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Herein, we have reported two isostructural mononuclear metal complexes [M(HL)2(ClO4)2], wherein, M= Co2+ (viz. SN‐1) and Ni2+ (viz. SN‐2) and HL is NNO donor Schiff‐base ligand i. e. ((E)‐2‐methyl‐2‐((pyridin‐2‐ylmethylene)amino)propan‐1‐ol) for unveiling as molecular sensor for S2− (sulphide) like hazardous entity. The molecular probes have been characterized by SCXRD, 1H‐NMR, FT‐IR, HRMS etc. X‐ray diffraction studies confirm the mono‐nuclear structures of both the complexes. Interestingly, SN‐1 exhibited remarkable sensitivity towards S2− by naked eye colour change in purely aqueous medium with detection limit of 33.5 nM and binding constant of 11.05 × 108 M−1 while the SN‐2 didn't show any subtle chromogenic changes upon interaction with the targeted analyte. Judicious choice of metal centre plays a pivotal role for such discriminative interacting behaviour. Spectroscopic and DFT studies shed light on the mechanistic pathway of host‐guest interaction, indicating a S2− mediated chemodosimetric approach following HSAB principle. Impressively, the SN‐1 has also been explored towards fabrication of test strips for on‐field detection of H2S/S2−via. "Dip‐Stick" approaches. In a nutshell, the presently developed simple mono‐nuclear metal complex can be utilised for detecting gasotransmitter like H2S/S2− from purely aqueous medium that may be helpful in fabricating "point‐of‐care" devices in coming days for better understanding of H2S as a key role maker in various health related issues. [ABSTRACT FROM AUTHOR]

Ten hetero- and homodinuclear MAIIIMBIII complexes, 1-10, containing the metal centers FeIIIZnII (1), FeIIICuII (2), FeIIINiII (3), FeIIIFeII (4), FeIIIMnII (5), CrIIINiII (6), CrIIIZnII (7), GaIIINiII (8), CoIIIFeII (9), and MnIIIMnII (10) are described. The tridentate ligation property of the divalent metal complexes tris(l -methylimidazole-2-aldoximato)metal(ll) with three facially disposed pendent oxime O-atoms has been utilized to generate the said complexes. Complexes were characterized by various physical methods including MS, IR, UV-vis, Mössbauer and EPR spectroscopy, cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, and X-ray diffraction techniques. Binuclear complexes 1-10 contain three oximato anions as bridging ligands and are isostructural in the sense that they all contain a metal(lll) ion, LMAIII (L= 1 ,4,7-trimethyl-l ,4,7-triazacyclononane), in a distorted octahedral environment MAIIIN3O3 and a second six-coordinated divalent metal ion, MBII, in a trigonally distorted MBIIN6 geometry. A comparison of the cyclic voltammograms of the complexes with those of similar systems reveal both ligand-centered and metal-centered redox processes. Complexes 2, 3, 5, and 6 display antiferromagnetic exchange coupling of the neighboring metal centers in the order FeIIIMnII (5) < FeIIINiII (3) < FeIIICuII (2) whereas FeIIINiII (3)> CrIIINiII (6). On the contrary, complex 10, containing high-spin Mn(lll) and Mn(ll) centers, exhibits ferromagnetic coupling yielding a "high-spin" molecule with an St= 9/2 ground state. X-band electron paramagnetic resonance (EPR) spectroscopy for 6, CIIINiII and 3, FeIIINiII has been used to establish the electronic ground state in great detail and to complement the magnetic susceptibility measurements. Moreover, computational results have been included to compare the σ-bonding character of the nitrogen lone pair in imidazole-containing ligand and the analogous pyridine-containing oxime. [ABSTRACT FROM AUTHOR]

Abstract: The tridentate unsymmetrical ligand N-(2-hydroxymethylphenyl)salicylideneimine H2L, derived from salicylaldehyde and 2-aminobenzylalcohol, with [ONO] donor atoms yields [L2FeIII 2Cl2] (1) and [L6FeIII 4] (2) complexes containing alkoxide bridges, which have been structurally characterized by X-ray diffraction. In complex 1, each ferric ion is five-coordinated with a distorted square-pyramidal geometry, the basal planes of which are symmetrically bridged by two alkoxide oxygen atoms. Analysis of the susceptibility data reveals antiferromagnetic interactions with an exchange parameter J =−15.8cm−1 between the high-spin d5 ferric centers. The structure of 2 can be considered as “linear (2,2,2)” to specify the number of enolate oxygen atoms between four iron atoms. Variable-temperature magnetic susceptibility data are fitted to a “three-J” model, yielding pairwise antiferromagnetic exchange interactions, J 12 = J 34 =−13.4cm−1, J 13 = J 24 =−7.1cm−1, J 23 =−14.9cm−1, between the neighboring ferric centers; J 14 is assumed to be negligible. Complex 2 has a complicated low-lying magnetic structure with a non-diamagnetic ground state. In addition, the Fe–O–Fe angles at the bridging ligands seem to be determinant for the strength of the antiferromagnetic interactions. [Copyright &y& Elsevier]

Eight hetero- and homometal complexes 1–6, containing the metal centers NiIIFeIII°NiII (1), MnIIINII (2), NiIINiII (3a—c and 4), ZnIINiII (5), and ZnIIZnII (6), are described. The tridentate ligation property of the metal complexes tris-(pyridine-2-aldoximato)nickel(ll) and tris(1-methylimidazole-2-aldoximato)nickel(ll) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2–290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2–6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN3O3 and a second six-coordinated NiII ion in a trigonally distorted octahedral NiN6 geometry. Complexes 1–4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural NiII2 complexes, 3a—c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, MnIIINiII, exhibits a reduction of MnIII to MnII and two subsequent oxidations of MnIII and NiII to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, St = ⅜, has been confirmed by the X-band EPR measurements. [ABSTRACT FROM AUTHOR]