A family of copper complexes supported by a π-acidic tridentate bis(azo-pyridyl) pincer ligand has been synthesized to elucidate the influence of the coordination environment and metal oxidation state on acceptorless dehydrogenative catalysis. The series comprises a coordinatively unsaturated pentacoordinate Cu(II) complex (1a), a coordinatively saturated Cu(II) complex (1b), and tetracoordinate Cu(I) complexes (1c-d). The strongly electron-withdrawing bis(azo) framework stabilizes reactive intermediates and facilitates efficient alcohol dehydrogenation under mild conditions. These air- and moisture-stable, earth-abundant, coordinatively unsaturated copper complexes catalyze the acceptorless coupling of aromatic diamines with both primary and secondary alcohols to furnish aza-heterocycles of diverse ring sizes. A broad substrate scope (47 examples) provides access to five- and six-membered heterocycles in good to excellent yields and even enables the formation of sterically demanding seven-membered annulated products from secondary alcohols. The catalytic transformation proceeds with high atom economy, generating merely water and hydrogen peroxide as byproducts. Tetracoordinate Cu(I) complexes exhibit markedly higher activity than their Cu(II) counterparts, whereas the coordinatively saturated Cu(II) complex remains largely inactive, highlighting the crucial role of coordinative unsaturation. Excellent catalyst robustness is demonstrated by turnover numbers (TON) approaching ∼104 at catalyst loadings as low as 0.005 mol %. Mechanistic investigations support a nonradical hydride-transfer (HT) pathway for Cu(I)-mediated alcohol dehydrogenation followed by oxidative N-annulation.

We report a homogeneous, phosphine-free and inexpensive NNN pincer-copper catalyst 1a that enables the efficient synthesis of quinazoline derivatives under fairly mild reaction conditions. The transformations proceed for the synthesis of quinazolines from 2-aminobenzylamine with primary aromatic alcohols, through a cascade sequence of alcohol dehydrogenation, imine formation, cyclization and oxidative aromatization. A strongly it-acidic bis-azo NNN pincer ligand was introduced to reinforce metal-ligand integrity while simultaneously acting as a redox-active chromophore, thereby enhancing catalytic sustainability. Complex 1a operates through a catalytic cycle involving alcohol dehydrogenation via a hydride-transfer (HT) pathway mediated by the reduced ligand backbone. This open-air and environmentally benign protocol demonstrates good substrate generality (14 examples) and generates only innocuous byproducts (H2O and H2O2), eliminating the need for external oxidants or additives. Overall, this cost-effective and sustainable catalytic strategy represents a notable advance in the green synthesis of biologically relevant quinazoline frameworks.

Two π-radical complexes containing bisazo-aromatic-centered radical anion (1⋅-) were synthesized through in-situ electron transfer from metal-to-ligand using [IrI] and 2-(2-Pyridylazo)azobenzene (1) in inert hydrocarbon solvent. These are characterized as diradical [IrIII(1⋅-)2]+ [2]+ and monoradical [IrIII(1⋅-)Cl2(PPh3)] 3. In contrast, a rare metal-mediated hydrolytic cleavage of the C(sp2)-N bond occurred in protic solvent resulting in quaternary radical complex [IrIII(1⋅-)(1')(PPh3)]+ (4)+. This provides an easy way to synthesize stable unsubstituted pyridine-2-diazotate (1'), an otherwise unstable organic template. Theoretical scrutiny has been performed at (U)B3LYP/6-31G(d,p)/LANL2DZ level to explore the origin of redox and optical properties in radical complexes. Magnetic study of [2]+ reveals that a weak antiferromagnetic (AF) spin-communication (J = -4.39 cm-1) exists between two radicals, leading to an open-shell singlet ground state. Broken symmetry density functional theory (BS-DFT) calculations were carried out to probe the nature of antiferromagnetic exchange interaction between the two radical centers in species [2]+. This method has been employed with different basis functionals (BP86, BLYP, OLYP, TPSS0, TPSSh, ωb97D and B3LYP) to comprehend the nature of the exchange in [2]+. The best result is obtained for pure functional OLYP with a J value -8.4 cm-1.

An electrode in triboelectric nanogenerator (TENG) plays a pivotal role in developing efficient and ultrasensitive devices. However, it has received relatively little attention from researchers, whereas numerous studies on TENG to date have primarily focused on device engineering, material selection, and efficiency improvements. Laser-induced graphene (LIG) demonstrates superior ability to collect charges generated through triboelectrification in TENGs. This article presents a successful fabrication of highly crystalline, conducting and sp2-hybridised LIG on a polyimide (PI) surface, which was subsequently transferred from the PI surface onto the cotton fabric substrate by controlling temperature and pressure. This facilitates the development of a TENG that delivers significantly higher electrical output compared to one using a conventional aluminium electrode. We report a comparative study of two TENGs: in both cases, cotton fabric and ecoflex were used as the tribo-positive and tribo-negative materials respectively. However, in one case the LIG electrode fabricated on cotton fabric was used and referred to as CLIG-TENG, while the conventional aluminium electrode was used in another TENG, referred to as C-TENG. The CLIG-TENG demonstrated 160%, 150%, and 190% higher voltage, current, and power output respectively, compared to the C-TENG. The enhanced performance of the CLIG-TENG is attributed to the strong adherence between LIG and cotton fabric, work function, and dielectric of the LIG attached cotton fabric. Furthermore, the CLIG-TENG exhibited excellent stability over 10,000 cycles demonstrating the durability of the transferred LIG. The ultrasensitive properties of the CLIG-TENG have also been validated through various healthcare sensing applications.

Stereochemically active lone-pair (SCALP) cations are attractive units for realizing optical anisotropy. Antimony (III) chloride perovskites with SCALP have remained largely unknown till date. We synthesized vacancy ordered Cs3Sb2Cl9 perovskite single crystals with SbCl6 octahedral linkage containing SCALP. Remarkably, Cs3Sb2Cl9 single crystals exhibit an exceptional birefringence of 0.12 +(-) 0.01 at 550 nm, which is the largest among pristine all-inorganic halide perovskites. The SCALP brings a large local structural distortion of the SbCl6 octahedra promoting birefringence optical responses in Cs3Sb2Cl9 single crystals. Theoretical calculations reveal that the considerable hybridization of Sb 5s with Sb 5p and Cl 3p states largely contribute to the SCALP. Furthermore, the change in the Sb-Cl-Sb bond angle creates distortion in the SbCl6 octahedral arrangement in the apical and equatorial directions within the crystal structure incorporating the required anisotropy for the birefringence. This work explores pristine inorganic halide perovskite single crystals as a potential birefringent material with prospects in integrated optical devices.

Herein, we describe an air- and moisture-stable, homogeneous zinc catalyst stabilised using an electron deficient N^N^N pincer-type ligand. This ternary, penta-coordinated neutral molecular catalyst [Zn(N^N^N)Cl2] selectively produces α-alkylated ketone derivatives (14 examples) through a one-pot acceptorless dehydrogenative coupling (ADC) reaction between secondary and primary alcohols using the borrowing hydrogen (BH) approach in good to excellent isolated yields (up to 93%). It is worth noting that this catalyst also provides an eco-friendly route for the synthesis of quinoline derivatives (30 examples) using 2-aminobenzyl alcohols as alkylating agents via successive dehydrogenative coupling and N-annulation reactions. This cost effective, easy to synthesize and environmentally benign catalyst shows excellent stability in catalytic cycles under open-air conditions, as evident from its high turnover number (∼104), and is activated by using a catalytic amount of base under milder conditions.

Correction for 'Iridium-mediated C-S bond activation and transformation: organoiridium(III) thioether, thiolato, sulfinato and thiyl radical compounds. Synthesis, mechanistic, spectral, electrochemical and theoretical aspects' by Ujjwal Das et al., Dalton Trans., 2015, 44, 8625-8639, DOI: 10.1039/C5DT00448A.

Coordination diversity of an aromatic diamine with Rh(iii) is presented together with the elucidation of the molecular and electronic structures, electron transfer, and electronic transitions.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Luminescent nickel(ii) complexes have been synthesized using redox-active azo-oximes. The superior π-acidity of the organic backbone is a key to the isolation of Ni(ii) anion radicals.

Bis-azoaromatic electron traps, viz. 2-(2-pyridylazo)azoarene 1, have been synthesized by colligating electron-deficient pyridine and azoarene moieties, and they act as apposite proradical templates for the formation of stable open-shell diradical complexes [(1•-)RhIII(1•-)]+ ([2]+), starting from the low-valent electron reservoir [RhI]. The less stable monoradical [RhIII(1•-)Cl2(PPh3)3] (3) has also been isolated as a minor product. These π-radical complexes are multiredox systems, and the electron transfer processes occur exclusively within the pincer-type NNN ligand backbone 1. Molecular and electronic structures of the diradicals and monoradicals have been ascertained with the aid of X-ray diffraction, electrochemical, spectroelectrochemical, and spectral (electronic, IR, NMR, and EPR) studies. In the diradicals [2]+, the orthogonal disposition of two ligand π orbitals linked via a closed-shell metal center (t26) impedes significant coupling between the radicals. Indeed, the observed magnetic moment of [2a]+ lies near ∼2.3 μB over the temperature range 50-300 K. A very weak antiferromagnetic (AF) intramolecular spin-spin interaction between two ligand π arrays in [(1•-)RhIII(1•-)]+ have been found experimentally (J ≈ -5 cm-1), and this is further substantiated by density functional theory (DFT) calculations at the (U)B3LYP/6-31G(d,p) level.

Non-trivial coordination mode of symmetrical NNN ligands with Rh(iii) leads to redox-active NNO-scaffolds via C(sp2)–H oxyfunctionalization at rt, opening an opportunity to juxtapose different redox-active domains.

The hydrogen bonded bis azo-oximato [IrCl2(L(NOH))(L(NO))] 2 and its deprotonated form (Et3NH)[IrCl2(L(NO))2] (Et3NH)(+)3(-) have been isolated in the crystalline state by a facile synthetic method. The azo-oxime frameworks in 3(-) have been conveniently transformed to the azo-imine by reduction with NaBH4 or ascorbic acid. Notably, the coordinated azo-imines accept an extra electron thereby furnishing the azo-imine radical anion complex 4. The underlying reductive transformation can be best described by proton-coupled electron transfer (PCET) process. Both the coordinated ligands (azo-oxime) in 3(-) are typically closed-shell monoanion (L(NO-)), but their reduced form (azo-imine) can behave as open-shell monoanion (L(NH•-)) owing to the presence of highly stabilized virtual orbitals. Remarkable enhancement of the π-acidity in azo-imine relative to the precursor azo-oxime has also been reflected from the electrochemical study. The irido complexes display rich optoelectronic properties, and the origin of the transitions has been scrutinized by the TD-DFT method. The molecular geometries of the complexes 2 and 3(-) reveal that the syn orientation of the azo-oximes frameworks is favored because of strong noncovalent H-bonding and π-π stacking interactions. In the course of the reduction of 3(-), the sterically encumbered disposition of the azo-oximes is converted to the relaxed anti form in the transformed azo-imines. Diffraction study reveals the electronic structure of 4 as [Ir(III)Cl2{(L(NH))2(•-)}]. The superior stabilization of the unpaired spin on the ligand array rather than metal has also been substantiated from EPR and DFT studies. Theoretical analysis reveals that the odd electron delocalizes primarily over both the azo-imine moieties ([IrCl2(L(NH•-))(L(NH))] ↔ ([IrCl2(L(NH))(L(NH•-))]) with no apparent contribution from metal, and this type of ligand-centered mixed valency (LCMV) can be best expressed as Robin-Day class III (fully delocalized) in nature.

An attractive methodology, single-electron transfer (SET) reductive cleavage of the C-S bond mediated by a metal in the presence of the external stimuli PPh3, has been applied to the kinetically inert IrCl3 in order to synthesize the thiolato complex [Ir(III)(L(S))Cl(PPh3)2] 3 from precursor thioether complexes [Ir(III)(L(SR))Cl2(PPh3)] (R = alkyl) 2. The aforesaid cleavage process in association with (arene)C-H activation furnishes a new class of organosulfur compounds of iridium(III). The thiolato chelate 3 displays a reversible oxidative wave at 0.75 V vs. Ag/AgCl signifying its remarkable nucleophilic character. The high electron density on the thiolato-S vis-à-vis superior nucleophilicity can be envisaged through the formation of a number of S-centered derivatives. This observation has been corroborated with the nature of HOMO in 3, which assumes 49% of S(3p). Notably, the facile oxidative nature of 3 makes it an apposite precursor for metal-stabilized thiyl radical species. Indeed, iridium(III)-stabilized 3˙(+) can be generated by chemical/electrochemical means. The axial EPR spectra with g ∼ 2.0 along with theoretical analysis of SOMO (S(3p) 24% + Ph(π) 43% + d(yz) 15%) and spin density (ρ(S) = +0.543, ρ(Ph) = +0.315, ρ(Ir) = +0.151) of one-electron oxidized 3˙(+) validate the iridium-stabilized thiyl radical description. This observation suggests that the CNS coordination mode in thiophenolato complex 3 is redox-active. Complex 3 is very prone to S-centered oxidation under normal aerobic conditions to yield metallosulfoxide [Ir(III)(L(SO2))Cl(PPh3)2] 4. The enhanced nucleophilicity of thiolato-S can also be manifested via the smooth S-C bond making process with alkyl halides (R'X, R' = Me and allyl; X = Br, I) and subsequent formation of thioether complexes of type [Ir(III)(L(SR'))ClX(PPh3)] 5. The organosulfur compounds of iridium(III) exhibit rich spectral properties including luminescence and the origin of these transitions is scrutinized with DFT and TD-DFT methods.

Reactions of alkyl/aryl (2-pyridylimine)phenyl thioether (LSR) with RuCl2(PPh3)3 in ethanolic medium afford thioether complexes of type [Ru(L-SR)Cl(PPh3)(2)]PF6 (R = benzyl, phenyl). The ligands behave as tridentate neutral NpyNimineSthioether donor retaining the C-S bond and bind to the metal atom in meridional fashion. The complexes were characterized by spectroscopic (IR, UV-Vis, and NMR) techniques. Crystallographic analysis reveals the octahedral geometry around ruthenium(H) with N2SP2Cl coordination. Complexes display rich optoelectronic features including luminescence. The complexes are electro-active and show quasi-reversible response near 1.1 V vs SCE. Theoretical (DFT) analyses were performed to explore the electronic transition and electron transfer behaviour.

The 2-(phenylazo)azobenzene furnished novel palladacycles in excellent yield, which showed luminescence at rt and catalytic activity. The optoelectronic and electrochemical responses were substantiated with DFT and TDDFT.

The reaction between a potential flexidentate pyridyl-azo-oxime HL1 and Co(ClO4)2 yields novel homoleptic complexes of types [Co(III)(L(-I))3], 2 and [Co(III)(L(-I))2]ClO4, 3⁺ClO₄ in N6 and N4O2 coordination environments respectively. The FMOs of these complexes vary appreciably and are strongly modified by the coordination environment. This has striking influences on the spectral and redox properties of the metallo conjugates of ligand HL. The synthesized bis 2 and tris chelates 3⁺ possess well-defined optoelectronic and redox properties and these are scrutinized by the density functional theory (DFT) and time dependent density functional theory (TD-DFT) analyses. The visible excitations are primarily mixed singlet-manifold (1)ILCT and (1)LLCT transitions, with different amounts of ligand π-π* character while in the UV region, the excitations are essentially π-π* ILCT/LLCT transitions for the 3⁺ and ILCT/LLCT transitions along with the LMCT component for 2. The luminescent cobalt(III) species are rarely cited albeit these are found to be moderately blue emissive with slight quenching of the emission quantum yield (Φ) as compared to that of a free ligand. Computation reveals that the cobalt d orbital is involved in the triplet emissive excited states and this phenomenon is plausibly responsible for the quenching of the emission quantum yield in the complexes. Both types of complexes are electro-active in solution and the first reductive response, associated with the redox orbital comprising delocalized π orbital of a ligand, is shifted in the more positive potential (0.6 V) in 3⁺ relative to 2 and this observation is corroborated with the appreciable stabilization (~0.5 eV) of LUMO of 3⁺ (coordination mode A) as compared to that in 2 (coordination mode B). This provides us an opportunity to explore the cobalt-bound azo-oxime anion radical compound by reduction of the diamagnetic precursor 3⁺. The best description of the one-electron paramagnetic 3 can be ascertained as [Co(III){(L(-I))2}˙(-)] from the EPR and DFT studies where the unpaired spin is delocalized essentially over π* orbital comprising both the coordinated ligands (97%) with little participation of cobalt d(yz) (3%).