Response surface optimization of cellulase production by Aspergillus stellatus NFCCI 5299 in shake flask submerged fermentation using wheat bran.

The expense of cellulase enzymes is the main barrier to the enzymatic saccharification of biomass. Numerous tactics, such as the utilizing inexpensive lignocellulosic substrates as well as economically feasible fermentation techniques for the production of the enzyme may reduce the cost of cellulases. The present investigation was aimed to improve cellulase production employing potential cellulolytic soil fungi, Aspergillus stellatus NFCCI 5299 using wheat bran as substrate. Employing response surface methodology (RSM) with central composite design (CCD), the most efficient process parameters were determined. The ideal conditions for the synthesis of carboxy methyl cellulase (CMCase) and filter paper cellulase activity (FPase) were 6 days of incubation, inoculum size of 4 mycelial disc, 125 rpm of agitation, and 3.5% of wheat bran. The significant mycelial development and enzymatic digestion of wheat bran were discovered by scanning electron microscopy (SEM) and fourier transform infrared (FTIR) analysis. The findings suggested that it can be practicable to use wheat bran as substrate under submerged fermentation utilizing Aspergillusstellatus NFCCI 5299 for efficient cellulase production.

Combined Experimental and Mechanoelastic Modeling Studies on the Low-Spin Stabilized Mixed Crystals of 3D Oxalate-Based Coordination Materials.

Structural studies involving single-crystal and powder X-ray diffraction analysis have been performed on dehydrated coordination networks of the [NixCo1-x(bpy)3][LiCr(ox)3] series, 0 ≤ x ≤ 1, (bpy = 2,2'-bipyridine). The high-symmetry cubic 3D structure of these materials is formed by oxalate anions bridging alternating Cr3+ and Li+ ions into an anionic framework, which contains large cavities that incorporate the [NixCo1-x(bpy)3]2+ cations. Irrespective of the Co/Ni ratio, all of the mixed samples are phase-pure and retain the high-symmetry cubic structure, with the lattice parameters gradually decreasing upon increasing Ni(II) concentration. The influence of the Ni(II) dilution on the magnetic behavior of these materials is substantial. For pure [Co(bpy)3][LiCr(ox)3], a gradual but incomplete thermal spin-crossover is evident due to the effect of the chemical pressure applied by the [LiCr(ox)3]2- framework, which stabilizes the low-spin (LS) 2E state relative to the high-spin (HS) 4T1 state of the Co(II) ion. Upon increasing the Ni(II) content, the spin-crossover becomes even more gradual and incomplete and eventually is not observed for pure [Ni(bpy)3][LiCr(ox)3]. The average spin-crossover temperature increases with the increasing Ni(II) content, suggesting a higher degree of chemical pressure applied by the oxalate framework manifested by changing the ΔE0HL toward positive values. The magnetic behavior of all these framework materials has been explained by the mechanoelastic model, considering different radii for Co and Ni molecules and different interactions between Co-Co sites and Co-Ni sites. The model reproduced the incomplete transition, with the HS residual fraction at 300 K decreasing with increasing Ni concentration, and provided microscopic snapshots of the systems, showing how the existence of impurities prevented the spreading of Co atoms in the HS state.

Utilization of ferrous slags as coagulants, filters, adsorbents, neutralizers/stabilizers, catalysts, additives, and bed materials for water and wastewater treatment: A review.

Solid waste is currently produced in substantial amounts by industrial activities. While some are recycled, the majority of them are dumped in landfills. Iron and steel production leaves behind ferrous slag, which must be created organically, managed wisely and scientifically if the sector is to remain more sustainably maintained. Ferrous slag is the term for the solid waste that is produced when raw iron is smelted in ironworks and during the production of steel. Both its specific surface area and porosity are relatively high. Since these industrial waste materials are so easily accessible and offer such serious disposal challenges, the idea of their reuse in water and wastewater treatment systems is an appealing alternative. There are many components such as Fe, Na, Ca, Mg, and silicon found in ferrous slags, which make it an ideal substance for wastewater treatment. This research investigates the potential of ferrous slag as coagulants, filters, adsorbents, neutralizers/stabilizers, supplementary filler material in soil aquifers, and engineered wetland bed media to remove contaminants from water and wastewater. Ferrous slag may provide a substantial environmental risk before or after reuse, so leaching and eco-toxicological investigations are necessary. Some study revealed that the amount of heavy metal ions leached from ferrous slag conforms to industrial norms and is exceedingly safe, hence it may be employed as a new type of inexpensive material to remove contaminants from wastewater. The practical relevance and significance of these aspects are attempted to be analyzed, taking into account all recent advancements in the fields, in order to help in the development of informed decisions about future directions for research and development related to the utilization of ferrous slags for wastewater treatment.

Anaerobic digestion of fruit and vegetable waste: a critical review of associated challenges.

The depletion of fossil fuels coupled with stringent environmental laws has encouraged us to develop sustainable renewable energy. Due to its numerous benefits, anaerobic digestion (AD) has emerged as an environment-friendly technology. Biogas generated during AD is primarily a mixture of CH4 (65-70%) and CO2 (20-25%) and a potent energy source that can combat the energy crisis in today's world. Here, an attempt has been made to provide a broad understanding of AD and delineate the effect of various operational parameters influencing AD. The characteristics of fruit and vegetable waste (FVW) and its feasibility as a potent substrate for AD have been studied. This review also covers traditional challenges in managing FVW via AD, the implementation of various bioreactor systems to manage large amounts of organic waste and their operational boundaries, microbial consortia involved in each phase of digestion, and various strategies to increase biogas production.

Feasibility and potential of laccase-based enzyme in wastewater treatment through sustainable approach: A review.

The worldwide increase in metropolitan cities and rise in industrialization have resulted in the assimilation of hazardous pollutants into the ecosystems. Different physical, chemical and biological techniques have been employed to remove these toxins from water bodies. Several bioprocess applications using microbes and their enzymes are utilized to achieve the goal. Biocatalysts, such as laccases, are employed explicitly to deplete a variety of organic pollutants. However, the degradation of contaminants using biocatalysts has many disadvantages concerning the stability and activity of the enzyme. Hence, they are immobilized on different supports to improve the enzyme kinetics and recyclability. Furthermore, standard wastewater treatment methods are not effective in eliminating all the contaminants. As a result, membrane separation technologies have emerged to overcome the limitations of traditional wastewater treatment methods. Moreover, enzymes immobilized onto these membranes have generated new avenues in wastewater purification technology. This review provides the latest information on laccases from diverse sources, their molecular framework and their mode of action. This report also gives information about various immobilization techniques and the application of membrane bioreactors to eliminate and biotransform hazardous contaminants. In a nutshell, laccases appear to be the most promising biocatalysts for green and cost-efficient wastewater treatment technologies.

Is there an association between public spending on health and choice of healthcare providers across socioeconomic groups in India? - Evidence from a national sample.

The role of public spending on health in reducing socioeconomic inequalities in healthcare is an emerging area of research, little supporting empirical evidence is available from low- and middle-income countries. This study examined: (1) the relationship between public spending on health per capita and the decision whether to seek healthcare or not, (2) the relationships between public spending on health per capita and choice of medical provider, and (3) whether these relationships varied by socioeconomic groups in India. Our study utilized the nationally representative 71st National Sample Survey of India, using 26,142 people who had been ailing in the past 15 days, the survey took place between the 1st of January and June 30, 2014. Two regression-based approaches were used to examine the association between public spending and choice of medical providers: (1) Multilevel multinomial regression; and (2) Instrumental variable regression. We examined the differential impacts of public spending on healthcare utilisation by socioeconomic groups. Increased public spending on health was not associated with changes in ailing people's decision whether to seek care or not (p > 0.05 in all analyses). However, increased public spending on health was associated with reductions in patients choosing private medical providers [adjusted odds ratio = 0.88 (95%CI 0.85-0.91) for outpatient private clinics] compared to outpatient government clinics. These associations may be greater among the lower economic groups compared with their counterparts. Across India, higher levels of government investment in health services are recognised by healthcare users and shown in their pattern of healthcare utilisation. That an increase in public spending on health results in a decrease in the use of private providers, particularly outpatient facilities with no inpatient capabilities, provides strong evidence for the effectiveness of 'regulation by competition'. This is a strong argument for focusing health system strengthening, and strategies for achieving universal healthcare on public investment.

Dataset on the electrical energy consumption and its conservation in the cement manufacturing industry.

The cement industry consumes huge amount of electrical energy than the other sectors. The higher percentage of the energy cost was found in its total cost of production. The available resources and environmental constraints are becoming increasingly severe because of the continuous development in the economy of the country. Therefore, the energy-saving and the reduction in the emission of gases in the cement industries have become one of the choices for the process development. The concept of energy-saving determines the realization of the national goals of energy conservation. Taking the reference of one of the cement industry in India (Emami Cement Ltd, Baloda Bazaar, Chhattisgarh) as the main focus, this paper investigates on the energy-saving by implementing the variable speed drives (VSD) along with the cooling fan and motor across the system. This report also analyses the energy-saving potential of the cement manufacturing industry by assuming some different scenarios. The data analysis show that the electrical energy-saving potential of the cement industry is 53.5% with VSD and 51.89% with the use of light-emitting diode (LED) instead of using metal halide (MH) ultraviolet source. Thus, the improvement in energy efficiency can reduce the emission of the carbon dioxide from fuel, use of electrical energy and consequently it has the potential of reducing the cost of the cement production unit.

Degradation of mixed dye via heterogeneous Fenton process: Studies of calcination, toxicity evaluation, and kinetics.

In this study, the degradation of mixed dye (mixture of Azure B and Congo red) was investigated using iron-loaded black soil as a catalyst via Fenton process. Iron-loaded black soil catalyst was prepared by the wet impregnation method, calcined at different temperatures with varying of iron loading on black soil. Their behavior was compared through characterization techniques (FTIR and XRD). Separately, the effect of calcination and aging of catalyst was investigated on the degradation of mixed dye with optimized conditions. Significant degradation (>90% only in 10 min) was observed in optimum conditions. Toxicity measurement was done by a seed germination test which gave significant results. In the kinetic study, it was found that Behnajady-Modirshahla-Ghanbery (BMG) model was the best suited for this process compared to other models. In addition, thermodynamic properties (Gibbs free energy [∆G], activation energy [Ea ], activation enthalpy [∆H], and activation entropy [∆S]) were also calculated. The stability of synthesized catalyst was found to be satisfactory. PRACTITIONER POINTS: Application of Iron-loaded black soil catalyst Mixed dye degradation and toxicity measurement Thermodynamic property studies.

Modeling and optimization data analysis on photocatalytic decolourization of amido black 10B using ZnO catalyst.

This article contains the experimental and statistical data related to decolourization of Amido Black 10B using photocatalytic process. Box-Behnken experimental design (BBD) has been used to study the influence of operational parameters on photocatalytic oxidation of Amido Black 10B by using zinc oxide (ZnO) as a catalyst. This data set presents a concise description of experimental conditions for variable factors such as initial dye concentration of 100 ppm, oxidant dosage 20 mMol/L and catalyst dose 1g/L at natural pH for 4 hr of reaction time in presence of 12W intensity ultra-violet radiation were optimized for over a response parameter, decolorization efficiency of Amido Black 10B. The effects of decolorization on process variables were investigated by developing a mathematical model, results indicated that ZnO can be used as an efficient catalyst for the decolorization of Amido Black 10B. Analysis of variance (ANOVA) showed a high coefficient of statistical measure value (R2 = 0.9915) and prediction of the driven regression model was found to be satisfactory.

Electronically Triggered Switchable Binding Modes of the C-Organonitroso (ArNO) Moiety on the {Ru(acac)2} Platform.

This work evaluated the switchable binding profile of the biochemically relevant and redox non-innocent C-organonitroso (ArNO) moiety with the selective {Ru(acac)2} (acac = acetylacetonate) metal fragment as a function of external stimuli, including the solvent medium (EtOH versus toluene) and aryl substituents (C6H5, p-OMe-C6H4, and p-Cl-C6H4) in the framework of ArNO. In this context, the reaction of ArNO (Ar = C6H5 or p-OMe-C6H4) with the metal precursor RuII(acac)2(CH3CN)2 in polar protic EtOH led to the formation of monomeric [RuII(acac)2(ArNOo)2] (1a or 1b) with η1-N-bonded terminal ArNOo and double-ArNOo-bridged dimeric [(acac)2RuII(µ-ArNOo)2RuII(acac)2], 2a or 2b, respectively. On the other hand, the use of p-Cl-substituted ArNO selectively yielded the corresponding dimeric 2c. However, the use of nonpolar toluene resulted in monomeric 1 irrespective of the nature of aryl substituents in ArNO. Molecular identities, including the redox state of ArNOo in 1 and 2, were authenticated by their single-crystal X-ray structures as well as by solution spectral features. Though monomeric 1 exhibited reversible one-electron oxidation and reduction processes, leading to the electron paramagnetic resonance active [RuIII(acac)2(ArNOo)2]+ (1+; S = 1/2) and [RuII(acac)2(ArNO•-)(ArNOo)]- (1•-; S = 1/2), respectively, redox states of dimeric 2 were found to be unstable on the electrolysis time scale. Interestingly, monomeric 1 underwent transformation to dimeric 2 in the presence of a strong reducing agent, hydrazine hydrate, and the reverse process, i.e., conversion of dimeric 2 to 1, took place under the influence of external coordinating agent ArNO. The detailed experimental exploration, including kinetic investigations related to 1 → 2 and 2 → 1 transformations, revealed that the electronic aspects of ArNO (redox non-innocence of ArNOo/•-, π-accepting and coordinating features of ArNOo) had facilitated its switchable binding event in combination with the {Ru(acac)2} metal fragment.

Effect of positional isomerism on the spectroelectrochemical response of 3,6-bis(2-pyridyl)-diketopyrrolopyrrolate bridged bis(carbonylhydridoruthenium) compounds.

Reaction of 3,6-bis(2-pyridyl)-diketopyrrolopyrrole (H2-BPDPP) with two equivalents of [Ru(H)(CO)(Cl)(PPh3)3] in EtOH produced two symmetrical dinuclear isomers, (µ-BPDPP)[Ru(CO)H(PPh3)2]2, green 1 and blue 2, which could be separated chromatographically and characterised spectroscopically (1H and 31P NMR, IR, and UV-VIS). Isomeric forms of 1 and 2 were authenticated using their single crystal X-ray structures. In addition to the essentially planar bis-chelating bridge BPDPP2- and the mutually trans positioned axial PPh3 ligands in both complexes, compound 1 was established with the CO groups trans to the pyrrolate-N atoms, whereas 2 has the π acceptors CO and pyridine-N situated trans to each other. While the reduction of 1 and 2 proceeds irreversibly at negative potentials, the reversible oxidations at rather low potentials could be monitored by EPR and UV-VIS-NIR absorption measurements. Together with TD-DFT calculations, these results reveal that the primary electron transfers are largely confined to the BPDPP ligand. Despite the bridge centred processes, small differences between the isomers 10/+ and 20/+ were found, affecting e.g. the near infrared absorption of the radical cation species.

Mononuclear and Dinuclear Ruthenium Complexes of cis- and trans-Thioindigo: Geometrical and Electronic Structure Analyses.

The compounds [Ru(acac)2(L)] (1) and [Ru2(acac)4(µ-L)] (2) with acac- = acetylacetonato and L = thioindigo were characterized crystallographically with a cis-configurated L and O,O'-coordinated metal in 1 and with trans-configurated L and two S,O-coordinated bridged ruthenium centers for 2. The electronic structures of 1 and 2 were confirmed by spectroscopy and density functional theory calculations, suggesting considerable metal-to-ligand electron transfer resulting in the formation of the thioindigo radical anion and oxidized metal(s). UV-Vis-Near-IR and IR (spectro)electrochemistry was used to investigate charged forms 1 n ( n = 1+, 1-) and 2 n ( n = 1+, 1-, 2-), which reveal electron transfer activity of both the metal and the thioindigo ligand as well as sizable orbital mixing. An intense near-IR absorption is observed for 2- at 2180 nm. The remarkable ligand properties of thioindigo are being discussed in connection to related coordination compounds of indigo derivatives such as dehydroindigo and corresponding ("Nindigo") diimines.

Solvent-Mediated Functionalization of Benzofuroxan on Electron-Rich Ruthenium Complex Platform.

An unprecedented reactivity profile of biochemically relevant R-benzofuroxan (R=H, Me, Cl), with high structural diversity and molecular complexity on a selective {Ru(acac)2 } (acac=acetylacetonate) platform, in conjugation with EtOH solvent mediation, is revealed. This led to the development of monomeric [RuIII (acac)2 (L1R )] (1 a-1 c; L1R =2-nitrosoanilido derivatives) and dimeric [{RuII (acac)2 }2 (L2R )] (2 a-2 b; L2R =(1E,2E)-N1 ,N2 -bis(2-nitrosophenyl)ethane-1,2-diimine derivatives) complexes in one pot with a change in the metal redox conditions. The functionalization of benzofuroxan in 1 and 2 implied in situ reduction of N=O to NH- in the former and solvent-assisted multiple N-C coupling in the latter. The aforesaid transformation processes were authenticated through structural elucidation of representative complexes, and evaluated by their spectroscopic/electrochemical features, along with C2 D5 OD labeling and monitoring of the impact of substituents (R) in the benzofuroxan framework on the product distribution process. The noninnocent potential of newly developed L1 and L2 in 1 and 2, respectively, was also probed by spectroelectrochemistry in combination with DFT calculations.

Isomeric Diruthenium Complexes Bridged by Deprotonated Indigo in cis and trans Configuration.

The doubly deprotonated form L2- of indigo=H2 L can bind two [Ru(acac)2 ] complex fragments in the cis (1) and trans configuration (2), as evidenced from crystal structure analysis. While the latter type of N,O; N' ,O' coordination has been observed earlier, for example, with [Ru(bpy)2 ]2+ , leading to two equivalent six-membered ring chelates, the cis arrangement in 1 is observed here for the first time in a dinuclear complex, producing one five-membered ring chelate with N,N' coordination and one seven-membered chelate with O,O' coordination. The different structures of the isomers result in differing electrochemical and spectroelectrochemical (EPR, UV-Vis-NIR) responses for various accessible charge states 1n and 2n , n=-, 0, +, 2+. The associated electronic structures were analyzed by DFT (structures, spin density) and TD-DFT calculations (electronic transitions), revealing mainly metal-based reduction but largely indigo ligand-based oxidation of both neutral precursors.

Ru-Complex Framework toward Aerobic Oxidative Transformations of ß-Diketiminate and α-Ketodiimine.

The impact of the {Ru(acac)2} (acac- = acetylacetonate) framework on the transformations of C-H and C-H/C-C bonds of coordinated ß-diketiminate and ketodiimine scaffolds, respectively, has been addressed. It includes the following transformations involving {Ru(acac)2} coordinated ß-diketiminate in 1 and ketodiimine in 2 with the simultaneous change in metal oxidation state: (i) insertion of oxygen into the C(sp2)-H bond of ß-diketiminate in 1, leading to the metalated ketodiimine in 2 and (ii) Bronsted acid (CH3COOH) assisted cleavage of unstrained C(sp2)-C(sp2)/C═N bonds of chelated ketodiimine (2) with the concomitant formation of intramolecular C-N bond in 3, as well as insertion of oxygen into the C(sp3)-H bond of 2 to yield -CHO function in 4 (-CH3 → -CHO). The aforesaid transformation processes have been authenticated via structural elucidation of representative complexes and spectroscopic and electrochemical investigations.

Ruthenium-Hydride Mediated Unsymmetrical Cleavage of Benzofuroxan to 2-Nitroanilido with Varying Coordination Mode.

The reaction of R-benzofuroxan (R = H, Me, Cl) with the metal precursor [Ru(Cl)(H)(CO)(PPh3)3] (A) or [Ru(Cl)(H)(CH3CN)(CO)(PPh3)2] (B) in CH3CN at 298 K resulted in the intermediate complex [Ru(Cl)(L1)(CH3CN)(CO)(PPh3)2] (L1 = monodentate 2-nitroanilido) (1, pink), which however underwent slow transformation to the final product [Ru(Cl)(L2)(CO)(PPh3)2] (L2 = bidentate 2-nitroanilido) (2, green). On the contrary, the same reaction in refluxing CH3CN directly yielded 2 without any tractable intermediate 1. Structural characterization of the intermediates 1a-1c and the corresponding final products 2a-2c (R = H, Me, Cl) authenticated their identities, revealing ruthenium-hydride mediated unsymmetrical cleavage of benzofuroxan to hydrogen bonded monodentate 2-nitroanilido (L1) in the former and bidentate 2-nitroanilido (L2) in the latter. The spectrophotometric monitoring of the transformations of B → 1 as well as 1 → 2 with time and temperature established the first order rate process with associatively activated pathway for both cases. Both 1 and 2 exhibited one reversible oxidation and an irreversible reduction within ±1.5 V versus saturated calomel reference electrode in CH3CN with slight variation in potential based on substituents in the benzofuroxan framework (R = H, Me, Cl). Spectroscopic (electron paramagnetic resonance and UV-vis) and density functional theory calculations collectively suggested varying contribution of metal based orbitals along with the ligand in the singly occupied molecular orbital of 1+ or 2+, ascertaining the noninnocent potential of the in situ generated (L1) or (L2).

Ruthenium Derivatives of in Situ Generated Redox-Active 1,2-Dinitrosobenzene and 2-Nitrosoanilido. Diverse Structural and Electronic Forms.

The article describes one-pot synthesis and structural elucidation of tc-[RuII(pap)2(L•-)]ClO4 [1]ClO4 and tc-[RuII(pap)2(L'-)]ClO4 [2]ClO4, which were obtained from tc-[RuII(pap)2(EtOH)2](ClO4)2 and benzofuroxan (L = 1,2-dinitrosobenzene, an intermediate tautomeric form of the biologically active benzofuroxan, L'- = 2-nitrosoanilido, pap = 2-phenylazopyridine, tc = trans and cis corresponding to pyridine and azo nitrogen donors of pap, respectively). The same reaction with the newly synthesized and structurally characterized metal precursor cc-RuII(2,6-dichloropap)2Cl2, however, affords isomeric ct-[RuII(2,6-dichloropap)2(L•-)]+ (3a+) and tc-[RuII(2,6-dichloropap)2(L•-)]+ (3b+) (cc, ct, and tc with respect to pyridine and azo nitrogens of 2,6-dichloropap) with the structural authentication of elusive ct-isomeric form of {Ru(pap)2} family. The impact of trans or cis orientation of the nitroso group of L/L' with respect to the N═N (azo) function of pap in the complexes was reflected in the relative lengthening or shortening of the latter distance, respectively. The redox-sensitive bond parameters of 1+ and 3+ reveal the intermediate radical form of L•-, while 2+ involves in situ generated L'-. The multiple redox processes of the complexes in CH3CN are analyzed via experimental and density functional theory (DFT) and time-dependent DFT calculations. One-electron oxidation of the electron paramagnetic resonance-active radical species (1+ and 3+) leads to [RuII(pap)2(L)]2+ involving fully oxidized L0 in 12+ and 32+; the same in 2+ results in a radical species [RuII(pap)2(L'•)]2+ (22+). Successive reductions in each case are either associated with pap or L/L'--based orbitals, revealing a competitive scenario relating to their π-accepting features. The isolated or electrochemically generated radical species either by oxidation or reduction exhibits near-IR transitions in each case, attributing diverse electronic structures of the complexes in accessible redox states.

Unsymmetric (µ-oxido)/(µ-pyrazolato) and Symmetric (µ-pyrazolato)2 Bridged Diosmium Frameworks: Electronic Structure and Magnetic Properties.

The present article deals with the structurally characterized unsymmetric oxido/pyrazolato-bridged [(bpy)2Os(III)(µ-oxido)(µ-pz)Os(III)(bpy)2](ClO4)3 ([1](ClO4)3) and symmetric dipyrazolato-bridged [(bpy)2Os(II)(µ-pz)2Os(II)(bpy)2](ClO4)2 ([2](ClO4)2) (pz = pyrazolato, bpy = 2,2'-bipyridine) complexes with the Os···Os separations of 3.484 and 4.172 Å, respectively. The anti-ferromagnetically coupled Os(III) centers [E(S = 1)-E(BS(1,1) S = 0) = 322.504 cm(-1)] in 1(3+) and diamagnetic (S = 0) 2(2+) exhibit well-resolved (1)H NMR resonances. [1](ClO4)3 shows temperature- and magnetic field-dependent paramagnetism at low magnetic field and diamagnetism at high magnetic field. 1(3+) and 2(2+) display successive metal-based oxidation processes involving the intermediate mixed-valent states and isovalent congeners: Os(IV)Os(IV) (1(5+))→Os(III)Os(IV) (1(4+))⇌Os(III)Os(III) (1(3+))⇌Os(III)Os(II) (1(2+)) and Os(III)Os(III) (2(4+))→Os(II)Os(III) (2(3+))⇌Os(II)Os(II) (2(2+)) as well as bpy-centered reductions. The effect of π donor O(2-) and σ/π-donating pz(-) in 1(3+) and 2(2+), respectively, leads to varying oxidation state of the metal ions in the isolated complexes: Os(III)Os(III) versus Os(II)Os(II). UV-visible-near-IR-electron paramagnetic resonance spectro-electrochemistry and density functional theory (DFT)/time-dependent DFT calculations collectively reveal overlapping of the metal- and ligand (pz, O, bpy)-based frontier orbitals in the delocalized mixed-valent states in 1(4+) and 1(2+) with comproportionation constant (Kc) value > 1 × 10(14) as well as in isovalent 1(3+), resulting in mixed metal/ligand to metal/ligand near-IR transitions in all the three states. The mixed-valent Os(II)Os(III) state in 2(3+) exhibits high Kc value of 1 × 10(22) corresponding to a strong electrochemical coupling situation. However, closeness of the bandwidth (Δν1/2, 4861 cm(-1)) of broad and weak intervalence charge transfer transition of 2(3+) at 1360 nm (ε/M(-1) cm(-1): 490) with the calculated Δν1/2 of 4121 cm(-1) based on the Hush formula as well as spin-density distributions of Os1: 0.811/0.799, Os2: 0.045/0042, and pz: 0.162/0.173 in meso and rac diastereomeric forms, respectively, attribute its localized class II state.

Impact of {Os(pap)2} in fine-tuning the binding modes and non-innocent potential of deprotonated 2,2'-bipyridine-3,3'-diol.

The reaction of ctc-Os(II)(pap)2Cl2 (pap = 2-phenylazopyridine, ctc = cis-trans-cis with respect to chlorides and pyridine/azo nitrogens of pap, respectively) and ambidentate 2,2'-bipyridine-3,3'-diol (H2L) leads to the simultaneous formation of isomeric [Os(II)(pap)2(HL(-))](+) ((2+)/(3+)), seven-membered chelate containing Os(II)(pap)2(L(2-)) (4) and diastereomeric [{Os(II)(pap)2}2(µ-L(2-))](2+) (5a(2+) (meso, ΔΛ)/5b(2+) (rac, ΔΔ/ΛΛ)). The reaction of 2,2'-biphenol (H2L') and ctc-Os(II)(pap)2Cl2 yields Os(II)(pap)2(L'(2-)) (6), an analogue of 4. The identities of the newly designed complexes have been established by different analytical, spectroscopic and X-ray diffraction techniques. (1)H-NMR spectra of the complexes and single crystal X-ray structures of selective derivatives [2]ClO4, [3]ClO4, [5a](ClO4)2, and 6 establish the retention of the tc-configuration of the precursor {Os(pap)2}. In isomeric 2(+) and 3(+), monodeprotonated HL(-) is linked to the {Os(II)(pap)2} fragment through N,N and N,O(-) donors, resulting in nearly planar five- and six-membered chelates with O-HO(-) and O-HN hydrogen bonds at its back face, respectively. The O(-),O(-) donating L'(2-) extends a severely twisted seven-membered chelate with the {Os(pap)2} unit in 6. The N,O(-)/O(-),N donors of deprotonated L(2-) bridge the two {Os(II)(pap)2} units in a symmetric fashion in 5a(2+), forming two moderately twisted six-membered chelates. Though the deprotonation of the O-HN hydrogen bond in (+) by another unit of {Os(II)(pap)2} generates a diastereomeric mixture of 5a(2+) and 5b(2+), attempts to deprotonate the relatively stronger O-H···O(-) hydrogen bond in 2(+) have failed. The isomeric 2(+)/3(+), seven-membered chelate containing 4/6 and diastereomeric 5a(2+)/5b(2+) exhibit distinctive (1)H-NMR and absorption spectra as well as electrochemical responses. The pap (N[double bond, length as m-dash]N) based two successive reductions and the participation of HL(-), L(2-), L'(2-) in the oxidation processes of the respective complexes have been revealed using EPR and DFT calculated MOs and Mulliken spin density plots at the intermediate paramagnetic states.