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1.
Dalton Trans ; 49(10): 3369-3371, 2020 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-32100805

RESUMO

Correction for 'Mixed azido/phenoxido bridged trinuclear Cu(ii) complexes of Mannich bases: Synthesis, structures, magnetic properties and catalytic oxidase activities' by A. Ghosh et al., Dalton Trans., 2018, 47, 9385-9399.

2.
Dalton Trans ; 49(10): 3372-3374, 2020 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-32104843

RESUMO

Correction for 'Tri- and hexa-nuclear NiII-MnII complexes of a N2O2 donor unsymmetrical ligand: synthesis, structures, magnetic properties and catalytic oxidase activities' by A. Ghosh et al., Dalton Trans., 2018, 47, 13957-13971.

3.
Dalton Trans ; 49(4): 1276-1291, 2020 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-31909778

RESUMO

A new, facile Cu(ii) template method has been employed for the unsymmetrical dicondensation of 1,2-ethylenediamine with salicylaldehyde and o-vanillin. The mononuclear complex, [CuL] (1), thus obtained, has been used as an O3 donor metalloligand for the synthesis of four new Cu(ii)-Mn(ii) complexes, [(CuL)MnCl2] (2), [(CuL)Mn(NO3)2(CH3OH)]n (3), {[(CuL)Mn(benz)(H2O)]2·(CuL)2(ClO4)2} (4) and [(CuL)Mn(benz)Cl]2 (5) (where benz = benzoate). Single-crystal structural analyses reveal that 2 is a dinuclear complex while complex 3 is polymeric with a repeating dinuclear [(CuL)Mn(NO3)2(CH3OH)] unit, linked via the nitrate ion. Both 4 and 5 are discrete tetranuclear complexes, where the dinuclear units [(CuL)Mn(benz)(H2O)] and [(CuL)Mn(benz)Cl] are connected by double benzoate and double chloride bridges, respectively. In complex 4, two monomeric [CuL] units are cocrystallized with the tetranuclear complex. An important difference in the structure of 4 from the other three complexes is that one solvent water molecule is coordinated to each Mn(ii) ion, which makes complex 4 catalytically very active towards mimicking catecholase and phenoxazinone synthase-like oxidation reactions. The turnover numbers (kcat) for the aerial oxidation of 3,5-di-tert-butylcatechol and o-aminophenol are 399 h-1 and 230 h-1, respectively. The evidence of the intermediate species in the mass spectra indicates possible heterometallic cooperation where the Mn(ii) center helps in substrate binding and Cu(ii) participates in the oxidation reactions with molecular oxygen. Cyclic voltammetry measurements suggest the reduction of Cu(ii) to Cu(i) during the catalytic process. Temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 2-5 are antiferromagnetically coupled with the exchange coupling constants (J) of J = -13.5 cm-1 and J = -13.5 cm-1 for 2 and 3, respectively, J1 = -12.6 cm-1 and J2 = -1.20 cm-1 for complex 4 and J1 = -13.24 cm-1 and J2 = 0.36 cm-1 for complex 5 as is expected from the Cu-O-Mn bridging angles.


Assuntos
Complexos de Coordenação/química , Complexos de Coordenação/síntese química , Cobre/química , Fenômenos Magnéticos , Manganês/química , Oxirredutases/metabolismo , Materiais Biomiméticos/síntese química , Materiais Biomiméticos/química , Catálise , Técnicas de Química Sintética , Eletroquímica , Ligantes , Modelos Moleculares , Conformação Molecular
4.
Chemistry ; 26(7): 1612-1623, 2020 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-31793668

RESUMO

Two mononuclear uranyl complexes, [UO2 L1 ] (1) and [UO2 L2 ]⋅0.5 CH3 CN⋅0.25 CH3 OH (2), have been synthesized from two multidentate N3 O4 donor ligands, N,N'-bis(5-methoxysalicylidene)diethylenetriamine (H2 L1 ) and N,N'-bis(3-methoxysalicylidene)diethylenetriamine (H2 L2 ), respectively, and have been structurally characterized. Both complexes 1 and 2 showed a reversible UVI /UV couple at -1.571 and -1.519 V, respectively, in cyclic voltammetry. The reduction potential of the UVI /UV couple shifted towards more positive potential on addition of Li+ , Na+ , K+ , and Ag+ metal ions to acetonitrile solutions of complex 2, and the resulting potential was correlated with the Lewis acidity of the metal ions and was also justified by theoretical DFT calculations. No such shift in reduction potential was observed for complex 1. All four bimetallic products, [UO2 L2 Li0.5 ](ClO4 )0.5 (3), [UO2 L2 Na(ClO4 )]2 (4), [UO2 L2 Ag(NO3 )(H2 O)] (5), and [(UO2 L2 )2 K(H2 O)2 ]PF6 (6), formed on addition of the Li+ , Na+ , Ag+ , and K+ metal ions, respectively, to acetonitrile solutions of complex 2, were isolated in the solid state and structurally characterized by single-crystal X-ray diffraction. In all the species, the inner N3 O2 donor set of the ligand encompasses the equatorial plane of the uranyl ion and the outer open compartment with O2 O'2 donor sites hosts the second metal ion.

5.
Dalton Trans ; 48(40): 15170-15183, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31565726

RESUMO

The strategic design and synthesis of a new Cu(ii) complex, [CuL] (1) of an asymmetrically dicondensed N2O4 donor ligand (where H2L = N-3-ethoxysalicylidene-N'-3-methoxysalicylidene-1,3-propanediamine) and its utilization as a metalloligand towards the synthesis of three new tetra-nuclear carbonato bridged Cu-Ln complexes [(µ4-CO3)2{(CuL)(MeOH)Ln(NO3)}2] (where Ln = Dy, Tb and Gd for complexes 2, 3 and 4 respectively) have been achieved. Each tetranuclear CuII2LnIII2 structure can be described as two µ2-phenoxo bridged CuIILnIII dinuclear units connected via two µ4-κ2:η1:η1CO32-. Single crystal X-ray diffraction studies show that complexes 2, 3 and 4 are isostructural and isomorphic. The LnIII centres are nona-coordinated with spherical capped-square antiprism geometry and the geometry around the CuII centre is distorted octahedral. The DC magnetic susceptibility and field dependent magnetization measurements reveal the ferromagnetic interactions between the CuII and LnIII centres in all three complexes. The ac susceptibility measurements under an applied bias field reveal the SMM behaviour of complexes 2 and 3 with Ueff 6.5 and 4.5 K, respectively. Complex 4 shows a notable magnetocaloric effect (MCE) with -ΔSm 23.5 J kg-1 K-1 for ΔH = 7 T at 3 K. The ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations predict that the observed SMM behaviour under an external dc field in 2 and 3 does not arise solely from the single ion anisotropy of the lanthanide ions. The exchange interactions (CuII-LnIII and LnIII-LnIII) lower the energy of the exchange coupled states as well as enhance QTM or tunnel splitting and play an important role in the overall magnetic properties of the complexes. Furthermore, to obtain more insight into the exchange interaction, BS-DFT calculations have been performed for complexes 2-4.

6.
Dalton Trans ; 48(39): 14898-14913, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31556419

RESUMO

A metalloligand [CuL] (H2L = N-α-methylsalicylidene-N'-salicylidene-1,3-propanediamine) was reacted with a series (Li+, Na+, K+, Mg2+, Ca2+, Zn2+, Cd2+, Pr3+, Nd3+ and Sm3+) of redox-inactive metal ions (in excess) with different Lewis acidities in acetonitrile to form heterometallic complexes in situ. In the cases of K+ and Zn2+, single crystals were isolated from their respective solutions and solved. The complexes were found to be trinuclear with the phenoxido bridge between the redox-inactive metals and the copper center having closest equilibrium distance. In solution, some metal ions (Na+, K+, Mg2+ and Ca2+) formed predominantly 1 : 1 [CuL] : Mn+ adducts whereas others did not. Spectroscopic studies revealed that both the energy and intensity of the LMCT band of [CuL] at 363 nm were influenced by the Lewis acidity of the guest metal ions. The blue shift and the hypochromic shift of this band showed a linear dependence on the Lewis acidity of the corresponding redox-inactive metal ions only for 1 : 1 adducts. A combined EPR and d-d transition spectral analysis of these 1 : 1 adducts in acetonitrile at 298 K indicates that there is a change in the coordination geometry around Cu(ii) on proximal cation binding of free [CuL]. The correlation of the half wave potential (E1/2) of the first oxidation of [CuL] with pKa of the corresponding metal(aqua)n+ ion as a measure of its Lewis acidity revealed that the potentials were linearly dependent for 1 : 1 adducts whereas in the case of the other metal ions an unexpected deviation from linearity was observed. An incremental addition of water to some of these mixtures revealed a decrease in the corresponding oxidation peak potential with a concomitant increase in the molar absorptivity. The molar absorptivities of different mixtures with their corresponding E1/2 values show a linear dependence with better correlation suggesting that the modulation of electron density around Cu(ii) regulates the electrochemical oxidation of the metalloligand.

7.
Dalton Trans ; 48(25): 9342-9356, 2019 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-31168555

RESUMO

Reaction of Mn(ii) salts with a flexidentate Mannich base ligand, N,N'-dimethyl-N,N'-bis(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine (H2L) in the presence of chloride or azide ions yielded two new tetranuclear complexes, [Mn4L2(µ3-Cl)2Cl2] (1) and [Mn4L2(µ1,1,1-N3)2(N3)2] (2). Single crystal X-ray structural analyses reveal that these two discrete tetranuclear Mn(ii) complexes possess defective dicubane cores with two µ3-Cl (for 1) or two µ1,1,1-N3 bridges (for 2). One of the triply bridging groups is situated above and the other one below the plane of the four Mn(ii) ions. In both complexes, all Mn(ii) ions are in a hexa-coordinated distorted octahedral environment. Both complexes 1 and 2 exhibit catecholase like activity and phenoxazinone synthase-like activity under ambient conditions. The turnover numbers (kcat) for the aerobic oxidation of 3,5-di-tert-butylcatechol are 1492.4 and 1431.2 h-1 and those of o-aminophenol are 2265.5 and 2132.2 h-1 for complexes 1 and 2, respectively. Mass spectral analyses were performed to get an idea about the probable mechanistic pathway for these catalytic reactions. Variable temperature magnetic susceptibility measurements of a solid sample reveal that both the complexes are antiferromagnetically coupled. The coupling constants are calculated to be J1 = -0.19 cm-1, J2 = -6.87 cm-1 and J3 = -0.70 cm-1 for 1 and J1 = 0.11 cm-1, J2 = -0.64 cm-1 and J3 = 0.11 cm-1 for 2 and these values are rationalized by DFT calculations.

8.
Inorg Chem ; 58(9): 5787-5798, 2019 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-31016970

RESUMO

The reaction of the Mannich base ligand (H2L = N, N'-dimethyl- N, N'-bis(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine) with Co(OAc)2·4H2O and Ln(III) nitrate salts (Ln = Gd, Tb, and Dy) under basic conditions afforded three carbonato-bridged isostructural tetranuclear heterometallic Co(II)-Ln(III) complexes (Co2Gd2L2(µ4-CO3)2(NO3)2] (1), [Co2Tb2L2(µ4-CO3)2(NO3)2] (2), and [Co2Dy2L2(µ4-CO3)2(NO3)2] (3)) by atmospheric CO2 fixation. In all structures, two dinuclear [(CoIIL)LnIII(NO3)] units are linked via two µ4-carbonato groups to form the tetranuclear CoII2LnIII2 core. The geometry around two penta-coordinated Co(II) ions is distorted square pyramid, and that around two nona-coordinated Ln(III) ions is intermediate between "spherical tricapped trigonal prism" and "spherical capped square antiprism" in all complexes. The complexes (1-3) showed catecholase-like and phenoxazinone-synthase-like catalytic activities. The kcat values calculated for the catecholase-like reaction were 254.5, 272.4, and 291.3 h-1, and for the phenoxazinone-synthase-like reaction they were 2930.6, 2965.2, and 2998.5 h-1 for complexes 1-3, respectively. The probable pathways for these two oxidase reactions have been proposed by the analyses of mass spectral data. For all of the compounds, the variable temperature magnetic susceptibility and isothermal magnetization data were investigated. The complexes exhibited overall ferromagnetic behavior, which was evident from the isothermal magnetization curves. AC magnetic susceptibility measurements revealed the slow relaxation of magnetization in complexes 2 and 3 but very negligible in 1. The activation energy barriers ( Ueff) for the slow relaxation process were evaluated and found to be 1.99, 2.79, and 8.98 K for 1, 2, and 3, respectively.


Assuntos
Materiais Biomiméticos/química , Dióxido de Carbono/química , Cobalto/química , Complexos de Coordenação/química , Elementos da Série dos Lantanídeos/química , Bases de Mannich/química , Oxirredutases/química , Catálise , Ligantes , Imãs/química , Modelos Moleculares
9.
Chempluschem ; 84(1): 130-135, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-31950737

RESUMO

The interaction between surfactants and cyclodextrins (CDs) is well known. Studies have focused mainly on destruction of micelles with CDs to release the encapsulated drugs. However, less emphasis has been given on understanding the formation of micelles with the CD encapsulated surfactants. We have used fluorescence spectroscopy to study the impact of CDs on micelles using a fluorophore that has been tactically designed as a reporter. This molecule has a pyrene moiety on one end and a cationic head group on the other so that the orientation of the compound can be prefixed on micelle formation in aqueous environment. We have observed that the CD encapsulated surfactants can form "hydrated micelles" that allow extensive penetration of water molecules toward the core. The mechanism for such a process involves inclusion of the hydrophobic surfactant tails within the CD core and participation of these inclusion complexes in micelle formation. The process could be controlled by tuning the concentration of CD. The degree of hydration varies as the micelles get more opened up due to the residence of the CDs inside them.


Assuntos
Ciclodextrinas/química , Micelas , Benzotiazóis/química , Pirenos/química , Espectrometria de Fluorescência , Tensoativos/química
10.
Inorg Chem ; 57(24): 15216-15228, 2018 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-30516050

RESUMO

Three Zn(II) complexes, [Zn2(HL)2(NO3)2]·H2O (1), [(Zn4L2)(µ3-OH)2](NO3)2·0.5H2O (2), and [(Zn6L2)( o-van)2(µ3-OCH3)2(µ3-OH)2](NO3)2 (3), have been synthesized by exploiting the flexidentate nature of a multidentate Schiff base ligand, H2L ( N, N'-bis(3-methoxysalicylidene)diethylenetriamine), by changing the reaction conditions and stoichiometry of the reactants. All three complexes are highly fluorescent in solution as well as in solid and have been used as luminescence sensors toward nitrophenol explosives in both the media. In aqueous/methanol medium, these complexes show very high selectivity and sensitivity with detection limit in ppb (2.03) or nM level (8.89 nM) for picric acid. The yellow color of all three Zn(II) complexes changes to red on mixing with small amount (∼5%) of picric acid in solid state, revealing the potential of these complexes for practical use in naked eye detection of 2,4,6-trinitrophenol (TNP) or picric acid in ambient light. In order to identify the host-guest interactions between Zn(II) complex and TNP, single crystals of the adduct of TNP with Zn(II) complex, [Zn2(HL)2(H2O)2][C6H2N3O7]2 (4), were grown. Its X-ray crystal structure reveals that two picrate ions are attached to a dinuclear host with the help of H-bonding and π···π interactions, throwing light into the quenching mechanism and selectivity of detection.

11.
Dalton Trans ; 47(39): 13957-13971, 2018 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-30229260

RESUMO

A new mononuclear Ni(ii) complex, [NiL] (1) of an unsymmetrically dicondensed N2O2 donor ligand, H2L (where H2L = N-α-methylsalicylidene-N'-salicylidene-1,3-propanediamine), has been synthesized. Complex 1, on reaction with Mn(ii) in the presence of different co-anions, yielded three heterometallic NiII-MnII complexes, [(NiL)2Mn(NCS)2]·CH3CN (2), [(NiL)2Mn(N3)(H2O)](ClO4)·H2O (3) and [{(NiL)2Mn(H2O)}2(µ1,3-N3)](ClO4)3 (4). Single crystal structural analyses show that complexes 2 and 3 contain similar bent trinuclear NiII2MnII structures, with the difference that in complex 2 two SCN- ions and in 3, one N3- and one H2O molecule are coordinated to the Mn(ii) centre. Complex 4 possesses a hexanuclear structure, in which two trinuclear NiII2MnII units are connected via a single µ1,3-azido bridge. Variable temperature dc molar magnetic susceptibility measurements reveal that the two Mn(ii) centres in complex 4 are antiferromagnetically coupled with an exchange coupling constant (J) of -3.73 cm-1. Among the three heterometallic complexes, only 3 and 4 show bio-mimetic catalytic oxidase activities. For catecholase like activity, the turnover numbers (Kcat) of complexes 3 and 4 are 984 and 2081 h-1, respectively, whereas for phenoxazinone synthase-like activity, the turnover numbers of complexes 3 and 4 are 6351 and 10 545 h-1, respectively. The high catalytic oxidase activities of complexes 3 and 4 in contrast to the inactivity of complex 2 are attributed to the coordination of a water molecule to the Mn(ii) centre in the former structures, which facilitates the binding of the substrate with the catalyst. Mass spectral analyses suggest the probable formation of a complex-substrate intermediate in these catalytic reactions and cyclic voltammetry measurements show that Ni(ii) is reducible to Ni(i).


Assuntos
Complexos de Coordenação/química , Complexos de Coordenação/síntese química , Fenômenos Magnéticos , Manganês/química , Níquel/química , Oxirredutases/metabolismo , Materiais Biomiméticos/síntese química , Materiais Biomiméticos/química , Catálise , Técnicas de Química Sintética , Oxirredução
12.
Langmuir ; 34(38): 11503-11509, 2018 09 25.
Artigo em Inglês | MEDLINE | ID: mdl-30193462

RESUMO

The physicochemical behavior and characteristics of lipid vesicles and micelles in aqueous medium are greatly tuned by changing the ambient physical parameters, such as temperature, pH, and ionic strength. The process is also controlled by external additives and the nature of the surfactants. In this work, we have used water-soluble surfactant and cyclodextrin to transform lipid vesicles to micelles to vesicles without changing the physical ambience. In this regard, we have used a special pyrene-tagged guest compound that readily forms excimer in water and thus acts as a reporter for the process. Giant lipid vesicles (biological cell mimics) are disrupted by cationic surfactants to form mixed elongated micelles that transform to vesicles on applying a cyclodextrin host.

13.
Spectrochim Acta A Mol Biomol Spectrosc ; 204: 425-431, 2018 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-29966895

RESUMO

Edge-oxidized graphene oxide (EOGO) nanosheets are good acceptors of electrons. We have employed a suitably designed pyrene-tailed fluorescent probe to establish that the electron acceptability of EOGO can be tuned by undulation of the GO sheet. Comparison between EOGO and single-walled carbon nanotubes (SWCNT) on electron acceptance from the probe molecule shows that the efficiency of π-π stacking between pyrene and the graphene sheet plays the key role.

14.
Dalton Trans ; 47(28): 9385-9399, 2018 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-29951682

RESUMO

Three similar Mannich base ligands viz. N,N-bis(3,5-dimethyl-2-hydroxybenzyl)-N',N'-dimethyl-1,3-diaminopropane (H2L1), N,N-bis(3,5-dimethyl-2-hydroxybenzyl)-N',N'-dimethyl-1,2-diaminoethane (H2L2) and N,N-bis(3,5-dimethyl-2-hydroxybenzyl)-N',N'-diethyl-1,2-diaminoethane (H2L3) upon reaction with Cu(CH3COO)2·H2O produced dinuclear complexes [Cu2L21-3]. The reaction of each of these isolated dimeric species with Cu(ClO4)2·6H2O and NaN3 resulted in three new trinuclear complexes, [(CuL1)2(µ1,1-N3)2Cu(H2O)]·CH3OH (1), [(CuL2)2(µ1,1-N3)2Cu(H2O)]·CH3OH (2) and [(CuL3)2(µ1,1-N3)2Cu(H2O)]·2CH3OH (3), respectively. The complexes (1-3) have been characterized by elemental analysis and single crystal X-ray diffraction. In all three complexes, the central Cu(ii) ion is coordinated by two terminal [CuL] units through a phenoxido and an azido bridge. These are the first trinuclear Cu(ii) complexes of this type of Mannich base ligands. Magnetic susceptibility measurements showed intramolecular antiferromagnetic interactions with J = -64.42, -9.60 and -4.54 cm-1 for 1, 2 and 3, respectively. All three complexes exhibited catecholase-like and phenoxazinone synthase-like activities towards the aerobic oxidation of 3,5-di-tert-butylcatechol and o-aminophenol, respectively. The turnover numbers (kcat) for the aerobic oxidation of 3,5-di-tert-butylcatechol are 568.8, 542.1 and 500.4 h-1 and those of o-aminophenol are 125.83, 118.9 and 114.7 h-1 for complexes 1-3, respectively. The X-band EPR spectroscopy and estimation of the produced hydrogen peroxide indicated that the aerobic oxidation of 3,5-di-tert-butylcatechol proceeded through the formation of a semiquinonate radical. The mechanism of phenoxazinone synthase-like activities is also proposed for trinuclear Cu(ii) catalysts with the help of mass spectral analysis.

15.
Inorg Chem ; 57(14): 8338-8353, 2018 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-29932329

RESUMO

A new mononuclear Ni(II) complex [NiL] (1) of an unsymmetrically dicondensed N2O3 donor ligand, H2L ( N-α-methylsalicylidene- N'-3-methoxysalicylidene-1,3-propanediamine), has been synthesized. Complex 1 on reaction with Mn(ClO4)2·6H2O and NaN3 in different molar ratios yielded three novel heterometallic NiII-MnII complexes, [(NiL)2Mn(N3)](ClO4) (2), [(NiL)2Mn2(N3)2(µ1,1-N3)2(CH3OH)2] (3), and [{(NiL)2Mn}2(µ1,3-N3)(H2O)]·(CH3OH),(ClO4)3 (4). The single crystal structure analyses show a trinuclear NiII2MnII structure for complex 2 and a tetranuclear NiII2MnII2 structure where two dinuclear NiIIMnII units are connected via µ1,1-azido and phenoxido bridges for complex 3. Complex 4 possesses a hexanuclear structure where two trinuclear NiII2MnII units are connected via a µ1,3-azido bridge. The temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 3 and 4 are antiferromagnetically coupled with the exchange coupling constants ( J) of -4.97, -0.14, -0.55 cm-1 for 3 and -3.94 cm-1 for 4. All complexes 2-4 show biomimetic catalytic oxidase activities. For catecholase like activity, the turnover numbers ( Kcat) are 768, 1985, and 2309 h-1 for complexes 2-4, respectively, whereas for phenoxazinone synthase like activity, the turnover numbers are 3240, 3360, and 13 248 h-1 for complexes 2-4, respectively. This difference in catalytic efficiencies is attributed to the variations in structures of the complexes and formation of active NiII-MnII species in solution during catalysis. The mass spectral analyses suggest the probable intermediate formation and cyclic voltammetry measurement suggest the reduction of Ni(II) to Ni(I) during catalytic reaction. The very high catalytic efficiencies for aerial dioxygen activation of all these heterometallic complexes as well as the highest activity of 4 is attributed to the coordinatively unsaturated penta-coordinated geometry or hexa-coordinated geometry with a solvent water molecule around Mn(II).


Assuntos
Materiais Biomiméticos/química , Complexos de Coordenação/química , Manganês/química , Níquel/química , Catecol Oxidase/química , Cinética , Ligantes , Fenômenos Magnéticos , Modelos Químicos , Estrutura Molecular , Óxidos de Nitrogênio/química , Oxirredução , Oxirredutases/química , Relação Estrutura-Atividade
16.
Dalton Trans ; 47(10): 3568-3579, 2018 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-29436544

RESUMO

Two new N2O3 donor ligands N-(3-methoxysalicylidene)-N'-(salicylidene)-1,3-propanediamine (H2L2) and N-(3-methoxysalicylidene)-N'-(α-methylsalicylidene)-1,3-propanediamine (H2L3) and their Cu(ii) complexes have been synthesized. Using these complexes and another Cu-complex with one asymmetric N2O2 donor ligand N-(α-methylsalicylidene)-N'-(salicylidene)-1,3-propanediamine (H2L1) as metalloligands, four new heterometallic Cu(ii)-Mn(ii) complexes [(CuL1)2Mn2Cl4]·3CH3OH (1), [(CuL1)2MnCl2]·2CH3CN (2), [CuL2MnCl2]·H2O (3) and [CuL3MnCl2] (4) have been synthesized with MnCl2·4H2O. The tetranuclear (1) and trinuclear (2) complexes were prepared by varying the ratio of the metalloligand [CuL1] and MnCl2 whereas dinuclear complexes 3 and 4 are the sole products irrespective of the metalloligand : MnCl2 ratio. All the complexes 1-4 were structurally characterized by single crystal X-ray diffraction. The tetranuclear (CuMn) structure of 1 is formed by the dimerization of phenoxido bridged CuIIMnII units whereas the bent CuMnII trinuclear species 2 is formed by the coordination of two metalloligands (CuL1) to Mn(ii) via a diphenoxido bridge. Complexes 3 and 4 possess a similar dinuclear CuIIMnII structure in which two phenoxido groups form a bridge between the two metal centres. The variable temperature dc magnetic susceptibility measurements reveal that the Cu(ii) and Mn(ii) ions are antiferromagnetically coupled in all the complexes, 1-4. The values of exchange coupling constants (JMn-Cu) are -45.54, -39.66, -71.54 and -48.40 cm-1 for complexes 1-4, respectively. A DFT study of all the complexes has also been performed to rationalize the experimental results of magnetic measurements.

17.
Dalton Trans ; 46(36): 12095-12105, 2017 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-28853756

RESUMO

A new series of heterometallic trinuclear Cu2Ln complexes [lanthanide ions Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5)] has been synthesized using a Cu(ii)-metalloligand derived from a N2O2 donor unsymmetrical Schiff base, H2L (where H2L = N-α-methylsalicylidene-N'-salicylidene-1,3-propanediamine), and structurally characterized. Among these complexes, [(CuL)2Gd(NO3)3(CH3CN)2] (1), [(CuL)2Tb(NO3)3(CH3CN)2] (2) and [(CuL)2Dy(NO3)3(CH3CN)2] (3) are isomorphic and isostructural. In these complexes two metalloligands coordinate to the central Ln(iii) (Ln = Gd, Tb and Dy respectively) ion in a transoid fashion viaµ2-phenoxido oxygen atoms. The Ln(iii) ions are deca-coordinated with a distorted tetradecahedron geometry. The two terminal Cu(ii) ions of the complexes possess a hexa-coordinated distorted octahedral geometry. In contrast, in complexes [(CuL)2Ho(NO3)3(CH3CN)], (4) and [(CuL)2Er(NO3)3(CH3CN)]·0.5(CH3CN) (5), the two metalloligands coordinated to the Ln(iii) ions in a cisoid fashion. The Ho(iii) ion in 4 is nona-coordinated with a distorted tricapped trigonal prismatic geometry and the Er(iii) ion in 5 is octa-coordinated with a distorted square antiprismatic geometry. The two terminal Cu(ii) ions in complexes 4 and 5 are penta-coordinated with a distorted square-pyramidal geometry. The dc magnetic susceptibilities and field dependent magnetization measurement of complex 1 reveal the occurrence of ferromagnetic interactions between Cu(ii) and Gd(iii) ions as well as intermolecular antiferromagnetic interactions. Both complexes 2 and 3 show ferromagnetic interactions between Cu(ii) and Ln(iii) ions. The ac magnetic susceptibilities of all the complexes were also recorded and it was found that only complexes 2 and 3 exhibit slow relaxation of magnetization reorientation below 10 K at 2000 Oe applied dc field, this being characteristic of single molecule magnets.

18.
Inorg Chem ; 56(9): 5105-5121, 2017 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-28387507

RESUMO

A new Cu(II) complex of an asymmetrically dicondensed Schiff base (H2L = N-(2-hydroxyacetophenylidene)-N'-salicylidene-1,3-propanediamine) derived from 1,3-propanediamine, salicylaldehyde, and o-hydroxyacetophenone has been synthesized. Using this complex, [CuL] (1), as a metalloligand, two new trinuclear Cu-Mn complexes, [(CuL)2Mn(N3)(H2O)](ClO4)·H2O (2) and [(CuL)2Mn(NCS)2] (3), have been prepared. Single-crystal structural analyses reveal that complexes 2 and 3 both have the same bent trinuclear {(CuL)2Mn}2+ structural unit in which two terminal bidentate square-planar (CuL) units are chelated to the central octahedral Mn(II) ion. This structural similarity is also evident from the variable-temperature magnetic susceptibility measurements, which suggest that compounds 2 and 3 are both antiferromagnetically coupled with comparable exchange coupling constants (-21.8 and -22.3 cm-1, respectively). The only difference between 2 and 3 lies in the coordination around the central Mn(II) ion; in 3, two SCN- groups are coordinated to the Mn(II), leaving a neutral complex, but in 2, one N3- group and one H2O molecule are coordinated to give a positively charged species. The presence of such a labile H2O coligand makes 2 catalytically active in mimicking two well-known polynuclear copper proteins, catecholase and phenoxazinone synthase. The turnover numbers (kcat) for the aerial oxidation of 3,5-di-tert-butylcatechol and o-aminophenol are 1118 and 6581 h-1, respectively, values which reflect the facility of the heterometallic catalyst in terms of both efficiency and catalytic promiscuity for aerial dioxygen activation. The mechanisms of these biomimetic oxidase reactions are proposed for the first time involving any heterometallic catalyst on the basis of mass spectral analysis, EPR spectroscopy, and cyclic voltammetry. The evidence of the intermediates indicates possible heterometallic cooperative activity where the substrates bind to a Mn(II) center and Cu(II) plays the role of an electron carrier for transformation of the phenolic substrates to their respective products with the reduction of aerial dioxygen.


Assuntos
Materiais Biomiméticos/química , Catecol Oxidase/química , Complexos de Coordenação/química , Cobre/química , Manganês/química , Oxirredutases/química , Bases de Schiff/química , Materiais Biomiméticos/síntese química , Catálise , Catecóis/química , Complexos de Coordenação/síntese química , Cinética , Ligantes , Estrutura Molecular , Oxirredução , Bases de Schiff/síntese química , Relação Estrutura-Atividade
19.
Dalton Trans ; 46(3): 697-708, 2017 Jan 17.
Artigo em Inglês | MEDLINE | ID: mdl-27904899

RESUMO

A nickel(ii) complex [Ni2LR2(CH3CN)4](ClO4)2·2CH3CN (1) has been synthesized by using a tridentate reduced Schiff base ligand, HLR, 2-[(3-methylamino-propylamino)-methyl]-4-nitrophenol and Ni(ClO4)2·6H2O. Stoichiometrically controlled addition of NH4SCN to the acetonitrile-water solution of 1 produced two other complexes, [Ni2LR2(µ1,1-NCS)(CH3CN)2](ClO4)·CH3CN (2) and [Ni2LR2(NCS)2 (CH3CN)2] (3) by replacing one and two coordinated CH3CN by NCS-, respectively. The dinuclear NiII complexes 1 and 3 are structurally very similar containing a diphenoxido bridge between the NiII ions. Complex 2 also consists of a dinuclear entity, but a µ1,1-isothiocyanato bridge is present in addition to the diphenoxido bridge. The magnetic measurements indicate that antiferromagnetic interactions (J = -33.85 cm-1) for 1, (J = -23.43 cm-1) and 3 and ferromagnetic interaction (J = 5.01 cm-1) for 2 are mediated between the intra-dimer NiII ions. The nature of coupling (ferromagnetic for 2 and antiferromagnetic for 1 and 3) is understandable from the phenoxido bridging angles (91.27° (av. angle) for 2, 102.41° for 1 and 102.42° for 3) but it cannot explain the considerable difference of J values between 1 and 3. Other important factors such as NiO bond distances, the out-of-plane shift of phenyl rings and the hinge distortions are also of no use for a possible explanation. With the help of computational evidence, we have identified for the first time that magnetic coupling could be dramatically modified by the non-bridging axially coordinated ligands: antiferromagnetic coupling becomes considerably stronger for a neutral ligand in comparison to the negatively charged ligand. Moreover, for a negatively charged axially coordinated ligand, antiferromagnetic coupling decreases with increase in crystal field strength.

20.
Dalton Trans ; 45(13): 5730-40, 2016 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-26931060

RESUMO

Three new trinuclear hetero-metallic complexes [(CuL)2Zn(NCS)2] (1), [(CuL(R))2Zn(NCS)(µ1,1-NCS)] (2) and [(CuL(R))2Cd(µ1,3-NCS)2] (4) have been synthesized using [CuL] and [CuL(R)] as "metalloligands" (where H2L = N,N'-bis(salicylidene)-1,3-propanediamine and H2L(R) = N,N'-bis(2-hydroxybenzyl)-1,3-propanediamine). All three complexes are characterized by elemental analysis, spectroscopic methods and single crystal XRD. Complex 1 is an angular trinuclear species, in which two terminal four-coordinate square planar "metalloligands" [CuL] are coordinated to a central Zn(ii) through double phenoxido bridges along with two mutually cis nitrogen atoms of terminal isothiocyanate ions as is usually found in such complexes. In contrast, in complex 2, the two terminal "metalloligands" [CuL(R)] are square pyramidal, as one of the SCN(-) ions makes an unusual µ1,1-NCS bridge between copper centers while the other one coordinates to Zn(ii) through a N atom in a usual fashion making its geometry also square pyramidal. For 4 which possesses an angular trinuclear structure, in addition to double phenoxido bridges from two terminal [CuL(R)], both the SCN(-) ions are S-bonded to Cd(ii) and form a bridge (cis-µ1,3-SCN) between Cd(ii) and each of the terminal Cu(ii) ions. This structure is different from its unreduced analogue in which NCS(-) was N-terminal coordinated to Cd(ii) (3/3'). All the structures have been optimized using density functional theory (DFT) calculations. It has been found that for H2L, optimized structures like 1 and 2 differ only by 0.4 kcal mol(-1) but the H2L(R) structure 2 is more stable by 5.5 kcal mol(-1) than the structure resembling 1. For Cd(ii) complexes also, H2L optimized structures such as 3 and 4 do not differ significantly in energy (1.0 kcal mol(-1)) but the H2L(R) structure 4 is more stable than that of 3 by 4.6 kcal mol(-1). In fact, structure 4 has been found to be the most stable one among the other possible isomers of H2L(R).

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