Suvendu Maity

Orthometalation of Dibenzo[1,2]quinoxaline with Ruthenium(II/III), Osmium(II/III/IV), and Rhodium(III) Ions and Orthometalated [RuNO]6/7 Derivatives

A new family of organometallics of ruthenium(II/III), osmium(II/III/IV), and rhodium(III) ions isolated from C-H activation reactions of dibenzo[1,2]quinoxaline (DBQ) using triphenylphosphine, carbonyl, and halides as coligands is reported. The CN-chelate complexes isolated are trans-[Ru(III)(DBQ)(PPh3)2Cl2] (1), trans-[Ru(II)(DBQ)(CO)(PPh3)2Cl] (2), trans-[Os(III)(DBQ)(PPh3)2Br2] (3), trans-[Os(II)(DBQ)(PPh3)2(CO)Br] (4), and trans-[Rh(III)(DBQ)(PPh3)2Cl2] (5). Reaction of 1 with NO affords trans-[Ru(DBQ)(NO)(PPh3)2Cl]Cl (6(+)Cl(-)), isoelectronic to 2, with a byproduct, [Ru(NO)(PPh3)2Cl3] (7). Complexes 1-5 and 6(+) were characterized by elemental analyses, mass, IR, NMR, and electron paramagnetic resonance (EPR) spectra including the single-crystal X-ray structure determinations of 1-3 and 5. The Ru(III)-C, Ru(II)-C, Os(III)-C, and Rh(III)-C lengths are 2.049(2), 2.074(3), 2.105(16), and 2.012(3) Å in 1, 2, 3, and 5. In cyclic voltammetry, 2, 3, and 4 undergo oxidation at 0.59, 0.39, and 0.46 V, versus Fc(+)/Fc couple, to trans-[Ru(III)(DBQ)(CO)(PPh3)2Cl](+) (2(+)), trans-[Os(IV)(DBQ)(PPh3)2Br2](+) (3(+)), and trans-[Os(III)(DBQ)(CO)(PPh3)2Br](+) (4(+)) ions. Complex 3(+) incorporates an Os(IV)(d(4) ion)-C bond. The 6(+)/trans-[Ru(DBQ)(NO)(PPh3)2Cl] (6) reduction couple at -0.65 V is reversible. 2(+), 3(+), 4(+) and 6 were substantiated by spectroelectrochemical measurements, EPR spectra, and density functional theory (DFT) and time-dependent (TD) DFT calculations. The frozen-glass EPR spectrum of the electrogenerated 6 exhibits hyperfine couplings due to (99,101)Ru and (14)N nuclei. DFT calculations on trans-[Os(III)(DBQ)(PMe3)2Br2] (3(Me)), St = 1/2 and trans-[Os(IV)(DBQ)(PMe3)2Br2](+) (3(Me+)), St = 0, trans-[Ru(DBQ)(NO)(PMe3)2Cl](+) (6(Me+)), St = 0 and trans-[Ru(DBQ)(NO)(PMe3)2Cl] (6(Me)), St = 1/2, authenticated a significant mixing between dOs and πaromatic* orbitals, which stabilizes M(II/III/IV)-C bonds and the [RuNO](6) and [RuNO](7) states, respectively, in 6(+) and 6, which is defined as a hybrid state of trans-[Ru(II)(DBQ)(NO(•))(PPh3)2Cl] and trans-[Ru(I)(DBQ)(NO(+))(PPh3)2Cl] states.

Mono- and di-nuclear photoluminescent complexes of zinc(II), cadmium(II) and mercury(II) of a chiral diimine ligand

Reaction of α-pyridoin and N-phenyl-o-phenylenediamine affords 2-(2-(phenylamino)phenylimino)-1,2-di(pyridin-2-yl)ethanol (L) which undergoes cyclization to a chiral diimine, 2-methoxy-1-phenyl-2,3-di(pyridin-2-yl)-1,2-dihydroquinoxaline, L(OMe) (conjugated 14πe system) in the presence of zinc(II), cadmium(II) and mercury(II) ions affording [Zn(L(OMe))Cl2] (1), [Cd2(L(OMe))2Cl4] (2) and [Hg2(L(OMe))2Cl4] (3) complexes. Ligand L and complexes 1-3 are substantiated by elemental analyses, mass, IR, (1)H NMR and UV-vis spectra including the single-crystal X-ray structures of 1 and 3. The possibility of the atropisomerism of L is restricted in cyclic L(OMe). L and complexes 1-3 are fluorescent in fluid solutions at 298 K (CH2Cl2: 1, λ(ex) = 470 nm, λ(em) = 627 nm, Φ = 0.014, τ(avg) = 2.5 ns; 2, λ(ex) = 430 nm, λ(em) = 599 nm, Φ = 0.08, τ(avg) = 7.6 ns; 3, λ(ex) = 415 nm, λ(em) = 600 nm, Φ = 0.021, τ(avg) = 2.8 ns). Time-resolved emission spectra (TRES) established that the two-component lifetimes of 1-3 are due to the existence of two conformers. Density functional theory (DFT) and time dependent (TD) DFT calculations authenticated that 1-3 complexes are fluorescent due to intra-ligand charge transfer (ILCT) to the π(diimines)* orbital.

Tris(2,2′-azobispyridine) Complexes of Copper(II): X-ray Structures, Reactivities, and the Radical Nonradical Bis(ligand) Analogues

Tris(abpy) complexes of types mer-[Cu(II)(abpy)3][PF6]2 (mer-1(2+)[PF6(–)]2) and ctc-[Cu(II)(abpy)2(bpy)][PF6]2 (ctc-2(2+)[PF6(–)]2) were successfully isolated and characterized by spectra and single-crystal X-ray structure determinations (abpy = 2,2′-azobispyridine; bpy = 2,2′-bipyridine). Reactions of mer-1(2+) and ctc-2(2+) ions with catechol, o-aminophenol, p-phenylenediamine, and diphenylamine (Ph–NH–Ph) in 2:1 molar ratio afford [CuI(abpy)2](+) (3(+)) and corresponding quinone derivatives. The similar reactions of [Cu(II)(bpy)3](2+) and [Cu(II)(phen)3](2+) with these substrates yielding [Cu(I)(bpy)2](+) and [Cu(I)(phen)2](+) imply that these complexes undergo reduction-induced ligand dissociation reactions (phen = 1,10-phenanthroline). The average −N═N– lengths in mer-1(2+)[PF6(–)]2 and ctc-2(2+)[PF6(–)]2 are 1.248(4), while that in 3(+)[PF6(–)]·2CH2Cl2 is relatively longer, 1.275(2) Å, due to dCu → πazo* back bonding. In cyclic voltammetry, mer-1(2+) exhibits one quasi-reversible wave at −0.42 V due to Cu(II)/Cu(I) and abpy/abpy(•–) couples and two reversible waves at −0.90 and −1.28 V due to abpy/abpy(•–) couple, while those of ctc-2(2+) ion appear at −0.44, −0.86, and −1.10 V versus Fc(+)/Fc couple. The anodic 3(2+)/3(+) and the cathodic 3(+)/3 redox waves at +0.33 and −0.40 V are reversible. The electron paramagnetic resonance spectra and density functional theory (DFT) calculations authenticated the existence of abpy anion radical (abpy(•–)) in 3, which is defined as a hybrid state of [Cu(I)(abpy(0.5•–))(abpy(0.5•–))] and [Cu(II)(abpy(•–))(abpy(•–))] states. 3(2+) ion is a neutral abpy complex of copper(II) of type [Cu(II)(abpy)2](2+). 3 exhibits a near-IR absorption band at 2400–3000 nm because of the intervalence ligand-to-ligand charge transfer, elucidated by time-dependent DFT calculations in CH2Cl2.

Radical and Non-Radical States of the [Os(PIQ)] Core (PIQ = 9,10-Phenanthreneiminoquinone): Iminosemiquinone to Iminoquinone Conversion Promoted o-Metalation Reaction

The coordination and redox chemistry of 9,10-phenanthreneiminoquinone (PIQ) with osmium ion authenticating the [Os(II)(PIQ(•-))], [Os(III)(PIQ(•-))], [Os(III)(C,N-PIQ)], [Os(III)(PIQ)], and [Os(III)(PIQ(2-)) ] states of the [Os(PIQ)] core in the complexes of types trans-[Os(II)(PIQ(•-))(PPh3)2(CO)Br] (1), trans-[Os(III)(PIQ(•-))(PPh3)2Br2] (2), trans-[Os(III)(C,N-PIQ)(PPh3)2Br2]·2CH2Cl2 (3·2CH2Cl2), trans-[Os(III)(C,N-PIQ(Br))(PPh3)2Br2]·2CH2Cl2 (4·2CH2Cl2), trans-[Os(III)(C,N-PIQ(Cl2))(PPh3)2Br2] (6), trans-[Os(III)(PIQ(•-))(PPh3)2Br2](+)1/2I3(-)1/2Br(-) (1(+)1/2I3(-)1/2Br(-)), [Os(III)(PIQ)(PPh3)2Br2](+) (2(+)), and [Os(III)(PIQ(2-))(PPh3)2Br2](-) (2(-)) are reported (PIQ(•-) = 9,10-phenanthreneiminosemiquinonate anion radical; C,N-PIQ = ortho-metalated PIQ, C,N-PIQ(Br) = ortho-metalated 4-bromo PIQ, and C,N-PIQ(Cl2) = ortho-metalated 3,4-dichloro PIQ). Reduction of PIQ by [Os(II)(PPh3)3(H)(CO)Br] affords 1, while the reaction of PIQ with [Os(II)(PPh3)3Br2] furnishes 2. Oxidation of 1 with I2 affords 1(+)1/2I3(-)1/2Br(-), while the similar reactions of 2 with X2 (X = I, Br, Cl) produce the ortho-metalated derivatives 3·2CH2Cl2, 4·2CH2Cl2, and 6. PIQ and PIQ(2-) complexes of osmium(III), 2(+) and 2(-), are generated by constant-potential electrolysis. However, 2(+) ion is unstable in solution and slowly converts to 3 and partially hydrolyzes to trans-[Os(III)(PQ(•-))(PPh3)2Br2] (2PQ), a PQ(•-) analogue of 2. Conversion of 2(+) → 3 in solution excludes the formation of aryl halide as an intermediate for this unique ortho-metalation reaction at 295 K, where PIQ acts as a redox-noninnocent ambidentate ligand. In the complexes, the PIQ(•-) state where the atomic spin is more localized on the nitrogen atom is stable and is more abundant. The reaction of 2PQ, with I2 does not promote any ortho-metalation reaction and yields a PQ complex of type trans-[Os(III)(PQ)(PPh3)2Br2](+)I5(-)·2CH2Cl2 (5(+)I5(-)·2CH2Cl2). The molecular and electronic structures of 1-4, 6, 1(+), and 5(+) were established by different spectra, single-crystal X-ray bond parameters, cyclic voltammetry, and DFT calculations.

Two isostructural linear coordination polymers: the size of the metal ion impacts the electrical conductivity

Two new one-dimensional coordination polymers (1D CPs) {[Zn(adc)(4-spy)2(H2O)2]}n (1), and {[Cd(adc)(4-spy)2(H2O)2]}n (2) (H2adc = acetylenedicarboxylic acid and 4-spy = 4-styrylpyridine), have been synthesized and well characterized. Single crystal X-ray diffraction data exhibit that compounds 1 and 2 are isostructural and undergo hydrogen bonding and C–H⋯π interactions to construct 3D supramolecular architectures. Electrical characterization reveals that both compounds show substantive electrical conductivity and exhibit Schottky diode nature. However, compound 2 has a higher mobility and higher conductivity compared to 1. The estimated values of effective carrier mobility, transit time, carrier concentration and diffusion length demonstrate that the charge transport properties have been improved for 2. Therefore, compound 2 has better performance in the fabrication of electronic devices.

Molecular and Electronic Structures of Ruthenium Complexes Containing an ONS-Coordinated Open-Shell π Radical and an Oxidative Aromatic Ring Cleavage Reaction

The coordination chemistry of 2,4-di-tert-butyl-6-[(2-mercaptophenyl)amino]phenol (LONSH3), which was isolated as a diaryl disulfide form, (LONSH2)2, with a Ru ion is disclosed. It was established that the trianionic LONS3- is redox-noninnocent and undergoes oxidation to either a closed-shell singlet (CSS), LONS-, or an open-shell π-radical state, LONS•2-, and the reactivities of the [RuII(LONS•2-)] and [RuII(LONS-)] states are different. The reaction of (LONSH2)2 with [Ru(PPh3)3Cl2] in toluene in the presence of PPh3 affords a ruthenium complex of the type trans-[Ru(LONS)(PPh3)2Cl] (1), while the similar reaction with [Ru(PPh3)3(H)(CO)Cl] yields a LONS•2- complex of ruthenium(II) of the type trans-[RuII(LONS•2-)(PPh3)2(CO)] (2). 1 is a resonance hybrid of the [RuII(LONS-)Cl] and [RuIII(LONS•2-)Cl] states. It is established that 2 incorporating an open-shell π-radical state, [RuII(LONS•2-)(CO)], reacts with an in situ generated superoxide ion and promotes an oxidative aromatic ring cleavage reaction, yielding a α-N-arylimino-ω-ketocarboxylate (LNS2-) complex of the type [RuII(LNS2-)(PPh3)(CO)]2 (4), while 1 having a CSS state, [RuII(LONS-)Cl], is inert in similar conditions. Notably, 2 does not react with O2 molecule but reacts with KO2 in the presence of excess PPh3, affording 4. The redox reaction of (LONSH2)2 with [Ru(PPh3)3Cl2] in ethanol in air is different, leading to the oxidation of LONS to a quinone sulfoxide derivative (LONSO0) as in cis-[RuII(LONSO0)(PPh3)Cl2] (3), via 1 as an intermediate. The molecular and electronic structures of 1-4 were established by single-crystal X-ray crystallography, electron paramagnetic resonance spectroscopy, electrochemical measurements, and density functional theory calculations. 1+ is a resonance hybrid of [RuIII(LONS-)(PPh3)2Cl ↔ RuIV(LONS•2-)(PPh3)2Cl]+ states, 2- is a LONS3- complex of ruthenium(II), [RuII(LONS3-)(PPh3)2(CO)]-, and 2+ is a ruthenium(II) complex of LONS- of the type [RuII(LONS-)(PPh3)2(CO)]+, where 35% diradical character of the LONS- ligand was predicted.

Coordination of o-benzosemiquinonate, o-iminobenzosemiquinonate, 4,4′-di-tert-butyl-2,2′-bipyridine and 1,10-phenanthroline anion radicals to oxidovanadium(IV)

This article reports on the stabilization of organic radical anions promoted by the oxidovanadium(IV) ion. A 3,5-di-tert-butylcatecholate (tBucatH−) complex of oxidovanadium(V) of the type [(LaONO2−)(VO3+)(tBucatH−)] (1) was isolated using tridentate (E)-N′-((3-hydroxynaphthalen-2-yl)methylene)benzohydrazide (LaONOH2) as a coligand, whereas o-benzosemiquinonate (sq˙−) and p-nitro-o-iminobenzosemiquinonate (NO2isq˙−) radical anion complexes of oxidovanadium(IV) of the types [(LNNO−)(VO2+)(sq˙−)] (2) and [(LNNO−)(VO2+)(NO2isq˙−)] (3) were successfully isolated using (1Z,N′E)-N′-(phenyl(pyridin-2-yl)methylene)benzohydrazonic acid (LNNOH) as a coligand. Oxidovanadium(IV) complexes of the types [(LbONO2−)(VO2+)(phen)] (4) and [(LbONO2−)(VO2+)(tBubpy)] (5), which undergo reversible reduction to the 4,4′-di-tert-butyl-2,2′-bipyridine radical anion (tBubpy˙−) and the 1,10-phenanthroline radical anion (phen˙−) to afford the coupled states [(LbONO2−)(VO2+)(phen˙−)]− (4−) and [(LbONO2−)(VO2+)(tBubpy˙−)]− (5−), respectively, were isolated (LbONOH2 = (E)-N′-(2-hydroxybenzylidene)benzohydrazide). The molecular geometries of the complexes were confirmed by the single-crystal X-ray structure determinations of 1, 3 and 4. In 1, the V–Ophenolato length cis to VO is 1.879(2) A and the dissimilar V–O and V–OH lengths corresponding to the tBucatH− ligand are 1.832(2) and 2.312(2) A, respectively. In 1, the average C–O lengths in tBucatH− are 1.351(3) A, whereas in 3 the average C–O and C–N lengths in NO2isq˙− are 1.293(4) and 1.355(5) A, respectively. In 4, the V–Ophenolato length cis to VO (1.937(3) A) is relatively longer. The 51V NMR spectrum of 1 displays a signal at −337.2 ppm, whereas the signals for 2 and 3 are deshielded to +382.4 and +71.8 ppm, respectively. The closed-shell singlet (CSS) solutions of 3 and 5− at the B3LYP/DFT level are unstable and the open-shell singlet (OSS) solutions are 0.5 and 7.3 kcal mol−1 lower in energy, respectively, than the CSS solutions. In 3 and 5− the alpha spin (100%) is localized on the vanadium ion, whereas the beta spin is delocalized across the aminophenol and bipyridine fragments. 2 and 3 exhibit lower-energy absorption bands at 785 and 585 nm, which are defined as CSS → OSS perturbation transitions.

Zinc(II), iron(II/III) and ruthenium(II) complexes of o-phenylenediamine derivatives: oxidative dehydrogenation and photoluminescence

Reactions of benzoyl pyridine, o-phenylenediamine and anhydrous ZnX2 in methanol afford imine complexes [Zn(L1)X2] (X = Cl, 1; X = Br, 2) in good yields (L1 = (E)-N(1)-(phenyl(pyridin-2-yl)methylene)benzene-1,2-diamine). The reduction of 1 with NaBH4 affords (E)-N(1)-(phenyl(pyridine-2-yl)methylene)benzene-1,2-diamine (L2H). The reaction of L2H with [Ru(II)(PPh3)3Cl2] results in the oxidative dehydrogenation to L1 generating cis-[Ru(II)(L1)(PPh3)Cl2] (3). The reaction of L2H with salicylaldehyde affords (E)-2-(((2-((phenyl(pyridin-2-yl)methyl)amino)phenyl)imino)methyl)phenol (L3H2). The reaction of L3H2 with anhydrous FeCl3 in CH3OH affords cis-[Fe(III)(L3H(-))Cl2] (4). Reaction of L3H2 with [Ru(II)(PPh3)3Cl2] results in the oxidative dehydrogenation to diimine, L4H, affording trans-[Ru(II)(L4(-))(PPh3)2](+), which is isolated as trans-[Ru(II)(L4(-))(PPh3)2]PF6 (5(+)PF6(-)) (L4H = 2-((E)-(2-((E)-phenyl(pyridin-2-yl)methyleneamino)phenylimino)methyl)phenol). The reduction of L3H2 with NaBH4 produces 2-(((2-((phenyl(pyridin-2-yl)methyl)amino)phenyl)amino)methyl)phenol (L5H3). With iron(III) L5H3 undergoes oxidative dehydrogenation to L3H2 affording 4, while with [Ru(II)(PPh3)3Cl2], L5H3 undergoes 4e + 4H(+) transfer giving 5(+). A fluid solution of L3H2 at 298 K exhibits an emission band at 470 nm (λ(ex) = 330 nm, τ1 = 3.70 ns) and a weaker band at 525 nm (λ(ex) = 330, 390 nm, τ1 = 1.1 ns) at higher concentrations due to molecular aggregation, which are temperature dependent. 4 is brightly emissive (λ(ex) = 330 nm, λ(em) = 450 nm, Φ = 0.586, τ1 = 3.70 ns). Time resolved emission spectra (TRES) and lifetime measurements confirm that the lower energy absorption band of L3H2 at 390 nm, which is absent in complex 4, has a larger non-radiative rate constant (k(nr)). The redox innocent Al(III) adduct of L3H2 is fluorescent (λ(ex) = 330 nm, λ(em) = 450 nm, τ1 = 3.70 ns). On the contrary, the cis-[Fe(II)(L3H(-))Cl2](-) and cis-[Co(L3H(-))Cl2](-) analogues are non emissive. Density function theory (DFT) calculations, redox potentials and the near infra-red (NIR) absorption data prove that 4 is emissive due to the stable [Fe(III)(L3H(-)*)] state, while 3, 5(+), cis-[Fe(II)(L3H(-))Cl2](-) and cis-[Co(L3H(-))Cl2](-) are non-emissive due to transformations of the [M(II)(L*)] to [M(III)(L˙(-)*)] states.

A hydrazine-based thiocarbamide probe for colorimetric and turn-on fluorometric detection of PO43− and AsO33− in semi-aqueous medium

2,6-Bis(N-ethylhydrazonethiocarbamide)-4-methyl-phenol (HTP) recognizes PO43− and AsO33− and is effective as a colorimetric and turn-on fluoremetric sensor in the presence of a large number of biologically important cations and anions. The limit of detection (LOD) is 34 nM for PO43− and 15 nM for AsO33−. The composition of the probe–anion association has been established by Jobs plot, 1H-NMR titration and HR-MS data. The Density Functional Theory (DFT) computation technique is used to optimize the structure that has been compared with an X-ray structure of HTP and the calculated electronic properties are correlated with the experimental results. Turn-on detection of PO43− and AsO33− is also successfully utilized for the fabrication of an ‘OR’ gate. The probe, HTP, is used for analysis of the ground water of Jadavpur, Kolkata.

An Iminosemiquinone-Coordinated Oxidovanadium(V) Complex: A Combined Experimental and Computational Study

Ligand H4Sar(AP/AP) contained two terminal amidophenolate units that were connected by a disulfane bridge. The ligand reacted with VOSO4·5H2O in the presence of Et3N under air and provided a mononuclear octahedral oxidovanadium complex (1). X-ray crystal structure analysis of complex 1 revealed that the oxidation state of the V ion was V and the VO3+ unit was coordinated to an iminosemiquinone radical anion. An isotopic signal at g = 1.998 in the X-band electron paramagnetic resonance (EPR) spectrum and the solution magnetic moment μeff = 1.98 μB at 298 K also supported the composition. The formation of complex 1 preceded through the initial generation of a diamagnetic VO2+-iminoisemiquinone species, as established by time-dependent UV-vis-near-IR (NIR), X-band EPR, and density functional theory studies. The UV-vis-NIR spectrum of complex 1 consisted of four ligand-to-metal charge-transfer transitions in the visible region, while an intervalence ligand-to-ligand charge transfer appeared at 1162 nm. The cyclic voltammogram of the complex showed four oxidation waves and one reduction wave. Spectroelectrochemical studies at fixed potentials revealed that the oxidation and reduction processes were ligand-based.