Tetranuclear Complex Research Articles

Di-aqua-bis-{μ-1,5-bis-[(pyridin-2-yl)methyl-idene]carbonohydrazide(1-)}di-μ-chlorido-tetra-chlorido-tetra-zinc(II).

A tetra-nuclear ZnII complex, [Zn4(C13H11N6O)2Cl6(H2O)2] or {[Zn2(HL)(H2O)(Cl2)](μCl)2[Zn2(HL)(H2O)(Cl)]}2, was synthesized by mixing an equimolar amount of a methanol solution containing ZnCl2 and a methanol solution containing the ligand H2 L [1,5-bis-(pyridin-2-yl-methyl-ene)carbono-hydrazide]. In the tetra-nuclear complex, each of the two ligand mol-ecules forms a dinuclear unit that is connected to another dinuclear unit by two bridging chloride anions. In each dinuclear unit, one ZnII cation is penta-coordinated in a N2OCl2 in a distorted square-pyramidal geometry, while the other ZnII cation is hexa-coordinated in a N3OCl2 environment with a distorted octa-hedral geometry. The basal plane around the penta-coordinated ZnII cation is formed by one chloride anion, one oxygen atom, one imino nitro-gen atom and one pyridine nitro-gen atom with the apical position occupied by a chloride anion. The basal plane of the hexa-coordinated ZnII cation is formed by one chloride anion, one hydrazinyl nitro-gen atom, one imino nitro-gen atom and one pyridine nitro-gen atom with the apical positions occupied by a water oxygen atom and a bridged chloro anion from another dinuclear unit, leading to a tetra-nuclear complex. A series of intra-molecular C-H⋯Cl hydrogen bonds is observed in each tetra-nuclear unit. In the crystal, the tetra-nuclear units are connected by inter-molecular C-H⋯Cl, C-H⋯O and N-H⋯O hydrogen bonds, forming a planar two-dimensional structure in the ac plane.

Mechanistic study in azide-alkyne cycloaddition (CuAAC) catalyzed by bifunctional trinuclear copper(I) pyrazolate complex: Shift in rate-determining step

Trinuclear copper(I) pyrazolate [Cu(3,5-(CF3)2Pz)]3 was employed in a mechanistic study of azide-alkyne cycloaddition (CuAAC). It was shown that the copper complex operates as a bifunctional catalytic system (copper source and Brønsted base) under mild conditions (RT and air atmosphere) at low catalyst loading (1 mol%). The rate-determining step of the reaction is the first C-N bond formation between azide and acetylene (azide migratory insertion) but not the copper(I) acetylide formation as commonly assumed. It was supported by the observed kinetic isotope effect equaling 1.1 and by DFT calculations. The reaction has a second-order dependence on the catalyst concentration implicating the two copper(I) centers participate in the metallacycle formation step from “bis-butterfly” tetranuclear complex Cu4L4(RC≡CH)2 in the rate-determining step. DFT calculations proved that the pyrazolate ligand acts as a Brønsted base and deprotonates the acetylene molecule providing successful catalysis. A plausible catalytic cycle of the reaction has constructed based on DFT calculations.

Syntheses, structures and catalysis of tetranuclear zinc N-alkoxide ketoiminate complexes for ring-opening polymerization of rac-lactide

Two tetranuclear zinc complexes 2a and 2b bearing tridentate N-alkoxide ketoiminate ligands have been synthesized and fully characterized by single-crystal X-ray structure analysis, NMR spectroscopy together with elemental analyses. Both of 2a and 2b can act as active catalysts in the ring-opening polymerization (ROP) of racemic-lactide (rac-LA) without additional co-initiators, either in solution or under industrially preferred melt conditions (130 °C no solvent). To be noted, 2a and 2b show remarkable activities for bulk rac-LA polymerization even with low catalyst loading of 0.1 mol%, yielding polymers with high molecular weights (Mn) of up to 91,200 g/mol (2b), and very high turnover frequencies (TOF) of 19,000 h−1 (2b) and 19,800 h−1 (2a).

Synthesis, characterization and DFT studies of water stable Cd(II) metal–organic clusters with better adsorption property towards the organic pollutant in waste water

In this report, two water stable Cd(II) metal–organic clusters using slow evaporation method are designed and synthesized in order to explore for functional applications. The complexes are formulated as [Cd2(pda)2(H2O)6].(H2pda)2 (1) and [Cd4(Hpda)4(µ2-OH)2(Cl)2(H2O)6].2H2O (2) where H2pda = 2,6-pyridine dicarboxylic acid. The synthesized complexes show unusual hepta-coordinated geometry around the central metal ion. 1 is dinuclear while 2 is a tetranuclear discrete complex. The tetranuclear complex is the very first example of cadmium with H2pda ligand. The two complexes were characterized by various spectroscopic studies and with the help of single crystal technique the, structures of 1 and 2 was elucidated. Various non covalent interactions such as π-π and CH…π consolidate the network against water solubility. The metal–organic clusters exhibit various non-covalent interactions which were further verified by Hirshfeld surface analysis. The DFT calculations were also performed on both the complex which corroborate the electronic and spectral aspects of complexes. The stability of 1 and 2 was checked using the PXRD pattern of 1 and 2 after 10 hrs in water and it shows the identical pattern even after the 24 hrs. Further, the metal–organic clusters were checked for their adsorption property towards the cationic dye such as Rhodamine B. Out of the two complexes, only 2 shows better adsorption property due to its better stability in water. The mechanism of dye adsorption is also explored.

Design and self-assembly of new [2 × 2] grids constructed by lanthanide ions and a Schiff base

[2 × 2] grids of general formula [Ln4L4Cl4(DMF)4].2H2O (Ln = Sm (1), Eu (2), Tb (3); H2L = (E)-N’-((E)-(hydroxyimino)butan-2ylidene)salicylolhidrazide; DMF = dimethylformamide) were successfully constructed using a lanthanide ion as corners and L2-, a Schiff base, as linkers. The single crystal X-ray diffraction study reveals that compounds 1 and 3 are neutral tetranuclear complexes. They feature a [2 × 2] grid distorted skeleton. Coordination sphere of Ln ions are completed by one chloro ligand and a solvent molecule. The grids were obtained after a careful study of the chemical speciation of these systems performed by potentiometric titrations (25.0 °C in 40:60 DMF:water mixture, I = 0.50 mol L-1 NMe4Cl).

The crystal structure of tetrameric copper(II) complexes, Hirshfeld surface analysis, and vector analyses of Cu4OCl6L4 complexes with N-donor ligands

It is known, that in the Cu4OX6L4 (X = Cl, Br) complexes can be present many different ligands L, including bioligands. The synthesis and characterization of Cu4OBCl6(ron)4 (1) and Cu4OCl6(3-Mepy)4 (2) (where ron is ronicol or 3-methanolpyridine and 3-Mepy is 3-methylpyridine) are reported. The complexes under study were X-ray structure analysis and Hirshfeld surface analysis. Tetranuclear Cu4OX6L4 complexes with molecular structure (Fig. 1) can help to better understand the role of donor–acceptor and electron-transfer properties in copper proteins. The coordination sphere about each copper(II) atom is trigonal bipyramidal with three chlorine atoms in the equatorial plane. The apical positions are occupied by the central oxygen atom and the nitrogen atom of the respective ligand (CuCl3ON). Here are studied chloridocomplexes of some N-donor ligands, L = chloro-promazine, ronicol (3-pyridylmethanol), 2-ethylpyrazine, seven derivatives of pyrazol and for comparisons 3-methylpyridine. The Cu4OCl6L4 molecule is regarded as a supramolecular model of interactions between bioligand L and hypothetical “round-shaped” coordination tetra-receptor Cu4OCl6. Vector calculations applied usualy to mechanical and electrical macroconstructions are here applied to microconstructions represented by structures of Cu4OX6L4 molecules. For vector calculations each Cu4OX6L4 structure is placed (Fig. 1) into the three-dimensional Cartesian coordinate system with the central oxygen atom O1 placed in its origin 0. Studied bioligands are compared and described by molecular structural dynamics and corresponding shifts of electron densities by means of bond lenghts (O1–Cu, Cu–L, Cu–X) and structural distances (O1···X, O1···L).

Cooperative Binding and Stepwise Encapsulation of Drug Molecules by Sulfonylcalixarene-Based Metal-Organic Supercontainers.

The cooperative binding behavior of a face-directed octahedral metal-organic supercontainer featuring one endo cavity and six exo cavities was thoroughly examined in chloroform solution through ultraviolet-visible (UV-Vis) titration technique using two representative drug molecules as the guests. The titration curves and their nonlinear fit to Hill equation strongly suggest the efficient encapsulation of the guest molecules by the synthetic host, which exhibit interesting cooperative and stepwise binding behavior. Based on the control experiments using tetranuclear complex as a reference, it is clear that two equivalents of the guest molecules are initially encapsulated inside the endo cavity, followed by the trapping of six additional equivalents of the drug molecules through six exo cavities (1 eq. per exo cavity), and the remaining guests are entrapped by the external pockets. The results provide an in-depth understanding of the cooperative binding behavior of metal-organic supercontainers, which opens up new opportunities for designing synthetic receptors for truly biomimetic functional applications.

Monomeric and tetrameric mercury(II) complexes with iodo and N2O2/N3O ligands: Structure and blue luminescence

The reaction of mercury(II) iodide and potential tetradentate ligand N-(2-pyridylmethyl)iminodiethanol (H2pmide) or N,N-bis(2-pyridylmethyl)-2-aminoethanol (bpaeOH) leads to the isolation of monomeric complex [Hg(H2pmide)(I)2] (1) and tetrameric {[Hg2(bpaeOH)2][Hg2I7]I} (2). The crystal structures of 1 and 2 have been characterized by single crystal X-ray crystallography. In mononuclear neutral complex 1, the Hg(II) ion is bonded with one H2pmide species and two iodide anions as a distorted square pyramidal structure. 2 is a tetranuclear neutral complex that is composed of two [Hg(bpaeOH)]2+ cations and one [Hg2I7]3− anion as well as additional I− anion. The [Hg2I7]3− species connected to both the [Hg(bpaeOH)]2+ and [Hg(bpaeOH)(I)]+ units on the opposite side, which gives rise to the tetranuclear structure. 1 shows strong fluorescent emission at 412 nm with a blue color in methanol solution, while 2 displays very weak emission at 467 nm in the solid state. Particularly, in the case of 1, quantum yield is ca. 8.1% and fluorescence decay lifetime is ca. 1.95 ns.

Aromatic dicarboxylate incorporated new di- and tetranuclear cobalt(II) complexes: Synthetic and structural aspects, and evaluation of properties and catalytic activity

The synthetic and structural aspects as well as evaluation of magnetic properties and catalytic activity toward aerial oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylbenzoquinone of three new, two di- and one tetranuclear cobalt(II) complexes, [Co2(cpdp)(Hphth)]∙5H2O (1), [Co2(cpdp)(Hisophth)] (2) and [Co4(cpdp)2(terephth)]∙4.5CH3OH·5.5H2O (3), based on a symmetrical multidentate ligand, N,N'-Bis[2-carboxybenzomethyl]-N,N'-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol (H3cpdp) in combination with exogeneous aromatic dicarboxylic acids, such as phthalic acid (H2phth), isophthalic acid (H2isophth) and terephthalic acid (H2terephth) are reported. All three coordination complexes are characterized by microanalysis, solution electrical conductivity, FTIR, UV–Vis, mass spectrometry and cyclic voltammetry, including single crystal X-ray diffraction studies of 1 and 3. Structural studies reveal that complexes 1, 2 and 3 are comprised of [CoII2(µ-Hphth)], [CoII2(µ-Hisophth)] and [CoII4(µ4-terephth)] cores, respectively, linked by symmetrical ligand, cpdp3−. In the present complexes, the cobalt(II) ions are penta-coordinated exhibiting trigonal bipyramidal/square pyramidal geometry that is substantially distorted. In fact, tetranuclear complex 3 can be viewed as a “dimer-of-dimers” formed by self-assembly of two [CoII2(cpdp)]+ units absolutely bridged by one μ4:η1:η1:η1:η1 terephthalate group. Magnetic susceptibility studies show that the cobalt(II) ions in 1 and 3 are coupled antiferromagnetically, with J values of −13.7(1) and −13.4(2) cm−1, respectively. The catalytic activity of all three complexes has been investigated toward aerial oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylbenzoquinone. Kinetic data analysis following Michaelis-Menten treatment discloses that the catecholase-like activity of the complexes is influenced by the flexibility of the ligand cpdp3− that maintains the favourable metal-metal cooperativity and also by the geometry around the metal centers. To the best of our knowledge, to date very few di- and tetranuclear cobalt(II) complexes have been found in the literature to manifest the catecholase-like activity.

Reaction Chemistry of the syn-[Mo2O2(μ-S)2(S2)(DMF)3] Complex with Cyanide and Catalytic Thiocyanate Formation.

Removal of cyanide as nontoxic thiocyanate under physiological conditions may serve as a catalytic detoxification route in vivo. Aqueous catalytic reaction conditions were explored where at the conditions employed the reaction proceeded to exhaustion in 1 h. The complex, syn-[Mo2O2(μ-S)2(S2)(DMF)3] 1, participates in a ligand exchange reaction of the dimethylformamide ligands and cyanide. Simultaneous sulfur abstraction reaction from the terminal disulfide group forms thiocyanate and terminal sulfido ligand. Respective reaction rates for the two reactions appear competitive where different products were isolated solely based on change of reaction temperature. The approach to determine the number of cyanide ligands participating in the ligand exchange reaction by varying the stoichiometry and reaction temperature led to identification and isolation of tetranuclear complexes 2 and 5 and dinuclear complexes 3, 4, and 6. A synthesized and fully characterized thiocyanate analog of 6 (7) supports spectroscopic characterization of 6. The tetranuclear anion, [Mo4O4(μ-S)6(CN)4]4-, 2, was crystallized from a reaction at ambient temperature. The dinuclear anion, [Mo2O2(μ-S)2(S)(CN)3]3-, 3, was crystallized from similar reaction conditions at lower temperature. The reaction yield of thiocyanate obtained at pH of 7.4 and at 9.2 as a function of time, for several ratios of cyanide, favors the sulfur abstraction reaction at elevated pH. The sulfur abstraction reaction is the first step in a proposed mechanism of the reaction of cyanide and thiosulfate to form thiocyanate and sulfite by 1.

Successive Protonation and Methylation of Bridging Imido and Nitrido Ligands at Titanium Complexes

The reactions of nitrido complexes [{Ti(η5-C5Me5)(μ-NH)}3(μ3-N)] (1) and [{Ti(η5-C5Me5)}4(μ3-N)4] (2) with electrophilic reagents ROTf (R = H, Me; OTf = OSO2CF3) in different molar ratios have allowed the structural characterization of a series of titanium intermediates en route to the formation of the ammonium salts [NR4]OTf and [NR4][Ti(η5-C5Me5)(OTf)4]. The treatment of the trinuclear imido-nitrido complex 1 with 5.5 equiv of triflic acid in toluene at room temperature led to the dinuclear complex [Ti2(η5-C5Me5)2(μ-N)(NH3)(μ-O2SOCF3)2(OTf)] (3) and [NH4]OTf. Compound 3, along with the ammonium salts [NMe4]OTf and [NMe4][Ti(η5-C5Me5)(OTf)4] (5), was also obtained in the reaction of 1 with 8 equiv of methyl triflate in toluene at 100 °C. The trinuclear complex [Ti3(η5-C5Me5)3(μ-N)(μ-NH)2(μ-O2SOCF3)(OTf)] (4), an intermediate in the formation of 3, was isolated in the treatment of 1 with 4 equiv of MeOTf, although compound 4 was prepared in better yield by treatment of 1 with Me3SiOTf (2 equiv). Addition of a large excess of MeOTf or HOTf reagents to solutions of 3 resulted in the clean formation of ammonium salts [NR4][Ti(η5-C5Me5)(OTf)4] (R = Me (5), H (6)). Treatment of the tetranuclear nitrido complex [{Ti(η5-C5Me5)}4(μ3-N)4] (2) with 1 equiv of ROTf in toluene afforded the precipitation of the ionic compounds [{Ti(η5-C5Me5)}4(μ3-N)3(μ3-NR)][OTf] (R = H (8), Me (9)), while a large excess of HOTf led to the formation of [{Ti(η5-C5Me5)}4(μ3-N)3(μ3-NH)][Ti(η5-C5Me5)(OTf)4(NH3)] (10) by rupture of a fraction of tetranuclear molecules. Complex 2 reacted with 1 equiv of [M(η5-C5H5)(CO)3H] (M = Mo, Cr) via hydrogenation of one nitrido ligand to give the molecular derivative [{Ti(η5-C5Me5)}4(μ3-N)3(μ3-NH)] (11) and [{M(η5-C5H5)(CO)3}2], while a second 1 equiv of [M(η5-C5H5)(CO)3H] produced the ionic compounds [{Ti(η5-C5Me5)}4(μ3-N)2(μ3-NH)2][M(η5-C5H5)(CO)3] (M = Mo (12), Cr (13)) by protonation of another nitrido group. The X-ray crystal structures of 3-5, 9, 10, and 13 were determined.

Molecular Thorium Trihydrido Clusters Stabilized by Cyclopentadienyl Ligands.

Hydrogenolysis of alkyl-substituted cyclopentadienyl (CpR ) ligated thorium tribenzyl complexes [(CpR )Th(p-CH2 -C6 H4 -Me)3 ] (1-6) afforded the first examples of molecular thorium trihydrido complexes [(CpR )Th(μ-H)3 ]n (CpR =C5 H2 (t Bu)3 or C5 H2 (SiMe3 )3 , n=5; C5 Me4 SiMe3 , n=6; C5 Me5 , n=7; C5 Me4 H, n=8; 7-10 and 12) and [(Cp# )12 Th13 H40 ] (Cp# =C5 H4 SiMe3 ; 13). The nuclearity of the metal hydride clusters depends on the steric profile of the cyclopentadienyl ligands. The hydrogenolysis intermediate, tetra-nuclear octahydrido thorium dibenzylidene complex [(Cpttt )Th(μ-H)2 ]4 (μ-p-CH-C6 H4 -Me)2 (Cpttt =C5 H2 (t Bu)3 ) (11) was also isolated. All of the complexes were characterized by NMR spectroscopy and single-crystal X-ray analysis. Hydride positions in [(CpMe4 )Th(μ-H)3 ]8 (CpMe4 =C5 Me4 H) were further precisely confirmed by single-crystal neutron diffraction. DFT calculations strengthen the experimental assignment of the hydride positions in the complexes 7 to 12.

Host-Guest Chemistry of Porphyrins in Liquid Crystalline Macrocycles

Structurally well-defined macrocyclic molecules have great potential to accommodate specific guest molecules in the hollow. Recently, we have reported a series of macrocycles which are composed of four carbazoles connected with four salphen ligands1, four dibenzothiophenes connected with four salen ligands2, or four diindrocarbazoles connected with four salphen ligands3 (MC1, MC2 and MC3, respectively). The macrocycles with appropriate peripheral alkyl chains and their tetranuclear metal complexes with square planar metal ions showed thermotropic columnar liquid crystalline properties1,2. These macrocycles stacked to form columns inside the fluid materials. Especially, the giant macrocycle MC3 contained a square hollow with a diagonal of 2.5 nm. This giant macrocycle has the largest inner cavity among known discrete shape-persistent macrocycles that exhibit thermotropic LC properties. The size and shape of the hollow structure make it interesting for molecular inclusion applications. For example, MC3 molecule can accommodate a tetrapyridylporphyrin inside the hollow to afford a planar conjugate, and the conjugate showed liquid crystalline behavior. Reference: [1] S. Kawano, Y. Ishida, and K. Tanaka, J. Am. Chem. Soc. 2015, 137, 2295.[2] Kawano, S.; Hamazaki, T.; Suzuki, A.; Kurahashi, K.; Tanaka, K. Chem. Eur. J. 2016, 22, 15674-15683.[3] Kawano, S.; Kato, M.; Somiya, S.; Nakayama, M.; Onoe, J.; Tanaka, K. Angew. Chem. Int. Ed. 2018, 57, 167–171. Figure 1

Periodicity of Single-Molecule Magnet Behaviour of Heterotetranuclear Lanthanide Complexes across the Lanthanide Series: A Compendium.

Acetato-bridged palladium-lanthanide tetranuclear heterometallic complexes of the form [Pd2 Ln2 (H2 O)2 (CH3 COO)10 ]⋅2 CH3 COOH [Ln2 =Ce2 (1), Pr2 (2), Nd2 (3), Sm2 (4), Tb2 (5), Dy2 (6), Dy0.2 Y1.8 (6''), Ho2 (7), Er2 (8), Er0.24 Y1.7 (8''), Tm2 (9), Yb2 (10), Y2 (11)] were synthesised and characterised by experimental and theoretical techniques. All complexes containing Kramers lanthanide ions [Ln3+ =Ce (1), Nd (3), Sm (4), Dy (6), DyY (6''), Er (8), ErY (8''), Yb (10)] showed field-induced slow magnetic relaxation, characteristic of single-molecule magnetism and purely of molecular origin. In contrast, all non-Kramers lanthanide ions [Ln3+ =Pr (2), Tb (5), Ho (7), Tm (9), Y3+ (11) is diamagnetic and non-lanthanide] did not show any slow magnetic relaxation. The variation in the electronic structure and accompanying consequences across the complexes representing all Kramers and non-Kramers lanthanide ions were investigated. The origin of the magnetic properties and the extent to which the axial donor-acceptor interaction involving the lanthanide ions and an electron-deficient orbital of palladium affects the observed magnetic and electronic properties across the lanthanide series are presented. Unique consistent electronic and magnetic properties of isostructural complexes spanning the lanthanide series with properties dependent on whether the ions are Kramers or non-Kramers are reported.

Synthesis, crystal structure and magnetic properties of tetranuclear copper complex based on [(4-bromophenyl)(hydroxy)methylene]bis(phosphonic acid)

The tetranuclear Cu(II) complex [Cu4(3-Mepy)8(H2L)2(ClO4)2]·(3-Mepy)2·(H2O)2 (1), where H5L = [(4-bromophenyl)(hydroxy)methylene]bis(phosphonic acid) and 3-Mepy = 3-methylpyridine, was prepared and characterized by elemental analysis, FT-IR spectroscopy, single-crystal X-ray analysis and magnetic measurements. The analysis of magnetic properties of 1 supported by DFT theoretical calculations revealed interplay between ferromagnetic exchange (J2 = J3 = 20.0 cm-1) and antiferromagnetic exchange (J1 = -64.4 cm-1) leading to S = 0 ground spin state.

A Mixed-Valence Tetra-Nuclear Nickel Dithiolene Complex: Synthesis, Crystal Structure, and the Lability of Its Nickel Sulfur Bonds

In this study, by employing a common synthetic protocol, an unusual and unexpected tetra-nuclear nickel dithiolene complex was obtained. The synthesis of the [Ni4(ecpdt)6]2− dianion (ecpdt = (Z)-3-ethoxy-3-oxo-1-phenylprop-1-ene-1,2-bis-thiolate) with two K+ as counter ions was then intentionally reproduced. The formation of this specific complex is attributed to the distinct dithiolene precursor used and the combination with the then coordinated counter ion in the molecular solid-state structure, as determined by X-ray diffraction. K2[Ni4(ecpdt)6] was further characterized by ESI-MS, FT-IR, UV-Vis, and cyclic voltammetry. The tetra-nuclear complex was found to have an uncommon geometry arising from the combination of four nickel centers and six dithiolene ligands. In the center of the arrangement, suspiciously long Ni–S distances were found, suggesting that the tetrameric structure can be easily split into two identical dimeric fragments or two distinct groups of monomeric fragments, for instance, upon dissolving. A proposed variable magnetism in the solid-state and in solution due to the postulated dissociation was confirmed. The Ni–S bonds of the “inner” and “outer” nickel centers differed concurrently with their coordination geometries. This observation also correlates with the fact that the complex bears two anionic charges requiring the four nickel centers to be present in two distinct oxidation states (2 × +2 and 2 × +3), i.e., to be hetero-valent. The different coordination geometries observed, together with the magnetic investigation, allowed the square planar “outer” geometry to be assigned to d8 centers, i.e., Ni2+, while the Ni3+ centers (d7) were in a square pyramidal geometry with longer Ni–S distances due to the increased number of donor atoms and interactions.

Structures, magnetic properties, and EPR studies of tetranuclear copper(II) complexes [Cu4(OH)4L4]4+ (L = bpa, bipy) stabilized by anions containing decahydro-closo-decaborate anion

Tetranuclear copper(II) cationic complex [Cu4(bpa)4(OH)4]4+ stabilized by chained polymeric silver(I) anionic complex {Ag[B10H10]}nn− and two DMF molecules with the general formula {[Cu4(bpa)4(OH)4(DMF)2][Ag[B10H10]]4·10 DMF}n has been synthesized. The target complex has been prepared in one step when [Ag2[B10H10]] was allowed to react with CuCl in the presence of bpa in DMF; the reaction has been performed in air. Copper(I) has been oxidized in air in the presence of bpa to form the tetranuclear cationic complex. The target compound has been studied by IR spectroscopy as well as powder and single crystal X-ray diffractions. The electronic structure and magnetic properties of the complex have been studied by EPR spectroscopy and magnetic susceptibility methods and the obtained data have been compared with those obtained for related tetranuclear bipy-contained copper(II) complexes [Cu4(bipy)4(OH)4][Cu2[B10H10]3]·4CH3CN and {[Cu4(bipy)4(OH)4][B10H10]2(DMSO)2} with the known structures. The magnetic properties of three compounds under study are different; the magnetic moment has been found to increase, to decrease and remain unchanged when increasing temperature.

Topological Analysis of Ag-Ag and Ag-N Interactions in Silver Amidinate Precursor Complexes of Silver Nanoparticles.

A series of silver amidinate complexes has been studied both experimentally and theoretically, in order to investigate the role of the precursor complex in the control of the synthesis of silver nanoparticles via an organometallic route. The replacement of the methyl substituent of the central carbon atom of the amidinate anion by a n-butyl group allows for the crystallization of the tetranuclear silver amidinate complex 3 instead of a mixture of di- and trinuclear silver amidinate complexes 1 and 2, as obtained with a methyl substituent. The relative stabilities and dissociation schemes of various isomeric arrangements of silver atoms in 3 are investigated at the computational DFT level of calculation, depending on the substituents of the amidinate ligand. The tetranuclear silver amidinate complex 4, exhibiting a diamondlike arrangement of the four silver atoms, is also considered. Ag-N bonds and argentophilic Ag-Ag interactions are finely characterized using ELF and QTAIM topological analyses and compared over the series of the related di-, tri-, and tetranuclear silver amidinate complexes 1-4. In contrast to the Ag-N dative bonds very similar over the series, argentophilic Ag-Ag interactions of various strengths and covalence degree are characterized for complexes 1-4. This gives insight into the role of the amidinate substituents on the nuclearity and intramolecular chemical bonding of the silver amidinate precursors, required for the synthesis of dedicated AgNPs with chemically well defined surfaces.

Self-assembled conjoined-cages

A self-assembled coordination cage usually possesses one well-defined three-dimensional (3D) cavity whereas infinite number of 3D-cavities are crafted in a designer metal-organic framework. Construction of a discrete coordination cage possessing multiple number of 3D-cavities is a challenging task. Here we report the peripheral decoration of a trinuclear [Pd3L6] core with one, two and three units of a [Pd2L4] entity for the preparation of multi-3D-cavity conjoined-cages of [Pd4(La)2(Lb)4], [Pd5(Lb)4(Lc)2] and [Pd6(Lc)6] formulations, respectively. Formation of the tetranuclear and pentanuclear complexes is attributed to the favorable integrative self-sorting of the participating components. Cage-fusion reactions and ligand-displacement-induced cage-to-cage transformation reactions are carried out using appropriately chosen ligand components and cages prepared in this work. The smaller [Pd2L4] cavity selectively binds one unit of NO3−, F−, Cl− or Br− while the larger [Pd3L6] cavity accommodates up to four DMSO molecules. Designing aspects of our conjoined-cages possess enough potential to inspire construction of exotic molecular architectures.

Heteronuclear Iron(III)-Schiff Base Complexes with the Hexacyanidocobaltate(III) Anion: On the Quest To Understand the Governing Factors of Spin Crossover.

Two heteronuclear compounds (1 and 2) containing three ferric centers linked in facial-like mode with the magnetically silent hexacyanidocobaltate(III) anion were prepared and studied. The structural investigation revealed that both compounds are tetranuclear complexes with molecular formulas of [{Fe(L1)NC}3Co(CN)3]·2CH3OH·2.5CH3CN (1) and [{Fe(L2)NC}3Co(CN)3]·2H2O·1CH3OH (2). The magnetic properties of both complexes are controlled by the molecular design of the corresponding pentadentate Schiff base anions L12- and L22-. While compound 2 with a symmetric ligand prepared from salicylaldehyde shows high-spin state properties, compound 1 containing the asymmetric ligand with naphthalene units either is low-spin in its solvated form or shows a gradual but hysteretic spin crossover event when desolvated. The magnetic behavior was analyzed with respect to the Ising-like model and spin Hamiltonian, respectively, and the results were confronted with ab initio calculations. Additionally, the influence of structural features, lattice solvent molecules, the distribution of electronic terms, and active orbitals on the spin state properties of reported complexes is discussed.