Synthesis of Fe(II) and Cu(II) building blocks for metal-organic frameworks

In situ reaction of the aminobenzoic acids 2-aminobenzoic acid and 3,5-diaminobenzoic acid with salicylaldehyde provide easy access to the ligands 2-[{(2-hydroxyphenyl)methylene}amino]benzoic acid (L1) and 3,5-bis[{(2-hydroxyphenyl)methylene}amino]benzoic acid (L2). Addition of a Fe(II) or Cu(II) salt to the solution of the ligand yields the corresponding Fe and Cu complexes. The species synthesized have been structurally characterized by single-crystal X-ray diffraction. The Fe(II) complex [Fe(L1)(MeOH)₃] (1) crystallizes in the triclinic space group . The Cu(II) complex [Cu(L1)] (2) is a one-dimensional chain and crystallizes in the monoclinic space group P2₁. The Cu(II) complex [Et₃NH]₂[Cu₂(L2)₂] (3) crystallizes in the monoclinic space group P2₁/n. The magnetic properties of 1, 2 and 3 have been studied, showing that the Cu(II) ions of 2 and 3 are ferromagnetically coupled. Complexes 1 and 3 have strong potential as metal-bearing building blocks for the synthesis of metal-organic frameworks.     

Novel cobalt(II) complexes with pyridyl/ether or pyridyl/thioether ligands. The conversion of pyridyl/thioether cobalt(II) complex to pyridyl/sulfinato cobalt(III) compound

Two new cobalt(II) complexes of symmetric hexadentate mixed-ligand N,O [1,12-bis(2-pyridyl)-5,8-dioxa-2,11-diazadodecane (pydado)] and N,S [1,12-bis(2-pyridyl)-5,8-dithia-2,11-diazadodecane (pydadt)] donor atoms have been synthesized as perchlorate salts. The crystal structures show that [Co(pydado)](ClO₄)₂ · H₂O (1) crystallizes in the triclinic space group and [Co(pydadt)](ClO₄)₂ (2) crystallizes in the monoclinic space group P2_1/c. The cation [Co(pydado)]²⁺ is pseudo-octahedral with the two pyridyl groups in trans position. However, in [Co(pydadt)]²⁺ complex, the size of thioether sulfur atoms imposes a distorted octahedral geometry; the pyridyl groups and the sulfur atoms are in trans position. The reaction of the complex 2 and hydrogen peroxide resulted to the oxidation of Co^II into Co^III and the thioether groups of the ligand to sulfinate groups with elimination of the central ethylenic group of pydadt. Thus, complex 2 was converted to bis[3-(2-pyridylmethylamino)ethanesulfinate] cobalt(III) complex (3) {[Co(pynso)₂](ClO₄) · 0.5H₂O}. The X-ray crystal structure reveals that the compound 3 crystallizes in the triclinic space group with the same donor atoms (N_pyridyl, N_amine and S) belonging to the two ligands in cis-position. In aqueous solution, the stability constants of the Co(II) chelates with these two ligands, determined by potentiometry, show the formation of [Co(LH)]³⁺ and [CoL]²⁺ species in all cases. The chelating power of pydadt ligand is slightly greater than that of pydado.     

Syntheses and crystal structures of three Mn(II) complexes with 2-hydroxynicotinate

Three new Mn(II) complexes [Mn(HnicO)₂(H₂O)₂] (1), [Mn₂(HnicO)₂SO₄(H₂O)₂]_n (2), and [NaMn(HnicO)₃]_n (3) (H₂nicO = 2-hydroxynicotinic acid) have been synthesized and determined by X-ray diffraction. For complex 1, the mononuclear units with two bidentate HnicO⁻ ions and two water molecules are assembled into a 3D architecture via hydrogen bonding and π-π interactions. For 2, Mn(II) ions are connected by μ₃-HnicO⁻ and bridging ligands, producing a 2D (6,3) coordination network. For 3, binuclear Na(I)-Mn(II) units with three carbonyl oxygen bridges are interlinked by carboxylate groups, resulting in a 3D 6-connected coordination network with distorted α-Po topology. The magnetic properties of 2 are discussed.     

New cationic palladium(II) compounds with several bidentate nitrogen-donor ligands: Synthesis, spectroscopic analyses and X-ray crystal structure

A series of PdN₄core complexes has been synthesised. Reaction of [PdCl₂(CH₃CN)₂] with N-alkylaminopyrazole (NN′) ligands, 1-[2-(ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[2-(ⁱpropylamino)ethyl]-3,5-dimethylpyrazole (deai), and 1-[2-(^tbutylamino)ethyl]-3,5-dimethylpyrazole (deat) in the presence of AgBF₄ led to [Pd(NN′)₂](BF₄)₂. These palladium(II) compounds were characterised by elemental analyses, conductivity measurements, IR, ¹H and ¹³C{¹H} NMR spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed. The X-ray analyses of one representative complex, [Pd(deat)₂](BF₄)₂, is reported. The crystal structure consists of discrete centrosymmetric cations involving a coordinated Pd(N_pz)₂(N_amino)₂core with planar geometry and anions.     

A new sterically loaded pentadentate N3S2 ligand and its zinc complexes

In quest of complexes having [MN₃S₂] cores in the monomeric form and trans-thiolate donor atoms, the new pentadentate thiolate amine py^tBuN₂H₂S₂-H₂ [] has been synthesized.The template condensation reaction of bis(2-mercapto-3,5-di-tert-butylaniline)zinc (II)[Zn(^tBu₂ma)₂] and pyridine-2,6-dicarbaldehyde in methanol at 40 °C leads to the formation of imine zinc complex [Zn(py^tBuN₂S₂)] (7), which is very unstable and decomposes to give thiazole 5. However, if the template condensation is followed by in situ reduction with an excess of NaBH₄, the stable saturated amine complex [Zn(py^tBuN₂H₂S₂)] (8) is formed. Demetallation of zinc complex 8 under acidic conditions leads to the formation of the desired dithiolate py^tBuN₂H₂S₂-H₂ ligand (9).     

Hydroxylation of a methyl group: synthesis of [Cu2(btmmO)2I] and of [Cu2(btmmO)2] containing the novel ligand {bis(trimethylmethoxy)guanidino}propane (btmmO) by copper-assisted oxygen activation

The reaction of the bisguanidine copper(I) compounds [Cu(btmgp)I] and [Cu₂(btmgp)₂][PF₆]₂ with molecular oxygen afforded at low temperatures complexes containing the bis-μ-oxo dicopper(III) core, which is capable to hydroxylate one of the N-CH₃-groups of the {bis(tetramethyl)guanidino}propane ligands. The formation of the novel ligand {bis(trimethylmethoxy)guanidino}propane (btmmO) is reported as it represents the first hydroxylation of a N-methyl group. The products of this reaction are novel alkoxo-bridged binuclear copper complexes, namely [Cu₂(btmmO)₂I]⁺ containing an iodide ion in a novel bridging situation, as well as [Cu₂(btmmO)₂]²⁺ which have been identified in their complex salts and [Cu₂(btmmO)₂][PF₆]₂ · 2MeCN, respectively. Concomitantly, the hydroxo-bridged binuclear copper compounds [Cu₂(btmgp)₂(μ-OH)₂]I₂ and [Cu₂(btmgp)₂(μ-OH)₂][PF₆]₂ are formed as couple products. The formation of the bis-μ-oxodicopper(III) complexes was monitored by UV/Vis-spectroscopy, and the reaction products were characterised by X-ray diffraction, vibrational spectroscopy and elemental analysis.     

Manganese(II) complexes of di-2-pyridinylmethylene-1,2-diimine di-Schiff base ligands: Structures and reactivity

Manganese(II) complexes [Mn(L)X₂] were prepared and characterized, where L is a neutral di-Schiff base ligand incorporating pyridylimine donor arms, including (1R,2R)-N,N′-bis(2-pyridylmethylidene)-1,2-diphenylethylenediimine (L¹), (1R,2R)-N,N′-bis(6-methyl-2-pyridylmethylidene)-1,2-cyclohexyldiimine (L²), or (1R,2R)-, (1S,2S)- or racemic N,N′-bis(2-pyridylmethylidene)-1,2-cyclohexyldiimine (L³), and X⁻ =  or Cl⁻. Product complexes were structurally characterized, specifically including [Mn(R,R-L¹)(NCCH₃)₃](ClO₄)₂, [Mn(R,R-L²)(OH₂)₂](ClO₄)₂ and racemic [Mn(L³)Cl₂]. The first of these complexes features a heptacoordinate ligand field in a distorted pentagonal bipyramid, and the latter two are hexacoordinate, but retain equatorially monovacant pentagonal bipyramidal structures. Complexes [Mn(L³)X₂] (X⁻ = Cl⁻, ) were reacted with the primary phosphine FcCH₂PH₂ (Fc = -C₅H₄FeC₅H₅), H₂O and ethyldiazoacetate (EDA). The first two substrates prompted reactivity at a single ligand imine bond, resulting in hydrophosphination and hydrolysis, respectively. Complexes of the derivative ligands were also structurally characterized. Evidence for EDA activation was obtained by electrospray ionization mass spectrometry, but catalytic carbene transfer was not obtained.     

Synthesis and structural characterisation of new mono and dinuclear pyrazolatopalladium (II) complexes self-assembled through robust hydrogen-bonds

This work describes the reactivity of compounds [Pd(dmpz)₂(Hdmpz)₂] (A) (dmpz = 3,5-dimethylpyrazolate, Hdmpz = 3,5-dimethylpyrazol) and [Pd₂(μ-dmpz)₂(dmpz)₂(Hdmpz)₂] (B) towards several dicarboxylic acids and also towards perchloric acid. The compounds [Pd(Hdmpz)₄](O₂C-(CH₂)_n-CO₂H)₂ [n = 1 (1), 3 (2)] have been obtained by treatment of [Pd(dmpz)₂(Hdmpz)₂] (A) with two equivalents of malonic (HO₂C-CH₂-CO₂H) and glutaric (HO₂C-(CH₂)₃-CO₂H) acids. The X-ray study on a crystal of [Pd(Hdmpz)₄](O₂C-(CH₂)₃-CO₂H)₂ (2) revealed that the glutarate anions link to the cationic complex [Pd(Hdmpz)₄]²⁺ through the carboxylate group by charge-assisted N-H⁽⁺⁾?O⁽⁻⁾ hydrogen bonds. Additionally, the carboxylate anions form uncommon dimeric rings on both sides of the metal complex via a pair of O-H?O hydrogen bonds, yielding a hydrogen bonded polymeric chain with alternating inorganic [Pd(Hdmpz)₄]²⁺ and organic fragments. The dinuclear complexes [Pd₂(μ-dmpz)₂(O₂C-(CH₂)_n-CO₂)(Hdmpz)₂] [n = 0 (5), 1 (6)] were obtained from equimolar amounts of [Pd₂(μ-dmpz)₂(dmpz)₂(Hdmpz)₂] (B) and the corresponding dicarboxylic acid, HO₂C-(CH₂)_n-CO₂H (n = 0, 1). However, the synthesis of 5 and 6 requires two steps, the protonation of both terminal dmpz groups in B with HClO₄ to give [Pd₂(μ-dmpz)₂(Hdmpz)₄](ClO₄)₂ (4) and the subsequent treatment of this cationic palladium complex with salts of the corresponding dicarboxylic acids. The X-ray structures of compounds 5 and 6 are reported. Both in 5 and 6, the Pd₂N₄ ring shows a typical boat-like conformation and the metal atoms are separated in about 3.3 Å. Both 5 and 6 are asymmetric and contain two Hdmpz groups - H-bond donors - at one end, and two CO groups from the dicarboxylate anion - H-bond acceptors - at the other, in such a way that the donor end of one molecule links with the acceptor end of its neighbour forming a hydrogen-bonded polymeric chain. The synthesis and X-ray study of compounds [Pd(Hdmpz)₄](ClO₄)₂ (3) and [Pd₂(μ-dmpz)₂(Hdmpz)₄](ClO₄)₂ (4), obtained by reaction of [Pd(dmpz)₂(Hdmpz)₂] (A) and [Pd₂(μ-dmpz)₂(dmpz)₂(Hdmpz)₂] (B) with two equivalents of perchloric acid, are also reported.     

Oxomolybdenum(III, IV and V) complexes of thiofunctional ligands

Reaction of [MoO₂(acac)₂] with (S is a thioether, S′ a thiophenolate function) yielded the compound Li₇(thf)₁₇{MoO}₈ · 10thf · hexane, where {MoO}₈ represents one 1, three (2, linked, via the oxo group, to [Li(thf)₃]⁺) and two (3a, linked by two [Li(thf)₂]⁺).A mixed-valent variant of 3, (3b, with an additional[Li(thf)₃]⁺ attached to S′), was also identified. The compounds model features pertinent to oxo-transferases containing the molybdopterin cofactor.     

The cyanocarbanion (C[C(CN)2]3) as monodentate ligand: Synthesis, structure and magnetic properties of [Mn2(bpym)3(tcpd)2(H2O)2] (tcpd = (C[C(CN)2]3) and bpym = 2,2′-bipyrimidine)

One-pot reaction between MnCl₂·4H₂O, K₂tcpd (tcpd²⁻ = [C₁₀N₆]²⁻ = (C[C(CN)₂]₃)²⁻ = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion) and 2,2′-bipyrimidine (bpym = C₈H₆N₄) in aqueous solution yields the new compound [Mn₂(bpym)₃(tcpd)₂(H₂O)₂] (1). The molecular structure of 1 consists of a centrosymmetrical binuclear complex which includes unprecedented unidentate tcpd ligands with two bidentate and a bis-chelate bpym units. Examination of the intermolecular distances reveals that the dinuclear units are held together by hydrogen bonds involving coordinated water molecules and two nitrile groups of the tcpd ligand, giving rise to a 2D structure overall. Variable-temperature magnetic susceptibility data show the occurrence of slight antiferromagnetic coupling (J = −0.58 cm⁻¹) between the Mn(II) ions through bridging bpym (the exchange Hamiltonian being defined as ).     

Copper (II) and cobalt (II) complexes of chiral tetrathiafulvalene-oxazoline (TTF-OX) and tetrathiafulvalene-thiomethyl-oxazoline (TTF-SMe-OX) derivatives

Synthesis and single crystal X-ray structures of the first paramagnetic transition metal complexes containing chiral ethylenedithio-tetrathiafulvalene-oxazoline (EDT-TTF-OX) 1a-c and ethylenedithio-tetrathiafulvalene-thiomethyloxazoline 2 (EDT-TTF-(SMe)OX) ligands based on copper (II) and cobalt (II) are described. The racemic [EDT-TTF-OX][Cu(hfac)₂] complex 3a crystallizes in the triclinic centrosymmetric space group , whereas the enantiopure counterparts 3b-c crystallize in the triclinic non-centrosymmetric space group P1. Cu(II) adopts a distorted square pyramidal coordination geometry, a much weaker Cu?S_TTF interaction also being identified. The same coordination pattern around Cu(II) is observed in the complex [(rac)-EDT-TTF-(SMe)OX][Cu(hfac)₂] (4) in spite of the bidentate nature of the redox active ligand. DFT theoretical calculations afforded two equilibrium configurations for a corresponding model complex, in which the metal centre establishes secondary coordination either with one S_TTF or with the SMe group. The same ligand coordinates the cobalt (II) to afford the octahedral complex [(rac)-EDT-TTF-(SMe)OX][Co(hfac)₂] (5). In all these novel complexes, the paramagnetic centres are structurally and magnetically isolated. Cyclic voltammetry measurements show the stability of the radical cation species.     

Coordination versatility of 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane: Co(II) and Ni(II) complexes

The ligand 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane (L⁸) has afforded six-coordinate monomeric and dimeric complexes [(L⁸)Co^II(H₂O)₂][ClO₄]₂ (1), [(L⁸)Ni^II(MeCN)₂][BPh₄]₂ (2), [(L⁸)Ni^II(O₂CMe)][BPh₄] (3), and . The crystal structures of 1, 2 · MeCN, 3, and 4 revealed that the ligand L⁸ is flexible enough to expand its coordinating ability by fine-tuning the angle between the chelating fragments and hence folds around cobalt(II)/nickel(II) centers to act as a tetradentate chelate, allowing additional coordination by two trans-H₂O, cis-MeCN, and a bidentate acetate affording examples of distorted octahedral , , and coordination. The angles between the two CoN₂/NiN₂ planes span a wide range 23.539(1)° (1), 76.934(8)° (2), and 69.874(14)° (3). In contrast, complex 4 is a bis-μ-1,3-acetato-bridged (syn-anti coordination mode) dicobalt(II) complex [Co?Co separation: 4.797(8) Å] in which L⁸ provides terminal bidentate pyridylpyrazole coordination to each cobalt(II) center. To our knowledge, this report provides first examples of such a coordination versatility of L⁸. Absorption spectral studies (MeCN solution) have been done for all the complexes. Complexes 1-3 are uniformly high-spin. Temperature-dependent (2-300 K) magnetic studies on 4 reveal weak ferromagnetic exchange coupling between two cobalt(II) (S = 3/2) ions. The best-fit parameters obtained are: Δ (axial splitting parameter) = −765(5) cm⁻¹, λ (spin-orbit coupling) = −120(3) cm⁻¹, k (orbital reduction factor) = 0.93, and J (magnetic exchange coupling constant) = +1.60(2) m⁻¹.     

The synthesis and characterization of iron cyanide building blocks: [K]2[CpFe(CN)3] and its pentamethylcyclopentadienyl (Cp*) analog

The synthesis of [K]₂[CpFe(CN)₃] (1) and its pentamethylcyclopentadienyl analog (2) has been described via the photolysis of the corresponding [K][CpFe(CO)(CN)₂] salts in methanol in the presence of KCN. The structure of complex 1 has been characterized by means of X-ray crystallography, where the potassium ions are interacting with the N atoms of the cyanide ligands. As expected, the average ν_CN stretching frequency in the anion is 16 cm⁻¹ higher than that in the more electron-donating pentamethylcyclopentadienyl derivative.     

Crystal structure of six and seven coordinate manganese(II) complexes with penta and hexadentate pyridylmethyl ligands

Two six-coordinated manganese(II) complexes [Mn(pydien)Cl](ClO₄) · C₂H₅OH (1), [Mn(pydien)NCS](ClO₄) (2) and two seven-coordinated manganese(II) complexes [Mn(pydado)Cl](ClO₄) (3), [Mn(pydado)NCS](ClO₄) (4) have been obtained using linear penta and hexadentate ligands pydien and pydado (pydien: 1,7-bis(2-pyridylmethyl)-1,4,7-triazaheptane and pydado: 1,10-bis(pyridylmethyl)-1,10-diaza-4,7-dioxadecane). The crystal structures for all compounds have been determined. 1 and 3 crystallize in the triclinic space group , 2 crystallizes in the orthorhombic space group Pbca, whereas 4 crystallizes in the monoclinic space group P2₁/c. The bound anion (chloro or isothiocyanato) in complexes 1 and 2 has no influence on the geometry of six-coordinate manganese(II) complexes, whereas the geometry and the wrapping of the hexadentate ligand (pydado) around Mn²⁺ cation depend on the nature of the bound anion. The complex 3 has a capped octahedron geometry with the two pyridyl groups in trans position, while the geometry of complex 4 can be described as pentagonal bipyramid with one pyridyl group and a thiocyanate anion in the axial positions.     

Two cyano-bridged heterotrinuclear complexes built from [(Tp)Fe(CN)3] (Tp = hydrotris(pyrazolyl)borate): synthesis, crystal structures and magnetic properties

Using an anionic precursor [(Tp)Fe^III(CN)₃]⁻ (1) as a building block, two cyano-bridged centrosymmetric heterotrinuclear complexes, (2) and (3) (en = ethylenediamine), have been synthesized and structurally characterized. In each complex, [TpFe(CN)₃]⁻ acts as a monodentate ligand toward a central [Mn(C₂H₅OH)₄]²⁺ or [Ni(en)₂]²⁺ core through one of its three cyanide groups, the other two cyanides remaining terminal. The intramolecular Fe-Mn and Fe-Ni distances are 5.2354(4) and 5.0669(11) Å, respectively. The magnetic properties of complexes 2 and 3 have been investigated in the temperature range of 2.0-300 K. A weak antiferromagnetic interaction between the Mn(II) and Fe(III) ions has been found in complex 2. The magnetic data of 2 can be fitted with the isotropic Hamiltonian: where J and J′ are the intramolecular exchange coupling parameters between adjacent and peripheral spin carriers, respectively. This leads to values of J = −1.37 cm⁻¹ and g = 2.05. The same fitting method is applied to complex 3 to give values of J = 1.2 cm⁻¹ and g = 2.25, showing that there is a ferromagnetic interaction between the Fe(III) and Ni(II) ions.     

Syntheses and structural determination of new bis(9-tungstoarsenato)tris(dioxouranate(VI)) and its monooxovanadate(IV) derivative complexes

The [As₂W₁₈U₃O₇₄]¹²⁻ complex is formed by the “self-assembly” reaction of and (uranyl nitrate) ions in acidic media. The anion complex is isolated as the potassium salt and characterized by elemental analysis, IR, UV-Vis, and X-ray single crystal analysis. The complex contains an anion in which three ions are unsymmetrically sandwiched between two A-α-[AsW₉O₃₄]⁹⁻ groups leading to a structure of C_3v symmetry. Each uranium atom adopts pentagonal-bipyramidal coordination, achieved by three equatorial bonds to one [AsW₉O₃₄]⁹⁻and two bonds to the other. The [As₂W₁₈U₂V₂O₇₃]¹²⁻and also [As₂W₁₈U₃O₇₄]¹²⁻ complexes are formed also, by reaction of the [KAs₂W₁₈U₂O₇₂]¹³⁻ with VO²⁺ and ions in 1:1 mole ratio. The cyclic voltammogram of [As₂W₁₈U₂VO₇₃]¹²⁻ in acetate buffer (pH 4.7) shows a reversible one-electron redox process for V^IV/V couple at +0.396 (E_pc) and +0.432 V (E_pa).     

Triaminoguanidine derivatives as supports to construct magnetic assemblies: Synthesis and characterization of trinuclear nickel(II) complexes

The synthesis of two nickel(II) complexes based on a central bridging triaminoguanidine scaffold and a capping ligand per metal ion is reported. When 2,2′-bipyridine (bipy) is utilized as co-ligand the complex [Ni₃L^Br(bipy)₃(H₂O)₃]NO₃ · 9H₂O · 1.5DMF (1) is obtained which crystallizes in the hexagonal space group P6₃/m. Complex 1 shows an interesting supramolecular structure pattern with alternating hydrophilic and hydrophobic layers characterized by extensive hydrogen-bonding and π-π-stacking, respectively. With 2,4,6-(2-pyridyl)-1,3,5-triazine (tptz) as capping ligand, complex [Ni₃L^Br(tptz)₃]ClO₄ · 7H₂O · 1.5DMF (2) is obtained. The magnetic susceptibility data can be fitted using an equilateral triangle model () with an isotropic coupling constant of J=-31.0±0.6 for 1 and for 2.     

Conductometric and voltammetric studies on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl2(L)(PPh3)2], where L: 2-(2′-pyridyl)quinoxaline

Conductometric investigation on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl₂(L)(PPh₃)₂] (A) (where PPh₃: triphenyl phosphine and L: 2-(2′-pyridyl)quinoxaline, C₁₃N₃H₉), in dimethylsulfoxide (DMSO) was performed at temperatures ranging from 25 to 50 °C. In addition, cyclic voltammograms of A were recorded on platinum working electrode in dichloromethane (DCM) and dimethylsulfoxide (DMSO) using n-tetrabutylammonium hexafluorophosphate (NBu₄PF₆) as supporting electrolyte at 25 °C. The molar conductivities (Λ) demonstrate that A behaves as uni-univalent electrolyte in DMSO over the whole temperature range. This behavior can be explained in terms of the replacement upon dissolution of chlorine and PPh₃ ligands by DMSO molecules, and consequently, the formation of the ion-pair [RuCl(L)(PPh₃)(DMSO)₂]Cl [B⁺Cl⁻] which is dissociated in some extent. The Λ values were analyzed by means of the Lee-Wheaton conductivity equation in order to estimate the limiting molar conductivities (Λ^o) and the ion-pair association constants (K_A) of [B⁺Cl⁻]. The limiting ion conductivities for the B⁺ ion were evaluated using n-tetrabutylammonium chloride (NBu₄Cl) as “reference electrolyte”. The thermodynamic functions related with the ion association, such as Gibbs free energy , enthalpy , and entropy , were evaluated as well. The mobility of B⁺ was found to increase linearly with rising temperature and the consequent decrease of the viscosity (η) of DMSO. The K_A and values indicate that the association of [B⁺Cl⁻] increases to some extent with the rise of the temperature followed by the decrease of the dielectric constant (ε) of DMSO. The voltammetric experiments indicated that the couple Ru^3+/2+ is reversible and diffusion controlled in DCM and completely irreversible in DMSO.     

X-ray structure and magnetic properties of dinuclear and polymer iron(II) complexes

Five new octahedral iron(II) complexes [FeL2(4-dpa)]_n(EtOH) (1), [FeL2(bipy)]_n(DMF) (2), [FeL1(bpee)]_n (3), [Fe₂L3(1-meim)₄](1-meim)₄ (4) and [FeL1(DMAP)₂] (5), with L1 and L2 being tetradentate coordinating Schiff base like ligands (L1 = (E,E)-[{diethyl-2,2′-[1,2-phenylenebis(iminomethylidyne)]bis[3-oxobutanato](2-)-N,N′,O³,O³′}, L2 = (3,3′)-[{1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentane-dionato)(2-)-N,N′,O²,O²′}) and L3 being a octadentate dinucleating coordinating Schiff base like ligand ({tetraethyl-(E,E,E,E)-2,2′,2′′,2′′′-[1,2,4,5-phenylentetra(iminomethylidine)]tetra[3-oxobutanoato](2-)-N,N′,N′′,N′′′,O³,O³′,O³′′,O³′′′}); 4-dpa = di(4-picolyl)-amine, bipy = 4,4′-bipyridine, bpee = trans-1,2-bis(4-pyridyl)ethylene, 1-meim = 1-methylimidazole and DMAP = 4-dimethylaminopyridine, have been synthesized and characterised using X-ray structure analysis and T-dependent susceptibility measurements. Both methods indicate that all iron(II) centres are in the paramagnetic high-spin state over the whole temperature range investigated. The O-Fe-O angle, the so called bit of the equatorial ligand, is with an average of 111° in the region typical for high-spin iron(II) complexes of this ligand type. In the case of compound 1 an infinite two-dimensional hydrogen bond network can be found, for the compounds 2-4 no hydrogen bond interactions are observed between the complex molecules. A comparison of the curve progression obtained from the magnetic measurements of the mononuclear complex 5 and the polymeric complexes 1-3 leads to the conclusion that no magnetic interactions are mediated over the bridging axial ligands. For the dinuclear complex 4 weak antiferromagnetic interactions between the two iron centres are found.     

High-temperature spin-crossover in coordination compounds of iron(II) with tris(pyrazol-1-yl)methane

Novel mononuclear Fe(II) complexes of tris(pyrazol-1-yl)methane [Fe{HC(pz)₃}₂]²⁺ with and p-sulfonatothiacalix[4]arene (TCAS⁴⁻) as counterions were obtained. The compounds were characterized by magnetic susceptibility method, IR and UV-Vis spectroscopy. The structure of [Fe{HC(pz)₃}₂]SiF₆ has been analyzed by single-crystal X-ray diffraction. The ¹H NMR spectroscopy measurements of [Fe{HC(pz)₃}₂]₂(TСAS) in aqueous solution reveal the outer sphere inclusion of [Fe{HC(pz)₃}₂]²⁺ into the cyclophanic cavity of TCAS⁴⁻. The temperature induced spin-crossover ¹А₁ ⇔ ⁵Т₂, accompanied by thermochromism, has been revealed from the temperature dependence of μ_eff and IR spectra for both complexes. The comparative analysis of magnetochemical and spectroscopy data elucidates the effect of the cyclophanic counterion on the physico-chemical properties of Fe(II) complex.