Double Phenoxido Bridges Research Articles

Trinuclear heterometallic CuII–MII (M = Mn and Co) complexes of N,O donor ligands with o-nitro benzoate anion: Structures, magnetic properties and catalytic oxidase activities

Three new heterometallic complexes [(CuL1)2Mn(o-(NO2)C6H4CO2)2] (1), and{[(CuL2)2Mn(o-(NO2)C6H4CO2)2]·2CH3CN} (2) and {[(CuL2)2Co(o-(NO2)C6H4CO2)2]·2H2O} (3) have been synthesized using [CuL1]/[CuL2] as metalloligands (where H2L1 = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine, H2L2 = N,Ń-bis(methyl2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Structural characterization of complexes (1–3) show that contains linear trinuclear architecture, where the terminal [CuL1]/[CuL2] units are coordinated to the central MnII (for 1 and 2)/CoII (for 3) through double phenoxido bridge along with a syn-syn bridging carboxylate anion. Complexes 1 and 2 exhibit biomimetic catecholase-like activity with the turn over numbers (kcat) of 164 and 140 h−1, respectively. The mass spectral study suggest the most probable mechanism of this biomimetic oxidase reaction whereas, cyclic voltammetry measurements indicate that CuII is reducible to CuI during catalysis. Variable temperature (2–300 K) magnetic susceptibility measurements reveal that all complexes (1–3) possess an overall antiferromagnetic coupling between CuII and the hetero metal ions with J values of –7.027(2), –7.076(1) and –2.2(1) cm−1, respectively.

Double dicyanamide decorated double phenoxide bridged MnIII dimer with single-molecule magnetic behaviour and bio-catalytic activity

Herein, we report the magnetic properties and bio-catalytic activity of a flying bee-like double phenoxido bridged dinuclear MnIII-Schiff base complex decorated with double dicyanamide (dca−) ligands and formulated as: [Mn2(L)2(dca)2] (1) (where H2L = 2,2′-((1E,1′E)-(ethane-1,2-diylbis(azanylylidene))-bis(ethan-1-yl-ylidene))diphenol). The complex has been synthesised by one-pot stepwise reaction of the tetradentate Schiff’s base ligand H2L with MnCl2 and dca− at 1:1:2 ratio under aerobic conditions. It has been characterized by single crystal X-ray diffraction (SC-XRD) and spectroscopic techniques. Complex 1 contains two MnIII ions connected by a double phenoxido bridge in an octahedral geometry and terminal dca− ligands. The dimers are connected to other dimers through both hydrogen bonding and π-interactions to form an extended supramolecular network. The present study reveals that in presence of tetradentate Schiff base ligands, the use of a 1:2 Mn:dca− ratio leads to formation of a dimeric MnIII complex in contrast to the discrete mononuclear complexes or 1D structures previously obtained for the Mn:dca− ratio of 1:1. The magnetic study indicates that the dimeric MnIII complex shows a negligible MnIII–MnIII interaction and a large anisotropy. The AC susceptibility measurements indicate that complex 1 behaves as a field-induced single-molecule magnet (SMM), with a high energy barrier of 73(4)K. The study of model catechol oxidase-like enzyme activity of complex 1 indicates that the dimeric MnIII complex acts as an active catalyst (kcat = 34.94 h−1) in the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) in presence of aerial O2 in acetonitrile medium.

Tri- and pentanuclear CuII–CdII complexes of N2O2 donor ligands with the variation of carboxylate coligands: Structural elucidation and theoretical study

Three new heterometallic copper(II)-cadmium(II) complexes [(CuL1)2Cd3(C6H5CO2)6] (1), {[(CuL2)2Cd(o-(NO2)C6H4CO2)2]·2NCMe} (2), and [{CuL2(H2O)0.65(NCMe)0.35}2Cd3(m-(NO2)C6H4CO2)6] (3) have been synthesized using [CuL1]/[CuL2] as metalloligand (where H2L1 = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine, H2L2 = N,Ń-bis(methyl2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Single crystal structure analyses reveal that complexes 1 and 3 exist as pentanuclear entities in which the [CuL1]/[CuL2] units are bonded to the terminal CdII centres of the benzoate (for 1)/m-nitro benzoate (for 3) bridged linear [Cd3(C6H5CO2)6] (for 1)/[Cd3(m-(NO2)C6H4CO2)6] (for 3) unit through double phenoxido oxygen atoms. On the other hand, complex 2 contains a linear, trinuclear structure in which the square pyramidal [CuL2] units are connected with the central octahedral CdII ion via double phenoxido bridges and also additionally through a syn-syn bridging o-nitro benzoate group. A theoretical investigation on the geometries and energies of the complexes reveals that in the presence of the naphthalene group in H2L1 the pentanuclear geometry of complex 1 is favored over the trinuclear ones, usually formed with the salen type ligands. In addition, substitution of benzoate ion at meta position by nitro group stabilizes pentanuclear structure more than ortho-substitution, corroborating the formation of pentanuclear complex 3 and trinuclear complex 2.

Heterometallic supramolecular architectures constructed from cyanido-based [CoIII(AA)(CN)4]- building-blocks (AA = 1,10-phenantroline and 2,2’-bipyridine)

A neutral, mixed-valence cyanido-bridged {Co2IICo2III} complex, with formula {[CoII2(L)(MeOH)2][CoIII(phen)(CN)4]2}·2H2O·0.5MeOH (1), and a cyanido-based ionic compound, with formula [MnII(MAC)(H2O)2][CoIII(bipy)(CN)4]2·3H2O (2) were obtained by reacting the heteroleptic Ph4P[CoIII(AA)(CN)4] building-block [AA = 1,10-phenanthroline, phen, (1) and 2,2’-bipyridine, bipy, (2)] with the dinuclear {Co2IIL}2+ (1) and mononuclear {MnII(MAC)}2+ (2) precursors, respectively [H2L = macrocyclic Schiff-base obtained by condensation of 2,6-diformyl-p-cresol with 1,3-diaminopropane and MAC = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-(18),2,12,14,16-pentaene]. The structures of 1 and 2 were determined by X-ray diffraction on single crystals. 1 is a neutral tetranuclear homometallic compound where two peripheral [CoIII(phen)(CN)4]- entities which act as end-cap ligands through one of its four cyanide groups towards the inner double phenoxido-bridged [Co2II(L)(MeOH)2]2+ dinuclear unit. Both cobalt(III) and cobalt(II) ions are six-coordinate with two phenanthroline-nitrogen and four cyanide-carbon atoms (at CoIII) and two phenoxido-oxygens and two imino-nitrogen atoms from the Schiff-base ligand plus a methanol molecule and a cyanide-nitrogen atom (at CoII) building somewhat distorted octahedral surroundings. The value of the cobalt(II)×××cobalt(II) separation is 3.11 Å and that of the angle at the phenoxo bridge is 99.4°. Compound 2 is a heterobimetallic ionic salt which is made up of [CoIII(bipy)(CN)4]- anions and [Mn(MAC)(H2O)2]2+ cations. Each cobalt(II) in 1 is six-coordinated, in a distorted octahedral environment built by a bidentate bipy ligand and four monodentate cyanide groups whereas the manganese(II) ion is seven-coordinated with five nitrogen atoms of the MAC ligand and two water molecules describing a distorted pentagonal bipyramid surrounding. The cryomagnetic investigation of 1 in the temperature range 1.9-300 K reveals the occurrence of strong spin-orbit coupling effects and a relatively weak antiferromagnetic interaction between the high-spin cobalt(II) ions linked by the double phenoxido bridge . The nature and magnitude of the magnetic coupling in 1 compares well with those from previous magneto-structural studies on the CoII2O2 motifs where antiferromagnetic interactions result in the examples having values at the phenoxido angle larger than 99.7º with dihedral angles smaller than 35.3°.

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 MnII 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 MnII 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 (kcat ) 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.

Heterometallic di- and trinuclear CuIILnIII (LnIII = La, Ce, Pr, Nd) complexes with an alcohol-functionalized compartmental Schiff base ligand: Syntheses, crystal structures, thermal and magnetic studies

The reaction of the multi-site Schiff base ligand 2,2′-{(2-hydroxypropane-1,3-diyl)bis[nitrilomethylidene]}bis(4-bromo-6-methoxyphenol) (H3L) with copper(II) acetate, followed by the addition of lanthanide(III) nitrate afforded the new heterotri- and heterodinuclear compounds [Cu2La(HL)2(NO3)2(MeOH)2]NO3·2MeOH·2H2O (1), [Cu2Ce(HL)2(NO3)2(MeOH)2]NO3·MeOH·2H2O (2), [Cu2Pr(HL)2(NO3)2H2O]NO3·H2O (3), and [CuNd(HL)(NO3)3H2O(MeOH)]·1.5MeOH (4). The single-crystal X-ray crystallography results show that in all reported complexes the LnIII and CuII ions are connected through double phenoxido bridges and trinuclear complexes 1–3 are not linear entities. Compounds 1–4 are stable at room temperature and their decomposition processes proceed in a similar way. During heating in an air or nitrogen atmosphere, in the first step a desolvation process is observed. TG-FTIR analysis shows that the main gaseous products released over the whole decomposition process are water, methanol, ammonia, carbon dioxide and carbon monoxide. The final solid products for the decomposition of 1–4 in air are principally mixtures of CuO and Ln2CuO4. The temperature dependence of the magnetic susceptibility indicated that in the reported heteronuclear complexes the interaction between the CuII and CeIII/PrIII/NdIII ions is antiferromagnetic.

Tri-nuclear copper-cadmium complexes of a N2O2-donor ligand with the variation of counter anions: Structural elucidation and theoretical study on inter-molecular interactions

Four new tri-nuclear hetero-metallic copper(II)-cadmium(II) complexes [(CuL)2CdCl2] (1), [(CuL)2CdBr2] (2), [(CuL)2CdI2] (3) and [(CuL)2Cd(NO3)2] (4) have been synthesized using [CuL] as ‘‘ligand complex’’ (where H2L = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine) and characterized by elemental analysis, IR, UV–Vis spectroscopy and single crystal X-ray diffraction studies. Crystal structure analyses reveal that all four complexes consist of a tri-nuclear moiety in which two square-pyramidal [CuL] units are bonded to a central Cd(II) ion through double phenoxido bridges. The Cd(II) is in a six-coordinate octahedral environment being bonded additionally to two mutually trans chloride (in 1), bromide (in 2), iodide (in 3) and oxygen atoms of nitrate (in 4) ions. Presence of several non-covalent interactions (i.e. π···π, CH···O and Cu···Cu interactions) has been observed in the crystal packing of all the four molecules that assist the formation of 1D supramolecular assemblies in the solid state. The interactions were investigated by means of high level DFT calculations (PBE0-D3/def2-TZVP) with the help of TURBOMOLE 7.0 program, characterized using Bader’s theory of “atoms-in-molecules” (AIM) and rationalized using molecular electrostatic potential (MEP) surface calculations.

A New phenoxido/trifluoroacetato bridged heterometallic NiII2[sbnd]CuII derivative: Structure, EPR interpretation and DFT computation

The trinuclear heterometallic Ni2II−CuII complex, [Ni2(L)2(CF3COO)2Cu] (1) is afforded incorporating a tetradentate Schiff base precursor, H2L [where H2L = N,N′-bis(salicylidene)-1,3-propanediamine]. In 1, the two terminal NiII atoms are linked to the central CuII by a syn-anti bridging trifluroacetate and a double phenoxido bridge, giving rise to a linear structure. The EPR spectra show that the trinuclear structure remains unchanged in non-coordinating solvents, whereas in DMF and DMSO the resonances of mononuclear CuII species with an axial symmetry and a well-resolved hyperfine structure are observed. DFT calculations reveal that the spin Hamiltonian parameters are gz 2.22 and Az 176.4 × 10−4 cm−1, which are in good agreement with the experimental values. The biological outcome of complex 1 on the viability of different human carcinoma cells are analyzed by MTT assay and the results suggest that it induces a decrease in cell-population growth with apoptosis.

Magnetism in Heterobimetallic and Heterotrimetallic Chains Based on the Use of [WV(bipy)(CN)6]– as a Metalloligand

Two new heterobi‐ and trimetallic chains of formula ∞1[{MnII(pyim)2}{(µ‐NC)2WV(bipy)(CN)4}][WV(bipy)(CN)6] (1) and ∞1[{CuIIMnIIL}{(µ‐NC)3WV(bipy)(CN)3}][WV(bipy)(CN)6]·0.75H2O·2MeCN (2) were obtained by reacting the cyanido‐based AsPh4[W(bipy)(CN)6] heteroleptic complex with the pre‐formed [MnII(pyim)2]2+ (1) and [CuIIMnIIL]2+ (2) complexes [bipy = 2,2′‐bipyridine, pyim = 2‐(1H‐imidazol‐2‐yl)pyridine and H2L = macrocyclic Schiff‐base resulting from the stepwise condensation of 2,6‐diformyl‐p‐cresol with ethylenediamine and diethylenetriamine]. The structure of 1 consists of cationic cyanido‐bridged {MnIIWV} chains, assembled from [WV(bipy)(CN)6]– spacers, each one coordinating in a bis‐monodentate fashion, two [MnII(pyim)2]2+ nodes, and [WV(bipy)(CN)6]– counteranions. Compound 2 comprises a positively charged 1D coordination polymer, built from [WV(bipy)(CN)6]– cyanido metalloligands that act as tris‐monodentate spacers towards [CuIIMnIIL]2+ complexes, the entire assembly being neutralized by [WV(bipy)(CN)6]– anions. Each manganese(II) ion in 1 is six‐coordinate in a somewhat distorted octahedral surrounding. Five‐coordinate copper(II) and seven‐coordinate manganese(II) ions exhibiting distorted square pyramidal and monocapped trigonal prism environments respectively, occur in each {CuIIMnII} node of 2. The magnetic susceptibility of 1 and 2 investigated down to 1.9 K is characteristic of 1D ferrimagnetic behavior with minima in the χMT vs. T plots at 35 (1) and 20 K (2) (χM is the magnetic susceptibility per one MnII plus two WV ions). The magnetic data of 1 in the whole temperature range were analyzed through a model considering SMn = 5/2 as a classical spin and SW = 1/2 as a quantum spin, with two interaction parameters J1 = J(1 – α) and J2 = J(1 + α) {the spin Hamiltonian being defined as H = –JΣiSW,i[(1 + α)SMn,j + (1 – α)SMn,i+1] + Σi(gWSW,i + gMnSMn,i)βH}. The values of the intrachain antiferromagnetic interactions for 1 through this model were –3.0(1) (J1) and –32.0(1) cm–1 (J2). The complexity of the spin topology in 2, a branched chain with four different intrachain antiferromagnetic interactions (double phenoxido bridge between MnII and CuII, two single cyanido bridges between MnII and CuII, and one single cyanido bridge between CuII and WV) precluded any simulation of its magnetic data.

H-bond assisted coordination bond formation in the 1D chains based on azido and phenoxido bridged tetranuclear Cu(II) complexes with reduced Schiff base ligands

Two new 1D chains [(CuL1R)2Cu2(N3)2(μ1,1,3-N3)2]n (1) and [{(CuL2R)2Cu2(N3)2(μ1,1,3-N3)2}·(CH3)2CO]n (2) based on rare μ1,1,3-N3 bridged tetranuclear Cu(II) complexes, have been synthesized using [CuL1R] and [CuL2R] as “metalloligands” [where H2L1R = N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine and H2L2R = N,N′-bis(2-hydroxybenzyl)-1,2-ethylenediamine]. Both complexes have been characterized by elemental analysis, spectroscopic methods, single crystal XRD, and magnetic study. In case of chain 1, the basic building block is a centrosymmetric tetranuclear unit whereas for 2, it is an asymmetric tetranuclear unit containing two types of square pyramidal Cu(II) centers (terminal and central). The μ1,1-N3 bridged central copper atoms of one tetranuclear unit are connected weakly to the axial position of the terminal copper atoms of neibouring units via the azide ions forming a rare μ1,1,3-N3 bridged novel 1D polymeric chain structure. Variable temperature magnetic susceptibility measurements show the presence of an overall strong antiferromagnetic exchange interactions mediated through the double phenoxido bridges with J values of −123.8 and −144.6 cm−1 for 1 and 2, respectively.

Rare trinuclear NiII2MII complexes (MII = Mn, Fe and Co) with a reduced Schiff base ligand: Synthesis, structures and magnetic properties

Abstract Three new trinuclear hetero-metallic NiII2MII complexes with MII = Mn, Fe and Co have been synthesized using a [NiLR] “metalloligand”, where H2LR = N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine. All complexes have been characterized by elemental analysis, spectroscopic methods, single crystal XRD and magnetic and electrochemical studies. In the three complexes, in addition to the double phenoxido bridges, the two terminal NiII atoms are linked to the central MII [M = Mn(1), Fe(2) and Co(3)] ion by means of a bridging carboxylato co-anion, giving rise to a linear NiII-MII-NiII structure. Variable temperature magnetic susceptibility measurements show the presence of weak ferromagnetic and antiferromagnetic exchange interactions mediated through the double phenoxido bridges with J values of +8.5 and −3.0 cm−1 for complexes 1 and 2, respectively. Compound 3 shows the presence of antiferromagnetic interactions. Cyclic voltammetry shows a common quasi-reversible one electron oxidation corresponding to the Ni(II)/Ni(III) process in 1–3 and an irreversible M(II)/M(III) oxidation for Mn(1) and Fe(2).

Rare examples of diphenoxido-bridged trinuclear NiII2FeIII complexes with a reduced salen type Schiff base ligand: Structures and magnetic properties

Three new trinuclear hetero-metallic complexes, [(NiLR)2Fe(N3)3] (1), [(NiLR(H2O))2Fe(C6H5CH2CO2)2]·(HSO4) (2) and [(NiLR(H2O))2Fe(C6H5CO2)2]·(HSO4)·(H2O)·(CH2Cl2) (3) have been synthesized using [NiLR] as a “metalloligand” (where H2LR=N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine). All complexes have been characterized by elemental analysis, spectroscopic methods, single crystal XRD and magnetic study. In the angular trinuclear units of 1, the two terminals [NiLR] coordinate through double phenoxido bridges to the central FeIII ion which is penta-coordinated having terminally coordinated azide ion. The two terminal NiII centers are connected to each other and also to neighbouring units through μ1,3-azido bridges to form an alternating chain. On the other hand, complexes, 2 and 3 are linear discrete trinuclear species [NiII–FeIII–NiII] in which two terminal octahedral [NiLR] units coordinate to the central octahedral FeIII ion, located on a crystallographic centre of symmetry, through a μ2-phenoxido oxygen atom and a bridging carboxylato ion. Variable temperature magnetic susceptibility measurements show the presence of antiferromagnetic exchange interactions in 1 mediated through the phenoxido bridges (J1=−33.2cm−1,) and μ1,3-N3 single bridges (J2=−19.9cm−1 and J3=−16.7cm−1). On the other hand, compounds 2 and 3 show ferromagnetic coupling interactions mediated through the double phenoxido bridges with J values of +4.9 and +3.0cm−1 for 2 and 3, respectively.

Synergistic treatment of triple-negative breast cancer by doxorubicin and thioridazine and its nano-formulation

Three new trinuclear hetero-metallic complexes, [(NiLR)2Fe(N3)3] (1), [(NiLR(H2O))2Fe(C6H5CH2CO2)2]·(HSO4) (2) and [(NiLR(H2O))2Fe(C6H5CO2)2]·(HSO4)·(H2O)·(CH2Cl2) (3) have been synthesized using [NiLR] as a “metalloligand” (where H2LR = N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine). All complexes have been characterized by elemental analysis, spectroscopic methods, single crystal XRD and magnetic study. In the angular trinuclear units of 1, the two terminals [NiLR] coordinate through double phenoxido bridges to the central FeIII ion which is penta-coordinated having terminally coordinated azide ion. The two terminal NiII centers are connected to each other and also to neighbouring units through μ1,3-azido bridges to form an alternating chain. On the other hand, complexes, 2 and 3 are linear discrete trinuclear species [NiII–FeIII–NiII] in which two terminal octahedral [NiLR] units coordinate to the central octahedral FeIII ion, located on a crystallographic centre of symmetry, through a μ2-phenoxido oxygen atom and a bridging carboxylato ion. Variable temperature magnetic susceptibility measurements show the presence of antiferromagnetic exchange interactions in 1 mediated through the phenoxido bridges (J1 = −33.2 cm−1,) and μ1,3-N3 single bridges (J2 = −19.9 cm−1 and J3 = −16.7 cm−1). On the other hand, compounds 2 and 3 show ferromagnetic coupling interactions mediated through the double phenoxido bridges with J values of +4.9 and +3.0 cm−1 for 2 and 3, respectively.

Unusual site selection of NCS− in trinuclear complexes of Cu(II) and Ni(II) with a reduced N2O2 donor Schiff base: Structural, theoretical and magnetic studies

Four new trinuclear linear homo-metallic complexes [(CuLR)2Cu(NCS)2]·(CH3)2CO (1), [(CuLR)2Cu(NO3)2] (2), [(NiLR)2Ni(NCS)2·(CH3CN)2] (3), [(NiLR)2Ni(NO3)2·((CH3)2CO)2] (4) have been synthesized using [CuLR] and [NiLR] as metalloligands (where H2LR=N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine) along with polyatomic anions, thiocyanato or nitrato. All four complexes have been characterized by elemental analysis, spectroscopic methods, single crystal XRD, DFT and magnetic study. In all complexes, two units of metalloligands, [CuLR] or [NiLR] coordinate to the central copper or nickel atom through double phenoxido bridges forming a linear trinuclear structure. In the structures of 1 and 3, the N-bonded thiocyanato ion coordinates to the terminal metal centers of the trinuclear unit to complete the distorted square pyramidal and octahedral geometry, respectively; the central metal ions remain square planar in both structures. The coordination of thiocyanato to terminal Cu(II) and Ni(II) instead of central metal ion is unusual compared to the complexes of analogous unreduced species. On the other hand, complexes 2 and 4 possess usual structures in which the anionic coligand, nitrato bridges the central and terminal metal centers. The geometries of central metal ions are octahedral in both structures and those of terminal metal ions are square pyramidal in 2 and octahedral in 4. DFT calculations show that experimentally obtained structure 1 is the most stable compared with the possible other hypothetical isomers but complex 3 is energetically slightly disfavored and possibly packing forces stabilize it in the solid state. Variable temperature magnetic susceptibility measurements show the presence of strong antiferromagnetic exchange interactions mediated through the phenoxido bridges with J values of −328.9, −474.8, and −11.13cm−1 for 1, 2, and 4, respectively. In complex 3, the central Ni(II) ion is diamagnetic, in agreement with its square planar geometry; however small antiferromagnetic interaction is found between the terminal Ni(II) ions with a J value equal to −5.36cm−1.

Antiferro- to ferromagnetic crossover in diphenoxido bridged NiII2MnII complexes derived from N2O2 donor Schiff base ligands

Three new trinuclear NiII–MnII complexes have been synthesized using three different “metalloligands” [NiL1], [NiL2] and [NiL3] derived from the Schiff bases H2L1=N,N′-bis(salicylidene)-1,3-pentanediamine, H2L2=N,N′-bis(salicylidene)-1,3-propanediamine and H2L3=N,N′-bis(salicylidene)-1,3,-diaminopropan-2-ol), respectively. In all three complexes, [(NiL1)2Mn(OOCPh)2(H2O)2]·CH3OH (1), [(NiL2)2Mn(OOCPh)2(CH3OH)2]·CH3OH (2) and [(NiL3)2Mn(OOCPh)2(H2O)2]·CH3OH (3), in addition to the double phenoxido bridge, the two terminal NiII atoms are linked to the central MnII by means of a syn–syn bridging benzoate, giving rise to a linear structure. Complex 1 with Ni–O–Mn angle of 97.35° exhibits antiferromagnetic interactions (JNi–Mn=−0.60cm−1) whereas ferromagnetic exchange is observed in 2 and 3 (JNi–Mn=+2.00 and +1.10cm−1 respectively) having Ni–O–Mn angle 97.34° (in 2), 97.27° (in 3). Theoretical calculations have been performed in order to understand the effect of structural parameters that can tune the magnetic properties of this type of complexes such as small differences in the Ni–O–Mn angle and/or slight variations in intermolecular contacts within the crystal.

Exploring the coordinative adaptation and molecular shapes of trinuclear CuM(II) (M = Zn/Cd) complexes derived from salen type Schiff bases: structural and theoretical studies.

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).

A two-dimensional coordination polymer constructed from binuclear copper(II) metalloligands and manganese(II) ions: Synthesis, crystal structure and magnetic properties

The self-assembly process between the binuclear [Cu2(HL)(L)]− complex and the manganese(II) ion affords a two-dimensional coordination polymer of formula [Mn{Cu2(HL)(L)}2(H2O)2]n (1) (H3L=3-hydroxyiminomethylsalicylic acid) where parallel ladder-like motifs of defective double cubanes of bis(phenoxo)dicopper(II) units as rods and anti-syn carboxylato bridges as rungs act as ligands towards tetraaqua-manganese(II) entities through the deprotonated oxime groups. The topology of 1 is compared with the one of another compound, [Mn{Cu2(HL)(L)}2(H2O)4]·4H2O·2DMF (1′) which was obtained in different conditions by Okawa et al. (J. Chem. Soc., Dalton Trans. (2001) 3119). Magnetic susceptibility measurements of 1 in the temperature range 2.0–300K are practically determined by the occurrence of a very large antiferromagnetic coupling between the two copper(II) ions through the double phenoxido bridge [J=−765(5)cm−1, the spin Hamiltonian being defined as H=−JSCu1·SCu2], a value which is as expected in the light of a recent magneto-structural correlation for bis(phenoxido)dicopper(II) complexes.

Unprecedented structural variations in trinuclear mixed valence Co(II/III) complexes: theoretical studies, pnicogen bonding interactions and catecholase-like activities.

Three new mixed valence trinuclear Co(II/III) compounds cis-[Co3L2(MeOH)2(N3)2(μ1,1-N3)2] (1), trans-[Co3L2(H2O)2(N3)2(μ1,1-N3)2]·(H2O)2 (2) and [Co3L(R)2(N3)3(μ1,3-N3)] (3) have been synthesized by reacting a di-Schiff base ligand (H2L) or its reduced form [H2LR] (where H2L= N,N'-bis(salicylidene)-1,3-propanediamine and H2LR= N,N'-bis(2-hydroxybenzyl)-1,3-propanediamine) with cobalt perchlorate hexahydrate and sodium azide. All three products have been characterized by IR, UV-Vis and EPR spectroscopies, ESI-MS, elemental, powder and single crystal X-ray diffraction analyses. Complex 2 is an angular trinuclear species in which two terminal octahedral Co(III)N2O4 centers coordinate to the central octahedral cobalt(II) ion through μ2-phenoxido oxygen and μ1,1-azido nitrogen atoms along with two mutually cis-oxygen atoms of methanol molecules. On the other hand, in linear trinuclear complex , in addition to the μ2-phenoxido and μ1,1-azido bridges with terminal octahedral Co(III) centres, the central Co(II) is bonded with two mutually trans-oxygen atoms of water molecules. Thus the cis-trans configuration of the central Co(II) is solvent dependent. In complex 3, the two terminal octahedral Co(III)N2O4 centers coordinate to the central penta-coordinated Co(II) ion through double phenoxido bridges along with the nitrogen atom of a terminal azido ligand. In addition, the two terminal Co(III) are connected through a μ1,3-azido bridge that participates in pnicogen bonding interactions (intermolecular N-N interaction) as an acceptor. Both the cis and trans isomeric forms of 1 and 2 have been optimized using density functional theory (DFT) calculations and it is found that the cis configuration is energetically more favorable than the trans one. However, the trans configuration of 2 is stabilized by the hydrogen bonding network involving a water dimer. The pnicogen bonding interactions have been demonstrated using MEP surfaces and CSD search which support the counter intuitive electron acceptor ability of the μ1,3-azido ligand. Complexes 1-3 exhibit catecholase-like activities in the aerial oxidation of 3,5-di-tert-butylcatechol to the corresponding o-quinone. Kinetic data analyses of this oxidation reaction in acetonitrile reveal that the catecholase-like activity follows the order: 1 (kcat = 142 h(-1)) > 3 (kcat = 99 h(-1)) > 2 (kcat = 85 h(-1)). Mechanistic investigations of the catalytic behaviors by X-band EPR spectroscopy and estimation of hydrogen peroxide formation indicate that the oxidation reaction proceeds through the reduction of Co(III) to Co(II).

Trinuclear complexes of [CuL] (H2L = N,N′-bis(salicylidene)-1,4-butanediamine) with HgX2 (X− = N3− and NCO−): Facile crystallization with Z′ = 1 and Z′ = 0.5 for both complexes

Two trinuclear centrosymmetric hetero-metallic copper(II)–mercury(II) complexes of general formula [(CuL)2HgX2] (where X=N3− for 1 and 1′ or OCN− for 2 and 2′) have been synthesized using [CuL] as ‘‘ligand complex” (where H2L=N,N′-bis(salicylidene)-1,4-butanediamine) and structurally characterized. Rapid crystallization of both the complexes yielded isomorphous crystals with two independent half molecules (Z′=1) in 1 and 2 but the crystals that were grown slowly from the same solutions are not isomorphous and contain single half molecule (1′ and 2′) in the asymmetric units (Z′=0.5). Crystal structure analyses reveal that the complexes have discrete trinuclear entity in which two square planar [CuL] units are bonded to a mercury ion through double phenoxido bridges. The Hg(II) is in a six-coordinate distorted octahedral environment being bonded additionally to two mutually trans nitrogen atoms of terminal azide (for 1 and 1′) and cyanate (for 2 and 2′). Higher Z′ compounds are stabilized probably due to weak interactions (C–H⋯N/O and C/H⋯π interactions) that help to hold two independent molecules together.