Pyridazine-bridged copper(I) complexes of bis-bidentate ligands: tetranuclear [2 x 2] grid versus dinuclear side-by-side architectures as a function of ligand substituents

Eight bis-bidentate Schiff-base ligands, derived from 3,6-diformylpyridazine and substituted amino-benzenes, have been prepared. A variety of electron donating/withdrawing and/or sterically demanding/undemanding substituents were employed. Two ligands and five of the six pure copper(I) complexes have been structurally characterised. The sterically unhindered ligand derived from 3,5-difluoroaniline, (m,m-F), was almost completely flat whereas the very sterically hindered ligand derived from trimethylaniline, (o,o,p-Me), was severely twisted. The only dinuclear side-by-side complex obtained, [Cu(I)(2)((o-Ph))(2)](PF(6))(2), was of the ligand derived from 2-aminobiphenyl. All five of the other complexes are believed to be [2 x 2] tetranuclear grid complexes, and this was unequivocally shown to be the case for four of these complexes, [Cu(I)(4)((p-Me))(4)](PF(6))(4), [Cu(I)(4)((o,p-Me))(4)](PF(6))(4), [Cu(I)(4)((m,m-F))(4)](PF(6))(4) and [Cu(I)(4)((m,m-Cl))(4)](PF(6))(4). In all cases the copper(I) centres are substantially distorted from tetrahedral, with the most severe distortion present in the side-by-side complex. In the absence of any special effects, tetracopper(I) [2 x 2] grid architectures are observed to be the favored outcome for 1 : 1 reactions of these bis-bidentate ligands with copper(I) ions. Only when the aromaticity of the ligand was extended by employing a phenyl substituent on the phenyl rings, (o-Ph), did a dicopper(I) side-by-side architecture result. Cyclic voltammetry in acetone revealed that the free ligands did not undergo reduction until potentials below -0.8 V, whereas between three and four reversible one electron reductions were observed, between +0.16 and -0.71 vs. AgCl/Ag, for the tetranuclear copper(I) [2 x 2] grid complexes. The redox potentials observed for these complexes are highly dependent on the nature of the ligand phenyl ring substituent(s). The side-by-side complex had one irreversible reduction process, E(pc)ca.-0.5 V.     

A novel tetraoxime and its dinuclear and tetranuclear transition metal complexes

A new bis(dioxime) ligand (H₄L) containing the diphenyl ether moiety has been prepared by reacting 3,3,4,4-tetraaminodiphenyl ether (1) with 2,3-butanedione monoxime (2). Dinuclear copper(II) and cobalt(III) complexes of H₄L exhibit a metal–ligand ratio of 2:1 and the ligand coordinates through the 4 nitrogen atoms, as do most bis(dioximes). The [Cu₂(H₂L)](ClO₄)₂ molecule coordinates to the other two copper(II) ions through the deprotonated oximate oxygens to yield a tetranuclear structure, doubly-bridged by the oximate groups in a cis arrangement. The structure of bis(dioxime) and its complexes were identified by elemental analyses, ¹H-, ¹³C-n.m.r, i.r and m.s. spectral data.     

A kinetics study of ligand substitution reaction on dinuclear platinum complexes: Stochastic versus deterministic approach

The kinetics on a basic ligand substitution reaction on dinuclear platinum complexes [Pt(PEt₃)₂PhPt(PEt₃)₂]²⁺ and [Pt(PEt₃)₂PhCOPhPt(PEt₃)₂]²⁺ , with the ligands pyridine and 3-chloropyridine, is studied. This is a fundamental step in a self-assembly, and the time evolution has been observed with a new experimental technique, QASAP (quantitative analysis of self-assembly process), which is recently developed by Hiraoka's group. As a result of numerical calculations based on master equation, we succeed in specifying the reaction rate constants with a simple reaction model. In addition, the time evolutions of all the intermediate components produced and consumed in chemical reaction are revealed, including those unobserved in the experiments. The convergence behavior of the existence ratios of specific chemical species calculated with the stochastic algorithm method is compared with those obtained from deterministic formalism based on rate equations, revealing a clear dependence on the number of constituent molecules. © 2018 Wiley Periodicals, Inc.     

Mixed-valent tetranuclear manganese complexes with pentadentate Schiff-base ligand having a Y-shaped core

Reaction of pentadentate Schiff-base ligands, 1,3-bis(3-methoxysalicylideneamino)-2-propanol (H₃msap) with manganese(II) salts afforded tetranuclear mixed-valent manganese complexes, [Mn₄(msap)₂(CH₃CO₂)₃(CH₃O)(H₂O)]·H₂O (1) and [Mn₄(msap)₂(C₆H₅CO₂)₃(CH₃O)] (2), which were characterized by elemental analysis, infrared and diffused reflectance spectra and temperature dependence of magnetic susceptibilities (4.5–300 K). Single-crystal X-ray crystallography of these complexes showed that four manganese atoms are chelated by two Schiff-base ligands and further coordinated by syn–syn bridging, syn–anti bridging, and monodentate or bidentate-carboxylato groups, forming a Y-shaped cluster made up of two Mn^II and two Mn^III atoms. Diffused reflectance spectra are featureless, showing broad bands around at near-UV and visible regions. Magnetic moments decrease with lowering of temperature, showing an antiferromagnetic behavior of these complexes.     

Tuning tetranuclear manganese-oxo core electronic properties: adamantane-shaped complexes synthesized by ligand exchange

A series of adamantane-shaped [Mn4O6]4+ aggregates has been prepared. Ligand substitution reactions of [Mn4O6(bpea)4](ClO4)4 (1) with tridentate amine and iminodicarboxylate ligands in acetonitrile affords derivative clusters [Mn4O6(tacn)4](ClO4)4 (4), [Mn4O6(bpea)2(dien)2](ClO4)4)(5), [Mn4O6(Medien)4](ClO4)4 (6), [Mn4O6(tach)4](ClO4)4 (7), [Mn4O6(bpea)2(me-ida)2] (8), [Mn4O6(bpea)2(bz-ida)2] (9), [Mn4O6(bpea)2((t)bu-ida)2] (10), and [Mn4O6(bpea)2((c)pent-ida)2] (11) generally on the order of 10 min with retention of core nuclearity and oxidation state. Of these complexes, only 4 had been synthesized previously. Characterization of two members of this series by X-ray crystallography reveals that compound 7 crystallizes as [Mn4O6(tach)4](ClO4)4 x 3CH3CN x 4.5H2O in the cubic space group Fmm and compound 11 crystallizes as [Mn4O6(bpea)2((c)pent-ida)2].7MeOH in the monoclinic space group C2/c. The unique substitution chemistry of 1 with iminodicarboxylate ligands afforded asymmetrically ligated complexes 8-11, the mixed ligand nature of which is most likely unachievable using self-assembly synthetic methods. A special feature of the iminodicarboxylate ligand complexes 8-11 is the substantial site differentiation of the oxo bridges of the [Mn4O6]4+ cores. While there are four site-differentiated oxo bridges in 8, the solution structural symmetry of 8H+ reveals essentially a single protonation isomer, in contrast to the observation of two protonation isomers for 1H+, one for each of the site-differentiated oxo bridges in 1. Magnetic susceptibility measurements on 4, 7, 8, and 9 indicate that each complex is overall ferromagnetically coupled, and variable-field magnetization data for 7 and 9 are consistent with an S = 6 ground state. Electrochemical analysis demonstrates that ligand substitution of bpea affords accessibility to the Mn(V)(Mn(IV))3 oxidation state.     

Di- and tetranuclear copper(II) complexes of a novel binucleating tetrathioether-tetrathiol ligand

A novel bi-tetradentate polythioether ligand, 6,6-methylene-bis(5- mercapto-3-thiahexyl)-4,8-dithiaundecane-1, 11-dithiol (H4L) was synthesized, and its di- and tetranuclear copper(II) complexes were prepared, and characterized by elemental analyses, magnetic moments, 1H-n.m.r., i.r., and Uv/vis spectra. The i.r. data show that the ligand acts in a tetradentate manner and coordinates via one S atom of the thioether and thiol groups. The geometry of the metal chelates is discussed with the help of magnetic and spectroscopic measurements. The elemental analyses, stoichiometry, and spectroscopic data of the complexes indicate that the copper(II) ions are coordinated to the bi-dianion of the ligand. The function of the thiol ligand is to release protons to form copper(II) complexes, (Cu2L).     

Photoswitching tetranuclear rhenium(I) tricarbonyl diimine complexes with a stilbene-like bridging ligand

Highly efficient photoswitching tetranuclear rhenium(I) tricarbonyl diimine complexes with a stilbene-like bridging ligand are reported. The ability to directly populate excited states localized on the bridging ligand is the key for the observed efficient photoisomerization.     

Solvent effects in ligand substitutions of square planar complexes

Data on solvent effects in ligand substitution in square planar complexes are reviewed. In view of the fact that solvent effects for reactions of the planar complexes are quite different from those observed for saturated carbon substrates, it is felt that previous explanations for protic-dipolar aprotic solvent effects may have to be reconsidered.     

Self-assembly in dinuclear, cyclic homotetranuclear and cyclic heterotetranuclear complexes with a picolylhydrazone ligand

Reactions among Cu(ClO₄)₂ · 6H₂O, Cu(acac)₂/VO(acac)₂ and 3-methoxysalicylaldehyde Picoloylhydrazone in different solvents give three complexes, [Cu₂L(acac)(H₂O)₂]ClO₄ (1), [Cu₄L₂(acac)₂(py)₂](ClO₄)₂ (2) and (VO₂)₂L₂Cu₂(acac)₂ (3) (acac = acetyl acetonate and py = pyridine). There is an extended 2D structure in complex 1 constructed by hydrogen bonds between the binuclear complex cation and the ClO₄⁻ anion, and an extended 1D structure in complex 2 constructed by weak ππ stacking interactions between neighboring cyclic tetranuclear complex molecules. Complex 3 is the first oxovanadium–copper complex with a bridging oxo oxygen atom between the V atom and the Cu atom. The solid-state photoluminescent properties of the three title complexes have been studied. There is an antiferromagnetic interaction in 1.     

Self-assembly as a route to dinuclear lanthanide complexes with rare coordination pattern of salen-type ligand

The self-assembled formation of dinuclear lanthanide salicylaldimines is proved by the X-ray diffraction analysis of europium and gadolinium nitrate complexes containing N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine (H₂L). The [Eu₂(H₂L)₂(μ-H₂L)₂(NO₃)₆] complex, isostructural with the gadolinium complex, displays nine-coordinate distorted tricapped trigonal prism geometry with a different coordination mode of four undeprotonated salicylaldimines, which act as terminal monodentate and μ-bridging ditopic ligands using exclusively the oxygens as donor atoms with the nitrogen atoms not being involved in the coordination environment. These complexes along with similar lanthanum, erbium, thulium, and lutetium complexes were prepared in situ in a one-step metal promoted condensation reaction between salicylaldehyde and 4-methyl-1,3-phenylenediamine in the presence of lanthanide nitrates. They were isolated and characterized by microanalysis and spectroscopic (IR, ESI–MS, UV–Vis, and ¹H NMR) data with reference to the preformed N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine, which was obtained separately and structurally determined by single crystal X-ray analysis.     

Mono- and dinuclear zinc complexes derived from unsymmetric binucleating ligands: synthesis, characterization, and formation of tetranuclear arrays

Zinc complexes of the unsymmetric, binucleating Schiff base ligands 3-(N-[2-(dimethylamino)ethyl]iminomethyl)-salicylic acid (H2L1) and 3-[N-(2-pyridylmethyl)iminomethyl]-salicylic acid (H2L2) have been studied in the solid state as well as in solution. Reaction of ZnX2 (X = NO3-, CH3CO2-) with 3-formylsalicylic acid and N,N-dimethylethylenediamine at neutral or slightly acidic pH afforded the dinuclear complexes [Zn2(HL1)2(H2O)2](NO3)2.2H2O (1a) and [Zn2(HL1)2(CH3CO2)2].6H2O (1b). The Zn ions, which are 3.126(1) A (1a) and 3.2665(7) A (1b) apart, are bridged by two phenolate oxygens. Further coordination sites of the ligand are the imine nitrogen and carboxylate oxygen, while the amino nitrogen is protonated. On dissolution in DMSO or DMF, 1a and 1b are converted into the mononuclear species [Zn(HL1)]+. Cleavage of the dinuclear complexes is accompanied by migration of the ammonium proton to the carboxylate group and coordination of the amino nitrogen to Zn. Reaction of 1b with base yielded the novel tetranuclear Zn complex [Zn4(L1)4].6.5H2O (2) that exhibits coordination number asymmetry. The four Zn ions having N2O3 and N2O4 coordination environments are located at the corners of a nearly square-planar rectangle. H2L2 binds Zn via the phenolate oxygen and, imine and pyridine nitrogens in acidic solution. Deprotonation of the carboxyl group in alkaline solution gave the tetranuclear compound [Zn4(L2)4].4.5H2O (4) with a cubane-like Zn4O4 core.     

Mononuclear,dinuclear and hydroxo-bridged tetranuclear complexes from reactions of Cu ions,mandelic acid and diimine ligands

The reaction of copper(II) hydroxocarbonate, mandelic acid (H₂MANO) and 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) in water affords [Cu(bpy)(μ₂-MANO)]₂ · 8H₂O (1), [Cu(bpy)(MANO)] · 4H₂O (2) and the opened tetranuclear hydroxo-bridged copper(II) complexes of formulae [Cu₄(μ₃-OH)₂(μ₂-MANO)₂(bpy)₄](phglyo)₂ · 8H₂O (3) (phglyo = phenylglyoxylate) or [Cu₄(μ₃-OH)₂(μ₂-OH)₂(OH₂)₂(phen)₄](Bza)₂(OH)₂ · 5H₂O (4) (Bza = benzoate), respectively. The compounds have been characterized by spectroscopic techniques and studied by single-crystal X-ray diffractometry. The formation of 3 and 4 takes place in basic media through dehydrogenation or oxidative dehydrogenation followed by in situ oxidative decarboxylation of mandelic acid to phenylglyoxylate or benzoate, respectively. These results indicate that cooperative catalysis of diimine ancillary ligands and copper(II) is essential.     

Influence of the bridging azine ligand on the rate of ligand substitution in a series of dinuclear platinum(II) complexes

A series of azine‐bridged dinuclear platinum(II) complexes of the type [{trans‐Pt(NH₃)₂(OH₂)}₂(μ‐azn)](ClO₄)₄ (where azn = pyrazine (pzn, Pt1 ), 2,3‐dimethylpyrazine (2,3‐pzn, Pt2 ), and 2,5‐dimethylpyrazine (2,5‐pzn, Pt3 )) were synthesized to investigate the influence of the bridging azine ligand on the reactivity of the platinum(II) centers. The pK_a values of the complexes were determined via acid–base titration, and the rate of substitution of the aqua moiety by a series of neutral nucleophiles, viz. thiourea (TU), 1,3‐dimethyl‐2‐thiourea (DMTU), and 1,1,3,3‐tetramethyl‐2‐thiourea (TMTU), was determined under pseudo‐first‐order conditions as a function of concentration and temperature using standard spectrophotometric techniques. The introduction of the methyl groups to the bridging azine linker in Pt2 and Pt3 leads to a moderate increase in the pK_a values obtained for the first and second deprotonation steps, respectively, as a result of the increased σ‐donor capacity of the bridging azine ligand trans to the aqua moiety. A comparison of the rate constants, k₁ and k₂, at 298 K, obtained for the substitution of the aqua moieties from Pt1 , Pt2 , and Pt3 by TU, shows that the introduction of the σ‐donating methyl groups on the bridging azine ligand in Pt2 and Pt3 results in a corresponding decrease in the reactivity, by ca. five times for the first substitution step and ca. 10 times for the second substitution step. Density functional theory calculations at the B3LYP/LACVP** level of theory for the complexes demonstrate that the introduction of electron‐donating methyl groups results in (i) increased steric hindrance over the metal centers and (ii) decreased the positive charge on the metal center and increases energy separation of the frontier molecular orbitals (E_HOMO – E_LUMO) of the ground‐state platinum(II) complexes, leading to a less‐reactive metal center. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 161–174, 2011     

Cyanide bridged tetranuclear complex with a novel terthiophene based ligand

A new terthiophene based ligand (L = 3-(2-pryridyl)-5-(2,2′:5′,2″-terthien-3′-yl) pyrazole was synthesized. The reaction of Ni(BF₄)₂·6H₂O, L and nBu₄N[Fe(CN)₃tp^∗] (tp^∗ = tris(3,5-dimethylpyrazol-1-yl)borohyrdide) with NaBPh₄ in MeOH/acetone yielded a cyanide bridged tetranuclear complex [Fe₂Ni₂(CN)₆(tp^∗)₂(L)₄](BPh₄)₂ (1). The electrochemical properties of both 1 and L were investigated, and magnetic susceptibility measurements of 1 were conducted, revealing that ferromagnetic interactions were operative within the tetranuclear core.     

Role of bridging diamine linkers on the rate of ligand substitution in a series of dinuclear PtII complexes

A series of dinuclear platinum^II complexes of the type [{trans‐Pt(H₂O)(NH₃)₂}₂‐NH₂(CH₂)_nH₂N]⁴⁺ (where n = 2, 3, 4, and 6) were synthesized to investigate the influence of the bridging diamine linker on the reactivity of the platinum centers. The pK_a values were determined, and the rates of substitution of the aqua moieties by a series of neutral nucleophiles viz. thiourea, 1,3‐dimethyl‐2‐thiourea, and 1,1,3,3‐tetramethyl‐2‐thiourea were studied as a function of concentration and temperature. All reactions studied gave excellent fits to a single exponential and obeyed the simple rate law, k_obs=k₂[Nu]. Negative activation entropies support an associative mode of substitution. The results obtained suggest that the rate of substitution is definitely influenced by the length of the diamine chain, with the rate of substitution decreasing as the length of the diamine chain increases. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 202–210, 2006     

Controlling aggregation of copper(II)-based coordination compounds: From mononuclear to dinuclear, tetranuclear, and polymeric copper complexes

The use of a strategy combining ligand design and changes of reaction conditions has been investigated with the goal of directing the assembly of mononuclear, dinuclear, tetranuclear, and polymeric copper(II) complexes. As a result, closely related copper monomers, alkoxo dimers, and hydroxo cubanes, along with a carbonate-bridged polymeric species, have been synthesized using the rigid, aliphatic amino ligands cis-3,5-diamino-trans-hydroxycyclohexane (DAHC), cis-3,5-diamino-trans-methoxycyclohexane (DAMC), and the glutaryl-linked derivative glutaric acid bis-(cis-3,5-diaminocyclohexyl) ester (GADACE). The composition of the monomeric complex has been determined by X-ray crystallography as [Cu(DAHC)2](ClO4)2 (1), the two dimers as [{Cu(DAHC)(OMe)}2](ClO4)2.MeOH (2) and [{Cu(DAMC)(OMe)(ClO4)}2] (3), the three Cu4O4 cubanes as [{Cu(DAHC)(OH)}4](ClO4)(4).2.5MeOH (4), [{Cu(DAMC)(OH)}4](ClO4)4.H2O (5), and [{Cu2(OH)2(GADACE)}2]Cl4.2MeOH.6H2O (6), and an infinite-chain structure as [{Cu(DAHC)(CO3)}n] (7). Furthermore, the cubane structures 4 and 5 have been investigated magnetically. Our studies indicate that formation of the monomeric, dimeric, and tetranuclear DAHC and DAMC complexes can be controlled by small changes in reaction conditions and that further preorganization of the ligand moiety by linking the DAHC cores (GADACE) allows more effective direction of the self-assembly of the Cu4O4 cubane core.     

Synthesis and in vitro cytotoxicity of novel dinuclear platinum(II) complexes containing a chiral tetradentate ligand

A series of novel dinuclear platinum(II) complexes with a chiral tetradentate ligand, (1R,1′R,2R,2′R)-N¹,N¹′-(1,2-phenylenebis(methylene))dicyclohexane-1,2-diamine (HL), and mono-carboxylic acid derivatives as ligands have been designed, synthesized, and characterized. In vitro cytotoxicity evaluation of synthesized complexes against human HepG-2, A549, HCT-116, and MCF-7 cancer cell lines has been conducted by MTT assays. All compounds showed antitumor activity to HepG-2 and HCT-116 cell lines. Compound L2 exhibited better cytotoxicity than that of carboplatin against HepG-2 and A549 cell lines and also showed comparable activity against HCT-116 cell line.     

Heterobridged dinuclear, tetranuclear, dinuclear-based 1-d, and heptanuclear-based 1-D complexes of copper(II) derived from a dinucleating ligand: syntheses, structures, magnetochemistry, spectroscopy, and catecholase activity

The work in this paper presents syntheses, characterization, crystal structures, variable-temperature/field magnetic properties, catecholase activity, and electrospray ionization mass spectroscopic (ESI-MS positive) study of five copper(II) complexes of composition [Cu(II)(2)L(μ(1,1)-NO(3))(H(2)O)(NO(3))](NO(3)) (1), [{Cu(II)(2)L(μ-OH)(H(2)O)}(μ-ClO(4))](n)(ClO(4))(n) (2), [{Cu(II)(2)L(NCS)(2)}(μ(1,3)-NCS)](n) (3), [{Cu(II)(2)L(μ(1,1)-N(3))(ClO(4))}(2)(μ(1,3)-N(3))(2)] (4), and [{Cu(II)(2)L(μ-OH)}{Cu(II)(2)L(μ(1,1)-N(3))}{Cu(II)(μ(1,1)-N(3))(4)(dmf)}{Cu(II)(2)(μ(1,1)-N(3))(2)(N(3))(4)}](n)·ndmf (5), derived from a new compartmental ligand 2,6-bis[N-(2-pyridylethyl)formidoyl]-4-ethylphenol, which is the 1:2 condensation product of 4-ethyl-2,6-diformylphenol and 2-(2-aminoethyl)pyridine. The title compounds are either of the following nuclearities/topologies: dinuclear (1), dinuclear-based one-dimensional (2 and 3), tetranuclear (4), and heptanuclear-based one-dimensional (5). The bridging moieties in 1-5 are as follows: μ-phenoxo-μ(1,1)-nitrate (1), μ-phenoxo-μ-hydroxo and μ-perchlorate (2), μ-phenoxo and μ(1,3)-thiocyanate (3), μ-phenoxo-μ(1,1)-azide and μ(1,3)-azide (4), μ-phenoxo-μ-hydroxo, μ-phenoxo-μ(1,1)-azide, and μ(1,1)-azide (5). All the five compounds exhibit overall antiferromagnetic interaction. The J values in 1-4 have been determined (-135 cm(-1) for 1, -298 cm(-1) for 2, -105 cm(-1) for 3, -119.5 cm(-1) for 4). The pairwise interactions in 5 have been evaluated qualitatively to result in S(T) = 3/2 spin ground state, which has been verified by magnetization experiment. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBCH(2)) as the substrate, catecholase activity of all the five complexes have been checked. While 1 and 3 are inactive, complexes 2, 4, and 5 show catecholase activity with turn over numbers 39 h(-1) (for 2), 40 h(-1) (for 4), and 48 h(-1) (for 5) in dmf and 167 h(-1) (for 2) and 215 h(-1) (for 4) in acetonitrile. Conductance of the dmf solution of the complexes has been measured, revealing that bridging moieties and nuclearity have been almost retained in solution. Electrospray ionization mass (ESI-MS positive) spectra of complexes 1, 2, and 4 have been recorded in acetonitrile solutions and the positive ions have been well characterized. ESI-MS positive spectrum of complex 2 in presence of 3,5-DTBCH(2) have also been recorded and, interestingly, a positive ion [Cu(II)(2)L(μ-3,5-DTBC(2-))(3,5-DTBCH(-))Na(I)](+) has been identified.