Synthesis, structures and spectroelectrochemistry of methyl-substituted bis(η-indenyl)iron(II) complexes

Several new methyl-substituted indenyl ferrocenes were prepared by metathesis reactions of the indenide (generated from the appropriate indene with BuLi) with ferrous chloride. The indenides used to prepare new ferrocenes were: 2-methyl-, 1,2-dimethyl-, 4,7-dimethyl-, 1,4,7-trimethyl-, and 1,3,4,7-tetramethyl-indenide. These indenyl ferrocenes, along with those prepared from indenide, 1-methylindenide, and 1,3-dimethylindenide, were then characterized by ¹H and ¹³C NMR, UV/visible spectroscopy, cyclic voltammetry and mass spectrometry. The cyclic voltammetry showed an additive relationship between oxidation potential and the number of methyl groups which is also position-dependent, whereas the UV/visible spectra showed two absorptions essentially unaffected by methyl substitution. Additionally, bis(2-methylindenyl)iron(II) and bis(4,7-dimethylindenyl)iron(II) were characterized by X-ray crystallography.     

A new iron(II) thiocyanato thiocyanogen complex

The reaction between Fe³⁺ and SCN^?, in glacial acetic acid medium, gave a dark red solution which differs from the classical FeSCN²⁺, prepared in aqueous medium, with regard to stability and composition. In contrast to [FeSCN]²⁺ which undergoes photochemical decomposition and is bleached by light and reduced by hydroxylammonium chloride, the new complex is stable towards these agents, but it reacts with water. In addition to the charge transfer band at 480 nm exhibited by both solutions, the new complex exhibits a sharp strong band at 253 nm characteristic of the trithiocyanate ion, [SCN^? + NCSSCN]; thiocyanogen being produced by oxidation of SCN^? by Fe³⁺. The reaction with water is attributed to the hydrolysis of thiocyanogen mainly into sulphate. The presence of thiocyanogen in the new complex enhanced polymerixation and subsequent deposition of solid complex. On the basis of chemical, spectral, and thermal analyses the formula K₂[Fe(SCN)₄(NCSSCN)], is assigned to the new compound.     

Electronic structure of iron chlorins: characterization of bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(III)triflate and bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(II)

The synthesis and characterization of the two iron chlorin complexes [Fe(III)(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) and Fe(II)(TPC)[(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2))](2) (2) are reported. The crystal structure of complex 1 has been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 2.034(4) A, and to the pyrrole trans to it N(2), 2.012(4) A, are longer than the distances to the two remaining nitrogens [N(1), 1.996(4) A, and N(3), 1.984(4) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. The (1)H NMR isotropic shifts at 20 degrees C of the different pyrrole protons of 1 varied from -0.8 to -48.3 ppm according to bis-ligated complexes of low-spin ferric chlorins. The EPR spectrum of [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) in solution is rhombic and gives the principal g values g(1) = 2.70, g(2) = 2.33, and g(3) = 1.61 (Sigmag(2) = 15.3). These spectroscopic observations are indicative of a metal-based electron in the d(pi) orbital for the [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) complex with a (d(xy))(2)(d(xz)d(yz))(3) ground state at any temperature. The X-ray structure of the ferrous complex 2 also shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 1.991(5) A, and to the pyrrole trans to it N(2), 2.005(6) A, are slightly different from the distances to the two remaining nitrogens [N(1), 1.988(5) A, and N(3), 2.015(5) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole.     

Supramolecular effects on anion-dependent spin-state switching properties in heteroleptic iron(II) complexes

We describe the preparations, characterizations, and spin-state properties of heteroleptic Fe(II) complexes containing 2,2'-bi-1,4,5,6-tetrahydropyrimidine (H(2)bip) and 2-(aminomethyl)pyridine (pic): [(H(2)bip)(2)Fe(pic)]X(2) (X = Br (1), BPh(4) (2)) and [(H(2)bip)(1.75)Fe(pic)(1.25)](BPh(4))(2) (3). The ditopic H(2)bip ligand serves as an anion binding group while pic is intended to adjust the Fe(II) ion's ligand field close to the thermal spin-crossover region. The solid state magnetic behavior of each complex salt is found to be heavily influenced by anion and solvate molecules, and is correlated with the first coordination sphere molecular structure, intermolecular interactions, and solvate-induced packing effects. Anion-dependent spin-state switching is observed in dichloromethane solution for samples of 2 treated with (n)Bu(4)NBr, albeit at significantly lower temperatures than what would be expected based on ligand field considerations alone. The origins of this behavior are discussed: circumstantial evidence points to unintended effects of anion-mediated complex pairing in solution as a significant contributor to the lower-than-expected operating temperatures.     

Complete solid state photoisomerization of bis(dipyrazolylstyrylpyridine)iron(II) to change magnetic properties

Iron(II) complexes of Z- and E-2,6-di(1H-pyrazol-1-yl)-4-styrylpyridine (Z-2 and E-2, respectively) exhibited visible light photoisomerization from Z-2 to E-2, both in solution and in solid phases. Z-2 occupied the high-spin state over the full temperature range examined, whereas E-2 displayed a spin crossover phenomenon between 100 K and 300 K.     

Polymeric bis(N,N‐dimethylacetamide)tetrakis(thiocyanato)cadmium(II)mercury(II)

The title complex, {[CdHg(SCN)₄(C₄H₉NO)₂]₂}_n, contains two crystallographically independent Cd^II centres and two Hg^II centres. Each Cd^II atom is bound to four N atoms belonging to SCN groups and to two O atoms from N,N‐di­methyl­acet­amide (DMA) ligands in an octahedral geometry. Each Hg^II centre is tetrahedrally coordinated by four SCN S atoms.     

The thiocyanato adduct of chromium(II) acetate

The first dichromium complex with axially bonded anions, [NEt₄]₂[Cr₂(O₂CCH₃)₄(NCS)₂], was obtained by reactions of [NEt₄]NCS with [Cr₂(O₂CCH₃)₄(OH₂)₂] in ethanol.     

Diverse heteroleptic ytterbium(III) thiocyanate complexes by oxidation from bis(thiocyanato)ytterbium(II)

The new ytterbium(II) thiocyanate complex [Yb(NCS)2(thf)2] (1), synthesised by redox transmetallation between [Hg(SCN)2] and ytterbium metal in THF at room temperature, gave monomeric, eight coordinate [Yb-(NCS)2(dme)3] (2, dme = 1,2-dimethoxyethane) on crystallisation from DME, and is a powerful, synthetically useful reductant. Thus, oxidation of 1 with Hg(SCN)2, Hg(C6F5)2/HOdpp (HOdpp = 2,6-diphenylphenol), TlCp (Cp = C5H5 or CH3C5H4), Tl(Ph2pz) (Ph2pz = 3,5-diphenylpyrazolate) and CCl3CCl3 in THF yielded the ytterbium(II) complexes [Yb(NCS)3(thf)4] (3), [Yb-(NCS)2(Odpp)(thf)3](4), [Yb(NCS)2Cp-(thf)3] (Cp = C5H5 (5), CH3C5H4 (6)), [Yb(NCS)2(Ph2pz)(thf)4] (7) and [Yb(NCS)2Cl(thf)4] (8). In the solid state, complexes 4, 6 and 7 were shown by X-ray crystallography to be six, eight and eight coordinate monomers, respectively. Exclusively terminal, N-bound transoid thiocyanate bonding is observed with eta1-Odpp (4), eta5/-C5H4Me (6) and eta2-Ph2Pz (7) ligands attached approximately perpendicular to the N...N vector. The chloride complex 8 is not a molecular species, but consists of discrete, seven coordinate [YbCl2(thf)5] cations and [Yb(NCS)4(thf)3] anions. By contrast, oxidation of 1 with TlO2CPh gave a mixture of [[Yb(NCS)-(O2CPh)2(thf)2]2] (9) and 3 through rearrangement of an initially formed [Yb(NCS)2(O2CPh)] species. The X-ray structure of 9 indicates a dimeric complex with a (Yb(mu-O2CPh)4Yb] core that contains both bridging bidentate and bridging tridentate benzoate groups, and with a terminal N-bound thiocyanate and two THF ligands on each ytterbium. Reduction of Ph2CO with 1 in THF yielded the dinuclear complex [[Yb(NCS)2(thf)3]2(mu-OC(Ph)2C(Ph)2O)] (10), in which two octahedral Yb centres are bridged by a 1,1,2,2-tetraphenylethane-1,2-diolate ligand, derived from reductive coupling of the benzophenone reagent.     

Thermal and photo control of the linkage isomerism of bis(thiocyanato)(2,2'-bipyridine)platinum(II)

Three linkage isomers, bis(thiocyanato-S)(2,2'-bipyridine)platinum(II) ([Pt(SCN)(2)(bpy)]), (thiocyanato-S)(thiocyanato-N)(2,2'-bipyridine)platinum(II) ([Pt(SCN)(NCS)(bpy)]), and bis(thiocyanato-N)(2,2'-bipyridine)platinum(II) ([Pt(NCS)(2)(bpy)]) were isolated, and their structures were elucidated. The crystal data are as follows: for [Pt(SCN)(2)(bpy)], C(12)H(8)N(4)S(2)Pt, orthorhombic, P2(1)2(1)2(1) (No. 19), a = 12.929(9) A, b = 18.67(1) A, c = 5.497(4) A, Z = 4; for [Pt(SCN)(NCS)(bpy)], C(12)H(8)N(4)S(2)Pt, monoclinic, P2(1)/n (No. 14), a = 10.909(7) A, b = 7.622(4) A, c = 16.02(1) A, beta = 102.323(7) degrees, Z = 4; for [Pt(NCS)(2)(bpy)], C(12)H(8)N(4)S(2)Pt, orthorhombic, Pbcm (No. 57), a = 10.3233(8) A, b = 19.973(2) A, c = 6.4540(5) A, Z = 4. The stacking structures of the isomers were found to be different depending on the coordination geometries based on the N- and S-coordination of the thiocyanato ligands, which control the color and luminescence of the crystals sensitively. The isomerization behaviors of the complex have been investigated both in solution and in the solid state. In solution, stepwise thermal isomerization from [Pt(SCN)(2)(bpy)] to [Pt(NCS)(2)(bpy)] by way of [Pt(SCN)(NCS)(bpy)] was observed using (1)H NMR spectroscopy. Reverse isomerization, from [Pt(NCS)(2)(bpy)] to [Pt(SCN)(NCS)(bpy)] and [Pt(SCN)(2)(bpy)], occurred when irradiated with near ultraviolet (UV) light. In contrast, the [Pt(SCN)(2)(bpy)] yellow crystals exhibited thermal isomerization directly to red crystals of [Pt(NCS)(2)(bpy)], as detected by changes in the emission spectrum, which indicates that the flip of two SCN(-) ligands correlatively occurred in the solid state. The yellow crystals of [Pt(SCN)(NCS)(bpy)] were also converted to the thermodynamically stable red crystal of [Pt(NCS)(2)(bpy)] though the reverse isomerization has never been observed to occur by photoirradiation in the solid state.     

The nature of spin-state transitions in Fe(II) complexes

The nature of the spin-state transition for three complexes of Fe(II), namely [Fe(phy)₂] (ClO₄)₂, [Fe(phy)₂] (BF₄)₂ and [Fe(bts)₂(NCS)₂] (where phy = 1,10-phenantroline-2-carbaldehyde phenyihydrazone and bts = 2.2′-bi-5-methyl-2-thiazoline) has been investigated by differential scanning calorimetry. For [Fe(phy)₂] (ClO₄)₂ and [Fe(phy)₂] (BF₄)₂, the spin transition is essentially of first order with ΔH = 15.7 ± 1. ΔS = 64 ± 4 and ΔH = 24.2 = 1kJ/mole. ΔS = 86 ± 5 J mol^?1 K^?1, respectively. For [Fe(bts)₂(NCS)₂] the DSC studies do not suggest a first-order transition. The observations conform to the conclusions drawn from previous studies. The relevance of ΔH and ΔS derived from ln K versus l/T plots is discussed.     

Crystal structures of bis(ethylenediamine) copper(II) diethyldithiophosphate and di(ethylenediamine)bis (diethyldithiophosphato) copper(II) thiocyanate

Journal of Structural Chemistry -     

O2 activation by bis(imino)pyridine iron(II)-thiolate complexes

The new iron(II)-thiolate complexes [((iPr)BIP)Fe(II)(SPh)(Cl)] (1) and [((iPr)BIP)Fe(II)(SPh)(OTf)] (2) [BIP = bis(imino)pyridine] were prepared as models for cysteine dioxygenase (CDO), which converts Cys to Cys-SO(2)H at a (His)(3)Fe(II) center. Reaction of 1 and 2 with O(2) leads to Fe-oxygenation and S-oxygenation, respectively. For 1 + O(2), the spectroscopic and reactivity data, including (18)O isotope studies, are consistent with an assignment of an iron(IV)-oxo complex, [((iPr)BIP)Fe(IV)(O)(Cl)](+) (3), as the product of oxygenation. In contrast, 2 + O(2) results in direct S-oxygenation to give a sulfonato product, PhSO(3)(-). The positioning of the thiolate ligand in 1 versus 2 appears to play a critical role in determining the outcome of O(2) activation. The thiolate ligands in 1 and 2 are essential for O(2) reactivity and exhibit an important influence over the Fe(III)/Fe(II) redox potential.     

The effect of diluents on extraction of copper(II) with di(2-ethylhexyl)phosphoric acid

The liquid–liquid extraction of copper(II) from sulfate medium with di(2-ethylhexyl)phosphoric acid (D2EHPA, HL) at 25°C is studied with the following parameters: pH, concentration of the extractant, and the nature of diluent. The effect of the diluent using polar and nonpolar solvents in the extraction of copper(II) is discussed. The extracted copper(II) species were CuL₂ in 1-octanol and methyl isobutyl ketone and CuL₂ · 2HL in toluene, carbon tetrachloride, and cyclohexane. The extraction constants are evaluated for different diluents.     

Synthesis and properties of iron (II) quinoline-2-carboxylates,crystal structure of trans-diaquabis(quinoline-2-carboxylato)iron (II) bis(dichloromethane) solvate

Two mononuclear iron complexes with the quinoline-2-carboxylate ion (quin-2-c ion) have been obtained by the reaction of iron powder with quinoline-2-carboxylic acid in dichloromethane. The compounds [Fe(quin-2-c)₂] (1), [Fe(quin-2-c)₂(H₂O)₂] · 2CH₂Cl₂ (2) and [Fe(quin-2-c)₂(H₂O)₂] · 2EtOH · 2H₂O (3) have been investigated by IR and UV–Vis spectroscopy, magnetic susceptibility and field-dependent magnetization measurements. The structure of 2 has been characterised by X-ray diffraction. The 2D bilayered frameworks of 2 and 3 are constructed by extensive hydrogen bonding interactions between water and the organic ligand coordinated to iron (II). The magnetic properties of 2 and 3 were interpreted on the basis of a spin Hamiltonian that included axial and rhombic crystal field components. The weak antiferromagnetic (2) and ferromagnetic (3) interactions are evident in the low temperature data and possibly occur via strong hydrogen bonds.