Grid-type Complexes Research Articles

Phosphorus guiding palladium: [4 + 4] metallomacrocyclic PdII complex and self-assembly of heterometallic PdII/ZnII grid-type complex.

The reaction of heteroditopic ligand 1 featuring a hard pyridine-hydrazone-pyrimidine (N,N,N) site and a softer pyrimidine-hydrazone-phosphane (N,N,P) pocket with [Pd(CH3CN)4](OTf)2 in different metal-to-ligand ratios (M : L) gave the homobimetallic PdII complex [Pd2(1)(CH3CN)2](OTf)4 (2, M : L ratio 2 : 1), the [4 + 4] metallomacrocyclic PdII complex [Pd(1)]4(OTf)8 (3, M : L ratio 1 : 1) and the monometallic complex [Pd(1)2](OTf)2 (4, M : L ratio 1 : 2). The soft N,N,P pocket preferably coordinates PdII, while the harder N,N,N coordination site selectively binds ZnII forming the homoleptic meridional "corner" complexes [Zn(1)2](OTf)2 (5) and [Pd2Zn(1)2](OTf)6 (6). The distinctive coordination behavior of ligand 1 is highlighted by the self-assembly of the heterometallic PdII/ZnII grid-type complex [Pd2Zn2(1)2](OTf)8 (7) in a one-pot reaction. Complexes 2-7 were characterized by mass spectrometry, UV/Vis and NMR spectroscopy including DOSY NMR, and single-crystal X-ray diffraction studies were performed for 2-4 and 7.

New Cu(I) square grid-type and Ni(II) triangle-type complexes: synthesis and characterization of effective binders of DNA and serum albumins.

Multivalent molecules are a potential group of bioactive compounds endowed with high affinity and specificity in innovative biomolecule-targeting therapeutic approaches. Herein, we report on a new and versatile N,N,N,N-donor ligand L (1R,4R)-N1,N4-bis(quinolin-2-ylmethylene)cyclohexane-1,4-diamine with two coordinating quinoline moieties connected with trans-1,4-diaminocyclohexane. It coordinates Cu+ forming a [2 × 2] square grid-type complex C1 [Cu4L4]4+ and Ni2+ giving a triangle-type complex C2 [Ni3L3]6+. We screened their potential as versatile metal-based Serum Albumin (SA), double helical and G-quadruplex DNA binders taking advantage of their shape, size and stability effects using different spectroscopic experiments (UV-Vis, fluorescence, circular dichroism). The findings of our work suggest the potential utility of the metal complexes herein described in the context of the new drug discovery.

Peripherally multi-functionalised metallosupramolecular grids: assembly, decoration, building blocks for dynamic covalent architectures

The sequential assembly of first terminally functionalized bishydrazone ligands followed by their coordination with Zn(ii) metal cations yields peripherally multi-functionalized [2 × 2] grid-type complexes.

Electropolymerization of [2 × 2] grid-type cobalt(II) complex with thiophene substituted dihydrazone ligand

The grid-type complex [Co4(L1-2H)4] containing dihydrazone ligand decorated with thiophene rings has been prepared. The complex undergoes oxidative electropolymerization onto ITO electrode to form purple thin film. The morphology of polymer film on ITO electrode was analyzed by SEM and AFM imagining. It was found that polymer obtained by electropolymerization method is homogenous and uniform. The obtained thin film exhibits color transition from purple via violet to blue due to the stepwise reduction of poly-[CoII4(L1-2H)4] into poly-[CoII2CoI2(L1-2H)4]2− and poly-[CoI4(L1-2H)4]4−. Its electrochromic properties such as long-term stability coloration efficiency and switching times have been investigated.

Electronic absorption and emission properties of bishydrazone [2 × 2] metallosupramolecular grid-type architectures

Several ditopic ligands containing two tridentate bishydrazone coordination subunits and their Zn(II) and Cd(II) [2 × 2] grid-type complexes were prepared and their photoluminescent properties studied. A special attention was devoted to the influence of the orientation of the hydrazone group NNin the core of the ligands and their complexes. Its reversal from [pyridineNNpyrimidine] (L1) to [pyridineNNpyrimidine] (L2) has a strong impact on the observed absorption and emission behaviour of particular ligands (L1 and L2) as well as of their [2 × 2] grid assemblies. The further lateral functionalization of the ligands led to different emission quantum yields of the resulting grids, while their emission and absorption spectra varied very little. The simplest derivative L1 turned out to have the best performance with, for its Zn(II) complex, relatively high quantum yield 60%.

Spin State Chemistry: Modulation of Ligand p Ka by Spin State Switching in a [2×2] Iron(II) Grid-Type Complex.

The iron(II) [2×2] grid complex Fe-8H has been synthesized and characterized. It undergoes spin-crossover (SCO) upon deprotonation of the hydrazine-based terpyridine-like ligand. The deprotonation patterns have been determined by X-ray crystallography and 1H NMR spectroscopy and discussed in relation to the spin state of the iron(II) centers, which influences greatly the p Ka of the ligand. The synthesis of the magnetically silent zinc(II) analogue is also reported, and its (de)protonation behavior has been characterized to serve as a reference for the study of the FeII grid complexes. DFT computations have also been performed in order to investigate how the successive deprotonation of the bridging ligands affects the SCO behavior within the grid.

Electronic and electrochemical properties of grid-type metal ion complexes (Fe+2 and Co2+) with a pyridine-pyrimidine-pyridine based bis(hydrazone)

Se reporta la síntesis de nuevos complejos metálicos de Co2+ y Fe2+ tipo rejilla que contienen como ligando orgánico una doble hidrazona altamente soluble en solventes orgánicos. Los datos obtenidos de resonancia magnética nuclear (RMN 1H), espectroscopía infrarroja con transformada de Fourier (FT-IR) y análisis elemental indican que los complejos adoptaron una estructura de tipo rejilla. Las propiedades electrónicas de las metalo-rejillas fueron analizadas a través de espectroscopía UV-Vis en cloroformo, metanol y diclorometano. Adicionalmente, se realizaron medidas de voltamperometría cíclica y voltametría de onda cuadrada en DMF. Los complejos exhibieron dos procesos de oxidación atribuidos al ligando orgánico y a varios eventos reductivos que comprometían al ligando y a los centros metálicos, por tanto, la interacción entre la naturaleza del ion metálico y la estructura del ligando fue analizada en detalle. Estos resultados representan un avance en la química de metalo-rejillas no solo por los escasos reportes de propiedades electroquímicas encontrados en la literatura, sino también por el diseño de nuevos ligandos hidrazónicos de alta solubilidad y fácil preparación.

Grid-type complexes of M2+ (M = Co, Ni, and Zn) with highly soluble bis(hydrazone)thiopyrimidine-based ligands: Spectroscopy and electrochemical properties

Herein we present the syntheses of two types of two-site symmetric bis(hydrazone) ligands (1 and 2) which contain two tridentate subunits suitable for metal ion complexation, with remarkable solubility in most organic solvents, contrary to other pyrimidine-based bis(hydrazones) used for the preparation of metallogrids. As expected, compounds 1 and 2 exhibit conformational changes when coordinated metal ions (Zn2+, Ni2+, Co2+) through the two terpyridine-like sites leading to the metal complexes 1a–c and 2a–c. The absorption spectra and redox properties of ligands 1 and 2 and of the metal complexes 1a–c and 2a–c were studied. Compounds 1 and 2 exhibit absorption spectra dominated by intense π–π∗ bands in the UV region, while the absorption spectra of the metal complexes 1a–c and 2a–c show intense bands in the UV region, due to the spin-allowed ligand-centred (LC) transitions, and in the visible region, due to spin-allowed metal-to-ligand charge transfer (MLCT) transitions. Cyclic voltammetry and square wave voltammetry were carried out in order to establish the relevance of the complexation, and the grid formation in the redox potentials of the ligands 1 and 2.

Surface Trapping and STM Observation of Conformational Isomers of a Bis(Terpyridine) Ligand from Metallosupramolecular Grids.

Tetranuclear Co-grid complexes incorporating bis-tridentate ligands, namely 4,6-bis(2,2'-bipyrid-6-yl)-2-phenylpyrimidine, were electrosprayed onto a Au(111) substrate under an ultrahigh vacuum. Fragmentation occurs leaving the ligands in four different conformations. Most ligands are found to form H-bonded dimers. The most abundant conformer of the ligand on the Au surface is an asymmetric form, which has not been observed before. The present results indicate that the fragmentation of coordination compounds during the deposition process, in principle, allows for surface trapping, identification, and investigation of high energy, out-of-equilibrium conformations of the ligand molecules at low temperatures, which otherwise would not be observable.

Hydrothermal Synthesis, Crystal Structures and Properties of Zinc(II) Di-nuclear Complex and Copper(I) Coordination Polymer Based on Building Block 2-Phenyl-4,6-di(pyridin-2-yl)pyrimidine

A tetradentate ligand of 2-phenyl-4,6-di(pyridin-2-yl)pyrimidine (L) has been synthesized and its complexes with ZnI2 and CuI have been obtained by hydrothermal method. single crystal X-ray diffraction analysis indicates that ligand L coordinates with Zn(II) ions to form a simple four-coordinate di-nuclear complex, while the complexation of L with Cu(I) constructs a one-dimensional chain polymer. The existence of I – ion hampers the L to assemble grid-type complexes with Zn(II) and Cu(I). Fluorescence spectra show that the L emits blue fluorescence while its Cu(I) polymer decrease the fluorescence intensity and Zn(II) complex quenches the fluorescence.

Novel self-assembled supramolecular architectures of Mn(ii) ions with a hybrid pyrazine–bipyridine ligand

A new hybrid pyrazine-bipyridine ligand L (C26H20N6) and its complexes with Mn(NO3)2, Mn(ClO4)2, MnCl2 and MnBr2 have been synthesised. By the self-assembly of L and Mn(II) ions three different kinds of supramolecular complexes have been obtained: binuclear baguette complex [Mn2L(H2O)6](NO3)4·2.5H2O 1 and tetranuclear [2 × 2] grid-type complex [Mn4L4](ClO4)8·2.5(CH3CN)·2CH3OH 2 and mononuclear complexes [MnL2]X2 (where X = Cl(-)3 and X = Br(-)4). Crystal structures and magnetic properties of Mn(II) complexes 1 and 2 have been also investigated. The crystal structures reveal that in both 1 and 2 complexes the Mn(II) ions have coordination number 6 and distorted octahedral coordination geometry. In 2 four metal cations and four ligands have assembled into a grid-type [2 × 2] array, with a perchlorate anion occupying the central cavity, with clearly a good fit for the center of the cavity. The perchlorate anion, in contrast to the nitrate anion, probably acts as a template in the formation of tetranuclear grid-type complexes. Magnetic susceptibility measurements indicate that the Mn(II) ions are all high spin, and in both 1 and 2 complexes there are weak antiferromagnetic interactions between Mn(II) ions.

Generation of metallosupramolecular polymer gels from multiply functionalized grid-type complexes

A ditopic ligand (1), containing two tridentate bis(acylhydrazone) subunits and bearing both long alkyl chains and hydrogen-bonding groups, has been synthesised. Metal cation binding in the presence of a base leads to hierarchical self-assembly, forming first a neutral [2 × 2] grid-type complex (2) that hierarchically assembles into metallosupramolecular polymer gels in toluene.

Cyclo-Tetra-kis(μ-3-acetyl-4-methyl-1H-pyrazole-5-carboxyl-ato-κN,O:N,O)tetra-kis[aqua-copper(II)] tetra-deca-hydrate.

The title compound, [Cu4(C7H6N2O3)4(H2O)4]·14H2O, a tetra­nuclear [2 × 2] grid-type complex with S4 symmetry, contains four CuII atoms which are bridged by four pyrazole­carboxyl­ate ligand anions and are additionally bonded to a water molecule. Each CuII atom is coordinated by two O atoms of the carboxyl­ate and acetyl groups, two pyrazole N atoms of doubly deprotonated 3-acetyl-4-methyl-1H-pyrazole-5-carb­oxy­lic acid and one O atom of a water mol­ecule. The geometry at each CuII atom is distorted square-pyramidal, with the two N and two O atoms in the equatorial plane and O atoms in the axial positions. O—H⋯O hydrogen-bonding interactions additionally stabilize the structure. One of the uncoordinated water molecules shows half-occupancy.

A series of tetranuclear [2 × 2] grid complexes derived from an asymmetric ligand: Structural differences based on metal ion affinities

A series of tetranuclear grid-type complexes were prepared by the reaction of the asymmetric multidentate ligand HL (HL = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridine carboxylic acid ethylester) with different metal sources. The tetranuclear copper complex, [Cu4(L1)4(NO3)4(H2O)4]·Et2O·2MeOH (1, HL1 = 2-[3-(2-hydroxyphenyl)-1H-pyrazol-5-yl]-6-pyridine carboxylic acid methyl ester) consists of four ligands, four copper ions, four nitrate ions and four water molecules, forming a [2 × 2] grid structure, in which all four copper ions have the same coordination environment. On the other hand, the corresponding nickel and cobalt complexes, [M4(L2)4(H2O)4]·4MeOH·6H2O (M = Ni (2) and Co (3), (H2L2 = 6-[1,3-dioxo-3-(2-phenyl)propionyl]pyridine-2-carboxylic acid)), have a similar grid core structure to the copper complex with four metal ions, four ligand molecules, and four water molecules, however, in these clusters there are two kinds of coordination site for the metal ions. Temperature-dependent magnetic susceptibility measurements for all complexes demonstrated that antiferromagnetic interactions between the metal ions were in operation. The magnetic susceptibility data of the copper and nickel complexes were analyzed using a tetranuclear model based on H = –2J(S1S2+S2S3+S3S4+S4S1) to give best-fit parameters of g = 2.11(1), J = –1.39(3) cm–1 and g = 2.19(1), J = –0.44(2) cm–1, respectively.

One-Pot Synthesis of a New Magnetically Coupled Heterometallic Cu2Mn2 [2 × 2] Molecular Grid

The heterometallic [2 x 2] grid-type complex [Cu(2)Mn(2)(pop)(4)(OAc)(4)].7H(2)O (1) has been selectively synthesized in a targeted one-pot reaction. Single-crystal X-ray analysis shows the expected structure with identical metal ions located at diagonal vertices of the grid. Magnetochemical studies reveal that 1 has a ferrimagnetic spin ground state with some admixture of low-lying excited states.

Quantum chemical studies on chameleonic ligand and its grid-type copper(I) and zinc(II) complexes

Abstract The reactions of the chameleonic ligand L , comprising NNO donor atom units, with appropriate metal ions lead to different structural motifs of resulting compounds depending on the kind of metal ions used in coordination. Quantum mechanical MP2 and B3LYP calculations provided insight into conformational diversity of the chameleonic ligand, its recognition process and the electronic structure of Zn(II) and Cu(I) complexes. The conformation of the chameleonic ligand capable of forming complexes with metals is energetically disfavored by about 5 kcal mol −1 for each half of the molecule due to steric repulsion between aromatic hydrogen atoms. Thus, energy exerted during complexes formation must at least balance the adoption of energetically unfavorable conformation of the ligand itself. We examined the self-organization process occurring between the chameleonic ligand and isoelectronic cation centers Zn(II) leading to tetranuclear grid-type complex with Zn center coordinated octahedrally and Cu(I) center generating [2 × 2] grid with Cu atom coordinated tetrahedrally. Our calculations suggest that the energetical cost of adopting geometry suitable for forming octahedral complexes is by further ca. 5 kcal mol −1 less favorable than for tetrahedral ones. In the case of Cu(I) and Zn(II) complexes it means that for Cu(I) tetrahedral coordination is energetically preferred by 15.2 kcal mol −1 while octahedral coordination is energetically favored by 18.5 kcal mol −1 over tetrahedral coordination for Zn(II). These results are a consequence of preferred metal coordination geometry and their electronic properties.

Self‐Assembly of Alkoxy‐Substituted Bis(hydrazone)‐Based Organic Ligands and of a Metallosupramolecular Grid on Graphite

Self-assembly of a bis(hydrazone) chelating ligand functionalized with octadecyloxy substituents is described, as well as the reproducible thermally activated self-assembly of its metallosupramolecular cationic Co(II) [2x2] grid-type complex, on a highly oriented pyrolitic graphite (HOPG) substrate. Scanning tunnelling microscopy measurements at the solid/liquid interface reveal that the grid units of the annealed films are oriented edge-on to the basal plane of the HOPG, which indicates that the influence of the octadecyl chains is not sufficient to tie the grids into a face-on orientation. To gain a detailed understanding of the self-assembly behaviour of the grid on HOPG, the results for the grid itself have been compared to those of its constituent ligands.

Highly Sensitive Magnetic Effects Induced by Hydrogen‐Bonding Interactions in a High‐Spin Metallosupramolecular Fe4II [2×2] Grid‐Type Complex

A sensitive magnetic nanoprobe: Hydrogen-bonding interactions are reflected with great sensitivity in the (1)H NMR spectra of a high-spin multinuclear Fe(4) (II) [2x2] grid-type complex (see scheme) and the measured shifts can be used to evaluate the hydrogen-bond donating ability. The grid complex also represents a prototype of a very sensitive magnetic nanoreceptor for the detection of very small changes around a magnetic center.

A [2 × 2] nickel(ii) grid and a copper(ii) square result from differing binding modes of a pyrazine-based diamide ligand

The potentially bis-terdentate diamide ligand N,N'-bis[2-(2-pyridyl)ethyl]pyrazine-2,3-dicarboxamide (H(2)L(Et)) was structurally characterised. Potentiometric titrations revealed rather low pK(a) values for the deprotonation of the first amide group of H(2)L(Et) (14.2) and N,N'-bis(2-pyridylmethyl)pyrazine-2,3-dicarboxamide (H(2)L(Me), 13.1). Two tetranuclear copper(ii) square complexes of H(2)L(Et) with a paddle-wheel appearance, in which each ligand strand acts as a linear N(3)-NO hybrid terdentate-bidentate chelate, have been isolated and structurally characterised. Complex [Cu(II)(4)(H(2)L(Et))(2)(HL(Et))(2)](BF(4))(6).3MeCN.0.5H(2)O (.3MeCN.0.5H(2)O), with two nondeprotonated zwitterionic ligand strands and two monodeprotonated ligand strands, is formed in the 1 : 1 reaction of H(2)L(Et) and Cu(BF(4))(2).4H(2)O. It has a polymeric chain structure of tetranuclear subunits connected by N-H[dot dot dot]N hydrogen bonds. The same reaction carried out with one equivalent of base gives the related compound [Cu(II)(4)(HL(Et))(4)](BF(4))(4) (), with all four ligand strands monodeprotonated. It consists of isolated tetranuclear units. In both .3MeCN.0.5 H(2)O and the copper(ii) ions are in five-coordinate N(4)O environments but the degree of trigonality (tau) differs [.3MeCN.0.5H(2)O 0.14 </=tau</= 0.26; tau = 0.45]. Under the same reaction conditions as for but using Ni(BF(4))(2).6H(2)O a tetranuclear [2 x 2] grid-type complex, [Ni(II)(4)(HL(Et))(4)](BF(4)).10H(2)O (.10H(2)O), is formed. The structure determination showed that the nickel(ii) ions have N(6) distorted octahedral coordination spheres and all four ligand strands are monodeprotonated and act as N(3)-N(3) bis-terdentate chelates. Magnetic susceptibility data show that the complexes .4H(2)O, and .10H(2)O exhibit very weak antiferromagnetic spin coupling. The energies and multiplicities of the spin states of .4H(2)O and were determined from the temperature dependence of the magnetic susceptibility and indicate that a singlet state is lowest and the quintet state highest. This is consistent with the X-band EPR spectra of polycrystalline powders of .4H(2)O and , measured down to 2.3 K, where the resonances observed at the lowest temperature are due to a triplet state. The g-values of the individual ions of are consistent with the expected d(x(2)-y(2)) ground state for five-coordinate copper(ii) in an approximately square pyramidal configuration.

Pyrazolate-based copper(ii) and nickel(ii) [2 × 2] grid complexes: protonation-dependent self-assembly, structures and properties

The pyrazole-based diamide ligand N,N'-bis(2-pyridylmethyl)pyrazole-3,5-dicarboxamide (H(3)L) has been structurally characterised and successfully employed in the preparation of [2 x 2] grid-type complexes. Thus, the reaction of H(3)L with Cu(ClO(4))2.6H(2)O or Ni(ClO(4))2.6H(2)O in the presence of added base (NaOH) affords the tetranuclear complexes [M(4)(HL(4))].8H(2)O (1: M = Cu, 2: M = Ni). Employment of a mixture of the two metal salts under otherwise identical reaction conditions leads to the formation of the mixed-metal species [Cu(x)Ni(4-x)(HL)(4)].8H(2)O (x<or= 4; for x = 2: 3). Complexes 1-3 have been structurally characterised and found to be isomorphous, with each ligand strand acting as a hybrid N3-NO chelator. The copper ions in 1 are in a distorted square-pyramidal N(4)O coordination environment with rather long M-O(apical) distances. The coordination sphere about the nickel ions in 2 is roughly the same, but with even longer M...O distances, and it is therefore best described as N4 square-planar with low-spin nickel(II) ions. The single crystal X-ray data obtained for the mixed-metal complex 3 gave the best results assuming a statistical distribution of copper and nickel ions. X-Band EPR spectra of 1 and 2 indicate magnetically coupled copper(II) ions and low-spin nickel(II), respectively. EPR spectra of a powdered sample of a complex with the general formulation [Cu(x)Ni(4-x)(HL)4].8H(2)O with a large excess of Ni(2+) (95%) was shown to be characteristic for individual copper(II) ions in the tetranuclear grid system. Magnetic susceptibility data of 1 indicate weak antiferromagnetic spin coupling between the copper ions (J = -8.2 +/- 0.4 cm(-1)), which is explained by the particular spatial arrangement of the magnetic orbitals.