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Abnormal levels (high/low) of urinary human serum albumin (HSA) are associated with a number of diseases and thus act as an essential biomarker for quick therapeutic monitoring and biomedical diagnosis, entailing the urgent development of an effective chemosensor to quantify the albumin levels. Herein, we have rationally designed and developed a small fluorogenic molecular probe, (Z)-2-(5-((8-hydroxy-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl) methylene)-4-oxo-2-thioxothiazolidin-3-yl) acetic acid (HJRA) with a twisted intramolecular charge transfer (TICT) property, which can easily self-assemble into nonfluorescent nanoaggregates in aqueous solution. However, HJRA nanoaggregates can selectively bind with serum albumin proteins (HSA/BSA) in ∼100% PBS medium, thereby facilitating the disassembly of nanoaggregates into monomers, exhibiting a clear turn-on red fluorescent response toward HSA and BSA. Analysis of the specific binding mechanism between HJRA and HSA using a site-selective fluorescence displacement assay and molecular docking simulations indicates that a variety of noncovalent interactions are responsible for the disassembly of nanoaggregates with the concomitant trapping of the HJRA monomer at site I in HSA, yielding a substantial red emission caused by the inhibition of intramolecular rotation of HJRA probe inside the hydrophobic cavity of HSA. The limit of detection (LOD) determined by the 3σ/slope method was found to be 1.13 nM, which is substantially below the normal HSA concentration level in healthy urine, signifying the very high sensitivity of the probe toward HSA. The comparable results and quick response toward quantification of HSA in urine by HJRA with respect to the Bradford method clearly point toward the superiority of this method compared to the existing ones and may lead to biomedical applications for HSA quantification in urine. It may also find potential application in live-cell imaging of HSA.

The reaction of MeO-salox (4-methoxy salicylaldehyde-oxime) with Mn(OAc)2·4H2O in a 1 : 1 molar ratio in methanol medium and in the presence of tetrabutylammonium hydroxide yields the hexanuclear complex [Mn6O2(4-MeO-salox)6(N3)2(MeOH)2(H2O)2·2H2O]n (1). Single crystal X-ray diffraction reveals that complex 1 adopts a 1D chain network facilitated by two EE-azido bridges. BSA binding studies reveal that complex 1 causes fluorescence quenching of BSA through both static and dynamic mechanisms. A 1 : 1 binding mode is established through a Benesi–Hildebrand plot with an intrinsic binding constant of (3.40 ± 0.01) × 104 M−1. The circular dichroism studies indicate variation of the secondary structure of BSA upon binding with complex 1. The site-selective binding and molecular docking studies reveal the probable binding site of complex 1 is at the mouth of site I in subdomain IIA of BSA.

Here, we present a detailed investigation on the interaction of 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD) embedded olanzapine derivative (OLA-NBD) with a model transport protein, human serum albumin (HSA). The thermodynamic parameters, Δ

Higher density of 98.66 and 94.60% ρth (theoretical density) was achieved for hot pressed Cu and Cu-15Al alloy, respectively. The microstructure of Cu-15Al alloy consists of α (Cu0.78Al0.22) and γ2 (Cu9Al4) phases. The hardness of Cu was significantly improved (from 1.32 to 6.03 GPa) with the addition of Al. Drastic reduction in corrosion of Cu-15Al (1.6 mpy) when compared to pure Cu (20.7 mpy) was noticed despite the low densification of Cu-Al. The higher impedance of Cu-15Al alloy corroborates the formation of protective layer. This work demonstrates the efficacy of high amount of Al in improving corrosion resistance of Cu.

We report a novel phenazine-embedded fluorescent probe (2-[2-(pyridin-2-ylmethoxy)-phenyl]-1H-imidazo[4,5-b]phenazine, PIP), which upon complexation with Cu(II)-ion-forming [(PIP)CuII(Cl)] becomes ...

A fluorescein hydrazone based conjugate (H2L3) was synthesized by coupling fluorescein hydrazide (L1) with 2-(pyridin-2-ylmethoxy)-naphthalene-1-carbaldehyde (L2). H2L3 was well characterized by several spectroscopic methods such as IR, 1H, 13C-NMR and ESI-MS. The probe H2L3 exhibited high selectivity and high sensitivity towards toxic Hg2+ ions in semi-aqueous medium (pH 7.2, 10 mM HEPES) over other metal ions. The significant enhancement in fluorescence emission centered at 520 nm was attributed to the Hg2+-induced ring opening of the spirolactam moiety in the fluorescein structure. The 1 : 1 binding of H2L3 to Hg2+ was established by Job's method and confirmed by ESI-MS+ (m/z) studies and the binding constant was calculated as (0.43 ± 0.04) × 104 M−1 with a detection limit of 1.24 μM. Then again, the [Hg(HL3)]+ ensemble could be utilized as a reversible fluorescent sensor for S2−. On addition of S2− to the [Hg(HL3)]+ complex, the fluorescence intensity was totally quenched because Hg2+ in the complex was grabbed by S2− because of the stronger binding force between Hg2+ and S2−. The tentative coordination environment in the [Hg(HL3)]+ complex was established by DFT studies. The fluorescence “OFF–ON–OFF” mode of H2L3 was examined in the presence of Hg2+ and S2− and finds applications in devices with logic gate functions. H2L3 also exhibits bio-compatibility and negligible cytotoxicity and is suitable for fluorescence cell imaging of Hg2+ ions in live HepG2 cells.

A dinuclear {CuII–EuIII} complex has been prepared and characterized by single crystal X-ray diffraction, where each metal atom is doubly phenoxido-bridged by the two phenolato oxygen atoms of a hexadentate Schiff-base ligand. The DC magnetic data is consistent with the population of the lowest electronic multiplets of the Eu(III) atom i.e., ground 7F0 and thermally accessible 7F1 (ΔE/hc ∼ 300 cm−1) tuned by a weak exchange with the Cu(II) centre that is of an antiferromagnetic nature. The AC susceptibility measurements confirm the presence of field supported slow magnetic relaxation: the relaxation time is τLF (1.9 K) = 25 ms for the low-frequency relaxation channel. Also the isostructural analogue {CuII–LaIII} shows slow magnetic relaxation, however with different dynamic characteristics.

A dual-emission pyrene-based new fluorescent probe (N-(4-nitro-phenyl)-N′-pyren-1-ylmethyl-ene-ethane-1,2-diamine (PyDA-NP)) displays green fluorescence for nitric oxide (NO) sensing, whereas it exhibits blue emission in the aggregated state. The mechanism of nitric oxide (NO/NO+) sensing is based on N-nitrosation of aromatic secondary amine, which was not interfered by reactive oxygen species and reactive nitrogen species. The aggregation-induced enhancement of emission (AIEE) behaviors of the PyDA-NP could be attributed to the restriction of intramolecular rotation and vibration, resulting in rigidity enhancement of the molecules. The AIEE behavior of the probe was well established from fluorescence, dynamic light scattering, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, optical fluorescence microscopy, and time-resolved photoluminescence studies. In a H2O/CH3CN binary mixture (8:2 v/v), the probe showed maximum aggregation with extensive (833-fold) increases in fluorescence intensity and high quantum yield (0.79). The aggregated state of the probe was further applied for the detection of nitroexplosives. It displayed efficient sensing of 2,4,6-trinitrophenol (TNP), corroborating mainly the charge-transfer process from pyrene to a highly electron-deficient TNP moiety. Furthermore, for the on-site practical application of the proposed analytical system, a contact-mode analysis was performed.

A novel di-coordinating rhodamine-based chemosensor, HL with NO donor atoms, selectively and rapidly recognizes Fe3+ in the presence of all biologically relevant as well as toxic metal ions and numerous anions and also with other reactive oxygen and nitrogen species.

A novel manganese(III)-Schiff base complex anchored SBA-15 based heterogeneous catalyst SBA-15-SB-Mn was synthesized and characterized by various physicochemical techniques. The catalyst was found to exhibit excellent green catalysis for the aerial oxidation of 3,5-di-tert-butyl catechol (3,5-DTBC) to the corresponding 3,5-di-tert-butylcatechol-1,2-benzoquinone (3,5-DTBQ) with 83.17% conversion (TON = 515) within 1 h at room temperature and relevant to catechol oxidase behavior.

Methodological synthesis of a new biocompatible bi-compartmental rhodamine based probe (L3) provides a multi-inputs and multi-outputs molecular logic circuit based on simple chemosensing phenomena. Spectroscopic responses of Cu2+ and Hg2+ towards L3 together with reversible binding of S2- with L3-Cu2+ and L3-Hg2+ complexes help us to construct a thee-input molecular circuit on their control and sequential addition to a solution of L3 in a mixed organo-aqueous medium. We have further successfully encoded binary digits out of these inputs and outputs which may convert a three-digit input string into a two-digit output string resulting a simple monomolecular logic circuit. Such a molecular ‘Boolean’ logic operation may improve the complexity of logic gate circuitry and computational speed and may be useful to employ in potential biocompatible molecular logic platforms.

Immobilization of transition metal complexes at the surface of 2D-hexagonal functionalized SBA-15 material is one of the promising strategies in designing an efficient catalytic system for the olefin epoxidation reaction. Here we have immobilized Mn(III) on the Schiff-base anchore 2D-hexagonally ordered functionalised mesoporous SBA-15 material. Powder X-ray diffraction (PXRD), N2-sorption and high resolution transmission electron microscopic (HRTEM) studies of the resulting SBA-15-SB-Mn material suggested 2D-hexagonally ordered porous nanostructure and X-ray photoelectron spectroscopy (XPS) analysis suggested the presence of surface bound Mn(III) species in this nanomaterial. This mesoporous material showed excellent performance in the selective catalytic oxidation of various alkenes to the corresponding epoxides in the presence of tert-butyl hydroperoxide (TBHP, 70% aqueous solution) as oxidant under solvent-free mild reaction conditions together with high recycling efficiency.

A sensor (HL5) based on rhodamine 6G–en and 3-(3,5-dimethyl-pyrazol-1-ylmethyl)-2-hydroxy-5-methyl-benzaldehyde (HL4) has been developed for a highly sensitive and selective CHEF based recognition of trivalent metal ions M3+ (M = Al, Fe and Cr) over mono- and di-valent and other biologically abundant trivalent metal ions with prominent enhancement in absorption and emission intensities. A large enhancement of fluorescence intensities for Fe3+ (21 fold), Al3+ (14 fold) and Cr3+ (10 fold) was observed upon addition of 1.8 equivalents of these metals into the probe in methanol/H2O (1 : 1, v/v, pH 7.2) with the possibility of naked eye detection. The corresponding Kf values were evaluated to be 6.7 × 104 M−1 (Fe3+); 8.2 × 104 M−1 (Al3+) and 6.0 × 104 M−1 (Cr3+). The quantum yields of HL5 and [HL5–Fe3+] and [HL5–Cr3+] and [HL5–Al3+] complexes in methanol/H2O (1 : 1, v/v, pH 7.2) are found to be 0.013, 0.290, 0.120, and 0.158, respectively, using rhodamine-6G as the standard. The LOD for Fe3+, Al3+ and Cr3+ were determined by 3σ methods with values 0.29, 0.34 and 0.31 μM, respectively. An arsenate ion snatches Al from the Al–HL5 complex and quenches its fluorescence via its ring closed spirolactam form. Advanced level molecular logic devices using the inputs 2 and 4 and memory devices, have been constructed. The low cytotoxicity and large enhancement in fluorescence intensity of HL5 upon complexation with M3+ metal ions make the probe suitable for bio-imaging of M3+ (M = Al, Fe and Cr) in living cells and native cellular iron pools.

A novel di-coordinating rhodamine-based chemosensor, HL with NO donor atoms, selectively and rapidly recognizes Fe3+ in the presence of all biologically relevant as well as toxic metal ions and numerous anions and also with other reactive oxygen and nitrogen species. It exhibits a lower detection limit (0.17 μM) and comparatively higher formation constant (Kf = 1.72 × 104 M−1). The DNA-binding properties of [LFe(NO3)2]+ complex have been comprehensively studied by using UV-Vis, fluorescence, and optical melting studies and circular dichroism, which clearly indicate that [LFe(NO3)2]+ interacts with DNA via a groove binding mode. In particular, competition experiments with Hoechst and DAPI constitute firm evidence for this binding mode, and clearly rule out intercalation. The negative ΔG0 and positive ΔS0 values obtained from a calorimetric technique confirm the spontaneity of the binding of [LFe(NO3)2]+ with DNA. The resulting [LFe(NO3)2]+/DNA composite material could be a valuable candidate for future photonics and/or biological applications.

Two new hybrid compounds based on phosphomolybdates, namely (NHEPH2)5[NiII(P4Mo6O31)2]·6H2O (1) and {(NHEPH2)2[CoII(H2O)6]}[P2Mo5O23]·2H2O (2) (NHEP = N-(2-hydroxyethyl)-piperazine), have been synthesized under hydrothermal conditions and characterized by elemental analyses, IR, TGA, single crystal X-ray diffraction and PXRD studies. In compound 1, Ni(II) is sandwiched between two {P4Mo6O31}6− clusters and the residual negative charges are neutralized by NHEPH22+. In compound 2, the [P2Mo5O23]6− ion exists as a discrete moiety and the negative charges are compensated by both [Co(H2O)6]2+ and NHEPH22+. The extensive hydrogen bonding involving the organic cations and water molecules yielded three-dimensional (3D) open framework structures in these systems. These phosphomolybdate based compounds showed good catalytic efficiency in heterogeneous oxidation of styrene in the presence of an environmentally benign oxidant, H2O2, under mild conditions.

A new 8-hydroxyquinoline-pyrazole based highly sensitive and selective Al3+ sensor, 8Q-NH-Pyz (H2L3), was found to exhibit a turn-on fluorescence enhancement (FE) as high as 157 fold with Kd = (1.76 ± 0.06) × 10−5 M. The 1:1 binding stoichiometry was revealed from the linear fit of (Fmax − F0)/(F − F0) vs. 1/[Al3+] of the fluorescence titration data which was further substantiated by Job's method and HRMS studies. The LOD determined by 3σ methods was found to be 4.29 nM and quantum yields were determined to be 0.002 and 0.28 for the ligand and its Al3+ complex, respectively. The tentative coordination environment in the [Al(L3)(H2O)]+ complex was delineated by DFT calculations. TDDFT calculations reveal spectral features comparable to the experimental ones. This constitutes the first report on the fluorescence sensing of Al3+ and hence F− in a purely aqueous medium.

We report herein the development of a novel, diformyl-p-cresol (DFC)–thiosemicarbazide (TS) based sensor (DFC–TS) that selectively and sensitively recognizes Zn2+ by both UV-Vis and fluorescence methods. The gradual addition of Zn2+ to a solution of the ligand developed a new absorption band at 430 nm, while the bands at 370 and 316 nm gradually decrease generating one well defined isosbestic point at 390 nm exhibiting ∼17 fold turn-on fluorescent enhancement (FE). When we plot absorbance (at 430 nm) vs. [Zn2+] there is a gradual increase in absorption with [Zn2+], becoming saturated at ∼1 equivalent of Zn2+ and then again it increases with the increase in [Zn2+] and ultimately becomes saturated at ∼2 equivalents of added Zn2+. This clearly demonstrates that the Zn2+ binding event to the ligand occurs in two steps, one at a time. Non-linear least-squares computer-fitting of these data gives the parameters: K′f1 = (9.70 ± 5.51) × 105 M−1, n = (1.28 ± 0.05) for the first step and K′f2 = (1.11 ± 0.65) × 105 M−1 and n = (1.01 ± 0.06) for the second step. So far, this study provides the opportunity where we have successfully, for the first time, determined the stepwise formation constants; though they have values of the same order of magnitude. The ground state geometries of DFC–TS, both enol and keto forms and [Zn(DFC–TS)(OAc)], [Zn(DFC–TS)(OAc)]−, and [Zn2(DFC–TS)(OAc)2] were optimized using the Gaussian-03 suit program and bond distances of all species are in reasonable agreement with the reported values.

A novel 3-hydroxymethyl-5-methylsalicylaldehydenaphthyl-hydrazone (H3SAL-NH) exhibits ESIPT behaviour due to proton transfer from the phenolic OH group to the azomethine N atom in the excited state. Through this ESIPT behaviour together with cis–trans isomerization of the azomethine group, the free ligand becomes very weakly fluorescent. However, in the presence of Zn2+ and Al3+ the ESIPT and isomerization are blocked due to coordination to the metal ions thereby causing turn on fluorescence for Al3+ and Zn2+. Moreover, Zn2+ can easily be displaced from the [H2SAL-NH–Zn2+] complex by Al3+ thereby enhancing the differential selectivity for Al3+ over Zn2+. This probe was found to be selective for Al3+ over Zn2+ in the presence of Na2H2EDTA, under both intra- and extracellular conditions. The LODs for Zn2+ and Al3+ were determined by 3σ methods and were found to be 3.1 nM and 0.92 nM, respectively. Thus, the differentially selective turn-on fluorescence behaviour of H3SAL-NH for Zn2+ and Al3+ is based on the combined blocking of ESIPT and CN isomerization, and a chelation-enhanced fluorescence (CHEF) effect. The coordination modes of the complexes were investigated through spectroscopic and computational studies. H3SAL-NH also exhibits good photostability and very low cytotoxicity and is useful for fluorescence imaging of Zn2+ and Al3+ ions in live HepG2 cells.

Organic molecules with the possibility of logic operations are highly useful building blocks for the development of molecule-based “intelligent” devices for information processing applications. We have designed herein a very simple bio-friendly chemosensor (LC) equipped with a rhodamine fluorophore moiety. This probe showed a chromo-fluorescence response profile for Al3+ but a colorimetric response for Cu2+ metal. The absorption responses of LC caused by these metal ions along with the “OFF–ON–OFF” fluorescence behavior of an LC–Al3+ complex towards EDTA were employed for the development of a three-input and one output combinatorial molecular system. Interactions of the mentioned metal ions with LC in controlled sequential experiments gave fluorescence responses, enabling us to fabricate a ‘key-pad-logic’ function. So, a single molecular system performing such multiple ‘Boolean’ operations not only simplifies the complexity of a chemical driven ‘Intelligence’ device but also enriches the security of such a device against information invasion due to the sequence controlled sensor–analyte interactions and may find potential applications in biocompatible molecular logic platforms.

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In this report, the interaction between a phenanthrene–pyrene-based fluorescent probe (PPI) and bovine serum albumin (BSA), a transport protein, has been explored by steady-state emission spectroscopy, fluorescence anisotropy, far-ultraviolet circular dichroism (CD), time-resolved spectral measurements, and molecular docking simulation study. The blue shift along with emission enhancement indicates the interaction between PPI and BSA. The binding of the probe causes quenching of BSA fluorescence through both static and dynamic quenching mechanisms, revealing a 1:1 interaction, as delineated from Benesi–Hildebrand plot, with a binding constant of ∼105 M–1, which is in excellent agreement with the binding constant extracted from fluorescence anisotropy measurements. The thermodynamic parameters, ΔH°, ΔS°, and ΔG°, as determined from van’t Hoff relationship indicate the predominance of van der Waals/extensive hydrogen-bonding interactions for the binding phenomenon. The molecular docking and site-selective binding studies reveal the predominant binding of PPI in subdomain IIA of BSA. From the fluorescence resonance energy transfer study, the average distance between tryptophan 213 of the BSA donor and the PPI acceptor is found to be 3.04 nm. CD study demonstrates the reduction of α-helical content of BSA protein on binding with PPI, clearly indicating the change of conformation of BSA.

A new, easily synthesizable chemosensor, DFC-EN-p-Ph-NO2, derived by the Schiff base condensation between 2,6-diformyl-p-cresol and N-(4-nitrophenyl)ethylenediamine, with potential N4O donor atoms was found to act as a dual channel (colori- and fluorimetric) sensor towards Al3+ and PPi emitting at 486 nm (blue region) and 534 nm (green region), respectively in MeOH–H2O (8 : 2, v/v) at pH 7.2 (10 mM HEPES buffer), μ = 0.05 M (LiCl), temperature 25 °C. The binding stoichiometries and formation constants of the sensor towards both Al3+ and PPi were determined by the combined UV-Vis and fluorescence titrations and Job's method, and confirmed by MS (m/z) studies. The corresponding detection limits as calculated by the 3σ method are: 7.55 μM and 3.34 μM. The most interesting part of this study is that on addition of 230 μM PPi to an ensemble of DFC-EN-p-Ph-NO2−Al3+ (20 μM Ligand and 380 μM Al3+) the fluorescence is totally quenched but on further addition of PPi a new emission peak appears at 534 nm. All biologically relevant metal ions and toxic heavy metals did not interfere with the detection of Al3+ ion. Its bio-compatibility with respect to its good solubility in mixed organo-aqueous media (MeOH–H2O) and cell permeability with no or negligible cytotoxicity provide good opportunities towards in vitro cell imaging studies of these ions. In particular, the fluorescent detection of PPi was not interfered by the presence of 400 μM of ATP or Pi although most reported PPi sensors that work in aqueous solution displayed cross-sensitivities toward ATP or Pi. The obvious excellent sensing capability of DFC-EN-p-Ph-NO2 towards PPi and Al3+ was further scrutinized in HCT116 cell lines without much cytotoxicity. The modes of 1 : 1 binding of DFC-EN-p-Ph-NO2 towards Al3+ and PPi were delineated by DFT calculations.

We have synthesized four mononuclear manganese(III) complexes (1–4) of four closely related bidentate NO donor Schiff-base ligands, out of which three (2–4) were structurally characterized. Crystal structure determination reveals that all these complexes are in octahedral geometries. Magnetic studies have been carried out on complexes 2, 3 and 4 in the temperature range 2–300 K under a magnetic field of 0.1 T which yielded negative ZFS parameters of −2.96, –3.51 and −3.72 cm−1 respectively. The catecholase activities of complexes 1–4 have been investigated following the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) with molecular oxygen in DCM at 25 °C, which were found to follow the Michalis–Menton type relation giving the highest TON (Kcat) for the so far reported Mn(III) complexes.

Two mononuclear complexes namely [NiII(L)] (1) and [CoIII(L)](NO3) (2) of a hexacoordinating N4O2 donor Schiff base ligand were synthesized and characterized by single crystal X-ray studies. In compound 2 the central cobalt is in + 3 oxidation state while ‘in’ compound 2, the nickel ion is in + 2 oxidation state. The two complexes are isostructural with octahedral coordination environment exhibiting helical twist topology. They also display strong H-bonding as well as CH-π interactions to generate 1D chain.

This study describes the solvent-dependent conversion of an oxime under identical reaction conditions ([Cu(bipy)Cl2]/NaN3/5-Br-H2salox/TEA=1:2:1:2 molar ratio; bipy=2,2′-bipyridyl, 5-Br-H2salox=5-bromosalicylaldoxime, TEA=triethylamine), but in different solvents. In DMSO/CH2Cl2 (2:1 v/v) only tetrazole is formed, whereas iminoacylation in MeCN and simple complexation takes place in MeOH. The formed tetrazole and iminoacylated ligands further undergo complexation with metal ions, as evidenced from single-crystal X-ray diffraction studies and ESI-MS analyses. Mechanistic models have been proposed in which coordination-assisted bonding of sodium azide across the CNOH double bond occurs to form a tetrazole and oxime–MeCN coupling forms an iminoacylated ligand. The former is a catalytic reaction, as evidenced from a turnover number of approximately 50, whereas the latter is stoichiometric in nature. This is the first report to demonstrate the dependence of solvent polarity on oxime transformation reactions through structural elucidation.

A new pyrene based highly sensitive and selective Al3+ sensor, pyrene-2-(pyridin-2-ylmethylsulfanyl)-ethylamine (PP), was found to exhibit a turn-on fluorescence enhancement (FE) as high as 7.4 fold with Kd (2.55 ± 0.10) × 10−4 M and n = 1. This probe binds reversibly with Al3+ in the presence of H2EDTA2−, both under intra- and exctracellular conditions. LOD determined by 3σ methods was found to be 15 nM while LOQ = 52.8 nM. The tentative coordination environment in the Al3+–PP complex was delineated by DFT calculations both on the free ligand and complex. The TDDFT calculations reveal spectral features comparable to the experimental ones.

A series of new manganese schiff base complexes have been prepared and characterized by single crystal X-ray diffraction studies, which showed that all the three complexes are mononuclear; 1 and 2 have square pyramidal geometry, whereas 3 has an octahedral geometry. Magnetic studies reveal that all these complexes exhibit (i) moderate frequency dependence of ac magnetic susceptibility at low temperature upon the application of a dc external field; (ii) significant magnetic anisotropy (D) and (iii) antiferromagnetic interaction that persist between the neighbouring molecules. Therefore, our systematic studies have shown the influence of electronic, geometric and packing effects of a new series of mononuclear manganese(III) complexes with axially elongated square pyramidal and octahedral geometries on the negative D values.

The aminolysis of α-isobutyl-α-(methylthio)methylene Meldrum's acid 7 with primary amines, namely, n-butylamine, glycinamide, and methoxyethylamine in DMSO–H2O (50:50, v/v) at 20 °C is overall second-order but first-order in both 7 and amines. The reaction with aminoacetonitrile (AA) is overall third-order, first-order in substrate, and second-order in amine at low amine concentration, while at high amine concentration and high pH the dependence on amine is first-order. A general three-step mechanism has been proposed for all these reactions. For the former group of amines, the first step is a rate-limiting attack of the amine to form the tetrahedral intermediate (TA±), followed by a fast acid–base equilibrium and a fast RNH3+- or H2O-assisted leaving group expulsion. For AA, general base catalysis was confirmed from the dependence of kA on [AA]f and on [OH–]. For all four amines, a good Brønsted plot of log k1 vs. pKaAH in DMSO–H2O (50:50, v/v) with βnuc = 0.34 ± 0.02 was observed. These observations are consistent with the suggested mechanism.Key words: nucleophilic vinylic substitution reactions, primary amines, α-isobutyl-α-(methylthio)methylene Meldrum's acid, three-step mechanism.

A cyano-bridged CuII–NiII dimeric complex [Cu(Me6Cy)][Ni(CN)4] has been synthesized and characterized by its single crystal X-ray structure determination. The square planar [Cu(Me6Cy)]2+ cation is converted to a distorted trigonal bipyramidal (TBP) geometry through ligation to one of the cyano groups of [Ni(CN)4]2− in the equatorial plane, keeping the other three as terminal. Inspection of the X-ray data reveals that the Cu–N(6)–C(6) angle of the bridging cyano group is perfectly linear (180°). The room temperature (RT) EPR spectrum of polycrystalline [Cu(Me6Cy)][Ni(CN)4] is typical for mononuclear copper(II) complexes of axial symmetry, where the flattened out symmetry axis is characterized by g⊥ = 2.143 ± 0.005 and g‖ = 2.002 ± 0.005. No half field (ΔM = 2) signals were observed. RT EPR spectrum of polycrystalline [CuII(Me6Cy)](ClO4)2 yields an EPR signal with g‖ = 2.394 ± 0.005 and g⊥ = 2.045 ± 0.005, indicating that this parent compound has a different geometry than [Cu(Me6Cy)][Ni(CN)4]. Variable temperature magnetic moment studies on [Cu(Me6Cy)][Ni(CN)4] indicate a very weak long-range ferromagnetic exchange through hydrogen bonding between copper(II) ions (S = ½). The present investigation provides a unique example where the original square planar [Cu(Me6Cy)]2+ moiety rearranges itself to a trigonal bipyramidal geometry under the influence of [Ni(CN)4]2−. This is probably only the second, rare example, and perhaps the first, for a macrocyclic precursor using only one cyano group of [Ni(CN)4]2− for bridging, leading to a discrete dinuclear complex.

A kinetic study of the aminolysis of [methyl(thiomethoxy)carbene]pentacarbonylchromium(0), (CO)5CrC(CH3)(SCH3) (2-Cr), with morpholine, a secondary amine, in 50% acetonitrile–50% water (v/v) at 25° C is reported. The second-order rate constant (kA in L mol−1 s−1) increases with amine concentration, giving a linear dependence with an intercept on the rate axis. The general base-catalyzed nature of the reaction was confirmed by the dependence of the rate on both amine and hydroxide ion concentrations. The mechanism proposed is very similar to those for ester reactions, involving a nucleophilic addition of amine to the substrate to yield a zwitterionic tetrahedral intermediate (TA#), followed by deprotonation of TA# to form TA− in a fast step, which, in the third step, is converted to product by a general acid-catalyzed thiomethoxide expulsion. As the carbene itself acts as an acid and only the acid form is active towards aminolysis reactions, the protic equilibrium was evaluated through the aminolysis reaction with morpholine and was found to be in good agreement with the value reported earlier.

Acidity constants of six substituted 1-benzyl-1-methoxy-2-nitroethylenes (2-Z with Z = m-NO(2), m-CF(3), m-Cl, H, p-Me, p-MeO) and their respective nitronic acids were determined in 50% DMSO-50% water (v/v) at 20 degrees C. Kinetic data were obtained on the reversible deprotonation of all six 2-Z by OH(-) and piperidine and on the reversible deprotonation of 2-NO(2)() by piperazine, 1-(2-hydroxyethyl)piperazine, and morpholine in the same solvent. These data allowed a determination of the Brønsted coefficients alpha (dependence on acidity of 2-Z) and beta (dependence on amine basicity). The fact that alphabeta indicates the presence of a transition state imbalance which, however, is much smaller than that for the deprotonation of arylnitromethanes. The reasons for this reduction in the imbalance and their relevance to a recent study of the deprotonation of Fischer carbene complexes are discussed.

Rate and equilibrium constants for the conversion of (CO)5CrC(OCH2CH2OH)Ph (8-CrOOH), (CO)5WC(OCH2CH2OH)Ph (8-WOOH), (CO)5CrC(SCH2CH2OH)Ph (8-CrSOH), and (CO)5WC(SCH2CH2OH)Ph (8-WSOH) into the corresponding cyclic adducts (9-CrOO- for M = Cr, X = O; 9-WOO- for M = W, X = O; 9-CrSO- for M = Cr, X = S; 9-WSO- for M = W, X = S) are reported. Under basic conditions the reaction occurs via the respective oxyanions, (CO)5CrC(OCH2CH2O-)Ph (8-CrOO-), etc.; under acidic conditions the reaction may either be concerted with water acting as a general base catalyst or stepwise via a zwitterionic intermediate. The absence of buffer catalysis suggests but does not prove the operation of the stepwise mechanism. The equilibrium constants for cyclization of 8-CrSO- and 8-WSO- are about 1 order of magnitude higher than for 8-CrOO- and 8-WOO-, respectively. For the rate constants the situation is reversed, with 8-CrOO- and 8-WOO- being substantially more reactive than 8-CrSO- and 8-WSO-, respectively. These results reflect t...

Rate constants for the reversible deprotonation of (CO)5CrC(SCH3)CH3 (9-Cr) and (CO)5WC(SCH3)CH3 (9-W) by OH-, water, a number of primary aliphatic and secondary alicyclic amines, and a series of carboxylate ions have been determined in 50% MeCN−50% water at 25 °C. This represents the first such study of Fischer carbene complexes stabilized by a thioalkoxy group. Comparison of our results to those of the corresponding methoxy derivatives (CO)5CrC(OCH3)CH3 (2-Cr) and (CO)5WC(OCH3)CH3 (2-W) reveals that the change in the π-donor group from MeO to MeS leads to (1) a strong increase in the thermodynamic acidity, (2) an increase in the dependence of the pKa on the nature of the metal, (3) a decrease in the intrinsic rate constants for proton transfer, and (4) a decrease in the dependence of the intrinsic rate constant on the metal. Observations 1, 2, and 4 can be attributed to the weaker π-donor capability of the MeS group while observation 3 is the combined result of a steric effect due to the larger size of ...

The kinetics of the reduction of [NiIII(L1)]2+ (where HL1 = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) by sulphur(IV) and selenium (IV) over the regions pH 2.50–8.02 and 2.01–4.00 respectively have been investigated at 30°C. Attempts were made to evaluate the reactivity of all the reacting species, of sulphur(IV) and selenium(IV) by considering suitable pH ranges. The oxidation of SC2·H2O and HSO 3 − is proposed to proceed through the formation of a hydrogen-bonded adduct. The reaction with SO 3 2− seems to follow a direct outer-sphere route which is well supported by Marcus crossrelation calculation. The oxidation of HSeO l3 − is ≈ 103 times slower than that of H2SeO3. The kinetic data indicate that the oxidation of sulphur(IV) by [NiIIIL1)]2+ is much more favourable as compared to the corresponding oxidation of selenium(IV).

The oxidation of ascorbic acid by [NiIIIL1]2+ and [NiIVL32]2+ complexes (where HL1= 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime and HL3= 6-amino-3-methyl-4-azahex-3-en-2-one oxime) has been investigated by stopped-flow spectrophotometry in the range pH 2.50–8.20, with /= 0.20 mol dm–3 NaClO4 and T= 30 °C, using variable concentrations of ascorbic acid. At a particular pH both the reactions are second order, first order with respect to ascorbic acid and the complexes, and follow the general rate law –1/m d[NiLxn+]/dt=k[NiLxn+][H2A]T where H2A = ascorbic acid and m represents the stoichiometric factor (m= 2 for [NiIIIL1]2+ and 1 for [NiIVL32]2+). In the reduction of [NiIVL32]2+, the monophasic reaction traces throughout the experimental pH range (2.50–8.20) imply the involvement of nickel(III) complexes in the rate-determining step. A detailed evaluation of the reduction was achieved by considering suitable pH regions and employing appropriate computer programs to fit the experimental data. Application of the Marcus theory in calculating the theoretical rate constants and a comparison of these constants with the respective experimental values reveals the occurrence of an outer-sphere mechanism for the oxidation of A2– by both [NiIIIL1]2+ and [NiIVL32]2+ as well as by [NiIIIL2]+ where H2L2= 3,14-dimethyl-4,7,10,13-tetra-azahexadec-3,13-diene-2,15-dione dioxime. The oxidation of H2A and HA– seems to follow a concerted electron–proton transfer with initial association of the reactants.

The electron transfer reactions of Mo(CN)8 4, W(CN)8 4− and Fe(CN)6 4− with the manganese (III) complex oftrans-cyclohexane-1,2-diamine-N,N,N′,N′-tetraacetic acid have been studied by stopped-flow spectrophotometry in the pH range 2.0–6.5. Analysis of kinetic data conforms to an outer-sphere process in each case. The validity of Marcus’ crossreaction relation to these reactions is fairly satisfactory.

The kinetics of the electron-transfer reactions of the manganese(III) complex of trans-cyclohexane-1,2-diamine-N,N,N′,N′-tetraacetate (cdta4–) with two thiols thioglycolic acid and glutathione has been investigated at 30 °C in aqueous media in the range pH 2.0–10.33 with varying reductant concentrations at constant ionic strength, I= 0.20 mol dm–3(NaClO4). The reactions are first order both in complex and reductants and follow the general rate law, –d[MnIII(cdta)–]/dt=Kobs[MnIII(cdta)–]=K[MnIII(cdta)–][reductant]. Both the reactions have been assumed to proceed via an inner-sphere mechanism with support for this coming from the observation of a rapid initial increase in absorption followed by a slower decay. This indicates the formation of an inner-sphere associated species which decomposes unimolecularly leading to the transfer of the electron from the thiol to the oxidant. Additional support for this mechanism comes from a comparison of the water-exchange rate of [Mn(cdta)(H2O)]– with the higher limit of the electron-transfer rates. The pH–rate profiles are bell-shaped curves and were successfully modelled by fitting the experimental data to a computer-fitted program thereby evaluating the reactivity of all the reacting species of the reductants.

The oxidation of sulfite by the two nickel(IV) oxime–imine complexes [NiIVL12+]2 and [NiIVL2]2+(HL1= 6-amino-3-methyl-4-azahex-3-en-2-one oxime and H2L2= 3,14-dimethyl-4,7,10,13-tetra-azahexadeca-3,13-diene-2,1 5-dione dioxime) has been investigated in aqueous medium at 30 °C over the range pH 2.0–8.0. Single-step two-electron transfer reactions were encountered in the regions 2.0 ⩽ pH ⩽ 5.50 for [NiIVL12]2+ and 2.0 ⩽ pH ⩽ 4.25 for [NiIVL2]2+ reductions. A distinct biphasic process with faster initial one-electron reduction of NiIV to NiIII followed by a slower conversion of NiIII into NiII was observed above pH 5.75 and 4.50 for the respective complexes. Attempts were made to evaluate the reactivity of all the reacting species of the complexes as well as of sulfur(IV) by considering suitable pH regions. The stoichiometries of the reactions ([SIV]:[NiIV]) were found to vary within the region ≈2.0–1.0 depending upon the mole ratios of the reactants. At pH 4.50 with an excess of complex over the reductant the ratio [SIV]:[NiIV] is less than 2:1 for both complexes giving a mixture of dithionate and sulfate as the oxidation products of sulfite. However, with an excess of sulfite over the complex this ratio reaches a limiting value of ≈2:1 at [SIV]:[NiIV] > 8 giving dithionate as the major oxidation product. The observed stoichiometric ratios for both complexes are in accord with the distribution of the sulfate and dithionate products. Attempts were made to correlate the experimentally observed rate constants with those obtained from Marcus cross-relation calculations. Calculated rate constants for the oxidation of SO32– by various nickel-(IV) and -(III) species were found to be one to two orders of magnitude lower than the corresponding experimental values. The oxidation of SO2·H2O and HSO3– is proposed to proceed through the formation of a hydrogen-bonded adduct.

The kinetics of the reduction of (trans-1,2-cyclohexanediamine-N,N,N′,N′-tetracetato)manganate(III) by formate and malonate have been investigated in the pH regions 3.6–5.25 and 4.5–8.30 respectively at constant ionic strength and temperature. In the oxidation of formate slight initial increase in absorbance was observed, whereas for malonate oxidation no such indication was noted. Both the reactions are overall second-order with first-order on both the oxidant and reductants. A general rate law for the oxidation of formate and malonate can be given as −d[oxidant]/dt = k[oxidant] × [reductant], where k is the electron-transfer rate constant. The reactivity of HCOO− is (3.26 ± 0.16) × 10−5 dm3 mol−1 s−1 (kK′) and that of Hmal− and mal2− are (4.28 ± 0.12) × 10−5 (k1) and (6.05 ± 0.12) × 10−4 (k2) dm3 mol−1 s−1 respectively at 40 °C. A plausible inner-sphere mechanism has been suggested for the formate oxidation, whereas malonate oxidation has been interpreted by an outer-sphere mechanism.

The oxidation of sulfite and thiosulfate by Co(dipic)2− (where H2dipic=2,6-pyridinedicarboxylic acid) was studied in aqueous medium. The reactions were carried out by varying reagent concentrations, pH, and ionic strength. For thiosulfate oxidation, the rate is zero order in complex and second order in thiosulfate. The reaction rates were found to increase with the acidity and the general rate law is expressed as kobs={k′0+k′1[H+]}[S2O32−]2 where k′0 and k′1 denote the acid independent and dependent paths respectively. The values of rate parameters are k′0=(2.87±0.20)×10−8 mol dm−3 s−1 and k′1=(0.57±0.02) mol−2 dm6 s−1 at 30°C. A plausible mechanism is suggested by considering the formation of an intermediate active species in the rate-determining step. The sulfite oxidation was, however, first order both in complex and reagent. An inverse dependence on [H+] was obtained for this reaction indicating a higher reactivity of the anionic species in solution. The general rate law is given by kobs=2(k1[SO2·H2O]...

Two dinuclear Cu(II) complexes [Cu2(3,5-dimethyl-pyrazole)4(1,1-N3)2(ClO4)2] (1) and [Cu2(3,5-dimethyl-pyrazole)2(N-hydroxymethyl-3,5-dimethyl-pyrazole)2(ClO4)2] (2) with rhombus [Cu2X2] cores exhibit σ-aromaticity that unprecedentedly interact with two closely disposed coordinated perchlorate ions with interaction energies, −53 and −47 kJ mol−1 respectively.

This constitutes the first crystallographic observation of hydrated Cu(II) ion retaining up to its third hydration layer which, along with the chair form water hexamer, builds up a unique water-cation layer. Moreover, an unprecedented supramolecular honeycomb network of [Cu(phen)3]2+ units templated by Anderson polyoxometallate units occupy the intervening spaces between successive water layers. Complex 1 is a rare example of parallel interpenetration of a 2D π–π network and a 3D pillar-layered hydrogen bonded network.

The kinetics of the oxidation of thioglycolic and thiomalic acids by [Ni III L 1 ] 2+ (where HL 1 =15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en- 2-one oxime) have been investigated at 30.0 °C; an inner-sphere mechanism for both the reactions has been proposed except for the fully deprotonated species of thiomalic acid which follows an outer-sphere route.

Rate and equilibrium constants for the nucleophilic attachment of various thiolate ions to (CO)5MC(SMe)Ph (M = Cr and W) and for the attachment of HOCH2CH2S- to (CO)5WC(SCH2CH2OH)C6H4Z (Z = CF3, Cl, F, H, Me, MeO, and Me2N) have been determined in 50% MeCN−50% water (v/v) at 25 °C. For some of the adducts, those of the general structure (CO)5MC(SR,SR‘)C6H4Z, a kinetic determination of the pKa of their metal-protonated conjugate acid, (CO)5M(H)C(SR,SR‘)C6H4Z, is also reported. On the basis of Bronsted coefficients, Hammett ρ values and comparisons with the reactions of the same thiolate ions with methoxy carbene complexes such as (CO)5MC(OMe)Ph, insights into the role played by desolvation of the nucleophile prior to C−S bond formation, by the smaller π-donor and inductive but larger steric effects of the MeS compared to the MeO group, by transition state imbalances, etc. are discussed. The pKa values obtained for (CO)5M(H)C(SR,SR‘)C6H4Z were used to resolve a mechanistic ambiguity in the hydrolysis of Fi...

The kinetics of oxidation of thiosulfate by the complexes [NiIVL32]2+ and [NiIVL2]2+(HL3= 6-amino-3-methyl-4-azahex-3-en-2-one oxime, H2L2= 3,14-dimethyl-4,7,10,13-tetraazahexadeca-3,13-diene-2,15-dione dioxime) was studied spectrophotometrically under pseudo-first-order conditions with an excess of thiosulfate in the range pH 2.50–8.0 with [NiIV]= 5.0 × 10–5 mol dm–3, [S2O32–]=(1.0–10.0)× 10–3 mol dm–3, I= 0.20 mol dm–3(NaClO4) at 20 °C. A monophasic two-electron transfer was found in the regions 3.0 ⩽ pH ⩽ 5.0 and 2.5 ⩽ pH ⩽ 4.0 for reduction of the two complexes respectively. Above these pH regions both reactions showed biphasic decay with an initial faster step NiIV→ NiIII and second slower step NiIII→ NiII, and the general rate law is –d[NiIV(Lx)2+]/dt=kobs[NiIV(Lx)2+]= 2nk[NiIV(Lx)2+][S2O32–] where 2n is a stoichiometric factor. All the kinetic parameters have been evaluated by choosing suitable pH regions. An additional protonation of the nickel(IV) complexes (pKa= 4.91 and 4.28 respectively) has been encountered and a realistic interpretation is achieved by considering a weak acid–base interaction arising out of outer-sphere protonation of the [NiIV(Lx)]2+ complexes. All the reaction steps have been scrutinised. The reduction [NiIV(Lx)]2+→[NiIII(Lx)]+ is assumed to follow an outer-sphere mechanism whereas [NiIII(Lx)]+→[NiII(Lx)] follows an inner-sphere route. The calculated electron-transfer rate constant (k12) obtained through Marcus cross-reaction relations can be considered as a proof of such delineation.