The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di-tert-butylphenol, H 2 L OCH3 , results in... more The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di-tert-butylphenol, H 2 L OCH3 , results in, as expected, a trisradical complex with a low-spin Co(III) center, [Co III (L OCH3• ) 3 ] (1), whereas the Ga(III) center yields a coordinated new hexadentate monoradical ligand, [Ga III L • 1 ] (2), presumably due to the ligand-derived redox activity involving C-H activation.
Ten hetero-and homodinuclear M A III M B III complexes, 1-10, containing the metal centers Fe III... more Ten hetero-and homodinuclear M A III M B III complexes, 1-10, containing the metal centers Fe III Zn II (1), Fe III Cu II (2), Fe III Ni II (3), Fe III Fe II (4), Fe III Mn II (5), Cr III Ni II (6), Cr III Zn II (7), Ga III Ni II (8), Co III Fe II (9), and Mn III Mn II (10) are described. The tridentate ligation property of the divalent metal complexes tris(1-methylimidazole-2-aldoximato)metal(II) 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, M€ ossbauer 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(III) ion, LM A III (L = 1,4,7-trimethyl-1,4,7-triazacyclononane), in a distorted octahedral environment M A III N 3 O 3 and a second sixcoordinated divalent metal ion, M B II , in a trigonally distorted M B II N 6 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 Fe III Mn II (5) < Fe III Ni II (3) < Fe III Cu II (2) whereas Fe III Ni II (3) > Cr III Ni II (6). On the contrary, complex 10, containing high-spin Mn(III) and Mn(II) centers, exhibits ferromagnetic coupling yielding a "high-spin" molecule with an S t = 9 / 2 ground state. X-band electron paramagnetic resonance (EPR) spectroscopy for 6, Cr III Ni II and 3, Fe III Ni II 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 imidazolecontaining ligand and the analogous pyridine-containing oxime.
Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), ... more Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) 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 MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 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, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) 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, S(t) = 3/2, has been confirmed by the X-band EPR measurements.
An acetonitrile (0.5 mL) solution of potassium benzoate (7.1 mg, 0.044 mmol) was reacted with an ... more An acetonitrile (0.5 mL) solution of potassium benzoate (7.1 mg, 0.044 mmol) was reacted with an acetonitrile solution (0.5 ml) of UI 3 (THF) 4 (20.0 mg, 0.022 mmol). 88 μL of a 0.5 M solution of water (0.044 mmol) in acetonitrile was added to the resulting green colour solution. The resulting dark green solution was stirred over 1 day at room temperature, filtered and then evaporated to dryness under vacuum. The resulting green solid was dissolved in pyridine (1 mL) and diisopropyl ether (1 mL) was added, causing the formation of white precipitate of KI which was removed after 2 days by filtration. The resulting green solution was evaporated to dryness and the residue was recrystallized in acetonitrile, X-ray quality crystals of 1.2MeCN were obtained over 6-7 hours in 75 % yield.
We have previously reported that the [U 6 O 4 (OH) 4 (C 6 H 5 COO) 12 (Py) 3 ] cluster (Figure 1)... more We have previously reported that the [U 6 O 4 (OH) 4 (C 6 H 5 COO) 12 (Py) 3 ] cluster (Figure 1) is obtained in good yield from the stoichiometric reaction of uranium triiodide with water in acetonitrile in the presence of potassium benzoate (with a benzoate/uranium ratio of 2:1) ...
We have developed a new way to introduce redox events at lanthanide centers which should lead to ... more We have developed a new way to introduce redox events at lanthanide centers which should lead to further expansion of the reductive chemistry of lanthanides.
Herein, two novel mononuclear transition metal Zn2+ complexes have been synthesised using a trid... more Herein, two novel mononuclear transition metal Zn2+ complexes have been synthesised using a tridentate clickable Schiff base ligand, HL (2-methyl-2-((pyridin-2-ylmethyl)amino)propan-1-ol) and the polyatomic monoanions N3− and ClO4−.
Herein, we have reported two isostructural mononuclear metal complexes [M(HL)2(ClO4)2], wherein, ... more 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− mediat...
We report two isostructural dinuclear transition metal complexes [M2(HL)2(N3)4], where M = Ni2+ (... more We report two isostructural dinuclear transition metal complexes [M2(HL)2(N3)4], where M = Ni2+ (BS-1) or Mn2+ (BS-2) and HL is (2-methyl-2-((pyridin-2-ylmethyl)amino)propan-1-ol) and investigate them as molecular sensors towards hazardous entities.
The role of anions towards the catalytic activities of antiferromagnetically coupled dinuclear ni... more The role of anions towards the catalytic activities of antiferromagnetically coupled dinuclear nickel(ii) complexes having end-off compartmental ligand was unveiled.
We have developed a new way to introduce redox events at lanthanide centers which should lead to ... more We have developed a new way to introduce redox events at lanthanide centers which should lead to further expansion of the reductive chemistry of lanthanides.
The homoleptic compounds [U(salan-R 2 ) 2 ] (R = Me (1), t Bu (2)) were prepared in high yield by... more The homoleptic compounds [U(salan-R 2 ) 2 ] (R = Me (1), t Bu (2)) were prepared in high yield by saltmetathesis reactions between UI 4 (L) 2 (L = Et 2 O, PhCN) and 2 equiv of [K 2 (salan-R 2 )] in THF. In contrast, the reaction of the tetradentate ligands salan-R 2 with UI 3 (THF) 4 leads to disproportionation of the metal and to mixtures of U(IV) [U(salan-R 2 ) 2 ] and [U(salan-R 2 )I 2 ] complexes, depending on the ligand to M ratio. The reaction of K 2 salan-Me 2 ligand with U(IV) iodide and chloride salts always leads to mixtures of the homoleptic bis-ligand complex [U(salan-Me 2 ) 2 ] and heteroleptic complexes [U(salan-Me 2 )X 2 ] in different organic solvents. The structure of the heteroleptic complex [U(salan-Me 2 )I 2 (CH 3 CN)] (4) was determined by X-ray studies. Heteroleptic U(IV) and Th(IV) chloride complexes were obtained in good yield using the bulky salan-t Bu 2 ligand. The new complexes [U(salan-t Bu 2 )Cl 2 (bipy)] ( ) and [Th(salan-t Bu 2 )Cl 2 (bipy)] ( ) were crystallographically characterized. The salan-t Bu 2 halide complexes of U(IV) and Th(IV) revealed good precursors for the synthesis of stable dialkyl complexes. The six-coordinated alkyl complexes [Th(salan-t Bu 2 )(CH 2 SiMe 3 ) 2 ] ( ) and [U(salan-t Bu 2 )(CH 2 SiMe 3 ) 2 ] (10) were prepared by addition of LiCH 2 SiMe 3 to the chloride precursor in toluene, and their solution and solid-state structures (for 9) were determined by NMR and X-ray studies. These complexes are stable for days at room temperature. Preliminary reactivity studies show that CO 2 inserts into the An-C bond to afford a mixture of carboxylate products. In the presence of traces of LiCl, crystals of the dimeric insertion product [Th 2 Cl(salan-t Bu 2 ) 2 (μ-η 1 :η 1 -O 2 CCH 2 SiMe 3 ) 2 (μ-η 1 :η 2 -O 2 CCH 2 SiMe 3 )] (11) were isolated. The structure shows that CO 2 insertion occurs in both alkyl groups and that the resulting carboxylate is easily displaced by a chloride anion.
The tridentate unsymmetrical ligand N-(2-hydroxymethylphenyl)salicylideneimine H 2 L, derived fro... more The tridentate unsymmetrical ligand N-(2-hydroxymethylphenyl)salicylideneimine H 2 L, derived from salicylaldehyde and 2-aminobenzylalcohol, with [ONO] donor atoms yields [L 2 Fe III 2 Cl 2 ] (1) and [L 6 Fe III 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 = À15.8 cm À1 between the high-spin d 5 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 = À13.4 cm À1 , J 13 = J 24 = À7.1 cm À1 , J 23 = À14.9 cm À1 , 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.
Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to med... more Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to mediate magnetic exchange interactions between the ions. Among them are star-shaped molecules in which antiferromagnetic couplings between the central and peripheral atoms are predominantly present. Those configurations lead to an appreciable spin moment in the nonfrustrated ground state. In spite of its topologically simple magnetic structure, the [Cr III Mn II 3 (PyA) 6 Cl 3 ] (CrMn 3 ) molecule, in which PyA represents the monoanion of syn-pyridine-2-aldoxime, exhibits nontrivial magnetic properties, which emerge from the combined action of single-ion anisotropy and frustration. In the present work, we elucidate the underlying electronic and magnetic properties of the heteronuclear, spin-frustrated CrMn 3 molecule by applying X-ray magnetic circular dichroism (XMCD), as well as magnetization measurements in high magnetic fields, density functional theory, and ligand-field multiplet calculations. Quantum-model calculations based on a Heisenberg Hamiltonian augmented with local anisotropic terms enable us not only to improve the accuracy of the exchange interactions but also to determine the dominant local anisotropies. A discussion of the various spin Hamiltonian parameters not only leads to a validation of our element selective transition metal L edge XMCD spin moments at a magnetic field of 5 T and a temperature of 5 K but also allows us to monitor an interesting effect of anisotropy and frustration of the manganese and chromium ions.
Ten hetero-and homodinuclear M A III M B III complexes, 1-10, containing the metal centers Fe III... more Ten hetero-and homodinuclear M A III M B III complexes, 1-10, containing the metal centers Fe III Zn II (1), Fe III Cu II (2), Fe III Ni II (3), Fe III Fe II (4), Fe III Mn II (5), Cr III Ni II (6), Cr III Zn II (7), Ga III Ni II (8), Co III Fe II (9), and Mn III Mn II (10) are described. The tridentate ligation property of the divalent metal complexes tris(1-methylimidazole-2-aldoximato)metal(II) 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, M€ ossbauer 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(III) ion, LM A III (L = 1,4,7-trimethyl-1,4,7-triazacyclononane), in a distorted octahedral environment M A III N 3 O 3 and a second sixcoordinated divalent metal ion, M B II , in a trigonally distorted M B II N 6 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 Fe III Mn II (5) < Fe III Ni II (3) < Fe III Cu II (2) whereas Fe III Ni II (3) > Cr III Ni II (6). On the contrary, complex 10, containing high-spin Mn(III) and Mn(II) centers, exhibits ferromagnetic coupling yielding a "high-spin" molecule with an S t = 9 / 2 ground state. X-band electron paramagnetic resonance (EPR) spectroscopy for 6, Cr III Ni II and 3, Fe III Ni II 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 imidazolecontaining ligand and the analogous pyridine-containing oxime.
The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di-tert-butylphenol, H 2 L OCH3 , results in... more The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di-tert-butylphenol, H 2 L OCH3 , results in, as expected, a trisradical complex with a low-spin Co(III) center, [Co III (L OCH3• ) 3 ] (1), whereas the Ga(III) center yields a coordinated new hexadentate monoradical ligand, [Ga III L • 1 ] (2), presumably due to the ligand-derived redox activity involving C-H activation.
Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), ... more Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) 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 MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 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, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) 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, S(t) = 3/2, has been confirmed by the X-band EPR measurements.
Syntheses, crystal structures, and magnetic properties are reported for a hexametallic and a mixe... more Syntheses, crystal structures, and magnetic properties are reported for a hexametallic and a mixed-valent tetrametallic vanadium cluster, namely [Na(L(1))(6)(V(IV)=O)(6)]ClO(4) (1) and [(L(2))(2)V(III)(2)V(IV)(2)(mu-Cl)(6)Cl(4)] (2), where H(2)L(1) represents N-methyldiethanolamine and H(2)L(2) N&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;N&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-di(3,5-di-tert-butyl-salicylidene)-1,3-diaminobenzene. The structure of the cation in 1 is comprised of a hexagon of six (V(IV)=O) units, in which a sodium ion is encapsulated in the center of the hexagon. Thus, the hexametalate ring contains six d(1) ions, each of which is in an octahedral environment of O(5)N atoms. Magnetic studies reveal the cluster to exhibit ferromagnetic exchange interactions (J = +16.7 +/- 0.3 cm(-1)), which is rationalized by the orthogonal neighboring xy planes of d(1) V(IV)=O ions. The structure of complex 2 can be considered as two mixed-valent face-sharing bioctahedral units of [V(III)(mu-Cl)(3)V(IV)] bridged by two m-phenylene linkers. The V(1)(III)...V(2)(IV) distances of av. 3.10 A preclude metal-metal bonding. Variable-temperature magnetic susceptibility data are fitted to obtain the parameters J(1) = -47.6 cm(-1), J(2) = +1.5 cm(-1), g(V(III)) = 1.95, g(V(IV)) = 1.85 (H = -2J x S(i).S(j)). The ferromagnetic coupling J(2) operates at a distance of approximately 7.09 A between two vanadium centers through the spin polarization mechanism due probably to the topology (1,3-substitution) of the m-phenylene bridges. The X-band electron paramagnetic resonance (EPR) spectrum analyzed with S(t) = 1 shows that the mixed-valent V(III)V(IV) species has indeed been formed and the tetranuclear core remains intact in solution. The hyperfine coupling constants indicate the localized mixed-valence nature of 2.
The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di-tert-butylphenol, H 2 L OCH3 , results in... more The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di-tert-butylphenol, H 2 L OCH3 , results in, as expected, a trisradical complex with a low-spin Co(III) center, [Co III (L OCH3• ) 3 ] (1), whereas the Ga(III) center yields a coordinated new hexadentate monoradical ligand, [Ga III L • 1 ] (2), presumably due to the ligand-derived redox activity involving C-H activation.
Ten hetero-and homodinuclear M A III M B III complexes, 1-10, containing the metal centers Fe III... more Ten hetero-and homodinuclear M A III M B III complexes, 1-10, containing the metal centers Fe III Zn II (1), Fe III Cu II (2), Fe III Ni II (3), Fe III Fe II (4), Fe III Mn II (5), Cr III Ni II (6), Cr III Zn II (7), Ga III Ni II (8), Co III Fe II (9), and Mn III Mn II (10) are described. The tridentate ligation property of the divalent metal complexes tris(1-methylimidazole-2-aldoximato)metal(II) 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, M€ ossbauer 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(III) ion, LM A III (L = 1,4,7-trimethyl-1,4,7-triazacyclononane), in a distorted octahedral environment M A III N 3 O 3 and a second sixcoordinated divalent metal ion, M B II , in a trigonally distorted M B II N 6 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 Fe III Mn II (5) < Fe III Ni II (3) < Fe III Cu II (2) whereas Fe III Ni II (3) > Cr III Ni II (6). On the contrary, complex 10, containing high-spin Mn(III) and Mn(II) centers, exhibits ferromagnetic coupling yielding a "high-spin" molecule with an S t = 9 / 2 ground state. X-band electron paramagnetic resonance (EPR) spectroscopy for 6, Cr III Ni II and 3, Fe III Ni II 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 imidazolecontaining ligand and the analogous pyridine-containing oxime.
Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), ... more Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) 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 MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 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, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) 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, S(t) = 3/2, has been confirmed by the X-band EPR measurements.
An acetonitrile (0.5 mL) solution of potassium benzoate (7.1 mg, 0.044 mmol) was reacted with an ... more An acetonitrile (0.5 mL) solution of potassium benzoate (7.1 mg, 0.044 mmol) was reacted with an acetonitrile solution (0.5 ml) of UI 3 (THF) 4 (20.0 mg, 0.022 mmol). 88 μL of a 0.5 M solution of water (0.044 mmol) in acetonitrile was added to the resulting green colour solution. The resulting dark green solution was stirred over 1 day at room temperature, filtered and then evaporated to dryness under vacuum. The resulting green solid was dissolved in pyridine (1 mL) and diisopropyl ether (1 mL) was added, causing the formation of white precipitate of KI which was removed after 2 days by filtration. The resulting green solution was evaporated to dryness and the residue was recrystallized in acetonitrile, X-ray quality crystals of 1.2MeCN were obtained over 6-7 hours in 75 % yield.
We have previously reported that the [U 6 O 4 (OH) 4 (C 6 H 5 COO) 12 (Py) 3 ] cluster (Figure 1)... more We have previously reported that the [U 6 O 4 (OH) 4 (C 6 H 5 COO) 12 (Py) 3 ] cluster (Figure 1) is obtained in good yield from the stoichiometric reaction of uranium triiodide with water in acetonitrile in the presence of potassium benzoate (with a benzoate/uranium ratio of 2:1) ...
We have developed a new way to introduce redox events at lanthanide centers which should lead to ... more We have developed a new way to introduce redox events at lanthanide centers which should lead to further expansion of the reductive chemistry of lanthanides.
Herein, two novel mononuclear transition metal Zn2+ complexes have been synthesised using a trid... more Herein, two novel mononuclear transition metal Zn2+ complexes have been synthesised using a tridentate clickable Schiff base ligand, HL (2-methyl-2-((pyridin-2-ylmethyl)amino)propan-1-ol) and the polyatomic monoanions N3− and ClO4−.
Herein, we have reported two isostructural mononuclear metal complexes [M(HL)2(ClO4)2], wherein, ... more 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− mediat...
We report two isostructural dinuclear transition metal complexes [M2(HL)2(N3)4], where M = Ni2+ (... more We report two isostructural dinuclear transition metal complexes [M2(HL)2(N3)4], where M = Ni2+ (BS-1) or Mn2+ (BS-2) and HL is (2-methyl-2-((pyridin-2-ylmethyl)amino)propan-1-ol) and investigate them as molecular sensors towards hazardous entities.
The role of anions towards the catalytic activities of antiferromagnetically coupled dinuclear ni... more The role of anions towards the catalytic activities of antiferromagnetically coupled dinuclear nickel(ii) complexes having end-off compartmental ligand was unveiled.
We have developed a new way to introduce redox events at lanthanide centers which should lead to ... more We have developed a new way to introduce redox events at lanthanide centers which should lead to further expansion of the reductive chemistry of lanthanides.
The homoleptic compounds [U(salan-R 2 ) 2 ] (R = Me (1), t Bu (2)) were prepared in high yield by... more The homoleptic compounds [U(salan-R 2 ) 2 ] (R = Me (1), t Bu (2)) were prepared in high yield by saltmetathesis reactions between UI 4 (L) 2 (L = Et 2 O, PhCN) and 2 equiv of [K 2 (salan-R 2 )] in THF. In contrast, the reaction of the tetradentate ligands salan-R 2 with UI 3 (THF) 4 leads to disproportionation of the metal and to mixtures of U(IV) [U(salan-R 2 ) 2 ] and [U(salan-R 2 )I 2 ] complexes, depending on the ligand to M ratio. The reaction of K 2 salan-Me 2 ligand with U(IV) iodide and chloride salts always leads to mixtures of the homoleptic bis-ligand complex [U(salan-Me 2 ) 2 ] and heteroleptic complexes [U(salan-Me 2 )X 2 ] in different organic solvents. The structure of the heteroleptic complex [U(salan-Me 2 )I 2 (CH 3 CN)] (4) was determined by X-ray studies. Heteroleptic U(IV) and Th(IV) chloride complexes were obtained in good yield using the bulky salan-t Bu 2 ligand. The new complexes [U(salan-t Bu 2 )Cl 2 (bipy)] ( ) and [Th(salan-t Bu 2 )Cl 2 (bipy)] ( ) were crystallographically characterized. The salan-t Bu 2 halide complexes of U(IV) and Th(IV) revealed good precursors for the synthesis of stable dialkyl complexes. The six-coordinated alkyl complexes [Th(salan-t Bu 2 )(CH 2 SiMe 3 ) 2 ] ( ) and [U(salan-t Bu 2 )(CH 2 SiMe 3 ) 2 ] (10) were prepared by addition of LiCH 2 SiMe 3 to the chloride precursor in toluene, and their solution and solid-state structures (for 9) were determined by NMR and X-ray studies. These complexes are stable for days at room temperature. Preliminary reactivity studies show that CO 2 inserts into the An-C bond to afford a mixture of carboxylate products. In the presence of traces of LiCl, crystals of the dimeric insertion product [Th 2 Cl(salan-t Bu 2 ) 2 (μ-η 1 :η 1 -O 2 CCH 2 SiMe 3 ) 2 (μ-η 1 :η 2 -O 2 CCH 2 SiMe 3 )] (11) were isolated. The structure shows that CO 2 insertion occurs in both alkyl groups and that the resulting carboxylate is easily displaced by a chloride anion.
The tridentate unsymmetrical ligand N-(2-hydroxymethylphenyl)salicylideneimine H 2 L, derived fro... more The tridentate unsymmetrical ligand N-(2-hydroxymethylphenyl)salicylideneimine H 2 L, derived from salicylaldehyde and 2-aminobenzylalcohol, with [ONO] donor atoms yields [L 2 Fe III 2 Cl 2 ] (1) and [L 6 Fe III 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 = À15.8 cm À1 between the high-spin d 5 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 = À13.4 cm À1 , J 13 = J 24 = À7.1 cm À1 , J 23 = À14.9 cm À1 , 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.
Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to med... more Molecular magnets incorporate transition-metal ions with organic groups providing a bridge to mediate magnetic exchange interactions between the ions. Among them are star-shaped molecules in which antiferromagnetic couplings between the central and peripheral atoms are predominantly present. Those configurations lead to an appreciable spin moment in the nonfrustrated ground state. In spite of its topologically simple magnetic structure, the [Cr III Mn II 3 (PyA) 6 Cl 3 ] (CrMn 3 ) molecule, in which PyA represents the monoanion of syn-pyridine-2-aldoxime, exhibits nontrivial magnetic properties, which emerge from the combined action of single-ion anisotropy and frustration. In the present work, we elucidate the underlying electronic and magnetic properties of the heteronuclear, spin-frustrated CrMn 3 molecule by applying X-ray magnetic circular dichroism (XMCD), as well as magnetization measurements in high magnetic fields, density functional theory, and ligand-field multiplet calculations. Quantum-model calculations based on a Heisenberg Hamiltonian augmented with local anisotropic terms enable us not only to improve the accuracy of the exchange interactions but also to determine the dominant local anisotropies. A discussion of the various spin Hamiltonian parameters not only leads to a validation of our element selective transition metal L edge XMCD spin moments at a magnetic field of 5 T and a temperature of 5 K but also allows us to monitor an interesting effect of anisotropy and frustration of the manganese and chromium ions.
Ten hetero-and homodinuclear M A III M B III complexes, 1-10, containing the metal centers Fe III... more Ten hetero-and homodinuclear M A III M B III complexes, 1-10, containing the metal centers Fe III Zn II (1), Fe III Cu II (2), Fe III Ni II (3), Fe III Fe II (4), Fe III Mn II (5), Cr III Ni II (6), Cr III Zn II (7), Ga III Ni II (8), Co III Fe II (9), and Mn III Mn II (10) are described. The tridentate ligation property of the divalent metal complexes tris(1-methylimidazole-2-aldoximato)metal(II) 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, M€ ossbauer 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(III) ion, LM A III (L = 1,4,7-trimethyl-1,4,7-triazacyclononane), in a distorted octahedral environment M A III N 3 O 3 and a second sixcoordinated divalent metal ion, M B II , in a trigonally distorted M B II N 6 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 Fe III Mn II (5) < Fe III Ni II (3) < Fe III Cu II (2) whereas Fe III Ni II (3) > Cr III Ni II (6). On the contrary, complex 10, containing high-spin Mn(III) and Mn(II) centers, exhibits ferromagnetic coupling yielding a "high-spin" molecule with an S t = 9 / 2 ground state. X-band electron paramagnetic resonance (EPR) spectroscopy for 6, Cr III Ni II and 3, Fe III Ni II 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 imidazolecontaining ligand and the analogous pyridine-containing oxime.
The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di-tert-butylphenol, H 2 L OCH3 , results in... more The redox-active ligand 2-(3,5-dimethoxyanilino)-4,6-di-tert-butylphenol, H 2 L OCH3 , results in, as expected, a trisradical complex with a low-spin Co(III) center, [Co III (L OCH3• ) 3 ] (1), whereas the Ga(III) center yields a coordinated new hexadentate monoradical ligand, [Ga III L • 1 ] (2), presumably due to the ligand-derived redox activity involving C-H activation.
Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), ... more Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) 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 MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 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, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) 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, S(t) = 3/2, has been confirmed by the X-band EPR measurements.
Syntheses, crystal structures, and magnetic properties are reported for a hexametallic and a mixe... more Syntheses, crystal structures, and magnetic properties are reported for a hexametallic and a mixed-valent tetrametallic vanadium cluster, namely [Na(L(1))(6)(V(IV)=O)(6)]ClO(4) (1) and [(L(2))(2)V(III)(2)V(IV)(2)(mu-Cl)(6)Cl(4)] (2), where H(2)L(1) represents N-methyldiethanolamine and H(2)L(2) N&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;N&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-di(3,5-di-tert-butyl-salicylidene)-1,3-diaminobenzene. The structure of the cation in 1 is comprised of a hexagon of six (V(IV)=O) units, in which a sodium ion is encapsulated in the center of the hexagon. Thus, the hexametalate ring contains six d(1) ions, each of which is in an octahedral environment of O(5)N atoms. Magnetic studies reveal the cluster to exhibit ferromagnetic exchange interactions (J = +16.7 +/- 0.3 cm(-1)), which is rationalized by the orthogonal neighboring xy planes of d(1) V(IV)=O ions. The structure of complex 2 can be considered as two mixed-valent face-sharing bioctahedral units of [V(III)(mu-Cl)(3)V(IV)] bridged by two m-phenylene linkers. The V(1)(III)...V(2)(IV) distances of av. 3.10 A preclude metal-metal bonding. Variable-temperature magnetic susceptibility data are fitted to obtain the parameters J(1) = -47.6 cm(-1), J(2) = +1.5 cm(-1), g(V(III)) = 1.95, g(V(IV)) = 1.85 (H = -2J x S(i).S(j)). The ferromagnetic coupling J(2) operates at a distance of approximately 7.09 A between two vanadium centers through the spin polarization mechanism due probably to the topology (1,3-substitution) of the m-phenylene bridges. The X-band electron paramagnetic resonance (EPR) spectrum analyzed with S(t) = 1 shows that the mixed-valent V(III)V(IV) species has indeed been formed and the tetranuclear core remains intact in solution. The hyperfine coupling constants indicate the localized mixed-valence nature of 2.
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