Pentanuclear MII–MnII (M = Ni and Cu) complexes of N2O2 donor ligands with a variation of carboxylate anions: syntheses, structures, magnetic properties and catecholase-like activities

One NiII2MnII3 and two CuII2MnII3 complexes have been synthesized using N2O2 donor ligands. The former complex exhibits spin crossover at 2 K temperature. All the complexes exhibit catecholase-like activities.

Fascinating interlocked triacontanuclear giant nanocages

We report herein three air, thermal and solvent stable interlocked triacontanuclear giant nanocages, generated using a node and spacer concept. Interestingly, the crystal structures of the cages are not only nano-dimensional but also exist in the nano-dimension range, which was corroborated with microscopic images. The combination of microscopic and crystallographic data, in effect, led us to a unique advantageous situation of generating nanomaterials with hard-to-come-by structural information at the molecular level.

Tailoring copper(ii) complexes with pyridine-4,5-dicarboxylate esters for anti-Candida activity

Five novel copper(ii) complexes with pyridine-4,5-dicarboxylate esters as ligands, [Cu(NO₃)(py-2tz)(H₂O)₃]NO₃ (1), [Cu(NO₃)₂(py-2metz)(H₂O)] (2), [Cu(NO₃)₂(py-2py)(H₂O)]·H₂O (3), [CuCl₂(py-2tz)]₂ (4) and [CuCl₂(py-2metz)]_n (5) (py-2tz is dimethyl 2-(thiazol-2-yl)pyridine-4,5-dicarboxylate, py-2metz is dimethyl 2-(4-methylthiazol-2-yl)pyridine-4,5-dicarboxylate and py-2py is dimethyl 2,2'-bipyridine-4,5-dicarboxylate), were synthesized and structurally characterized by different spectroscopic and electrochemical methods. The structure of these complexes was determined by single-crystal X-ray diffraction analysis, confirming the bidentate coordination mode of the corresponding pyridine-4,5-dicarboxylate ester to the Cu(ii) ion through the nitrogen atoms. The antimicrobial potential of copper(ii) complexes 1-5 was assessed against two bacterial and two Candida species. These complexes showed better growth inhibiting activity against Candida spp. with respect to the tested bacterial species, also being moderately toxic towards normal human lung fibroblast cells (MRC-5). Complexes 1 and 4 showed the greatest ability to inhibit the filamentation of C. albicans, which is an important process during fungal infection, and these two complexes efficiently inhibited the biofilm formation of C. albicans at subinhibitory concentrations. Complex 4 also successfully prevented the adhesion of C. albicans in an in vitro epithelial cell model. The mechanism of the antifungal activity of copper(ii) complexes 1-5 was studied through their interaction with ct-DNA, as one of the possible target biomolecules, by fluorescence spectroscopy and gel electrophoresis. Finally, the ability of these complexes to bind to bovine serum albumin (BSA) was studied by fluorescence emission spectroscopy.

Modulation of Nuclearity in CuII -MnII Complexes of a N2 O2 Donor Ligand Depending upon Carboxylate Anions: Structures, Magnetic Properties and Catalytic Oxidase Activities

Three new hetero-metallic copper(II)-manganese(II) complexes, [(CuL)₂ Mn₃ (C₆ H₅ CO₂ )₆ ] (1), [(CuL)₂ Mn(CH₃ CO₂ )₂ ] (2), and {[(CuL)₂ Mn(C₆ H₅ CH₂ CO₂ )₂ ] ⋅ 2CH₃ CN} (3), have been synthesized using [CuL] as ''metalloligand'' (where H₂ L=N,N'-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Single-crystal structural analyses show an almost linear penta-nuclear structure for complex 1 where a square planar [CuL] unit is connected to each of the two terminal Mn^II ions of a linear, centrosymmetric [Mn₃ (benzoate)₆ ] unit through the double phenoxido bridges. Both complexes 2 and 3 possess a linear tri-nuclear structure where two terminal square-pyramidal [CuL] units are bonded to the central Mn^II ion through double phenoxido oxygen atoms along with a syn-syn bridging acetate (for 2)/phenyl acetate (for 3). All three complexes exhibit catecholase, and phenoxazinone synthase-like activities under aerial conditions. For catecholase like activity, the turnover numbers (k_cat ) are 595, 40, and 205 h^-1 whereas, for phenoxazinone synthase like activity, the turnover numbers are 25, 4, and 11 h^-1 for complexes 1-3, respectively. The mechanism of both catalytic oxidase activities is proposed on the basis of mass spectral evidences. Variable-temperature (2-300 K) dc molar magnetic susceptibility measurements of 1 reveal antiferromagnetic interactions between the Cu-Mn centres (J₁ =-29.3 cm^-1 ), and also between the Mn-Mn centres of the [Mn₃ (benzoate)₆ ] unit (J₂ =-0.68 cm^-1 ). On increasing the magnetic field at 2 K, its ground spin state changes from S=3/2 to S=5/2 at 4 T, attributable to the low value of J₂ which makes the excited spin states close in energy with the ground spin state. Complexes 2 and 3 show antiferromagnetic coupling interactions between the Cu-Mn pairs with J values of -9.51, and -5.32 cm^-1 , respectively.

Reaction of Cu(II) Chelates with Uranyl Nitrate to Form a Coordination Complex or H-Bonded Adduct: Experimental Observations and Rationalization by Theoretical Calculations

Four new heterometallic Cu(II)-U(VI) species, [{(CuL¹)(CH₃CN)}UO₂(NO₃)₂] (1), [{(CuL²)(CH₃CN)}UO₂(NO₃)₂] (2), [{(CuL³)(H₂O)}UO₂(NO₃)₂] (3), and [UO₂(NO₃)₂(H₂O)₂]·2[CuL⁴]·H₂O (4), were synthesized using four different metalloligands ([CuL¹], [CuL²], [CuL³], and [CuL⁴], respectively) derived from four unsymmetrically dicondensed N,O-donor Schiff bases. Single-crystal structural analyses revealed that complexes 1, 2, and 3 have a discrete dinuclear [Cu-UO₂] core in which one metalloligand, [CuL], is connected to the uranyl moiety via a double phenoxido bridge. Two chelating nitrate ions complete the octa-coordination around uranium. Species 4 is a cocrystal, where a uranyl nitrate dihydrate is sandwiched between two metalloligands [CuL⁴] by the formation of strong hydrogen bonds between the H atoms of the coordinated water molecules to U(VI) and the O atoms of [CuL⁴]. Spectrophotometric titrations of these four metalloligands with uranyl nitrate dihydrate in acetonitrile showed a well-anchored isosbestic point between 300 and 500 nm in all cases, conforming with the coordination of [CuL¹], [CuL²], [CuL³], and the H-bonding interaction of [CuL⁴] with UO₂(NO₃)₂. This behavior of [CuL⁴] was utilized to selectively bind metal ions (e.g., Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, and La³⁺) in the presence of UO₂(NO₃)₂·2H₂O in acetonitrile. The formation of these Cu(II)-U(VI) species in solution was also evaluated by steady-state fluorescence quenching experiments. The difference in the coordination behavior of these metalloligands toward [UO₂(NO₃)₂(H₂O)₂] was studied by density functional theory calculations. The lower flexibility of the ethylenediamine ring and a large negative binding energy obtained from the evaluation of H bonds and supramolecular interactions between [CuL⁴] and [UO₂(NO₃)₂(H₂O)₂] corroborate the formation of cocrystal 4. A very good linear correlation (r² = 0.9949) was observed between the experimental U═O stretching frequencies and the strength of the equatorial bonds that connect the U atom to the metalloligand.

Roles of basicity and steric crowding of anionic coligands in catechol oxidase-like activity of Cu(ii)-Mn(ii) complexes

Five new heterometallic Cu(ii)-Mn(ii) discrete trinuclear complexes, [(CuL)2Mn(CH3COO)2] (1), [(CuL)2Mn(NO3)2] (2), [(CuL)2Mn(C6H5COO)(H2O)]Cl (3), [(CuL)2Mn((p-OH)C6H5COO)(H2O)]ClO4 (4) and [(CuL)2Mn(HCOO)(H2O)]ClO4 (5), have been synthesized using a metalloligand, CuL derived from an N2O2 donor Schiff base, H2L (N,N'-bis(α-methylsalicylidene)-1,3-propanediamine). Single-crystal structural analyses reveal that all five complexes have a common [(CuL)2Mn] core, where two terminal metalloligands, CuL, are connected to the central metal ion, Mn(ii), via double phenoxido bridges. Among the complexes, 1 and 2 possess linear structures where the terminal Cu(ii) atoms are bridged to the central Mn(ii) atoms by acetate and nitrate ions, respectively along with the double phenoxido bridges, whereas 3, 4 and 5 have bent structures in which the respective anionic coligands, benzoate, p-hydroxybenzoate and formate ions are coordinated only to central Mn(ii) in monodentate fashion along with a water molecule that completes its hexa-coordinated geometry. Among the complexes, 1, 3, 4 and 5 show quite high bio-mimicking catecholase-like activity for the aerial oxidation of 3,5-di-tert-butylcatechol with turnover numbers (Kcat) of 139 h-1, 439 h-1, 348 h-1 and 730 h-1, respectively, whereas complex 2 is practically inactive towards this reaction. The presence of the coordinated water molecule to Mn(ii) in the bent complexes, 3-5, appears to be responsible for their high catalytic activity and the difference in their activity may be attributed to steric crowding due to the anionic coligand, whereas the inactivity of 2 seems to be associated with the low basicity of the nitrate ion. The temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 1-5 are antiferromagnetically coupled with the exchange coupling constants (J) = -8.54 cm-1, -11.50 cm-1, -19.83 cm-1, -10.65 cm-1 and -10.27 cm-1 for 1, 2, 3, 4 and 5 respectively as is expected from the Cu-O-Mn bridging angles.

Facile synthesis of a new Cu(ii) complex with an unsymmetrical ligand and its use as an O3 donor metalloligand in the synthesis of Cu(ii)-Mn(ii) complexes: structures, magnetic properties, and catalytic oxidase activities

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 (k_cat) 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.

SMM behaviour of heterometallic dinuclear CuIILnIII (Ln = Tb and Dy) complexes derived from N2O3 donor unsymmetrical ligands

Four heterometallic dinuclear Cu^IILn^III (Ln = Tb and Dy) complexes derived from two different N₂O₃ donor unsymmetrical Schiff base ligands exhibit SMM behaviour.

Variation of nuclearity in NiII complexes of a Schiff base ligand: crystal structures and magnetic studies

Four Ni^II complexes have been synthesized by changing the reaction conditions and stoichiometry of the reactants. The magnetic coupling in the NiII4 complex is ferromagnetic whereas that in the NiII6 complex is antiferromagnetic.

Elucidating the secondary effect in the Lewis acid mediated anodic shift of electrochemical oxidation of a Cu(ii) complex with a N2O2 donor unsymmetrical ligand

The causes behind the fluctuations from a linear dependence of the electrochemical signal of a guest bound metalloligand [CuL] with the Lewis acidity of redox-inactive cations were established by using UV-vis spectroscopy and cyclic voltammetry.

The role of 3d–4f exchange interaction in SMM behaviour and magnetic refrigeration of carbonato bridged CuII2LnIII2 (Ln = Dy, Tb and Gd) complexes of an unsymmetrical N2O4 donor ligand

The role of exchange interaction between Cu(ii) and Ln(iii) ions in SMM behaviour and magnetocaloric effects has been extensively investigated by both experimental and theoretical CASSCF/RASSI-SO/SINGLE_ANISO methods.

A series of CuII–LnIII complexes of an N2O3 donor asymmetric ligand and a possible CuII–TbIII SMM candidate in no bias field

Among four isostructural heterometallic Cu^II–Ln^III complexes (Ln = Tb, Dy, Ho or Er) of an N₂O₃ donor asymmetric ligand, only the Cu^II–Tb^III complex shows SMM behavior at zero bias field but at applied bias field both the Cu^II–Tb^III and Cu^II–Dy^III complexes show SMM behavior.

Rare azido and hydroxido bridged tetranuclear Co(ii) complexes of a polynucleating Mannich base ligand with a defect dicubane core: structures, magnetism and phenoxazinone synthase like activity

Triply azido/hydroxido bridged defect dicubane tetranuclear Co(ii) complexes of a Mannich base ligand show ferromagnetic/antiferromagnetic coupling and phenoxazinone synthase like activity.

Joining of trinuclear (CuL)2M (M = MnII and CdII) nodes by 1,3- and 1,4-benzenedicarboxylate linkers: positional isomeric effect on co-crystallization

Among the four one-dimensional coordination polymers obtained by joining (CuL)₂M (M = Mn^II and Cd^II) nodes with 1,3- and 1,4-benzenedicarboxylate linkers, the chains derived from 1,3-benzenedicarboxylate are co-crystallized with dimeric Cu^II units.

Tri- and hexa-nuclear NiII–MnII complexes of a N2O2 donor unsymmetrical ligand: synthesis, structures, magnetic properties and catalytic oxidase activities

Among two trinuclear and a hexanuclear Ni^II–Mn^II complexes, synthesized by using a Ni(ii) metalloligand of a N₂O₂ donor unsymmetrical ligand, only those containing a H₂O molecule coordinated to the Mn^II center show very high catalytic oxidase activities.