A strategically synthesized arseno-discriminatory tetra-phenoxido hetero-trinuclear complex envisioned for the recognition of iAs and oAs from Oryza sp. and aquatic crustaceans.

A heterotrimetallic [MnII(CuII)2(C18H18N2O2)2] complex VBCMERI has been unveiled herein to monitor its synergistic propensity towards aqueous phase As3+ (iAs and oAs) detection. VBCMERI was structurally probed by numerous analytical tools like ESI-MS, FT-IR, and SCXRD. The aqueous phase selective chromogenic alteration of the sensory probe from greenish-yellow to colorless was observed owing to interaction with As3+ (cationic form, iAs). This phenomenon can be ascribed to the displacement of the Mn2+ center with As3+, which has further been experimentally validated through cyclic voltammetric titration studies, FT-IR, and ESI-MS, and theoretically corroborated with density functional theory calculations. Interestingly, aqueous phase selective turn-on fluorogenic enhancement of the sensory probe was observed upon interaction with AsO2- (anionic form, iAs) owing to the displacement of the arsenite anion with the pivalic acid group. The distinct chromogenic alteration from greenish-yellow to colorless and the fluorogenic enhancement of VBCMERI upon interaction with the respective As3+ (iAs) and AsO2- (iAs) were successfully implemented for monitoring arsenic contamination in groundwater samples and diverse types of Oryza sp. grains from the assorted arsenic-affected zones. The competitive accumulation of arsenobetaine (oAs) in the exoskeleton and muscles of aquatic crustaceans (herein, Penaeus sp.) can be distinctly differentiated based on the turn-on fluorogenic response. Based on the sensing response and competitive accumulation tendency of different forms of arsenic in different environments, arseno-adducts with VBCMERI have been theoretically modeled for corroboration with experimental findings. The VBCMERI-AsO2- adduct was also highly efficient in regenerating the VBCMERI sensor selectively in the presence of contaminants like Pb2+. This reversible behavior was further exploited to mimic a molecular-level 3-input-2-output logic gate ensemble.

Series of Functionalized 5-(2-Arylimidazo[1,2-a]pyridin-3-yl)pyrimidine-2,4(1H,3H)-diones: A Water-Mediated Three-Component Catalyst-Free Protocol Revisited.

A water-mediated and catalyst-free practical method for the synthesis of a new series of pharmaceutically interesting functionalized 5-(2-arylimidazo[1,2-a]pyridin-3-yl)pyrimidine-2,4(1H,3H)-diones has been accomplished based on a one-pot multicomponent reaction between arylglyoxal monohydrates, 2-aminopyridines/2-aminopyrimidine, and barbituric/N,N-dimethylbarbituric acids under reflux conditions. The salient features of this protocol are avoidance of any additive/catalyst and toxic organic solvents, use of water as reaction medium, clean reaction profiles, operational simplicity, ease of product isolation/purification without the aid of tedious column chromatography, good to excellent yields, and high atom-economy and low E-factor.

Switching the regioselectivity in the copper-catalyzed synthesis of iodoimidazo[1,2-a]pyridines.

A unique copper-catalyzed binucleophilic switching of 2-aminopyridine has been developed for the regioselective synthesis of 2- and 3-iodoimidazo[1,2-a]pyridines using alkenes/alkynes as coupling partners in the presence of molecular iodine under aerobic reaction conditions. This method was also applied to the synthesis of 2-iodo-3-phenylbenzo[d]imidazo[2,1-b]thiazoles. This protocol offers an easy route towards the synthesis of 2,3-diarylimidazo[1,2-a]pyridines.

Stepwise formation of a pentanuclear Ni4Cu heterometallic complex exhibiting a vertex-sharing defective double-cubane core and diphenoxo- and phenoxo/azide bridging groups: a magnetostructural and DFT theoretical study.

Sequential reaction of a N5O3 octadentate tripodal ligand with Ni(2+) and subsequently with Cu(2+) and azide ligand afforded the first example of a heterobridged (phenoxo/µ(1,1)-azido) pentanuclear heterometallic (Ni4Cu) compound, which exhibits a centrosymmetric vertex-sharing defective double-cubane structure. The study of the magnetic properties reveals that the compound shows ferromagnetic interaction interactions, leading to an S = 9/2 spin ground state. Density functional theory calculations on the X-ray structure and model compounds predict ferromagnetic interactions through the magnetic exchange pathways involving each couple of metal ions.

A versatile series of nickel(II) complexes derived from tetradentate imine/pyridyl ligands and various pseudohalides: azide and cyanate compared.

The chemical reactions of a family of tetradentate pyridyl/imine ligands, L1, L2, and L3 (L1=[ N, N'-bis(2-pyridinylmethylene)]ethane-1,2-diamine; L2=[ N, N'-bis(pyridin-2-yl)benzylidene]ethane-1,2-diamine; L3=[ N, N'-bis(2-pyridinylmethylene)]propane-1,3-diamine), with Ni (II) in the presence of various pseudohalides (N3(-), SCN(-), and NCO(-)) have served to prepare six different complexes, [Ni 2(L1)2(N3)2](ClO4)2.H2O (1), [Ni 2(L2)2(N3)2](ClO4)2 (2), [Ni2(L2)2(NCS)4] (3), [Ni2(L2)2(NCO) 2](ClO4)2 (4), [Ni2(L3)2(NCO)2](ClO4)2 (5), and [Ni(L3)(N 3)2] (6), which have been characterized by X-ray crystallography. Interestingly, four of these complexes are dinuclear and exhibit end-on (EO) pseudohalide bridges (1, 2, 4, and 5), one is dinuclear and bridged exclusively by the tetradentate ligand (3), and one is mononuclear (6). The bulk magnetization of the complexes bridged by EO pseudohalides has been studied, revealing these ligands to mediate ferromagnetic coupling between the Ni(II) ions, with modeled coupling constants, J, of +31.62 (1), +28.42 (2), +2.81 (4), and +1.72 (5) cm(-1) (where the convention H=-2JS1S2 was used). The striking difference in the coupling intensity between N3(-) and NCO(-) has prompted an investigation by means of density functional theory calculations, which has confirmed the experimental results and provided insight into the reasons for this observation.

Magneto-structural correlations: synthesis of a family of end-on azido-bridged manganese(II) dinuclear compounds with S = 5 spin ground state.

The preparation of a series of multidentate pyridyl-imine ligands, L1-L3, and their reactivity with the Mn(II)/N3- system is described (L1 = [N,N-bis(pyridine-2-yl)benzylidene]ethane-1,2-diamine; L2 = [N,N-bis(pyridine-2-yl)benzylidene]propane-1,3-diamine, and L3 = [N,N-bis(pyridine-2-yl)benzylidene]butane-1,4-diamine). Complexes comprising dinuclear end-on bis(mu-azido)-bridged manganese(II) units of formulas [Mn2(L1)2(N3)4][Mn2(L1)2(N3)2(CH3OH)2](ClO4)2 (two cocrystallized dinuclear units, 1.2), [Mn2(L2)2(N3)2](ClO4)2 (3), and [Mn2(L3)2(N3)2](ClO4)2 (4) have been synthesized. The crystal structures of complexes 1-4 as well as their magnetic properties are presented. Each manganese atom of cocrystallized complexes in compound 1.2 is heptacoordinated, displaying Mn-N-Mn angles, theta, of 102.53(12) and 101.70(12) degrees and Mn...Mn distances of 3.5091(7) and 3.4680(7) A. On the other hand, each manganese center in compounds 3 and 4 is located within an octahedral coordination environment, the complexes displaying theta angles of 104.29(11) and 103.60(18) degrees , respectively, and Mn...Mn vectors of 3.5371(7) and 3.5338(10) A, respectively. Magnetic susceptibility studies revealed the presence of intramolecular ferromagnetic superexchange, yielding an S = 5 spin ground state in all complexes. Fitting of the experimental data led to coupling constants, intermolecular exchange values, and g factors (in the J/zJ'/g format) of 0.77 cm(-1)/0.01 cm(-1)/2.20 (1.2), 2.04 cm(-1)/0.01 cm(-1)/1.99 (3), and 1.75 cm(-1)/-0.05 cm(-1)/2.04 (4), respectively (using H = -2JS1S2 as the convention for the Heisenberg spin-Hamiltonian). These results are consistent with predictions from recent DFT calculations performed on end-on bis(mu-N3-)-bridged Mn(II) dinuclear complexes. A plot of experimental J vs theta, including data from the only preexisting compound of this kind, reveals a linear relationship, which could be the first evidence of a possible magneto-structural correlation between these two parameters.

Synthesis, structure and magnetism of a new dicubane-like ferromagnetic tetranuclear nickel cluster containing versatile azido-only bridges and a bis(bidentate) Schiff base blocker.

A new tetranuclear double-open dicubane complex [Ni4(mu 2-N3)4(mu 3-N3)2(N3)2(enbzpy)2].2H2O (enbzpy = [N,N-bis(pyridin-2-yl)benzylidene]ethane-1,2-diamine) has been characterised structurally and magnetostructurally.

Electron Transfer. 134. Reduction of Bound Ruthenium(III) by Indium(I)(1).

Aqueous solutions of the hypovalent state indium(I) react with oxidants of the type [(NH(3))(5)Ru(III)(Lig)](3+), in which the sixth ligand, "Lig", is devoid of groups allowing inner-sphere bridging. Reaction stoichiometry conforms to the relationship In(I) + 2Ru(III) --> In(III) + 2Ru(II). Kinetic profiles are consistent with a two-step sequence initiated by the formation of metastable In(II), which then reacts rapidly with Ru(III). Rate constants for the rate-determining steps in this series (k(Ru,In) values) are proportional to those for reductions of the corresponding (NH(3))(5)Co(III) oxidants with V(2+)(aq), Cr(2+)(aq), Eu(2+)(aq), and U(3+)(aq), even though, for each comparison, no metal center is common to the two series chosen. This implies that changes in DeltaG()(redox) arising from substitution of one N-donor ligand for another are nearly independent of the metal centers involved in the net transfer. The rate for the reduction of (NH(3))(6)Ru(3+), considered in the framework of the Marcus model, leads to an estimated rate constant of 10(-9) M(-1) s(-1) for electron self-exchange in the system In(2+/+). This value lies well below the range characteristic of the most usual aqua-substituted cationic couples, suggesting a more severe H(2)O-metal bond contraction in going from the uni- to the dipositive cation.

Electron Transfer. 135. Pendant Carbonyl Groups in the Mediation of the Reactions of Indium(I) with Bound Ruthenium(III)(1).

Reductions, using In(I)(aq) and Ti(III)(aq), of (NH(3))(5)Ru(III) derivatives of pyridines having carbonyl-bearing substituents (-CONH(2), -COOCH(3), and -COC(6)H(5)) yield the corresponding (NH(3))(5)Ru(II) complexes. Reactions with Ti(III) are kinetically straightforward, exhibit only slight responses to structural alteration, and give no indication of inner-sphere mediation involving the carbonyl group. Kinetic profiles for In(I) reductions of the 3-CONH(2), 3-COOCH(3), and 3-COC(6)H(5)-substituted complexes (in the range [H(+)] = 0.030-0.15 M) begin with a nearly linear section, with rates independent of [In(I)], but show curvature during the later stages of reaction. These profiles are consistent with a reaction sequence in which the predominant carbonyl form of the oxidant is hydrated to a more reactive gem-diol form (>C=O + H(2)O right harpoon over left harpoon >C(OH)(2)), which undergoes reduction by In(I), yielding the observed Ru(II) product and In(II). The latter is then rapidly consumed by a second unit of Ru(III). Rate constants for the hydration step giving optimal fit to the experimental curves are 6 x 10(-4) s(-1) (for the 3-CONH(2) complex) and 1.3 x 10(-3) s(-1) (for the 3-COOCH(3) oxidant). Lower limits for the rate of attack by In(I) on the active forms of the oxidants are estimated as 10(3.3)-10(4.6) M(-1) s(-1), about 10(2)-10(3) times are rapid as the reduction of the unsubstituted pyridine complex. Our results suggest the utilization, by In(I), of a hydroxyl-bridged path featuring the sequence In(I)-OH-C(OH)-py in these reductions, a path which is overshadowed, in the case Ti(III) reactions, by a more facile outer-sphere process.

Electron Transfer. 130. Reductions with Indium(I)(1).

Aqueous solutions of the hypovalent state indium(I) have been prepared by treatment of In(Hg) with silver triflate in acetonitrile, followed by dilution with oxygen-free water. These solutions are stable for over 5 h at 25 degrees C. In(I)(aq) reacts with oxidants of the type [(NH(3))(5)Co(III)(Lig)](2+) (In(I) + 2Co(III) --> In(III) + 2Co(II)), and kinetic profiles are consistent with a two-step sequence proceeding with formation of the metastable state In(II), which reacts rapidly with Co(III). Rate ratios for reductions of halogeno-substituted oxidants point to predominance of halide-bridged paths for the chloro, bromo and iodo complexes. Reductions of carboxylato-substituted derivatives are slow but appear to entail inner-sphere precursors if aided by an O-donor group in a position favorable for chelation. In no case is there evidence for reaction via initial reduction of the ligand (the radical-cation mechanism) although the potential of the In(I,II) couple (-0.40 V) allows this path for carbonyl-substituted oxidants. Reductions by In(I), like those by Eu(II), make no significant use of bridging by heterocyclic donor nitrogen centers in pyridine and pyrazine complexes.