Synthetic, spectral and structural studies of ruthenium(II) compounds based on 2,6-diacetylpyridinemonoxime

Article abstract of DOI:10.1016/j.molstruc.2007.11.022

Reaction of the ruthenium complexes [RuCl₂(EPh₃)₃] (E = P, As), [(η⁵-C₅H₅)RuCl(EPh₃)₂] (E = P, As), [(η⁵-C₅Me₅)RuCl(PPh₃)₂] and [(η⁵-C₉H₇)RuCl(PPh₃)₂] with 2,6-diacetylpyridinemonoxime (dapmoH) have been investigated. Compounds with the formulations [Ru(κ³-dapmoH)Cl(PPh₃)₂]PF₆ (1), [Ru(κ³-dapmoH)Cl(PPh₃)₂]BF₄ (2) and [Ru(κ³-dapmoH)Cl(AsPh₃)₂]Cl (3) have been isolated and fully characterized by elemental analyses, IR, NMR, electronic, emission spectral and electrochemical studies. Molecular structures of the complexes [Ru (κ³ -dapmoH) Cl (PPh₃)₂] PF₆ · H₂ O (1) and [Ru (κ³ -dapmoH) Cl (PPh₃)₂] BF₄ · 1.5 H₂ O (2) have been determined by single crystal X-ray diffraction studies. A structural feature of interest for both the compounds is that the counter anions in 1 and 2 play vital role in the self-assembly of cages through intermolecular weak interactions in which water dimers or trimers are encapsulated. Compounds 1 and 2 strongly emit upon excitation at their respective MLCT transitions.

Full text of DOI:10.1016/j.molstruc.2007.11.022

Available online at www.sciencedirect.com
Journal of Molecular Structure 886 (2008) 136–143
www.elsevier.com/locate/molstruc
Synthetic, spectral and structural studies of ruthenium(II)
compounds based on 2,6-diacetylpyridinemonoxime
a
a
a,
b
*
Manoj Trivedi , Sanjay K. Singh , Daya S. Pandey , Ru-Qiang Zou ,
Manish Chandra b, Qiang Xu b,*
a Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, UP, India
b National Institute of Advanced Industrial Science and Technology, (AIST) 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
Received 21 August 2007; received in revised form 31 October 2007; accepted 8 November 2007
Available online 22 November 2007
Abstract
Reaction of the ruthenium complexes [RuCl2(EPh3)3] (E = P, As), [(g5-C5H5)RuCl(EPh3)2] (E = P, As), [(g5-C5Me5)RuCl(PPh3)2] and
[(g5-C9H7)RuCl(PPh3)2] with 2,6-diacetylpyridinemonoxime (dapmoH) have been investigated. Compounds with the formulations
[Ru(j3-dapmoH)Cl(PPh3)2]PF6 (1), [Ru(j3-dapmoH)Cl(PPh3)2]BF4 (2) and [Ru(j3-dapmoH)Cl(AsPh3)2]Cl (3) have been isolated and
fully characterized by elemental analyses, IR, NMR, electronic, emission spectral and electrochemical studies. Molecular structures of
the complexes ½ Ruðj3-dapmoHÞClðPPh3Þ2ꢀPF6 ꢁ H2O (1) and ½Ruðj3-dapmoHÞClðPPh3Þ2ꢀBF4 ꢁ 1:5H2O (2) have been determined by sin-
gle crystal X-ray diffraction studies. A structural feature of interest for both the compounds is that the counter anions in 1 and 2 play
vital role in the self-assembly of cages through intermolecular weak interactions in which water dimers or trimers are encapsulated. Com-
pounds 1 and 2 strongly emit upon excitation at their respective MLCT transitions.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; Tertiary phosphines; dapmoH; X-ray; Weak interactions; Luminescence
1. Introduction
metal ions according to Pearson’s hard–soft Lewis acid–
base index [6]. In the oxime-bridging mode metal binds
with the ligand 2,6-diacetylpyridinemonoxime (dapmoH)
in j3-manner. The major coordination site in this molecule
consists of two nitrogen and an oxygen atom and should
show preference for softer Lewis acids, while deprotona-
tion of OH group generates an oxide-like species which
prefers to bind a hard Lewis acid. Although, a number of
first row transition metal complexes containing 2,6-diac-
etylpyridinedioxime (dapdoH2) are reported in the litera-
ture, complexes containing 2,6-diacetylpyridinemonoxime
(dapmoH) have scarcely been studied and to our knowl-
edge structural data on any such complex is yet to be
reported [7]. On the other hand, water clusters have been
extensively studied both theoretically and experimentally,
in attempts to provide insight into the structure and prop-
erties of liquid water or ice [8]. A variety of water clusters,
such as dimers, trimers, tetramers and pentamers having
cyclic and quasi-planar minimum energy structures are
Considerable attention has been paid towards the con-
struction of molecules and molecular assemblies of differ-
ent size and shapes to encapsulate guest molecules
because of their potential use as selective hosts for anion
sensing [1], separation and selective recognition [2], cataly-
sis [3] and gas sorption and storage [4]. The self-assembly
of relatively small molecules, through covalent or hydro-
gen-bonding interactions has proved to be very useful in
forming large capsular cavities [5]. Furthermore, use of
the functional groups such as oxime to bridge metal centres
is also an interesting area as they are easy to prepare and
such systems can take advantage of site-preference for
*
Corresponding authors. Tel.: +91 9450960400 (D.S. Pandey); +81 72
751 9652 (Q. Xu).
E-mail addresses: dspbhu@bhu.ac.in (D.S. Pandey), q.xu@aist.go.jp
(Q. Xu).
0022-2860/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.11.022

M. Trivedi et al. / Journal of Molecular Structure 886 (2008) 136–143
137
particularly interesting among the possible clusters. A
2.2. General synthesis of the complexes
number of reports dealing with water clusters of different
nuclearities and structures have been reported in the litera-
ture [9,10].
2.2.1. [Ru(j3-dapmoH)Cl(PPh3)2]PF6ꢁH2O (1)
To a suspension of [RuCl2(PPh3)3] (0.958 g, 1.0 mmol)
in methanol (25 mL) dapmoH (0.178 g, 1.0 mmol) was
added and the resulting solution was heated under reflux
for 4 h. The brown solution thus obtained was cooled to
room temperature and filtered through Celite to remove
any solid impurity. The filtrate was concentrated to one
third of its volume under vacuum and a solution of
NH4PF6 (0.200 g, 1.22 mmol) dissolved in methanol
(5 mL) was added to it and left for slow crystallization at
ꢂ4 °C. In a couple of days crystalline product appeared
which was separated by filtration and washed twice with
methanol, diethyl ether and dried in vacuo. Yield: 0.80 g
(80%). Anal. Calc. for C45F6H42ClN2O3P3Ru (1002): C,
53.89; H, 4.19; N, 2.79%. Found: C, 53.86; H, 4.17; N,
2.81%. IR (KBr): m/cmꢃ1 3400(b), 1675(w), 1590(m),
1458(s), 1430(m), 1350(m), 1253(w), 1165(w), 1145(s),
1090(s), 1018(s), 961(w), 845(m), 670(m), 660(w), 630(m),
355(m) cmꢃ1. dH (300 MHz; CDCl3; Me4Si) 10.06 (s, 1H,
NAOH), 7.41 (d, J = 6.0 Hz, 2H, Py-3H and 5H), 7.52
(d, J = 9.0 Hz, 1H, Py-4H), 7.36–6.98 (br m aryl protons,
PPh3), 2.22 (s, 2H, H2O), 1.57 (s, 3H, CH3), 1.25 (s, 3H,
CH3). dP (300 MHz; CDCl3; PCl3) 27.12 (s, PPh3),
ꢃ141.22 ðPF6ꢃÞ. 13C{1H} NMR (d6-acetone): 155.97
[AC@NOH], 154.50 [py-1(6C)], 137.74 [py-4C], 130.09
[ACAPPh3] 120.50[py-3(5C)], 10.09 [ACH3]. FAB-MS:
m/z 839(838), 29, [Ru(j3-dapmoH)Cl(PPh3)2]+, 577(577),
54, [Ru(j3-dapmoH)Cl(PPh3)]+, 315(316), 35, [Ru(j3-dap-
moH)Cl]+. UV/vis: kmax (CH2Cl2, e[dm3 molꢃ1 cmꢃ1]) 406
(7202), 236 (44980).
During our studies devoted in this direction ruthe-
nium(II) compounds with the formulations [Ru(j3-dap-
moH)Cl(PPh3)2]PF6 (1), [Ru(j3-dapmoH)Cl(PPh3)2]BF4
(2) and [Ru(j3-dapmoH)Cl(AsPh3)2]Cl (3) were isolated
from the reactions of [RuCl2(EPh3)3] (E = P, As), [(g5-
C5H5)RuCl(EPh3)2] (E = P, As), [(g5-C5Me5)RuCl(PPh3)2]
and [(g5-C9H7)RuCl(PPh3)2], respectively, with dapmoH
in methanol under refluxing conditions. In this paper, we
present reproducible syntheses and spectral characteriza-
tion of ruthenium compounds with the general formula-
tions [Ru(j3-dapmoH)Cl(EPh3)2]+ (E = P, As). We also
describe herein the crystal structures of representative com-
pounds 1 and 2 and encapsulation of water dimer in D2
pattern and trimer in D3 pattern in the molecular cages
of 1 and 2 assisted by counter ions.
2. Experimental
2.1. Materials and physical measurements
All the synthetic manipulations were performed under
nitrogen atmosphere. The solvents were of AR grade
and were purified rigorously by standard procedures
prior to their use [11]. Ammonium hexafluorophosphate,
ammonium tetrafluoroborate, 2,6-diacetylpyridine, ruthe-
nium(III) chloride hydrate (all Aldrich) were used as
received without further purifications. The precursor
complexes [RuCl2(EPh3)3] (E = P, As), [(g5-C5H5)Ru-
Cl(EPh3)2] (E = P, As), [(g5-C5Me5)RuCl(PPh3)2] and
[(g5-C9H7)RuCl(PPh3)2] were synthesized following the
literature methods [12]. 2,6-diacetylpyridinemonoxime
(dapmoH) was synthesized following the method of Turn-
bull et al., using 2,6-diacetylpyridine and hydroxylamine
hydrochloride [13].
Compound 1 was also obtained from the reactions of
ruthenium arene complexes [(g5-C5H5)RuCl(PPh3)2], [(g5-
C5Me5)RuCl(PPh3)2] and [(g5-C9H7)RuCl(PPh3)2] with
2,6-diacetylpyridinemonoxime following the above
procedure.
Elemental analyses were performed by Micro-analytical
section of the Sophisticated Analytical Instrumentation
Centre, Central Drug Research Institute, Lucknow. IR in
KBr discs and electronic spectra were recorded on a Shima-
dzu-8201PC and Shimadzu-UV-1601 spectrophotometers,
2.2.2. [Ru(j3-dapmoH)Cl(PPh3)2]BF4ꢁ1.5H2O (2)
The compound 2 was prepared following the above pro-
cedure for 1 using NH4BF4 instead of NH4PF6. Yield:
0.74 g (78%). Anal. Calc. for BC45F4H40ClN2O3.50P2Ru
(950): C, 56.84; H, 4.21; N, 2.94%. Found: C, 56.86; H,
4.17; N, 2.88%. IR (KBr): m/cmꢃ1 3404(b), 1678(w),
1596(m), 1454(s), 1432(m), 1358(m), 1248(w), 1161(w),
1142(s), 1094(s), 1045(s), 963(w), 818(m), 674(m), 662(w),
634(m), 356(m) cmꢃ1. dH (300 MHz; CDCl3; Me4Si)
10.16 (s, 1H, NAOH), 7.44 (d, J = 6.0 Hz, 2H, Py-3H
and 5H), 7.56 (d, J = 9.0 Hz, 1H, Py-4H), 7.36-6.98 (br
m aryl protons, PPh3), 2.21 (s, 2H, H2O), 1.59 (s, 3H,
CH3), 1.22 (s, 3H, CH3). dP (300 MHz; CDCl3; PCl3)
27.02 (s, PPh3). 13C{1H} NMR (d6-acetone): 155.97
[AC@NOH], 154.71 [py-1(6C)], 137.62 [py-4C], 130.09
[ACAPPh3] 120.50 [py-3(5C)], 10.09 [ACH3]. FAB-MS:
m/z 839(838), 24, [Ru(j3-dapmoH)Cl(PPh3)2]+, 577(577),
50, [Ru(j3-dapmoH)Cl(PPh3)]+, 315(316), 32, [Ru(j3-
1
respectively. H and 31P NMR spectra were acquired on
a Bruker DRX-300 NMR instrument. FAB mass spectra
were recorded on a JEOL SX 102/DA 6000 mass spectrom-
eter using Xenon (6 kV, 10 mA) as the FAB gas. The accel-
erating voltage was 10 kV and the spectra were recorded at
room temperature with m-nitrobenzyl alcohol as the
matrix. Electrochemical data were acquired on a BAS-
100 Epsilon Electrochemical Analyzer using TBAP as a
supporting electrolyte. The three electrode measurement
was carried out under nitrogen atmosphere with a platinum
working electrode, platinum wire auxiliary electrode and
calomel reference electrode. Luminescence spectra in the
solid state and solution were recorded on a Perkin-Elmer
LS-45 luminescence spectrophotometer.

138
M. Trivedi et al. / Journal of Molecular Structure 886 (2008) 136–143
dapmoH)Cl]+. UV/vis: kmax (CH2Cl2, e[dm3 molꢃ1 cmꢃ1])
404(7412), 232(43680).
0.35 ꢄ 0.30 ꢄ 0.25 (1) and 0.40 ꢄ 0.30 ꢄ 0.25 (2) in the
x ꢃ 2h scanning technique with 2h range 4.0–50.0°, respec-
tively. Intensities of these reflections were measured period-
ically to monitor crystal decay. The structure was solved by
direct methods and refined by full matrix least squares on
F2 (SHELX-97) [14]. In the final cycles of refinement all
the non-H atoms were treated anisotropically. The contri-
bution due to H-atoms attached to carbon atoms was
included as fixed contribution. Final value of
2.2.3. [Ru(j3-dapmoH)Cl(AsPh3)2]ClꢁH2O (3)
It was prepared following the above procedure for 1
except that [RuCl2(AsPh3)3] (1.090 g, 1.0 mmol) was used
in place of [RuCl2(PPh3)3] and was isolated as chloride salt.
Yield: 0.85 g (78%). Anal. Calc. for As2C45H42ClN2O3Ru
(980): C, 55.10; H, 4.28; N, 2.85%. Found: C, 55.47; H,
4.78; N, 2.52. IR (KBr): m/cmꢃ1 3395(b), 1675(w),
1590(m), 1454(s), 1438(m), 1350(m), 1240(w), 1155(w),
1140(s), 1090(s), 1018(s), 961(w), 810(m), 675(m), 650(w),
620(m), 360(m) cmꢃ1. dH (300 MHz; CDCl3; Me4Si)
10.24 (s, 1H, NAOH), 8.41 (d, J = 6.0 Hz, 2H, Py-3H &
5H), 7.78 (d, J = 9.0 Hz, 1H, Py-4H), 7.35–7.07 (br m aryl
protons, AsPh3), 2.28 (s, 2H, H2O), 1.77 (s, 3H, CH3), 1.45
(s, 3H, CH3). 13C{1H} NMR (d6-acetone): 155.80
[AC@NOH], 154.65 [py-1(6C)], 137.62 [py-4C], 128.20
[ACAPPh3] 120.50 [py-3(5C)], 10.19 [ACH3]. FAB-MS:
R1 = 0.0433, GOF = 1.043 for
1
and R1 = 0.0631,
GOF = 1.031 for 2.
3. Results and discussion
3.1. Synthesis
[RuCl2(EPh3)3] (E = P, As) reacted with 2,6-diac-
etylpyridinemonoxime (dapmoH) in methanol under
refluxing conditions to afford compounds 1–3 as shown
in Scheme 1. Furthermore, reactions of the ruthenium com-
plexes containing g5-bonded hydrocarbon ligands with
dapmoH were also examined under analogous conditions.
Surprisingly, reactions of the ruthenium g5-C5H5, g5-
C5Me5 and g5-C9H7 complexes [(g5-C5H5)RuCl(PPh3)2],
[(g5-C5Me5)RuCl(PPh3)2] and [(g5-C9H7)RuCl(PPh3)2]
with dapmoH also led to the formation of compound 1
in good yield, while reaction of [(g5-C5H5)RuCl(AsPh3)2]
gave compound 3. Interestingly, in these reactions rather
strong ruthenium to g5-C5H5, g5-C5Me5 or g5-C9H7 bonds
were broken and dapmoH interacted with the metal centre
through the major coordination sites in the j3-mode.
Substitution of the g5-bonded C5H5, C5Me5 and C9H7
groups by dapmoH may be attributed to the stronger r
donor ability of the latter as compared to the g5-bonded
m/z
927(926),
25,
[Ru(j3-dapmoH)Cl(AsPh3)2]+,
891(890), 30, [Ru(j3-dapmoH)(AsPh3)2]+. UV/vis: kmax
(CH2Cl2, e[dm3 molꢃ1 cmꢃ1]) 438(6286), 232(29805).
Compound 3 was also synthesized by reaction of [(g5-
C5H5)RuCl(AsPh3)2] with 2,6-diacetylpyridinemonoxime
following the above procedure.
2.3. X-ray crystallographic study
Crystals suitable for single crystal X-ray diffraction
analyses for 1 and 2 were obtained from CH2Cl2/petroleum
ether (60–80°) at room temperature. Intensity data were
collected at 293(2) K on Enraf-Nonius CAD 4 diffractom-
eter using graphite monochromatised Mo-Ka radiation
(k = 0.70930) from plate-like crystals with the dimensions
Ru
Ph3E
Cl
Ph3E
L, MeOH, Δ
X
N
L, MeOH, Δ
L, MeOH, Δ
O
N
Ru
Ru
OH
Ru
Cl
Ph3E
Ph3E
Cl
Cl
Ph3E
Ph3E
EPh3
Ph3E
L, MeOH, Δ
[RuCl2(EPh3)3]
Scheme 1.
E = P; X = PF6 1; X = BF4 2
E = As; X = Cl 3
N
L =
O
N
OH

M. Trivedi et al. / Journal of Molecular Structure 886 (2008) 136–143
139
hydrocarbon ligands. This observation is consistent with
earlier reports [15].
TBAP at 27 °C. Both the compounds displayed quasi-
reversible redox waves corresponding to Ru(II)/Ru(III)
oxidation couple at 1.23 and 1.20 V with peak-to-peak sep-
aration of 51 and 76 mV, respectively, for 1 and 2. The
ligand based quasi-reversible reduction couples were
observed at ꢃ1.38, 0.75 and ꢃ1.38, 0.78 V vs. SCE in 1
and 2, respectively. In the electronic absorption spectrum
of 1, 2 and 3, the MLCT transitions appeared in visible
region at 406, 404 and 438 nm and the ligand-centred tran-
sitions were observed at 236, 232 and 232 nm, respectively.
3.2. Characterization
Compounds 1–3 are air stable solids and does not show
any signs of decomposition in solution even exposure to air
for several days. These were fully characterized by IR,
NMR (1H, 13C and 31P), UV–vis, FAB-MS spectroscopy.
Analytical data of the compounds (recorded in Section 2)
corroborated well to their formulations. FAB-MS spectra
of the compounds corresponded to their respective formu-
lations. Infrared spectra of the compounds in Nujol dis-
played bands due to oxime m(C@N) and m(NAO) at
1590–1596 cmꢃ1 and 1090–1094 cmꢃ1, while the band due
to carbonyl m(C@O) appeared at 1675–1678 cmꢃ1. This
indicated coordination of dapmoH ligand with the metal
centre in j3-mode through its major coordination sites.
Broad bands in the region 845 and 1045 cmꢃ1 have been
3.3. X-ray crystallography
The molecular structures of 1 and 2 were determined
crystallographically.Perspective view of the cations of 1
and 2 with the atomic labels are shown in Fig. 1. Details
about the data collection, solution and refinement are
enlisted in Table 1 and selected bond lengths and angles
are recorded in Table 2. Compounds 1 and 2 crystallize
in monoclinic crystal systems, but with different space
groups P21/c and C2/c, respectively. The Ru(II) centres
in both the 1 and 2 adopted distorted octahedral geometry
by coordinating to dapmoH ligand in NNO j3-mode, two
ꢃ
ꢃ
assigned to counter anion PF6 and BF4
.
1H and 13C NMR spectra gave expected integration pat-
terns and suggested coordination of dapmoH with ruthe-
nium in the j3-manner. 31P{1H} NMR spectra of 1 and 2
showed a single resonance at ꢂ27 ppm assignable to the
metal-bound 31P nuclei. It suggests that both the 31P nuclei
are chemically equivalent and triphenylphosphine ligands
are trans disposed [16]. The signal assꢃociated with 31P
triphenylphosphine and
N(1)ARu(1)AN(2) and N(1)ARu(1)AO(1) in
a
Cl atom. The angles
are
1
79.26(15)° and 75.92(14)°, while those in 2 are 78.0(2)°
and 77.7(2)°, respectively. The N(2)ARu(1)AO(1) angles
in 1 and 2 are 155.18(15)° and 155.7(2)°, respectively, and
the RuAP distances and PARuAP angles in 1 and 2 are
essentially equal and comparable to the reported ones
[16]. Ruthenium to pyridyl nitrogen Ru(1)AN(1) bonds
nuclei of the counter anion PF6
appeared at
ꢃ141.22 ppm in its characteristic septet pattern. Electro-
chemical behavior of 1 and 2 were followed by cyclic vol-
tammetry in acetonitrile solutions containing 0.1 M
Fig. 1. ORTEP view of the complex cation of 1 with thermal ellipsoids shown at the 30% level; hydrogen atoms were omitted for clarity.

140
M. Trivedi et al. / Journal of Molecular Structure 886 (2008) 136–143
Table 1
while compound 2 displays interlocking of two cationic
moieties by strong CAHꢁ ꢁ ꢁp intermolecular interactions
where the molecular cavꢃity is located in the space of these
dimeric cations and BF4 ions do not participate in active
interactions. It shoꢃuld be noted that, although most of fluo-
ride atoms of PF6 ions in 1 participated in non-covalent
interactions, two distinct bifurcated CAHꢁ ꢁ ꢁF interactions
incurred by two trans-fluoride atoms (F2 and F4) deter-
mine the geometry of observed cavity in 1.
Crystallographic data and refinement parameters for 1 and 2
1
2
Empirical Formula
Molecular weight
Color and habit
Crystal size (mm)
Space group
C45H42ClF6N2O3P3Ru C45H40BClF4N2O3.5P2Ru
1002.24
950.06
Brown, needles
0.35 ꢄ 0.30 ꢄ 0.25
P21/c
Monoclinic
11.672(2)
20.189(4)
19.576(4)
104.71(3)
4462.0(15)
4
Brown, blocks
0.40 ꢄ 0.30 ꢄ 0.20
C2/c
Monoclinic
21.851(2)
11.916(2)
35.414(3)
101.707(7)
9029.2(13)
8
System
˚
a (A)
˚
b (A)
Interestingly, the guest water molecules trapped in
the molecular cavity of 1 are congregated together to
form a water dimer in D2 pattern with intermolecular
OAHꢁ ꢁ ꢁO hydrogen-bonding interactions [O1WAAH1-
WAꢁ ꢁ ꢁO1W#1] but, lacking any interaction with the host
cations. Geometrical parameters of the water dimer are
recorded in Table 3. It should be noted that the Oꢁ ꢁ ꢁO sep-
˚
c (A)
b (°)
3
˚
V (A )
Z
dcalc (g cmꢃ3
)
1.492
0.586
293 (2)
8206/7806
1.398
0.536
293 (2)
8080/7937
l (mmꢃ1
)
Temperature (K)
Reflections
collected/unique
˚
aration in the dimer is 2.808 A, which is comparable to that
˚
˚
in regular ice (2.74 A), liquid water (2.85 A) and in the
R1 factor [I > 2r(I)] 0.0443
0.0631
0.1809
0.1535
1.031
˚
vapor phase (2.89 A) [9a]. Theory and calculations are in
wR2
wR2 [I > 2r(I)]
Goodness of fit
0.1068
0.1310
1.043
fairly good agreement with the trans-linear structure of
water dimer determined by Dyke et al. [10a,10b]. The water
dimer in 1 has (Fig. 2a) a cyclic structure (D2 pattern) sim-
ilar to the one reported for water polymers (H2O)n wherein
each monomer acts both as single donor and acceptor, and
the two free hydrogen atoms oriented above and below the
ring, respectively [10]. It is well established that by judi-
cious choice of the counter ion, distinct framework geom-
etries can be designed [20a,20b]. The hydrogen-bonding
Table 2
˚
Selected bond length (A), bond angles (°) and torsion angles (°) in 1 and 2
1
2
Ru(1)ACl(1)
Ru(1)AP(1)
Ru(1)AP(2)
Ru(1)AN(1)
Ru(1)AN(2)
Ru(1)AO(1)
O(2)AN(2)
N(2)ARu(1)AN(1)
O(1)ARu(1)AN(1)
N(2)ARu(1)AO(1)
N(2)ARu(1)ACl(1)
N(1)ARu(1)ACl(1)
O(1)ARu(1)ACl(1)
P(2)ARu(1)ACl(1)
P(1)ARu(1)ACl(1)
P(2)ARu(1)AP(1)
2.4920(14)
2.3402(12)
2.3711(12)
1.970(4)
2.025(3)
2.104(3)
2.4630(17)
2.391(2)
2.3768(19)
1.935(5)
2.011(5)
2.096(5)
1.391(7)
78.0(2)
77.7(2)
155.7(2)
93.53(16)
171.51(16)
110.73(17)
88.81(6)
ꢃ
strength for PF6 is slightly higher than BF4ꢃ, it corre-
sponds well with the observedꢃ compactnessꢃ in
1
[20a,20b,20c]. Replacing anion PF6 of 1 by BF4 leads
to a completely different motif in 2. In absence of any
bridging co-operative interaction, compound 2 shows the
formation of a loose cavity, encapsulating linear water tri-
mers (D3 pattern) (Fig. 2b). Closer look revealed an abso-
lute linear arrangement (180°) in D3 pattern for three of
the water molecules with the central water molecule, keep-
ing it as the symmetry centre to two terminal water mole-
1.398(5)
79.26(15)
75.92(14)
155.18(15)
92.20(12)
171.44(11)
112.61(11)
92.48(5)
83.07(5)
175.05(4)
87.69(6)
175.60(6)
Table 3
0
ꢀ
Hydrogen bond distances [A] and angles [°] for 1 and 2
DAHꢁ ꢁ ꢁA
1
d(Hꢁ ꢁ ꢁA)
d(Dꢁ ꢁ ꢁA)
<(DHA)
˚
are 1.970(4) and 1.935(5) A and ruthenium oxime nitrogen
˚
Ru(1)AN(2) bonds are 2.025(3) and 2.011(5) A, respec-
tively. All RuAN, RuAO and RuACl bonds fall into nor-
mal ranges [17,18].
O(1W)AH(1WA)ꢁ ꢁ ꢁO(1W)#1
C(35)AH(35)ꢁ ꢁ ꢁF(2)#2
C(39)AH(39)ꢁ ꢁ ꢁF(1)#3
C(43)AH(43A)ꢁ ꢁ ꢁF(2)
C(40)AH(40)ꢁ ꢁ ꢁF(4)
C(11)AH(11)ꢁ ꢁ ꢁF(4)
O(2)AH(2A)ꢁ ꢁ ꢁCl(1)
2.69
2.42
2.65
2.48
2.52
2.64
2.64
2.808(9)
3.216(6)
3.206(7)
3.428(8)
3.053(6)
3.075(6)
3.286(4)
90
144
119
170
117
110
137
Directionality and specificity of hydrogen bonding rec-
ognized it as a powerful tool for designing molecular
frameworks. In addition to traditional hydrogen bonding,
charge-assisted co-operative interactions have inherent
effect on overall geometry of the framework. Such interac-
tions are strong and occur in ionic or zwitterionic systems.
Compounds 1 and 2 exhibit strong intra- and intermolecu-
lar CAHꢁ ꢁ ꢁX (F, Cl, O, N or p) interactions [19]. PF6ꢃ ions
in 1 undergo bifurcated CAHꢁ ꢁ ꢁF interactions with the
phenyl hydrogen atoms to form a compact rectangular cav-
ity where four cationic units are head-to-tail linked [20],
2
C(5)AH(5)ꢁ ꢁ ꢁpA
2.73
2.82
3.571(3)
5.651(4)
151
180
O(1W)aꢁ ꢁ ꢁO(2W)ꢁ ꢁ ꢁO(1W)b
Symmetry operations for 1: #1 x,y,z; #2 ꢃx + 1,ꢃy + 1,ꢃz + 2; #3
a
ꢃx + 1,y + 1/2,ꢃz + 1/2; #4 x,ꢃy + 3/2,z + 1/2; 2: ꢃx + 3/2, ꢃy + 3/2,
ꢃz + 1; bx,y,z ꢃ 1.
A
Centroid
of
the
phenyl
ring
represented
by
C(25)AC(26)AC(27)AC(28)AC(29)AC(30).

M. Trivedi et al. / Journal of Molecular Structure 886 (2008) 136–143
141
Fig. 2. (a) Encapsulated water dimer in 1 and its close view, and (b) water trimer in 2 and its close view.
˚
cules. In this trimer the Oꢁ ꢁ ꢁO separation is 2.825(19) A
[21]. Similar to the water dimer in 1, the water molecules
from the trimer also lack any intermolecular interactions
with its host. The shortening of Oꢁ ꢁ ꢁO distance indicated
stronger H-bonding interactions due to the co-operative
nature of hydrogen bonding [9a]. The Oꢁ ꢁ ꢁO distance of
water dimer in 1 is lower than water trimer in 2, indicated
that the water dimers are more stable because of tightly
held hydrogen bonding than the water trimers in com-
concluded that position of the emission peak and emis-
sion intensity in 1 and 2 strongly depends on polarity
of the solvent. The solvent effect varies not only with
˚
˚
pound 2 (Oꢁ ꢁ ꢁO 2.808 A vs. 2.825 A).
3.4. Luminescence properties
Compounds 1 and 2 are luminescent at room temper-
ature both in the solid state and in solution. In the solid
state 1 and 2 shows a yellow-orange emission at kem
566 nm (kex = 404 nm) (Fig. 3a) which is significantly
blue shifted by ꢂ56 nm in solution (Fig. 3b). The non-
structured solid state emission band can be attributed
to the metal to ligand (MLCT) electron transition and
the blue-green emission of 1 and 2 in solution is believed
to be associated with deactivation of the intermolecular
interactions and segregation of superstructure into indi-
vidual molecules [22]. Furthermore, it is interesting to
observe the solid state emission intensity of 79.8 a.u.
for 1 is significantly reduced to 53.7 a.u. for 2 suggesting
that the crystal packing in 1 is more tightly held than in
2 [23]. In addition to the compactness of the framework,
the encapsulated water trimer in the loosely bound
framework of 2 induces solvent quenching in a more
pronounced way than that of the compact framework
for 1. To have an idea about the solvent dependency,
emission spectra were acquired in the solvents of varying
polarity viz., methanol, dimethylsulfoxide, acetonitrile,
acetone and chloroform. Excitation and emission spectra
of 1 and 2 in dichloromethane is shown in Fig. 3b. A
distinct bathochromic shift of the emission bands were
observed in polar solvents. Furthermore, along-with the
Fig. 3. (a) Emission spectra of 1 and 2 in the solid state (kex 404 nm), and
(b) excitation spectra and emission (kex 404 nm) for 1 (kem 510 nm) and 2
(kem 490 nm) in dichloromethane.
generation of
a secondary peak, emission intensity
quenched with an increase in the solvent polarity. It is

142
M. Trivedi et al. / Journal of Molecular Structure 886 (2008) 136–143
5. Supplementary data
Crystallographic data for the structures reported in this
paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication Nos.
CCDC numbers 623811 (1) and 623812 (2). Copies of this
information can be had free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB2 IEZ, UK (fax:
+44-1223-336033; e-mail: deposit@ccdc.com.ac.uk or
www: http://www.ccdc.com.ac.uk).
Acknowledgements
Financial support from the Council of Scientific and
Industrial Research (CSIR), New Delhi, India [HRDG,
01(1784)/02/EMR-II], AIST Osaka and JSPS of Japan is
gratefully acknowledged. We also thank the Head, SAIF,
Central Drug Research Institute, Lucknow for analytical
and spectral data and Prof. P. Mathur, Department of
Chemistry, Indian Institute of Technology, Bombay for
single crystal X-ray measurements.
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