Thermal investigation and infrared evolved gas analysis of light lanthanide(III) complexes with pyridine-3,5-dicarboxylic acid

The characterisation of light lanthanide(III) complexes with pyridine-3,5-dicarboxylic acid of the formula Ln₂pdc₃·nH₂O where Ln denotes lanthanides from La to Gd, pdc = C₇H₅NO₄²⁻; n = 6 for Ce(III), n = 7 for Pr(III) and Sm(III), n = 8 for La and n = 13 for Nd(III), Eu(III) and Gd(III) was performed by the thermal analysis TG-DTA and the simultaneous infrared evolved gas analysis TG-FTIR. Heating of the crystalline complexes resulted in the dehydration process at first. Next, dehydrated compounds decompose releasing of CO₂, CO, CH₄ and hydrocarbons. Free pyridine molecules were detected only in the gaseous products of lanthanum(III) complex decomposition.     

Enantiomeric recognition of amino acid derivatives by chiral schiff bases of calix[4]arene

Novel calix[4]arene Schiff bases bearing chiral substituents both on the upper and the lower rims have been developed. These chiral receptors exhibit good chiral recognition ability towards α-amino acid ester hydrochlorides (up to K_D/K_L = 4.36, ΔΔG₀ = − 3.65 kJ mol⁻¹) in CHCl₃. The molecular recognition abilities and enantioselectivities for guests are also discussed from a thermodynamic point of view.     

Heptanuclear high-spin complex compounds based on S-donors

The precursors [Fe(III)(^SYL)Cl] (^SYLH₂) = N,N′-bis(1-hydroxy-Y-2-benzyliden)-1,6-diamino-3-thiohexane, (Y = H, 3EtO, 5Me) are high-spin (S = 5/2) complexes. The precursors are combined with [Fe(II)(CN)₆]⁴⁻ and [Co(III)(CN)₆]³⁻ to yield star-shaped heptanuclear clusters, [Fe(II)(CN–Fe(III)^SYL)₆]Cl₂ and [Co(III)(CN–Fe(III)^SYL)₆]Cl₃. The star-shaped compounds are high-spin (HS) systems at room temperature. On cooling to 20 K some of the iron(III) centers perform some HS–HS transition.     

Ruthenium and chromium complexes bearing pH-indicators as the η6-arene ligand: Synthesis,characterization, and protonation behavior

A series of ruthenium and chromium complexes bearing pH indicators as the η⁶-arene ligand, (η⁶-X)(ML_n)_y [X = methyl yellow, crystal violet lactone, phenolphthalein; ML_n = RuCp¹⁺, RuCl₂(L), Cr(CO)₃; y = 1, 2] is prepared and characterized by spectroscopic and crystallographic methods. Of the plural arene rings in the indicators, a specific arene ring can be successfully coordinated to the metal center in a selective manner under appropriate conditions (i.e. use of the precursors of different oxidation states and reaction with the non-protonated and protonated pH indicator). The obtained indicator complexes show halochromic behavior depending on pH as observed for the parent molecules but the transition pH ranges are shifted to the more acidic side because of the attachment of the electron-withdrawing metal fragments, which decrease the basicity of the attached pH indicators.     

Novel sucrose-based macrocyclic receptors for enantioselective recognition of chiral ammonium cations

A new synthetic route to macrocyclic sucrose-based receptors with different substituents at the ring nitrogen atom is described. Very good enantioselectivity toward phenylethylammonium chloride was observed [a much stronger complex with the cation of the (S)-amine was formed] although the K_a values were low. Much higher K_a (1.4 × 10⁴ M^?1 in CDCl₃/CD₃OD) values of the complexes with aminoacid derivatives (especially valine) were found although this time the enantioselectivities were moderate.     

Unprecedented multistability in dodecanuclear complex compound observed by Mössbauer spectroscopy

The precursors [Fe(III)(^5XL)Cl] (^5XLH₂ = N,N′-bis(1-hydroxy-2-benzyliden)-1,6-diamino-3-X-hexane, X = N,S) are high-spin (S = 5/2) complexes. This precursors are combined with the bridging unit [(NC)₅Fe(II)-CN-Co(III)(CN)₅]⁶⁻ to yield star-shaped dodecanuclear clusters, [(^5XLFe(III)-NC)₅Fe(II)-CN-Co(III)(CN-Fe(III)^5XL)₅]Cl₄. The star-shaped compounds are high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers in the N-star switch to the low-spin state as proven by Mössbauer spectroscopy, i.e. multiple electronic transitions, while the S-star remains in the high-spin state.     

Synthesis,characterization, powder XRD and antimicrobial-antioxidant activity evaluation of trivalent transition metal macrocyclic complexes

The in vitro antimicrobial and antioxidant activities of metal complexes derived from 1,8-diaminonaphthalene and 5,5-dimethylcyclohexane-1,3-dione were evaluated. The complexes were synthesized by template method in the presence of trivalent metal salts, resulting in the formation of tetraaza macrocyclic complexes of the type [M (C₃₆H₃₆N₄) X] X₂, where M = Cr(III), Fe(III) and X = Cl^–, NO₃^–, CH₃COO^–. The synthesized complexes were characterized with the aid of elemental analyses, molar conductance measurements, magnetic susceptibility measurements, electronic, IR, mass and powder XRD studies. Based on various studies, a five-coordinated square pyramidal geometry was proposed for these complexes. The X-ray diffraction studies suggest a monoclinic crystal system for the complexes.     

Cyclometallated ruthenium(III) complexes: Synthesis,structure and properties

Reactions of Schiff bases (H₂apahR) derived from acetophenone and acid hydrazides, triethylamine and [Ru(PPh₃)₃Cl₂] (1:2:1 mole ratio) in methanol provide cyclometallated ruthenium(III) complexes of formula trans-[Ru(apahR)(PPh₃)₂Cl] in 74–81% yields. The complexes have been characterized by elemental analysis, magnetic susceptibility, spectroscopic (infrared, electronic and EPR) and electrochemical measurements. X-ray crystal structures of two representative complexes have been determined. In each complex, the metal centre is in distorted octahedral CNOClP₂ coordination sphere assembled by the C,N,O-donor meridionally spanning apahR^2?, the chloride and the two mutually trans-oriented PPh₃ molecules. All the complexes are one-electron paramagnetic (μ_eff. = 1.85–1.98 μ_B) and display rhombic EPR spectra in frozen (120 K) dichloromethane-toluene (1:1) solution. Electronic spectra of the complexes display several absorptions within 470–270 nm due to ligand-to-metal charge transfer and ligand centred transitions. The complexes are redox active and display a Ru(III) → Ru(II) reduction and a Ru(III) → Ru(IV) oxidation in the potential ranges ?0.66 to ?0.70 V and 0.75 to 0.80 V (vs. Ag/AgCl), respectively.     

New chloro and triphenylsiloxy derivatives of dioxomolybdenum(VI) chelated with pyrazolylpyridine ligands: Catalytic applications in olefin epoxidation

Dioxomolybdenum(VI) complexes of general formula [MoO₂X₂L₂] (X = Cl, OSiPh₃; L₂ = 2-(1-butyl-3-pyrazolyl)pyridine, ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate) were prepared and characterised by ¹H NMR, IR and Raman spectroscopy. The assignment of the vibrational spectra was supported by ab initio calculations. A single crystal X-ray diffraction study of the complex [MoO₂Cl₂{ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate}] showed that the compound is monomeric and crystallises in the tetragonal system with space group P4₁. The four complexes are active and selective catalysts for the liquid-phase epoxidation of olefins by tert-butylhydroperoxide. Selectivities to the corresponding epoxides were mostly 100% (for conversions of at least 34%) for the substrates cyclooctene, cyclododecene, 1-octene, trans-2-octene and (R)-(+)-limonene. For styrene epoxidation, the corresponding diol was also formed in significant quantities. The turnover frequencies for cyclooctene epoxidation at 55 °C were around 340 mol mol_Mo⁻¹ h⁻¹ for the chloro complexes and 160 mol mol_Mo⁻¹ h⁻¹ for the triphenylsiloxy complexes. The addition of co-solvents (1,2-dichloroethane or n-hexane) had a detrimental effect on catalytic activities. Kinetic studies for the two complexes bearing the ligand ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate revealed an apparent first order dependence of the initial rate of cyclooctene conversion with respect to cyclooctene or oxidant concentration.     

Effect of various cations on the acidity of p-sulfonatocalixarenes

Photometric and pH-metric titration curves of p-sulfonatocalixarenes, C[n]ASO₃H (n=4, 6, 8), were measured in the presence of electrolytes of various cations. These titration curves revealed that the presence of tetramethylammonium (TMA⁺) and tetraethylammonium (TEA⁺) ions largely decreased pK_a values for C[n]ASO₃H (n=4, 6, 8), while alkali and alkaline-earth metal cations had small effects. Comparison of the pH dependence of absorption spectra for C[n]ASO₃H (n=4, 6, 8) with that for corresponding monomer, p-hydroxybenzenesulfonate, indicated that the small values of pK_a1 and pK_a2 observed for C[8]ASO₃H were attributable to dissociation of its OH groups in this compound. The dependence of pK_a values for C[4]ASO₃H and p-hydroxybenzenesulfonate on the concentration of NaCl was due to the difference in their activity coefficients before and after their deprotonation steps estimated on the basis of Debye-Hückel theory. These results suggested that C[n]ASO₃H (n=4, 6, 8) hardly formed stable complexes with Na⁺ or other alkali metal cations in aqueous solutions while C[n]ASO₃H (n=4, 6, 8) formed stable complexes with tetraalkylammonium cations. It was also shown that the p-sulfonatophenol or p-sulfonatophenoxide units in the calixarene interacted independently with ionic atmospheres formed around the phenol units.     

Synthesis and properties of alkylruthenium complexes bearing primary and secondary amine ligands

A series of 18-electron alkylruthenium complexes, RuR[κ²(N,N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) (Ph = C₆H₅, R′ = p-CH₃C₆H₄ and CH₃), bearing a N-sulfonylated diamine ligand was synthesized from the reaction of RuCl[κ²(N, N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) with alkylzinc reagents, in which transmetalation proceeded smoothly to give the desired alkyl complexes in good yield and selectivity. Although the isolable amine Ru complexes bearing functionalized alkyl ligands were thermally stable, the simple methyl and ethyl Ru complexes underwent intramolecular deprotonation from NH protons to give the amido Ru complexes with release of the alkanes. The reactivity of the alkyl Ru complexes is highly affected by the structures of the arene ligands.     

Molecular switching complexes with iron and tin as central atom

The precursor [Fe^III(L)Cl] (LH₂ = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-N-hexane is a high-spin (S = 5/2) complex. This precursor is combined with the bridging units [Sn^IV(X)₄] (X = CN^?, NCS^?) to yield star-shaped pentanuclear clusters, [(LFe^III–X)₄Sn]Cl₄. For X = CN^? the ⁵⁷Fe-Mössbauer data show a multiple spin transition between iron(III) in the high-spin and low-spin state, while the ^119mSn-Mössbauer data indicate a valence tautomerism between Sn(IV) and Sn(II). Changing the bridging unit from X = CN^? to X = NCS^? turns the switchability off.     

Synthesis and spectral studies on heterobimetallic complexes of manganese and ruthenium derived from bis[N-(2-hydroxynaphthalen-1-yl)methylene]oxaloyldihydrazide

The complex [Mn(L)(H₂O)₂] [H₄L = bis[N-(2-hydroxynaphthalen-1-yl)methylene]-oxaloyldihydrazide] reacts with activated ruthenium(III) chloride in methanol in 1:1.2 M ratio under reflux resulting in heterobimetallic complex of the composition [Mn(L)(H₂O)₄RuCl₂]Cl. The complexes of the composition [Mn(L)(A)₄RuCl₂]Cl were obtained when the above reaction was carried out in presence of heterocyclic nitrogen bases(A) such as pyridine(py), 3-picoline(3-pic) and 4-picoline(4-pic). The molar conductance values for these complexes in DMF(N,N-dimethyl formamide) solution indicate their 1:1 electrolytic nature. Magnetic moment values suggest that these heterobimetallic complexes contain Mn(IV) and Ru(III) in the same structural unit. Electronic spectral studies suggest six coordinated metal ions in these complexes. IR spectra reveal that the H₄L ligand coordinates in its keto-form to Mn(IV) and Ru(III).     

Lanthanide complexes derived from hexadentate macrocyclic ligand: Synthesis,spectroscopic and thermal investigation

The lanthanide complexes derived from (3,5,13,15-tetramethyl 2,6,12,16,21-22-hexaazatricyclo[15.3.I^1-17I^7-11]cosa-1(21),2,5,7,9,11(22),12,15,17,19-decane) were synthesized. The complexes were found to have general composition [Ln(L)X₂·H₂O]X, where Ln = La³⁺, Ce³⁺, Nd³⁺, Sm³⁺ and Eu³⁺ and X = NO₃^? and Cl^?. The ligand was characterized by elemental analyses, IR, Mass, and ¹H NMR spectral studies. All the complexes were characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, Mass, electronic spectral techniques and thermal studies. The ligand acts as a hexadentate and coordinates through four nitrogen atoms of azomethine groups and two nitrogen of pyridine ring. The lanthanum complexes are diamagnetic while the other Ln(III) complexes are paramagnetic. The spectral parameters i.e. nephelauxetic ratio (β), covalency factor (b^1/2), Sinha parameter (δ%) and covalency angular overlap parameter (η) have been calculated from absorption spectra of Nd(III) and Sm(III) complexes. These parameters suggest the metal–ligand covalent bonding. In the present study, the complexes were found to have coordination number nine.     

Synthesis and spectroscopic characterization of new tetradentate Schiff base and its coordination compounds of NOON donor atoms and their antibacterial and antifungal activity

New Schiff base (H₂L) ligand is prepared via condensation of o-phthaldehyde and 2-aminobenzoic acid in 1:2 ratio. Metal complexes are prepared and characterized using elemental analyses, IR, solid reflectance, magnetic moment, molar conductance, ¹H NMR, ESR and thermal analysis (TGA). From the elemental analyses data, the complexes were proposed to have the general formulae [MCl(L)(H₂O)]·2H₂O (where M = Cr(III) and Fe(III)); [M(L)]·yH₂O (where M = Mn(II), Ni(II), Cu(II) and Zn(II), y = 1–2) and [M(L)(H₂O)_n]·yH₂O (where M = Co(II) (n = y = 2), Co(II) (n = y = 1), Ni(II) (n = 2, y = 1). The molar conductance data reveal that all the metal chelates were non-electrolytes. IR spectra show that H₂L is coordinated to the metal ions in a bi-negative tetradentate manner with NOON donor sites of the azomethine-N and carboxylate-O. The ¹H NMR spectral data indicate that the two carboxylate protons are also displaced during complexation. From the magnetic and solid reflectance spectra, it was found that the geometrical structure of these complexes are octahedral (Cr(III), Fe(III), Co(II) and Ni(II)), square planar (Cu(II)), trigonal bipyramidal (Co(II)) and tetrahedral (Mn(II), Ni(II) and Zn(II)). The thermal behaviour of these chelates showed that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the ligand molecule in the subsequent steps. The biological activity data show that the metal complexes to be more potent/antibacterial than the parent Shciff base ligand against one or more bacterial species.     

Synthesis,structures, and ligating ability of 4-tert-butylcalix[n]arene (iso)nicotinoylate

4-tert-Butylcalix[n]arenes react with an excess of (iso)nicotinoyl chloride, yielding selectively n-2 acylated products, calix[n]-(nico)_n?2(OH)₂, (calix = 4-tert-butylcalix[n]arene; n = 4, 6, and 8; nico = (iso)nicotinoylate) of alternate conformations. Their structures were determined by X-ray single crystallography and NMR spectra. The UV–vis spectra indicated that a new absorption band of the complexes appears upon the addition of cobalt(II) dichloride, and its crystal structure was resolved.     

Re-investigation of ortho-metalated N,N-dialkylbenzylamine complexes of rare-earth metals. First structurally characterized arylates of neodymium and gadolinium Li[LnAr4]

The influence of the ether ligand in [LnCl₃(solv)_n], solv = THF, DME; n = 1–3 in reactions with ortho-lithiated dimethyl-benzylamine Li(dmba) has been studied. An improved protocol towards homoleptic tris-aryl complexes of the type [Ln(dmba)₃], Ln = Y, Er and Yb has been developed and molecular structures of these complexes have been established by X-ray crystallography. For the first time stable homoleptic lithium ate-complexes of the type Li[Ln(dmba)₄] (Ln = Gd, Nd) have been isolated and structurally characterized. The success in their synthesis strongly depends on the choice of the appropriate [LnCl₃(solv)_n] precursor, such as [GdCl₃(dme)₂], [NdCl₃(dme)], and THF-free reaction conditions. Factors influencing on possible degradation pathways of lanthanide tris-aryl complexes with dmba-type ligands are discussed.     

Synthesis and investigations of mixed-ligand lanthanide complexes with N,N′-dipyrrolidine-N′′-trichloracetylphosphortriamide,dimethyl-N-trichloracetylamidophosphate, 1,10-phenanthroline and 2,2′-bipyrimidine

Coordination compounds with general formula [Ln(L¹)₃phen], where Ln = Nd, Eu, Er, Yb, HL¹ = N,N′-dipyrrolidine-N′′-trichloracetylphosphortriamide, phen = 1,10-phenanthroline; [Ln(L¹)₃bpm], where Ln = La, Nd, Eu, Gd, Er, Y, bpm = 2,2′-bipyrimidine and [{Ln(L²)₃}₂(μ-bpm)], where Ln = La, Nd, Eu, Gd, Er, Y, HL² = dimethyl-N-trichloracetylamidophosphate have been synthesized and characterized by means of IR and UV–Vis spectroscopy. Crystal structures of [Nd(L¹)₃phen] (1), [Nd(L¹)₃bpm] (2) and [{Nd(L²)₃}₂(μ-bpm)] (3) have been determined. It was found, that in the deprotonated form the phosphoryl ligands (L¹)^? and (L²)^? are coordinated to the neodymium atoms in a bidentate manner via the oxygen atoms of the phosphoryl and the carbonyl groups with formation of six-membered metallocycles. In the case of compounds 1 and 2 the 1,10-phenanthroline (or 2,2′-bipyrimidine) molecules are coordinated to the metals in a bidentate manner via the nitrogen atoms. In contrast 2,2′-bipyrimidine acts in the bidentate-bridge mode forming binuclear complex 3. Variable-temperature magnetic susceptibility measurements of 3 and [{Gd(L²)₃}₂(μ-bpm)] (4) reveal a weak antiferromagnetic interaction between the two magnetic centres, whereas in the case of [{Eu(L²)₃}₂(μ-bpm)] (5) the presence of spin–orbit coupling leads to a deviation from the Curie and Curie–Weiss laws.     

Construction of Cd(II)–ferrocenesuccinate coordination complexes via changing adjuvant ligands and anions

Seven Cd(II)–ferrocenesuccinate coordination complexes with the formulas [Cd(η²-FcCOC₂H₄COO)₂(pbbbm)]₂ (1), [Cd(η²-FcCOC₂H₄COO)(pbbbm)Cl]₂ (2), [Cd(η²-FcCOC₂H₄COO)(pbbbm)I]₂ (3), {[Cd(η²-FcCOC₂H₄COO)₂(btx)₂]₂(CH₃OH)_0.5} (4), [Cd(η²-FcCOC₂H₄COO)₂(bix)]₂(H₂O) (5), {[Cd(η²-FcCOC₂H₄COO)(bbbm)_1.5Cl] · (CH₃OH)_0.5}_n (6), and {[Cd(η²-FcCOC₂H₄COO)(mbbbm)Cl] · (H₂O)_2.75}_n (7) [pbbbm = 1,4-Bis(benzimidazole-1-ylmethyl)benzene), btx = 1,4-bis(triazol-1-ylmethyl)benzene), mbbbm = 1,3-bis(benzimidazole-1-ylmethyl)benzene), bix = 1,4-bis(imidazol-1-ylmethyl)benzene, bbbm = 1,1-(1,4-Butanediyl)bis-1H-benzimidazole)] have been synthesized and characterized. Single-crystal X-ray analysis reveals that complexes 1–5 are all dimers and bridged by pbbbm, btx and bix, respectively. But the five complexes present some differences in their dimeric conformations, which can be ascribed to the impacts of adjuvant ligands and counter anions. In contrast to complexes 1–5, both 6 and 7 are of 1-D structures (with the same counter anions), and the former is double ladder-like structure only bridged by bbbm, while the latter is chain-like structure bridged by chlorine anions and adjuvant ligand mbbbm. Notably, various π–π interactions are found in complexes 1–7, and they have significant contributions to molecular self-assembly processes. The electrochemical studies of complexes 1–7 in DMF solution display irreversible redox waves and indicate that the half-wave potentials of the ferrocenyl moieties in these complexes are all shifted to positive potential compared with that of ferrocenesuccinate.     

Synthesis,structure and magnetic properties of pyrazolate-bridged dinuclear complexes [{M(NCS)(4-Phpy)}2(μ-bpypz)2] (M = Co2+ and Fe2+)

The synthesis and magnetic characterization of pyrazolato-bridged dinuclear complexes [{M(NCS)(4-Phpy)}₂(μ-bpypz)₂] (Hbpypz = 3,5-bis(2-pyridyl)-pyrazole; 4-Phpy = 4-phenylpyridine; M = Co²⁺ (1) and Fe²⁺ (2)) are described together with the X-ray crystal analysis of the cobalt complex. The structure of 1 shows that the desired coordination has been achieved with the cobalt atoms being coordinated to two bpypz to form the dimer. The X-ray diffraction patterns show 1 and 2 to be isomorphous at room temperature. 2 displays a single spin-crossover transition between the [HS–HS] and [LS–LS] states with T_c = 150 K.