Study of new mononuclear platinum group metal complexes containing η5 and η6 - Carbocyclic ligands and nitrogen based derivatives and formation of helices due to NH?Cl interactions

Article abstract of DOI:10.1016/j.molstruc.2010.06.028

A quite general approach for the preparation of η⁵- and η⁶-cyclichydrocarbon platinum group metal complexes is reported. The dinuclear arene ruthenium complexes [(η⁶-arene)Ru(μ-Cl)Cl] ₂ (arene = C₆H₆, C₁₀H₁₄ and C₆Me₆) and η⁵- pentamethylcyclopentadienyl rhodium and iridium complexes [(η⁵- C₅Me₅)M(μ-Cl)Cl]₂ (M = Rh and Ir) reacts with two equivalents of the ligands 2-chloro-3-(pyrazolyl)quinoxaline (L ₁) and di-(2-pyridyl)amine (L₂) in presence of NH ₄PF₆ to afford the corresponding mononuclear complexes of the type [(η⁶-arene)Ru(L₁)Cl]PF₆ {arene = C₆H₆ (1), C₁₀H₁₄ (2) and C ₆Me₆ (3)}, [(η⁶-arene)Ru(L ₂)Cl]PF₆ {arene = C₆H₆ (4), C ₁₀H₁₄ (5) and C₆Me₆ (6)}, and [(η⁵-C₅Me₅)M(L₁)Cl]PF ₆ {M = Rh (7), Ir (8)} and [(η⁵-C₅Me ₅)M(L₂)Cl]PF₆ {M = Rh (9), Ir (10)}. However the mononuclear η⁵-cyclopentadienyl analogues such as [(η⁵-C₅H₅)Ru(PPh₃) ₂Cl], [(η⁵-C₅H₅)Os(PPh ₃)₂Br], [(η⁵-C₅Me ₅)Ru(PPh₃)₂Cl] and [(η⁵-C ₉H₇)Ru(PPh₃)₂Cl] complexes react in presence of one equivalent of ligands 2-chloro-3-(pyrazolyl)quinoxaline (L ₁) and di-(2-pyridyl)amine (L₂) and one equivalent of NH₄PF₆ in methanol yielded mononuclear complexes [(η⁵-C₅H₅)Ru(PPh₃)(L ₁)]PF₆ (11), [(η⁵-C₅H ₅)Os(PPh₃)(L₁)]PF₆ (12), [(η⁵-C₅Me₅)Ru(PPh₃)(L ₁)]PF₆ (13) and [(η⁵-C₉H ₇)Ru(PPh₃)(L₁)]PF₆ (14) and [(η⁵-C₅H₅)Ru(PPh₃)(L ₂)]PF₆ (15), [(η⁵-C₅H ₅)Os(PPh₃)(L₂)]PF₆ (16), [(η⁵-C₅Me₅)Ru(PPh₃)(L ₂)]PF₆ (17) and [(η⁵-C₉H ₇)Ru(PPh₃)(L₂)]PF₆ (18) respectively. These compounds have been systematically characterized by IR, NMR and mass spectrometry. The molecular structures of 2, 4 and 15 have been established by single crystal X-ray diffraction study and some of the representative complexes have also been studied by UV-visible spectroscopy. The crystal packing diagram of complex 4 reveals that the cation [(η⁶-C₆H₆)Ru(L₂)Cl]⁺ is engaged in non-covalent interaction. This compound gives rise to a 1D helical architecture along the 'a' axis via intermolecular NH?Cl hydrogen bonds.

Full text of DOI:10.1016/j.molstruc.2010.06.028

Journal of Molecular Structure 979 (2010) 205–213
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Study of new mononuclear platinum group metal complexes containing
g5 and g6 – Carbocyclic ligands and nitrogen based derivatives
and formation of helices due to NAHꢀ ꢀ ꢀCl interactions
Gajendra Gupta a, Sairem Gloria a, Babulal Das b, Kollipara Mohan Rao a,
*
a Department of Chemistry, North Eastern Hill University, Shillong 793 022, India
b Department of Chemistry, Indian Institute of Technology, Guwahati, India
a r t i c l e i n f o
a b s t r a c t
g g
5- and
6-cyclichydrocarbon platinum group metal
6-arene)Ru(
-Cl)Cl]2 (arene = C6H6,
5-pentamethylcyclopentadienyl rhodium and iridium complexes [(g5
-Cl)Cl]2 (M = Rh and Ir) reacts with two equivalents of the ligands 2-chloro-3-(pyrazolyl)quin-
oxaline (L1) and di-(2-pyridyl)amine (L2) in presence of NH4PF6 to afford the corresponding mononuclear
complexes of the type [(
6-arene)Ru(L1)Cl]PF6 {arene = C6H6 (1), C10H14 (2) and C6Me6 (3)}, [( 6-arene)R-
u(L2)Cl]PF6 {arene = C6H6 (4), C10H14 (5) and C6Me6 (6)}, and [(
5-C5Me5)M(L1)Cl]PF6 {M = Rh (7), Ir (8)}
and [(
5-C5Me5)M(L2)Cl]PF6 {M = Rh (9), Ir (10)}. However the mononuclear 5-cyclopentadienyl
analogues such as [(
5-C5H5)Ru(PPh3)2Cl], [( 5-C5H5)Os(PPh3)2Br], [( 5-C5Me5)Ru(PPh3)2Cl] and
[(
5-C9H7)Ru(PPh3)2Cl] complexes react in presence of one equivalent of ligands 2-chloro-3-(pyrazol-
yl)quinoxaline (L1) and di-(2-pyridyl)amine (L2) and one equivalent of NH4PF6 in methanol yielded
mononuclear complexes [(
5-C5H5)Ru(PPh3)(L1)]PF6 (11), [( 5-C5H5)Os(PPh3)(L1)]PF6 (12), [( 5-C5Me5)-
Ru(PPh3)(L1)]PF6 (13) and [(
5-C9H7)Ru(PPh3)(L1)]PF6 (14) and [( 5-C5H5)Ru(PPh3)(L2)]PF6 (15), [(g5
C5H5)Os(PPh3)(L2)]PF6 (16), [(
5-C5Me5)Ru(PPh3)(L2)]PF6 (17) and [( 5-C9H7)Ru(PPh3)(L2)]PF6 (18)
Article history:
Received 6 May 2010
Received in revised form 22 June 2010
Accepted 22 June 2010
Available online 25 June 2010
A quite general approach for the preparation of
complexes is reported. The dinuclear arene ruthenium complexes [(
10H14 and C6Me6) and
C5Me5)M(
g
l
C
g
-
l
g
g
Keywords:
Arene
Cyclopentadienyl
Ruthenium
Rhodium
g
g
g
g
g
g
g
Iridium
g
g
g
g
g
-
g
g
respectively. These compounds have been systematically characterized by IR, NMR and mass spectrom-
etry. The molecular structures of 2, 4 and 15 have been established by single crystal X-ray diffraction
study and some of the representative complexes have also been studied by UV–visible spectroscopy.
The crystal packing diagram of complex 4 reveals that the cation [(g
6-C6H6)Ru(L2)Cl]+ is engaged in
non-covalent interaction. This compound gives rise to a 1D helical architecture along the ‘a’ axis via
intermolecular NAHꢀ ꢀ ꢀCl hydrogen bonds.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
activities. Half-sandwich complexes have proved to be extremely
useful in stoichiometric and catalytic asymmetric syntheses and
Mononuclear compounds of platinum group metals containing
nitrogen-based ligands have received considerable attention ow-
ing to their photochemical properties [1–5], catalytic activities
[6–12], electrochemical behavior [13–16], as well as in the
development of new biological active agents [17–21]. In particu-
therefore attracted more attention [11,24–26]. In addition, the
four-coordinated, pseudo-tetrahedral geometry makes them par-
ticularly suitable for investigation of the stereochemistry of reac-
tions at the metal center [27]. In recent years we have been
carrying out reactions of
g g
5- and 6-cyclic G-perimeter hydrocar-
lar,
g
6-arene metal complexes have emerged as versatile
bons metal complexes with a variety of nitrogen-based ligands
[28–35] including various poly-pyridyl ligands. Ruthenium com-
pounds of these types of nitrogen-based ligands have a capacity
to function as catalysts for the oxidation of water to dioxygen
[36,37]. Recently, we have reported a number of compounds of
ruthenium containing tetra-dentate nitrogen bases as a model
compounds for water oxidation studies [38–40]. However till
intermediates in organic synthesis as a consequence of the avail-
ability of three labile coordinate sites and rigid arene ring occupy-
ing another three coordinate sites [22,23]. They have found
applications in catalysis, supramolecular assemblies, molecular
devices, and have shown antiviral, antibiotic, and anticancer
now there is no investigations have been made on
g -
5- and g6
ruthenium compounds containing quinoxaline and pyridine
* Corresponding author.
derivatives of the type shown below:
E-mail address: mohanrao59@gmail.com (K.M. Rao).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.06.028

206
G. Gupta et al. / Journal of Molecular Structure 979 (2010) 205–213
Herein we describe the syntheses of eighteen mononuclear
6-cyclic G-perimeter hydrocarbons platinum group metal com-
g
5- and
g
pounds bearing quinoxaline and pyridine derivative ligands. All
these compounds are completely characterized by IR, NMR and
mass spectrometry. Molecular structures of the three representative
compounds are also presented in this paper. Notably complex 4
considered here generate helical structures via NAHꢀ ꢀ ꢀCl
interactions.
2. Experimental
Fig. 2. Molecular structure of a complex 4 with 35% probability thermal ellipsoids.
Hydrogen atoms and PF6ꢁ are omitted for clarity.
2.1. Physical measurements
Infrared spectra were recorded on a Perkin–Elmer Model 983
spectrophotometer with the sample prepared as KBr pellets. The
NMR spectra were obtained using Bruker Avance II 400 spectrom-
eter in CD3CN, CDCl3 and Acetone-d6 respectively for complexes
using TMS as an internal standard. Mass spectra were obtained
from a Waters ZQ – 4000 mass spectrometer by the ESI method.
All chemicals used were of reagent grade. Elemental analyses of
the complexes were performed on a Perkin–Elmer 2400 CHN/S
analyzer. All reactions were carried out in distilled and dried sol-
2.2. Single-crystal X-ray structure analyses
Crystals of 2 and 15 were grown from dichloromethane/petro-
leum ether as small red plates. Crystals of 4 were grown by slow
diffusion of petroleum ether into a mixture of acetonitrile and
dichloromethane solution of the respective complex as deep brown
blocks. The crystallizations were done at room temperature. The
intensity data of 2, 4 and 15 were collected using a Bruker SMART
APEX-II CCD diffractometer, equipped with a fine focus 1.75 kW
vents. The precursor complexes [(
ne = C6H6, C10H14 and C6Me6), [(
5-C5Me5)M(
and Ir) [41–45], [(
5-C5H5)Ru(PPh3)2Cl], [( 5-C5H5)Os(PPh3)2Br],
[(
5-C5Me5)Ru(PPh3)2Cl] and [( 5-C9H7)Ru(PPh3)2Cl] were pre-
g
6-arene)Ru(
-Cl)Cl]2 (M = Rh
l-Cl)Cl]2 (are-
g
l
sealed tube Mo K
a radiation (a = 0.71073 Å) at 273(3) K, with
g
g
increasing (width of 0.3° per frame) at a scan speed of 3 s/frame.
x
g
g
The SMART [51] software was used for data acquisition. Data inte-
gration and reduction were undertaken with the SAINT [51] soft-
ware. Structures were solved by direct methods using SHELXS-97
[52] and refined with full-matrix least squares on F2 using SHEL-
XL-97 [53]. All non-hydrogen atoms were refined anisotropically.
The hydrogen atoms were located from the difference Fourier
maps and refined. Structural illustrations have been drawn with
ORTEP-3 [54] for Windows. The ORTEP presentations of the repre-
sentative complexes are shown in Figs. 1–3, respectively. The data
collection parameters and bond lengths and angles are presented
in Tables 2 and 3.
pared by following the literature methods [46–50].
2.3. Preparation of [(
[1](PF6); C10H14, [2](PF6); C6Me6, [3](PF6), M = Rh, arene = C5Me5,
[7](PF6) and M = Ir, arene = C5Me5, [8](PF6)} and [(
6-arene)M(L2)Cl]-
g
6-arene)M(L1)Cl](PF6) {M = Ru, arene = C6H6,
g
(PF6) {M = Ru, arene = C6H6, [4](PF6); C10H14, [5](PF6); C6Me6, [6](PF6);
M = Rh, arene = C5Me5, [9](PF6) and M = Ir, arene = C5Me5, [10](PF6)}
6-arene)Ru(
l
-Cl)Cl]2 or [(g5-Cp )M(
l
-Cl)Cl]2
*
A mixture of [(
g
(M = Rh and Ir) (0.17 mmol or 0.23 mmol), 2-chloro-3-(pyrazol-
yl)quinoxaline (L1) (40 mg, 0.17 mmol) or di-(2-pyridyl)amine
(L2) (40 mg, 0.23 mmol) and two equivalents of NH4PF6 was stirred
in dry methanol (30 ml) for 4 h at room temperature. The yellow
compound which formed was filtered, washed with ethanol,
diethyl ether and dried under vacuum.
Compound [1](PF6): Yield: 75 mg, 63.3%. Elemental Anal. (%)
Calc. for C17H13Cl2F6N4PRu: C 34.61; H 2.23; N 9.48; found: C
34.79; H 2.41; N 9.17; IR (KBr pellets, cmꢁ1): 1616 (m), 1445 (s),
844 (s), 773 (s), 558 (s); 1H NMR (400 MHz, CD3CN): d = 9.43
(d, J = 2.8 Hz, 1H), 8.76 (d, J = 7.6 Hz, 1H), 8.22–8.09 (m, 2H), 7.50
Fig. 1. Molecular structure of a complex 2 with 35% probability thermal ellipsoids.
Hydrogen atoms, CH2Cl2 and PFꢁ are omitted for clarity.
6

G. Gupta et al. / Journal of Molecular Structure 979 (2010) 205–213
207
Fig. 3. Molecular structure of a complex 15 with 35% probability thermal ellipsoids. Hydrogen atoms and PFꢁ6 are omitted for clarity.
39.31; H 3.45; N 8.35; IR (KBr pellets, cmꢁ1): 1617 (m), 1438 (s),
843 (s), 773 (s), 558 (s); 1H NMR (400 MHz, Acetone-d6): d = 9.51
(d, J = 2.8 Hz, 1H), 8.95 (d, J = 7.2 Hz 1H), 8.72 (d, J = 8.8 Hz, 1H),
8.25–8.08 (m, 2H), 7.94 (d, J = 7.2 Hz, 1H), 7.43 (t, J = 6 Hz, 1H),
6.18 (d, J = 5.6 Hz, 1H, Arpꢁcy), 6.04 (d, J = 6 Hz, 1H, Arpꢁcy), 6.01
(d, J = 5.6 Hz, 1H, Arpꢁcy), 5.97 (d, J = 6 Hz, 1H, Arpꢁcy), 2.60 (sept,
1H), 2.28 (s, 3H), 1.09 (d, J = 6.8 Hz, 6H), 1.04 (d, J = 6.8 Hz, 3H);
ESI-MS (m/z): 502.2 [M–PF6]+, 410.4 [M–PF6–Cl]+.
Compound [3](PF6): Yield: 68 mg, 67.32%. Elemental Anal. (%)
Calc. for C23H25Cl2F6N4PRu: C 40.97; H 3.76; N 8.30; found: C
41.21; H 3.91; N 8.08; IR (KBr pellets, cmꢁ1): 1624 (m), 1384 (s),
847 (s), 775 (s), 561 (s); 1H NMR (400 MHz, CDCl3): d = 9.41 (d,
J = 2.8 Hz, 1H), 8.10 (d, J = 7.6 Hz, 1H), 7.90–7.53 (m, 2H), 7.32 (d,
J = 7.6, 1H), 7.05 (d, J = 7.2, 1H), 6.68 (t, J = 6, 1H), 6.17 (s, 1H),
2.17 (s, 18H, C6Me6); ESI-MS (m/z): 530.01 [M–PF6]+, 495.5
[M–PF6–Cl]+.
Table 1
UV–visible absorption data of the representative complexes in acetonitrile at 298 K.
Complex
kmax/nm (e )
/10ꢁ4 Mꢁ1 cmꢁ1
1
2
4
6
7
10
11
17
231 (1.10)
235 (0.45)
231 (0.64)
232 (0.07)
230 (0.67)
244 (0.15)
250 (0.17)
220 (0.27)
259 (0.96)
283 (0.58)
290 (0.80)
298 (1.05)
288 (0.46)
298 (0.19)
297 (0.24)
291 (0.21)
405 (0.09)
415 (0.06)
393 (0.05)
394 (0.06)
387 (0.05)
341 (0.11)
425 (0.08)
352 (0.06)
(d, J = 7.2, 1H), 7.34 (d, J = 7.2, 1H) 6.85 (t, J = 6, 1H), 6.11 (s, 6H,
C6H6); ESI-MS (m/z): 445.2 [M–PF6]+, 410.4 [M–PF6–Cl]+.
Compound [2](PF6): Yield: 70 mg, 66.35%. Elemental Anal. (%)
Calc. for C21H21Cl2F6N4PRu: C 39.04; H 3.29; N 8.65; found: C
Table 2
Crystallographic and structure refinement parameters for complexes [2](PF6)ꢀ ꢀ ꢀCH2Cl2, [4](PF6) and [15](PF6).
[2]PF6
[4]PF6
[15]PF6
Chemical formula
Formula weight
Crystal system
Space group
Crystal size
a (Å)
C22H23Cl4F6N4PRu
731.28
Monoclinic
P2(1)/n
0.40 ꢂ 0.25 ꢂ 0.15
9.3287(2)
15.4331(4)
19.6616(6)
90
C16H15ClF6N3PRu
530.80
Orthorhombic
Pca2(1)
0.48 ꢂ 0.30 ꢂ 0.22
13.3507(3)
10.1397(2)
13.8247(3)
90
C33H29F6N3P2Ru
744.60
Rhombohedral
R-3
0.40 ꢂ 0.26 ꢂ 0.18
21.3111(8)
21.3111(8)
38.2490(14)
90
b (Å)
c (Å)
a
(°)
b (°)
100.9600(10)
90
2779.06(13)
4
90
90
90
120
15044.0(10)
18
c
(°)
V (Å3)
Z
1871.48(7)
4
T (K)
296(2)
1.748
1.068
296(2)
1.884
1.130
296(2)
1.479
0.625
Dc (g cmꢁ3
)
l
(mmꢁ1
)
Unique reflections
Reflections used [I > 2
Rint
43,028
6766
0.0457
0.0358, wR2 = 0.096
0.0535, wR2 = 0.109
0.995
0.932 and ꢁ0.706
28,723
4607
0.0624
0.0280, wR2 = 0.073
0.0292, wR2 = 0.072
1.078
0.733 and ꢁ0.610
89,248
8652
0.0634
0.0508, wR2 = 0.1597
0.0744, wR2 = 0.1744
1.002
1.309 and ꢁ0.639
r
(I)]
Final R indices [I > 2
R indices (all data)
Goodness-of-fit
r
(I)]*
Max, Min
D
q
/e (Åꢁ3
)
2
2
1=2
2
Structures were refined on F02
:
wR2 ¼ ½
R
½wðF20 ꢁ F2c Þ ꢃ=
R
wðF20Þ ꢃ , where wꢁ1 ¼ ½
R
ðF20Þ þ ðaPÞ þ bPꢃ and P ¼ ½maxðF02; 0Þ þ 2Fc2ꢃ=3.
*

208
G. Gupta et al. / Journal of Molecular Structure 979 (2010) 205–213
Table 3
2.4. Preparation of [(
[11](PF6); Os, [12](PF6), Cp = C5Me5, M = Ru, [13](PF6) and Cp = C9H7,
M = Ru, [14](PF6)} and [(
5-Cp)M(L2)(PPh3)](PF6) {Cp = C5H5, M = Ru,
g
5-Cp)M(L1)(PPh3)](PF6) {Cp = C5H5, M = Ru,
Selected bond lengths and angles for complexes 2, 4 and 15.
g
Distances (Å)
2
4
15
[15](PF6); Os, [16](PF6), Cp = C5Me5, M = Ru, [17](PF6) and Cp = C9H7,
M = Ru, [18](PF6)}
N1–Ru1
N2–Ru1
N3–Ru1
Ru1–Cl1
Ru–CNT
P–Ru
2.054(2)
–
2.121(2)
2.3776(7)
1.692
–
2.092(2)
2.090(2)
–
2.3955(7)
1.674
–
2.123(3)
2.118(3)
–
A mixture of [(g
5-Cp)M(PPh3)2X] {M = Ru, X = Cl and M = Os,
–
1.835
2.3306(9)
X = Br} (0.17 mmol or 0.23 mmol), 2-chloro-3-(pyrazolyl)quinoxa-
line (L1) (40 mg, 0.17 mmol) or di-(2-pyridyl)amine (L2) (40 mg,
0.23 mmol) and one equivalents of NH4PF6 in dry methanol
(30 ml) were refluxed for 12 h until the color of the solution chan-
ged from pale yellow to orange. The solvent was removed under
vacuum, the residue was dissolved in dichloromethane (10 ml),
and the solution was filtered to remove ammonium halide. The or-
ange solution was concentrated to 5 ml, upon addition of diethyl-
ether the orange–yellow complex was precipitated, which was
separated and dried under vacuum.
Angles (°)
N1–Ru1–N2
N1–Ru–N2
75.14(9)
–
–
–
83.80(8)
87.67(12)
CNT = metal to centroid distance of arene groups.
Compound [4](PF6): Yield: 70 mg, 66%. Elemental Anal. (%) Calc.
for C16H15ClF6N3PRu: C 36.22; H 2.86; N 7.90; found: C 36.49; H
2.99; N 7.72; IR (KBr pellets, cmꢁ1): 3287 (br), 1626 (m), 1473
(s), 836 (s), 776 (s), 557 (s); 1H NMR (400 MHz, CD3CN): d = 9.23
(s, 2H), 8.62 (d, J = 6.4 Hz, 2H), 7.76 (t, J = 7.6 Hz, 2H), 7.22–7.10
(m, 2H), 6.22 (s, 6H, C6H6), NH not observed; ESI-MS (m/z):
386.02 [M–PF6]+, 351.5 [M–PF6–Cl]+.
Compound [5](PF6): Yield: 75 mg, 78.2%. Elemental Anal. (%) Calc.
for C20H23ClF6N3PRu: C 40.93; H 3.94; N 7.15; found: C 41.17; H
4.17; N 7.01; IR (KBr pellets, cmꢁ1): 3441 (br), 1625 (m), 1438 (s),
844 (s), 775 (s), 558 (s); 1H NMR (400 MHz, Acetone-d6): d = 9.25
(s, 2H), 8.56 (d, J = 6 Hz, 2H), 7.87 (t, J = 7.6 Hz, 2H), 7.23–7.01 (m,
2H), 5.51 (d, J = 6 Hz, 2H, Arpꢁcy), 5.41 (d, J = 6 Hz, 2H, Arpꢁcy),
2.67 (sept, 1H), 2.15 (s, 3H), 1.26 (d, J = 9.2 Hz, 6H), NH not
observed; ESI-MS (m/z): 443.7 [M–PF6]+, 408.3 [M–PF6–Cl].
Compound [6](PF6): Yield: 69 mg, 75%. Elemental Anal. (%) Calc.
for C22H27ClF6N3PRu: C 42.99; H 4.44; N 6.82; found: C 43.31; H
4.67; N 6.51; IR (KBr pellets, cmꢁ1): 3443 (br), 1614 (m), 1387 (s),
846 (s), 777 (s), 561 (s); 1H NMR (400 MHz, CDCl3): d = 9.32 (s,
2H), 8.61 (d, J = 7.6 Hz, 2H), 7.95 (t, J = 7.4 Hz, 2H), 7.34–7.06 (m,
2H), 2.18 (s, 18H, C6Me6), NH not observed; ESI-MS (m/z): 470.1
[M–PF6], 435.6 [M–PF6–Cl]+.
Compound [11](PF6): Yield: 69 mg, 62.3%. Elemental Anal. (%)
Calc. for C34H27ClF6N4P2Ru: C 50.81; H 3.39; N 6.95; found: C
51.03; H 3.55; N 6.73; IR (KBr pellets, cmꢁ1): 1629 (m), 1442 (s),
843 (s), 777 (s), 558 (s); 1H NMR (400 MHz, CDCl3): d = 9.23 (d,
J = 2 Hz, 1H), 8.55 (d, J = 8.4 Hz, 1H), 7.95–7.93 (m, 2H), 7.85–7.60
(m, 15H, PPh3), 6.78 (d, J = 7.6 Hz, 1H), 6.65 (d, J = 7.6 Hz, 1H),
6.22 (t, J = 6.4 Hz, 1H), 5.24 (s, 5H, C5H5); 31P {1H} NMR (CDCl3,
d): 50.83 (s, PPh3), ꢁ143 (sept, PF6); ESI-MS (m/z): 659.4 [M–PF6],
661.6 [M–PF6]2+
.
Compound [12](PF6): Yield: 68 mg, 63%. Elemental Anal. (%) Calc.
for C34H27ClF6N4OsP2: C 45.74; H 3.07; N 6.27; found: C 45.91; H
3.31; N 6.09; IR (KBr pellets, cmꢁ1): 1625 (m), 1444 (s), 845 (s),
773 (s), 554 (s); 1H NMR (400 MHz, CDCl3): d = 9.31 (d, J = 2.4 Hz,
2H), 8.69 (d, J = 6 Hz, 1H), 8.01–7.94 (m, 2H), 7.87–7.69 (m, 15H,
PPh3), 6.77 (d, J = 7.2 Hz, 1H), 6.32 (t, J = 6.4 Hz, 1H), 4.59 (s, 5H,
C5H5); 31P {1H} NMR (CDCl3, d): ꢁ0.26 (s, PPh3), ꢁ143 (sept, PF6);
ESI-MS (m/z): 749.3 [M–PF6], 750.2 [M–PF6]+.
Compound [13](PF6): Yield: 71 mg, 64.5%. Elemental Anal. (%)
Calc. for C39H37ClF6N4P2Ru: C 53.58; H 4.28; N 6.40; found: C
53.35; H 4.41; N 6.71; IR (KBr pellets, cmꢁ1): 1627 (m), 1448 (s),
844 (s), 770 (s), 557 (s); 1H NMR (400 MHz, CDCl3): d = 9.32 (d,
J = 2.4 Hz, 2H), 8.74 (d, J = 5.6 Hz, 1H), 8.12–7.84 (m, 2H) 7.31–
7.09 (m, 15H, PPh3), 6.78 (d, J = 6.4 Hz, 1H), 6.44 (t, J = 5.6 Hz, 1H),
Compound [7](PF6): Yield: 74 mg, 70.6%. Elemental Anal. (%) Calc.
for C21H22Cl2F6N4PRh: C 38.87; H 3.44; N 8.61; found: C 39.06; H
3.71; N 8.54; IR (KBr pellets, cmꢁ1): 1617 (m), 1448 (s), 843 (s),
772 (s), 558 (s); 1H NMR (400 MHz, Acetone-d6): d = 9.53 (d,
J = 2.4 Hz, 1H), 8.44 (d, J = 7.2 Hz, 1H), 8.41 (d, J = 8.4 Hz, 1H), 8.23–
8.06 (m, 2H), 7.95 (d, J = 7.6 Hz, 1H), 7.44 (t, J = 6 Hz, 1H), 1.66
(s, 15H, C5Me5); ESI-MS (m/z): 504.03 [M–PF6]+, 468.6 [M–PF6–Cl].
Compound [8](PF6): Yield: 66 mg, 71.2%. Elemental Anal. (%) Calc.
for C21H22Cl2F6IrN4P: C 34.16; H 3.01; N 7.57; found: C 34.39; H
3.35; N 7.35; IR (KBr pellets, cmꢁ1): 1615 (m), 1444 (s), 845 (s),
770 (s), 558 (s); 1H NMR (400 MHz, Acetone-d6): d = 9.46 (d,
J = 3.2 Hz, 1H), 8.33 (d, J = 8.4 Hz, 1H), 8.23–8.06 (m, 2H), 7.47 (d,
J = 7.6 Hz, 1H), 2.25 (d, J = 7.2 Hz, 1H), 6.95 (t, J = 6.4 Hz, 1H), 1.64
2.03 (s, 15H, C5Me5); 31P {1H} NMR (CDCl3,
49.70 (s, PPh3),
d):
ꢁ143 (sept, PF6); ESI-MS (m/z): 730.2 [M–PF6]+, 731.1 [M–PF6]2+
.
Compound [14](PF6): Yield: 69 mg, 62.7%. Elemental Anal. (%)
Calc. for C38H29ClF6N4P2Ru: C 53.45; H 3.44; N 6.55; found: C
53.69; H 3.71; N 6.78. 1H NMR (400 MHz, CDCl3): d = 9.32 (d,
J = 2.4 Hz, 2H), 8.78 (d, J = 6.4 Hz, 1H), 8.21–7.83 (m, 2H), 7.55–
7.10 (m, 22H), 6.78 (d, J = 7.2 Hz, 1H), 6.51 (t, J = 6 Hz, 1H), 4.89
(t, J = 2.4 Hz, 1H), 4.52 (d, J = 8 Hz, 1H), 4.42 (d, J = 7.6 Hz, 1H);
31P {1H} NMR (CDCl3, d): 57.18 (s, PPh3), ꢁ143 (sept, PF6); ESI-MS
(s, 15H, C5Me5); ESI-MS (m/z): 593.5 [M–PF6], 495.6 [M–PF6]2+
.
(m/z): 709.1 [M–PF6], 711.2 [M–PF6]2+
.
Compound [9](PF6): Yield: 61 mg, 64%. Elemental Anal. (%) Calc.
for C20H24ClF6N3PRh: C 40.72; H 4.11; N 7.11; found: C 40.97; H
4.39; N 7.36; IR (KBr pellets, cmꢁ1): 3405 (br), 1625 (m), 1470
(s), 847 (s), 774 (s), 558 (s); 1H NMR (400 MHz, Acetone-d6):
d = 9.07 (s, 1H), 8.41 (d, J = 5.6 Hz, 2H), 7.92 (t, J = 7.6 Hz, 2H),
7.37 (d, J = 1.6 Hz, 1H), 7.27 (t, J = 6.4 Hz, 2H), 1.48 (s, 15H,
C5Me5), NH not observed; ESI-MS (m/z): 444.1 [M–PF6], 409.6
[M–PF6–Cl]+.
Compound [15](PF6): Yield: 67 mg, 65.3%. Elemental Anal. (%)
Calc. for C33H29F6N3P2Ru: C 53.24; H 3.94; N 5.62; found: C
53.55; H 4.36; N 5.41; IR (KBr pellets, cmꢁ1): 3482 (br), 1629
(m), 1461 (s), 844 (s), 770 (s), 558 (s); 1H NMR (400 MHz, Ace-
tone-d6): d = 8.48 (s, 1H), 7.89 (d, J = 6 Hz, 2H), 7.39 (t, J = 7.6 Hz,
2H), 7.32–7.29 (m, 15H), 7.11–6.95 (m, 1H), 6.24 (t, J = 6.4 Hz,
2H), 4.49 (s, 5H, C5H5), NH not observed. 31P {1H} NMR (CDCl3,
d): 50.88 (s, PPh3), ꢁ143 (sept, PF6); ESI-MS (m/z): 600.1 [M–PF6],
601 [M–PF6]+.
Compound [16](PF6): Yield: 62 mg, 61.6%. Elemental Anal. (%)
Calc. for C33H29F6N3P2Os: C 47.55; H 3.50; N 5.03; found: C 47.83;
H 3.89; N 5.37; IR (KBr pellets, cmꢁ1): 3451 (br), 1631 (m), 1458
(s), 847 (s), 771 (s), 557 (s); 1H NMR (400 MHz, Acetone-d6):
d = 8.55 (s, 1H), 7.90 (d, J = 6 Hz, 2H), 7.46 (t, J = 7.6 Hz, 2H), 7.39–
7.14 (m, 15H), 6.96–6.82 (m, 1H), 6.34 (t, J = 6.6 Hz, 2H), 4.51
(s, 5H, C5H5), NH not observed. 31P {1H} NMR (CDCl3, d): ꢁ0.27
Compound [10](PF6): Yield: 59 mg, 69.2%. Elemental Anal. (%)
Calc. for C20H24ClF6IrN3P: C 35.38; H 3.57; N 6.17; found: C
35.61; H 3.33; N 6.01; IR (KBr pellets, cmꢁ1): 3362 (br), 1619
(m), 1455 (s), 843 (s), 770 (s), 559 (s); 1H NMR (400 MHz, Ace-
tone-d6): d = 9.11 (s, 1H), 8.56 (d, J = 5.6 Hz, 2H), 8.00 (t,
J = 7.4 Hz, 2H), 7.45 (d, J = 1.6 Hz, 1H), 7.34 (t, J = 6.4 Hz, 2H), 1.54
(s, 15H, C5Me5), NH not observed; ESI-MS (m/z): 534.1 [M–PF6],
500.6 [M–PF6–Cl]2+
.

G. Gupta et al. / Journal of Molecular Structure 979 (2010) 205–213
209
(s, PPh3), ꢁ143 (sept, PF6); ESI-MS (m/z): 690.2 [M–PF6], 691.3 [M–
PF6]+.
tained a strong band between 836 and 847 cmꢁ1 due to the
stretching frequency of mPꢁF of PF6 for these complexes. The 1H
NMR spectra of the free ligands L1 and L2 show seven and four sig-
nals respectively in the aromatic region. In the 1H NMR spectra of
the complexes with the ligand L1 and L2, the signals are spread over
a wide range compared to the spectra of the free ligands. The com-
plexes 1–3 shows four doublets in the range of 9.51–7.05 ppm, a
multiplet between 8.25 and 7.53 ppm and a triplet at around
7.43–6.68 ppm which corresponds to the protons of the chelated
ligand L1. In addition to all these peaks, compound 1 shows a sin-
glet at around 6.11 ppm, this corresponds to the six protons of the
benzene ring, whereas compound 3 exhibits a singlet at around
2.17 ppm corresponding to the eighteen protons of the hexameth-
ylbenzene ring. Compound 2 exhibits different pattern of reso-
nances for the p-cymene ligand as compared to that of the
starting precursor. For instance, the aromatic protons of the p-cym-
ene ligand display four doublets at ca. 6.18–5.97 ppm, instead of
doublet signals as found in the starting precursor. This pattern is
due to the diastereotopic nature of the aromatic protons of the p-
cymene ligand. It may also be attributed to the behavior of the
ruthenium atom which is stereogenic when coordinated with four
different ligand atoms [55]. In other words, it is obvious that the
different signals are entirely due to chiral nature of the metal
[56,57], or it just reflects a lack of symmetry in the complex and
is quite expected since rotation of the cymene ligand is slow. Li-
gand L2 also shows four signals, viz., singlet, doublet, triplet and
a multiplet in the aromatic region for the different protons of the
pyridyl group of the ligand. In addition to the different peaks as
mentioned in the experimental section, compound 4 exhibits a sin-
glet at around 6.22 ppm which corresponds to the six protons of
the benzene ring. Compound 5 exhibit two doublets at ca., 5.51
and 5.41 ppm corresponding to the aromatic p-cymene ring of
the CH protons. It also exhibits a singlet at 2.15 ppm, a doublet
at 1.26 ppm and a septet at around 2.67 ppm for the protons of
the methyl and isopropyl groups of the p-cymene ligands. However
compound 6 exhibits a strong peak at 2.18 ppm for the hexameth-
ylbenzene ligand, which is slightly shifted downfield in compari-
Compound [17](PF6): Yield: 66 mg, 64.5%. Elemental Anal. (%)
Calc. for C38H39F6N3P2Ru: C 56.03; H 4.81; N 5.16; found: C
56.39; H 5.07; N 4.97; IR (KBr pellets, cmꢁ1): 3448 (br), 1639
(m), 1459 (s), 843 (s), 770 (s), 559 (s); 1H NMR (400 MHz,
Acetone-d6): d = 8.62 (s, 1H), 7.92 (d, J = 6.4 Hz, 2H), 7.49 (t,
J = 7.4 Hz, 2H), 7.37–7.10 (m, 15H), 6.99–6.79 (m, 1H), 6.44 (t,
J = 6.4 Hz, 2H), 2.09 (s, 5H, C5Me5), NH not observed. 31P {1H}
NMR (CDCl3, d): 50.35 (s, PPh3), ꢁ143 (sept, PF6); ESI-MS (m/z):
670.2 [M–PF6].
Compound [18](PF6): Yield: 86 mg, 66.4%. Elemental Anal. (%)
Calc. for C37H31F6N3P2Ru: C 55.94; H 3.94; N 5.28; found: C
56.38; H 4.31; N 5.01; IR (KBr pellets, cmꢁ1): 3431 (br), 1637
(m), 1462 (s), 843 (s), 771 (s), 559 (s); 1H NMR (400 MHz, CDCl3):
d = 8.69 (s, 1H), 7.911 (d, J = 6.4 Hz, 2H), 7.40 (t, J = 7.4 Hz, 2H),
7.37–7.10 (m, 19H), 6.99–6.79 (m, 1H), 6.44 (t, J = 6.4 Hz, 2H),
4.88 (t, J = 7.4 Hz, 1H), 4.58 (d, J = 7.2 Hz, 1H), 4.41 (d, J = 6.4 Hz,
1H), NH not observed. 31P {1H} NMR (CDCl3, d): 57.20 (s, PPh3),
ꢁ143 (sept, PF6); ESI-MS (m/z): 650.15 [M–PF6], 651.2 [M–PF6]+.
3. Results and discussion
The arene ruthenium complexes [(g
6-arene)RuCl2]2 (arene =
*
*
benzene, p-cymene, hexamethylbenzene), Cp Rh and Cp Ir dimers
reacts at room temperature in methanol with the N,N-donor ligand
L1 and L2 to give the expected cationic chloro complexes 1–10 as
the only product in good yields ranging from 60% to 75%.
All the complexes, which were isolated as chloride salts are sol-
uble in common organic and polar solvent but are not soluble in
non-polar solvents and are stable in air as well as in solution. Com-
plexes 4, 5, 6, 9 and 10 are soluble in water as well. They have been
characterized by IR, 1H NMR and mass spectrometry. The NMR
spectra reveal symmetrical structures that prove no coordination
from the bridging nitrogen atom and only the coordination of the
two pyridyl moieties. In the mass spectra, they show the expected
molecular ion peaks m/z at 445.2, 502.2, 530.01, 386.02, 443.7 and
son to the starting complex [(g l-Cl)Cl]2. The
6-C6Me6)Ru(
6-arene)Ru(L1)Cl](PF6) {are-
molecular structures of representative compounds 2 and 4 are
solved by single crystal X-ray diffraction study and the structures
are discussed below (Figs. 1 and 2).
470.1 corresponding to compounds [(
ne = C6H6, [1](PF6); C10H14, [2](PF6); C6Me6, [3](PF6) and [(
g
g
6-are-
ne)Ru(L2)Cl](PF6)} {arene = C6H6, [4](PF6); C10H14, [5](PF6); C6Me6,
[6](PF6)} (Scheme 1). All these halogenated complexes also dis-
played prominent peaks corresponding to the loss of chloride ions
from the molecular ion peak [M–PF6]+, but the loss of arene group
is not observed indicating the stronger bond of metal to arene
group. The IR spectra of these complexes exhibit a sharp bands
due to chelated N,N-donor bi-dentate ligands in between 1626
and 1384 cmꢁ1 corresponding to the different stretching frequen-
cies of C@C and C@N bond of these complexes as mentioned in
the experimental section. In addition, the infrared spectra con-
The reaction of the dimeric chloro complexes [(g l-
5-C5Me5)M(
Cl)Cl]2 (M = Rh or Ir) with two equivalent of bi-dentate ligands L1
and L2 in methanol results in the formation of the yellow colored,
air stable cationic mononuclear complexes [(
(7) and [(
5-C5Me5)Ir(L1)Cl]+ (8) and [( 5-C5Me5)Rh(L2)Cl]+ (9)
and [(
5-C5Me5)Ir(L2)Cl]+ (10) which are isolated as their hexa-
g
5-C5Me5)Rh(L1)Cl]+
g
g
g
fluorophosphate salts (Scheme 2). All these complexes are charac-
terized by 1H NMR, IR and mass spectroscopy. The infrared spectra
of both the complexes exhibit a sharp bands due to chelating
Scheme 1. General method of syntheses of complexes 1–6.

210
G. Gupta et al. / Journal of Molecular Structure 979 (2010) 205–213
Scheme 2. General method of syntheses of complexes 7–10.
Chart 1. Schematic structures of complexes 11–18.
ligands in between 1625 and 1443 cmꢁ1 corresponding to the
stretching frequencies of C@C and C@N bond of these complexes.
The 1H NMR spectra of these complexes show ligand peaks a
downfield shift in the position of signals associated with protons
of ligands L1 and L2 compared to that of the uncoordinated ligand
suggesting coordination of the nitrogen atoms to the metal center
in a bi-dentate fashion. The 1H spectra of the complexes 7 and 8 ex-
hibit seven signals whereas 9 and 10 show four signals associated
with the protons of the ligands in the aromatic region and are pre-
sented in the experimental section. Beside this peaks, the 1H NMR
spectra of these complexes display a singlet at around 1.64–
1.48 ppm corresponding to the protons of the pentamethylcyclo-
pentadienyl groups. The m/z values of all these complexes and their
stable ion peaks obtained from the ESI mass spectra, as listed in the
experimental section, which are in good agreement with the theo-
retically expected values.
All these complexes are stable in solid state as well as in solution.
All complexes were characterized by IR, 1H NMR, 31P {1H} NMR
spectroscopy and mass spectrometry. The analytical data of these
compounds are consistent with the formulations. Besides the IR
bands as mentioned in the experimental section, these complexes
also display a strong band between 843 and 847 cmꢁ1 due to the
mPꢁF stretching frequency of the counter ion of these complexes.
The 1H and 31P {1H} NMR spectra of complexes were recorded in
CDCl3 and spectral data are summarized in the experimental
section. Shift in the position of signals associated with protons of
ligands L1 and L2, suggested coordination of nitrogen atom to the
metal center ruthenium and osmium in bi-dentate fashion. The li-
gand protons in these complexes 11–18 show downfield shift with
respect to the protons of the uncoordinated ligand. In addition to
the aromatic protons mentioned in the experimental section, com-
plexes 11, 12, 15 and 16 shows singlet between d 5.24–4.49 which
corresponds to the protons of the cyclopentadienyl ligand, while in
the case of complexes 13 and 17 it displays a singlet at d 2.04 and
2.10 corresponding to the methyl protons of the pentamethylcy-
clopentadienyl ligand. These complexes also show multiplets in
the range of d 7.87–6.95 due to the protons of the coordinated
triphenylphosphine ligands. Complexes 14 and 18 exhibit three
sets of signals, triplet at around d 4.86, doublet at d 4.52 and d
4.42 corresponding to the protons of the indenyl group. The
protons of the triphenylphosphine ligands exhibit a large multiplet
centered at d 7.32. In the 31P {1H} NMR spectra of the complexes
11, 13–15, 17 and 18, the 31P nuclei of the coordinated PPh3
resonates as a sharp singlet in the range of d 57.20–49.70 respec-
tively whereas in the starting precursors the signal appears in
the up field region. In the case of complexes 12 and 16 the
ESI mass spectra of the complexes also displayed prominent
peaks corresponding to the molecular ion fragment. These haloge-
nated complexes displayed the prominent peak corresponding to
the loss of chloride ion from the molecular ion peak, but the loss
*
of Cp group is not observed indicating the stronger bond of metal
to this group and remains intact.
One equivalent of mononuclear cyclopentadienyl complexes
[(Cp)M(PPh3)2Cl] (M = Ru, Os; Cp =
g g g
5-C5H5, 5-C9H7, 5-C5Me5)
react with bi-dentate ligands L1 and L2 in refluxing methanol to
give the corresponding mononuclear complexes 11–18 which are
isolated as their hexafluorophosphate salts (Chart 1).
The cationic complexes 11–18 are soluble in halogenated sol-
vents and polar organic solvents such as tetrahydrofuran, metha-
nol or dimethylsulfoxide but are insoluble in non-polar solvents.

G. Gupta et al. / Journal of Molecular Structure 979 (2010) 205–213
211
Fig. 4. View of helix formation through NAHꢀ ꢀ ꢀCl hydrogen bonding in [(
g
6-C6H6)Ru(L2)Cl]+ unit in complex 4. Space-filling view of the inner channel running parallel to the
helical axis is also shown.
31P {1H} NMR spectrum displays a sharp singlet at ꢁ0.26 and
ꢁ0.27 ppm as compared to the starting complex which is found
at d ꢁ6.29. The data listed in the experimental section are taken
from ESI mass spectra and are in good agreement with the theoret-
ically expected values. ESI mass spectra of the complexes also
displayed prominent peaks corresponding to the molecular ion
fragment. The molecular structure of representative compound
15 is solved by single crystal X-ray diffraction study and the struc-
ture is discussed below (Fig. 3).
boring quinoxaline and pyridyl nitrogen atoms. The aromatic ring
occupies three coordination sites in these complexes to complete
the octahedral geometry around the metal center. The molecular
structures of complexes 2, 4 and 15 are shown in Figs. 1–3 respec-
tively, and selected bond lengths and angles are presented in
Table 3.
Complexes 2, 4 and 15 crystallize in monoclinic (P2(1)/n),
orthorhombic (Pca2(1)) and rhombohedral (R-3) space groups
respectively. Complex 2 crystallize with a molecule of dichloro-
methane per asymmetric unit. The bond lengths for this cationic
complex are very similar to those reported for related, three-legged
piano-stool ruthenium complexes. The distances between the
ruthenium atoms and the centroid and the arene and cyclopenta-
dienyl ring in the complexes 2, 4 and 15 are 1.692, 1.674 and
1.835 Å. These bond distances are comparable to those in the re-
lated complex cations reported earlier from our laboratory [28–
35]. The NARu bond distances in these complexes are centered
at around 2.089 (2) Å and are in good agreement with similar type
of complexes reported earlier [28–35]. The RuACl bond distance in
complexes 2 and 4 are 2.3776(7) and 2.3955(7) Å whereas in com-
plex 15 the Ru–P distance is 2.3306(6) Å. There are no significant
differences in the CAC bond lengths in the pentamethylcyclopen-
4. Molecular structures of complexes [2](PF6)ꢀCH2Cl2, [4](PF6)
and [15](PF6)
In order to confirm the identity and chelate-ring conformation
of the coordinated ligands, single crystal X-ray structure determi-
nation was done for the chloride bound complexes 2 and 4 and
triphenylphosphine bound complex 15 as their hexafluorophos-
phate salts. X-ray crystallographic analysis confirms the structure
of the complexes. The complexes show typical piano-stool geom-
etry with the metal center coordinated by the arene or cyclopen-
tadienyl ligand occupying one face of the octahedron, a terminal
chloride in complexes 2 and 4, triphenylphosphine in complex
15 and the chelating ligands L1 in case of complex 2 and L2 in
complexes 4 and 15 respectively. The metal atom is in an octahe-
dral arrangement with two cis-nitrogen atoms of the ligands L1
and L2 acting as a bi-dentate chelating ligand through the neigh-
tadienyl ring, all being about 1.418 Å and pointing to uniform
p-
electron delocalization in the ring. As expected, the two pyridyl
groups of the L2 ligand are in equatorial positions, which is the
more stable conformation. Moreover, the central (secondary
amine) N atom is nearly planar. The crystal packing diagram of

212
G. Gupta et al. / Journal of Molecular Structure 979 (2010) 205–213
sized. All these complexes have been fully characterized by a
combination of NMR, IR, UV–visible spectroscopy and mass spec-
trometry. The crystal packing diagram of complex 4 reveals that
the cation [(g
6-C6H6)Ru(L2)Cl]+ is engaged in non-covalent interac-
tion. This compound gives rise to a 1D helical architecture along
the ‘a’ axis via intermolecular NAHꢀ ꢀ ꢀCl hydrogen bonds.
7. Supplementary data
CCDC 775721 [2](PF6)ꢀCH2Cl2, 775722 [4](PF6) and 775723
[15](PF6) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/data_request/cif, by e-mailing data_re-
quest@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033.
Acknowledgements
K.M. Rao gratefully acknowledges financial support from the
Department of Science and Technology, New Delhi, through the Re-
search Grant No. SR/S1/IC-11/2004. G.G. is also thankful for finan-
cial support from University Grant Commissions, New Delhi.
Fig. 5. UV–visible absorption spectra of mononuclear complexes 1, 2, 4, 6, 7, 10, 11
and 17 in acetonitrile at 298 K.
complex 4 reveals that the cation [(g
6-C6H6)Ru(L2)Cl]+ is engaged
in non-covalent interaction. Compound 4 gives rise to a 1D helical
architecture along the ‘a’ axis via intermolecular NAHꢀ ꢀ ꢀCl hydro-
gen bonds (Fig. 4). In fact, the chloride connected to the ruthenium
metal is involved in bifurcated hydrogen bonding interaction with
H3 of the secondary amine N of the neighboring molecule. The
hydrogen bonding NAHꢀ ꢀ ꢀCl parameter observed here is around
2.742 Å. The presence of hydrogen bonding is also confirmed from
the IR spectra of complex 4. The NAH stretching frequency of this
complex is observed to be much lower than the other complexes
with L2 ligand as mentioned in the experimental section. This is
attributed to the weakening of the NAH bond due to the formation
of NAHꢀ ꢀ ꢀCl type hydrogen bond in the complex 4.
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UV–visible spectra of the complexes 1, 2, 4, 6, 7, 10, 11 and 17
were acquired in acetonitrile and spectral data are summarized in
Table 1. Electronic spectra of representative complexes are de-
picted in Fig. 5. The low spin d6 configuration of these mononuclear
complexes provides filled orbitals of proper symmetry at the Ru(II)
*
p orbital of the li-
gands. One should therefore expect a band attributable to the me-
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? p transition in their
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