Journal of Molecular Structure 975 (2010) 335–342

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Journal of Molecular Structure

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Synthetic, spectral and structural study of mono bis(pyridine)dichlorobis(dimethyl sulfoxide-S) ruthenium(II) complex, [RuCl2(py)2(dmso-S)2] and itsreactivity with nitrogen donor bases in polar and non-polar solvent

Manoj Trivedi a,*, Yogesh K. Sharma a, R. Nagarajan a, Nigam P. Rath b,**

a Department of Chemistry, University of Delhi, Delhi 110 007, Indiab Department of Chemistry & Biochemistry and Centre for Nanoscience, University of Missouri – St. Louis, One University Boulevard, St. Louis, MO 63121-4499, USA

a r t i c l e i n f o

Article history:Received 7 March 2010Received in revised form 30 April 2010Accepted 30 April 2010Available online 11 May 2010

Keywords:Ruthenium–dmsoPyridineReactivity with nitrogen donor basesX-rayWeak interactions

0022-2860/$ - see front matter � 2010 Elsevier B.V. Adoi:10.1016/j.molstruc.2010.04.047

* Corresponding author. Tel.: +91 (0) 9811730475.** Corresponding author. Tel.: +1 (314) 516 5333.

E-mail addresses: manojtri@gmail.com (M. Trivedi)

a b s t r a c t

Reaction of the cis-[RuCl2(dmso)4] with pyridine (py) at room temperature in MeOH/H2O afforded a neu-tral mononuclear complex cis,cis,cis-[RuCl2(py)2(dmso-S)2] 1. The complex 1 reacted with nitrogen donorbases such as pyridine (py), pyrazine (pyz), 4,40-bipyridine (bp) and 1,4-bis(4-pyridyl)ethane (bpeta) indifferent solvents to give substitution products. The nature of the substitution product was governedby the polarity of the solvents employed in the reaction. Resulting complexes have been characterizedby elemental analyses, IR, NMR (1H and 1H–1H COSY), ESI-MS, FAB-MS and electronic spectral studies.Molecular structures of the complexes 1 and 5 have been determined crystallographically. Complex 1exhibits the strong intra- and inter-molecular CAH� � �X (X = Cl, p) and face-to-face p–p stacking interac-tions but only intra- and inter-molecular CAH� � �Cl and p–p stacking interactions are present in 5 whichplay important roles to stabilize crystal packing. Furthermore, the CAH� � �O interactions in 1 andCAH� � �Cl interactions in 5 lead to a single and double-helical motif.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction

Coordination chemistry of ruthenium complexes have beenstudied in last few decades because of their versatile and diverseapplications in various fields such as catalysis [1–3], photochemis-try and photophysics [4–6] and more recently, in supramolecular[7,8] and bioinorganic chemistry [9–11].

To this end, one of the most fascinating and promising applica-tions of ruthenium complexes are their use as chemotherapeuticagents [12]. The majority of the new drugs based on rutheniumcomplexes that have been prepared and tested recently (some ofthem already in clinical trials like NAMI-A) [13–15] are based oncoordination complexes of ruthenium that contain chloro, dmsoas well as a pyridine type of ligands [16–18]. Furthermorecis- and trans-[RuCl2(dmso)4] are widely used as starting materialsfor the synthesis of other ruthenium complexes [19,20] throughthe substitution of the labile chloro and dmso groups by thedesired ligands. The substitution processes are important to supra-molecular chemistry because these complexes are used as buildingblocks to assemble complex three-dimensional architectures

ll rights reserved.

, rathn@umsl.edu (N.P. Rath).

[21–23]. [RuCl2(dmso)4] [24–26] as well as other RuAClAdmsocomplexes containing other ligands, are particularly attractive asprecursors [27] and catalysts for a variety of reactions such ashydrogen-atom transfer [28–30], hydrogenation [31], R-alkylationof ketones [32], aerobic oxidation of alcohols [33], oxidation of ali-phatic ethers to esters [34], isomerization of alcohols [35], selectiveoxidation of aryl sulfides with molecular oxygen [36–38], etc. Fur-ther, metal to ligand bond strength has remarkable importance incoordination/organometallic synthetic process [39–43]. Metal–ligand link can be targeted as a strong or a weak bond. The strengthof the metal–ligand link depends on the nature of the transitionmetal, i.e. its oxidation state and coordination number, but for asingle metal targeted complex the polarity of the solvent and theavailability of the counter ion in the reaction medium becomesdetermining factor for resulting complexes [44,45]. For neutralapproaching ligands, the polar solvent facilitates the reaction bypolarizing the reactant, but for a non-polar solvent such type ofpolarization is not possible, leading to entirely different products.During our studies directed towards synthesis and characterizationof ruthenium(II) complexes, we have isolated and structurallycharacterized a new neutral mononuclear complex cis,cis,cis-[RuCl2(py)2(dmso-S)2] 1. We also describe herein, the effects ofpolarity of the solvent on the ligand substitution reaction of 1and molecular structure of the mononuclear complex trans-[RuCl2(py)4] 5.

336 M. Trivedi et al. / Journal of Molecular Structure 975 (2010) 335–342

2. Experimental

2.1. Materials and physical measurements

All the synthetic manipulations were performed under ambientatmosphere. The solvents were dried and distilled before use fol-lowing the standard procedures. Pyridine (S.D. Fine), pyrazine (Al-drich), 4,40-bipyridine (Aldrich), 1,4-bis(4-pyridyl)ethane (Aldrich),Ammonium hexafluorophosphate (Aldrich) and hydrated ruthe-nium(III) chloride (Aldrich) were used as received. The precursorcomplex cis-[RuCl2(dmso)4] [19] was prepared and purified follow-ing the literature procedure.

Elemental analyses were performed on a Carlo Erba Model EA-1108 elemental analyzer and data of C, H and N is within ±0.4% ofcalculated values. IR(KBr) and electronic spectra were recordedusing Perkin–Elmer FT-IR spectrophotometer and Shimadzu UV-1601 spectrometer, respectively. Mass spectral data were recordedusing a Waters micromass LCT Mass Spectrometer/Data system.FAB mass spectra were recorded on a JEOL SX 102/DA 6000 massspectrometer using Xenon (6 kV, 10 mA) as the FAB gas. The accel-erating voltage was 10 kV and the spectra were recorded at roomtemperature with m-nitrobenzyl alcohol as the matrix. The 1Hand 1H–1H COSY NMR spectra were recorded on a Bruker Spectro-spin spectrometer at 300 MHz using TMS as an internal standard.The chemical shift values are recorded on the d scale and the cou-pling constants (J) are in Hz.

2.2. Synthesis of complexes

2.2.1. Synthesis of complex 12.2.1.1. [RuCl2(py)2(dmso-S)2] (1). Cis-[RuCl2(dmso)4] (0.484 g,1 mmol) was added slowly to a solution of CH3OH (15 mL), and water(15 mL) containing pyridine (160 lL, 2 mmol). The resulting solutionwas stirred at room temperature for 24 h. Slowly, color of the solu-tion changed from light yellow to dark yellow. The resulting solutionwas filtered and left at room temperature for slow crystallization. In acouple of days diffraction quality crystals appeared as very fineyellow shiny rods. These were separated and washed several timeswith diethyl ether, and vacuum-dried. Yield: (0.388 g, 80%). Anal.Calc. for C14H22Cl2N2O2S2Ru: C, 34.56; H, 4.53; N, 5.76. Found: C,34.76; H, 4.56; N, 5.64. IR(cm�1, Nujol): m = 3443, 3103, 3005, 2924,2675, 1631, 1486, 1447, 1351, 1302, 1224, 1158, 1088, 1020,976, 923, 766, 701, 424. Far-IR: mas = 301, ms = 273, mRuAN(pyridine) =325 cm�1. 1H NMR (d ppm, 300 MHz, CDCl3, 298 K): 8.42(m, 4H,J = 5.7 Hz), 7.86(m, 4H, J = 7.5 Hz), 7.25(m, 2H, J = 8.1 Hz), 3.42(s,12H). UV/Vis: kmax (CHCl3, e [dm3 mol�1 cm�1]) = 399 (4781), 260(26,808). ESI-MS (m/z): 486.4 (M+).

2.2.2. Synthesis of neutral complexes2.2.2.1. [RuCl2(py)2(pyz)2] (2). Cis-[RuCl2(py)2(dmso-S)2] (0.243 g,0.5 mmol) was added slowly to a solution pyrazine (80 mg, 1 mmol)in toluene (15 mL). The resulting solution was refluxed with stirringat boiling temperature for 12 h. Slowly, color of the solution changedfrom yellow to yellowish orange. The resulting solution was filteredand left at room temperature for slow crystallization. In a couple ofdays yellowish orange powder was precipitated which was washedseveral times with diethyl ether, and vacuum-dried. Yield: (0.171 g,70%). Anal. Calc. for C18H18Cl2N6Ru: C, 44.08; H, 3.67; N, 17.14.Found: C, 44.36; H, 3.76; N, 17.64. IR(cm�1, Nujol): m = 3435, 3025,2929, 1617, 1482, 1216, 990, 806, 765, 697, 608. Far-IR: mas = 319,ms = 271, mRuAN(pyridine) = 328 cm�1. 1H NMR (d ppm, 300 MHz, CDCl3,298 K): 8.75(m, 8H, J = 7.0 Hz), 8.60(m, 4H, J = 6.0 Hz), 7.75(m, 4H,J = 6.0 Hz), 7.38(m, 2H, J = 6.1 Hz). UV/Vis: kmax (CHCl3, e [dm3

mol�1 cm�1]) = 400 (23,139), 259 (35,441). ESI-MS (m/z): 492.2(M+).

2.2.2.2. [RuCl2(py)2(bp)2] (3). Cis-[RuCl2(py)2(dmso-S)2] (0.243 g,0.5 mmol) was added slowly to a solution of 4,40-bipyridine(156 mg, 1 mmol) in toluene (15 mL). The resulting solution wasrefluxed with stirring at boiling temperature for 12 h. Slowly, colorof the solution changed from light yellow to dark red. The resultingsolution was filtered and left at room temperature for slow crystal-lization. In a couple of days red crystalline powder was precipi-tated which was washed several times with diethyl ether, andvacuum-dried. Yield: (0.256 g, 80%). Anal. Calc. for C30H26Cl2N6Ru:C, 56.07; H, 4.04; N, 13.08. Found: C, 56.36; H, 4.36; N, 13.64.IR(cm�1, Nujol): m = 3429, 3025, 2910, 1593, 1480, 1406, 1213,990, 806, 760, 690, 605. Far-IR: mas = 292, ms = 265, mRuAN(pyridine) =300 cm�1. 1H NMR (d ppm, 300 MHz, CDCl3, 298 K): 8.66(m, 8H,J = 6.0 Hz), 8.59(m, 4H, 7.5 Hz), 7.75(t, 2H, 6.0 Hz) 7.66(m, 8H,J = 5.1 Hz), 7.25(m, 4H, J = 8.1 Hz). UV/Vis: kmax (CHCl3, e[dm3 mol�1 cm�1]) = 465 (3205), 258 (39,721). ESI-MS (m/z):642.2 (M+).

2.2.2.3. [RuCl2(py)2(bpeta)2] (4). Cis-[RuCl2(py)2(dmso-S)2] (0.243 g,0.5 mmol) was added slowly to a solution of 1,4-bis(4-pyridyl)eth-ane (184 mg, 1 mmol) in toluene (15 mL). The resulting solutionwas refluxed with stirring at boiling temperature for 12 h. Slowly,color of the solution changed from light yellow to dark yellow. Theresulting solution was filtered and left at room temperature forslow crystallization. In a couple of days dark yellow color powderprecipitated which was washed several times with diethyl ether,and vacuum-dried. Yield: (0.226 g, 65%). Anal. Calc. forC34H34N6Cl2Ru: C, 58.45; H, 4.87; N, 12.03. Found: C, 58.66; H,4.76; N, 12.20 IR(cm�1, Nujol): m = 3439, 3150, 3010, 2940, 2840,1621, 1540, 1480, 1430, 1240, 1008, 950, 810, 750, 680. Far-IR:mas = 320, ms = 271, mRuAN(pyridine) = 324 cm�1. 1H NMR (d ppm,300 MHz, CDCl3, 298 K): 8.41(m, 8H, J = 6.9 Hz), 8.25(t, 4H,5.4 Hz), 7.72(m, 4H, 7.5 Hz) 7.29(m, 8H, J = 4.5 Hz), 7.07(m, 2H,J = 6.0), 3.01(t, 4H, 12.9 Hz), 2.78(t, 4H, 4.2 Hz). UV/Vis: kmax

(CHCl3, e [dm3 mol�1 cm�1]) = 402 (4237), 261 (5709). ESI-MS (m/z):698.8 (M+).

2.2.2.4. [RuCl2(py)4] (5). Cis-[RuCl2(py)2(dmso-S)2] (0.243 g,0.5 mmol) was added a solution of toluene (15 mL) containing pyr-idine (80 lL, 1 mmol). The resulting solution was refluxed withstirring at boiling temperature for 12 h. Slowly, color of the solu-tion changed from light yellow to dark red color. The resultingsolution was filtered and left at room temperature for slow crystal-lization. In a couple of days diffraction quality crystals appeared asred blocks. These were separated and washed several times withdiethyl ether, and vacuum-dried. Yield: (0.195 g, 80%). Anal. Calc.for C20H20Cl2N4Ru: C, 49.18; H, 4.09; N, 11.47. Found: C, 49.36;H, 4.16; N, 11.64. IR(cm�1, Nujol): m = 3440, 3106, 3005, 2924,2674, 1630, 1540, 1488, 1447, 1250, 1006, 960, 810, 750, 688.Far-IR: mas = 300, ms = 271, mRuAN(pyridine) = 326 cm�1. 1H NMR (dppm, 300 MHz, CDCl3, 298 K): 7.59(m, 8H, J = 7.5 Hz), 7.40(m, 4H,J = 6.0 Hz), 7.38(m, 8H, J = 6.9 Hz). UV/Vis: kmax (CHCl3, e[dm3 mol�1 cm�1]) = 450 (53,761), 248 (23,535). ESI-MS (m/z):488.9 (M+).

2.2.3. Synthesis of cationic complexes2.2.3.1. [Ru(py)2(pyz)2(dmso)2]�(PF6)2 (6). Cis-[RuCl2(py)2(dmso-S)2](0.243 g, 0.5 mmol) was added to a solution of CH3OH (15 mL) andpyrazine (80 mg, 1 mmol).The resulting solution was refluxed withstirring at boiling temperature for 12 h. Slowly, color of the solutionchanged from yellow to red. The resulting red solution was cooled toroom temperature and filtered through Celite. Ammonium hexa-fluorophosphate dissolved in 10 mL of methanol was added to thefiltrate, whereupon a red crystalline solid separated. It was filteredand washed several times with diethyl ether. Yield: (0.266 g, 70%).Anal. Calc. for C22F12H30N6O2S2P2Ru: C, 30.52; H, 3.47; N, 9.71.

Table 1Crystallographic data for 1 and 5.

Empirical formula Complex 1 Complex 5C14H22Cl2N2O2S2Ru C20H20Cl2N4Ru

Formula weight 486.43 488.37Colour and habit Yellow, rod Dark red, blockCrystal size (mm) 0.10 � 0.14 � 0.28 0.20 � 0.24 � 0.30Crystal system, space group Triclinic, P-1 Tetragonal, I41/acda (Å) 8.1100(16) 15.69510(10)b (Å) 8.7800(18) 15.69510(10)c (Å) 13.400(3) 16.9576(2)b (�) 103.18(3) 90V (Å3) 912.1(4) 4177.27(6)Z, Dc (mg m�3) 2, 1.771 8, 1.553l (mm�1) 1.390 1.018T (K) 296(2) 293(2)k(Mo Ka) (Å) 0.71073 0.71073No. of reflections/unique 41,892/5894 41,832/1847No. of refined parameter 212 70R factor [I > 2r(I)] 0.0265 0.0492wR2 [I > 2r(I)] 0.0948 0.1133R factor (all data) 0.0332 0.0670wR2 (all data) 0.1123 0.1214GoF 0.915 1.088

M. Trivedi et al. / Journal of Molecular Structure 975 (2010) 335–342 337

Found: C, 30.76; H, 3.56; N, 9.64. IR(cm�1, Nujol): m = 3410, 3103,2928, 1634, 1576, 1486, 1447, 1350, 1308, 1230, 1160, 1088, 1020,980, 923, 845, 760, 710, 423. Far-IRmRuAN(pyridine) = 322 cm�1.1H NMR (d ppm, 300 MHz, DMSO-d6, 298 K): 8.91(d, 8H, J = 8.4 Hz),8.76(m, 4H, J = 5.1 Hz), 7.94(m, 2H, J = 7.5 Hz), 7.60(m, 2H,J = 7.5 Hz), 3.48(s, 12H). UV/Vis: kmax (CHCl3, e [dm3 mol�1 cm�1]) =501 (5364), 380 (6882), 261 (4037). FAB-MS m/z 575(575), [M]2+;497(496), [M]2+–dmso; 419(420), [M]2+–(dmso)2; 340(341)[M]2+–(dmso)2–py; 261(260) [M]2+–(dmso)2–(py)2.

2.2.3.2. [Ru(py)2(bp)2(dmso)2]�(PF6)2 (7). Cis-[RuCl2(py)2(dmso-S)2](0.243 g, 0.5 mmol) was added to a solution of CH3OH (15 mL) con-taining 4,40-bipyridine (156 mg, 1 mmol).The resulting solutionwas refluxed with stirring at boiling temperature for 12 h. Slowly,color of the solution changed from yellow to dark red. The resultingdark red solution was cooled to room temperature and filteredthrough Celite. Ammonium hexafluorophosphate dissolved in10 mL of methanol was added to the filtrate, whereupon a red crys-talline solid separated. It was filtered and washed several timeswith diethyl ether, and vacuum-dried. Yield: (0.279 g, 70%). Anal.Calc. for C34F12H38N6O2S2P2Ru: C, 40.12; H, 3.74; N, 8.26. Found:C, 40.36; H, 3.56; N, 8.44. IR(cm�1, Nujol): m = 3343, 3150, 3005,2924, 1640, 1631, 1540, 1486, 1351, 1230, 1158, 1088, 1030,980, 930, 845, 766, 701, 424. Far-IR mRuAN(pyridine) = 302 cm�1. 1HNMR (d ppm, 300 MHz, CDCl3, 298 K): 8.67(m, 8H, J = 6.0 Hz),8.55(m, 4H, J = 5.1 Hz) 7.59(m, 8H, J = 6.7 Hz), 7.47(m, 2H,J = 3.9 Hz) 7.30(m, 4H, J = 7.2 Hz), 3.41(d, 12H). UV/Vis: kmax

(CHCl3, e [dm3 mol�1 cm�1]) = 468 (17,260), 261 (10,441). FAB-MS m/z 727(726), [M]2+; 649(649), [M]2+–dmso; 571(571), [M]2+–(dmso)2; 492(493) [M]2+–(dmso)2–py; 413(413) [M]2+–(dmso)2–(py)2.

2.2.3.3. [Ru(py)2(bpeta)2(dmso)2]�(PF6)2 (8). Cis-[RuCl2(py)2(dmso-S)2] (0.243 g, 0.5 mmol) was added a solution of CH3OH (15 mL)containing 1,4-bis(4-pyridyl)ethane (184 mg, 1 mmol). The result-ing solution was refluxed with stirring at boiling temperature for12 h. Slowly, color of the solution changed from light yellow todark yellow color. The resulting red solution was cooled to roomtemperature and filtered through Celite. Ammonium hexafluoro-phosphate dissolved in 10 mL of methanol was added to the fil-trate, whereupon a red crystalline solid separated. It was filteredand washed several times with diethyl ether, and vacuum-dried.Yield: (0.277 g, 65%). Anal. Calc. for C38F12H46N6O2S2P2Ru: C,42.49; H, 4.28; N, 7.82. Found: C, 42.46; H, 4.56; N, 7.64. IR(cm�1,Nujol): m = 3439, 3150, 3010, 2940, 2840, 1621, 1540, 1480, 1430,1240, 1158, 1088, 1020, 980, 923, 845, 766, 710, 424. Far-IRmRuAN(pyridine) = 310 cm�1. 1H NMR (d ppm, 300 MHz, CDCl3,298 K): 8.44(m, 8H, J = 14.1 Hz), 8.23(m, 4H), 7.76(m, 4H), 7.10(d,2H, J = 4.8), 6.89(d, 8H, J = 4.5 Hz) 3.48(d, 12H), 2.93(s, 8H). UV/Vis: kmax (CHCl3, e [dm3 mol�1 cm�1]) = 402 (4364), 261 (17,457).FAB-MS m/z 783(782), [M]2+; 705(705), [M]2+–dmso; 627(626),[M]2+–(dmso)2; 548(549) [M]2+–(dmso)2–py; 469(469) [M]2+–(dmso)2–(py)2.

2.2.3.4. [Ru(py)4(dmso)2]�(PF6)2 (9). Cis-[RuCl2(py)2(dmso-S)2](0.243 g, 0.5 mmol) was added to a solution of CH3OH (15 mL)and pyridine (80 lL, 1 mmol). The resulting solution was refluxedwith stirring at boiling temperature for 12 h. Slowly, color of thesolution changed from yellow to dark red. The resulting dark redsolution was cooled to room temperature and filtered through Cel-ite. Ammonium hexafluorophosphate dissolved in 10 mL of meth-anol was added to the filtrate, whereupon a dark red crystallinesolid separated. It was filtered and washed several times withdiethyl ether. Yield: (0.302 g, 70%). Anal. Calc. for C24F12H32N4O2S2-

P2Ru: C, 33.37; H, 3.71; N, 6.49. Found: C, 33.66; H, 3.96; N, 6.64.

IR(cm�1, Nujol): m = 3420, 2928, 1638, 1578, 1486, 1446, 1340,1230, 1170, 1088, 1026, 985, 922, 846, 760, 720, 424. Far-IRmRuAN(pyridine) = 320 cm�1. 1H NMR (d ppm, 300 MHz, DMSO-d6,298 K): 7.60(m, 8H, J = 6.0 Hz), 7.42(m, 4H, J = 4.5 Hz), 7.38(m,8H, J = 9.0 Hz), 3.48(s, 12H). UV/Vis: kmax (CHCl3, e[dm3 mol�1 cm�1]) = 398 (10,443), 242 (33,069). FAB-MS m/z573(573), [M]2+; 495(496), [M]2+–dmso; 417(417), [M]2+–(dmso)2;338(339) [M]2+–(dmso)2–py; 259(260) [M]2+–(dmso)2–(py)2.

2.2.3.5. [Ru(py)6]�(PF6)2 (10). Cis-[RuCl2(py)2(dmso-S)2] (0.243 g,0.5 mmol) was added to a solution of CH3OH (15 mL) and pyridine(160 lL, 2 mmol).The resulting solution was refluxed with stirringat boiling temperature for 24 h. Slowly, color of the solution chan-ged from green to orange red. The resulting orange red solutionwas cooled to room temperature and filtered through Celite.Ammonium hexafluorophosphate dissolved in 10 mL of methanolwas added to the filtrate, whereupon an orange red crystalline so-lid separated. It was filtered and washed several times with diethylether. Yield: (0.260 g, 60%). Anal. Calc. for C30F12H30N6P2Ru: C,41.61; H, 3.46; N, 9.71. Found: C, 41.85; H, 3.41; N, 9.61. IR(cm�1,Nujol): m = 3445, 2924, 2359, 2341, 1635, 1540, 1520, 1506, 1479,1444, 1384, 1209, 1150, 841, 758, 720, 690, 668, 631, 558. Far-IRmRuAN(pyridine) = 326 cm�1. 1H NMR (d ppm, 300 MHz, CDCl3,298 K): 8.60(m, 12H, J = 7.5 Hz), 7.42(m, 6H, J = 5.1 Hz), 7.38(m,12H, J = 6.9 Hz). UV/Vis: kmax (CHCl3, e [dm3 mol�1 cm�1]) = 395(8151), 249 (7120). ESI-MS (m/z): 576.1 (M+).

2.3. X-ray crystallographic study

Suitable crystals for X-ray crystallographic studies for 1 and 5were grown at room temperature. X-ray data for 1 and 5 were col-lected on a Bruker APEX II and X-calibur S oxford area detector dif-fractometers using graphite monochromatized Mo-Ka radiation at296(2) and 293(2) K. Apex-II, X-calibur S and SAINT software pack-ages [46] were used for data collection and data integration for 1and 5. Structure solution and refinement were carried out usingthe SHELXTL-PLUS software package [46]. The non-hydrogenatoms were refined with anisotropic thermal parameters. All thehydrogen atoms were treated using appropriate riding models.The computer programme PLATON was used for analyzing the in-ter and intra-molecular interactions and stacking distances [47,48].

338 M. Trivedi et al. / Journal of Molecular Structure 975 (2010) 335–342

3. Results and discussion

3.1. Synthesis

Reaction of the cis-[RuCl2(dmso)4] with pyridine in 1:2 stoichi-ometric ratio in a mixture of water and methanol (1:1, v/v) understirring at RT afforded neutral mononuclear complex cis,cis,cis-[RuCl2(py)2(dmso-S)2] (1) in a reasonably good yield. The synthesisand characterization of trans,cis,cis-[RuCl2(dmso)2(py)2] [49] hasbeen previously reported by Scandola and Alessio et al. However,structurally characterized motif of this type has not been reportedtill now. The complex 1 reacted with various nitrogen donor basessuch as pyridine, pyrazine, 4,40-bipyridine and 1,4-bis(4-pyri-dyl)ethane under varying reaction conditions. The substitutionchemistry depends primarily on the lability and inertness of themetal–dmso link. The strength of the metal–dmso link dependson the nature (acidity or basicity) of different substituents aroundthe center along with the nature of the metal center itself. Takingthese observations into account, one can use polarity of a solventas a tool to control the metal to dmso bond strength, to yield aset of complexes with tailored charges and substituted ligand. Inthe present study, we observed that treatment of complex 1 withdifferent nitrogen donor bases in a non-polar solvent like tolueneafforded neutral mononuclear complexes with the formulations[RuCl2(L)2(py)2] (L = pyz, 2; bp, 3; bpeta, 4; py, 5). On the otherhand, its reaction in a polar solvent like methanol led to theformation of cationic mononuclear complexes with the formula-tions [Ru(L)2(py)2(dmso)2]2+ (L = pyz, 6; bp, 7; bpeta, 8; py, 9). Fur-ther, it was observed that, reaction of 1 with pyridine in 1:4 Mratio in methanol, gave mononuclear complex [Ru(py)6]2+(10)(Scheme 1).

3.2. Characterization

All the complexes were isolated as air-stable, non-hygroscopicsolids and are soluble in dimethylformamide, dimethylsulfoxideand halogenated solvents like chloroform but are insoluble inpetroleum ether and diethyl ether. Information about the composi-tion of the complexes and structure and bonding has been derivedfrom the analytical spectral studies. Analytical data of the com-plexes confirmed well to their respective formulations. More infor-mation about composition of the complexes was also obtainedfrom ESI-MS and FAB-MS. Resulting data is given in the Section 2and representative ESI-MS spectrum of the neutral complex 2and FAB-MS spectrum of the cationic complex 7 is shown in F-1,Supporting material. The positions of different peaks and overallfragmentation patterns in the ESI-MS and FAB-MS of the respectivecomplexes are consistent with their formulations.

The infrared spectra of the complexes 1, 6, 7, 8, and 9 in Nujoldisplayed a strong band at 1088 cm�1, which has been assignedto the SAO stretching vibrations. The RuAS vibration occurred at424 cm�1 (see F-2, Supporting material). It supports linkage ofdmso to the metal centre ruthenium through sulfur [50], whilethe band due to the counter anion PF�6 in the IR spectra of the cat-ionic complexes 6, 7, 8, 9 and 10 appeared at 845 cm�1. The infra-red spectra of complexes 2, 3, 4, and 5 did not show any bands at1088 and 424 cm�1, which clearly indicates absence of dmso groupin these complexes. All the complexes displayed bands in the re-gion of 1674–1490 cm�1, assignable to m(CAN) and m(C@C) stretch-ing vibrations of pyridyl and NAN donor ligands. The Far-IR spectraof 1, 2, 3, 4, and 5 exhibited two bands at 292–320 and 265–273 cm�1 associated with RuACl symmetric and asymmetricstretching vibrations [51,52]. The RuAN(pyridine) stretching vibra-tions for all the complexes are generally found in the region from300 to 328 cm�1.

The 1H NMR spectral data of the complexes (recorded in the Sec-tion 2) are in good agreement with the proposed molecular formula.To facilitate the assigned resonances, 1H–1H COSY experiment wascarried out and the resulting spectrum for the complex 6 is shownin F-3, Supporting material. The 1H NMR spectrum of 1 exhibitedresonances at 8.40(m, 4H, J = 5.7 Hz), 7.86(m, 4H, J = 7.5 Hz),7.25(m, 2H, J = 8.1 Hz) ppm assignable to protons of the coordi-nated pyridine. The methyl protons of dmso resonated at3.42 ppm as a singlet [49]. However, 1H NMR spectra of the substi-tuted product 2 exhibited resonance at 8.75(m, 8H, J = 7.0 Hz),8.60(m, 4H, J = 6.0 Hz), 7.75(m, 4H, J = 6.0 Hz), 7.38(m, 2H,J = 6.1 Hz) ppm assignable to protons of the coordinated pyridyland NAN donor ligand. Complex 2 did not show any resonance at3.42 ppm, which confirmed well to the absence of dmso molecules(see F-4 and F-5, Supporting material). These protons exhibited adownfield shift compared with that in complex 1 on coordinationwith pyridyl and NAN donor ligand to the metal center. The posi-tion and integrated intensity of different signals corroborated wellwith the formation of 2. A similar trend of resonance was observedfor the complexes 3–5. On the other hand, the 1H NMR spectra ofthe cationic complex 8 displayed signals at 8.44(m, 8H,J = 14.1 Hz), 8.23(m, 4H), 7.76(m, 4H), 7.10(d, 2H, J = 4.8), 6.89(d,8H, J = 4.5 Hz), 2.93(s, 8H) ppm, corresponding to protons of thecoordinated pyridyl and NAN donor ligand. The resonance at3.48 ppm as a doublet for methyl groups confirmed well to thepresence of two non-equivalent dmso molecules bound to Ru(II)(see F-6 and F-7, Supporting material). Analogous trends were ob-served in the 1H NMR spectra of the complexes 6, 7 and 9. The pro-tons of cationic complexes 6, 7, 8 and 9 displayed similar downfieldshift trends in the 1H NMR spectra compared with that in 1. Thecomplex 10 in its 1H NMR spectrum exhibited signals in the region8.60(m, 12H, J = 7.5 Hz), 7.42(m, 6H, J = 5.1 Hz), 7.38(m, 12H,J = 6.9 Hz) ppm characteristic for pyridyl protons strongly sug-gested coordination of the pyridine with the metal center.

The absorption spectral data of all the complexes were recordedin chloroform and resulting data is summarized in the Section 2along with other selected analytical and spectral data (Fig. 1).The electronic spectra shows a band at 242–261 nm correspondingto intra-ligand p�p transition and another band of lower energy inthe region 380–501 nm assignable to MLCT transition. The MLCT ofthe substituted products (2–10) of complex 1 shifted towards low-er energy side with an increase in the r donor ability of the ligand.

3.3. Molecular structure determination

Molecular structure of 1 and 5 were determined crystallograph-ically. The details of data collection, structure solution and refine-ment are listed in Table 1. ORTEP [53] depiction of 1 and 5 withatom-labels is shown in Fig. 2 and selected geometrical parametersand hydrogen bond parameters are listed in Tables 2 and 3, respec-tively. The structure of the 5 was already reported in the literatureby Elsegood [54]. Complex 1 and 5 crystallizes in triclinic andtetragonal system with P-1 and I41/acd space group, respectively.The coordination geometry of the 1 and 5 shows a distorted octa-hedral with NNCl2S2 and NNNNCl2 coordination sphere around themetal ion. The two S-coordinated dmso molecules and the two Cl�

ions in the coordination sphere are found to be cis pairs, and theother two remaining cis sites are occupied by two N-donor pyri-dine ligands, with a bite angle of 85.75(7)� in 1, while in 5 four pyr-idine and two chlorine are found to be trans. The dmso is bonded tothe ruthenium through sulfur atom. The RuAS bond distance[2.228(8)–2.241(9) Å] is within the range reported for other ruthe-nium(II) dmso derivatives [17,21,29,55,56]. The geometry of thecoordinated dmso is approximately tetrahedral with angles rang-ing from 105� to 113�. The SAO bond distance [1.4786(17)–1.4828(17) Å] and the SAC bond distance [1.768–1.784 Å] are

Scheme 1.

Fig. 1. Electronic absorption spectra of the complexes 1–10.

M. Trivedi et al. / Journal of Molecular Structure 975 (2010) 335–342 339

within the range reported for other ruthenium–dmso complexes[17,21,29,55,56]. The RuAN bond distance falls in the range of

2.087(19)–2.121(19) Å in 1 and 2.075(2) Å in 5, and is consistentwith the values reported in the literature [57]. The RuACl bond dis-tances in 1 and 5 are 2.395(8)–2.430(9) and 2.407(11), respec-tively. These bond distances are comparable to those reported inother Ru(II) complexes [21,29,56,58,59]. The Cl2ARuACl1 bond an-gle of 86.54(3)� deviates noticeably from the ideal value of 90� in 1.The deviation of the S1ARuAS2 bond angle [93.61 (3)�] from 90� ismost probably due to steric repulsion between the dmso mole-cules, with the larger angle being accommodated by the small che-late angle of the pyridine ligand, while in 5 the two chlorine aretrans disposed as indicated by the Cl(1)#3ARu(1)ACl(1) bond angleof 180.00(3). The pyridine ring is planar in 1 and 5 and averageCAC and CAN bond distances are 1.374(6)–1.379(3) and1.345(4)–1.351(3) Å, respectively and the angles are close to 120�.

Crystal packing in 1 is stabilised by inter- and intra-molecularCAH� � �X (X = Cl, O, p) and p–p interactions, while in 5 only intra-and inter-molecular CAH� � �Cl and p–p interactions are present. Aninteresting feature of the crystal packing in 1 is a single helical mo-tif (Fig. 3) resulting from CAY� � �J interactions. Contact distancesfor CAY� � �J interactions are 2.34–2.56 Å [60]. CAH� � �Cl type intra-and inter-molecular interactions results in the formation of dou-ble-helical motif in 5 (Fig. 4) and only inter-molecular CAH� � �Clinteractions are present in 1 (see F-8, Supporting material). The

Fig. 2. ORTEP diagram of 1 and 5 (ellipsoids with 50% probability, hydrogen atoms are omitted for clarity).

Table 2Selected bond lengths (Å) and bond angles (�) for 1 and 5.

Complex 1 Complex 5

Ru(1)AN(1) 2.0877(19) Ru(1)ACl(1) 2.4070(11)Ru(1)AN(2) 2.1205(19) Ru(1)AN(1) 2.075(2)Ru(1)AS(1) 2.2289(8) N(1)AC(1) 1.345(4)Ru(1)AS(2) 2.2409(9) N(1)AC(5) 1.345(4)Ru(1)ACl(1) 2.4301(9) C(1)AC(2) 1.372(4)Ru(1)ACl(2) 2.3954(8) C(2)AC(3) 1.380(7)S(1)AO(1) 1.4828(17) C(3)AC(4) 1.375(7)S(2)AO(2) 1.4786(17) C(4)AC(5) 1.372(5)S(1)AC(11) 1.779(2) N(1)ARu(1)ACl(1) 89.69(6)S(1)AC(12) 1.784(2) Cl(1)#3ARu(1)ACl(1) 180.00(3)S(2)AC(13) 1.768(2) N(1)ARu(1)AN(1)#2 179.38(13)S(2)AC(14) 1.778(2) N(1)#1ARu(1)AN(1)#3 179.38(13)N(1)ARu(1)AN(2) 85.75(7)S(1)ARu(1)AS(2) 93.61(3)Cl(2)ARu(1)ACl(1) 86.54(3)

Table 3Hydrogen bond parameters for 1 and 5.

DAH� � �AAX d H� � �A (Å) D D� � �A (Å) h DAH� � �A (�)

Complex 1C(1)AH(1A)� � �O1 2.40 2.961(3) 118C(2)AH(2A)� � �O1a 2.35 3.176(3) 148C(5)AH(5A)� � �Cl2 2.69 3.205(3) 116C(5)AH(5A)� � �Cl2b 2.77 3.536(2) 140C(10)AH(10A)� � �Cl2 2.82 3.235(3) 109C(11)AH(11A)� � �O1c 2.56 3.433(3) 152C(12)AH(12B)� � �O1c 2.53 3.403(3) 151C(12)AH(12C)� � �Cl1 2.79 3.363(3) 119C(12)AH(12D)� � �O2 2.26 3.040(3) 138C(14)AH(14B)� � �O2d 2.42 3.332(3) 158C(14)AH(14C)� � �Cl2 2.76 3.341(2) 119a = �x, �y, 1 � z; b = �x, �y, �z; c = �x, 1 � y, 1 � z; d = 1 � x, �y, 1 � z

Complex 5C(1)AH(1)� � �Cl1a 2.83 3.288(3) 112C(5)AH(5)� � �Cl1 2.81 3.261(3) 111a = �1/4 � y, 1/4 � x, 1/4 � z

340 M. Trivedi et al. / Journal of Molecular Structure 975 (2010) 335–342

CAH� � �Cl contact distances are in the range of 2.77–2.88 Å. Thesedistances are within the range reported in the literature [61]. Theintra and inter-molecular CAH� � �p weak interactions are also pres-ent in 1 but this type of interactions has been absent in 5. Contactdistances for intra and inter-CAY� � �p interactions are in the rangeof 3.18–3.29 and 2.84–2.85 Å (see F-9, Supporting material) [62].The importance of p–p stacking interactions between aromaticrings has been widely recognized in the intercalation of drugs withDNA which lie in the range of 3.4–3.5 Å. Complexes 1 and 5 exhibitinter-molecular face-to-face (p pyridyl/(p pyridyl (ct/ct distances3.238–3.385 Å))) and intra-molecular edge-to-face p–p interac-tions (p pyridyl/(p pyridyl (ct/ct distances 3.320–3.364 Å))) (seeF-10 and F-11, Supporting material) [63,64].

Fig. 3. Wire-frame model representation for single hel

4. Conclusions

In this work we have presented the preparation, structural char-acterization and reactivity of a mononuclear ruthenium complex[RuCl2(py)2(dmso-S)2] [1] with various nitrogen donar bases in dif-ferent solvent. Poor quality of crystals of the complexes 6–10 hasrestricted us to provide any structural support at this stage. Dueto the presence of vacant donar sites, it is expected that it maybe used as building block for the construction of networks that ex-hibit some predictable structural features. Investigations are inprogress for preparation of bimetallic and polymetallic frames

ical motif in 1 resulting from CAH� � �O interaction.

Fig. 4. Wire-frame model representation for double-helical motif in 5 resulting from CAH� � �Cl interaction.

M. Trivedi et al. / Journal of Molecular Structure 975 (2010) 335–342 341

based on this building block, with potential electronic properties,and on architectures assembled by joining these building blocksthrough hydrogen-bond bridges.

Acknowledgement

The authors sincerely thank the reviewers for their valuablesuggestions and comments. We gratefully acknowledge financialsupport from University Grants Commission, New Delhi (GrantNo. F.4–2/2006(BSR)/13–76/2008(BSR)). We also thank the Head,Department of Chemistry, University of Delhi, INDIA and ProfessorD. S. Pandey, Department of Chemistry, Faculty of Science, BanarasHindu University for their kind encouragement and help. Weacknowledge funding from the National Science Foundation(CHE0420497) for the purchase of the APEX II diffractometer.

Appendix A. Supplementary material

The crystallographic data in CIF format has been deposited withCCDC (CCDC deposition number 676950(1) and 768521(2)). Thisdata can be obtained free of charge at www.ccdc.cam.ac.uk/con-ts/retrieving.html [or from the Cambridge Crystallographic DataCentre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internet.)+441223/336 033; E-mail: deposit@ccdc.cam.ac.uk]. Supplementarydata associated with this article can be found, in the online version,at doi:10.1016/j.molstruc.2010.04.047.

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