Selenadiazolopyridine: A synthon for supramolecular assembly and complexes with metallophilic interactions

Article abstract of DOI:10.1021/ic3005272

The synthesis and characterization of the complexes of Cu(I), Ag(I), Cu(II), and Co(II) ions with 1,2,5-selenadiazolopyridine (psd) is reported. The following complexes have been prepared: [Cu₂(psd)₃(CH ₃CN)₂]²⁺2(PF₆^-); [(CuCl)₂(psd)₃]; [Cu₂(psd)₆] ²⁺2(ClO₄)^-; [Ag₂(psd) ₂]²⁺2(NO₃)^-; [Ag₂(psd) ₂]²⁺2(CF₃COO)^-; [Cu(psd) ₂(H₂O)₃]²⁺2(ClO₄) ^-·(psd)₂; [Cu(psd)₄(H ₂O)]²⁺2(ClO₄)^-·(CHCl ₃); [Cu(psd)₂(H₂O)₃] ²⁺2(NO₃)^-·(H₂O)·(psd) ₂, and [Co(psd)₂(H₂O)₄] ²⁺2(ClO₄)^-·(psd)₂. The electronic structure of ligand psd, in particular the bond order of Se-N bonds, has been probed by X-ray diffraction, ⁷⁷Se NMR, and computational studies. A detailed analysis of the crystal structures of the ligand and the complexes revealed interesting supramolecular assembly. The assembly was further facilitated by the presence of neutral ligands for some complexes (Cu(II) and Co(II)). The molecular structure of the ligand showed that it was present as a dimer in the solid state where the monomers were linked by strong secondary bonding Se···N interactions. The crystal structures of Cu(I) and Ag(I) complexes revealed the dinuclear nature with characteristic metallophilic interactions [M···M] (M = Cu, Ag), while the Cu(II) and Co(II) complexes were mononuclear. The presence of M···M interactions has been further probed by Atoms in Molecules (AIM) calculations. The paramagnetic Cu(II) and Co(II) complexes have been characterized by UV-vis, ESI spectroscopy, and room temperature magnetic measurements.

Full text of DOI:10.1021/ic3005272

Article
pubs.acs.org/IC
Selenadiazolopyridine: A Synthon for Supramolecular Assembly and
Complexes with Metallophilic Interactions
†
†
†
†
,†
Goutam Mukherjee, Puspendra Singh, Chandrasekhar Ganguri, Sagar Sharma, Harkesh B. Singh,*
‡
‡
§
Nidhi Goel, Udai P. Singh, and Ray J. Butcher
†Department of Chemistry, Indian Institute of Technology, Bombay, Mumbai 400076, India
‡Department of Chemistry, Indian Institute of Technology, Roorkee 247667, India and
§Department of Chemistry, Howard University, Washington, DC 20059, United States
*
S Supporting Information
ABSTRACT: The synthesis and characterization of the
complexes of Cu(I), Ag(I), Cu(II), and Co(II) ions with
1
,2,5-selenadiazolopyridine (psd) is reported. The following
2+
complexes have been prepared: [Cu (psd) (CH CN) ] 2-
2
3
3
2
−
2+
−
(
[
(
(
(
(
PF6 ); [(CuCl) (psd) ]; [Cu (psd) ] 2(ClO ) ;
2 3 2 6 4
2
+
−
2+
−
Ag (psd) ] 2(NO ) ; [Ag (psd) ] 2(CF COO) ; [Cu-
psd) (H O) ] 2(ClO ) ·(psd) ; [Cu(psd) (H O)] 2-
2
2
3
2
2
3
2
+
−
2+
2
2
3
4
2
4
2
−
2 +
C l O ) · ( C H C l ) ; [ C u ( p s d ) ( H O ) ] 2 -
NO ) ·(H O)·(psd) , and [Co(psd) (H O) ] 2-
4
3
2
2
3
−
2+
3
2
2
2
2
4
−
ClO ) ·(psd) . The electronic structure of ligand psd, in
4
2
77
particular the bond order of Se−N bonds, has been probed by X-ray diffraction, Se NMR, and computational studies. A detailed
analysis of the crystal structures of the ligand and the complexes revealed interesting supramolecular assembly. The assembly was
further facilitated by the presence of neutral ligands for some complexes (Cu(II) and Co(II)). The molecular structure of the
ligand showed that it was present as a dimer in the solid state where the monomers were linked by strong secondary bonding
Se···N interactions. The crystal structures of Cu(I) and Ag(I) complexes revealed the dinuclear nature with characteristic
metallophilic interactions [M···M] (M = Cu, Ag), while the Cu(II) and Co(II) complexes were mononuclear. The presence of
M···M interactions has been further probed by Atoms in Molecules (AIM) calculations. The paramagnetic Cu(II) and Co(II)
complexes have been characterized by UV−vis, ESI spectroscopy, and room temperature magnetic measurements.
INTRODUCTION
is highest in the case of Te. The electronic origin of secondary
interaction between two chalcogenadiazole moieties is due to
the donation of electron density from the lone pair of nitrogen
to the antibonding E−N σ* orbital of another chalcogenadia-
zole moiety (Figure 1b). Interestingly, apart from neutral
chalcogenadiazoles, their cationic counterparts can too exhibit
secondary E···N interactions. The upsurge in the interest of
such interactions involving heavier chalcogens is due to the fact
that they are often instrumental in the construction of large
supramolecular structures.
■
Heavier chalcogens and halogens are known to display short
interatomic contacts either between them or with the elements
1
of other groups. More recently such kinds of contacts have
been attributed to secondary bonding interactions (SBIs) that
are attractive in nature and have both orbital and electrostatic
4
,5
2
2,3
contributions. All four 1,2,5-chalcogenadiazoles (1−4) have
been a favorite case-study to understand SBIs and the
formation of supramolecular association through these SBIs
(
Figure 1a). The strength of electrostatic interaction between
the negative nitrogen and the positive chalcogen atoms is
guided by the electronegativity difference between them, which
Two 1,2,5-selenadiazole rings can associate themselves
through antiparallel Se···N SBIs to form a four-membered
cyclic supramolecular synthon. This synthon can repeat itself to
link another molecule, thus, giving a ribbon like polymer. It is
interesting to note that the association of the chalcogenadia-
zoles can be controlled by suitable coordination of the nitrogen
atom. For instance, the 1:1 triphenylborane adduct of 1,2,5-
telluradiazolobenzene exists as a dimer, whereas the 2:1 adduct
6
is monomeric. The phenyl rings of the 2:1 adduct block the
Figure 1. 1,2,5-Chalcogenadiazoles (1−5) shown in (a) and (c).
Directional bonding between two chalcogenadiazoles by a nitrogen
nonbonded orbital with a lone pair and an antibonding orbital of the
E−N bond is shown in (b).
access of the nitrogen atoms from the second molecule to
Received: March 10, 2012
Published: July 17, 2012
©
2012 American Chemical Society
8128
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Inorganic Chemistry
Article
2
6
tellurium, which in turn prevents the formation of a dimer.
Sisco Research Laboratories, India. Silver trifluoroacetate, tetrakis-
27
2
,7
2,7
(
acetonitrile)copper(I) perchlorate, and tetrakis(acetonitrile)copper-
Benzo-1,2,5-telluradiazole,
1,2,5-telluradiazole,
and
28
8
(I) chloride were prepared according to literature procedures.
Caution! Perchlorate salts are potentially explosive. Although no
detonation tendencies have been observed, caution is advised and handling
of only small quantities is recommended.
phenanthro[9,10-C]-1,2,5-telluradiazole form ribbon poly-
mers, while 4,6-di-tert-butyl- and 4,6-dibromo-benzo-1,2,5-
telluradiazole only form dimers through the formation of
2
,9
[
Te···N]2 supramolecular synthon. Recently, Vargas-Baca
General Physical Measurements. Melting points were recorded
and co-workers reported the two thermochromic [α(yellow)
1
13
77
in capillary tubes and are uncorrected. The H, C, and Se NMR
spectra were recorded on a Varian VXR 400 or VXR 300 spectrometer.
and β(red)] packing polymorphs of 4,5,6,7-tetrafluorobenzo-
1
13
1,2,5-telluradiazole and a pyridine coordinated telluradiazole.
Chemical shifts cited were referenced to TMS ( H, C) as internal
Se ( Se) as external standard. Electron spray mass spectra
ESI-MS) were performed on a Q-Tof micro (YA-105) mass
spectrometer. Mass spectra were obtained with a Platform II single
quadrupole mass spectrometer (Micromass, Altrincham, UK) using a
CH OH mobile phase. Elemental analyses were performed on a Carlo-
77
The α phase is metastable; at 127 °C the material undergoes an
exothermic irreversible transition to the red polymorph. A third
phase is also yellow and transforms into the red phase after the
loss of solvent. In the crystal structures, the molecules are also
and Me
2
(
3
associated through [Te···N] supramolecular synthon forming
2
Erba model 1106 elemental analyzer. IR spectra were recorded as KBr
pellets on a Nicolet Impact 400 and Perkin FT-IR spectrometer. All
UV−vis spectra and reflectance spectra were recorded on a Jasco-570
10
ribbon polymers and dimers, respectively.
In 1984 Kaim has reported the carbonyl substitution
reactions of M(CO) (M = Cr, Mo, W) with the radical
6
spectrophotometer. Reflectance spectra were recorded by using BaSO
4
anions of ligands 1, 2, and 3, which result in the replacement of
CO and the formation of mononuclear paramagnetic
complexes at first and then get converted to binuclear
as standard. Emission spectra were recorded by using a Perkin-Elmer
LS55 luminescence spectrometer. Cyclic voltammetric measurements
were carried out using a CH 1600 model electrochemistry system. A
platinum wire working electrode, platinum wire auxiliary electrode,
and saturated calomel reference electrode were used in a standard
three-electrode configuration. Tetraethylammonium perchlorate was
11
paramagnetic complexes. Subsequently, the mononuclear
1
2
13
14
15
16
17,18
17
17
Ni, Co, Cu, Zn, Hg, Ru,
Os, and Ir complexes
based on the ligands 2 and 3 were reported. The first report
bearing Se···N SBIs for the construction of periodic supra-
molecular architectures reported was by Tong and co-
−1
the supporting electrolyte, the scan rate used was 50 mV s , and
ferrocene was used as the standard. All of the electrochemical
experiments were carried out under a nitrogen atmosphere, and all of
the redox potentials are uncorrected for junction potentials. The ESR
measurements were made with a Varian model 109CE-line X-band
spectrometer fitted with a quartz Dewar for measurements at 77 K.
ESR has been studied at room temperature as well as at liquid nitrogen
temperature. TCNQ was taken as the standard. Magnetic susceptibility
was measured on a PAR vibrating sample magnetometer.
1
9
workers. It has been demonstrated that the silver(I) complex
of 1,2,5-benzeneselenadiazole (bsd), along with neutral bsd
leads to the formation of two polymorphs of silver(I) bsd
complexes (α and β-[Ag(bsd) (NO )]·0.5bsd) with interesting
2
3
three-dimensional supramolecular networks through Se···N
interactions. Also, it has been shown that the use of 3 as an
auxiliary ligand to construct the two-dimensional hexagonal
honeycomb networks of Ag(I) ion in the crystal structures of
29
Preparation of 1,2,5-Selenadiazolopyridine (5). 2,3-Diami-
nopyridine (1.23 g, 11.27 mmol) and selenium dioxide (1.25 g, 11.27
mmol) were ground using a porcelain mortar and pestle at room
temperature for 30 min. The crude black colored mixture obtained was
extracted with benzene and filtered. The filtrate was concentrated
under vacuum to get a yellow residue. The residue obtained was again
dissolved in a mixture of acetone and ether (1:1 v/v) as a solvent, a
pinch of charcoal was added, and the mixture was filtered. The solvent
was concentrated under vacuum to obtain 5 as a pale yellow solid
[
Ag (btc)(bsd) ]·0.5H O and [Ag (ctc)(bsd) ]·1.5bsd·3.5H O
3 6 2 3 3 2
where btc =1,3,5-benzenetricarboxylate and ctc =1,3,5-cyclo-
20
hexanetricarboxylate. We envisaged that the introduction of
one more nitrogen atom in the bsd ring (i.e., 1,2,5-
selenadiazolopyridine, psd shown in Figure 1c) should lead
to more interesting assemblies due to additional Se···Npy
interactions. Since nitrogen based bidentate ligands with one
carbon linker are capable of binding to two metal centers, it can
also be used to synthesize metal complexes with closed shell
metal···metal interactions. Reviews on such types of metal···-
metal interactions have been published by Leznoff et al. in
(
(
1.55 g, 75% yield). Mp 118−120 °C (lit. mp 116−118 °C). FT-IR
KBr) 3049, 1590, 1504, 1485, 1375, 1208, 781; UV−visible, λ 335
max
7
2
−1
1
nm (ε: 1.42 × 10 cm mol ); H NMR (400 MHz, CDCl ) δ 8.99
3
(dd, J = 3.7, 1.6 Hz, 1H), 8.10 (dd, J = 8.8, 1.5 Hz, 1H), 7.32 (dd, J =
13
9
1
.2, 4.0 Hz, 1H); C NMR (400 MHz, CDCl ) δ 164.5, 156.9, 153.4,
3
77
31.5, 123.8; Se NMR (300 MHz, CDCl ) δ 1476; ES-MS m/z
3
2
1
22
+
2
008 and more recently by Sculfort and Braunstein. The
(relative intensity, nature of peak) 186 (100, [M+1] ); Anal. Calcd. for
C H N Se: C, 32.63; H 1.64; N 22.83. Found C, 32.56; H, 1.29; N
23
24
25
25c
ligands of type NCN, PCP, PNP, SCS, PCN, and OCO 1
show metallophilic interactions when coordinated with d 0
metal ions. With these ideas, we have chosen psd (5) as our
ligand of choice for the study. The ligand has similar
coordination sites i.e. NCN type and metallophilic interactions
are expected despite the presence of an extra selenium atom
which can play a part in the formation of supramolecular
assemblies. Herein, we report the synthesis and characterization
of 5 and its complexes with Cu(I), Ag(I), Cu(II), and Co(II).
The nature of the short metal···metal distances in these
complexes is further probed by theoretical studies.
5
3
3
23.07.
Synthesis of [Cu (psd) (CH CN) ](PF ) (6). To a 50 mL two-
2
3
3
2
6 2
necked flask was taken an acetonitrile solution (15 mL) of 5 (0.30 g,
.63 mmol). To it was added an acetonitrile solution (2 mL) of
Cu(CH CN) ]PF (0.30 g, 0.81 mmol). The mixture was stirred for 1
1
[
3
4
6
h to obtain a brown-colored solution, and then the excess acetonitrile
was removed by using vacuum. The precipitate obtained was
recrystallized from acetonitrile (0.38 g, 90% yield). Mp 220−223 °C.
FT-IR (KBr) 3550, 3414, 3236, 1637, 1617, 1519, 1019, 838, 767
−
1
4
2
−1
cm ; UV−visible, λ 335 nm (ε: 6.06 × 10 cm mol ), λ 507
max
max
3
2
−1
1
nm (ε: 2.26 × 10 cm mol ); H NMR (400 MHz, DMSO-d
) δ
.09 (br, 3H), 8.33 (d, J = 8.7 Hz, 3H), 7.57 (br, 3H); Se NMR (300
MHz, CD CN) δ 1492; ES-MS m/z (relative intensity, nature of peak)
6
7
7
9
3
EXPERIMENTAL SECTION
+
+
■
247 (40, [Cu(psd)] ); 433 (20, [Cu(psd) ] ); Anal. Calcd. for
2
Materials and Procedures. Solvents were dried and distilled by
standard procedures. 2,3-Diaminopyridine, selenium dioxide, tetrakis-
C H Cu F N P Se : C, 21.71; N, 14.66; H, 1.44. Found C, 21.82;
19
15
2
12 11
2
3
N, 14.25; H, 0.82.
Synthesis of [Cu (Cl) (psd) ] (7). An acetonitrile solution of
(
acetonitrile)copper(I) hexafluorophosphate, copper(II) perchlorate
2
2
3
hexahydrate, and cobalt(II) perchlorate hexahydrate were purchased
from Aldrich. Silver nitrate and cupric nitrate were purchased from
CuCl(CH CN)4 (0.26 g, 1.00 mmol) was prepared in situ by
dissolving CuCl (0.10 g, 1 mmol) in 10 mL of acetonitrile in a 25 mL
3
8
129
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Inorganic Chemistry
Article
28
one-necked flask. To it was added a chloroform solution (5 mL) of 5
0.28 g, 1.50 mmol). The mixture was stirred for 1 h to obtain a black-
Synthesis of [Cu(psd) (H O)](ClO ) ·CHCl (12). To a solution
4
2
4 2
3
(
of Cu(ClO ) ·6H O (0.18 g, 0.50 mmol) in 3 mL of chloroform was
4 2 2
colored precipitate. The precipitate obtained was recrystallized from
acetonitrile to give rectangular shaped crystals of 7 (0.21 g, 60% yield).
added a 5 mL solution of 5 (0.37 g, 2.00 mmol) in the same solvent.
The reaction mixture was stirred at room temperature for 1 h to afford
a green solid of 11, which was removed by filtration. The resulting
solution was further stirred at room temperature for 16 h and afforded
a magenta-colored precipitate of 12 which was recrystallized from a 1:1
−
1
Mp 141 °C. FT-IR (KBr) 1593 (υ
), 1529 (υ
) cm ; UV−
CC
−1
CN
4
2
visible, λmax 336 nm (ligand) (ε: 7.50 × 10 cm mol ). ES-MS m/z
+
(
relative intensity, nature of peak) 750 (17, [M] ); 715 (18, [M+H−
+ + +
Cl] ); 615 (20, [M−CuCl−Cl] ); 530 (55, [M−psd−Cl] ); 432 (50,
mixture of CHCl −MeOH to give violet colored crystals of 12 (0.36 g,
3
+
+
[
2
1
M−psd−CuCl−Cl] ); 345 (60, [M−2psd−Cl] ); 185 (100, [M−
63% yield). Mp 267 °C (dec). FT-IR (KBr) 3456, 3049, 1590, 1525,
+
−1
psd−2CuCl] ); Anal. Calcd. for C H Cl Cu N Se : C, 24.02; N,
1505, 1374, 1298, 1211, 1142, 1089, 763, 625 cm ; UV−visible, λmax
15
9
2
2
9
3
4
2
−1
3
34 nm (ε: 7.80 × 10 cm mol ); ES-MS m/z (relative intensity,
+
6.80; H, 1.21. Found C, 24.26; N, 16.08; H, 1.61.
Synthesis of [Cu(psd) ](ClO ) (8). To a 50 mL two-necked flask
nature of peak) 523 (5, [Cu (psd) +MeO−3H] ); 370 (12, [2psd
H] ); 253 (50, [Cu(psd)+6H] ); 218 (100, [psd+CH OH+2H] );
85 (32, [psd+H] ); Anal. Calcd. for C H Cl CuN O Se : C, 22.20;
2
2
3
4
+
+
+
+
1
was taken an acetonitrile solution (7 mL) of 5 (0.28 g, 1.50 mmol). To
3
+
it was added an acetonitrile solution (5 mL) of [Cu(CH CN) ]ClO
21 15 5 12 9 4
3
4
4
N, 14.79; H, 1.33. Found C, 22.27; N, 14.66; H, 1.05.
Synthesis of Cu(psd) (H O) (NO ) ·(H O)·(psd) (13). To a 10
(0.16 g, 0.51 mmol). The mixture was stirred for 1 h to obtain a
brown-colored solution, and then the excess of acetonitrile was
removed by using vacuum. The precipitate obtained was recrystallized
from acetonitrile to give 8 (0.23 g, 63% yield). Mp 208−210 °C. FT-
IR (KBr) 3441, 3071, 1590, 1510, 1379, 1296, 1223, 1088, 777, 621
2
2
3
3 2
2
2
mL acetonitrile/water (v/v 3:1) solution of 5 (0.49 g, 2.67 mmol) was
added an acetonitrile/water (6 mL, v/v 3:1) solution of copper nitrate
trihydrate (0.32 g, 1.33 mmol), and then the mixture was stirred for 30
min to give a clear solution. A deep green precipitate was obtained on
stirring for 2 days. The precipitate obtained was recrystallized from an
acetonitrile/water solvent mixture to give green colored crystals of 13
−
1
4
2
−1
1
cm ; UV−visible, λ 335 nm (ε: 8.04 × 10 cm mol ); H NMR
max
(
400 MHz, CDCl ) δ 9.11 (br, 1H), 8.22−8.19 (m, 1H), 7.44−7.41
m, 1H); ES-MS m/z (relative intensity, nature of peak) 185 (100,
psd+H] ); 345 (5, [Cu(psd)ClO +H] ); 432 (8, [Cu(psd) +2H] );
30 (5, [Cu(psd) ClO +H] ); Anal. Calcd. for C H ClCuN O Se :
3
(
[
5
+
+
+
(0.36, 32% yield). Mp 155−158 °C. FT-IR (KBr) 3444, 1590, 1526,
4
2
−1
+
1511, 1384, 1312, 1296, 1220, 768 cm ; UV−visible, λ 335 nm (ε:
max
2 4 15 9 9 4 3
4
2
−1
2
−1
5
.59 × 10 cm mol ), λ 786 nm (ε: 34.66 cm mol ); ES-MS m/
max
+
C, 25.19; N, 17.63; H, 1.27. Found C, 25.66; N, 17.83; H, 1.12.
Synthesis of [Ag (psd) ](NO ) (9). To an acetonitrile solution (2
z (relative intensity, nature of peak) 185 (100, [psd] ); 433 (20,
2
2
3 2
+
[
Cu(psd) ] ); Anal. Calcd. for C H CuN O Se : C, 24.12; N,
2 20 20 14 10 4
mL) of AgNO3 (0.35 g, 2.06 mmol) was added dropwise an
acetonitrile solution (10 mL) of 5 (0.38 g, 2.06 mmol), and the
reaction mixture was stirred further for 30 min. The precipitate
obtained was filtered, washed with acetonitrile, and dried under
vacuum. Recrystallization from acetonitrile/water (2:1) gave golden
yellow prismatic crystals of 9 (0.67 g, 92% yield). Mp > 272 °C. FT-IR
1
9.69; H, 2.02. Found C, 24.20; N, 20.46; H, 1.43.
Synthesis of [Co(psd) (H O) (ClO ) ·(psd) (14). To a 5 mL
2
2
4
4 2
2
methanol solution of 5 (0.19 g, 1.07 mmol) was added a methanol (5
mL) solution of cobalt perchlorate hexahydrate (0.11 g, 0.28 mmol),
and then the mixture was stirred for 12 h to give a clear solution. The
solution was allowed to slowly evaporate at room temperature to
afford orange rectangular crystals of 14 (0.24, 88% yield). These
−1 1
(
KBr) 1587, 1515, 1385, 1135, 1020, 773 cm ; H NMR (400 MHz,
DMSO-d ) δ 9.09 (dd, J = 4.2, 1.9 Hz, 2H), 8.40 (dd, J = 7.7, 1.8 Hz,
6
1
3
crystals slowly become opaque over time. Mp 223−224 °C. FT-IR
2
H), 7.61 (dd, J = 7.7, 3.7 Hz), 2H);7 C NMR (400 MHz, DMSO-d6)
−1
(
KBr) 3189, 1650, 1592, 1505, 1174, 1090, 774, 627 cm ; ES-MS m/
7
δ 163.1, 157.7, 152.6, 132.4, 124.3; Se NMR (300 MHz, DMSO-d )
+
6
z (relative intensity, nature of peak) 185 (30, [psd] ); 215 (20, [psd
MeO] ); 306 (100, [Co(psd)+2OMe] ); 429 (15, [Co(psd) ] );
4
2
−1
1
498; UV−visible, λ 336 nm (ε: 5.37 × 10 cm mol ); ES-MS m/
z (relative intensity, nature of peak) 292 (100, [M-NO ] ), 477 (5,
+
+
+
max
+
4
+
2
3
+
+
63 (20, [Co(psd) +OH+H O] ); 528 (50, [Co(psd) +ClO ] );
+
2 2 2 4
[
Ag(psd) ] ); Anal. Calcd. for C H N O Se Ag : C, 16.97; N, 15.83;
5
2
−1
77
2
10
6
8
6
2
2
UV−visible, λ 335 nm (ligand) (ε: 1.79 × 10 cm mol ); Se
max
H, 0.85. Found C, 17.08; N, 15.75; H, 0.59.
Synthesis of [Ag (psd) ](CF OCO) (10). To a 50 mL round-
NMR (400 MHz, DMSO-d ) δ 1507 (broad); Anal. Calcd. for
6
2
2
3
2
C H Cl CoN O Se : C, 22.53; H, 1.89. Found C, 22.96; H, 1.81.
20
20
2
12 12
4
bottomed flask containing a solution of Ag(CF OCO) (0.32 g, 1.47
3
μ : 4.88 μ .
eff
B
mmol) in 2 mL of acetonitrile was added a 10 mL acetonitrile solution
of 5 (0.27 g, 1.47 mmol). A deep yellow-colored precipitate appeared
immediately. The mixture was further stirred for 30 min and filtered.
The precipitate obtained was dried under vacuum and recrystallized
from acetonitrile or acetonitrile/water (2:1) mixture to give orange
plate shaped crystals of 10 (0.47 g, 81% yield). Mp 257−260 °C. FT-
X-ray Crystallography. The diffraction measurements for
compounds 5, 9, 12, 13, and 14 were performed on an Oxford
diffraction Gemini diffractometer, and X-ray data for compound 6, 7,
8
, 10, and 11 were collected on a Bruker Apex 2 diffractometer with
graphite-monochromated Mo Kα radiation (λ = 0.7107 Å). The
structures were solved by direct methods and full matrix least-squares
−1
1
IR (KBr) 1683, 1587, 1208, 1136, 773, 724 cm ; H NMR (400
2
30
refinement on F (program SHELXL-97). Hydrogen atoms were
localized by geometrical means. A riding model was chosen for
refinement. The isotropic thermal parameters of the H atoms were
fixed at 1.5 times (CH groups) or 1.2 times U (Ar−H) of the
MHz, DMSO-d ) δ 9.08 (dd, J = 4.1, 1.8 Hz, 2H), 8.36 (dd, J = 8.7,
6
13
1
.4 Hz, 2H), 7.59 (dd, J = 8.7, 3.6 Hz, 1H); C NMR (400 MHz,
DMSO-d ) δ 161.3, 159.4, 159.0, 158.9, 152.4, 133.5, 124.5; F NMR
1
9
6
3
eq
77
(
1
300 MHz, CD CN) δ −74.7; Se NMR (300 MHz, DMSO-d ) δ
3
6
corresponding C atom. Three ligands in complexes 6 and 7 and the
chloride atom in 7 are disordered. The ligand occupancies refined to
values of 0.730(2)/0.270(2); 0.858(2):0.142(2); and 0.744(3)/
0.256(3) for 6, 0.897(2)/0.103(2) for ligand of 7, and 0.898(4)/
3
2
−1
502; UV−visible, λ 337 nm (ε: 8.51 × 10 cm mol ); ES-MS m/
max
+
z (relative intensity, nature of peak) 292 (100, [M−C F O ] ), 477
2
3
2
+
(
95, [Ag(psd) ] ); Anal. Calcd. for C H N O Se F Ag : C, 20.76; N,
2 14 6 6 4 2 6 2
10.38; H, 0.75. Found C, 20.69; N, 10.43; H, 0.57.
0
.102(4) for chloride ion of 7. For 7, one ligand lies on a symmetry
Synthesis of [Cu(psd) (H O) ](ClO ) ·(psd) (11). To a solution
2
2
3
4 2
2
element and thus has an occupancy of exactly 0.5. The CF groups in
3
of Cu(ClO ) ·6H O (0.18 g, 0.50 mmol) in 10 mL of methanol was
4
2
2
10 were refined with occupancy factors of 0.648(14)/0.352(14) and
0.738(9)/0.262(9). The perchlorate anions in complexes 12 and 14
are disordered and refined with occupancy factors of 0.539(9)/
0.461(9) and 0.573(9)/0.427(9), respectively. In complex 13, the
water molecule and nitrate anion are disordered and were refined with
occupancy factors 0.541(9)/0.459(9) for water molecule and
0.565(6)/0.435(6) and 0.579(8)/0.421(8) for nitrate anion.
added a 10 mL solution of 5 (0.37 g, 2.00 mmol) in the same solvent.
The reaction mixture was stirred at room temperature for 1 h to afford
a green solid, which was recrystallized from methanol to give green
crystals of 11 (0.35, 66% yield). Mp 205 °C. FT-IR (KBr) 3419, 1590,
−
1
1
3
526, 1505, 1373, 1130, 1145, 1089, 770, 626 cm ; UV−visible, λ
6 2 −1
max
34 nm (ε: 2.19 × 10 cm mol ); ES-MS m/z (relative intensity,
nature of peak) 185 (100, [psd+H] ); 247 (12, [Cu(psd)] ); 432 (38,
Cu(psd) ] ); 531 (10, [Cu(psd) +ClO ] ); Anal. Calcd. for
+
+
Theoretical Calculations. DFT calculations were carried out
+
+
31
[
using the Gaussian 03 suite of programs. Atoms in molecules (AIM)
2
2
4
3
2
C H Cl CuN O Se : C, 22.82; N, 15.97; H, 1.72. Found C,
analysis was carried on the crystal geometry using the AIM 2000
20
18
2
12 11
4
33
22.59; N, 15.88; H, 1.14.
program. The wave functions for AIM analysis were generated by
8
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Scheme 1. Synthesis of Cu(I) Complexes
Scheme 2. Synthesis of Ag(I) Complexes
B3LYP using the WTBS basis set for Ag and Cu and 6-31 g(d) for the
rest of the atoms.
peaks observed for complex 8 at 530 and 345 were assigned to
+
+
[
Cu(psd) ClO +H] and [Cu(psd)ClO +H] ions, respec-
2 4 4
tively. Similarly complex 7 also shows four additional peaks at
+
RESULTS AND DISCUSSION
715, 615, 530, and 345 assigned to [M+H−Cl] , [M−CuCl−
■
+
+
+
Cl] , [M−psd−Cl] , and [M−2psd−Cl] , respectively. For
Synthesis. Selenadiazolopyridine 5 was prepared by the
+
+
Ag(I) complexes, peaks due to [Ag(psd) ] and [Ag(psd)]
solid-state synthesis from 2,3-diaminopyridine and SeO in 76%
2
2
2
9
yield. The reactions of Cu(I) and Ag(I) salts with 5 afforded
were observed at 477 and 292, respectively.
Copper(II) complexes 11, 12, and 13 with selenadiazolopyr-
2
+
−
[
[
[
Cu (psd) (CH CN) ] 2(PF6) (6); [(CuCl) (psd) ] (7);
2
3
3
2
2
3
2+
−
2+
−
Cu (psd) ] 2(ClO ) (8); [Ag (psd) ] 2(NO ) (9); and
idine were synthesized by the reaction of 5 with [Cu(H O) ]
2
6
4
2
2
3
2
6
2+
−
Ag (psd) ] 2(CF COO) (10). Complexes 6, 7, and 8, were
(ClO ) and Cu(NO ) ·3H O, respectively (Scheme 3). The
4 2 3 2 2
orange-colored Co(II) complex 14 was prepared similarly by
2
2
3
synthesized by the reaction of 5 with Cu(CH CN) PF ,
3
4
6
CuCl(CH CN) , and Cu(CH CN) ClO , respectively
3
4
3
4
4
the use of [Co(H O) ](ClO ) (Scheme 3). The Cu(II)
2
6
4 2
(
[
Scheme 1). The silver complexes [Ag(psd)NO ] (9) and
3
complexes are green in color, monomeric, and also soluble in
common organic solvents such as acetonitrile, acetone, and
dimethylsulfoxide. In the Cu(II) and Co(II) complexes, the
ligand metal ions ratio is 4:1 where two ligands are coordinated
to metal ions and the other two are present as neutral ligands
except for 12 where all four ligands are coordinated to the
metal ion. These aspects were confirmed by elemental analysis
and X-ray structure determination. The ES-MS spectra of
Cu(II) complexes show a similar trend to that observed for the
Cu(I) complexes. The Co(II) complex 14 shows five
prominent peaks at 528, 463, 429, 306, and 215 for [psd
Ag(psd)CF COO] (10) of selenadiazolopyridine were pre-
3
pared by the treatment of 5 with corresponding silver salts in a
:1 molar ratio in acetonitrile at room temperature (Scheme 2).
1
All the complexes were obtained in high yields (>75%) and are
soluble in common organic solvents and found to be air stable.
In the Cu(I) and Ag(I) complexes, the ligand metal ions ratios
are 3:1 and 1:1, respectively, and these ratios were also
confirmed by elemental analysis and X-ray structure determi-
nation. (vide infra). The ES-MS spectra of these complexes did
+
not show the molecular ion peaks, except for 7 (750 M ) and
+
ligand 5 (186 M ). Two intense peaks seen at 433 and 247 for
+
+
+
+
all the Cu(I) complexes were assigned to [Cu(psd) ] and
+MeO] , [Co(psd)+2OMe] , [Co(psd)
2
] , [Co(psd)
2
+OH
2
+
+
+
[
Cu(psd)] ions, respectively. In addition, the other prominent
+H O] , and [Co(psd) +ClO ] ) ions, respectively (Figure
2
2
4
8
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Inorganic Chemistry
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Scheme 3. Synthesis of Cu(II) and Co(II) Complexes
S7 in the ESI). From these data it is evident that the
metal···ligand bond dissociates under ES-MS conditions.
Spectroscopic Studies. The complexes were characterized
at 335 nm can be assigned as π−π* transition which was further
35
confirmed by TD-DFT calculations. Compound 6 shows an
additional weak and broad band at 507 nm which may be due
to the metal to ligand charge-transfer (MLCT transition). In
the solid state it gives a broad peak at ∼548 nm (Table S2 in
the ESI). The room temperature electronic spectrum of Cu(II)
complex 13 in methanol exhibits a very weak transition at ∼786
1
13
77
77
by FT-IR, H, C, and Se spectroscopy. The Se NMR
spectrum of 5 exhibited a peak at 1477 ppm (Figure S3 in the
1
ESI). The H NMR spectrum of Cu(I) complexes showed
three peaks in the aromatic region corresponding to three types
of aromatic protons; however, the peaks were relatively broad.
35
nm which can be assigned to a d-d (t -e ) band. The UV−vis
2g
g
1
For the silver complexes, there was a very small shift of H and
spectrum of 9 in the solid state showed a band at 407 nm,
whereas for 10 it appeared at 393 nm and corresponds to a
ligand based transition. The silver complexes were found to be
luminescent in the solid state. The solid-state emission
spectrum of 9 and 10 exhibited peaks at 480 and 525 nm
when excited at 407 and 393 nm, respectively (Figures S8 and
S9 in the ESI). These emission bands are ligand based
emissions, which also appear in the emission spectrum of
selenadiazolopyridine. However, the intensity of these fluo-
rescence peaks of the complexes is greater than that observed
for the ligand.
1
3
19
C signals as compared to that of free ligand 5. The F NMR
spectrum of 10 showed a peak for the fluoro group at −74.7
7
7
ppm (Figure S4 in the ESI). The Se NMR spectrum of 10
exhibited a peak at 1498 ppm (Figure S5 in the ESI), whereas
for 9 it was observed at 1502 ppm (Figure S6 in the ESI). This
7
7
downfield shift in the Se NMR as compared to 5 (1476 ppm)
can be attributed to the loss of electron density in the psd ring
due to coordination of the nitrogens with the metal ion. The
small downfield shift indicates no coordination of selenium
7
7
with the metal ions. Though the Se NMR chemical shift is in
the range reported for coordination with Se(II) to Cu(I), the
structure determination does not show any coordination in this
The ESR spectrum of the Cu(II) complexes were recorded at
77 K in a methanol−acetone (4:1) mixture and DMSO solvent.
3
4
case (vide infra).
The analysis of spectra shows g
and 185 G and g⊥(av) at 2.07 (Table 1). The higher value of
gII(av) as compared to g⊥(av) indicates a d ground state for the
at 2.30−2.48 with A 166
II(av)
(av)
The electronic spectra of the ligand and the complexes were
recorded in solution and in the solid state. The solution phase
electronic spectra of the ligand as well as all the complexes
show an intense band at ∼335 nm. This ligand based transition
2
2
x ‑y
12 and 13 complexes. The trend g > 2.1 > g observed for the
||
⊥
Cu(II) complexes indicates that the unpaired electron is
8
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Table 1. EPR Parameters of Cu(II) 12, 13, and Co(II) 14
Complexes
ESI). However, when the cycle is reversed one of the Cu(II) is
reduced to Cu(I) at 0.509 V and results in the formation of a
mixed valence Cu(I)−Cu(II) system. The other Cu(I) center
reduces at 0.258 V to give back the dinuclear Cu(I) complex.
Complex 8 shows only the oxidation peak at 0.0336 V
indicating the decomposition of the complex in the solution
under redox conditions (Figure S11 in the ESI). In the cyclic
voltammetry experiment, Cu(II) complex 13 showed two
irreversible redox peaks (E −0.309 V and E −0.025) (Figure
4
complex
g
10− A (cm−10
)
1
2 in MeOH−actone
gll 2.48; g⊥ 2.07
All 185.44
(
4:1)
1
1
3 in DMSO
4 in DMSO
gll 2.30; g⊥ 2.07
All 166.39
A 89.75; A 96.71; A
3
g 2.17; g 2.11; g
1
2
3
1
2
2
.04;
86.28;
g 1.98; g 1.90; g
A 94.33; A 88.28
4
1
5
6
4
5
pc
pa
.86
S12 in the ESI). The rest of the Cu(I) 7 and Cu(II) 11 and 12
complexes did not show any oxidation reduction peak. Cyclic
voltammogram of Ag(I) complexes 9 and 10 showed reduction
peaks at −0.211 and 0.0242 V, respectively. When the scan was
reversed, the oxidation peaks occurred at 0.072 V and −0.246
V, respectively (Figures S13 and S14 in the ESI). The reduction
2
2
localized in the dx ‑y orbital of the Cu(II) ion, and spectral
features are characteristic of axial symmetry. The g and A
||
||
values are strongly affected by the ligand environment in a
36
tetragonal Cu(II) site. The higher g value of 12 compared to
ll
+
+
−
reaction of Ag is Ag + 1e → Ag. Silver ion in the solution
13 suggest the presence of strong axial interaction. The EPR
takes one electron and becomes Ag and after that the oxidation
spectra of Co(II) complex were recorded as a polycrystalline
sample and in DMSO solutions at liquid nitrogen temperature.
The ‘g’ values were found to be almost the same in both cases.
This indicates that the complexes have the same geometry in
solid form as well as in the solution. Additionally, complexes
+
−
reaction Ag → Ag + 1e occurs where the silver atom loses an
+
electron to become the Ag ion. The ΔE = ∼245 mV for both
p
the copper (6 and 13) and silver complexes (9 and 10)
indicating the redox process is irreversible.
Solid-State Structure Analysis. Crystal data and structure
refinement details for 5−14 are given in Tables 2 and 3. The
molecular structure of 5 is shown in Figure 2a. Ligand 5
1
2−14 exhibit superhyperfine structure in the g region.
⊥
The room-temperature magnetic moment of the complex 13
was found to be μeff (299.2 K) = 2.12 μ which is higher than
B
9
crystallizes in a monoclinic crystal system with the P2 /c space
expected for spin only magnetic moment for the d system.
1
group. In solid state, the pyridine ring of the molecule exhibits a
quinoid type of structure. The C5A−N2A and C1A−N1A
bond lengths are 1.318(6) Å and 1.329(6) Å, respectively, and
thus have a double bond character. The C5A−C1A bond,
which is common to the five- and six-membered rings of 5, has
a bond length of 1.454(6) Å. This bond distance represents an
exclusive single bond and is longer than that observed for
Such a value is typical of magnetically dilute complexes and
may result from the contribution of excited state orbital angular
momentum. The magnetic moment of the complex 14 was
3
7
found to be μeff (299.2 K) = 4.88 μ corresponding to three
B
unpaired electrons as expected for high-spin Co(II) in an
octahedral environment.
The cyclic voltammetric experiments of the complexes 6−13
were recorded at 0.5 mM concentration using tetrabutylammo-
nium perchlorate as supporting electrolyte. Since complex 6
3c
selenadiazolobenzene, where it has a value of 1.437(9) Å.
However in 4, the corresponding distance is longer and has
I
exists as a dinuclear copper(I) unit, the two Cu units are
values of 1.658(10) and 1.475(9) Å in the two asymmetric
2a
oxidized to form dinuclear Cu(II) at 0.665 V (Figure S10 in the
units. The two psd rings are associated by two antiparallel
Table 2. Crystallographic Data and Refinement Details for 5, 6, 7, 8, 9, and 10
compound
5
6
7
8
9
10
empirical formula
C H N Se
C H Cu F
C H Cl
C H ClCu
C H Ag
C H Ag F
4 12
5
3
3
43 35
4
24
15
9
2
15
9
10
6
2
28 12
N OP Se
Cu N Se
N O Se
N O Se
N O Se
4
2
5
4
7
2
9
3
9
4
3
8
6
12
8
formula weight
crystal system
space group
a (Å)
184.06
2304.72
750.17
715.18
707.89
1619.82
triclinic
P-1
monoclinic
orthorhombic
Pbca
monoclinic
C2/c
monoclinic
C2/c
monoclinic
P2 /c
1
P2 /a
1
11.2836(8)
8.3584(5)
12.7110(8)
90
11.823(3)
24.824(6)
48.413(11)
90
17.964(2)
9.3797(9)
12.7632(17)
90
21.297(4)
13.268(3)
14.070(3)
90
7.0106(3)
11.4083(3)
10.3530(3)
90
7.870(4)
b (Å)
10.539(5)
12.227(6)
94.575(16)
93.754(18)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
111.156(8)
90
90
112.678(70)
90
96.189(12)
90
91.257(3)
90
90
102.847(16)
982.0(8)
1
1118.01(14)
8
14209(6)
8
1984.3(4)
4
3952.7(14)
8
827.82(5)
2
Z
3
D(calcd) (Mg/m )
2.187
2.155
2.511
2.404
2.840
2.739
T (K)
173(2)
4.8 to 32.5
6.603
293(2)
1.64 to 21.11
4.977
100(2)
173(2)
2.91 to 25.25
6.815
173(2)
4.99 to 32.52
6.816
173(2)
2.48 to 28.55
5.797
range of θ (deg)
abs coeff (mm−1)
obsd reflens [I > 2σ]
2.75 to 30.04
7.942
3569
7620
2825
3553
2768
4638
final R [I > 2σ(I)]
0.0509
0.0961
0.0614
0.0541
0.0295
0.0425
1
wR indices [I > 2σ]
2
0.1051
0.2224
0.1270
0.1194
0.0552
0.0861
data/restraints/parameters
goodness of fit on F2
3569/0/163
1.131
7620/1284/1067
0.975
2825/197/178
1.139
3553/0/298
0.979
2768/0/127
0.896
4638/84/364
1.074
8
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Table 3. Crystallographic Data and Refinement Details for 11, 12, 13, and 14
compound
11
12
13
14
C H Cl Co
empirical formula
C H Cl Cu
C H Cl Cu
21 15
C H Cu
20 20
2
0
18
2
5
30 26
2
N O Se
N O Se
N O Se4
14 10
N O Se
6
1
2
11
4
12
9
4
18 12
formula weight
crystal system
space group
a (Å)
1052.74
triclinic
P-1
1136.08
995.88
1434.28
triclinic
P-1
monoclinic
triclinic
P2 /c
1
P-1
11.2674(7)
11.4607(8)
13.3644(8)
100.188(4)
96.877(7)
106.360(3)
1603.31(18)
2
17.2767(7)
11.5563(3)
18.8398(6)
90
11.4192(3)
14.1808(5)
20.6650(6)
79.063(3)
74.977(2)
86.968(2)
3173.23(17)
2
8.5454(3)
11.7953(5)
11.8973(5)
78.854(4)
74.315(4)
81.414(3)
1126.77(8)
1
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
114.083(4)
90
3434.0(2)
4
Z
3
D(calcd) (Mg/m )
2.181
2.197
2.143
2.114
T (K)
173(2)
173(2)
3.22 to 30.11
5.333
200(2)
295(2)
range of θ(deg)
abs coeff (mm−1)
obsd reflens [I > 2σ]
3.09 to 30.86
5.465
4.6 to 32.5
5.352
5.10 to 35.96
5.425
9578
8173
19932
9176
final R [I > 2σ(I)]
0.0338
0.0454
0.0742
0.0533
1
wR indices [I > 2σ]
2
0.0664
0.0975
0.1962
0.1023
data/restraints/parameters
goodness of fit on F2
9578/9/469
1.010
8173/43/468
1.078
19932/283/917
1.188
9176/78/363
1.009
Figure 2. Molecular structure of the 5 (a) and 3-D supramolecular motif via π···π, Se···N SBIs, and C−H···N hydrogen bonding in the lattices of 5
b). Selected bond distances [Å] and angles [°]: molecule A (molecule B); Se−N(1) 1.781(5) (1.780(6)), Se−N(2) 1.792(4) (1.793(4)), (A) =
(
3
.601(0), (B) = 2.956(5), (C) = 2.888(5), (D) 2.632(4), (E) = 2.537(5), (F) = 2.568(4); N(1)−Se−N(2) 94.41(19) (94.40(19)). Only relevant
hydrogen atoms are shown for clarity.
Se···N SBIs forming a four-membered cyclic supramolecular
synthon. The intermolecular Se···N distances in this dimeric
unit are 2.888(7) Å and 2.956(7) Å. These synthons are
interconnected in the lattice via π···π interactions and C−H···N
hydrogen bonding interactions (Figure 2b).
The structure of chalcogenadiazolopyridine can be repre-
sented by two Kekule structures (Figure 3), one having
chalcogen atom, E as divalent (I) and the other structure
having it as tetravalent (II).
Crystal Structures of Cu(I) Complexes 6, 7, and 8. The
molecular structures of 6, 7, and 8 are shown in Figure 4a, 4b,
and 4c, respectively. Complex 6 crystallizes in an orthorhombic
crystal system with the Pbca space group, while 7 and 8
crystallize in a monoclinic system with the C2/c space group.
The primary geometry around the Cu atoms of 6 and 7 is
distorted trigonal bipyramidal (for 6, τ values range from 0.78
Figure 3. Kekule structures of 5.
to 0.51 with an average value of 0.68, while for 7, τ is 0.69),
while for 8 it is best described as trigonal planar but with a weak
Cu···Se out of plane interaction. Distortion of molecular
geometry in these complexes is caused by the steric demands of
the ligands attached to the central atom. The copper atoms in
complexes 6, 7, and 8 are coordinated through three nitrogen
atoms from ligands, with acetonitrile and chloride ion
coordinating axially in 6 and 7, respectively. The core of the
complexes 6 and 7 is propeller-shaped, and 8 has a fan shaped
8
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Inorganic Chemistry
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Figure 4. Molecular Structures of compounds 6 (a), 7 (b), and 8 (c). The PF6− (for 6) and ClO4− (for 8) anions along with the hydrogen atoms of
aryl carbon frames are omitted. Only one set of atoms for the disordered Cl and psd in (7) is shown. Selected bond parameters are summarized in
Table 4.
Table 4. Selected Bond Parameters for Compounds 6, 7, and 8
bond lengths [Å]
bond angles [deg]
6
Cu(1)−N(1A) 2.071(8)
Cu(1)−N(2C) 2.059(6)
Cu(2)−N(2B) 2.032(7)
Cu(1)−N(1S) 2.134(7)
Cu(1)···Cu(2) 2.884(2)
7
Cu(1)−N(1B) 2.016(8)
Cu(2)−N(2A) 2.005(8)
Cu(2)−N(1C) 2.026(7)
Cu(2)−N(2S) 2.167(8)
N(1A)−Cu(1)−N(2C) 102.7(4)
N(1B)−Cu(1)−N(2C) 127.7(3)
N(1C)−Cu(2)−N(2B) 120.0(3)
N(1A)−Cu(1)−N(1B) 124.9(4)
N(1C)−Cu(2)−N(2A) 108.7(4)
N(2A)−Cu(2)−N(2B) 125.5(4)
Cu−N(1A) 2.054(5)
Cu−N(1C) 2.158(49)
Cu···Cu 2.860(1)
Cu−N(1B) 2.045(7)
Cu−Cl(1A) 2.488(2)
N(1A)−Cu−N(1C) 104.4(14)
N(1B)−Cu−N(1C) 129.4(16)
N(1A)−Cu−N(1B) 123.2(6)
8
Cu−N(1A) 1.979(7)
Cu−(1C) 1.987(8)
Se(1A)···N(3B) 2.714(9)
Se(1C)···N(3A) 2.697(7)
Cu−N(1B) 1.982(7)
Cu···Se(1C) 3.160(2)
Se(1B)···N(3C) 2.711(8)
N(1A)−Cu−N(1B) 120.2(3)
N(1B) −Cu−N(1C) 120.8(3)
N(2B)−Se(1B)···N(3C) 174.0(3)
N(1A)−Cu−N(1C) 118.6(3)
N(2A)−Se(1A)···N(3B) 179.7(3)
N(2C)−Se(1C)···N(3A) 175.8(3)
structure with the ligands. The ligands are acting as the blades
of the propeller and fan. The crystal structures revealed a
unique feature i.e. the presence of Cu···Cu [2.869(2) and
together with near linearity of the N···Se−N(trans) triad(s)
(N···Se−N ∼ 176.5°), make n→σ* orbital interaction;
therefore, it appears to be the major component of the
attractive interaction between the lone pair of hypervalent Se
and N atoms (Figure 4c). Among the crystal lattices of these
complexes, C−H···O and C−H···X interactions are thus the
only associative forces that give rise to supramolecular motifs
via self-assembly (Supporting Information, Figures S15 and
S16).
2
[
.860(1) Å] metallophilic interactions in 6, 7, and Cu···Se
3.160(2) Å], metal···metalloid interactions in 8, which is
longer than most of the complexes which exhibit Cu(I)···Cu(I)
3
8
interactions and is shorter than Σ rvdw of Cu···Cu (4.0 Å) and
3
9
Cu···Se(3.9). For 8, where the coordination environment
about the Cu is trigonal planar, the ligands are arranged so that
there are interatomic Se···N(pyridine) distances which range
Selected bond parameters for 6, 7, and 8 are summarized in
from 2.697(7) Å to 2.714(9) Å. These are longer than Σ r
Table 4.
cov
(
Se,N), 1.90 Å, but significantly shorter than Σ r (Se,N),
Crystal Structures of Ag(I) Complexes 9 and 10. The
molecular structures and supramolecular assemblies of 9 and 10
are given in Figure 5. Complex [Ag(psd)NO ] 9 crystallizes in
a monoclinic crystal system with the P2 /a space group. The
asymmetric unit consists of four formula units, and, therefore,
there are four crystallographically unique (but chemically
vdw
3.45 Å indicating the presence of attractive intramolecular 1,6-
Se···N secondary bonding interactions. In spite of possible
rotation about the Cu−N bonds, the ligands in 8 are oriented
so that the selenium and nitrogen atoms of pyridine rings and
copper atom are almost in the equatorial plane. Coplanarity,
3
2
1
8
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Inorganic Chemistry
Article
Figure 5. Molecular units for complexes 9 and 10 are shown in (a) and (d). The assembly into a two-dimensional ladder type network for 9 is
shown in (b) and (c), while (e) shows the supramolecular motif and intermolecular Se···N interactions in 10 leading to one-dimensional network.
Only one set of atoms for the disordered CF groups is shown. The hydrogen atoms of aryl carbon frames are omitted for clarity.
3
similar) silver atoms, four unique psd ligands, and four nitrate
ions. Complex 9 has a dinuclear structure with an almost planar
eight-membered metallacycle ring. Selenadiazolopyridine acts
as a bridging bidentate ligand as it is bonded to two silver atoms
through its nitrogen atoms (N1, N3, N1#, N3#). The Ag−N
bond distances are Ag−N1 2.206(3) Å and Ag−N3 2.204(3) Å
and are less than the Σ rcov (Ag,N), 2.27 Å. The silver atom is
coordinated by the two psd ligands almost linearly, and the N−
Ag−N# bond angle is 161.4°. The N1−Ag−Ag#−N3 and N1−
Ag−Ag#−N1# dihedral angles are 180.0° and 9.69°,
respectively.
One of the important features of the complex is the relatively
short Ag···Ag distance (2.931(0) Å) in the eight-membered
metallacycle ring. This distance of 2.931 Å is shorter than Σ r
of Ag−Ag 3.54 Å. The intramolecular Ag···Ag separation in 9
vdw
38
is longer than Ag···Ag distances in [Ag (p-
2
40
CH C H NCHNC H -p-CH ) ] (2.705(1) Å), [Ag L(μ-
3
6
4
6
4
3 2
2
ONO )](NO )·2H O (2.901 Å; L = 1,4-bis(2-
2
3
2
4
1
hexahydropyrimidyl)benzene), and [Ag L ](ClO ) ·CH CN
(2.776(1) Å; L = 4,5-diazospirobifluorene) but shorter than
[Ag (Ph PCH PPh ) ](NO ) (3.085(1) Å). This short
2
2
4 2
3
4
2
4
3
2
2
2
2
2
3 2
distance between the silver atoms may be a consequence of
8
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Inorganic Chemistry
Article
Table 5. Selected Bond Parameters for Compounds 9 and 10
bond lengths [Å]
bond angles [deg]
9
Ag−N(1) 2.206(3)
Ag−O(1) 2.577(3)
Se···O(2) 2.831(3)
Ag−N(3) 2.204(3)
Ag···Ag 2.931(0)
N(1) −Ag−N(3) 161.46(10)
N(1)−Ag−O(1) 109.11(9)
N(3)−Ag−O(1) 87.68(10)
N(1)−Ag−Ag 80.92(7)
N(3)−Ag−Ag 83.25(7)
10
Ag(1)−N(1) 2.160(4)
Ag(2)−N(2) 2.245(4)
Ag(1)−O(3) 2.355(5)
Ag(1)···Ag(2) 2.969(1)
Ag(1)−N(4) 2.201(4)
Ag(2)−N(3) 2.186(4)
Ag(2)−O(1) 2.328(4)
N(1)−Ag(1)−N(4) 164.98(15)
N(4)−Ag(1)−Ag(2) 78.55(10)
N(4)−Ag(1)−O(3) 77.82(15)
N(2)−Ag(2)−Ag(1) 75.26(10)
N(2)−Ag(2)−O(1) 75.89(14)
N(1)−Ag(1)−Ag(2) 88.37(11)
N(1)−Ag(1)−O(3) 114.01(16)
N(2)−Ag(2)−N(3) 158.89(15)
N(3)−Ag(2)−Ag(1) 84.81(11)
N(3)−Ag(2)−O(1) 119.06(15)
Figure 6. AIM pictures of 6 (a) and 9 (b) showing the presence of bond critical points between Cu···Cu and Ag···Ag atoms, respectively.
metallophilic interaction which in the case of silver is
commonly known as an argentophilic interaction.
The nitrate group in the crystal acts as a bridging ligand to
Interestingly, in complex 10, the carboxylate group of
trifluoroacetate acts as a bridge between two adjacent dinuclear
[Ag (psd) (CF COO) ] units and leads to the formation of
2
2
3
2
connect antiparallel binuclear Ag (psd) (NO ) units (Figure
Ag cluster. In this Ag cluster, the Ag1 atom of one unit is at a
2
2
3 2
4
4
5
b) thus forming a two-dimensional ladder type chain network
distance of 3.521 Å and 3.327 Å from the Ag2 and Ag1 atom of
the next unit of tetramer. The molecule can be expanded in one
dimension via intermolecular Se···N interactions, the Se···N
distances being 2.912 Å and 2.928 Å. These intermolecular
(
Figure 5c). Apart from the Ag−O (nitrate) bond, two nitrate
oxygen atoms are involved in intermolecular Se···O inter-
actions, in which the distance between Se and O are 2.770 Å
and 2.831 Å. In addition, there is a short intermolecular contact
between selenium and nitrogen atoms between two antiparallel
binuclear units, and this distance is 3.340 Å.
Se···N interactions formed between two Ag clusters is the first
4
example of unique Ag supramolecular assembly mediated by
4
short Se···N interactions (Figure 5e).
The single crystals of the complex 10 were isolated as orange
plates from an acetonitrile and water solution (2:1) for the X-
ray diffraction study. [Ag(psd) (CF COO)] crystallizes in the
Selected bond parameters for 9 and 10 are summarized in
Table 5.
To investigate the presence of metal···metal interactions in
complexes 6, 9, and 10, we carried out Atoms in Molecules
(AIM) analysis on their crystal geometries using the AIM2000
program. The cationic part of 9 was chosen for the analysis of
Ag complexes, as both the complexes 9 and 10 have the same
cation. The single point calculation on crystal geometry was
performed by Gaussian 03 quantum chemical program. The
AIM analysis involves topological properties of the electron
density (ρ) to describe bonds among interacting atoms.
Chemical bonding can be identified by the presence of a
bond critical point (bcp), which is defined in AIM formalism as
a point where electron density reaches a minimum along the
bond path. For both the complexes 6 and 9, the bond critical
point exists between Cu···Cu (Figure 6a) and Ag···Ag (Figure
6b) which substantiates the metal···metal bonding in the
3
2
triclinic crystal system with the P-1 space group. Complex 10
has similar structural features as that of the nitrate complex 9
which includes a binuclear structure with an almost planar
eight-membered metallacycle ring (Figure 5c). In complex 10
also, psd acts as a bridging bidentate ligand and is bonded to
two silver atoms through nitrogen atoms with Ag−N bond
distances being Ag1−N1 2.161(4) Å, Ag1−N4 2.203(4) Å,
Ag2−N2 2.253(4) Å, and Ag2−N3 2.191(4) Å. The N1−Ag1−
Ag2−N3 torsion angle is 175.51(17)°, whereas the N1−Ag1−
Ag2−N2 angle is 2.74(17)°. The N1−Ag1−N4 and N2−Ag2−
N3 bond angles are deviated from linearity and have the values
1
65.09(17)° and 158.72(16)°, respectively. The Ag···Ag
distance is longer than the distance observed in nitrate complex
and has the value 2.969 Å.
9
8
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Inorganic Chemistry
Article
Figure 7. Molecular structures of compounds 11 (a), 12 (b), and 14 (c). The ClO4− (for 11, 12, and 14) anions along with the hydrogen atoms of
aryl carbon frames are omitted. A 2D supramolecular motif in crystal lattice of 14 (d) involving Se···N SBIs, C−H···F, and C−H···N hydrogen
bonding interactions.
Table 6. Selected Bond Parameters for Compounds 11, 12, and 14
bond lengths [Å]
bond angles [deg]
11
Cu−N(1A) 2.015(3)
Cu−N(1B) 2.024(3)
O(1W)−Cu−O(2W) 96.93(9)
O(2W) −Cu−O(3W) 93.47(9)
Cu−O(1W) 1.949(2)
Cu−O(3W) 1.946(2)
Se(1C)···N(3A) 3.016(2)
Se(1D)···N(2C) 2.871(3)
Cu−O(2W) 2.308(2)
O(1W)−Cu−O(3W) 169.60(9)
Se(1A)···N(3C) 2.834(2)
Se(1C)···N(3D) 3.000(3)
H(3W1)···N(1D) 1.962(33)
12
Cu(1)−N(1) 2.061(4)
Cu(1)−N(7) 2.016(4)
Cu(1)−O(1) 2.184(4)
Cu(1)−N(4) 2.011(5)
Cu(1)−N(10) 2.092(3)
N(1)−Cu(1)−N(4) 90.77(15)
N(4)−Cu(1)−N(10) 89.36(15)
N(1)−Cu(1)−O(1) 100.41(15)
N(7)−Cu(1)−O(1) 92.46(16)
N(1)−Cu(1)−N(7) 88.60(15)
N(7)−Cu(1)−N(10) 89.17(15)
N(4)−Cu(1)−O(1) 92.80(17)
N(10)−Cu(1)−O(1) 102.70(15)
14
Co−N(1A) 2.123(3)
Co−O(2W) 2.079(3)
Se(1C)···N(2A) 2.9306(2)
Co−O(1W) 2.099(2)
Se(1A)···N(2C) 2.746(3)
N(1A)−Co−O(1W) 87.44(11)
O(1W)−Co−O(2W) 92.09(11)
N(1A)−Co−O(2W) 88.97(10)
N(1A)−Co−O(2W) 91.03(10)
O(2W)−Co−O(1W) 87.92(11)
N(1A)−Co−O(1W) 92.56(11)
synthesized complexes. The value of ρbcp for Ag−Ag bcp (0.018
au) and Cu−Cu bcp (0.013 au) is much lower than a normal
Crystal Structures of Cu(II) Complexes 11, 12, 13, and
Co(II) Complex 14. These monomeric metal(II) complexes
crystallize in the triclinic crystal system with space group P-1
except 14 which crystallizes in a monoclinic crystal system with
40
covalent bond but in the range of metal···metal bonds. It has
been observed that the total energy density (H = G + V), which
is the sum of the electronic kinetic energy density (G) and the
electronic potential energy density (V), is a more reliable
parameter in ascertaining the nature of a chemical bond.
Covalent interactions are characterized by a negative value of
the P2 /c space group. Molecular structures of Cu(II) (11, 12)
1
and Co(II) (14) complexes are shown in Figure 7a, 7b, and 7c,
respectively.
The three Cu(II) complexes are all five-coordinate and all
have a distorted square pyramidal structure (τ = 0.101, 0.298,
and 0.217/0.242 for 11, 12, and 13, respectively), while the
Co(II) complex is six-coordinate. For the Cu(II) complexes the
stoichiometry is different in that two have a CuL (H O)
44
H, while ionic ones are characterized by positive values. The
positive values of HAg−Ag (0.0374 au) and HCu−Cu (0.0199 au)
obtained for Ag···Ag and Cu···Cu interactions respectively
indicate more contribution from the ionic character.
2
2
3
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Inorganic Chemistry
Article
coordination sphere, while the third has a CuL (H O)
ACKNOWLEDGMENTS
4
2
■
coordination sphere. This shows that even slight changes in
synthetic conditions lead to complexes of different composi-
tion.
In complexes 11 and 13 the two psd ligands are in trans
position, and two water molecules occupy the equatorial plane.
The axial position is occupied by the third water molecule,
while in complexes 12 the four psd ligands are occupied in an
equatorial plane and one water molecule is occupied in an axial
position. The Cu−N and equatorial Cu−O distances in Cu(II)
complexes are in the range of 2.011(5) to 2.092(3) Å and
H.B.S. is grateful to the Department of Science and Technology
DST), New Delhi, for funding. P.S. thanks Indian Institute of
Technology, Bombay for a Post Doctoral Fellowship, and S.S.
thanks UGC for a SRF.
(
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(
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(
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AUTHOR INFORMATION
■
Corresponding Author
́
*
E-mail: chhbsia@chem.iitb.ac.in.
(
2
Notes
The authors declare no competing financial interest.
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35) TD-DFT calculations (at B3LYP/6-31G(d), SDD level; SDD
̈ ̈
ttingen: Gottingen, Germany, 1997.
(
̈
̈
(
(
(
̈
̈
2
(
3
2
(
basis set with corresponding pseudopotential was used for the metal
atoms and 6-31G(d) for the remaining atoms including Se in gas phase
on crystal geometry. The calculations were performed on some of the
representative complexes and ligand to predict the nature of electronic
transitions. TD-DFT analysis on ligand 5 showed an intense peak at
288 nm (f = 0.234) that corresponds to the experimental λmax of 335
nm and is primarily a π-π* transition (see the ESI). For compound 6,
TD-DFT analysis showed an intense peak at 296 nm (f = 0.138)
corresponding to ligand based π-π* transition and the peak at 549 nm
(
f = 0.04) due to MLCT (see the ESI), which are in agreement with
experimental values. For complex 13, the band at 786 nm in UV−
visible spectrum was in good agreement with 761 nm obtained from
TD-DFT analysis (761 nm, f = 0.0001, see the ESI) and is a metal
based d-d transition.
(
1
(
36) Lal, T. K.; Gupta, R.; Mahapatra, S.; Mukherjee, R. Polyhedron
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1
(
2
996, 35, 6466.
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(
e) Coyle, J. P.; Monillas, W. H.; Yap, G. P. A.; Barry, S. T. Inorg.
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(
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(
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988, 110, 7077.
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