FeIII in a low‐spin state in caesium bis[3‐ethoxysalicylaldehyde 4‐methylthiosemicarbazonato(2–)‐κ3O2,N1,S]ferrate(III) methanol monosolvate

The synthesis and crystal structure (at 100 K) of the title compound, Cs[Fe(C₁₁H₁₃N₃O₂S₂)₂]·CH₃OH, is reported. The asymmetric unit consists of an octahedral [Fe^III(L)₂]⁻ fragment, where L²⁻ is 3‐ethoxysalicylaldehyde 4‐methylthiosemicarbazonate(2−) {systematic name: [2‐(3‐ethoxy‐2‐oxidobenzylidene)hydrazin‐1‐ylidene](methylamino)methanethiolate}, a caesium cation and a methanol solvent molecule. Each L²⁻ ligand binds through the thiolate S, the imine N and the phenolate O atoms as donors, resulting in an Fe^IIIS₂N₂O₂ chromophore. The O,N,S‐coordinating ligands are orientated in two perpendicular planes, with the O and S atoms in cis positions and the N atoms in trans positions. The Fe^III cation is in the low‐spin state at 100 K.     

Ammonium bis(salicylaldehyde thiosemicarbazonato)ferrate(III), a supramolecular material containing low‐spin FeIII

The synthesis and crystal structure (100 K) of the title compound, ammonium bis[salicylaldehyde thiosemicarbazonato(2?)‐κ³O,N¹,S]iron(III), NH₄[Fe(C₈H₇N₃OS)₂], is reported. The asymmetric unit consists of an octahedral [Fe^III(thsa)₂]^? fragment, where thsa^2? is salicylaldehyde thiosemicarbazonate(2?), and an NH₄⁺ cation. Each thsa^2? ligand binds via the thiolate S, the imine N and the phenolate O donor atoms, resulting in an Fe^IIIS₂N₂O₂ chromophore. The ligands are orientated in two perpendicular planes, with the O and S atoms in cis and the N atoms in trans positions. The Fe^III ion is in the low‐spin state at 100 K. The crystal structure belongs to a category I order–disorder (OD) family. It is a polytype of a maximum degree of order (MDO). Fragments of the second MDO polytype lead to systematic twinning by pseudomerohedry.     

FeIII Quinolylsalicylaldimine Complexes: A Rare Mixed‐Spin‐State Complex and Abrupt Spin Crossover

A new synthesis of (8‐quinolyl)‐5‐methoxysalicylaldimine (Hqsal‐5‐OMe) is reported and its crystal structure is presented. Two Fe^III complexes, [Fe(qsal‐5‐OMe)₂]Cl ? solvent (solvent=2 MeOH ? 0.5 H₂O ( 1 ) and MeCN ? H₂O ( 2 )) have been prepared and their structural, electronic and magnetic properties studied. [Fe(qsal‐5‐OMe)₂] Cl ? 2 MeOH ? 0.5 H₂O ( 1 ) exhibits rare crystallographically independent high‐spin and low‐spin Fe^III centres at 150 K, whereas [Fe(qsal‐5‐OMe)₂]Cl ? MeCN ? H₂O ( 2 ) is low spin at 100 K. In both structures there are extensive π–π and C? H???π interactions. SQUID magnetometry of 2 reveals an unusual abrupt stepped‐spin crossover with T_1/2=245 K and 275 K for steps 1 and 2, respectively, with a slight hysteresis of 5 K in the first step and a plateau of 15 K between the steps. In contrast, 1 is found to undergo an abrupt half‐spin crossover also with a hysteresis of 10 K. The two compounds are the first Fe^III complexes of a substituted qsal ligand to exhibit abrupt spin crossover. These conclusions are supported by ⁵⁷Fe Mössbauer spectroscopy. Both complexes exhibit reversible reduction to Fe^II at ?0.18 V and irreversible oxidation of the coordinated qsal‐5‐OMe ligand at +1.10 V.     

Synthesis,Crystal Structure,and Electrochemistry of Iron and Cobalt Complexes Supported by a Pentadentate Amine‐bis(phenolate) Ligand

The pentadentate amine‐bis(phenolate) ligand 6,6′‐(dipyridin‐2‐ylmethylazanediyl)bis(methylene)bis(2,4‐dimethylphenol) (H₂L) was prepared and characterized. This ligand readily coordinates with Fe^III or Co^III ions, and the resulting complexes [Fe^IIILCl] ( 1 ) and [Co^IIIL(H₂O)]Cl ( 2 ) were characterized by elemental analysis. X‐ray structural studies show that the ligand in complexes 1 and 2 acts as a pentadentate ligand, leaving one coordination side of the transition metal available for exogenous ligands such as chloride ion ( 1 ) or water ( 2 ) ligand, and the central metal atoms are hexacoordinate in a similar distorted octahedral arrangement. Electrochemical studies reveal that each of the complexes exhibits multiple redox processes in the potential window investigated. Complex 1 shows one reversible oxidative event at 0.32 V and one quasi‐reversible reduction event at –1.03 V, while the complex 2 displays one reversible oxidative event at 0.18 V and one quasi‐reversible reduction at –0.64 V.     

Trigonal (-3) symmetry octahedral lanthanide(III) complexes of zwitterionic tripodal ligands: luminescence and magnetism

Sandwich coordination complexes, [Ln^III(H₃L)₂]X₃?solvents, of Tb(III), Eu(III), Dy(III), Ho(III) and Er(III) were prepared with two new zwitterionic ester-substituted tripodal amine ligands, tris((2-hydroxy-5-n-butyl benzoate)aminoethyl)-amine (H₃L¹) and tris((2-hydroxy-5-methyl benzoate)aminoethyl)-amine (H₃L²). These ligands were synthesised by condensation of the appropriately substituted salicylaldehyde with tris(2-aminoethyl)amine (tren) followed by in situ reduction of the tris-imine to tris-amine. Subsequent 2:1 reaction with lanthanide(III) ions yields [Ln^III(H₃L)₂]X₃?solvents (L = L¹, L²; X = Cl^?, NO₃^?; solvents = MeOH or H₂O). All complexes were characterised by microanalysis, infrared spectroscopy, high resolution mass spectrometry and solid-state photoluminescence measurements. The crystal structures of [Tb^III(H₃L¹)₂]Cl₃·6MeOH, [Dy(H₃L¹)₂]Cl₃·6MeOH, [Eu^III(H₃L¹)₂]Cl₃·6MeOH and [Tb^III(H₃L¹)₂](NO₃)₃ reveal high-crystallographic ?3 symmetry at the O₆-coordinated octahedral lanthanide(III) ions and that the tripodal ligands are bound in zwitterionic form: the protons from the phenolic oxygens have migrated to the amino nitrogens. Photoluminescence measurements indicate various degrees of energy transfer of the ligand chromophore to the lanthanide ions, as both ligand and lanthanide emission features are observed. Despite the high-crystallographic symmetry and the likely small transverse magnetic anisotropy of the complexes, no evidence of slow relaxation of the magnetisation, characteristic of a single-molecule magnet, was observed for [Tb^III(H₃L¹)₂]Cl₃·MeOH·3H₂O, [Dy^III(H₃L¹)₂]Cl₃·6H₂O, [Ho^III(H₃L¹)₂](NO₃)₃·2H₂O, [Er^III(H₃L¹)₂]·H₂O and [Tb^III(H₃L¹)₂](NO₃)₃ down to 2.0 K.     

The Building Block [FeIII(pzphen)(CN)4]– and its Lanthanide Complexes: Synthesis,Crystal Structure,and Magnetic Properties

The cyanide building block [Fe^III(pzphen)(CN)₄]^– and its four lanthanide complexes [{Fe^III(pzphen)(CN)₄}₂Ln^III(H₂O)₅(DMF)₃] · (NO₃) · 2(H₂O) · (CH₃CN) [Ln = Nd ( 1 ), Sm ( 2 ), DMF = dimethyl formamide] and [{Fe^III(pzphen)(CN)₄}₂Ln^III(NO₃)(H₂O)₂(DMF)₂](CH₃CN) [Ln = Gd ( 3 ), Dy ( 4 )] were synthesized and structurally characterized by single‐crystal X‐ray diffraction. Compounds 1 and 2 are ionic salts with two [Fe^III(pzphen)(CN)₄]^– cations and one Ln^III ion, but compounds 3 and 4 are cyano‐bridged Fe^III‐Ln^III heterometallic 3d‐4f complexes exhibiting a trinuclear structure in the same conditions. Magnetic studies show that compound 3 is antiferromagnetic between the central Fe^III and Gd^III atoms. Furthermore, the trinuclear cyano‐bridged Fe^III₂Dy^III compound 4 displays no single‐molecular magnets (SMMs) behavior by the alternating current magnetic susceptibility measurements.     

Cyanide-bridged complexes based on dinuclear Cu(II)-M(II) [M = Pb and Cu] building blocks: Synthesis, crystal structures and magnetic properties

Four cyanide-bridged heterometallic complexes {[CuPb(L 1 )][Fe III (bpb)(CN) 2 ]} 2 ·(ClO 4 ) 2 ·2H 2 O·2CH 3 CN (1), {[CuPb(L 1 )] 2 [Fe II (CN) 6 ](H 2 O) 2 }·10H 2 O (2), {[Cu 2 (L 2 )][Fe III (bpb)(CN) 2 ] 2 }·2H 2 O·2CH 3 OH (3) and {[Cu 2 (L 2 )] 3 [Fe III (CN) 6 ] 2 (H 2 O) 2 }·10H 2 O (4) have been synthesized by treating K[Fe III (bpb)(CN) 2 ] [bpb 2-=1,2-bis(pyridine-2-carboxamido)benzenate] and K 3 [Fe III (CN)] 6 with dinuclear compartmental macrocyclic Schiff-base complexes [CuPb(L 1 )] (ClO 4 ) 2 or [Cu 2 (L 2 )]·(ClO 4 ) 2 , in which H 2 L 1 was derived from 2,6-diformyl-4-methyl-phenol, ethylenediamine, and diethylenetriamine in the molar ratio of 2:1:1 and H 2 L 2 from 2,6-diformyl-4-methyl-phenol and propylenediamine in the molar ratio of 1:1. Single crystal X-ray diffraction analysis reveals that compound 1 displays a cyclic hexanuclear heterotrimetallic molecular structure with alternating [FeⅢ (bpb)(CN) 2 ]- and [CuPb(L 1 )] 2+ units. Complex 2 is of a neutral dumb-bell-type pentanuclear molecular configuration consisting of one [Fe(CN)6] 4- anion sandwiched in two [CuPu(L 1 )] 2+ cations, and the pentanuclear moieties are further connected by the hydrogen bonding to give a 2D supramolecular framework. Heterobimetallic complex 3 is a tetranuclear molecule composed of a centrosymmetric [Cu 2 (L2)] 2+ segment and two terminal cyanide-containing blocks [FeⅢ (bpb)(CN)2 ]- . Octanuclear compound 4 is built from two [Fe(CN)6]3- anions sandwiched in the three [Cu 2 L 2 ] 2+ cations. Investigation of their magnetic properties reveals the overall antiferromagnetic behavior in the series of complexes except 2.     

Synthese von N-phenolat-funktionalisierten Makrocyclen des 1,4,7-Trazacyclononans sowie des 1-Oxa-4,7-diazacyclononans und ihre Komplexchemie mit Eisen(III)

Synthesis of N-Phenolate-functionalized Macrocycles of 1,4,7-Triazacyclononane and of 1-Oxa-4,7-diazacyclononane and their Coordination Chemistry with Iron(III) Six new tetra- or pentadentate, N-phenolate functionalized, pendant, arm macrocyclic containing a 1,4,7-traizacyclononane or a 1-oxa-4,7-diazacyclononane backbone have been synthesized and their coordination chemistry with iron(III) has been investigated. Electronic spectra of these octahedral high-spin Fe^III complexes have been measured. The Phenolate-to-iron(III) charge transfer band has been studied as a function of the number of coordinated phenolate residues (1,2, or 3) and of the substituents at the phenolate arms. The dinuclear complex [LFe₂(μ-O₂CPh)](C1O)₄)₃ has been synthesized where the two Fe^III centres are connected via a symmetric μ-benzoato bridge and two phenolate oxygen atoms (L⁷ = N-(2-hydroxybenzyl)-1,4,7-triazacyclononane).     

Boron Cluster Anions [BnHn]2– (n = 10, 12) in Reactions of Iron(II) and Iron(III) Complexation with 2, 2′‐Bipyridyl and 1, 10‐Phenanthroline

Complexation of Fe^II and Fe^III with azaheterocyclic ligands L (L = phen or bipy) were studied in the presence and in the absence of boron cluster anions [B_nH_n]^2– (n = 10, 12). The reactions were carried out in air at room temperature in organic solvents and/or water. In all the solvents used, well known [FeL₃]An (An = 2Cl^– or SO₄^2–) ferrous complexes were formed from Fe^II salts. Composition of ferric complexes with L ligands depends on the nature of solvent: either dinuclear oxo‐iron(III) chlorides [L₂ClFe^III–O–Fe^IIIL₂Cl]Cl₂ or ferric ferrates(III) [Fe^IIIL₂Cl₂][Fe^IIICl₄], or [Fe^IIIL₂Cl₂][Fe^IIICl₄L] were isolated from Fe^III salts. Introduction of the closo‐borate anions to a Fe³⁺(or Fe²⁺)/L/solv. mixture stabilizes ferrous cationic complexes [FeL₃]²⁺ in all the solvents used: only ferrous [FeL₃][B_nH_n] (n = 10, 12) complexes were isolated from all the reaction mixtures in the presence of boron cluster anions.     

Caesium bis(5‐bromosalicylaldehyde thiosemicarbazonato‐κ3O,N,S)ferrate(III): supramolecular arrangement of low‐spin FeIII complex anions mediated by Cs+ cations

The synthesis and crystal structure determination (at 293 K) of the title complex, Cs[Fe(C₈H₆BrN₃OS)₂], are reported. The compound is composed of two dianionic O,N,S‐tridentate 5‐bromosalicylaldehyde thiosemicarbazonate(2−) ligands coordinated to an Fe^III cation, displaying a distorted octahedral geometry. The ligands are orientated in two perpendicular planes, with the O‐ and S‐donor atoms in cis positions and the N‐donor atoms in trans positions. The complex displays intermolecular N—H...O and N—H...Br hydrogen bonds, creating R₄⁴(18) rings, which link the Fe^III units in the a and b directions. The Fe^III cation is in the low‐spin state at 293 K.     

Complex Formation of 2, 6‐Bis‐(2′‐hydroxyphenyl)pyridine with AlIII,FeIII and CuII

Complex formation of 2, 6‐bis(2′‐hydroxyphenyl)pyridine (H₂Lⁱ) with Fe³⁺ and Cu²⁺ was investigated in a H₂O/DMSO medium (mole fraction x_DMSO = 0.2) by potentiometric and spectrophotometric methods. The pK_a values of [H₃Lⁱ]⁺ are 2.25, 10.51 and 14.0 (25 °C, 0.1 M KCl). The formation constants of [Fe^III(Lⁱ)]⁺ and [Cu^II(Lⁱ)] (25 °C, 0.1 M KCl) are log β₁ = 21.5 for Fe³⁺ and log β₁ = 18.5 for Cu²⁺. The crystal structures of [Al(Lⁱ)₂Na(EtOH)₃], [Fe(Lⁱ)₂Na(EtOH)₃], and [Cu(Lⁱ)(py)]₂ were investigated by single‐crystal X‐ray diffraction analyses. The Fe^III and the Al^III compound are isotypic and crystallize in the monoclinic space group P2₁/n. Al‐compound (215 K): a = 12.599(3) Å, b = 16.653(3) Å, c = 17.525(4) Å, β = 100.27(3)°, Z = 4 for C₄₀H₄₀AlN₂NaO₇; Fe‐compound (293 K): a = 12.753(3) Å, b = 16.715(3) Å, c = 17.493(3) Å, β = 99.68(3)°, Z = 4 for C₄₀H₄₀FeN₂NaO₇. Both compounds contain a homoleptic, anionic bis‐complex [M(Lⁱ)₂]^‐ of approximate D₂ symmetry. The Cu compound crystallized as an uncharged, dinuclear and centrosymmetric [Cu(Lⁱ)(py)]₂ complex in the monoclinic space group P2₁/n with (293 K) a = 13.386(3) Å, b = 9.368(2) Å, c = 14.656(3) Å, β = 100.65(3)°, Z = 2 for C₄₄H₃₂Cu₂N₄O₄. The structural properties and in particular the possible influence of the ligand geometry on the stability of the metal complexes is discussed.     

catena‐Poly[hexaaquamagnesium(II) [bis(μ3‐5‐nitro‐2‐oxidoisophthalato)dicopper(II)] dihydrate]

In the centrosymmetric dinuclear anions of the title bimetallic complex, {[Mg(H₂O)₆][Cu₂(C₈H₂NO₇)₂]·2H₂O}_n, each Cu^II ion is strongly coordinated by four O atoms in a distorted square‐planar geometry. Two of these O atoms belong to phenolate groups and the other two to carboxylate groups from 5‐nitro‐2‐oxidoisophthalate (L1) trianions, derived from 5‐nitrobenzene‐1,2,3‐tricarboxylic acid (O₂N–H₃L). The phenolate O atoms bridge the two Cu^II ions in the anion. In addition, each Cu^II cation interacts weakly with a symmetry‐related carboxylate O atom of an adjacent L1 ligand, giving a square‐pyramidal coordination geometry. The copper residue forms a ladder‐like linear coordination polymer via L1 ligands. The [Mg(H₂O)₆]²⁺ cations sit on centres of inversion. The polymeric anions, cations and free water molecules are self‐assembled into a three‐dimensional supramolecular network via O—H...O hydrogen bonds.     

Two Heterometallic–Organic Frameworks Composed of Iron(III)‐Salen‐Based Ligands and d10 Metals: Gas Sorption and Visible‐Light Photocatalytic Degradation of 2‐Chlorophenol

Two examples of heterometallic–organic frameworks (HMOFs) composed of dicarboxyl‐functionalized Fe^III‐salen complexes and d¹⁰ metals (Zn, Cd), [Zn₂(Fe‐L)₂(μ₂‐O)(H₂O)₂] ? 4 DMF ? 4 H₂O ( 1 ) and [Cd₂(Fe‐L)₂(μ₂‐O)(H₂O)₂] ? 2 DMF ? H₂O ( 2 ) (H₄L=1,2‐cyclohexanediamino‐N,N′‐bis(3‐methyl‐5‐carboxysalicylidene), have been synthesized and structurally characterized. In 1 and 2 , each square‐pyramidal Fe^III atom is embedded in the [N₂O₂] pocket of an L^4? anion, and these units are further bridged by a μ₂‐O anion to give an (Fe‐L)₂(μ₂‐O) dimer. The two carboxylate groups of each L^4? anion bridge Zn^II or Cd^II atoms to afford a 3D porous HMOF. The gas sorption and magnetic properties of 1 and 2 have been studied. Remarkably, 1 and 2 show activity for the photocatalytic degradation of 2‐chlorophenol (2‐CP) under visible‐light irradiation, which, to the best of our knowledge, is the first time that this has been observed for Fe^III‐salen‐based HMOFs.     

Proton-Induced Spin State Switching in an FeIII Complex

Reversible proton-induced spin state switching of an Fe^III complex in solution is observed at room temperature. A reversible magnetic response was detected in the complex, [Fe^III(sal₂323)]ClO₄ ( 1 ), using Evans’ method ¹H NMR spectroscopy which indicated cumulative switching from low-spin to high-spin upon addition of one and two equivalents of acid. Infrared spectroscopy suggests a coordination-induced spin state switching (CISSS) effect, whereby protonation displaces the metal-phenoxo donors. The analogous complex, [Fe^III(4-NEt₂-sal₂323)]ClO₄ ( 2 ), with a diethylamino group on the ligand, was used to combine the magnetic change with a colorimetric response. Comparison of the protonation responses of 1 and 2 reveals that the magnetic switching is caused by perturbation of the immediate coordination sphere of the complex. These complexes constitute a new class of analyte sensor which operate by magneto-modulation, and in the case of 2 , also yield a colorimetric response.     

Heterotrimetallic Coordination Polymers: {CuIILnIIIFeIII} Chains and {NiIILnIIIFeIII} Layers: Synthesis,Crystal Structures,and Magnetic Properties

The use of the [Fe^III(AA)(CN)₄]^? complex anion as metalloligand towards the preformed [Cu^II(valpn)Ln^III]³⁺ or [Ni^II(valpn)Ln^III]³⁺ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and 1,10‐phenathroline (phen); H₂valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {[Cu^II(valpn)Ln^III(H₂O)₃(μ‐NC)₂Fe^III(phen)(CN)₂ {(μ‐NC)Fe^III(phen)(CN)₃}]NO₃ ? 7 H₂O}_n (Ln=Gd ( 1 ), Tb ( 2 ), and Dy ( 3 )) and the trinuclear complex [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃] ? NO₃ ? H₂O ? CH₃CN ( 4 ) were obtained with the [Cu^II(valpn)Ln^III]³⁺ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[Ni^II(valpn)Ln^III(ONO₂)₂(H₂O)(μ‐NC)₃Fe^III(bipy)(CN)] ? 2 H₂O ? 2 CH₃CN}_n (Ln=Gd ( 5 ), Tb ( 6 ), and Dy ( 7 )) resulted with the related [Ni^II(valpn)Ln^III]³⁺ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃]⁺, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {Fe^III(bipy)(CN)₄} moiety in 5 – 7 acts as a tris‐monodentate ligand towards three {Ni^II(valpn)Ln^III} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the Cu^II?Ln^III ( 1 – 3 ) and Ni^II?Ln^III ( 5 – 7 ) units, as well as through the single cyanide bridge between the Fe^III and either Ni^II ( 5 – 7 ) or Cu^II ( 4 ) account for the overall ferromagnetic behavior observed in 1 – 7 . DFT‐type calculations were performed to substantiate the magnetic interactions in 1 , 4 , and 5 . Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τ_o) and energy barrier (E_a) through the Arrhenius equation being 2.0×10^?12 s and 29.1 cm^?1, respectively. In the case of 7 , the ferromagnetic interactions through the double phenoxo (Ni^II–Dy^III) and single cyanide (Fe^III–Ni^II) pathways are masked by the depopulation of the Stark levels of the Dy^III ion, this feature most likely accounting for the continuous decrease of χ_M T upon cooling observed for this last compound.     

FeIII and FeII Phosphasalen Complexes: Synthesis,Characterization, and Catalytic Application for 2-Naphthol Oxidative Coupling

We report on the synthesis and characterization of three iron(III) phosphasalen complexes, [Fe^III(Psalen)(X)] differing in the nature of the counter-anion/exogenous ligand (X⁻=Cl⁻, NO₃⁻, OTf⁻), as well as the neutral iron(II) analogue, [Fe^II(Psalen)] . Phosphasalen (Psalen) differs from salen by the presence of iminophosphorane (P=N) functions in place of the imines. All the complexes were characterized by single-crystal X-ray diffraction, UV/Vis, EPR, and cyclic voltammetry. The [Fe^II(Psalen)] complex was shown to remain tetracoordinated even in coordinating solvent but surprisingly exhibits a magnetic moment in line with a Fe^II high-spin ground state. For the Fe^III complexes, the higher lability of triflate anion compared to nitrate was demonstrated. As they exhibit lower reduction potentials compared to their salen analogues, these complexes were tested for the coupling of 2-naphthol using O₂ from air as oxidant. In order to shed light on this reaction, the interaction between 2-naphthol and the Fe^III(Psalen) complexes was studied by cyclic voltammetry as well as UV/Vis spectroscopy.     

Ligational behaviour of two biologically active N−S donors towards cobalt(III), iron(III), iron(II) and rhodium(III)

Summary The chelating behaviour of two biologically active ligands, pyridine-2-carboxaldehyde(4-phenyl) thiosemicarbazone(L₁H) and pyridine-2-carboxaldehyde thiosemicarbazone(LH), towards Fe^III, Co^III, Fe^II and Rh^III has been investigated. The ligands act as tridentate N–N–S donors, resulting in the formation of bis-chelate complexes of the type M^III(A)₂X·nH₂O (A=L₁ or L; X=Cl, ClO₄; M=Co^III, Rh^III, Fe^III), Fe^II(L₁H)₂SO₄·2H₂O and Fe^II(L₁)₂·H₂O. Biological activity of the ligands and the metal complexes in the form ofin vitro antibacterial activities towardsE. coli has been evaluated and the possible reasons for enhancement of the activity of ligands on coordination to metal ion is discussed.     

Slow Magnetic Relaxation,Antiferromagnetic Ordering,and Metamagnetism in MnII(H2dapsc)-FeIII(CN)6 Chain Complex with Highly Anisotropic Fe-CN-Mn Spin Coupling

Reactions of [Mn(H₂dapsc)Cl₂] ⋅ H₂O (dapsc=2,6- diacetylpyridine bis(semicarbazone)) with K₃[Fe(CN)₆] and (PPh₄)₃[Fe(CN)₆] lead to the formation of the chain polymeric complex {[Mn(H₂dapsc)][Fe(CN)₆][K(H₂O)_3.5]}_n ⋅ 1.5n H₂O ( 1 ) and the discrete pentanuclear complex {[Mn(H₂dapsc)]₃[Fe(CN)₆]₂(H₂O)₂} ⋅ 4 CH₃OH ⋅ 3.4 H₂O ( 2 ), respectively. In the crystal structure of 1 the high-spin [Mn^II(H₂dapsc)]²⁺ cations and low-spin hexacyanoferrate(III) anions are assembled into alternating heterometallic cyano-bridged chains. The K⁺ ions are located between the chains and are coordinated by oxygen atoms of the H₂dapsc ligand and water molecules. The magnetic structure of 1 is built from ferrimagnetic chains, which are antiferromagnetically coupled. The complex exhibits metamagnetism and frequency-dependent ac magnetic susceptibility, indicating single-chain magnetic behavior with a Mydosh-parameter φ=0.12 and an effective energy barrier (U_eff/k_B) of 36.0 K with τ₀=2.34×10⁻¹¹ s for the spin relaxation. Detailed theoretical analysis showed highly anisotropic intra-chain spin coupling between [Fe^III(CN)₆]³⁻ and [Mn^II(H₂dapsc)]²⁺ units resulting from orbital degeneracy and unquenched orbital momentum of [Fe^III(CN)₆]³⁻ complexes. The origin of the metamagnetic transition is discussed in terms of strong magnetic anisotropy and weak AF interchain spin coupling.     

Excited State Properties of Lanthanide(III) Complexes with a Nonadentate Bispidine Ligand

Eu^III, Tb^III, Gd^III and Yb^III complexes of the nonadentate bispidine derivative L² (bispidine=3,7-diazabicyclo[3.3.1]nonane) were successfully synthesized and their emission properties studied. The X-ray crystallography reveals full encapsulation by the nonadentate ligand L² that enforces to all Ln^III cations a common highly symmetrical capped square antiprismatic (CSAPR) coordination geometry (pseudo C_4v symmetry). The well-resolved identical emission spectra in solid state and in solution confirm equal structures in both media. As therefore expected, this results in long-lived excited states and high emission quantum yields ([Eu^IIIL²]⁺, H₂O, 298 K, τ=1.51 ms, ϕ=0.35; [Tb^IIIL²]⁺, H₂O, 298 K, τ=1.95 ms, ϕ=0.68). Together with the very high kinetic and thermodynamic stabilities, these complexes are a possible basis for interesting biological probes.     

Synthesis,characterization and magnetic properties of mixed-valence iron complexes with 2-pyridyl oximes

Abstract

Two new mixed-valence iron complexes with 2-pyridyl oximes, [Fe(mpko)₃Fe(H₂O)₂(NO₃)](NO₃)·2H₂O (1) (mpko^? = methyl(2-pyridyl)ketone oximate) and [{Fe(dpko)₃}₂Fe](ClO₄)·4H₂O (2) (dpko^? = bis(2-pyridyl)ketone oximate), have been prepared by reaction of Fe^III with mpkoH in methanol (1) and Fe^II with dpkoH in methanol/water (2). Dinuclear Fe^II(low-spin)Fe^III(high-spin) and trinuclear Fe^II(low-spin)Fe^III(high-spin)Fe^II(low-spin) cations are present in the crystal structure of 1 and 2, respectively. Intermolecular hydrogen bonds in 1 lead to weak antiferromagnetic interactions between pairs of neighboring Fe^III centers, which allows observation of single-ion zero-field splitting effects.