Linear Trinuclear Complexes Research Articles

Synthesis of Six New Transition Metal Complexes: Structural Characterization and in vitro α‐Glucosidase Inhibitions Studies

AbstractThree one‐pot reactions leading to six new transition metal complexes are presented. The one‐pot reactions involved transformations of 2‐(N’‐dicyanomethylene‐hydrazino)‐benzoic acid (DHB) into three new ligands (Lig‐I)2−, (Lig‐II)2−, and (Lig‐III)2−. The complex [Ni2(Lig‐I)2] ⋅ 3H2O (1) was prepared in a one‐pot synthesis in which ligand, (Lig‐I)2− was formed by the amination of DHB resulting from the nucleophilic attack of an amino group of ethylenediamine (en). The complex [Cu(Lig‐II)(en)(H2O)] (2) was prepared in a one‐pot synthesis in which ligand, (Lig‐II)2− was formed by the nucleophilic attack of an amino group of en resulting in an imidazole ring formation. The dinunclear complexes [Zn2(Lig‐III)2(CH3OH)2] (3) and [Cu2(Lig‐III)2(CH3OH)2] (4), a linear trinuclear complex [Ni3(Lig‐III)(en)2(CH3OH)] (5), and a mononuclear complex [Mn(Lig‐III)(CH3OH)4] (6) were synthesized using a preparation involving conversion of one of the nitriles on DHB into an imino‐ester. The resulting complexes were characterized using a variety of analytical techniques including infra‐red and UV‐vis spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction analysis. The complexes displayed α‐glucosidase enzyme inhibition with IC50 values in the range of 1.57–207 μM.

Unprecedented pseudo-zeroth-order kinetics of the catecholase-like activity of mixed-valence MnIIMn2III complexes

The pseudo-zero-order kinetics of the catecholase-like activity of biologically active linear trinuclear mixed-valence manganese complexes have been explored; the formation of singlet oxygen is thought to be the rate-limiting step.

Modeling of Spin Crossover in Linear Trinuclear Complexes: Effects of External Pressure.

In the present study, a model is suggested to explain the course of spin transformation in crystals containing linear trinuclear iron(II) clusters as structural units. The energy spectrum of an isolated trimer is described with due allowance of the effects of the cubic crystal field formed by the nearest surrounding of each FeII ion as well as by consideration of intracluster interactions in the nearest neighbor approximation. The intercluster cooperative interaction promoting the spin transition is assumed to arise from the coupling of molecular modes with phonons, that is, a feature characteristic for molecular crystals containing as a structural element single spin-crossover ions or complexes formed by these ions. It is demonstrated that in dependence on the relative strengths of intra- and intercluster interactions, the trinuclear systems can exhibit a variety of different types of spin transitions and, namely, gradual, step-like transitions and those characterized by a hysteresis loop. The effects of external pressure on the spin transitions in crystals of trinuclear clusters are explored taking into account that pressure affects both the energy gap between the high-spin and low-spin states and the characteristic parameters of cooperative interaction. In the framework of the suggested model, the spin transformation in the Fe3(bntrz)6(tcnset)6 compound is comprehensively explained. The model also allows a qualitative and quantitative reproduction of the temperature and course of the spin transition in this compound under applied pressure.

Trinuclear Magnesium Imidazolate Borohydride Complex.

A new type of hybrid compound, combining properties of MOFs and borohydrides, was synthesized solvothermally using Mg(BH4)2 and imidazole as precursors. Material in the form of acetonitrile solvate with formula [Mg3{(Im)BH2(Im)}6(ImH)6]·CH3CN crystallizes in the space group R3̅, having the unit cell parameters a = 15.1942(2) Å and c = 28.3157(3) Å as determined by single crystal X-ray diffraction. The structure was further investigated by solid-state NMR and DFT quantum chemical calculations. The main feature of the structure, reported here for the first time, is a linear trinuclear complex, where octahedrally nitrogen-coordinated Mg2+ ions are bridged with {(Im)BH2(Im)}− units, forming inside voids of 4.6 Å in diameter between the magnesium ions. Polar intermolecular interactions hold the molecules in a dense rhombohedral stacking, where a disordered acetonitrile molecule plays a cohesive role. The compound is stable in air and upon heating to about 160 °C. Using an alternative synthesis method from an imidazole melt, an imidazole solvate with the formula [Mg3{(Im)BH2(Im)}6(ImH)6]·ImH and a very similar crystal structure to acetonitrile solvate was prepared. It is stable up to 220 °C. Upon further heating, it transformed into a layered structure with the formula Mg(Im3BH)2, space group P3̅1c, and unit cell parameters a = 8.7338(9) Å and c = 17.621(2) Å determined by synchrotron powder diffraction. Besides its structural novelty, two types of potentially reactive hydrogens, bonded to boron and nitrogen in the same molecule, make the material highly interesting for future investigations in the fields of energy storage applications.

Synthesis, characterization, superoxide dismutase, and antimicrobial activities of Co (II) complexes with Schiff base ligand and their hybrid proteins

AbstractMetal complexes have been reported to possess excellent free radical scavenging and antimicrobial properties. In the present study, seven linear trinuclear complexes were synthesized based on bis Schiff base ligand and complexes 1, 3–7 are reported for the first time. Their structure was characterized by IR spectroscopy and single crystal diffraction. BSA was used as carrier to hybridize the synthesized complexes to construct hybrid proteins. The interaction between metal complex and BSA was studied by UV–Vis spectrophotometry and fluorescence spectroscopy. Static quenching was the main mechanism identified for the interaction between metal complex and BSA. In the superoxide dismutase (SOD) activity test, IC50 values of complexes and hybrid proteins range between 2.89 and 26.53 μM, with hybrid proteins demonstrating a stronger activity than the complexes. Among all the complexes studied, complex 5 exhibited the strongest inhibition against Candida albicans (MIC 12.5 μg ml−1) and Cryptococcus neoformans (MIC 6.5 μg ml−1).

Synthesis, Structure, and Magnetic Properties of Linear Trinuclear CuII and NiII Complexes of Porphyrin Analogues Embedded with Binaphthol Units

A porphyrin analogue embedded with (S)-1,1′-bi-2-naphthol units was synthesized without reducing optical purity of the original binaphthol unit. This new macrocyclic ligand provides the hexaanionic N4O4 coordination environment that enables a linear array of three metal ions. That is, it provides the square planar O4 donor set for the central metal site and the distorted square planar N2O2 donor set for the terminal metal sites. In fact, a CuII3 complex with a Cu(1)–Cu(2) distance of 2.910 Å, a Cu(1)–Cu(2)–Cu(1′) angle of 174.7°, and a very planar Cu2O2 diamond core was obtained. The variable-temperature 1H-NMR study of the CuII3 complex showed increasing paramagnetic shifts for the naphthyl protons as temperature increased, which suggests strong antiferromagnetic coupling of CuII ions. The temperature dependence of the magnetic susceptibility indicated antiferromagnetic coupling both for the CuII3 complex (J = −434 cm−1) and for the NiII3 complex (J = −49 cm−1). The linear (L)M(µ-OR)2M(µ-OR)2M(L) core in a rigid macrocycle cavity made of aromatic components provides robust metal complexes that undergo reversible ligation at the apical sites of the central metal.

Halido‐bridged Copper(II) Complexes with 1‐tert‐Butyl‐1H‐tetrazole: Crystal Structure and Magnetic Properties

Complex [Cu(tbt)Cl2]n (tbt = 1‐tert‐butyl‐1H‐tetrazole) was prepared by reaction of tbt with copper(II) chloride in solution. According to single‐crystal X‐ray analysis, this complex presents 1D coordination polymer, formed at the expense of double chlorido bridges between neighboring pentacoordinate copper(II) cations. 1‐tert‐Butyl‐1H‐tetrazole acts as monodentate ligand coordinated by CuII cations via the heteroring N4 atoms. The temperature‐dependent magnetic susceptibility measurements of novel complex [Cu(tbt)Cl2]n as well as described previously 1D coordination polymer [Cu(tbt)2Cl2]n, and linear trinuclear complex [Cu3(tbt)6Br6], were carried out. Magnetic studies revealed that the copper(II) ions were weakly ferromagnetically coupled in polymeric copper(II) chloride complexes, whereas complex [Cu3(tbt)6Br6] showed antiferromagnetic coupling.

High temperature Fe(iii) spin crossover behaviours in three unprecedented FeIII–MII–FeIII(M = Fe, Cd) linear trinuclear complexes

An azo-based ligand of azotetrazolyl-2,7-dihydroxynaphthalene (H3ATD) was used to synthesize three FeIII–MII–FeIII(M = Fe, Cd) linear trinuclear complexes with different high temperature spin crossover (SCO) behaviours for the terminal FeIIIions.

Element-Selective Molecular Charge Transport Characteristics of Binuclear Copper(II)-Lanthanide(III) Complexes.

A series of isostructural dinuclear 3d-4f complexes, isolated as [CuLn(L·SMe)2(OOCMe)2(NO3)]· xMeOH (Ln = Gd 1, Tb 2, Dy 3, and Y 4; x = 0.75-1) and comprising one acetate and two thioether-Schiff base (L·SMe-) bridging ligands based on 4-(methylthio)aniline and 2-hydroxy-3-methoxybenzaldehyde (HL·SMe = C15H15NO2S), was synthesized and fully characterized. The magnetic properties of the charge-neutral {CuLn} complexes are dominated by ferromagnetic CuII-LnIII exchange interactions. Large-area electron transport studies reveal that the average conductivity of robust, self-assembled {CuLn} monolayers on a gold substrate is significantly lower than that of common alkanethiolates. Theoretical calculations of transmission spectra of individual complexes 1 and 4 embedded between two metallic electrodes show that the molecular current-voltage ( I- V) characteristics are strongly influenced by electron transport through the Cu centers and thus fully independent of the lanthanide ion, in excellent agreement with the experimental I- V data for 1-4. The β-polarized transmission indicated by calculations of 1 and 4 points out their potential as spin filters. In addition, the reactivity of the title compound 1 with CuII in a square-pyramidal coordination environment toward methanolate and azide was examined, resulting in the formation of a linear trinuclear complex, [Cu2Na(L·SMe)4]NO3·3MeOH (5), characterized by antiferromagnetic exchange interactions between the two copper ions.

Copper(II) Halide Complexes with 1‐tert‐Butyl‐1H‐1,2,4‐triazole and 1‐tert‐Butyl‐1H‐tetrazole

1‐tert‐Butyl‐1H‐1,2,4‐triazole (tbtr) was found to react with copper(II) chloride or bromide to give the complexes [Cu(tbtr)2X2]n and [Cu(tbtr)4X2] (X = Cl, Br). 1‐tert‐Butyl‐1H‐tetrazole (tbtt) reacts with copper(II) bromide resulting in the formation of the complex [Cu3(tbtt)6Br6]. The obtained crystalline complexes as well as free ligand tbtr were characterized by elemental analysis, IR spectroscopy, thermal and X‐ray analyses. For free ligand tbtr, 1H NMR and 13C NMR spectra were also recorded. In all the complexes, tbtr and tbtt act as monodentate ligands coordinated by CuII cations via the heteroring N4 atoms. The triazole complexes [Cu(tbtr)2Cl2]n and [Cu(tbtr)2Br2]n are isotypic, being 1D coordination polymers, formed at the expense of single halide bridges between neighboring copper(II) cations. The isotypic complexes [Cu(tbtr)4Cl2] and [Cu(tbtr)4Br2] reveal mononuclear centrosymmetric structure, with octahedral coordination of CuII cations. The tetrazole compound [Cu3(tbtt)6Br6] is a linear trinuclear complex, in which neighboring copper(II) cations are linked by single bromide bridges.

Ruthenium Carbon-Rich Group as a Redox-Switchable Metal Coupling Unit in Linear Trinuclear Complexes.

The preparation and properties of novel ruthenium carbon-rich complexes [(Ph-C≡C-)2-nRu(dppe)2(-C≡C-bipyM(hfac)2)n] (n = 1, 2; M = CuII, MnII; bipy = 2,2'-bipyridin-5-yl) characterized by single-crystal X-ray diffraction and designed for molecular magnetism are reported. With the help of EPR spectroscopy, we show that the neutral ruthenium system sets up a magnetic coupling between two remote paramagnetic CuII units. More specifically, these copper compounds are unique examples of bimetallic and linear heterotrimetallic compounds for which a complete rationalization of the magnetic interactions could be made for exceptionally long distances between the spin carriers (8.3 Å between adjacent Cu and Ru centers, 16.6 Å between external Cu centers) and compared at two different redox states. Surprisingly, oxidation of the ruthenium redox-active metal coupling unit (MCU), which introduces an additional spin unit on the carbon-rich part, leads to weaker magnetic interactions. In contrast, in the simpler parent complexes bearing only one paramagnetic metal unit [Ph-C≡C-Ru(dppe)2-C≡C-bipyCu(hfac)2], one-electron oxidation of the ruthenium bis(acetylide) unit generates an interaction between the Cu and Ru spin carriers of magnitude comparable to that observed between the two far apart Cu ions in the above corresponding neutral trimetallic system. Evaluation and rationalization of this coupling with theoretical tools are in rational agreement with experiments for such complex systems.

Silver complexes stabilized by large silanethiolate ligands - crystal structures and luminescence properties.

Bulky silanethiolate and disiladithiolate ligands were applied to synthesize one mononuclear and three trinuclear silver complexes including two cyclic "microclusters" and a linear tri-nuclear silanethiolate complex. All obtained compounds are characterized by X-ray diffraction and FT-IR. NMR and emission spectroscopies were used where possible. The first trinuclear anionic silver thiolate is structurally characterized. The influence of the different charge of cyclic silver complexes as well as the overall ligand environment on the structural properties is demonstrated. The impact of the different synthetic routes on the final structures of the obtained clusters - cyclic or linear - is discussed.

Influence of geometric and electronic features of pyridine derivatives and triethylamine on the formation of a metal carboxylate core in reactions producing cadmium(ii) pivalate complexes

The reaction products of [Cd(piv)2] (piv is–O2CBut) with isoquinoline (iqn), 2,4-lutidine (lut), phenanthridine (phend), 2,3-cyclododecenopyridine (cpy), and triethylamine (Et3N) were synthesized and their structures were determined. The steric factors were found to play a more important role in cadmium(ii) pivalate complexes compared to 3d metal carboxylates in the +2 oxidation state. The reaction of [Cd(piv)2] with isoquinoline produces only the mononuclear complex [Cd(piv)2(iqn)3] (1). The reaction of [Cd(piv)2] with pyridine derivatives bearing a bulky substituent at the α position is accompanied by the formation of symmetrical dinuclear complexes of the composition [Cd2(piv)4(L)2]. In the complexes with L = lut (2) or phend (3), the cadmium(ii) atoms are linked by two chelating-bridging carboxylate groups; in the complex with L = cpy (4), by four bidentate-bridging groups. The reaction of [Cd(piv)2] with Et3N in a solution of MeCN gives the centrosymmetric linear trinuclear complex [Cd3(piv)6(Et3N)2] (6); in a mixture of benzene and hexane, the ionic compound (HEt3N)[Cd2(piv)5(H2O)] (7). The crystal structures of all synthesized compounds were determined by X-ray diffraction.

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).

Substituent position-induced diverse architectures of polyoxovanadate-based hybrid materials constructed from a linear trinuclear transition metal complex and a hexanuclear [V6O18]6−cluster

Four new hexavanadate cluster-based hybrid materials [Ni(3-atrz)2V2O6]·2H2O (1) and [M3(4-atrz)6V6O18]·4H2O [atrz = amino-1,2,4-triazole; M = Ni (2), Co (3) and Zn (4)] have been synthesized under hydrothermal conditions by the reaction of transition metal salts, amino-triazole ligands and sodium metavanadate. Single crystal X-ray diffraction analyses reveal that compound 1 shows a one-dimensional (1D) chain formed by the alternative arrangement of linear trinuclear complexes [Ni3(3-atrz)6]6+ and hexanuclear [V6O18]6− clusters. Compounds 2–4 are isostructural three-dimensional (3D) frameworks, which are constructed from the linear trinuclear transition metal complexes and 2D inorganic layers derived from transition metal ions and hexanuclear [V6O18]6− clusters. The distinct amino positions in the two types of triazole ligands play the key role in determining the final dimensionality and structures of the title compounds. The thermal stability, photocatalytic activity and magnetic properties of 1–4 have been investigated.

Three Linear Trinuclear Zinc(II) Complexes with Acenaphthenequinone Dioxime and the Ancillary Ligand 2‐Amino‐2‐methyl‐1‐propanol in Different Coordination Modes

AbstractThree linear trinuclear complexes [Zn3L3(HAMP)2]·2MeOH (1), [Zn3L3(HAMP)2]·2DMF·2EtOH (2), and [Zn3L3(HAMP)2]·DMF·EtOH (3) were separated from the reactions of ZnII salts with acenaphthenequinone dioxime (H2L) and 2‐amino‐2‐methyl‐1‐propanol (HAMP) under different reaction conditions. They were structurally characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffractional analysis. All of them present a similar linear trinuclear skeleton with the three ZnII ions linked by three L2– ligands. The coordination arrangements of their terminal ZnII ions and the coordination modes of the two HAMP ancillary ligands are different. 1 has two five‐coordinate bipyramidal terminal ZnII ions with the two HAMP molecules chelated to the two terminal ZnII ions, while the two terminal metal ions in 3 are both tetracoordinate in tetrahedral arrangements with the two HAMP molecules in monodentate coordination modes. However, 2 shows different coordination modes (bipyramidal and tetrahedral) for the two terminal ZnII ions with the two HAMP molecules in chelated and monodentate coordination modes, respectively. Their luminescent properties were also investigated.

Linear, Edge‐Sharing Heterometallic Trinuclear [CoII–LnIII–CoII] (LnIII = GdIII, DyIII, TbIII, and HoIII) Complexes: Slow Relaxation of Magnetization in the DyIII Derivative

AbstractThe sequential reaction of a multisite coordination ligand (LH4) with lanthanide (III) nitrates followed by the addition of Co(NO3)2·6H2O in a 4:1:2 ratio in the presence of triethylamine afforded a series of heterometallic, linear trinuclear complexes [Co2Ln(LH3)4]·3NO3 [Ln = DyIII (1), GdIII (2), TbIII (3), and HoIII (4)]. These tricationic complexes contain nitrate counteranions. The cationic portion of these complexes consists of three metal ions that are arranged in a linear fashion; a central LnIII is present between the two terminal CoII ions and is attached to the latter through two phenoxide bridging groups. This arrangement generates two contiguous four‐membered CoLnO2 rings. The CoII ions are six‐coordinate (2N, 4O) in a distorted octahedral geometry, whereas the central lanthanide ion is eight‐coordinate (8O) in a distorted square‐antiprismatic geometry. Magnetic studies of these complexes have been performed and indicate a slow relaxation of the magnetization for the DyIII derivative 1.

Synthesis, structures, and magnetic properties of carboxylate-bridged trinuclear complexes based on low-spin manganese(III)/iron(III) building blocks

Four linear trinuclear transition metal complexes have been prepared and characterized. The complexes [MII(MeOH)4][FeIII(L)2]2·2MeOH (M = Fe (1) or Ni (2)), [CoII(EtOH)2(H2O)2][FeIII(L)2]2·2EtOH (3), and [MnII(phen)2][MnIII(L)2]2·4MeOH (4) (H2L = ((2-carboxyphenyl)azo)-benzaldoxime, phen = 1,10-phenanthroline) possesses a similar syn–anti carboxylate-bridged structure. The terminal Fe(III) or Mn(III) ions are low spin, and the central M(II) ions are high spin. Magnetic measurements show that antiferromagnetic interactions were present between the adjacent metal ions via the syn–anti carboxylate bridges. The antiferromagnetic coupling between low-spin Fe(III) and Ni(II) is unusual, which has been tentatively assigned to the structural distortion of Fe(III).

Syntheses, crystal structures and magnetic properties of mixed-valence linear trinuclear cobalt and 2D nickel complexes

Abstract Two new complexes, [CoL2]2[Co(CH3OH)4] (1), and [Ni2L2(CH3OH)2]n (2) (H2L = 2-(((2-hydroxynaphthalen-1-yl)methylene)amino)acetic acid), have been synthesized and structurally characterized. Single-crystal X-ray analysis reveals that complex 1 is linear trinuclear mixed valence cobalt complex, while complex 2 is a 2D complex by double naphtholate bridged and syn–anti carboxylate bridged. Magnetic susceptibility measurements indicate that 1 shows mononuclear CoII behavior whereas 2 exhibits an antiferromagnetism behavior.

Assembling 1D magnetic chain based on octacyanotungstate(v) and [Cu2L2Ln] sub-building units (Ln = Eu, Gd, Tb and Dy)

Reaction of (NBu3H)3[W(CN)8]·H2O and linear trinuclear complexes [Cu(II)2L2Ln(III)(NO3)3] (L = 2,6-di(acetoacetyl)pyridine, Ln = Eu (1), Gd (2), Tb (3) and Dy (4)) leads to the formation of four one-dimensional (1D) complexes. Single crystal X-ray analysis reveals that [W(CN)8](3-) bridges between the [Cu(II)2L2Ln(III)] sub-building units to construct the alternative chains. Magnetic investigation indicates that ferromagnetic interaction occurred between all paramagnetic ions and the slow magnetic relaxation properties were observed in complexes 3 and 4.