[(η6-C6H6)RuII(L)(Cl/N3/CN/CH3CN)]+/2+ complexes of non-planar pyrazolylmethylpyridine ligands: Formation of helices due to C-H?X (X?=?Cl, N) interaction

Article abstract of DOI:10.1016/j.jorganchem.2010.03.022

Structural analysis of a previously reported half-sandwich complex having three-legged "piano-stool" geometry [(η⁶-C₆H₆)Ru^II(L¹)Cl][PF₆] (1) (L¹?=?2-(pyrazol-1-ylmethyl)pyridine) is described. Treatment of 1 with (i) Ag(CF₃SO₃) in CH₃CN and (ii) NaN₃ in CH₃OH, and (iii) the reaction between [(η⁶-C₆H₆)Ru(L²)Cl]-[PF₆]?(2) (previously reported) and NaCN in C₂H₅OH led to the isolation of [(η⁶-C₆H₆)Ru(L¹)(CH₃CN)][PF₆]₂ (3), [(η⁶-C₆H₆)Ru(L¹)(N₃)][PF₆] (4), and [(η⁶-C₆H₆)Ru(L²)(CN)][PF₆] (5), respectively (L²?=?2-(3,5-dimethyl-pyrazol-1-ylmethyl)pyridine). The complex [(η⁶-C₆H₆)Ru(L⁴)Cl][PF₆] (6) with a new ligand (L⁴?=?2-[3-(4-fluorophenyl)pyrazol-1-ylmethyl]pyridine) has also been synthesized. The structures of 3-6 have been elucidated (¹H NMR spectra; CD₃CN). The molecular structures of 1, 4, and 6·C₆H₅CH₃ have been determined. Notably, the crystal-packing in these structures is governed by C-H?X (X?=?Cl, N) interactions, generating helical architectures.

Full text of DOI:10.1016/j.jorganchem.2010.03.022

Journal of Organometallic Chemistry 695 (2010) 1753e1760
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
[(h
6-C6H6)RuII(L)(Cl/N3/CN/CH3CN)]þ/2þ complexes of non-planar
pyrazolylmethylpyridine ligands: Formation of helices due to
CeH/X (X ¼ Cl, N) interaction
Haritosh Mishra, Rabindranath Mukherjee
*
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Structural analysis of a previously reported half-sandwich complex having three-legged “piano-stool”
geometry [(
h
6-C6H6)RuII(L1)Cl][PF6] (1) (L1 ¼ 2-(pyrazol-1-ylmethyl)pyridine) is described. Treatment of 1
Received 2 December 2009
Received in revised form
18 March 2010
with (i) Ag(CF3SO3) in CH3CN and (ii) NaN3 in CH3OH, and (iii) the reaction between [(h
6-C6H6)Ru(L2)Cl]-
[PF6] (2) (previously reported) and NaCN in C2H5OH led to the isolation of [(h
6-C6H6)Ru(L1)(CH3CN)][PF6]2
Accepted 23 March 2010
(3), [(
h
6-C6H6)Ru(L1)(N3)][PF6] (4), and [(
h
6-C6H6)Ru(L2)(CN)][PF6] (5), respectively (L2 ¼ 2-(3,5-dimethyl-
pyrazol-1-ylmethyl)pyridine). The complex [(
h
6-C6H6)Ru(L4)Cl][PF6] (6) with a new ligand (L4 ¼ 2-[3-(4-
fluorophenyl)pyrazol-1-ylmethyl]pyridine) has also been synthesized. The structures of 3e6 have been
elucidated (1H NMR spectra; CD3CN). Themolecular structures of 1, 4, and6$C6H5CH3 havebeendetermined.
Notably, the crystal-packing in these structures is governed by CeH/X (X ¼ Cl, N) interactions, generating
helical architectures.
Keywords:
Benzene-coordinated Ru(II)
Pyrazolylmethylpyridines
1H NMR spectra
Ó 2010 Published by Elsevier B.V.
Crystal structure
Non-covalent interaction
Helical structure
1. Introduction
to its ubiquitous presence in biology [10]. Although in recent years
many helical networks have been reported, examples of helices fully
Continued interest in half-sandwich areneeruthenium
compounds [1] having “piano-stool” geometry, arises due to their
(i) catalytic potential in a wide range of organic reactions [2,3]
assembled by CeH/Cl interaction are relatively scarce [11].
This work is part of our continuing efforts in the synthesis of
new half-sandwich complexes of the types [(h
6-C6H6)RuII(L)Cl]þ
and (ii) very promising anticancer activity of {(
h
6-arene)RuII(L)
(Fig. 1) and [(h6-C6H6)RuII(L0/L00)]þ/2þ (L ¼ neutral bidentate planar/
non-planar heterocyclic N-donor ligands [7a,12a]; L0 ¼ mono-
negative phenolate-based tridentate (2-pyridyl)alkylamine/alkyl-
amine ligands [7b]; L00 ¼ neutral tridentate (2-pyridyl)alkylamine
ligands [12a]) to investigate their structure and properties (nucle-
ophilic addition onto the RuII-coordinated benzene ring [12b,12c],
electrochemical generation and stabilization of phenoxyl radical-
Cl}þ (L ¼ neutral bidentate N-donor ligand) complexes both in
vitro and in vivo [4,5], strengthened by non-covalent interactions
[5a,5c].
In recent years considerable attention is being paid toward weak
interactions such as CeH/X (X ¼ O, F, Cl,
p) and NeH/Cl, and pep
stackingbetweenaromaticrings indirectingcrystal-packingtopology
in organometallic molecules [6e9]. Such studies on half-sandwich
coordinated {(
h
6-C6H6)RuII}2þ species [7b]), and the potential of
complexes having “piano-stool” geometry [(
h
h
6-C6H6)-RuII(L)Cl]þ
[(h
6-C6H6)RuII(L)Cl]þ complexes to involve in non-covalent inter-
(L ¼ bidentate neutral N-donor ligand) [7], [(
6-C6H6)-RuII(HPz/
actions generating various supramolecular architectures with
varying dimensionality [7a,7b]. Herein we describe (a) reactivity
Me2HPz)2Cl]þ (HPz/Me2HPz ¼ pyrazole/3,5-dimethylpyrazole) [8],
and [(
h
6-C6H6)RuII(CPI)(PPh3)Cl]þ (CPI ¼ 1-(4-cyanophenyl)imid-
properties of previously reported complexes [(h
6-C6H6)RuII(L1)Cl]
azole) [9] have revealed creation of interesting supramolecular
architectures. It is worth mentioning here that among the assembly of
all the supramolecular networks, helices belong to a unique class due
[PF6] (1) and [(
h
6-C6H6)RuII(L2)Cl][PF6] (2) (L1 ¼ 2-(pyrazol-1-yl-
methyl)pyridine; L2
¼
2-(3,5-dimethyl-pyrazol-1-ylmethyl)pyri-
dine), (b) nucleophilic halide displacement/substitution reactions of
1and 2 with Ag(CF3SO3), NaN3 or NaCN to synthesize [(
6-C6H6)-
RuII(L1)(CH3CN)][PF6]2 (3), [( 6-C6H6)RuII(L1)(N3)][PF6] (4), and [(h6
C6H6)RuII(L2)(CN)][PF6] (5), and structural characterization of 4,
and (c) synthesis and properties of a new complex [(
6-C6H6)RuII(L4)-
h
h
-
* Corresponding author. Tel.: þ91 512 2597437; fax: þ91 512 2597436.
E-mail address: rnm@iitk.ac.in (R. Mukherjee).
h
0022-328X/$ e see front matter Ó 2010 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2010.03.022

1754
H. Mishra, R. Mukherjee / Journal of Organometallic Chemistry 695 (2010) 1753e1760
over anhydrous MgSO4, and filtered. Solvent removal afforded
R'
a thick yellowish white solid. Yield: 1.06 g (w70%). The ligand was
NR
further purified by recrystallization from chloroform/n-hexane. 1H
R
NMR (CDCl3; 80 MHz; 298 K):
d 5.42 (s, 2H, CH2), 6.54 (d, 1H,
HN
N
N
N
N
N
pyrazole H4), 7.00e7.68 (m, 7H, pyridine H3,4,5 and phenyl H2,3,5,6),
N
7.80 (d, 1H, pyrazole H5), 8.62 (d, 1H, pyridine H6).
2.3. Syntheses of complexes
N
The complexes [(h h
6-C6H6)RuII(L1)Cl][PF6] (1) and [( 6-C6H6)
RuII(L2)Cl][PF6] (2)were preparedasbefore [12a]. X-rayqualitysingle-
crystals of 1 were obtained by diffusion of diethyl ether into a solution
of the complex in a mixture (1:5; v/v) of CH3OH and CH3CN.
HL7
R = R' = H (L1)
R = H (HL5)
2.3.1. [(h
6-C6H6)Ru(L1)(CH3CN)][PF6]2 (3)
R = R' = Me (L2)
= -CH2-C6H5 (L6)
R = -C6H4-p-Cl, R' = H (L3)
R = -C6H4-p-F, R' = H (L4)
To a solution of 1 (0.102 g, 0.2 mmol) in CH3CN (10 mL) was
added Ag(CF3SO3) (0.051 g, 0.2 mmol). The mixture was then
refluxed for 4 h. A white precipitate of AgCl appeared which was
discarded. To the lemon yellow filtrate solid NH4PF6 (0.032 g,
0.2 mmol) was added. The volume of the solution was reduced to
w3 mL by evaporation. Addition of diethyl ether precipitated the
product, which was filtered, washed with a mixture (1:5; v/v) of
CH3CN and diethyl ether, and dried under vacuum. The product was
recrystallized from a mixture (1:5; v/v) of CH3CN and diethyl ether.
Yield: 0.096 g (70%). Anal. Calc. for C17H18N4P2F12Ru (3): C, 30.50; H,
2.71; N, 8.37. Found: C, 30.59; H, 2.70; N, 8.34%. IR (KBr, cmꢀ1): 2327
Fig. 1. The ligands of pertinence to this work.
Cl][PF6] (6) (L4 ¼ 2-[3-(4-fluorophenyl)pyrazol-1-ylmethyl]pyridine),
and X-ray structure of 6$C6H5CH3. The crystal structure of [(h
6-C6H6)-
RuII(L3)Cl][PF6] (L3
¼
2-[3-(4-chlorophenyl)pyrazol-1-ylmethyl]-
pyridine) has already been reported [7a]. Notably, the complexes
considered here generate helical structures via CeH/CleRu,
CeH/FeC, and CeH/N3eRu interactions.
n
(CH3CN), 839 n d 9.04 (d,
(PFꢀ6 ). 1H NMR (CD3CN; 400 MHz; 298 K):
JHH ¼ 5.6 Hz, 1H, H6 of py), 8.14 (t, 1H, JHH ¼ 7.9 Hz, 1H, H4 of py),
8.04 (d, 2H, JHH ¼ 6.6 Hz, 2H, H30 and H50 of pz), 7.78 (d, JHH ¼ 6.6 Hz,
1H, H3 of py), 7.60 (t, JHH ¼ 7.3 Hz, 1H, H5 of py), 6.61 (t, JHH ¼ 6.6 Hz,
1H, H40 of pz), 6.21 (s, 6H, C6H6), 5.74 (d, Jgem ¼ 15.9 Hz, 1H, NCH2e),
5.28 (d, Jgem ¼ 16.1 Hz, 1H, NCH2e), 2.33 (s, 3H, CH3CN). Molar
2. Experimental
2.1. Materials
conductance, LM (CH3CN, 298 K) ¼ 118
CH3CN): /nm (
sh (670), 370 (330).
U
ꢀ1 cm2 molꢀ1. UVeVis (in
Reagent or analytical grade chemicals were obtained from
commercial sources and used, without further purification. The
ligands 2-(pyrazol-1-ylmethyl)pyridine (L1) [13], 2-(3,5-dimethyl-
l
3
/dm3 molꢀ1 cmꢀ1) 264 (4600), 270 sh (3500), 300
pyrazol-1-ylmethyl)pyridine (L2) [13], and the dimer [{( 6-C6H6)
h
RuII(
m-Cl)Cl}2] [14] were prepared following reported procedures.
2.3.2. [(h
6-C6H6)Ru(L1)(N3)][PF6] (4)
To a solution of 1 (0.102 g, 0.2 mmol) in CH3OH (10 mL) was
added solid NaN3 (0.013 g, 0.2 mmol) and the mixture was refluxed
for 5 h. During this period the color of the solution changed from
yellow to orange. On cooling, an orange crystalline solid that
formed was filtered, washed with cold CH3OH, and dried under
vacuum. The product was recrystallized from hot CH3OH solution
as an orange crystalline solid. X-ray diffraction-quality crystals
were obtained by diffusion of diethyl ether into a solution of the
2.2. Preparation of ligand
2.2.1. 2-[3-(4-Fluorophenyl)pyrazol-1-ylmethyl]pyridine (L4)
The starting material 3-(4-fluorophenyl)-1-pyrazole necessary
for the synthesis of L4 was prepared following a procedure similar
to that used for the synthesis of L3 [7a]. A solution of 1-(4-fluoro-
phenyl)ethanone (2.0 g, 0.013 mol) in N,N-dimethylformamide
dimethylacetal [4.7 g (5 mL), 0.039 mol] was refluxed for 10 h. After
cooling to 298 K, the excess of solvent was removed under
a reduced pressure. The resulting sticky solid was dried in vacuo
and used in the next step without further purification. Yield: 1.64 g
(w70%). A mixture of the resulting compound 1-(4-fluorophenyl)-
but-2-en-1-one (1.64 g, 0.009 mol) and hydrazine hydrate [4.5 g
(4 mL), 0.09 mol] in C2H5OH (3 mL) was stirred at 333 K for 30 min.
After cooling to 298 K, the reaction mixture was poured into 20 g of
ice which afforded a white precipitate. It was filtered, washed with
cold water several times, and dried in air. Recrystallization from
a mixture (1:2; v/v) of chloroform/n-hexane afforded a white
crystalline solid. Yield: 1.04 g (65%). 1H NMR (CDCl3; 80 MHz;
298 K): 6.32 (d, 1H, pyrazole H4), 7.30e7.58 (m, 4H, benzene), 7.65
(d, 1H, pyrazole H5).
complex in CH3CN. Yield: 0.070
g (70%). Anal. Calc. for
C15H15N6PF6Ru (4): C, 34.29; H, 2.88; N, 16.00. Found: C, 34.36; H,
2.89; N, 16.14%. IR (KBr, cmꢀ1): 2035 (N3ꢀ), 839 (PFꢀ6 ). 1H NMR
n n
(CD3CN; 400 MHz; 298 K):
d
8.98 (d, JHH ¼ 5.36 Hz, 1H, H6 of py)0,
8.03 (t, JHH ¼ 7.8 Hz, 1H, H4 of py), 7.95 (d, JHH ¼ 6.8 Hz, H30 and H5
of pz), 7.67 (d, JHH ¼ 7.8 Hz, 1H, H3 of py), 7.54 (t, JHH ¼ 6.1 Hz, 1H, H5
of py), 6.56 (t, JHH ¼ 6.8 Hz, 1H, H40 of pz), 5.90 (s, 6H, C6H6), 5.67 (d,
Jgem ¼ 15.6 Hz, 1H, NCH2e), 5.39 (d, Jgem ¼ 15.6 Hz, 1H, NCH2e).
Molar conductance, L (CH3CN, 298 K) ¼ 118 Uꢀ1 cm2 molꢀ1
.
M
UVeVis (in CH3CN):
l
/nm (
e
/dm3 molꢀ1 cmꢀ1) 240 sh (11 000), 266
(8500), 390 (850).
2.3.3. [(h
6-C6H6)Ru(L2)(CN)][PF6] (5)
To a solution of 2 (0.102 g, 0.2 mmol) in C2H5OH (10 mL) was
added solid NaCN (0.0098 g, 0.2 mmol). The mixture was refluxed
for 5 h and the color of the solution changed from yellow to orange.
On cooling, an orange crystalline solid that formed was filtered,
washed with cold CH3OH, and dried under vacuum. The product
was recrystallized by diffusion of diethyl ether into a solution of the
complex in a mixture (2:1; v/v) of CH3CN and CH3OH. Yield: 0.080 g
A mixture of 2-(chloromethyl)pyridine hydrochloride (0.92 g,
5.62 mmol), 3-(4-fluorophenyl)-1-pyrazole (1.0 g, 5.62 mmol),
benzene (60 mL), 40% aqueous NaOH (8 mL), and 40% aqueous
tetra-n-butylammonium hydroxide (8 drops) was refluxed with
stirring for 8 h and then stirred at 298 K for 12 h. The organic layer
was then separated, washed twice with brine water (100 mL), dried

H. Mishra, R. Mukherjee / Journal of Organometallic Chemistry 695 (2010) 1753e1760
1755
Table 1
(75%). Anal. Calc. for C18H19N4PF6Ru (5): C, 40.23; H, 3.56; N, 10.43.
Found: C, 40.36; H, 3.62; N,10.54%. IR (KBr, cmꢀ1): 2057 (CNꢀ), 839
(PFꢀ6 ). 1H NMR (CD3CN; 400 MHz; 298 K):
¼ 9.10 (d, JHH 5.6 Hz,
Data collection and structure refinement parameters for [(
h
6-C6H6)RuII(L1)Cl][PF6]
n
(1), [(
h
6-C6H6)RuII(L1)(N3)][PF6] (4), and [( 6-C6H6)RuII(L4)Cl][PF6] (6$C6H5CH3).
h
n
d
1
6.C6H5CH3
4
1H, H6 of py), 7.99 (t, JHH 8.0 Hz, 1H, H4 of py), 7.69 (d, JHH ¼ 7.6 Hz,
1H, H3 of py), 7.49 (t, JHH ¼ 6.2 Hz, 1H, H5 of py), 6.13 (s, 1H, H40 of
pz), 5.92 (s, 6H, C6H6), 5.47 (d, Jgem ¼ 16.0 Hz, 1H, NCH2e), 5.13 (d,
Jgem ¼ 15.6 Hz, 1H, NCH2e), 2.50 (s, 3H, 5-CH3 of pz), 2.41 (s, 3H, 3-CH3
Chemical formula
C
15H15ClF6-
C
28H26ClF7N3Pru C15H15F6N6PRu
N3PRu
518.79
Yellow, needle
293(2)
Tetragonal
I41/a (#88)
22.928(5)
22.928(5)
14.181(5)
90.0
90.0
90.0
7455(3)
16
1.849
M
705.01
525.37
Orange, block
100(2)
Orthorhombic
P212121 (#19)
10.818(5)
12.803(5)
13.402(5)
90.0
90.0
90.0
1856.2(13)
4
1.880
Crystal color, habit
T, K
Yellow, block
100(2)
of pz). Molar conductance, LM (MeCN, 298 K) ¼ 224
U .
ꢀ1 cm2 molꢀ1
UVeVis (in CH3CN): l/nm (e
/dm3 molꢀ1 cmꢀ1) 230 sh (9150), 270
Cryst system
Space group
Orthorhombic
P212121 (#19)
12.991(5)
13.105(5)
16.376(5)
90.0
(4050), 385 (1100).
ꢀ
a/A
ꢀ
b/A
2.3.4. [(
L4 (0.084 g, 0.4 mmol) was dissolved in CH3OH (15 mL) and to it was
added solid [{( -Cl)Cl}2] (0.100 g, 0.2 mmol). The mixture
6-C6H6)RuII(
h
6-C6H6)RuII(L4)Cl][PF6] (6)
ꢀ
c/A
ꢁ
ꢁ
a
/
b
/
90.0
90.0
2788.0(17)
4
1.680
0.787
1416
18075
h
m
ꢁ
g
/
was stirred for 12 h at 298 K. The resulting yellow solution was filtered
and the volume of the filtrate was reduced (w7 mL) and to it solid
NH4PF6 (0.065 g, 0.4 mmol) was added. The yellow microcrystalline
solid that formed was filtered, washed with cold CH3OH, and dried in
vacuo. Recrystallization was achieved from hot CH3OH solution. Yield:
0.130 g (57%). Anal. Calc. for C21H18ClF7N3PRu (6): C, 41.15; H, 2.96; N,
3
ꢀ
V/A
Z
dcalcd/g cmꢀ3
m
/mmꢀ1
1.133
4096
6592
3248 [0.0897]
1.004
1040
12189
4577 [0.0165]
F(000)
No. of reflns collected
No. of indep reflns
[R (int)]
6809 [0.0342]
6.86. Found: C, 40.94; H, 2.94; N, 6.81%. IR (KBr, cmꢀ1): 841 (PF6ꢀ). 1H
n
NMR (CD3CN; 400 MHz; 298 K):
d
9.09 (d, JHH ¼ 6.8 Hz, 1H, H6 of py),
No. of reflns used
2043
6238
4567
0
8.04(t,JHH ¼7.6 Hz, 1H, H4 ofpy), 7.99 (d, JHH ¼ 7.2 Hz, 1H, H5 of pz), 7.77.
(m, 3H, H5 of py, H300, H400 of phenyl), 7.68 (d, JHH ¼ 7.8 Hz, 1H, H3 of py)
7.56, 7.52 (t, JHH ¼ 7.2 Hz, 1H, H5 of py), 7.26 (m, 2H, H200, H500 of phenyl),
6.54 (d, JHH ¼ 7.2 Hz, 1H, H40 of pz), 5.67 (s, 6H, C6H6), 5.67 (1H, eCH2e,
overlaps with C6H6 resonance), 5.42 (d, Jgem ¼ 15.6 Hz, 1H, eCH2e).
[I > 2s(I)]
GOF on F2
1.014
1.104
1.185
Final R indices [I > 2
Final R indices (all data)
s
(I)]a,b 0.0604, 0.1513
0.0350, 0.0694 0.0267, 0.0634
0.0426, 0.0890 0.0268, 0.0634
0.1073, 0.1779
a
R1 ¼ S(jFoj e jFcj)/SjFoj.
b
2
2
2
wR2 ¼ {S[w(jFoj e jFcj )2]/S[w(jFoj )2]}1/2
.
Molar conductance, LM (CH3CN, 298 K) ¼ 150
U
ꢀ1 cm2 molꢀ1. UVeVis
(in CH3CN): /nm (e
l
/dm3 molꢀ1 cmꢀ1) 265 (8500), 295 (3500), 415
(450). X-ray quality single-crystals of composition 6$C6H5CH3 were
obtained by layering of toluene on a solution of the complex in
a mixture of CH3CN and CH2Cl2.
3. Results and discussion
3.1. The complexes and their general characterization
2.4. Instrumentation
In our previous work, we presented the molecular structures of
Elemental analyses were obtained using Thermo Quest EA 1110
CHNS-O, Italy. Conductivity measurements were done with an Elico
type CM-82T conductivity bridge (Hyderabad, India). Spectroscopic
measurements were made using the following instruments: IR
(KBr, 4000e600 cmꢀ1), Bruker Vector 22; electronic, Perkin Elmer
Lambda 2 and Agilent 8453 diode-array spectrophotometer. 1H
NMR spectral measurements were performed on a JEOL-JNM-LA-
400 FT (400 MHz) NMR spectrometer.
half-sandwich complexes of the type [(h
6-C6H6)RuII(L)Cl]þ [7a]
having piano-stool geometry using a series of neutral bidentate
N-donor ligands [two heterocycles directly attached, thus allowing
the rings to electronically communicate (HL5, L6, and HL7) and also
with a non-planar ligand L3, in which two heterocycles are sepa-
rated by a methylene spacer, thus preventing electronic commu-
nication between the two rings] (Fig. 1). The present work is
concerned with non-planar bidentate N-donor ligands (L1, L2, and
L4), giving us an opportunity to (i) investigate the effect of these
ligands on the structure and bonding aspects of half-sandwich
2.5. Crystal structure determination
complexes of composition {(h
6-C6H6)RuII(L)Cl}þ (L represents
Diffraction intensities were collected either on an Enraf Nonius
CAD-4-mach four-circle diffractometer at 298(2) K (1) or on
bidentate neutral N-donor ligands) and (ii) to look for generaliza-
tions from the standpoint of non-covalent interactions
[6e9,11,17e22].
a Bruker SMART APEX CCD diffractometer at 100(2) K (4 and
6$C6H5CH3) using graphite-monochromated Mo K
a
(l
¼ 0.71073 A)
Treatment of previously reported complex [(
[PF6] (1) [12a] with (i) Ag(CF3SO3) in CH3CN and (ii) NaN3 in CH3OH,
and (iii) the reaction between previously reported complex [(h6
C6H6)Ru(L2)Cl][PF6] (2) [12a] and NaCN in C2H5OH led to the
isolation of complexes [(
6-C6H6)Ru(L1)(CH3CN)][PF6]2 (3), [(h6
C6H6)Ru(L1)(N3)][PF6] (4), and [( 6-C6H6)Ru(L2)(CN)][PF6] (5),
respectively (Scheme 1). Reaction of the dimer [{(
6-C6H6)RuII(
Cl)Cl}2] [14] with L4 in CH3OH in the presence of NH4PF6 afforded
h
6-C6H6)RuII(L1)Cl]-
ꢀ
radiation. Intensity data were corrected for Lorentz polarization
effects. Empirical absorption correction (SADABS) was applied. The
structures were solved by SIR-97, expanded by Fourier-difference
syntheses, and refined with SHELXL-97, incorporated in WinGX
1.64 crystallographic collective package [15]. Hydrogen atoms were
placed in idealized positions, and treated using riding model
approximation with displacement parameters derived from those
of the atoms to which they were bonded. All non-hydrogen atoms
were refined with anisotropic thermal parameters by full-matrix
least-squares procedures on F2. A summary of the data collection
and structure refinement information is provided in Table 1.
Intermolecular contacts of the CeH/Cl and CeH/N types were
examined with the DIAMOND package [16]. CeH distances were
normalized along the same vectors to the neutron derived values of
-
h
-
h
h
m-
isolation of a new complex [(h
6-C6H6)Ru(L4)Cl][PF6] (6). It has to be
stressed here that the ligand L4 present in 6 was deliberately
designed to investigate the effect of a fluorine atom in 6$C6H5CH3 in
the place of a chlorine atom present in L3 ligand in [( 6-C6H6)-
h
RuII(L3)Cl][PF6] [7a]. We anticipated that owing to small size and
high electronegativity of fluorine, the CeF bond would be a better
candidate than CeCl to participate in CeH/X (X ¼ Cl or F) inter-
actions. Thus complex 6$C6H5CH3 is an ideal candidate to explore
ꢀ
1.083 A [17].

1756
H. Mishra, R. Mukherjee / Journal of Organometallic Chemistry 695 (2010) 1753e1760
z+
+
-
-
xPF6
PF6
Ag(CF3SO3); CH3CN
NH4PF6
X
X
Ru
Ru
N
N
R
R
NaN3; CH3OH
N
N
NaCN; C2H5OH
N
N
R
R
-
R = H, X = Cl ; 1
R = H, X = CH3CN, x = z = 2; 3
-
R = H, X = N3 , x = z = 1; 4
-
R = Me, X = Cl ; 2
R = Me; X = CN-, x = z = 1; 5
Scheme 1.
the participation of both CeH/Cl [6b,6e,6g,7a,8,9,11,17e20] and
CeH/F [6e,6g,9,21] interactions.
N-donor ligands containing either both soft donors [26h] (six-
membered nitrogen heterocycle pyridine due to its -electron
deficiency behaves as excellent -acceptors and in turn they
provide soft site for metal coordination) or combination of both
a soft pyridine and a hard pyrazole (the -excessive five-membered
nitrogen heterocycle pyrazole is a poorer -acceptor. In fact, it is
a better
p
Characterization of the new complexes was accomplished by
elemental analysis, solution electrical conductivity, IR and 1H NMR
spectroscopy. Consistent with their formulation, IR stretching
vibration of PFe6 at w840 cmꢀ1 confirms cationic nature of the
complexes 3e6. IR spectra of the solvent-bound complex 3 and
anion-bound complexes 4, 5, and 6 show common features, in
addition to attesting to the vibrations expected due to the presence
of coordinated CH3CN, Ne3 , and CNe. Conductivity studies revealed
that 3, 5, and 6 behave as 1:1 electrolyte and 3 as 1:2 electrolyte
[23].
p
p
p
p
-donor and hence acts as hard donor site) [7a]; S ¼
solvent and X ¼ monodentate anion); z ¼ 1 for X and z ¼ 2 for S) is
scarce. The obvious effect of these donor sites (non-planar pyr-
azolylmethylpyridine ligands) to the properties of the resulting
complexes is the differential flow of electron density from the
bidentate ligands to the {(h
6-C6H6)RuIICl}þ moieties. This in turn
Complexes 3e6 exhibit absorption spectral band at 415, 365,
390, and 388 nm, respectively.
modulates (i) the electron density on the RuII-coordinated benzene
ring (1H NMR spectra) and (ii) the hydrogen-bonding donor prop-
erties of RuII-coordinated chloride ion and the hydrogen-bonding
acceptor properties of various CeH moieties present on the ligand
backbone (see below).
3.2. Molecular structures of [(
h
6-C6H6)Ru(L1)Cl][PF6] (1), [(
h
6-C6H6)-
Ru(L1)(N3)][PF6] (4), and [(
(6$C6H5CH3)
h
6-C6H6)Ru(L4)Cl][PF6]$C6H5CH3
In order to confirm the identity and chelate-ring conformation of
the coordinated ligands, single-crystal X-ray structure determina-
tion was done for the chloride-bound complexes 1 and 6$C6H5CH3,
and azide-bound complex 4. X-ray crystallographic analysis
confirms the structure of the complexes (Fig. 2 and Table 2).
The cations exhibit the expected and usual pseudo-octahedral
half-sandwich “piano-stool” disposition around the Ru(II) cation
[1c,7e9,26], with the benzene ligand occupying one face of the
3.3. Comparison of metric parameters
For complexes 1 and 6$C6H5CH3 the observed trend in RueC,
RueN(py) (py ¼ pyridine), RueN(pz) (pz ¼ pyrazole), and RueCl
distances (Table 3), reflecting mutual trans influence, is a conse-
quence of interplay between steric and electronic factors associated
with the coordinating ability of bidentate ligands L1 or L4, in
a closely similar metal coordination environment.
octahedron (the Ru(II) center is
p
-bonded to the
h
6-C6H6 group) and
Average RueC distances in 1, 6.C6H5CH3, and 4 (Table 2)
compare well with that reported in the literature [1c,8,26c,26g],
including our previous report [7a] on similar three-legged piano-
the coordination of a bidentate heterocyclic N-donor ligand [N(1) of
pyridine and N(3) of pyrazole] and a chloride (1, 6$C6H5CH3) or azide
(4) ion on the other face.
stool complexes having {(h
6-C6H6)RuIICl}þ moiety. The RueN(py)
The NeRueN angles have values of 83.7(3)ꢁ (1), 88.04(14)ꢁ
(6$C6H5CH3), and 86.03(10)ꢁ (4), deviated from 90ꢁ as per demand
of the bite of the ligand.
and RueN(pz) bond lengths in 1, 6.C6H5CH3, and 4 (Table 3) also
compare well with reported values [8,26a,26e], including our
previous report [7a]. The RueCl distances in 1 and 6.C6H5CH3 are
comparable to that reported in the literature for closely similar
complexes [1c,8,26c,26e,26g], including our previous observa-
tion [7a]. The RueN(azide) bond length in 5 is comparable to
that reported in the literature for a closely similar three-legged
In 1 and 6$C6H5CH3 the pyridyl mean plane is tilted to adjacent
pyrazole ring at an angle of 55.116(11)ꢁ and 46.38(6)ꢁ, respectively,
attesting their non-planar nature [24,25]. In addition, the pyrazole
ring and p-fluourophenyl group of L4 in 6$C6H5CH3 make an angle
of 70.07(6)ꢁ.
ꢀ
piano-stool complex [1c]. The average RueC distance [2.191(3) A]
ꢀ
It is worth mentioning here that although several examples of
structurally characterized mononuclear half-sandwich complexes
in 4 is longer than [2.158(10) A] in 1. It might be due to greater
trans influence of the azide ion compared to the chloride ion [the
azide ion is a stronger s-donor than chloride ion because RueN
(azide) bond length is much shorter (w0.3 A) than that of RueCl
bond lengths (Tables 2 and 3)].
having {(
number of structurally characterized complexes of the type
“[( (L neutral bidentate heterocyclic
6-C6H6)Ru(L)(S/X)]zþ
h
6-C6H6)Ru}2þ unit are now known [1c,7e9,26], the
ꢀ
h
”
¼

H. Mishra, R. Mukherjee / Journal of Organometallic Chemistry 695 (2010) 1753e1760
1757
Table 2
6-C6H6)RuII(L1)Cl][PF6] (1), [(
h
6-C6H6)
ꢁ
ꢀ
Selected bond lengths (A) and angles ( ) in [(
h
RuII(L1)(N3)][PF6] (4), and [(
h
6-C6H6)RuII(L4)Cl][PF6]$C6H5CH3 (6$C6H5CH3).
1
6$C6H5CH3
4
Ru(1)eN(1)
Ru(1)eN(3)
Ru(1)eCl(1)
Ru(1)eN(4)
Ru(1)eC(1)
Ru(1)eC(2)
Ru(1)eC(3)
Ru(1)eC(4)
Ru(1)eC(5)
Ru(1)eC(6)
C(1)eC(2)
C(2)eC(3)
C(3)eC(4)
C(4)eC(5)
C(5)eC(6)
C(1)eC(6)
2.111(7)
2.087(6)
2.386(2)
e
2.122(3)
2.091(3)
2.4025(12)
e
2.112(3)
2.087(3)
e
2.107(2)
2.192(3)
2.188(3)
2.194(3)
2.181(3)
2.193(3)
2.198(3)
1.403(5)
1.425(4)
1.398(5)
1.421(5)
1.399(5)
1.416(5)
2.155(11)
2.150(9)
2.180(12)
2.151(10)
2.151(10)
2.161(10)
1.390(20)
1.355(19)
1.317(17)
1.359(18)
1.340(18)
1.460(20)
2.177(4)
2.189(4)
2.168(4)
2.189(4)
2.181(5)
2.190(4)
1.423(7)
1.392(6)
1.413(7)
1.381(6)
1.426(7)
1.379(8)
N(1)eRueN(3)
N(1)eRueCl(1)
N(3)eRueCl(1)
N(1)eRueN(4)
N(3)eRueN(4)
83.7(3)
85.14(18)
86.60(19)
e
88.04(14)
81.66(9)
85.79(9)
e
86.03(10)
e
e
84.31(9)
85.47(10)
e
e
similar complexes [7a,12a]. Formation of the complexes provides
rigidity to the ligand structure. In essence, the 1H NMR results
clearly indicate that the solid state structures (vide supra) are
retained in solution.
3.5. Non-covalent interaction
A closer inspection of the crystal-packing diagrams of 1, 4, and
6$C6H5CH3 reveals that these organometallic molecules are
engaged in interesting non-covalent interactions (see below).
Relevant bond distances and bond angles are summarized in Table
4, which are in good agreement with prior results
[5c,6,8,9,17,18,20e22], including our own findings [7a,11,12].
3.5.1. [(
C6H5CH3 (6$C6H5CH3)
h h
6-C6H6)Ru(L1)Cl][PF6] (1) and [( 6-C6H6)Ru(L4)Cl][PF6]$
In 1 intermolecular CeH/Cl hydrogen-bonding interaction
[5c,6,7a,8,9,11,18] linking the neighboring molecules gives rise to
a 1D helical architecture [11] along the c axis (Fig. 3).The RuII-
coordinated chloride ion is involved in hydrogen-bonding inter-
action with CeH(2) of the benzene ring of a neighboring molecule.
In 6$C6H5CH3 intermolecular CeH/Cl interactions link the
neighboring molecules to give rise to a 1D helical architecture along
the a axis (Fig. 4). Here the RuII-coordinated Cle ion is involved in
interaction with the methylene CeH of L4 of a neighboring mole-
cule. The 1D helical chains thus formed in turn are involved in
CeH/F contacts with molecules in the adjacent layer, involving
CeH of pyridine ring and the organic fluorine atom F(1) present in
Fig. 2. Perspective views of (a) [(
h
6-C6H6)RuII(L1)Cl]þ in 1, (b) [(
h
6-6H6)RuII(L4)Cl]þ in
6.C6H5CH3, and (c) [(
h
6-C6H6)RuII(L1)(N3)]þin 4. Hydrogen atoms have been omitted for
clarity.
Table 3
Summary of relevant bond distances (A) in [(
h
6-C6H6)RuII(L1)Cl][PF6] (1), [(
h
6-C6H6)-
ꢀ
RuII(L1)(N3)][PF6] (4), and [( 6-C6H6)RuII(L4)Cl][PF6]$C6H5CH3 (6$C6H5CH3).
h
3.4. 1H NMR spectra
1
6$C6H5CH3
4
Av RueC
RueC6H6 centroid
Av CeC
RueN(py)
RueN(pz)
RueN(azide)
RueCl
2.158(10)
1.667
1.370(16)
2.111(7)
2.087(6)
e
2.182(2)
1.672
1.402(7)
2.122(3)
2.091(3)
e
2.191(4)
1.677
1.410(6)
2.112(3)
2.087(3)
2.107(2)
e
The new complexes (3e6) were characterized by 1H NMR
spectroscopy. The data in CD3CN along with their assignments are
recorded in the Experimental Section, supporting their expected
“piano-stool” structure [Figs. S1eS4 (Supplementary material)].
The proton resonances were assigned based on the available 1H
NMR spectral results for the free ligands [13], and those for closely
2.386(2)
2.4025(12)

1758
H. Mishra, R. Mukherjee / Journal of Organometallic Chemistry 695 (2010) 1753e1760
Table 4
Hydrogen-bonding (CeH/Cl/N) parameters for [(
h -
6-C6H6)RuII(L1)Cl]þ in 1, [(h6
C6H6)RuII(L1)(N3)]þ in 4 and [( 6-C6H6)RuII(L4)Cl]þ in 6$C6H5CH3.
h
ꢀ
ꢀ
DeH/A H/A, A
[(
6-C6H6)RuII(L1)Cl]þ unit in 1
C2eH2/Cl1
D/A, A
DeH/A
h
2.739a
3.621(10)
158.7ꢁ
b
[(
h
6-C6H6)RuII(L4)Cl]þ unit in 6.C6H5CH3
c
C12eH12B/Cl
C10eH10/F
3.001
3.5547(10)
3.2328(9)
114.8ꢁ
123.9ꢁ
c
2.5598
[(h
6-C6H6)RuII(L1)(N3)]þ unit in 4
d
C3eH3/N6
C15eH15/N6
2.434b
2.533c
3.290(6)
3.552 (10)
134.9ꢁ
156.4ꢁ
e
a
0.25 þ y, 1.25 ꢀ x, 0.25 þ z.
1.25 ꢀ y, ꢀ0.25 þ x, ꢀ0.25 þ z.
x, 1 þ y, z.
b
c
d
e
0.5 þ x, 0.5 ꢀ y, 1 ꢀ z.
ꢀ0.5 þ x, 0.5 ꢀ y, 1 ꢀ z.
p-fluorophenyl group of L4. Such interactions result in the forma-
tion of a 2D hydrogen-bonded network (Fig. S5).
3.5.2. [(
The crystal-packing diagram of 4 reveals that the cation [(h6
h
6-C6H6)Ru(L1)(N3)][PF6] (4)
-
C6H6)Ru(L1)(N3)]þ is engaged in non-covalent interaction. Like the
helical structures observed in the case of 1 and 6$C6H5CH3,
compound 4 also gives rise to a 1D helical architecture along the
a axis, via intermolecular CeH/N hydrogen bonds (Fig. 5). In fact,
the azide nitrogen N(6) is involved in bifurcated hydrogen-bonding
interaction with H(3) of the benzene ring and with H(15) of pyr-
azole ring of a neighboring molecule. The hydrogen-bonding
Fig. 4. (a) View of helix formation through CeH / Cl hydrogen-bonding in [(h
6-C6H6)-
Ru(L4)Cl]þ unit in (6.C6H5CH3). All the hydrogen atoms except those involved in
hydrogen bonding have been omitted for clarity. (b) Space-filling view of inner channel
running parallel to the helical axis.
ꢁ
ꢀ
ꢀ
parameters observed here [2.532(23) A and 137.1 ; 2.655(3) A and
157.6ꢁ] fall in the range observed in the literature (CeH/N:
ꢁ
ꢀ
2.522e2.721 A; 124.6e157.3 ) [22].
3.5.3. Rationalization of observed non-covalent interaction
Inspection of the non-covalent interaction which results in the
formation of supramolecular architecture (Figs. 3e5) has led us to
present the following hypotheses. (i) From literature reports
[6g,7a,8,9] and the present work it has been observed that the RuII-
coordinated Cle ion in half-sandwich complexes with “piano-stool”
geometry acts as an efficient hydrogen bond acceptor to engage in
CeH/Cl interaction. (ii) From the point of view of charge density (it
should be mentioned here that there exists no spectroscopic or
other evidence for consideration of electron density related to the
CeH/Cl and CeH/N interactions; the following description of
charge distribution is purely based on fundamental considerations)
on the coordinated benzene ring, which is tuned by the extent of
donation of electron density to the RuII ion. The rings are deacti-
vated when comparatively weak donor sites provide “three-legged”
coordination. This will cause the CeH groups of RuII-coordinated
C6H6 to be ideally suited to take part in CeH/(Cl or N) interactions.
This has been realized in this work, as before [7a]. (iii) Considering
charge distribution in the pyridine ring present in L1 and L4, which
is tuned by the withdrawal of electron density from the ring-carbon
atoms towards the nitrogen atom for donation to the metal ion, the
rings are deactivated. This causes the positions 4 and 6 electron-
deficient, and such CeH groups would thereby be ideally suited to
take part in CeH/Cl interaction. This has been observed in this
work. (iv) For pyrazole groups present in L1 and L4, 3- and 5-posi-
tions are electron-deficient [7a,11a]. The contribution of stereo-
chemistry should, however, not be ignored (the 3 and 5 positions
on the pyrazole ring are much more sterically demanding than
other positions). Therefore, the involvement of pyrazole 5-H in
CeH/Cl interaction observed here justifies our hypothesis. (v) We
have shown in our previous reports [11] that within the framework
of CeH/Cl interactions the geometry of the complex plays a vital
role in the helix formation, the tetrahedral geometry favors the
Fig. 3. (a) View of helix formation through CeH / Cl hydrogen-bonding in [(h
6-C6H6)-
Ru(L1)Cl]þ unit in 1. All the hydrogen atoms except those involved in hydrogen bonding
have been omitted for clarity. (b) Space-filling view of inner channel running parallel
to the helical axis.
helix
formation
through
hydrogen-bonding
interaction.

H. Mishra, R. Mukherjee / Journal of Organometallic Chemistry 695 (2010) 1753e1760
1759
RuII(L)Cl}þ (L ¼ neutral bidentate heterocyclic N-donor hybrid
ligands), few systematic studies have been made to design this class
of half-sandwich complexes with the intention of pinpointing
critical roles that the ancillary ligands play in fine-tuning structure-
bonding properties of these organometallic molecules. In this work
a particular attention has been placed to non-planar bidentate N-
donor ligands with two different heterocyclic rings. The ligands
used in this work carry sites suitable for linking molecules prefer-
entially through non-covalent interactions. Nucleophilic chloride
displacement reaction and ligand substitution reaction of [(h6
-
C6H6)RuII(L1/L2)Cl][PF6] with Ag(O3SCF3) and NaN3/NaCN to
prepare CH3CN/Nꢀ3 /CNꢀ-bound complexes have also been achieved.
In continuation of our previous observation we discover that Ru-
coordinated benzene rings and non-planar bidentate ligands
chosen here had a pronounced tendency to participate in non-
covalent interactions (CeH∙∙∙Cl and CeH/N) in the solid state,
generating helical architectures. The present study thus provides
further information pertinent to a better understanding of the non-
covalent interactions in the structure directing organometallic unit
[(h
6-C6H6)RuII(L)Cl]þ.
Acknowledgements
Financial assistance received from the Department of Science
and Technology (DST), Government of India is gratefully acknowl-
edged. HM gratefully acknowledges University Grants Commission
(UGC), New Delhi for a Senior Research Fellowship. RM sincerely
thanks the DST for the award of JC Bose fellowship. We thank Dr
Apurba Kumar Patra for the crystal structure of complex 1.
Fig. 5. (a) View of helix formation through CeH/N hydrogen-bonding in [(h
6-C6H6)-
RuII(L1)(N3)]þ unit in the crystal of 4. All the hydrogen atoms except those involved in
hydrogen bonding have been omitted for clarity. (b) Space-filling view of inner channel
running parallel to the helical axis.
Appendix. Supplementary data
CCDC 736278, 290123, and 736277 contain the supplementary
crystallographic data for 1, 4, and 6$C6H5CH3, respectively. These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2010.03.022.
Considering benzene ring as a single donor group, all the RuII
complexes, having three-legged “piano-stool” geometry, can be
considered to assume distorted pseudo-tetrahedral geometry at the
metal center. The observed results justify our hypothesis. Previ-
ously [7a] we identified a large variety of non-covalent interactions
using planar bidentate ligands. Such interactions afforded network
structures but helix formation was not observed [7a]. The present
work demonstrates that the non-planar nature of the given ligand
plays a crucial role in helix formation through non-covalent inter-
action. The methylene spacer which separates the two donor units
(pyridine and pyrazole in L1 and L4) provides the required turn for
the helix formation due to proper angular disposition of the
interacting hydrogen atom(s).
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