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Three gene families in plants viz. Argonaute (AGOs), Dicer-like (DCLs) and RNA dependent RNA polymerase (RDRs) constitute the core components of small RNA mediated gene silencing machinery. The present study endeavours to identify members of these gene families in tea and to investigate their expression patterns in different tissues and various stress regimes. Using genome-wide analysis, we have identified 18 AGOs, 5 DCLs and 9 RDRs in tea, and analyzed their phylogenetic relationship with orthologs of Arabidopsis thaliana. Gene expression analysis revealed constitutive expression of CsAGO1 in all the studied tissues and stress conditions, whereas CsAGO10c showed most variable expression among all the genes. CsAGO10c gene was found to be upregulated in tissues undergoing high meristematic activity such as buds and roots, as well as in Exobasidium vexans infected samples. CsRDR2 and two paralogs of CsAGO4, which are known to participate in biogenesis of hc-siRNAs, showed similarities in their expression levels in most of the tea plant tissues. This report provides first ever insight into the important gene families involved in biogenesis of small RNAs in tea. The comprehensive knowledge of these small RNA biogenesis purveyors can be utilized for tea crop improvement aimed at stress tolerance and quality enhancement.

Rice is a food crop of global importance, cultivated in diverse agro-climatic zones of the world. However, in the process of domestication many beneficial alleles have been eroded from the gene pool of the rice cultivated globally and eventually has made it vulnerable to a plethora of stresses. In contrast, the wild relatives of rice, despite being agronomically inferior, have inherited a potential of surviving in a range of geographical habitats. These adaptations enrich them with novel traits that upon introgression to modern cultivated varieties offer tremendous potential of increasing yield and adaptability. But, due to the unavailability of their genetic as well as genomic resources, identification and characterisation of these novel beneficial alleles has been a challenging task. Nevertheless, with the unprecedented surge in the area of conservation genomics, researchers have now shifted their focus towards these natural repositories of beneficial traits. Presently, there are several generic and specialized databases harboring genome-wide information on wild species of rice, and are acting as a useful resource for identification of novel genes and alleles, designing of molecular markers, comparative analysis and evolutionary biology studies. In this review, we introduce the key features of these databases focusing on their utility in rice breeding programs.

Department of Chemistry, Jadavpur University, Kolkata-700 032, India E-mail: crsjuchem@gmail.com Fax: 91-33-2413-7121 Manuscript received 30 June 2018, accepted 10 July 2018 [OsH(CO)(PPh3)2(SRaaiNR/)]+ (2) (SRaaiNR/ (1) = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole) act as catalyst to the oxidation of primary/secondary alcohols to aldehyde/ketone by N-methylmorpholine N-oxide (NMO). The catalysts have been charac­terized by the spectroscopic data and two of the complexes [OsH(CO)(PPh3)2(SMeaaiNMe)]PF6 (2a) and [OsH(CO)(PPh3)2(SMeaaiNEt)]PF6 (2b) have been structurally characterized by single crystal X-ray diffraction measurements. The complexes are redox active and show OsIII/OsII (~0.8 V) and OsIV/OsIII (~1.5 V) couples. The catalytic activity of the com­plexes may be due to oxidation to OsIV=O species by NMO (supported by v(Os=O), 857 cm–1) which could oxidize alcohols to aldehydes or ketones.

To elucidate the intrinsic biological activities displayed by platinum versus gold-based organometallic reagents, the isoelectronic and isostructural square planar complexes [Pt(C∩N)(C)Cl][PF6] (2) and [Au(C∩N)(C)Cl][PF6]2 (3), which are supported by a common N-heterocyclic carbene, 1-methyl-2-pyridin-2-yl-2H-imidazo[1,5-a]pyridin-4-ylidene (1), were synthesized. The complexes were characterized using a range of spectroscopic techniques as well as single crystal X-ray diffraction and a series of computational studies were also performed to gain additional insight into their fundamental electronic bonding structures. The cytotoxicities of the complexes were tested in vitro against non-small lung carcinoma (A549), colorectal carcinoma (HCT-116) and human hepatocellular carcinoma (HepG2) cell lines. The measured IC50 values showed that the Au(III)–NHC complex is more potent than its Pt analogue.

Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata-700 032, India E-mail : tapank.mondal@jadavpuruniversity.in Manuscript received 24 October 2017, accepted 01 November 2017 A ruthenium(II) complex (Ru-L) with hexadentate thioether containing N2O2 S2 donor azo functional ligand (H2L) is synthesized and characterized by several spectroscopic techniques. Structure of the complex is confirmed by single crystal X-ray diffraction studies. The complex exhibits two successive RuII/RuIII and RuIII/RuIV oxidation couples along with a ligand based reduction in cyclic voltammetric study. The electronic structure and redox property of the complex are interpreted by DFT calculation. The electronic transitions, calculated by TDDFT/CPCM method are used to assign the UV-Vis absorption b

Department of Chemistry, Jadavpur University, Kolkata-700 032, India E-mail : tkmondal@chemistry.jdvu.ac.in Manuscript received 02 May 2017, accepted 08 May 2017 A new azo-phenol based chemosensor has been designed, synthesized and its structure is confirmed through different spectroscopic techniques. The synthesized chemosensor (HL) has shown a marked colorimetric response from light yellow to purple upon complexation with Cu2+ which is easily detectable through naked eyes, makes the sensor efficient one to detect Cu2+ and remain nonresponsive in presence of other competitive metal ions. The 1 : 1 complex formation of HL with Cu2+ is determined from Job’s plot analysis and mass spectroscopic studies. Association constant (Ka, 8.94×104 M–1) of HL-Cu2+ complex suggests HL has high affinity towards Cu2+.

Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata-700 032, India E-mail : tkmondal@chemistry.jdvu.ac.in The cis-(Cl)-[Ru(PMAQ)(PPh3 )Cl2 ] (1) (where, PMAQ = 8-{(2´-pyridylmethylene)amino}quinoline) complex has been synthesized and characterized by several spectroscopic techniques. The absorption and emission properties of the complex have been studied. Upon excitation in ILCT band at 331 nm, the complex exhibits emission at 475 nm. The emission decay profile has bi-exponential in nature with life time of 3.98 ns. The complex exhibits a quasi-reversible one electron RuII/RuIII oxidation couple along with a ligand based reduction in cyclic voltammetric study. The redox properties are well supported by DFT data. The electronic structure of the complex has been interpreted by DFT method. The spin allowed electronic transitions computed by TDDFT method have a good agreement with the experimental spectrum of the complex. The complex efficiently catalyzes the oxidation of primary and secondary alcohols to the respective aldehydes and ketones with moderate to high conversions in presence of N-methylmorpholine-N-oxide (NMO) as co-oxidant.

Four dinuclear and three mononuclear Zn(II) complexes of phenol-based compartmental ligands (HL(1)-HL(7)) have been synthesized with the aim to investigate the viability of a radical pathway in catecholase activity. The complexes have been characterized by routine physicochemical studies as well as X-ray single-crystal structure analysis: [Zn(2)(H(2)L(1))(OH)(H(2)O)(NO(3))](NO(3))(3) (1), [Zn(2)L(2)Cl(3)] (2), [Zn(2)L(3)Cl(3)] (3), [Zn(2)(L(4))(2)(CH(3)COO)(2)] (4), [Zn(HL(5))Cl(2)] (5), [Zn(HL(6))Cl(2)] (6), and [Zn(HL(7))Cl(2)] (7) [L(1)-L(3) and L(5)-L(7) = 2,6-bis(R-iminomethyl)-4-methylphenolato, where R= N-ethylpiperazine for L(1), R = 2-(N-ethyl)pyridine for L(2), R = N-ethylpyrrolidine for L(3), R = N-methylbenzene for L(5), R = 2-(N-methyl)thiophene for L(6), R = 2-(N-ethyl)thiophene for L(7), and L(4) = 2-formyl-4-methyl-6-N-methylbenzene-iminomethyl-phenolato]. Catecholase-like activity of the complexes has been investigated in methanol medium by UV-vis spectrophotometric study using 3,5-di-tert-butylcatechol as model substrate. All complexes are highly active in catalyzing the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ). Conversion of 3,5-DTBC to 3,5-DTBQ catalyzed by mononuclear complexes (5-7) is observed to proceed via formation of two enzyme-substrate adducts, ES1 and ES2, detected spectroscopically, a finding reported for the first time in any Zn(II) complex catalyzed oxidation of catechol. On the other hand, no such enzyme-substrate adduct has been identified, and 3,5-DTBC to 3,5-DTBQ conversion is observed to be catalyzed by the dinuclear complexes (1-4) very smoothly. EPR experiment suggests generation of radicals in the presence of 3,5-DTBC, and that finding has been strengthened by cyclic voltammetric study. Thus, it may be proposed that the radical pathway is probably responsible for conversion of 3,5-DTBC to 3,5-DTBQ promoted by complexes of redox-innocent Zn(II) ion. The ligand-centered radical generation has further been verified by density functional theory calculation.

Three Ni(II) complexes of cresol-based Schiff-base ligands, namely [Ni2(L1)(NCS)3(H2O)2], (1) [Ni2(L2)(CH3COO)(NCS)2(H2O)] (2) and [Ni2(L3)(NCS)3] (3), (where L1 = 2,6-bis(N-ethylpyrrolidineiminomethyl)-4-methylphenolato, L2 = 2,6-bis(N-ethylpiperidineiminomethyl)-4-methylphenolato and L3 = 2,6-bis{N-ethyl-N-(3-hydroxypropyl iminomethyl)}-4-methylphenolato), have been synthesized and structurally characterized by X-ray single-crystal diffraction in addition to routine physicochemical techniques. Density functional theory calculations have been performed to understand the nature of the electronic spectra of the complexes. Complexes 1–3 when reacted with 4-nitrophenyl phosphate in 50:50 acetonitrile–water medium promote the cleavage of the O–P bond to form p-nitrophenol and smoothly convert 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) either in MeOH or in MeCN medium. Phosphatase- and catecholase-like activities were monitored by UV–vis spectrophotometry and the Michaelis–Menten equation was applied to rationalize all the kinetic parameters. Upon treatment with urea, complexes 1 and 2 give rise to [Ni2(L1)(NCS)2(NCO)(H2O)2] (1′) and [Ni2(L2)(CH3COO)(NCO)(NCS)(H2O)] (2′) derivatives, respectively, whereas 3 remains unaltered under same reaction conditions.

Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata-700 032, India E-mail : c_r_sinha@yahoo.com Manuscript received online 14 May 2012, revised 31 May 2012, accepted 04 June 2012 [MH(CO)(PPh3)z(L)]PF6 (L1: N-[(2-pyridyl)methyliden]-2-aminopyridine; L2 : N-[(2-pyridyl)methyliden]-2- aminopyrimidine; M = Ru (L1 = 1; L2 = 2) and Os (L1 = 3; L2 = 4)) are characterized by microanalytical and spectroscopic (FT-IR, UV-Vis, mass spectral and 1H NMR) results. The ligands are emissive where as the complexes are non-emissive. Electrochemistry of all the compounds show Mill/Mil couple; additionally OsIV /OsIIIcouple is seen in 3 and 4 along with ligand reductions. The DFT computation is carried out to the optimized structures. The spectral and redox properties of the ligands and the complexes are explained on the basis of calculated results. The complexes act as mild reducing agent and has been used to synthesise of silver nanoparticles (AgNPs) from AgNO3 which are characterized by UV-Vis spectra and HR TEM analyses.

Two ruthenium(II) complexes of newly designed pyrrol-azo ligands(L) and bipyridine(bpy) formulated as [Ru(L)(bpy)2]ClO4, where HL1 = (4-chloro-phenyl)-(1H-pyrrol-2-yl)-diazene (1) complex 1 and HL2 = (4-nitro-phenyl)-(1H-pyrrol-2-yl)-diazene for 2, were isolated in pure form. The complexes were characterized by physicochemical and spectroscopic methods. The electrochemical behavior of the complexes showed the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The study of cytotoxicity effects of 1 and 2 on human breast cancer cells (MCF 7, MDA-MB 231) and cervical cancer cell (HeLa) taking Cisplatin as a positive reference showed that 1 exhibited higher cytotoxicity against cancer cell lines than 2, but less activity than Cisplatin. The interaction of 1 with calf thymus DNA (CT-DNA) using absorption, emission spectral studies, viscosity-measurement, and electrochemical techniques has been used to determine the binding constant Kb and the linear Stern–Volmer quenching constant KSV. The results indicate that 1 strongly interacts with CT-DNA in groove binding mode. The interaction of bovine serum albumin (BSA) with 1 was also investigated with the help of spectroscopic tools. Absorption spectroscopy proved the formation of a BSA-[Ru(L1)(bpy)2]ClO4 complex.

Two diastereomeric forms of the μ4-oxo-bridged tetranuclear copper(II) complex [Cu4(O)(L)2(Ac)4] (where L = N2,O-donor Schiff-base ligand and Ac = acetate anion), differing for the bridging arrangement of the carboxylate groups, were individually synthesized and structurally characterized. Their formation was rationalized by DFT calculation and their catecholase-like activity was studied.

Five diruthenium(II) complexes [Cl(L)Ru(mu-tppz)Ru(L)Cl](1-5) containing differently substituted beta-diketonato derivatives (1: L = 2,4-pentanedionato; 2: L = 3,5-heptanedionato; 3: L = 2,2,6,6-tetramethyl-3,5-heptanedionato; 4: L = 3-methyl-2,4-pentanedionato; 5: L = 3-ethyl-2,4-pentanedionato) as ancillary ligands (L) were synthesized and studied by spectroelectrochemistry (UV-Vis-NIR, electron paramagnetic resonance (EPR)). X-ray structural characterisation revealed anti (1, 2, 5) or syn (3) configuration as well as non-planarity of the bis-tridentate tppz bridge and strong d pi(Ru-II) -> pi*(pyrazine, tppz) back-bonding. The widely separated one-electron oxidation steps, (RuRuII)-Ru-II/(RuRuIII)-Ru-II and (RuRuIII)-Ru-II/(RuRuIII)-Ru-III, result in large comproportionation constants (K-c) of >= 10(10) for the mixed-valent intermediates. The syn-configurated 3(n) exhibits a particularly high K-c of 10(12) for n = 1+, accompanied by density functional theory (DFT)-calculated minimum Ru-N bond lengths for this (RuRuIII)-Ru-II intermediate. The electrogenerated mixed-valent states 1(+)-5(+) exhibit anisotropic EPR spectra at 110 K with average values < g > of 2.304-2.234 and g anisotropies Delta g = g(1)-g(3) of 0.82-0.99. Metal-to-metal charge transfer (MMCT) absorptions occur for 1(+)-5(+) in the NIR region at 1660 nm-1750 nm (epsilon approximate to 2700 dm(3) mol(-1) cm(-1), Delta nu(1/2) approximate to 1800 cm(-1)). DFT calculations of 1(+) and 3(+) yield comparable Mulliken spin densities of about 0.60 for the metal ions, corresponding to valence-delocalised situations (Ru-2.5)(2). Rather large spin densities of about -0.4 were calculated for the tppz bridges in 1(+) and 3(+). The calculated electronic interaction values (V-AB) for 1(+)-5(+) are about 3000 cm(-1), comparable to that for the Creutz-Taube ion at 3185 cm(-1). The DFT calculations predict that the (RuRuIII)-Ru-III forms in 12(+)-52(+) prefer a triplet (S = 1) ground state with Delta E (S = 0 - S = 1) similar to 5000 cm(-1). One-electron reduction takes place at the tppz bridge which results in species [Cl(L)Ru-II(mu-tppz(.-)) Ru-II(L)Cl](-) (1(.-)-3(.-), 5(.-)) which exhibit free radical-type EPR signals and NIR transitions typical of the tppz radical anion. The system 4(n) is distinguished by lability of the Ru-Cl bonds.

The diruthenium(III) compound [(μ-oxa){Ru(acac)(2)}(2)] [1, oxa(2-) =oxamidato(2-), acac(-) =2,4-pentanedionato] exhibits an S=1 ground state with antiferromagnetic spin-spin coupling (J=-40 cm(-1)). The molecular structure in the crystal of 1⋅2 C(7)H(8) revealed an intramolecular metal-metal distance of 5.433 Å and a notable asymmetry within the bridging ligand. Cyclic voltammetry and spectroelectrochemistry (EPR, UV/Vis/NIR) of the two-step reduction and of the two-step oxidation (irreversible second step) produced monocation and monoanion intermediates (K(c) =10(5.9)) with broad NIR absorption bands (ε ca. 2000 M(-1)cm(-1)) and maxima at 1800 (1(-)) and 1500 nm (1(+)). TD-DFT calculations support a Ru(III)Ru(II) formulation for 1(-) with a doublet ground state. The 1(+) ion (Ru(IV)Ru(III)) was calculated with an S=3/2 ground state and the doublet state higher in energy (ΔE=694.6 cm(-1)). The Mulliken spin density calculations showed little participation of the ligand bridge in the spin accommodation for all paramagnetic species [(μ-oxa){Ru(acac)(2)}(2)](n), n=+1, 0, -1, and, accordingly, the NIR absorptions were identified as metal-to-metal (intervalence) charge transfers. Whereas only one such NIR band was observed for the Ru(III)Ru(II) (4d(5)/4d(6)) system 1(-), the Ru(IV)Ru(III) (4d(4)/4d(5)) form 1(+) exhibited extended absorbance over the UV/Vis/NIR range.

Coordination compounds [Ru(acac)(2)(Q)] (acac = acetylacetonate; Q = o-benzoquinone) were prepared as complexes 1 (Q = o-benzoquinone), 2 (Q = 3-methoxy-o-benzoquinone), 3 (Q = 4-methyl-o-benzoquinone), and 4 (Q = 3,5-di-tert-butyl-o-benzoquinone). The structures of 1 and 2 were determined to reveal a Ru(III)/o-benzosemiquinone formulation, supported by analysis of experimental data (spectroscopy, magnetism of 1) and by DFT calculations. The S = 1 ground state calculated for 1 stands in contrast to the spin-paired analogues with arylimino-o-benzosemiquinonato and diimino-o-benzoquinone ligands. The close contacts of about 5.3 angstrom possible between semiquinone O atoms of different molecules in the crystal allow for intermolecular spin-spin interactions and an overall complex magnetic behavior. One quasireversible oxidation and two reversible one-electron reductions yielded the corresponding molecular ions, which were characterized by UV-visible-NIR and EPR spectroelectrochemistry in terms of [Ru(III)(acac)(2)(Q(0))](+), [Ru(III)(acac)(2)(Q(2-))](-), and [Ru(II)(acac)(2)(Q(2-))](2-) descriptions in agreement with DFT results. The use of acceptor-substituted 1,2-dioxolenes resulted in the isolation of ionic species Na[Ru(acac)(2)(Q)] (Na(5); Q = 4-chloro-o-benzoquinone) and Na(6) (Q = 4-nitro-o-benzoquinone), which were similarly investigated as compounds 1-4. Magnetic susceptibility and EPR results confirm an S = 1/2 ground state based on ruthenium(III). The combined studies reveal a remarkable substituent sensitivity, and in comparison to recently analyzed Ru(acac)(2) complexes with o-benzoquinone monoimine and diimine ligands, the all-O-donor-containing new systems are distinguished by a qualitatively different metal-ligand interaction based on closer intermolecular radical-radical contacts and on weaker intramolecular d pi-pi* interactions.

The diruthenium(III) complex [(acac)(2)Ru(mu-L(2-))Ru(acac)(2)] (1) with acac(-) = acetylacetonato = 2,4-pentanedionato and a 2,5-pyrazine-dicarboxylato bridge, L(2-), has been obtained and structurally characterized as the rac (Delta Delta,Lambda Lambda) diastereomer. The Ru(III)Ru(III) configuration in 1 (d(Ru-au) = 6.799 angstrom) results in a triplet ground state (mu = 2.82/2 mu(B) at 300 K) with a density functional theory (DFT) calculated triplet-singlet gap of 10840 cm-and the metal ions as the primary spin-bearing centers (Mulliken spin densities: Ru, 1.711; L, 0.105; acac, 0.184). The paramagnetic 1 exhibits :broad, upfield shifted (1)H NMR signals with delta values ranging from -10 to -65 -65 ppm and an anisotropic electron paramagnetic resonance (EPR), spectrum (< g > = 2.133, g(1) - g(3) = Delta g = 0.512), accompanied by a weak half-field signal at g = 4.420 in glassy frozen acetonitrile at 4 K Compound 1 displays two closely spaced oxidation steps to yield labile cations. In contrast, two well separated reversible reduction steps of 1 signify appreciable electrochemical metal-metal interaction in the Run Rum mixed-valent state 1(-) (K(c) approximate to 10(7)). The intermediate 1(-) shows a weak, broad Ru(II)-> Ru(III) intervalence charge transfer (IVCT) band at about 1040 nm (epsilon = 380 M(-1) cm(-1)); the DFT approach for 1(-) yielded Mulliken spin densities of 0.460 and 0.685 for the two metal centers. The monitoring of the frequencies of the uncoordinated C=O groups of L(2-) in 1" by IR spectroelectrochemistry suggests valence averaging (Ru(2.5)Ru(2.5)) in 1(-) on the vibrational time scale. The mixed-valent 1(-) displays a rhombic EPR signal (< g > = 2.239 and Delta g = 0.32) which reveals non-negligible contributions from the bridging ligand, reflecting a partial hole-transfer mechanism and being confirmed by the DFT-calculated spin distribution (Mulliken spin density of -0.241 for L in 1(-)). The major low energy electronic transitions in 1(n) (n = 0,-,2-) have been assigned as charge transfer processes with the support of TD-DFT analysis.

The complexes, cis-(CO)-trans-(Cl)-[Ru(SRaaiNR)(CO)(2)Cl-2] (2) and trans-(Cl)-[Ru(SRaaiNR)(CO)Cl-2] (3) (SRaaiNR = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazoles; R = Me (1a) and Et (1b)) have been synthesized and characterized. The structural confirmation is achieved by single crystal X-ray structure determinations. The complexes show Ru(III)/Ru(II) couple and ligand reductions. Electronic structure and spectral properties of the complexes have been explained with the DFT and TDDFT calculation. (C) 2009 Elsevier B.V. All rights reserved.

A new dinuclear nickel(II) complex, [Ni(2)(LH(2))(H(2)O)(2)(OH)(NO(3))](NO(3))(3) (1), of an "end-off" compartmental ligand 2,6-bis(N-ethylpiperazine-iminomethyl)-4-methyl-phenolato, has been synthesized and structurally characterized. The X-ray single crystal structure analysis shows that the piperazine moieties assume the expected chair conformation and are protonated. The complex 1 exhibits versatile catalytic activities of biological significance, viz. catecholase, phosphatase, and DNA cleavage activities, etc. The catecholase activity of the complex observed is very dependent on the nature of the solvent. In acetonitrile medium, the complex is inactive to exhibit catecholase activity. On the other hand, in methanol, it catalyzes not only the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) but also tetrachlorocatechol (TCC), a catechol which is very difficult to oxidize, under aerobic conditions. UV-vis spectroscopic investigation shows that TCC oxidation proceeds through the formation of an intermediate. The intermediate has been characterized by an electron spray ionizaton-mass spectrometry study, which suggests a bidentate rather than a monodentate mode of TCC coordination in that intermediate, and this proposition have been verified by density functional theory calculation. The complex also exhibits phosphatase (with substrate p-nitrophenylphosphate) and DNA cleavage activities. The DNA cleavage activity exhibited by complex 1 most probably proceeds through a hydroxyl radical pathway. The bioactivity study suggests the possible applications of complex 1 as a site specific recognition of DNA and/or as an anticancer agent.

The ruthenium-nitrosyl complexes [Ru(II)(trpy)(tmp)(NO(+))](ClO(4))(3) ([4](ClO(4))(3)) and [Ru(II)(trpy)(tmp) (NO(center dot))](ClO(4))(2) ([5](ClO(4))(2)) with {Ru-NO}(6) and {Ru-NO}(7) configurations, respectively (trpy = 2,2':6',2"-ter-pyridine, tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline) have been isotaled. The nitrosyl complexes [4](3+) and [5](2+) have been generated by following a stepwise synthetic procedure: [Ru(II)(trpy)(tmp)(X)](n), X/n = Cl/+ (1(+))-> CH(3)CN/2+ (2(2+))-> NO(2)/+ (3(+))-> NO(+)/3+ (4(3+))-> NO(center dot)/2+ (5(2+)). The single-crystal X-ray structures of two precursor complexes [1]ClO(4) and [3]ClO(4) have been determined. The DFT optimized structures of 4(3+) and 5(2+) suggest that the Ru-N-O geometries in the complexes are linear (177.9 degrees) and bent (141.4 degrees), respectively. The nitrosyl complexes with linear (4(3+)) and bent (5(2+)) geometries exhibit nu(NO) frequencies at 1935 cm (1) (DFT: 1993 cm (1)) and 1635 cm (1) (DFT: 1684 cm (1)), respectively. Complex 4(3+) undergoes two successive reductions at 0.25 V (reversible) and -0.48 V (irreversible) versus SCE involving the redox active NO function, Ru(II)-NO(+)reversible arrow Ru(II)-NO(center dot) and Ru(II)-NO(center dot) -> Ru(II)-NO , respectively, besides the reductions of trpy and tmp at more negative potentials. The DFT calculations on the optimized 4(3+) suggest that LUMO and LUMO+1 are dominated by NO(+) based orbitals of around 65% contribution along with partial metal contribution of similar to 25% due to (d pi)Ru(II)->pi*(NO(+)) back-bonding. The lowest energy transitions in 4(3+) and 5(2+) at 360 nm and 467 nm in CH(3)CN (TD-DFT: 364 and 459 nm) have been attributed to mixed MLLCT transitions of tmp(pi)-> NO(+)(pi*), Ru(d pi)/tmp(pi)-> NO(+)(pi*) and Ru(d pi/NO(center dot)(pi)-> trpy(pi*), respectively. The paramagnetic reduced species 5(2+) exhibits an anisotropic EPR spectrum with g(1) = 2.018, g(2) = 1.994, g(3) = 1.880 (< g > = 1.965 and Delta g = 0.138) in CH(3)CN, along with (14)N (I = 1) hyperfine coupling constant, A2 = 35 G at 110 K due to partial metal contribution in the singly occupied molecular orbital (DFT:SOMO: Ru (34%) and NO(center dot) (53%)). Consequently, Mulliken spin distributions in 5(2+) are calculated as 0.115 for Ru and 0.855 for NO (N, 0.527; O, 0.328). The reaction of moderately electrophilic nitrosyl center in 4(3+) with the nucleophile, OH yields the nitro precursor, 3(+) with the second-order rate constant value of 1.7 x 10 (1) M (1) s (1) at 298 K in CH(3)CN-H(2)O (10:1). On exposure to light (Xenon 350W lamp) both the nitrosyl species, 4(3+) ({Ru(II)-NO(+)}) and 5(2+) ({Ru(II)-NO(center dot)}) undergo photolytic Ru-NO bond cleavage process but with a widely varying k(NO), s (1) (t(1/2), s) of 1.56 x 10 (1)(4.4) and 0.011 x 10 (1)(630), respectively. (C) 2010 Elevier B. V. .