Synthesis of 4′-substituted-2,2′;6′,2″-terpyridine Ru(II) complexes electrochemical, fluorescence quenching and antibacterial studies

Article abstract of DOI:10.1016/j.molstruc.2016.12.102

Three new Ru(II) terpyridine complexes viz. [Ru(BBtpy)₂](PF₆)₂ [Ru(L1)] (BBtpy?=?4′-(4-benzyloxybenzaldehyde)-2,2′:6′,2″-terpyridine), [Ru(BMBtpy)₂](PF₆)₂ [Ru(L2)] (BMBtpy?=?4′-(4-benzyloxy

Full text of DOI:10.1016/j.molstruc.2016.12.102

Accepted Manuscript
Synthesis of 4′-substituted-2,2′;6′,2″-terpyridine Ru(II) complexes electrochemical,
fluorescence quenching and antibacterial studies
Tamilarasu Ezhilarasu, Anbazhagan Sathiyaseelan, Pudupalayam Thangavelu
Kalaichelvan, Sengottuvelan Balasubramanian
PII:
S0022-2860(16)31421-1
10.1016/j.molstruc.2016.12.102
MOLSTR 23300
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 2 November 2016
Revised Date: 28 December 2016
Accepted Date: 29 December 2016
Please cite this article as: T. Ezhilarasu, A. Sathiyaseelan, P.T. Kalaichelvan, S. Balasubramanian,
Synthesis of 4′-substituted-2,2′;6′,2″-terpyridine Ru(II) complexes electrochemical, fluorescence
quenching and antibacterial studies, Journal of Molecular Structure (2017), doi: 10.1016/
j.molstruc.2016.12.102.
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Synthesis of 4'-substituted-2,2';6',2"-terpyridine Ru(II) complexes
Electrochemical, Fluorescence quenching and antibacterial studies
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Tamilarasu Ezhilarasu , Anbazhagan Sathiyaseelan , Pudupalayam Thangavelu
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Kalaichelvan , Sengottuvelan Balasubramanian *
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Department of Inorganic Chemistry, Guindy Campus, University of Madras, Chennai-600 025,
Tamilnadu, India.
CAS in Botany, Guindy Campus, University of Madras, Chennai-600 025, Tamilnadu, India.
Corresponding Author: Dr. S.Balasubramanian, Tel: +91-44- 2220 2794,
Email: bala2010@yahoo.com
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Abstract
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Three new Ru(II) terpyridine complexes viz. [Ru(BBtpy) ](PF ) [Ru(L1)] (BBtpy = 4'-
2
6 2
(4-benzyloxybenzaldehyde)-2,2':6',2"-terpyridine), [Ru(BMBtpy)
2
](PF
6
)
2
[Ru(L2)] (BMBtpy =
6 2
[Ru(BEBtpy) ](PF )
4'-(4-benzyloxy-3-methoxybenzaldehyde)-2,2':6',2"-terpyridine)
and
2
[Ru(L3)] (BEBtpy = 4'-(4-benzyloxy-3-ethoxybenzaldehyde)-2,2':6',2"-terpyridine) have been
synthesized and characterized. The MALDI-TOF/MS fragmentation pattern of
2
+
[Ru(BMBtpy) ](PF ) complex exhibits a molecular ion peak at m/z = 987.09 [M-2PF ]
2
6 2
6
fragment. These Ru(II) complexes are redox active, show both metal centered oxidation and
ligand centered reduction processes. The peak potential and peak current I and I also undergo
pa
pc
definite shift and increase with increase in the scan rate (20-120 mV/s). The fluorescence of
Ru(II) complexes [Ru(L1)], [Ru(L2)] and [Ru(L3)] are effectively quenched by 1,4-
benzoquinone and 1,4-naphthoquinone in acetonitrile. The antibacterial activity of ruthenium(II)
complexes were screened against four human pathogens both gram-positive bacteria (Bacillus
subtilis, Staphylococcus aureus) and gram negative bacteria (Escherichia coli, Klebsiella
pneumonia) by the well diffusion method. The antibacterial activity of Ru(II) complexes is
comparable to that of standard antibiotics like tetracycline.

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Keywords: Terpyridine; Ruthenium(II) complex; Spectral study; Thermal study; Cyclic
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voltammetry; Antibacterial activity
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1. Introduction
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2,2';6',2"-terpyridine(tpy) derivatives are chelating ligands suitable for the formation of
transition metal complexes [1]. The introduction of different functional groups at 4ʹ- position of
2,2':6',2''-terpyridine results in the modification of photophysical properties of the complexes.
The two tpy ligands chelate a ruthenium(II) ion in octahedral complexes and they are also known
to form stable bis-terpyridine complexes with other transition metal ions [1-3]. Ruthenium(II)
complexes with terpyridine derivatives play an important role in the field of macromolecular
chemistry, photochemistry, supramolecular chemistry, nanoscience, photophysics and catalysis
[4,5]. Ruthenium(II) terpyridine complexes are used in biochemical applications including the
DNA-binding and cleavage agents for non-covalent interactions, groove binding and
intercalative binding [6,7].
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+
2+
The [Ru(tpy) ] and [Ru(bpy) ] complexes have attracted the attention of researchers,
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because of unique combination of excited state reactivity, chemical stability, redox properties,
luminescence and excited state life time. The photosensitizer is covalently linked with electron
donating and accepting units [8,9]. Metal and metal based drugs play an important role in the
field of medicinal chemistry. Ruthenium complexes also exhibit significant antibacterial activity,
which is related to the chemical structure and biological properties. The antimicrobial activity of
ruthenium complexes depends on the lipophilicity, charge and charge separation. These
complexes are more active in both bacteria and eukaryotic cells when simultaneously increasing
lipophilicity and charge separation [10]. Ruthenium complexes strongly bind to nucleic acids and
proteins, ligand exchange properties similar to platinum counterparts, accessible oxidation states

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(II and III) and its ability to mimic iron in binding to biological molecules [11,12]. Ruthenium
complexes exhibit various biological activities such as toxicity in mice, inhibition of enzyme
acetylcholinesterase and bactericidal action towards Escherichia coli and Staphylococcus
haemolyticus [13].
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[Ru(mttpy) ](PF ) and [Ru(mttpy)(MeOPhttpy)](PF ) complexes showed very good
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antibacterial and antifungal activity against human pathogens with minimum inhibitory
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concentration (MIC) lying in the range of 10–20 mg ml which is better than that of standard
tetracycline and carbendazim [14]. The dinuclear polypyridyl ruthenium(II) complexes ∆∆/ΛΛ-
4
+
[{Ru(phen) } {m-bbn}] {where phen = 1,10-phenanthroline; bbn = bis[4(4'-methyl-2,2'-
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-1
bipyridyl)]-1 exhibit high activity, with MIC values of 1 mg ml against both S. aureus and
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MRSA, and 2–4 and 8–16 mg ml respectively against E. coli and P. aeruginosa and it is
considered less toxic to human eukaryotic cells [15]. [Ru(dmob) ]Cl (dmob = 4,4'-dimethoxy-
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-1
2,2'-bipyridine) complex shows good antimicrobial activity (MIC = 12.5 mg ml against
Pseudomonas aureus) and is employed in photodynamic antimicrobial chemotherapy [16].
In the present investigation, three new ruthenium terpyridine complexes viz.,
[Ru(BBtpy) ](PF ) (1), [Ru(BMBtpy) ](PF ) (2) and [Ru(BEBtpy) ](PF ) (3) have been
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synthesized and characterized by UV-Visible, Fluorescence, FT-IR, NMR and Mass spectral
studies as well as by TGA and electrochemical studies. All the three complexes are evaluated by
fluorescence quenching and antibacterial activity.
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2. Experimental
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2.1. Materials and methods

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2-Acetylpyridine (AR), p-Tolualdehyde (AR), N-bromosuccinimide (AR), N-
ethylmorpholine (AR) were obtained from Sigma-Aldrich. Sodium hydroxide (AR), Ruthenium
trichloride monohydrate (RuCl .H O) (AR), Potassium hexafluorophosphate (KPF ) (AR) were
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purchased from SRL. Ammonium acetate (AR), Poly(ethyleneglycol) (PEG300) (AR),
Benzoquinone, Naphthoquinone, anhydrous Sodium sulfate were purchased from Merck.
Azobis(isobutyronitrile) (AIBN) (AR) and Tetrahydrofuran(LR) were purchased from Thomas
Baker. Ethanol (AR), Carbon tetrachloride (LR), Ammonia and Methanol (commercial) were
purchased from Merck. Acetonitrile (LR) and Perchloric acid (AR) were obtained from
Qualigens. Mueller-Hinton agar (MHA) and antibiotic Tetracycline were obtained from Himedia
and other laboratory chemicals and solvents from Rankem and Qualigens.
Melting points were determined by open capillary tube method using Raaga melting point
apparatus and they were uncorrected. The UV-Visible spectra were recorded on Perkin-Elmer
-5
Lambda 35 in the range of 200-800 nm. Fluorescence studies were carried out in 10 M
concentration of Ru(II) complexes in acetonitrile solution at room temperature. The emission
spectra were recorded on Perkin-Elmer LS 50 spectrofluorimeter. The emission quantum yield of
ruthenium(II) complexes were calculated according to the Eq. 1.
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Where, Ф is a fluorescence quantum yield, A is absorption intensity, S is integrated emission
f
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band area and n is solvent refractive index, u and s represent the unknown and standard [17].
Rhodamine was used as a reference standard in ethanol solution. The FT-IR spectra were
recorded on a Bruker Tensor-27 FT-IR spectrometer. The sampling was done by making use of
KBr pellets with required amount of sample. Pure KBr pellet was used to perform background

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calibrations. All the measurements were carried out between 4000-400 cm at 27 C. H and C
NMR spectra of the terpyridine ligands and ruthenium(II) complexes were measured by using a
Bruker NMR spectrometer operating at 500 MHz and 125 MHz respectively. Tetramethylsilane
was used as standard for all the measurements. Electrospray mass spectra (ESI/MS) were
obtained on a LCQ Fleet, Thermo Fisher instruments limited. The samples were dissolved in
acetonitrile and introduced into the ESI source through a syringe pump. Matrix-assisted laser
desorption ionization time-of-flight mass spectroscopy (MALDI-TOF/MS) was performed on a
Applied Biosystems 4700 Proteomics Analyzer 72015. 2,5-Dihydroxy benzoic acid was used as
the matrix for MALDI-TOF/MS analysis. Cyclic voltammetry was carried on a CH1 620A
electrochemical analyzer. The measurements were carried out under oxygen free condition, using
a three-electrode cell assembly in which a glassy carbon electrode was the working electrode, a
saturated Ag/AgCl electrode was reference electrode and platinum wire was used as the auxiliary
electrode. The electrochemical data were obtained in aqueous medium containing 0.1 M Tetra
(n-butyl) ammonium perchlorate (TBAP) as a supporting electrolyte.
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2.2. Synthesis of 4-substituted terpyridine ligands
2.2.1. Synthesis of 4ʹ-(4-Methylphenyl)-2,2ʹ:6ʹ,2ʺ-terpyridine (ttpy)
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Ttpy was synthesized by following the previously reported method [14,18]. 2-
Acetylpyridine (2.31 ml, 20.65 mmol) was added to a mixture of crushed NaOH (0.825 g, 20.65
mmol) in PEG300 (17 ml) and stirred at 0˚C for 10 min. p-Tolualdehyde (1.22 ml, 10.33 mmol)
was added and the reaction mixture was stirred at 0˚C for 2 h. After 2 h, NH OAc (5 g, 64 mmol)
4
was added in excess and the mixture was heated at 95 °C for 2 h. During this time, the color of

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the mixture changed from reddish orange to reddish brown. Then millipore water (50 ml) was
added to the reaction mixture and the viscous yellow precipitate of 4ʹ-(4-methylphenyl)-
2,2ʹ:6ʹ,2ʺ-terpyridine was isolated by filtration, washed with water, cold ethanol and dried under
vacuum.
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Yield: 1.8 g, 53%, mp 159 °C; UV-VIS (DMF); λmax nm (ԑ/L mol cm ): 279 (71 193); IR (KBr
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disc ѵ/cm ): 3460, 1581; H NMR (500 MHz, CDCl ) δ : 2.46 (s, 3H), 7.34-7.39 (m, 5H), 7.85-
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7.91 (m, 4H), 8.69-8.777 (m, 5H); C NMR (125 MHz, CDCl ) δ: 21.27, 118.74, 121.45,
123.79, 127.18, 129.67, 135.46, 136.98, 139.13, 149.02, 150.25, 155.77, 156.29; ESI-MS: m/z
+
324(M+H) ; Anal. Calc for: C22
H
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N
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(323.39 g / mol).
2.2.2. Synthesis of 4′-(4-Bromomethylphenyl)-2,2′:6′,2′′-terpyridine (Brttpy)
Brttpy was synthesized by following the reported method [19]. A mixture of 4′-(4-
methylphenyl)-2,2′:6′,2′′-terpyridine (1.0 g, 3.1 mmol), N-bromosuccinimide (NBS, 0.669 g, 3.7
mmol), and α,αʹ-azobis(isobutyroniltrile) (AIBN, 0.040 g, 0.24 mmol) in dry CCl (20 ml) was
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refluxed for 3 h. The warm reaction mixture was filtered to remove succinimide and the solvent
was evaporated under reduced pressure. The crude product was recrystallized from EtOH to give
a pale-yellow solid.
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Yield: 1.1042 g, 88%, mp: 153 °C; UV-VIS (DMF); λmax nm (ԑ/L mol cm ): 291
-1
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(20 240); IR (KBr disc ѵ/cm ): 1577, 1260, 789; HNMR (500 MHz, CDCl ) δ: 4.59 (s, 2H),
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7.39-7.4 (m, 3H), 7.57 (d, J= 5 Hz), 7.92-7.96 (m, 4H), 8.77 (dd, J=10 Hz): C NMR (125 MHz,
CDCl ) δ: 32.93, 118.91, 119.02, 121.58, 121.64, 123.99, 127.20, 127.80, 129.68, 137.27,
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138.45, 138.73, 148.89, 149.62, 155.72, 155.83; ESI-MS: m/z 403 (M+H) ; Anal. Calc for:
22 3
C H16BrN (402.29 g / mol).

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2.2.3. Synthesis of 4′-(4-Benzyloxybenzaldehyde)-2,2′:6′,2′′-terpyridine (BBtpy) (L1)
To a solution of 4-hydroxybenzaldehyde (0.242 g, 1.98 mmol) in 6 ml of dry DMF were
added anhydrous potassium carbonate (0.305 g, 2.2 mmol) and Brttpy (0.8 g, 1.98 mmol). The
ᵒ
reaction was stirred at 80 C for 24 h, and the reaction mixture was cooled then poured into 100
ml of water and extracted with ethyl acetate. The combined organic phases were washed with
water, brine solution and dried over anhydrous sodium sulfate and the solvent was evaporated on
a rotary evaporator. The residue was purified by column chromatography (neutral alumina,
hexane/ethyl acetate = 4:1) to give the product as a yellow solid [20].
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Yield: 0.68 g, 77%, mp: 164°C; UV-VIS (CHCl ); λ nm (ԑ/L mol cm ): 256
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max
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(84 490), 281(121 090), 312(27 360); IR (KBr disc ѵ/cm ): 2744, 2819, 1591; HNMR (300
MHz, CDCl ) δ: 9.82(1H, s, -CHO), 8.66(4H, d, J=5.4Hz), 8.60(2H, d, J=8.1Hz), 7.88-7.77(7H,
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m), 7.49(2H, d, J=7.8Hz), 7.28(2H, t, J=6.94Hz), 7.03(2H, d, J=8.4Hz), 5.15(2H, s, -OCH2);
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C NMR (75 MHz, CDCl ) δ: 189.76, 162.61, 155.15, 155.00, 148.67, 148.12, 137.55, 135.89,
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135.82, 131.01, 129.23, 126.92, 126.69, 122.87, 120.37, 117.82, 114.20, 68.87; ESI-MS: m/z =
+
444.17 (M+H) ; Anal. Calc for: C29
H
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N
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O
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(443.50 g / mol).
2.2.4. Synthesis of 4′-(4-Benzyloxy-3-methoxy benzaldehyde)-2,2′:6′,2′′-terpyridine (BMBtpy)
(L2)
This compound was prepared by a procedure similar to the preparation of BBtpy using 4-
hydroxy-3-methoxy-benzaldehyde (0.228 g, 1.5 mmol), potassium carbonate (0.222 g, 1.6
mmol), Brttpy (0.6 g, 1.5 mmol), and 6 ml of dry DMF; yellow solid.

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Yield: 0.58 g, (81%); mp 170 °C; UV-VIS (CHCl
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); λmax nm (ԑ/L mol cm ): 254(66 563),
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279(87 426), 310(41 335); IR (KBr disc ѵ/cm ): 2852, 2920, 1590; HNMR (300 MHz, CDCl )
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δ: 9.76(1H, s, -CHO), 8.65(4H, s), 8.59(2H, d, J=8.1Hz), 7.86-7.77(4H, m), 7.49(2H, d,
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J=7.8Hz), 7.57-7.25(3H, m), 6.92(1H, d, J=8.1Hz), 5.24(2H, s, -OCH ), 3.90(3H, s,-OCH ); C
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NMR (75 MHz, CDCl ) δ: 189.83, 155.20, 155.01, 152.51, 149.21, 148.72, 148.13, 137.49,
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135.96, 135.85, 129.51, 126.70, 126.52, 125.51, 122.83, 120.35, 117.83, 111.67, 108.57, 69.58,
+
55.09; ESI-MS: m/z = 474.25 (M+H) ; Anal. Calc for: C30
H
23
N
3
O
3
(473.52 g / mol).
2.2.5. Synthesis of 4′-(4-Benzyloxy-3-ethoxy-benzaldehyde)-2,2′:6′,2′′-terpyridine (BEBtpy) (L3)
This compound was prepared by a procedure similar to the preparation of BBtpy using 4-
hydroxy-3-ethoxy-benzaldehyde (0.206 g, 1.24 mmol), potassium carbonate (0.185 g, 1.34
mmol), Brttpy (0.5 g, 1.24 mmol), and 6 ml of dry DMF; yellow solid
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Yield: 0.52 g, (86%); mp: 173 °C; UV-VIS (CHCl ); λmax nm (ԑ/L mol cm ): 255(85 140),
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279(113 350), 308(51 190); IR (KBr disc ѵ/cm ): 2861, 2979, 1587; HNMR (300 MHz,
CDCl ) δ: 9.83(1H, s, -CHO), 8.73(4H, s), 8.66(2H, d, J=7.8Hz), 7.93-7.84(4H, m), 7.57(2H, d,
J=7.8Hz), 7.44-7.84(4H, m), 6.99(1H, d, J=8.1Hz), 5.29(2H, s, -OCH ), 4.19(2H, q, J=13.65Hz,
-OCH ), 1.51(3H, t, J=6.9Hz, -CH ); C NMR (75 MHz, CDCl ) δ: 190.91, 156.24, 156.03,
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153.85, 149.77, 149.63, 149.15, 138.34, 137.27, 136.87, 130.60, 127.63, 127.59, 126.31, 123.86,
+
121.39, 118.84, 113.18, 111.17, 70.57, 64.69, 14.76; ESI-MS: m/z = 488.25 (M+H) ; Anal. Calc
for: C H N O (487.55 g / mol).
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2.3. Synthesis of ruthenium(III) complexes
2.3.1. [Ru(BBtpy)]Cl
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4′-(4-formylphenyl)-oxymethylphenyl-2,2′:6′,2′′-terpyridine (0.200 g, 0.45 mmol) was
added to RuCl .3H O (0.102 g, 0.45 mmol) in 20 ml ethanol and the reaction mixture was
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refluxed for 8 h under nitrogen atmosphere. The mixture was cooled and the dark brown
precipitate was filtered, washed with ethanol, diethyl ether and dried under vacuum [14].
Yield: 0.196 g (67%)
2.4. Synthesis of ruthenium(II) complexes
2 6 2
2.4.1. Synthesis of [Ru(BBtpy) ](PF ) [Ru(L1)]
[Ru(BBtpy) ](PF was synthesized by a methanolic solution of [Ru(BBtpy) ]Cl (0.154
2
6
)
2
2 3
g, 0.24 mmol) with BBtpy (0.105 g, 0.24 mmol) in few drops of N-ethylmorpholine was added
and refluxed for 8 h under nitrogen atmosphere. The reddish brown solution was filtered and the
excess of potassium hexafluorophosphate was added to the filtrate. After the reaction, the dark
reddish brown precipitate was filtered, washed with cold methanol, water, diethyl ether and dried
-1
-1
under vacuum. Yield: 0.276 g, 89%; UV-VIS (CH CN); λmax nm (ԑ/L mol cm ): 210(64 526),
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-1
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285(89 994), 308(72 415), 490(29 603); IR (KBr disc ѵ/cm ): 3055, 1595, 1404, 838; HNMR
(300 MHz, CDCl ) δ: 9.92(2H, s, -CHO), 9.47(4H, s), 9.08(4H, d, J=6Hz), 8.45(4H, t, J=7.5Hz),
8.06(6H, t, J=4.5Hz), 7.95(2H, d, J=6Hz), 7.85(4H, q, J=12Hz), 7.55(4H, d, 6Hz), 7.33-7.27(6H,
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m), 7.06(2H, d, J=9Hz), 5.47(3H, s, -OCH ); C NMR (75 MHz, CDCl ) δ: 191.43, 163.15,
2
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157.94, 155.01, 152.14, 138.04, 134.21, 131.85, 128.63, 128.36, 127.99, 127.71, 124.77, 121.11,
115.44, 115.07, 114.60, 62.48; MALDI-TOF/MS, (Dihydroxy benzoic acid matrix) m/z: 987.09
2
+
+
[M-2PF ] , 1133.03 [M-PF ] ; Anal. Calc for: C H F N O P Ru (1277.99 g / mol):
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58 42 12
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4 2
2 6 2
2.4.2. Synthesis of [Ru(BMBtpy) ](PF ) [Ru(L2)]

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This complex was prepared by a procedure similar to the preparation of
[Ru(BBtpy) ](PF ) [Ru(L1)] using [Ru(BMBtpy) ]Cl (0.130 g, 0.19 mmol), BMBtpy (0.090 g,
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0.19 mmol) in methanolic solution. Yield: 0.195 g (74%); UV-VIS (CH CN): λ nm (ԑ/L mol
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max
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cm ): 227(65668), 284(86588), 310(88156), 489(29029); IR (KBr disc ѵ/cm ): 3075, 1595,
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1401, 848; HNMR (300 MHz, CDCl ) δ: 9.89(2H, s, -CHO), 9.47(4H, s), 9.08(4H, d, J=6Hz),
3
8.47(4H, d, J=6Hz), 8.07(4H, t, J=6Hz), 7.86(4H, d, J=6Hz), 7.62(2H, d, J=6Hz), 7.56(4H, d,
J=6Hz), 7.50(2H, s), 7.38(2H, d, J=6Hz), 7.29(4H, t, J=4.5Hz), 5.46(4H, s, -OCH
2
), 3.92(6H, s, -
) δ: 191.52, 157.94, 155.03, 153.01, 152.16, 149.49, 146.57,
138.62, 138.04, 135.84, 129.99, 128.71, 127.87, 127.72, 125.80, 124.77, 121.12, 112.91, 109.97,
1
3
3 3
OCH ); C NMR (75 MHz, CDCl
2
+
69.53, 55.70; MALDI-TOF/MS, (Dihydroxy benzoic acid matrix) m/z: 1047.07 [M+H-2PF ] ,
6
+
1189.13 [M-PF ] ; Anal. Calc for: C H F N O P Ru (1338.07 g / mol):
6
60 46 12
6
6 2
2.4.3. Synthesis of [Ru(BEBtpy) ](PF ) [Ru(L3)]
2
6 2
This complex was prepared by a procedure similar to the preparation of
[Ru(BBtpy) ](PF [Ru(L1)] using [Ru(BEBtpy) ]Cl (0.120 g, 0.17 mmol), BEBtpy (0.082 g,
0.17 mmol) in methanolic solution. Yield: 0.180 g ( 77%); UV-VIS (CH
2
6
)
2
2
3
-1
3
CN): λmax nm (ԑ/L mol
-1
-1
cm ): 227(55485), 285(71 231), 310(69 839), 489(22572); IR (KBr disc ѵ/cm ): 3082, 1588,
1
1507, 841; HNMR (300 MHz, CDCl ) δ: 9.88(2H, s, -CHO), 9.47(4H, s), 9.08(4H, d, J=6Hz),
3
8.47(4H, d, J=6Hz), 8.07(4H, t, J=6Hz), 7.86(4H, d, J=6Hz), 7.57(6H, q, J=10.5Hz), 7.49(2H, s),
7.36(2H, d, J=6Hz), 7.29(4H, t, J=4.5Hz), 5.48(4H, s, -OCH ), 4.19(4H, q, J=10.5Hz, -OCH ),
2
2
13
1.43(6H, t, J=6Hz, -CH3); C NMR (75 MHz, CDCl ) δ: 191.55, 157.95, 155.03, 153.15,
3
152.13, 148.73, 146.56, 138.82, 138.05, 135.70, 130.03, 128.37, 127.85, 127.72, 125.59, 124.78,
121.09, 113.27, 111.29, 69.45, 64.06, 14.63; MALDI-TOF/MS, (Dihydroxy benzoic acid matrix)

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+
+
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232
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234
m/z: 1076.17 [M-2PF ] , 1223.16 [M-PF ] ; Anal. Calc for: C H F N O P Ru (1366.12 g /
6
6
62 50 12
6
6 2
mol).
2.5. Fluorescence quenching studies
235
236
237
238
239
240
Fluorescence quenching studies of ruthenium(II) terpyridine complexes were carried out
by adding different quencher concentrations (0.02 0.30 µM) of benzoquinone and
̶
-5
naphthoquinone to the fixed concentration of the complexes (10 M). The fluorescence spectra
of ruthenium(II) complexes at each quencher concentration were recorded and the variation in
the fluorescence intensity is related to quinone concentration by the Stern-Volmer equation
[17,21].
241
2
42
43
where, I and I are the fluorescence intensity in the absence and presence of quencher, [Q] is the
0
2
concentration of quencher and K is the Stern-Volmer quenching constant.
SV
2
44
45
2
2.6. Antibacterial activity
246
247
248
249
250
251
Ruthenium(II) complexes were tested against human pathogens by the well diffusion
method [22]. The ruthenium(II) complexes [Ru(BBtpy)
2 6 2 2 6 2
](PF ) [Ru(L1)], [Ru(BMBtpy) ](PF )
[Ru(L2)] and [Ru(BEBtpy) ](PF [Ru(L3)] exhibit antibacterial activity against human
2
6 2
)
pathogens comprising both gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus)
and gram negative bacteria (Escherichia coli, Klebsiella pneumonia). The bacteria were
incubated in MHA medium at 37 °C before inoculating in the plate. The incubated bacterial

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2
2
52
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suspension (10 cells/ml) was uniformly spread into the plate. 100 µg/µl of ruthenium
complexes was poured into each well while DMSO and tetracycline were used as control. The
plates were incubated overnight and after incubation, the clear zone was measured.
2
2
55
56 3. Results and discussion
2
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3.1. Synthesis of terpyridine ligands and complexes
Terpyridine is an important synthon in supramolecular chemistry. 4ʹ-(4-methylphenyl)-
2,2ʹ:6ʹ,2ʺ-terpyridine (ttpy) [14,18] was synthesized by the previously reported procedure
(Scheme-1). 4ʹ-(4-Methylphenyl)-2,2ʹ:6ʹ,2ʺ-terpyridine (ttpy) was subjected to free radical
bromination using NBS to yield 4ʹ-(4-Bromomethylphenyl)-2,2ʹ:6ʹ,2ʺ-terpyridine (Brttpy)
(Scheme-1) [19]. The new 4'-substituted-2,2':6',2"-terpyridine ligands (L1-L3) were synthesized
by the reaction of 4'-(4-bromomethylphenyl-2,2':6',2"-terpyridine) (Brttpy) with 4-hydroxy
benzaldehyde / 4-hydroxy-3-methoxy-benzaldehyde / 4-hydroxy-3-ethoxy-benzaldehyde in the
presence of K CO in DMF at 80 ºC for 24 h by o-alkylation method [20] (Scheme-1). The
2
3
1
13
terpyridine ligands were characterized by UV-VIS, IR and H, C NMR spectral studies.
Ruthenium(II)-bis(2,2':6',2"-terpyridine) complexes were synthesized by the stepwise
addition of two terpyridine ligands to the ruthenium center [14]. The reaction of BBtpy, BMBtpy
and BEBtpy (4'-(4-benzyloxybenzaldehyde)-2,2':6',2"-terpyridine) (1 equiv) with ruthenium(III)
chloride (1 equiv) at reflux in ethanol under inert atmosphere yielded ruthenium(III) mono
terpyridine complexes (yield 67%). The precursor Ru(III) complex was reacted with
BBtpy/BMBtpy/BEBtpy at reflux in methanol with N-ethylmorpholine as a reducing agent under
nitrogen atmosphere [23]. The resulting dark brown solution of ruthenium(II) complex was
precipitated by the addition of excess of potassium hexafluorophosphate and the products

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2
75
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77
[Ru(BBtpy)
2 6 2 2 6 2 2 6 2
](PF ) , [Ru(BMBtpy) ](PF ) , [Ru(BEBtpy) ](PF ) were isolated as dark red
brown solids (Yield: 70-90%) (Scheme-2).
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
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2
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96
3.2. Characterization of terpyridine ligands and complexes
The 4'-functionalized-2,2':6',2"-terpyridine ligands and ruthenium(II) complexes were
1
13
characterized by UV-Vis, fluorescence, FT-IR, H & C NMR, ESI mass, MALDI-TOF, TGA
and CV studies.
3.2.1 Photophysical properties
The electronic spectra of the terpyridine ligands were recorded in DCM. The UV-Vis
spectra of BBtpy, BMBtpy and BEBtpy exhibit three bands at 256, 281, 308 and 254, 279, 310
and 255, 279, 312 nm respectively (Fig. S1).
The photophysical properties of the complexes were recorded in acetonitrile solution and
the data are summarized in table-1. The UV-Vis spectra of the complexes [Ru(BBtpy)
2 6 2
](PF )
[Ru(L1)], [Ru(BMBtpy) ](PF [Ru(L2)] and [Ru(BEBtpy) ](PF [Ru(L3)] are shown in Fig.
2
6
)
2
2
6 2
)
1 and Figs. S2, S3. The UV-Vis spectra of the complexes exhibit highly intense bands in the UV
region which can be assigned to ligand-centered π→π* transitions at 210, 285 and 308 nm for
the complex [Ru(L1)] and 227, 284 and 310 nm for the complex [Ru(L2)] and 227, 285 and 310
nm for the complex [Ru(L1)]. The relatively less intense and broad absorption band in the
visible region, which is responsible for the deep red color, is due to spin-allowed d→π metal-to-
-1
-1
ligand charge transfer (MLCT) transition at 490 (20408 cm ), 489 (20449 cm ) and 489 (20449
-1
-1
cm ) nm respectively. Electronic spectra of Ru(II) complexes display a sharp band at 20040 cm
1
1
characteristic of octahedral geometry corresponding to T1(g)← A1(g) transition [24].

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The emission spectra of Ru(II) complexes are shown in Fig 1. The Ru(II) complexes
show maximum emission at 620 nm for the complex [Ru(BBtpy) ](PF ) , 630 nm for the
2
6 2
complex [Ru(BMBtpy) ](PF ) and 629 nm for the complex [Ru(BEBtpy) ](PF ) , when excited
2
6 2
2
6 2
at λ at 480 nm [25]. The fluorescence quantum yield of ruthenium(II) complexes is altered by
ex
the nature of substitution at 4'-position of the tpy ligand which influences the properties of Ru(II)
terpyridine complexes. [Ru(L1)] complex shows higher fluorescence quantum yield when
compared to that of [Ru(L2)] and [Ru(L3)] because of the absence of electron donating
substituents. The calculated quantum yields of ruthenium(II) complexes lie in the range of 0.482-
3 6 2
0.685. which are comparable to the reported values[ [Ru(bpy) ](PF ) (Ф = 0.59 in acetonitrile)
2
+
and [Ru(tpy-py) ] (Ф = 0.4 in acetonitrile) ][26].
2
3
3
3
3
3
3
3
3
3
3
3
3
3
07
08
09
10
11
12
13
14
15
16
17
18
19
3.2.3 Infrared Spectroscopy
-1
-1
The FT-IR spectra of terpyridine ligands show bands at 1591 cm and 1383 cm
corresponding to C=C and C=N stretching vibration (Figs. S4-S6). A weak, band around 3061
-1
-1
cm is attributed to aromatic C-H stretching frequency. The band appearing at 789 cm
corresponds to the C-H out of plane bending vibration. Two medium intensity bands observed at
-1
2744 and 2829 cm are attributed to aldehyde C-H stretching. The ruthenium complexes exhibit
-1
characteristic peaks due to C=C and C=N stretching frequency in the region 1588 and 1404 cm
-
1
respectively [27]. The weak band observed at 2845 cm is assigned to C=H stretching vibrations
-1
of the aldehyde group. A weak band around 3075 cm is attributed to aromatic C-H stretching
-1
frequency. The strong band appearing at 1683 cm is assigned to the C=O stretching vibrations
of the aldehyde group. Balachandran et al. have reported that the very strong band appearing at
-1
1687 cm is attributed to C=O stretching vibrations of the aldehyde group [27(d)]. The strong

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3
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20
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6
stretching frequency at 838 cm is associated with the PF as a counter ion of the complex [28]
(Fig. 2).
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39
40
41
42
1
13
3.2.4 H and C-NMR Spectroscopic Studies
1
13
The H and C NMR spectra of the terpyridine ligands were recorded in CDCl solution.
3
1
In the H NMR spectra of BBtpy, BMBtpy and BEBtpy ligands, the aromatic proton signals of
the pyridine rings were observed in the region δ 6.91-8.65 ppm. The benzyloxy (-CH O-) proton
2
appears as a singlet at δ 5.15 ppm with an increase in the downfield shift by δ 0.6 ppm for
BBtpy, BMBtpy and BEBtpy ligands (Figs. S7-S9), which is attributed to the removal of -Br
group and subsequent addition of RO-substituted hydroxy benzaldehyde. The aromatic -CHO
proton was observed as a singlet at δ 9.82 ppm. A singlet proton in the aliphatic region appeared
at δ 3.89 ppm which is assigned to –OCH of BMBtpy. The ethoxy proton appeared as a quartet
3
2 3
at δ 4.19 ppm (2H, q, J=13.65Hz, -OCH ), while the triplet at δ 1.51 ppm (3H, t, J=6.9Hz, -CH )
1
3
is attributed to methyl protons of BEBtpy. The C NMR spectra of terpyridine ligand showed
16 aromatic carbons which appear in the region δ 114.20-162.61 ppm for BBtpy. The aliphatic (–
OCH ) carbon signal appeared at δ 68.87 ppm and the aldehyde carbon signal was observed at δ
2
189.76 ppm for BBtpy. BMBtpy ligand showed the carbon signals at δ 55.09 ppm, 69.58 ppm
and 189.83 ppm for -OCH , -OCH and CHO respectively. BEBtpy ligand showed the ethyl
3
2
vanillin carbon signals at δ 14.76 ppm (-CH ), 64.69 ppm (-OCH ) and 190.91 ppm (CHO),
3
2
while the terpyridine (-OCH ) carbon signal was observed at δ 70.57 ppm (Figs. S10-S12).
2
1
The H NMR spectra of Ru(II)-bis(terpyridine) complexes were recorded in DMSO-d
6
solution and the spectra are shown in Fig. 3 and Figs. S13 and S14. The data are summarized in
Table-2. The aromatic proton signals of the complex appear in the region δ 7.05-9.47 ppm. After

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the formation of complex, the chemical shift value is shifted towards downfield region. The
proton spectrum of [Ru(BBtpy) ](PF ) complex shows a singlet which is shifted from δ 5.15 to
2
6 2
5.47 ppm (-OCH ) and δ 9.82 to 9.92 ppm (-CHO). Adeloye et al. have reported that homoleptic
2
complex [Ru(L1) ](PF ) shows the proton signals at δ 8.68–6.94 ppm expected from the two
2
6 2
1
3
coordinating ligands [28]. The C NMR spectrum of [Ru(BBtpy) ](PF ) complex shows the
2
6 2
carbon signals of both terpyridine and phenyl substituent moieties. The (-OCH ) carbon signal
2
appear at δ 62.48 ppm, whereas the aldehyde carbon signals appear at δ 191.43 ppm with an
1
3
increasing downfield shift of the free ligand. The C NMR spectra of [Ru(BBtpy)
2 6 2
](PF ) ,
[Ru(BMBtpy) ](PF and [Ru(BEBtpy) ](PF complexes are shown in Figs. S15-S17.
2
6
)
2
2
6 2
)
3
53
3.2.5 Mass spectral analysis
3
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60
61
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The mass spectra of 4'-substitued terpyridine ligands were obtained by electrospray
ionization mass spectrometry (ESI-MS). ESI/MS provides analysis of accurate determination of
molecular mass with high sensitivity. ESI-MS spectra of terpyridine ligands showed signals for
+
+
the molecular ions, at m/z = 444.17 g/ mol (M+H) , 474.25 g/ mol (M+H) and 488.25 g/ mol
+
(M+H) for BBtpy, BMBtpy and BEBtpy ligands respectively (Fig. S18-S20). The mass spectra
of ruthenium(II)-bis(terpyridine) complexes were recorded on MALDI-TOF/MS spectrometer
using 2,5-dihydroxy benzoic acid matrix. The [Ru(BMBtpy) ](PF ) complex exhibits a peak at
2
6 2
2
+
m/z =1047.07 g/ mol [M(L)+H-2PF
complex. The peak at m/z =1189.13 g/ mol [M(L)-PF
of -PF
of 4-hydroxy-3-methoxy benzaldehyde and two hexafluorophosphate ions i.e [RuC H N -
6
]
(RuC58H
42
N
6
), due to the loss of -2PF
6
ions from the
+
6
] (RuC58
H
42
F
12
N
6
PF
6
), represents the loss
6
ion from the complex. The base peak at m/z = 745.06 g/ mol is assignable to the removal
4
4
32
6
2
+
+
+
C H O P F ] . The peak at m/z = 576.96 g/ mol [M(L)-PF ] [M-(C H N O P F )] is
8
7
3
2
12
6
30 23
3
3 2 12

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obtained by the loss of -2PF
6
ions and one ligand molecule of BMBtpy from the molecular ion.
+
The peak at m/z = 474.99 g/ mol is assigned to the (BMBtpy) fragment (Figure. 4). The
MALDI-TOF/MS fragmentation pattern of [Ru(BMBtpy) ](PF ) complex is shown in Fig. 5.
2
6 2
The [Ru(BBtpy) ](PF ) complex exhibits a molecular ion peak at m/z = 987.09 g/ mol, which
2
6 2
2
+
can be assigned to [M-2PF ] fragment. The base peak at m/z = 745.07 g/ mol is assignable to
6
the removal of 4-hydroxy benzaldehyde and two hexafluorophosphate ions i.e [RuC H N -
4
4
32
6
2
+
C
8
H
7
O
3
P
2
F
12] . (Fig. S21) and [Ru(BEBtpy)
2
](PF
6
)
2
shows the peak at m/z =1076.17 g/ mol
2
+
+
[M(L)-2PF ] and 1223.16 g/ mol [M(L)-PF ] fragment respectively (Fig. S22).
6
6
3.2.6. Electrochemistry of ruthenium(II) terpyridine complexes
3
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3
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81
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83
84
85
86
87
88
The electrochemical properties of ruthenium(II) complexes were determined by the cyclic
voltammetry. The data are summarized in tables 3 & 4. The voltammograms of the complexes
exhibit redox active both metal centered (oxidation) and ligand centered (reduction) processes.
3 2 2 2 4 2
Meyer et al. and Leem et al. have reported that [Ru(tpy)(4,4′-(PO H ) bpy)(H O)](ClO ) and
(Ps-Ru) complexes shows a reversible one-electron oxidation process at E1/2 = +0.86 V and E1/2
=
II
III
+1.35 V which is attributed to the metal centered Ru /Ru redox couple [29]. The cyclic
voltammogram of the [Ru(BBtpy) ](PF ) complex shows a quasi-reversible oxidation peak at
2
6 2
II
III
+1.175V (E ) which is assignable to Ru /Ru process and the two terpyridine ligand reduction
1
/2
peaks are observed at -1.150 V and -1.596 V (E ) respectively (Fig. 6). [Ru(BMBtpy) ](PF )
6 2
1
/2
2
complex shows a quasi-reversible oxidation peak at +1.282 V (E ) which is assignable to
1
/2
II
III
Ru /Ru process and the two terpyidine ligand reduction peaks are observed at -0.822 V and -
1.499 V (E1/2) respectively (Fig. S23). [Ru(BEBtpy)
2
](PF
6
)
2
complex shows a reversible
II
III
oxidation peak at +1.240 V (E ) which is assignable to Ru /Ru process and the terpyridine
1
/2

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ligand reduction peaks are observed at -0.957 V and -1.167 V (E1/2) respectively (Fig. S24). The
present complexes exhibit oxidation potentials which are higher than those of reversible process
exhibited by model complexes [14,30] [Ru(mttpy) ](PF ) (E = +1.29 V), [Ru(tpy) ](PF )
2
6 2
1/2
2
6 2
(E = +1.30 V) and [Ru(tpy-PhCH ) ](PF ) (E = +1.25 V).
1
/2
3 2
6 2
1/2
3
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3
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3
3
4
4
4
4
4
93
94
95
96
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00
01
02
03
04
Further the multiscan voltammograms of Ru(BBtpy) ](PF ) , [Ru(BMBtpy) ](PF ) and
2 6 2 2 6 2
2 6 2
[Ru(BEBtpy) ](PF ) clearly show that the complexes do not undergo any considerable change
even after eight cycles indicating the stable nature of the complexes (Fig. 7, S25). The peak
potentials also undergo definite shift when the scan rate is increased (20-120 mV/s), the
reduction wave is shifted cathodically, indicating a chemical reaction while the oxidation wave
shifts anodically, suggesting that these systems are quasi-reversible. The cyclic voltammograms
of Ru(II) complexes show that the peak current, I and I increase with increase in the scan rate.
pa
pc
The peak current I and I are directly proportional to the square root of the scan rate. The plots
pa
pc
of anodic and cathodic peak current for [Ru(BBtpy)
coefficient of 0.950 for Ipa and 0.966 for Ipc. The representative voltammograms of
[Ru(BBtpy) ](PF , [Ru(BMBtpy) ](PF and [Ru(BEBtpy) ](PF at different scan rates are
2 6 2
](PF ) complex exhibits the regression
2
6
)
2
2
6
)
2
2
6 2
)
shown in Fig. 8 and Fig. S26.
4
4
05
06
3.2.7. TGA Studies
4
4
4
07
08
09
The TGA studies were carried out for ruthenium(II) complexes in the temperature range
of 25-800 °C under N atmosphere. The TGA plots for ruthenium(II) complexes are shown in
2
Fig. S27-S29. The data are summarized in table 5.

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19
20
21
22
2 6 2
Thermogram of [Ru(BBtpy) ](PF ) [Ru(L1)] complex shows no weight loss below 300 °C
indicating that there is no trace of water molecule in the sample. The first stage of weight loss
16.4% (Calc. 15.72%) between 302-344 °C is attributed to the removal of aldehyde molecule and
-
one PF ion. The second stage of decomposition is observed in the temperature range of 344-436
6
2
+
°C for [Ru(BBtpy) ] and it starts losing weight by 25.53% (Calc. 27.06%) due to the removal
2
-
of PF ion. The third stage of weight loss 55% (Calc. 55.58%) in the temperature range between
6
436-520 °C corresponds to the elimination of phenyl group. After 520 °C; the complex
decomposes continuously till the temperature reaches 800 °C. The decomposition was not
complete at 800 °C even though 18.97% (Calc.18.32%) of the residue was left.
[Ru(itpy) ](PF ) .DEG.3H O complex does not show any weight loss up to 160 °C. The first
2
6 2
2
stage of decomposition at 162 °C represents the removal of diethylene glycol (11.8% weight
loss). The second stage of weight loss (12.5%) at 443 °C may be attributed to the elimination of
-
PF ion from the complex [31].
6
4
4
4
4
4
4
4
4
23
24
25
26
27
28
29
30
2 6 2
The thermogram of [Ru(BMBtpy) ](PF ) [Ru(L2)] complex does not show any weight
loss up to 200 °C indicating the absence of water molecule in the complex. The first stage of
decomposition between 230.9-320.1 °C with a weight loss of 23.2% (Calc. 21.74%) is assigned
-
to the removal of PF ion. The second stage of decomposition in the temperature range of 320.1-
6
463.4 °C with a 62.4% (Calc. 60.37%) weight loss may be attributed to the removal of ligand
moiety. After 463.4 °C the complex decomposes continuously till the temperature reaches 800
°C and the decomposition is not complete at 800 °C. At the last stage only 14.2% (Calc. 16.29%)
of the residue was left which may be attributed to the formation of ruthenium oxide.
4
4
31
32
The thermogram of the [Ru(BEBtpy) ](PF ) [Ru(L3)] complex shows no weight loss
2
6 2
upto 250 °C indicating the absence of water molecule in the complex. The first stage of

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decomposition between 258.4-326.9 °C with a weight loss of 14.2% (Calc. 13.84%) is assigned
-
to the removal of one PF ion. The second stage of decomposition observed in the temperature
6
-
range of 326.9-497.2 °C is attributed to the loss of 32.88% (Calc. 31.77%) another PF ion and
6
ethoxy group from the complex. The third stage of decomposition in the temperature range of
497.2-599.9 °C with a weight loss of 56.3% (Calc. 58.45%) shows the loss of ligand moiety.
After 599.9 °C, the complex undergoes continuous decomposition till the temperature reaches
800 °C. The decomposition was not complete at 800 °C and 17.66% (Calc. 18.32%) of the
residue was obtained.
4
4
4
4
41
42
43
44
The TGA data of [Ru(BEBtpy) ](PF ) complex obtained is comparable with that of
2
6 2
2
+
MALDI-TOF/MS, in which the molecular ion peak corresponds to [Ru(BEBtpy)2] indicating
the elimination of both counter ions. [Ru(L1)] exhibits higher thermal stability when compared
to that of [Ru(L2)] and [Ru(L3)], which is indicated by the initial decomposition temperature.
4
4
45
46
3.3. Fluorescence quenching studies
4
4
4
4
4
4
4
4
47
48
49
50
51
52
53
54
The fluorescence quenching experiments of ruthenium(II) terpyridine complexes
[Ru(BBtpy)
2
](PF
6
)
2
[Ru(L1)], [Ru(BMBtpy)
2
](PF
6
)
2
[Ru(L2)] and
2 6 2
[Ru(BEBtpy) ](PF )
[Ru(L3)] were carried out in acetonitrile medium and the Stern-Volmer quenching constant
was determibed [32]. Fig. 9 shows the Stern-Volmer plot and fluorescence quenching spectrum
of [Ru(BEBtpy) ](PF ) complex by benzoquinone as a quencher. The quinones act as redox
2
6 2
active guests which are responsible for the fluorescence properties of ruthenium(II) cyclodextrin
complexes The quinone derivatives are electron acceptors for photoinduced reduction process
involved in supramolecular assemblies of cyclodextrin porphyrin and calix[4]arene substituted

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57
58
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62
2 6 2
Zn(II) porphyrin complex acts as a donor [33]. The [Ru(BEBtpy) ](PF ) complex shows the
MLCT band at 489 nm and the emission intensity at 698 nm decrease with increasing
concentration of the quinone acceptor. The addition of the quenchers benzoquinone and
naphthoquinone to ruthenium(II) complexes result in quenching of MLCT emission. The
fluorescence quenching constant (KSV) and regression coefficient values are summarized in table
6. The [Ru(L2)] complex exhibits comparatively higher KSV value than that of [Ru(L1)] and
[Ru(L3)] complexes. The corresponding fluorescence quenching spectrum and Stern-Volmer
2 6 2 2 6 2
plots of [Ru(BBtpy) ](PF ) and [Ru(BMBtpy) ](PF ) complexes are shown in fig.
4
4
63
64
3.4. Antibacterial assay
4
4
4
4
4
4
4
4
4
4
4
4
65
66
67
68
69
70
71
72
73
74
75
76
The antibacterial activity of Ru (II) complexes is shown in Fig. 10. [Ru(L2)] complex
shows maximum activity as evidenced from the zone of inhibition which is 15mm, 16mm,
14mm, 14mm against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Klebsiella
pneumonia respectively. The [Ru(L1)] and [Ru(L3)] complexes also show moderate activity.
[Ru(L1)] exhibits a zone of inhibition 12mm, 13mm, 10mm, 10mm against Bacillus subtilis,
Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia respectively while [Ru(L3)]
shows 10mm, 12mm, 8mm, 8mm against Bacillus subtilis, Staphylococcus aureus, Escherichia
coli, Klebsiella pneumonia respectively at 100 µg/L concentration. Standard antibiotic
tetracycline showed significant activity against all pathogens. The overall summary of
antibacterial activity is: [Ru(L2)] complex shows higher inhibitory activity while [Ru(L1)] and
[Ru(L3)] show moderate inhibitory activity. All the complexes show significant antibacterial
activity and the gram positive bacteria (Bacillus subtilis and Staphylococcus aureus) show

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77
78
maximum zone of inhibition than that of the gram negative bacteria (Escherichia coli, Klebsiella
pneumonia).
4
4
79
80 4. Conclusions
4
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4
4
4
4
4
4
4
4
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4
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4
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
The synthesis of Ru(II)-bis(terpyridine) complexes derived from 4′-(4-
Benzyloxybenzaldehyde)-2,2′:6′,2′′-terpyridine (BBtpy), BMBtpy and BEBtpy ligands was
achieved by O-alkylation in a multi-step procedure. The Ru(II)-bis(terpyridine) complexes were
1
13
structurally confirmed by the analysis of H & C NMR spectra and their MALDI-TOF/MS
2
+
spectra exhibit fragmentation of [M-2PF ] moiety. The complexes exhibit a quasi-reversible
6
redox process and also show both metal centered oxidation and ligand centered reduction
processes. The peak current, I and I increase with increase in the scan rate and are directly
pa
pc
proportional to the square root of the scan rate. The fluorescence quantum yield of Ru(II)
complexes lie in the range of 0.482-0.685. The Stern-Volmer quenching constants of Ru(II)
4
-1
4
-1
4
complexes [Ru(L1)], [Ru(L2)] and [Ru(L3)] are 8.5×10 mol , 14.27×10 mol and 10.27×10
-1
4
-1
4
-1
4
-1
mol for 1,4-benzoquinone and 8.57×10 mol , 18.5×10 mol and 16.58×10 mol for 1,4-
naphthoquinone in acetonitrile. The antibacterial activity of [Ru(BBtpy) ](PF ) ,
2
6 2
[Ru(BMBtpy) ](PF ) and [Ru(BEBtpy) ](PF ) complexes against four human pathogens
2
6 2
2
6 2
indicate that these complexes are fairly active when compared to that of standard antibiotics
like tetracycline.
4
97 Acknowledgements

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One of the authors (T. Ezhilarasu) gratefully acknowledges the University of Madras,
Chennai for the financial support (URF). The authors thank the SAIF, CDRI, Lucknow, India,
for recording the mass spectra.
5
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Table 1 Photophysical data of Ru(II) terpyridine complexes
3
-1
-1
Absorption λmax (nm) (ԑ/dm mol cm )
Emission
Фem
0.68
0.48
0.49
Ru(II) Complexes
Ru(BBtpy) ](PF
MLCT
LMCT
λem (nm)
[
[
[
2
)
6 2
490(29 603)
308(72 415), 285(89 994),
712
2
10(64 526),
310(88 156), 284(86 588),
27(65 668)
310(69 839), 285(71 231),
27(55 485)
Quantum yields were calculated using Rhodamine (Ф = 0.49 in ethanol) as a reference standard.
Ru(BMBtpy) ](PF )
489(29 029)
489(22 572)
704
698
2
6 2
2
Ru(BEBtpy) ](PF )
2
6 2
2
5
6
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02
03
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05

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Table 2 Spectral data of Ruthenium(II) terpyridine complexes
1
13
Sl.
No
Ru(II) Complexes
Frequency
υ(cm )
HNMR
CNMR
MALDI-
TOF/MS,
m/z:
-1
(300MHz,
DMSO-d6)
δ (ppm)
(75MHz, DMSO-
d )
6
δ (ppm)
191.43
(-CHO),
163.15- 114.60,
62.48(-OCH2)
1
2
[Ru(BBtpy)2]
PF6)2
3055, 1595,
1404, 838
9.92(2H, s,
-CHO),
.47-7.06(ArH)
.47(3H, s,
987.09
[M-2PF6]
2+
(
9
5
-
OCH2)
[Ru(BMBtpy) ](PF ) 3075, 1595,
9.89(2H, s,
-CHO),
191.52
(-CHO),
1047.07
[M+H-PF6]
2
6 2
2
+
1
401, 842
9
5
.47- 7.29(ArH), 157.94- 109.97,
.46(4H, s,
69.53, 55.70
-
OCH ), 3.92
2
(
3
6H, s, -OCH )
3
[Ru(BEBtpy)
2
] (PF
6
)
2
3082, 1588,
507, 841
9.88(2H, s,
-CHO),
191.55
(-CHO),
1076.17
[M-2PF ]
6
2+
1
9
5
.47- 7.29(ArH), 157.95- 111.29,
.48(4H, s, - 69.45, 64.06,
), 4.19(4H, 14.63
OCH
2
q, J=10.5Hz, -
OCH ), 1.43(6H,
2
t, J=6Hz, -CH3)
6
6
6
6
6
09
10
11
12
13