z201600260e (1)

Journal of Inorganic and General Chemistry

Zeitschrift für anorganische und allgemeine Chemie

www.zaac.wiley-vch.de ARTICLE

DOI: 10.1002/zaac.201600260

Study of the Bonding Modes of Di-2-pyridyl ketoxime Ligand towardsRuthenium, Rhodium and Iridium Half Sandwich Complexes

Sanjay Adhikari,[a] Werner Kaminsky,[b] and Kollipara Mohan Rao*[a]

Keywords: Arene; Ruthenium; Rhodium; Iridium; Oxime

Abstract. The bonding modes of the ligand di-2-pyridyl ketoximetowards half-sandwich arene ruthenium, Cp*Rh and Cp*Ir complexeswere investigated. Di-2-pyridyl ketoxime {pyC(py)NOH} react withmetal precursor [Cp*IrCl2]2 to give cationic oxime complexes

of the general formula [Cp*Ir{pyC(py)NOH}Cl]PF6 (1a) and

[Cp*Ir{pyC(py)NOH}Cl]PF6 (1b), for which two coordination iso-mers were observed by NMR spectroscopy. The molecular structuresof the complexes revealed that in the major isomer the oxime nitrogenand one of the pyridine nitrogen atoms are coordinated to the centraliridium atom forming a five membered metallocycle, whereas in the

Introduction

Half sandwich platinum group metal complexes play apivotal role in the field of organometallic chemistry. These ar-ene complexes [(arene)MCl2]2 serve as potential precursors forthe synthesis of half sandwich complexes by facile cleavageof chloride bridge to react with a variety of ligands to formcationic or neutral complexes.[1–3] Arene RuII complexes havebeen extensively studied and found to be promising candidatesas anticancer, antitumor, antiviral, antibiotic, and antiparasiticagents.[4–7] Analogous to arene ruthenium, Cp*Rh/Cp*Ir com-plexes are also well established and have found applicationin various areas.[8–10] Cyclometalated iridium(III) complexesprovide good thermal- and photo-stability, which makes thesecomplexes suitable for various optical applications, such asbiological labeling agents and as photocatalyst.[11,12]

Furthermore ligands involving two pyridyl units particularly2,2�-dipyridyl have been widely explored in the field of coordi-nation chemistry for synthesis of mononuclear, dinuclear, andtetranuclear transition metal complexes.[13,14] Recently Mac-chioni and co-workers reported arene ruthenium complexes of2,2�-dipyridyl ketone, in which the ligand afforded tridentatecoordination to the central metal atom.[15] 2,2�-Dipyridylketone has been employed as a versatile ligand for preparing

* Dr. K. M. RaoFax: +91-364-2550076E-Mail: [email protected]

[a] Centre for Advanced Studies in ChemistryNorth-Eastern Hill UniversityShillong 793022, India

[b] Department of ChemistryUniversity of WashingtonSeattle, WA 98195, USA

Z. Anorg. Allg. Chem. 2016, 642, (17), 941–946 © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim941

minor isomer both the pyridine nitrogen atoms are coordinated tothe iridium atom forming a six membered metallacyclicring. Di-2-pyridyl ketoxime react with [(arene)MCl2]2 to form

complexes bearing formula [(p-cymene)Ru{pyC(py)NOH}Cl]PF6 (2);

[(benzene)Ru{pyC(py)NOH}Cl]PF6 (3), and

[Cp*Rh{pyC(py)NOH}Cl]PF6 (4). In case of complex 3 the ligandcoordinates to the metal by using oxime nitrogen and one of the pyr-idine nitrogen atoms, whereas in complex 4 both the pyridine nitrogenatoms are coordinated to the metal ion. The complexes were fullycharacterized by spectroscopic techniques.

2,2�-dipyridyl imine and di-2-pyridyl ketoxime ligands.[16–18]

These ligands may bind to the metal by using two pyridylnitrogen atoms forming a six membered chelate ring or byimine nitrogen and just one pyridyl nitrogen forming a fivemembered chelate ring.[19–21]

This variety of coordinating modes offered by the ligandmay lead to formation of several compounds with differentstructural motifs and coordination modes. Interesting workwith 2,2�-dipyridyl imine was carried out by Georg Süss-Finkand co-workers, in which they reported the cationic complexes[(arene)Ru(η2-N,N-L)Cl]+ (arene = benzene and p-cymene)and (L = 2,2�-pyridyl N-aryl imines) where they found twocoordination isomers in contrast to the findings reported byKaminsky and co-workers with aliphatic imines.[17,22] In themajor isomer the imine nitrogen and one pyridine nitrogen co-ordinates to ruthenium, while in the minor isomer both thepyridyl nitrogen coordinates to the metal atom.

Based on the reactivity and different binding modes of 2,2�-pyridyl N-aryl imines we anticipated that the substitution ofaryl group with oxime group would give distinctly unusualbinding modes and we have therefore explored this possibility.Herein we investigated the bonding modes of di-2-pyridylketoxime ligand towards [(arene)RuCl2]2, (arene = p-cymene,benzene) and [Cp*MCl2]2 (M = Rh, Ir) half-sandwich com-plexes.

Experimental Section

Materials and Methods: All reagents were purchased from commer-cial sources and used as received. RuCl3·nH2O, RhCl3·nH2O, andIrCl3·nH2O was purchased from Arora Matthey Limited, α-Phellan-drene, 1,4-cyclohexadiene, and pentamethylcyclopentadiene were pur-




chased from Aldrich. Di-2-pyridyl ketone was purchased from Merckand hydroxylamine hydrochloride was obtained from HiMedia. Thesolvents were purified and dried according to standard procedures.[23]

The starting metal precursor complexes [(p-cymene)RuCl2]2, [(benz-ene)RuCl2]2, and [Cp*MCl2]2 (M = Rh, Ir)[24,25] were prepared accord-ing to reported procedures. Di-2-pydridyl ketoxime {pyC(py)NOH}was synthesized by following a reported procedure.[26] 1H NMR spec-tra were recorded with a Bruker Avance II 400 MHz spectrometer.Infrared spectra were recorded as KBr pellets with a Perkin-Elmer 983spectrophotometer. Mass spectra were recorded using Q-Tof APCI-MSinstrument (model HAB 273). Elemental analyses were performedwith a Perkin-Elmer-2400 CH/N analyzer.

Single-Crystal X-ray Structure Analyses: Suitable single crystals ofcomplexes 1a, 1b, 3, and 4 were obtained by slow diffusion of hexaneinto acetone or DCM solution. Single crystal X-ray diffraction data forthe complexes were collected with an Oxford Diffraction Xcalibur EosGemini diffractometer at 293 K using graphite monochromated Mo-

Table 1. Crystal data and structure refinement details of complexes.

[1a]·PF6 [1b]·PF6 [3]·PF6 [4]·PF6

Chemical formula C21H24ClF6N3OPIr C21H24ClF6N3OPIr C17H15ClF6N3OPRu C21H24ClF6N3OPRhFormula mass 707.05 707.05 558.81 617.76T /K 295(2) 296(2) 293(2) 294(2)λ /Å 0.71073 0.71073 0.71073 0.71073Crystal system monoclinic orthorhombic monoclinic orthorhombicSpace group P21/c Pnam P21/c Pnama /Å 7.8033(4) 13.900(10) 12.9013(15) 13.8615(4)b /Å 12.3116(7) 14.287(8) 22.188(2) 14.3890(4)c /Å 25.7612(11) 12.137(7) 14.4020(14) 12.1930(3)α /° 90 90 90 90β /° 91.171(5) 90 107.645(12) 90γ /° 90 90 90 90V /Å3 2474.4(2) 2410(3) 3928.7(7) 2431.93(11)Z 4 4 8 4Dc /g·cm–3 1.898 1.948 1.890 1.687μ /mm–1 5.633 5.783 1.086 0.943F(000) 1368 1368 2208 1240Crystal size /mm3 0.15�0.15�0.09 0.56�0.23 �0.21 0.23�0.21�0.19 0.25�0.19�0.19θ range 3.08 to 28.65 3.62 to 29.01 3.323 to 29.090 3.19 to 28.64Index ranges –10 � h � 6 –17 � h � 9 –10 � h � 17 –18 � h � 15

–13 � k � 16 –10 � k � 17 –29 � k � 28 –19 � k � 9–34 � l � 31 –10 � l � 16 –18 � l � 16 –10 � l � 16

Reflections collected 11973 6054 16492 8056Independent reflections 5635 [R(int) = 0.0382] 2783 [R(int) = 0.0484] 8988 [R(int) = 0.0467] 2947 [R(int) = 0.0235]Completeness to θ = 25.00° 99.7% 97.4% 99.4 % 99.7%Data/restraints/parameters 5635/85/348 2783/79/203 8988/0/543 2947/89/192Goodness-of-fit on F2 1.041 1.051 1.126 1.080Final R indices [I�2σ (I)]a) 0.0479, wR2 = 0.0880 0.0470, wR2 = 0.0844 0.1359, wR2 = 0.3460 0.0449, wR2 = 0.1284R indices (all data)a) 0.0720, wR2 = 0.0972 0.0723, wR2 = 0.0953 0.1653, wR2 = 0.3627 0.0524, wR2 = 0.1361Max, Min Δρ /e·Å–3 1.531, –1.587 2.651, –1.553 3.362, –1.253 1.215, –0.722

a) Structures were refined on F02: wR2 = [Σ[w(Fo

2–Fc2)2]/Σw(Fo

2)2]1/2, where w–1 = [Σ(Fo2)+(aP)2+bP] and P = [max(F0

2, 0)+2Fc2]/3.

Table 2. Selected bond lengths /Å and bond angles /° of complexes (M = Ru, Rh, and Ir).

1a 1b 3 4

M(1)-CNTa) 1.789 1.803 1.692 1.803M(1)–N(1) 2.107(3) 2.053(4) 2.064(13) 2.132(2)M(1)–N(2) 2.107(3) 2.067(5) 2.042(14) 2.068(2)M(1)-Cl(1) 2.4071(16) 2.3937(17) 2.396(4) 2.390(3)N(1)–M(1)–N(2) 85.71(19) 76.80(19) 76.4(5) 84.8(9)N(1)–M(1)–Cl(1) 88.28(10) 84.5(1) 84.3(4) 88.2(6)N(2)–M(1)–Cl(1) 85.71(19) 89.71(1) 85.5(4) 85.2(7)

a) CNT represents the centroid of the arene/Cp* ring.

Z. Anorg. Allg. Chem. 2016, 941–946 © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim942

Kα radiation (λ = 0.71073 Å). The strategy for the data collection wasevaluated using the CrysAlisPro CCD software. Crystal data were col-lected by standard “phi-omega scan” techniques and were scaled andreduced using CrysAlisPro RED software. The structures were solvedby direct methods using SHELXS-97 and refined by full-matrix least-squares with SHELXL-97 refining on F2.[27,28] The positions of all theatoms were obtained by direct methods. Metal atoms in the complexwere located from the E-maps and non-hydrogen atoms were refinedanisotropically. The hydrogen atoms bound to the carbon were placedin geometrically constrained positions and refined with isotropic tem-perature factors, generally 1.2 Ueq of their parent atoms. Crystallo-graphic and structure refinement parameters for the complexes aresummarized in Table 1, and selected bond lengths and bond angles arepresented in Table 2. Figure 1, Figure 2 and Figure 3 are drawn withthe ORTEP3 program.[29]

Because of poor crystal quality the crystal structure of complex 3 has“R” value little high and we have presented the data herein only toestablish the structure.




Syntheses of Metal Complexes: A mixture of starting metal precursor[(arene)RuCl2]2, (arene = p-cymene, benzene) or [Cp*MCl2]2 (M =Rh/Ir) (0.1 mmol), ligand di-2-pydridyl ketoxime {pyC(py)NOH}(0.2 mmol), and 2.5 equivalents of NH4PF6 were dissolved in drymethanol (10 mL) and stirred at room temperature for 8 h (Scheme 1).A yellow colored compound precipitated out from the reaction mix-ture. The precipitate was filtered, washed with cold methanol(2�5 mL) and diethyl ether (3�10 mL) and dried.

Scheme 1. Preparation of metal complexes.

[Cp*Ir{pyC(py)NOH}Cl]PF6 (1a and 1b): Yield 92 mg (65%). IR(KBr): ν̃ = ν(OH) 3480 s, (CH) 2925 m, ν(C=N, C=C) 1600–1480 m,ν(P–F) 844 vs cm–1. 1H NMR (400 MHz, [D6]DMSO + CDCl3,25 °C): δ = 13.37 (s, 2 H, OH), 8.86 [d, J(H,H) = 8 Hz, 1 H, CH(py)],8.76 (d, JH,H = 4 Hz, 1 H, CH(py)), 8.72 (d, JH,H = 8 Hz, 1 H,CH(py)), 8.65 (d, JH,H = 8 Hz, 1 H, CH(py)), 8.22 (t, 1 H, CH(py)), 8.14(d, JH,H = 8 Hz, 1 H, CH(py)), 7.91–8.03 (m, 5 H, CH(py)), 7.74 (d,JH,H = 8 Hz, 1 H, CH(py)), 7.69 (t, 1 H, CH(py)), 7.52–7.57 (m, 3 H,CH(py)), 1.70 (s, 15 H, CH(Cp*)), 1.38 (s, 15 H, CH(Cp*)). HRMS-APCI(m/z): 562.1341 (M-PF6)+ peak. C21H24N3OIrClPF6 (707.06): C 35.79(calcd. 35.67); H 3.56 (3.42); N 5.78 (5.94)%.

[(p-cymene)Ru{pyC(py)NOH}Cl]PF6 (2): Yield 92 mg (78%). IR(KBr): ν̃ = ν(OH) 3436 b, ν(CH) 2969 m, ν(C=N, C=C) 1600–1450m, ν(P–F) 844 vs cm–1. 1H NMR (400 MHz, [D6]DMSO + CDCl3,25 °C): δ = 9.27 (d, JH,H = 8 Hz, 1 H, CH(py)), 8.72 (d, JH,H = 4 Hz, 1H, CH(py)), 7.99 (t, 1 H, CH(py)), 7.86 (t, 1 H, CH(py)), 7.69 (t, 1 H,CH(py)), 7.51–7.57 (m, 3 H, CH(py)), 5.97 (d, JH,H = 8 Hz, 1 H,CH(p–cym)), 5.84 (d, JH,H = 4 Hz, 1 H, CH(p–cym)), 5.81 (d, JH,H = 4 Hz,1 H, CH(p–cym)), 5.60 (d, JH,H = 8 Hz, 1 H, CH(p–cym)), 2.75 (sept. 1H, CH(p–cym)), 2.29 (s, 3 H, CH(p–cym)), 1.09 (d, JH,H = 8 Hz, 3 H,CH(p–cym)), 1.18 (d, JH,H = 8 Hz, 3 H, CH(p–cym)), OH not observed.HRMS-APCI (m/z): 470.0674 (M-PF6)+ peak. C21H23N3ORuClPF6

(614.9): C 35.79 (calcd. 35.91); H 3.56 (3.41); N 6.97 (6.83)%.

[(benzene)Ru{pyC(py)NOH}Cl]PF6 (3): Yield 84 mg (75%). IR(KBr): ν̃ = ν(OH) 3449 b, ν(CH) 3101 m, ν(C=N, C=C) 1599–1485m, ν(P–F) 840 vs cm–1. 1H NMR (400 MHz, [D6]DMSO + CDCl3,25 °C): δ = 8.73 (d, JH,H = 8 Hz, 1 H, CH(py)), 7.97 (t, 1 H, CH(py)),7.89 (t, 1 H, CH(py)), 7.72 (d, JH,H = 8 Hz, 1 H, CH(py)), 7.48–7.52 (m,3 H), 7.43 (d, JH,H = 4 Hz, 1 H, CH(py)), 6.07 (s, 6H, CH(benzene)), OHnot observed. HRMS-APCI (m/z): 413.9821 (M-PF6)+ peak.C17H15N3ORuClPF6 (558.8): C 36.67 (calcd. 36.54); H 2. 86 (2.71);N 7.63 (7.52)%.


[Cp*Rh{pyC(py)NOH}Cl]PF6 (4): Yield 102 mg (82%). IR (KBr):ν̃ = ν(OH) 3480 b, ν(CH) 2990 w, ν(C=N, C=C) 1595–1470 m,ν(P–F) 851 s cm–1. 1H NMR (400 MHz, [D6]DMSO + CDCl3, 25 °C):δ = 13.3 (s, 1 H,OH), 8.89 (d, JH,H = 4 Hz, 1 H, CH(py)), 8.80 (d,JH,H = 4 Hz, 1 H, CH(py)), 8.11–8.15 (m, 3 H, CH(py)), 7.92 (d, JH,H =8 Hz, 1 H, CH(py)), 7.65–7.70 (m, 2 H, CH(py)), 1.42 (s, 15H,CH(Cp*)). HRMS-APCI (m/z): 472.0807 (M-PF6)+ peak.C21H24N3ORhClPF6 (617.7): C 40.92 (calcd. 40.83); H 3.85 (3.92); N6.94 (6.80) %.

Crystallographic data (excluding structure factors) for the structures inthis paper have been deposited with the Cambridge CrystallographicData Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copiesof the data can be obtained free of charge on quoting the depositorynumbers CCDC-1494091 (1a), CCDC-1494092 (1b), CCDC-1494093(3), and CCDC-1494094 (4) (Fax: +44-1223-336-033; E-Mail:[email protected], http://www.ccdc.cam.ac.uk)

Results and Discussion

Syntheses of Complexes

[Cp*IrCl2]2 reacts with di-2-pyridyl ketoxime inmethanol in presence of NH4PF6 to give cationic oximecomplexes of the type [Cp*Ir{pyC(py)NOH}Cl]PF6 and[Cp*Ir{pyC(py)NOH}Cl]PF6, for which two isomers were ob-served by NMR spectroscopy. Our attempt to separate the iso-mers was unsuccessful and we predicted the NMR spectrafrom the crude mixture containing both the isomers. However,we were successful to isolate the single crystals of both theisomers by physical separation and get the molecular structureof both the isomers, whereas in the case of rhodium precursorit exclusively yielded only one isomer with the ligand coordi-nating to the metal through both the pyridine nitrogen atomsforming a six membered chelate ring. However in the case ofarene ruthenium dimers it yielded solely one isomer with li-gand binding through pyridyl nitrogen and oxime nitrogenforming a five membered chelated ring. All these metal com-plexes were isolated as yellow solids with PF6 counterion.These complexes are soluble in common organic solvents suchas DCM, CH3CN, and acetone but partially soluble in CHCl3,CH3OH, whereas they are insoluble in hexane and diethylether.

IR Spectroscopy

The formation of the cationic metal complexes was con-firmed by the IR spectra of the complexes, which show sharpbands around 842–846 cm–1 due to the P–F stretching fre-quency of the counterion. The OH stretching vibrations in thecomplexes were found around 3300–3500 cm–1. The strongabsorption band for C=N around 1630–1650 cm–1 at higherwave numbers as compared to the free ligand around 1615–1626 cm–1 suggest the coordination of the ligand to the centralmetal atom.

1H NMR Spectroscopy

In the 1H NMR spectra of the complexes the signals for thearomatic protons of the ligand was observed in the downfield




region around 7.32–9.50 ppm. This shift of the ligand protonsignals in the complexes clearly indicates the coordination ofthe ligand to the metal. The 1H NMR spectroscopic data of theiridium complex were taken from the crude mixture containingboth the isomers. The NMR spectrum of complexes (1a and1b) showed singlets at δ = 1.38 and 1.70 ppm, which corre-sponds to the methyl protons of Cp* group. In addition to thesignals for the aromatic protons of the ligand, complex 2 dis-played four doublets at around 5.60–6.19 ppm for the aromaticprotons of the p-cymene moiety. The methyl protons of theisopropyl group displayed two doublets around 1.01–1.18 ppm. It also displayed septet at δ = 2.75 ppm and singletat δ = 2.29 ppm to the methine protons of the isopropyl groupand methyl group of the p-cymene ligand. Complexes 3 and 4displayed a singlet at δ = 6.07 ppm and 1.52 ppm due to pro-tons of the benzene ring and methyl protons of Cp* moiety.

Mass Spectrometry

In the mass spectra of complexes 1–4 the molecular ionpeaks were observed at m/z: 562.1341, m/z: 470.0674, m/z:413.9821, m/z: 472.0807 which can be assigned as [M–PF6]+

ion peaks respectively.

Molecular Structures of Complexes

The molecular structures of some of the complexes wereestablished by single-crystal X-ray analysis. Suitable singlecrystals were attached to a glass fiber and transferred into theOxford Diffraction Xcalibur Eos Gemini diffractometer. Thecrystallographic details and structure refinement details aresummarized in Table 1. The geometrical parameters around themetal atom involving ring centroid are listed in Table 2. Theiridium complex 1a and 1b crystallized in the monoclinic andorthorhombic crystal system with space group P21/c andPnam, respectively Complex 3 crystallized in the monoclinicsystem with space group P21/c, whereas complex 4 crys-tallized in the orthorhombic system with Pnam space group.The molecular structure of benzene ruthenium, Cp* rhodiumand both the isomers of iridium oxime complexes were con-firmed by single-crystal X-ray diffraction studies in order toconfirm the bonding mode of the ligand and to understand thearrangement of the complexes.

The ORTEP views of the complexes are shown in Figure 1,Figure 2, and Figure 3. The molecular structures of these com-plexes display a typical three legged “piano stool” arrangementaround the central metal atom with coordination sites occupiedby two nitrogen donor atoms from chelating ligand in a biden-tate κ2-NN� fashion, one chloride atom and the arene/Cp* ringin a η6/η5 manner. By carrying out the single crystal analysiswe were able to confirm the different coordination mode ofthe ligand to the metal. The X-ray structure of both the isomersof iridium complex revealed the different coordination modesto the metal ion. In the major isomer 1a the ligand is coordi-nated to the iridium atom through oxime nitrogen and one ofthe pyridine nitrogen atoms, whereas in the minor isomer 1bthe ligand coordinates to iridium by using both the pyridine


Figure 1. (a) ORTEP diagram of complex 1a and (b) ORTEP diagramof complex 1b. Hydrogen atoms and counterions are omitted for clar-ity.

nitrogen atoms. In complex 3 the ligand is coordinated to theruthenium atom in a bidentate fashion by using one pyridineand oxime nitrogen atoms forming a five-membered chelatering. In complex 4 the ligand is coordinated to the central rho-dium atom through both the pyridine nitrogen atoms forminga six membered chelate ring. The iridium to centroid of theCp* ring distance in the major isomer 1a is 1.789 Å and themetal-to-centroid of Cp* ring in minor isomer 1b and rhodiumcomplex 4 are equal to 1.803 Å. In case of complex 3 theruthenium to centroid distance in 1.692 Å. The bond angle val-ues N–M–N and N–M–Cl in these complexes are less than 90°and are comparable to the piano stool arangement about the




central metal atoms. The M–N and M–Cl bond lengths (whereM = Ru, Rh, and Ir) in these complexes are found to be inclose agreement with previously reported values for relatedcomplexes with NN‘ donor ligands.[30] We were unsuccessfulto isolate single crystals for complex 2, so based on the NMRspectroscopic data and previous works carried out by Kamin-sky and co-workers[17] we assumed that the coordination of theligand to the ruthenium atom may be through one of the pyr-idine and oxime nitrogen atoms.

Figure 2. ORTEP diagram of complex 3. Hydrogen atoms and coun-terions are omitted for clarity.

Figure 3. ORTEP diagram of complex 4. Hydrogen atoms and coun-terions are omitted for clarity.

Conclusions

We have successfully examined the coordination behaviorof di-2-pyridyl ketoxime ligand towards arene ruthenium,


Cp*Rh and Cp*Ir half-sandwich complexes. The molecularstructures of both the isomers of the iridium complex wereestablished by X-ray diffraction studies. In the case of majorisomer the oxime nitrogen and one of the pyridine nitrogenatoms is coordinated to the metal, whereas in the case of minorisomer both the pyridine nitrogen atoms are coordinated to thecentral metal atom. In contrast, rhodium precursor formed ex-clusively only one coordination isomer, where both the pyr-idine nitrogen atoms of the ligand are coordinated to the metalion. In the case of ruthenium complex the ligand is coordinatedto the metal through oxime nitrogen and one of the pyridinenitrogen atoms. This work displays the use of di-2-pyridyl ke-toxime as a ligand to form complexes with interesting bindingmodes.

Acknowledgements

Sanjay Adhikari thanks UGC, New Delhi, India for providing financialassistance in the form of university fellowship (UGC-Non-Net). KMRthanks UGC New Delhi (F. No. 39–793/2010 (SR) for financial sup-port in the form of major Research Project. We thank DST-PURSESCXRD, NEHU-SAIF, Shillong, India for providing Single crystal X-ray analysis and other spectral studies.

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Received: July 21, 2016Published Online: August 12, 2016

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