Mn(II) complexes of different nuclearity: synthesis, characterization and catecholase-like activity

The origin of catecholase-like activity of Mn(ii)–Schiff-base complexes has been explored by studying structurally characterized mono-, di- and polynuclear Mn(ii) complexes of two "end-off" compartmental Schiff-base ligands

Auxiliary Part of Ligand Mediated Unique Coordination Chemistry of Copper (II)

Six N,N,O-donor Schiff-base ligands, HL1-HL6, [HL1/HL2/HL3= {2-(2-piperazin-1-yl)ethylimino)methyl)-4-(Cl/H/Me)-phenol}; HL4/HL5/HL6={2-(2-morpholine/piperidine/ pyrrolidine 1-yl)ethylimino)methyl)-4-chlorophenol}, have been designed by combining 5-R-2-hydroxy-benzaldehyde, (R=Cl/H/Me) and N-(2-aminoethyl)-Y, (Y=piperazin/morpholine/ piperidine/pyrrolidine) with the view to explore the role of R and X (part of Y excluding coordinating N) on the coordination chemistry of Cu (II) in presence of bromide as counter anion. HL1-HL6 formed in situ on reaction with Cu(II)Br2 produce complexes 1\u20136, respectively. Complex 1, [Cu(II)2Cu(I)2(L1)(MeOH)2Br7.30], is a mixed valence Cu(I)-Cu(II) species having phenyl ring brominated at ortho position with 0.65 occupancy. Complexes 2\u20134 are mononuclear species with general formula [Cu{L2/L3/L4)}Br2]. Complexes [Cu3(L5)Br4] (5) and [Cu3(L6)Br4] (6) are trinuclear species having similar structure but exhibit different magnetic property, 5 is ferro- (J= +16.64 cm1 ) and 6 is antiferromegnetic (J= \u201311.76 cm1). The influence of R and X on bromination, magnetic property and nuclearity issues have been rationalized by DFT calculations

Bioactive Heterometallic CuII–ZnII Complexes with Potential Biomedical Applications

[EN]A series of multinuclear heterometallic Cu-Zn complexes of molecular formula [(CuL)2Zn(dca)2] (1), [(CuL)2Zn(NO3)2] (2), [(CuL)2Zn2(Cl)4] (3), and [(CuL)2Zn2(NO2)4] (4) have been synthesized by reacting [CuL] as a "metalloligand (ML)" (where HL = N,N′-bis(5-chloro-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine) and by varying the anions or coligands using the same molar ratios of the reactants. All of the four products including the ML have been characterized by infrared and UV-vis spectroscopies and elemental and single-crystal X-ray diffraction analyses. By varying the anions, different structures and topologies are obtained which we have tried to rationalize by means of thorough density functional theory calculations. All of the complexes (1-4) have now been applied for several biological investigations to verify their therapeutic worth. First, their cytotoxicity properties were assessed against HeLa human cervical carcinoma along with the determination of IC50 values. The study was extended with extensive DNA and protein binding experiments followed by detailed fluorescence quenching study with suitable reagents to comprehend the mechanistic pathway. From all of these biological studies, it has been found that all of these heterometallic complexes show more than a few fold improvement of their therapeutic values as compared to the similar homometallic ones probably because of the simultaneous synergic effect of copper and zinc. Among all of the four heterometallic complexes, complex 3 exhibits highest binding constants and IC50 values suggest for their better interaction toward the biological targets and hence have better clinical importance

Coordinating and non-coordinating anion controlled synthesis of different nuclearity cadmium(II) complexes of 2-((E)-((pyridin-2-yl)methylimino)methyl)phenol: Crystal structure and photophysical study

The tridentate Schiff base ligand 2-((E)-((pyridin-2-yl)methylimino)methyl)phenol (HL) was used to synthesize four new cadmium(II) complexes, namely [Cd4L6](ClO4)2 (1), [CdL(SCN)]n (2), [CdL(dca)]n (3) and [CdL(N3)]n (4), with the aim of exploring the role of the coordinating and non-coordinating anion in governing the architecture as well as the photophysical behavior of the complexes. In addition to common physicochemical techniques, complexes 1 and 2 have further been characterized by X-ray single crystal structural analysis. Complex 1 is a tetranuclear cationic Cd(II) species where each metal ion has a distorted octahedral geometry. Three Cd atoms have the N4O2 chromophoric environment, whereas the fourth and central Cd has an O6 chromophore. Complex 2 is a polynuclear species having a 2D network of (4,4) topology where dinuclear [Cd2L3] metal entities located at the nodes are bridged by SCN anions. The ligand and all four complexes are highly fluorescent. Quantum yield calculations reveal that the fluorescence efficiency of the complexes is higher than that of the ligand and the efficiency is largely influenced by the nature of the co-ligand

Phosphatase models: Synthesis, structure and catalytic activity of zinc complexes derived from a phenolic Mannich-base ligand

A series of dinuclear [Zn2(L1)2X2] (1\u20133) and mononuclear [Zn(HL2)X2] complexes (4\u20136), (X = Cl, Br, I) were synthesised from two Mannich-base compartmental ligands, namely [bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL1) and 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL2), respectively. They were characterised by routine physicochemical techniques (CHN, UV, IR, ESI-MS and NMR) and complex 2\u20135 was further structurally characterised by single crystal X-ray analysis where the Zn. . .Zn bond-distance is 3.10\u20133.12 \uc5. All the quintessential complexes exhibit excellent phosphatase activity and the experimental first order rate constant values (kcat) for the hydrolysis of 4-nitrophenyl phosphate ester (PNPP) reaction in methanol are in the range from 1.05 to 214 s1 at 25 C evaluated by monitoring spectrophotometrically the gradual release of p-n nitrophenolate (kmax = 427 nm, e = 18500 M1 cm1). The coordinated X halides affect the phosphatase activity in the order Br > Cl > I (in dinuclear complexes) and Cl > Br > I (in mononuclear) and the trend in the two cases has been well recognised to be due to a different rate determining step. Moreover the influence of chloro atom in para-position of the phenol ring and the role of solvent have been rationalised by comparing the kinetic parameters with those obtained for the corresponding methyl analogues having reasonably close structural resemblance as reported by Sanyal et al. (2014)

Group 12 metal complexes of (2-piperazine-1-yl-ethyl)-pyridin-2-yl-methylene-amine: rare participation of terminal piperazine N in coordination leads to structural diversity

By using a potential tridentate ligand L ((2-piperazine-1-yl-ethyl)-pyridin-2-yl-methylene-amine), a series of group 12 metal complexes namely, [ZnLHCl2][Zn2LCl5]\ub72H2O (1), [CdL(SCN)2(CH3OH)]n (2), and [Hg(L-pyCO)Cl2] (3), were synthesized and structurally characterized. In all the complexes the piperazine nitrogen of the ligand takes part in coordination and leads to the complexes of group 12 metal ions having structural diversity. The X-ray diffraction analysis of complex 1 indicates for one Zn(II) ion a geometry in between trigonal bipyramidal/square pyramidal and for the second a distorted tetrahedral sphere. In the polymeric complex 2 the Cd(II) ion shows a distorted octahedral environment, while in the mononuclear complex 3, where Hg(II) exhibits a square-pyramidal geometry, an unexpected condensation between the uncoordinated NH piperazine fragment with 2-pyridinecarboxaldehyde was detected. The M\u2013N bond lengths in all the complexes are in accordance with the metal ionic radius. Continuous shape measures through a DFT approach provide the coordination environment around each metal centre that is comparable with the experimental observations. We have also investigated the importance of hydrogen bonding of methanol in the generation of the polymeric Cd complex 2 along with the rearrangement of the tridentate ligand to generate an octahedral complex. The photoluminescence properties of the complexes as well as of the ligand were investigated in solution at ambient temperature. The low quantum yield of the ligand was ascribed due to a very fast photoinduced electron transfer (PET) from the nitrogen lone pair to the conjugated pyridine moiety. Complexation prevents the electron transfer, and consequently an increase in quantum yield was observed in the complexes. Among the three complexes the highest photoluminescence was exhibited by a Zn complex, being lower in Cd and Hg complexes as a consequence of the heavy atom perturbation effect

Phenoxo bridged luminescent dinuclear zinc(II) and cadmium(II) complexes of 2-[[[2-(2-pyridyl)ethyl]imino]methyl]phenol: Crystal structure, photophysical and thermal studies

Reactions of zinc(II) and cadmium(II) halides with an N,N,O-donor Schiff-base ligand HL (obtained by the 1:1 condensation of salicylaldehyde and 2-(2-aminoethyl)pyridine) yield six new phenoxo bridged dinuclear complexes of the general formula [Zn2L2X2] (1\u20133) and [Cd2L2X2] (4\u20136), where X = Cl, Br and I, respectively. The complexes have been characterized by routine physicochemical techniques: elemental analyses, IR, electronic spectral studies, conductivity and solid state thermal studies. Complexes 1, 2 and 6 have further been characterized by single crystal X-ray structural analyses. The ligands, as well as all six complexes, are highly fluorescent. For the ligand, the emission band is attributed to a p\u2013p\u2044 transition, whereas for the complexes the emissions may be assigned to ligand-to-metal charge transfers (LMCT). Quantum yield calculations revealed that the metal complexes exhibit more intense fluorescence compared to the ligand, which is supposed to be due to the enhancement of rigidity of the ligand on chelation, which reduces the loss of energy through non-radiative channels of the intraligand emission excited state. Thermogravimetric analyses of the complexes suggest that upon heating the thermally stable final product in the case of complexes 1\u20133 is ZnO, 6 gives CdO, whereas for complexes 4 and 5 the final product remains unidentified

A Deep Insight into the Photoluminescence Properties of Schiff Base Cd(II) and Zn(II) Complexes

A tridentate N,N,O donor ligand 2,4-dichloro-2-[(2-piperazine-4-yl-ethylimino)-methyl]-phenol (HL) was designed, and eight new Zn(II) and Cd(II) complexes, namely, [Zn(LH)(SCN)2] (1), [Zn(LH)(N3)2] (2), [Zn(LH)(NO2)2] (3), [Zn(LH)(dca)(OAc)] (4), [Cd2(LH)2(SCN)4] (5), [Cd(LH)(N3)2] (6), [Cd(LH)(NO2)2] (7), and [Cd(LH)(dca)(OAc)] (8) [where dca = dicyanamide anion] were synthesized. Five of them (1, 2, 4, 5, 7) were structurally characterized through single-crystal X-ray diffraction analysis. H-Bonding interactions are found to be the major stabilizing factor for crystallization in the solid state. Experimental and computational studies were performed in cooperation to provide a rationalization of the photoluminescence properties of those complexes. The quantum yields are anion-dependent, with enhanced efficiencies in the following order: LH < Cd-SCN(5) < Cd-dca(8) < Cd-N3(6) < Cd-NO2(7) < Zn-dca(4) < Zn-N3(2) < ZnNO2(3) < ZnSCN(1). By using quantum chemical calculations we rationalized the above trends. Moreover, the diverse lifetimes observed for those eight complexes were also quantitatively explained by considering the subtle competition between different photo-deactivation pathways

Halide Ion Mediated Aldehyde-Amine Condensation Leading to Schiff-base and Cyclized Non-Schiff-base Ligand Complexes of CdII: A Combined Experimental and Theoretical Investigation

The reactions of pyridine-2-carbaldehyde with aminoalcohols N-(2-hydroxyethyl) ethylenediamine and 2-(3-aminopropylamino) ethanol in presence of (CdX2)-X-II (X=Cl, Br, I) have been investigated. Structure analyses reveal that four complexes, namely [Cd-2(L-1)(2)(Br)4] (2), [Cd(L-1)(I)(2)] (3), [Cd(L-1)(Br)2] (5) and [Cd(L-2)(I)(2)] (6) are formed with the expected Schiff-base ligands (E)-2-(2-(pyridin-2-ylmethyleneamino) ethylamino) ethanol (L1) and (E)-2-(3-(pyridin-2-ylmethyleneamino) propylamino) ethanol (L2). Interestingly, when X= Cl two dinuclear complexes of general formula [Cd2(L1C/L2C)2(Cl)4](complex 1 and 4, respectively) have been structurally characterized, where the ligands are no longer Schiff-bases but contain an imidazolidine/hexahydro-pyrimidine cyclic part instead [L1C = 2-(2-Pyridin-2-yl-imidazolidin-1-yl)-ethanol and L2C = 2-(2-Pyridin-2-yl-tetrahydro-pyrimidin-1-yl)-ethanol]. In order to understand whether the solid state structure is retained in solution various NMR analysis like 1H, 13CNMR and DEPT-135 have been performed. When X= I, the equilibrium is shifted towards the formation of the Schiff-base ligands, thus complexes 3 and 6 are obtained as sole products. However, with X= Br or Cl, a mixture of products is present, comprising complexes containing both Schiff-bases as well as cyclized ligands. DFT calculations have been performed to rationalize the influence of the halide ligands on the reactivity of the Schiff-base and the formation of the cyclized ligand

Zinc(ii) complexes with uncommon aminal and hemiaminal ether derivatives: Synthesis, structure, phosphatase activity and theoretical rationalization of ligand and complex formation

Condensation of N-(2-hydroxyethyl)ethylenediamine and pyridine-2-carbaldehyde in the presence of ZnX2 salts (X = ClO4, Cl, Br, I) generates four complexes, namely, [ZnL1Cl](ClO4) (1), [ZnL1Cl][ZnCl3(H2O)].2H2O (2), [ZnL1Br][ZnBr3(H2O)].2H2O (3), and [Zn(L2)3]I2 (4), where L1 and L2 are aminal and hemiaminal ether derivatives, i.e., (E)-N-((pyridine-2-yl)methylene)-2-((2-pyridine-2- yl)oxazolidin-3-yl)ethanamine and 2-(2-pyridin-2-yl-imidazolidin-1-yl)-ethanol, respectively. No complex with the expected Schiff-base ligand (E)-2-(2-(pyridin-2-ylmethyleneamino)ethylamino)ethanol (L) or with 2-(2-pyridyl-3-(2-hydroxyethyl))oxazolidine (L3) was obtained. The structures of complexes 1, 3, and 4 have been elucidated by single crystal X-ray diffraction. All the complexes have been characterized by detailed NMR (1H, 13C and DEPT-135) and ESI-MS analyses, indicating retention of solid state structures in the solution phase. Complex 1 deserves special mention as during its formation, the ClO4 ion undergoes reduction to Cl and thus, it forms a mixed anionic ligand complex. Thorough DFT calculations have been performed at the BP86-D3/def2-TZVP level of theory to rationalize the ligand and complex formation. The calculations suggest that the aminal form (L1) is the most favored species followed by the Schiff-base, whereas the hemiaminal ether form (L3) is the least preferred one. The role of halides during the formation of the monoanionic [ZnX3(H2O)] species is crucial, and the achieved complex is highly favored when X = Cl and disfavored for X = I; this trend has been rationalized by the DFT calculations. The phosphatase activities of the complexes have been investigated, and their efficiencies follow the order 2 >1 > 3 > 4