC in model c, calculated with the MP2/
6-311+G(3d,2p) method. The orbital interactions imply fac-
tors based on specific structures. Factors controlling the fine
structures are summarized as shown below, although the role
of the p(Z)–ꢁ(Nap/Ph) conjugations must also be considered
in the real compounds, especially for Z ¼ O.
which demonstrates how the noncovalent Z Z interactions
act as the factors to determine the fine structures. CC is pre-
ꢁꢁꢁ
E/au
1. The double p(O)–ꢁ(Nap) conjugations determine the
structure of 1a (BB). The p(Z)–ꢁ(Nap) conjugations in BB
become weaker in the order Z ¼ O > S > Se > Te.
ꢀ
2. The hypervalent n (Z) ꢀ (Z–C) 3c–4e interactions
ꢁꢁꢁ
p
–4880.61
(Z ¼ S, Se, and Te) operate in AB, which stabilize the system.
The p(Z)–ꢁ(Nap/Ph) conjugations also support stabilization
of AB.
AA-t
3. CC is formed by the distortion of BB. The donor–accep-
tor interactions of n (Z) ꢀ (Z–C) and n (Z) ꢀ (Z–C) sub-
ꢀ
ꢀ
stantially stabilize CC. The disappearance of the nodal plane
ꢁꢁꢁ
ꢁꢁꢁ
s
p
–4880.62
ꢀ
in ꢁ (Z Z: HOMO) in CC contributes to stabilize CC, where
ꢁꢁꢁ
the nodal plane appears apparently in BB. The relative stability
of CC increase in the order Z ¼ O ꢅ S < Se < Te.
4. AA-t is constructed by ꢀ(2c–4e). AA-t of the symmetric
structure is a local minimum. The stability decreases as AA-t
becomes unsymmetrical.
BB
AB
CC
–4880.63
φ
1/°
180
60
90
120
150
Factors to control the structures of 1–3 are well visualized in
Scheme 5, as summarized above.
Figure 4. Plots of E versus ꢃ1 in model c, calculated with
the MP2/6-311+G(3d,2p) method.
AA-t
2 = 80.3°)
AB
BB
CC
(φ1
=
φ
(
(
φ
φ
1 = 87.5°)
2 = 186.0°)
(
φ1
=
φ
2 = 180.0°)
(
φ1
=
φ
2 = 157.5°)
HOMO
HOMO-1
Scheme 5. HOMO and HOMOꢂ1 of AA-t, AB, BB, and CC in model c.

1612 Bull. Chem. Soc. Jpn. Vol. 81, No. 12 (2008)
Noncovalent Z Z Interactions
ꢁꢁꢁ
1,8-Bis(methylselanyl)naphthalene (1c). To a solution which
was prepared by reduction of naphtho[1,8-c,d]-1,2-diselenole48
with NaBH4 in an aqueous THF solution, was added methyl io-
dide at room temperature. After a usual workup, the crude was
chromatographed on silica gel containing basic alumina. Recrys-
tallization of the chromatographed product from hexane gave 1c
as colorless prisms in 98% yield, mp 85.0–85.5 ꢃC; 1H NMR
(300 MHz, CDCl3, 23 ꢃC, TMS): ꢄ 2.33 (s, 6H), 7.32 (t,
J ¼ 7:7 Hz, 2H), 7.70 (dd, J ¼ 1:2 and 8.2 Hz, 2H), 7.73 (dd, J ¼
1:2 and 7.5 Hz, 2H); 13C NMR (75 MHz, CDCl3, 23 ꢃC, TMS):
ꢄ 13.3, 125.7, 128.3, 131.9, 132.3, 135.3, 135.6; 77Se NMR
(76 MHz, CDCl3, 23 ꢃC, MeSeMe): ꢄ 234.06; elemental analysis:
Calcd for C12H12Se2 (314.14): C 45.88, H 3.85%. Found: C,
45.73; H, 3.77%.
Conclusion
Weak interactions determine fine structures of molecules and
create high functionalities of materials. We investigated weak
interactions originating from orbital overlap as the first step
to establish the cause-and-effect in weak interactions. It is in-
evitable to set up a system so as to analyze each phenomenon
in question as the result of the weak interactions. Weak nonco-
valent interactions become weakly covalent. Homonuclear
Z Z interactions were investigated, employing 1,8-(MeZ) -
2
ꢁꢁꢁ
C10H6 (1a–1d), 1-MeZ-8-PhZC10H6 (2a–2c), and 1,8-(PhZ)2-
C10H6 (3a–3d). It was elucidated how the fine structures of
1a–3d are controlled by the weak interactions and how weak
interactions act to determine the fine structures, after determi-
nation of the structures by X-ray crystallographic analysis.
QC calculations were performed on 1a–1d and 3c, together
with model c at both B3LYP and MP2 levels. Factors to
control the fine structures of 1a–3d, caused by noncovalent
1-Methoxy-8-phenoxynaphthalene (2a).49
To a 2,4,6-tri-
methylpyridine solution of phenol, was added 1-iodo-8-methoxy-
naphthalene50 and copper I oxide. The solution was refluxed for
4 h under argon atmosphere. After usual work-up, the crude prod-
uct was chromatographed on silica gel containing basic alumina
and gave 2a as colorless prisms in 95% yield; mp 97–98 ꢃC;
1H NMR (300 MHz, CDCl3, 23 ꢃC, TMS): ꢄ 3.65 (s, 3H), 6.77
(dt, J ¼ 1:0 and 7.6 Hz, 1H), 6.82 (dd, J ¼ 1:1 and 7.5 Hz, 2H),
6.96 (dt, J ¼ 1:1 and 7.3 Hz, 1H), 7.10 (dd, J ¼ 1:1 and 7.5 Hz,
1H), 7.24 (dd, J ¼ 7:4 and 8.5 Hz, 2H), 7.37 (t, J ¼ 7:8 Hz,
1H), 7.42 (t, J ¼ 7:6 Hz, 1H), 7.46 (dd, J ¼ 1:3 and 8.3 Hz,
1H), 7.65 (dd, J ¼ 1:1 and 8.3 Hz, 1H); 13C NMR (75 MHz,
CDCl3, 23 ꢃC, TMS): ꢄ 55.9, 106.1, 116.0, 119.0, 119.9, 120.7,
121.1, 125.0, 126.5, 126.5, 129.3, 137.5, 151.2, 155.9, 160.1; ele-
mental analysis: Calcd for C17H14O2 (250.29): C, 81.58; H,
5.64%. Found: C, 81.60; H, 5.64%.
1-Methylthio-8-phenylthionaphthalene (2b). To a solution
which was prepared by reduction of bis(8-phenylthionaphthyl)-
1,10-disulfide51 with NaH in DMF solution at 70 ꢃC, was added
methyl iodide at room temperature. After a usual workup, the
crude was chromatographed on silica gel containing basic alu-
mina. Recrystallization of the chromatographed product from hex-
ane gave 2b as colorless prisms in 96% yield, mp 52.0–53.0 ꢃC;
1H NMR (300 MHz, CDCl3, 23 ꢃC, TMS): ꢄ 2.50 (s, 3H), 7.12–
7.19 (m, 3H), 7.20–7.27 (m, 2H), 7.34 (t, J ¼ 7:7 Hz, 1H),
7.39–7.44 (m, 2H), 7.59 (dd, J ¼ 1:3 and 7.3 Hz, 1H), 7.66 (dd,
J ¼ 3:5 and 5.9 Hz, 1H), 7.79 (dd, J ¼ 1:3 and 8.3 Hz, 1H);
13C NMR (75 MHz, CDCl3, 23 ꢃC, TMS): ꢄ 19.8, 125.8, 126.2,
126.3, 126.7, 129.1, 129.4, 130.0, 132.1, 133.0, 135.6, 135.9,
137.7, 139.3; elemental analysis: Calcd for C17H14S2 (282.42):
C, 72.30; H, 5.00%. Found: C, 72.06; H, 5.04%.
n (Z) n (Z) interactions, were established based on experi-
p
ꢁꢁꢁ
p
mental and theoretical investigations. AB and CC are the most
important structures for Z ¼ S and Se. AB and CC must
also be important for Z ¼ Te although 1a (AB) optimized to
1a (CC) in the QC calculations. AB is stabilized by
ꢀ
n (Z) ꢀ (Z–C) 3c–4e interactions and CC is stabilized by
ꢁꢁꢁ
p
ꢀ
also be briefly stated that CC is stabilized with the disappear-
ꢀ
both n (Z) ꢀ (Z–C) and n (Z) ꢀ (Z–C) interactions. It can
ꢁꢁꢁ
ꢁꢁꢁ
s
p
ꢀ
ly appearing in BB. The energy profile of model c helps us to
ance of the nodal plane in ꢁ (Z Z: HOMO) in CC, apparent-
ꢁꢁꢁ
imagine the whole picture of the noncovalent n (Z) n (Z)
p
ꢁꢁꢁ
p
interactions. The factors are visualized employing the HOMO
or HOMOꢂ1 of model c.
Superficial factors are sometimes mistakenly identified as
sources of fine structure in systems where weak interactions
play an important role, since weak interactions usually work
behind other factors of superficial contribution. Such cases
are found even in the literature. A firm guideline is necessary
for the phenomena caused by the weak interactions. The
above results will supply one such guideline, which will enable
the study of more insights into the phenomena caused by weak
interactions.
Investigations on the role of the noncovalent heteronuclear
Z Z0 interactions (Z, Z0 ¼ O, S, Se, and Te) are in progress.
ꢁꢁꢁ
The results will be reported elsewhere.
1,8-Diphenoxynaphthalene (3a).49 To a 2,4,6-trimethylpyri-
dine solution of phenol, was added an 1,8-diiodonaphthalene52
and copper I oxide. The solution was refluxed for 10 h under argon
atmosphere. After usual work-up, the crude product was chroma-
tographed on silica gel containing basic alumina and gave 3a
as colorless prisms in 68% yield; mp 84–85 ꢃC; 1H NMR
(300 MHz, CDCl3, 23 ꢃC, TMS): ꢄ 6.64–6.68 (m, 4H), 6.93–
6.98 (m, 2H), 7.01 (dd, J ¼ 0:7 and 7.3 Hz, 2H), 7.14–7.22 (m,
2H), 7.42 (t, J ¼ 7:9 Hz, 2H), 7.66–7.72 (m, 4H); 13C NMR
(75 MHz, CDCl3, 23 ꢃC, TMS): ꢄ 117.1, 117.7, 121.9, 124.5,
126.6, 129.3, 137.7, 151.3, 158.8; elemental analysis: Calcd for
C22H16O2 (312.36): C, 84.59; H, 5.16%. Found: C, 84.53; H,
5.07%.
Experimental
General.
Manipulations were performed under an argon
atmosphere with standard vacuum-line techniques. Glassware
was dried at 130 ꢃC overnight. Solvents and reagents were purified
by standard procedures as necessary. The melting points were
determined on a Yanako MP-S3 melting point apparatus and are
uncorrected. NMR spectra were recorded at 25 ꢃC on a JEOL
AL-300 spectrometer (1H, 300 MHz; 13C, 75 MHz) and JEOL
Lambda-400 spectrometer (77Se, 76 MHz). The 1H, 13C, and
77Se chemical shifts are given in parts per million relative to
those of Me4Si and external MeSeMe, respectively. Flash column
chromatography was performed with 400-mesh silica gel and
basic alumina and analytical thin layer chromatography was per-
formed on precoated silica gel plates (60F-254) with the systems
(v/v) indicated.
1,8-Bis(phenylthio)naphthalene (3b).27 To a 2,4,6-trimethyl-
pyridine solution of benzenethiol, was added 1,8-diiodonaphtha-
lene52 and copper I oxide. The solution was refluxed for 10 h un-
der argon atmosphere. After usual work-up, the crude product was

S. Hayashi et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 12 (2008) 1613
chromatographed on silica gel containing basic alumina and gave
3b as colorless prisms in 94% yield; mp 68–69 ꢃC; 1H NMR
(300 MHz, CDCl3, 23 ꢃC, TMS): ꢄ 7.16–7.31 (m, 10H), 7.32 (t,
J ¼ 7:6 Hz, 2H), 7.47 (dd, J ¼ 1:5 and 7.3 Hz, 2H), 7.76 (dd, J ¼
1:5 and 8.1 Hz, 2H); 13C NMR (75 MHz, CDCl3, 23 ꢃC, TMS): ꢄ
125.8, 126.7, 129.1, 129.2, 131.0, 133.1, 133.8, 134.0, 136.1,
138.5; elemental analysis: Calcd for C22H16S2: C, 76.70; H,
4.68%. Found: C, 76.53; H, 4.71%.
1,8-Bis(phenylselanyl)naphthalene (3c). To a DMF solution
of diphenyl diselenide, was added NaH under argon atmosphere.
The mixture was held at 110 ꢃC for 30 min, then to it was added
1,8-diiodonaphthalene52 and copper I oxide. The solution was held
at 140 ꢃC for 12 h under argon atmosphere. After usual work-up,
the crude product was chromatographed on silica gel containing
basic alumina and gave 3c as pale yellow needles in 59% yield;
mp 64.0–64.8 ꢃC; 1H NMR (300 MHz, CDCl3, 23 ꢃC, TMS): ꢄ
7.22–7.28 (m, 8H), 7.39–7.45 (m, 4H), 7.64 (dd, J ¼ 1:1 and
7.3 Hz, 2H), 7.74 (dd, J ¼ 1:1 and 8.3 Hz, 2H); 13C NMR
(75 MHz, CDCl3, 23 ꢃC, TMS): ꢄ 126.0, 127.4, 129.2, 129.4,
131.4, 133.4, 135.18, 135.19, 135.5, 135.9; 77Se NMR (76 MHz,
CDCl3, 23 ꢃC, MeSeMe): ꢄ 435.4; elemental analysis: Calcd for
C22H16Se2 (438.28): C, 60.29; H, 3.68%. Found: C, 60.21; H,
3.75%.
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X-ray Crystal Structural Determination. The crystals of 1c,
2a, 2b, 3a, 3b, and 3c were grown by slow evaporation of di-
chloromethane–hexane solutions at room temperature. The inten-
sity data were collected on a CCD diffractometer equipped with
˚
graphite-monochromed Mo Kꢅ radiation (ꢆ ¼ 0:71070 A) at
103(2) K for 1c, 2a, 3a, and 3c and on a four-circle diffractometer
˚
5
a) W. Nakanishi, S. Hayashi, H. Kihara, J. Org. Chem.
with graphite-monochromated Mo Kꢅ radiation (ꢆ ¼ 0:71069 A)
1999, 64, 2630. b) W. Nakanishi, S. Hayashi, T. Uehara, Eur. J.
Org. Chem. 2001, 3933.
for 2b, and 3b at 298(1) K. The structures of 1c, 2a, 3a, and 3c
were solved by direct method (SIR97)53 and refined by full-matrix
least-square method on F2 for all reflections (SHELXL-97).54 The
structures were solved by Patterson interpretation using the pro-
gram DIRDIF9255 for 2b and 3b and by and refined by full-matrix
least-square techniques. All the non-hydrogen atoms were refined
anisotropically. CCDC-640537 for 1c, CCDC-640538 for 2a,
CCDC-640539 for 2b, CCDC-640540 for 3a, CCDC-640591 for
3b, and CCDC-640541 for 3c contain the supplementary crystallo-
graphic 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
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Chemistry of Hypervalent Compounds, ed. by K.-y. Akiba,
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8
Handbook of Chalcogen Chemistry: New Perspectives in Sulfur,
Selenium and Tellurium, ed. by F. A. Devillanova, Royal Society
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We are grateful to Prof. Norihiro Tokitoh and Dr. Takahiro
Sasamori, Institute for Chemical Research, Kyoto University,
for the X-ray diffraction measurements of 1c, 2a, 3a, and
3c. This work was partially supported by a Grant-in-Aid for
Scientific Research (Nos. 16550038 and 19550041) from the
Ministry of Education, Culture, Sports, Science and Tech-
nology, Japan.
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ORTEP drawing of 1cB, 2aA, 2aB, 3a, and 3b are shown in
Figures S1–S4, respectively. Results of QC calculations by fre-
quency analysis on 1a–1d are shown in Tables S1–S4, respective-
ly. Optimized structures given by Cartesian coordinates for 1a–1d,
3c, and model c, together with the total energies and the method
for the calculations. These materials are available free of charge
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29 One might wonder that the determination of AB seems
sometimes unclear, since the Z1–C1 and Z8–C8 bonds in 1,8-
(PhZ)2C10H6 deviate out of the naphthalene plane. In such case,
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=
AB is identified by = Z8Z1Ci and Z1Z8Ci being close to 90
0
À
À
and 180ꢃ, respectively.
30 Efforts were also made to determine the structures of 1d
and 2d but as of yet have not been successful, due to their insta-
bility. The structures are expected to be also CC, judging from the
CC of 1c and 2c.
31 The n (Z) ꢀ (Z–C) interactions seem not to be effective
ꢀ
ꢁꢁꢁ
p
ꢀ
for Z ¼ O and the n (Z) ꢀ (Z–H) interactions are not effective
ꢁꢁꢁ
p
ꢀ
maybe due to the weak accepting ability of ꢀ (Z–H).
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32 Details of the factors to control the Z Z distances will be
reported elsewhere.
ꢁꢁꢁ
33 The energy differences due to the conformers around the
Se–CAr bonds in 1-MeSeNap and MeSePh are calculated at both
MP2 and DFT levels. The results are closely related to the p–ꢁ
conjugation of p(Se)–ꢁ(Nap/Ph), which will be reported else-
where.32
34 The AB conformers play a crucial role in the heteronuclear
Z Z0 interactions at naphthalene 1,8-positions. The role of the
ꢁꢁꢁ
phenyl group(s) will be discussed again in the Z Z0 interactions.
ꢁꢁꢁ
35 C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785;
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37 The DFT level is also employed to optimize the structures
here. However, the DFT level should be carefully employed when
the system contains noncovalent interactions. DFT would not
evaluate the noncovalent interactions correctly, since DFT with
most functionals are not treated by the exchange-correlation func-
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around the C2v axis in BB maintaining the plane for the four
¨
40 C. Møller, M. S. Plesset, Phys. Rev. 1934, 46, 618;
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C
plane moving inverse direction.
46 The factor to stabilize CC is called Mobius stabilization,
¨
Me, Z, Z, and CMe atoms (Z ¼ S, Se, or Te) with the naphthyl
although CC is not cyclic. See Ref. 4f.
47 The r(Z Z) values become larger in the order r(BB) <
ꢁꢁꢁ
r(CC) < r(AB) ꢅ r(AA-t), which must also be accounted for
based on the weak interactions.
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43 Two Se atoms in model c are placed on the x-axis with the
Se Se distances fixed at the observed values and two Se–H bonds
1
ꢁꢁꢁ
¨
¨
2
1
=
=
are in the z-directions with
Consequently, the four atoms are placed in the xz plane, for each.
Se Se H = 1Se2Se2H = 90.0ꢃ.
55 P. T. Beurskens, G. Admiraal, G. Beurskens, W. P.
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Nijmegen, The Netherlands, 1992.
À
À
The torsional angle of H1Se2Se2H (ꢃ) is fixed at zero.
44 Although CC (C2) is the desirable structure for 1c, the
structure gives one negative (imaginary) frequency for an internal
1