Bis(O2S2 macrocycle) complexes of palladium(II)

Two isomeric dibenzo-O₂S₂ macrocycles L¹ and L² have been synthesised and their coordination chemistry towards palladium(II) has been investigated. Two-step approaches via reactions of 1:1-type complexes, [cis-Cl₂LPd] (1a: L = L¹, 1b: L = L²), with different O₂S₂ macrocycle systems (L¹ and L²) have led to the isolation of the following bis(O₂S₂ macrocycle) palladium(II) complexes in the solid state: [Pd(L¹)₂](ClO₄)₂ (2a) and a mixture of [Pd(L¹)₂](ClO₄)₂ (2a) + [Pd(L²)₂](ClO₄)₂ (2b).     

Sn-S and Ru-Ru bonds cleavage reactions between [Ph3SnS(CH2)3SSnPh3] and Ru3(CO)12: X-ray crystal structures of [Ph3SnS(CH2)3SSnPh3] and trans-[Ru(CO)4(SnPh3)2]

The organotin complex [Ph₃SnS(CH₂)₃SSnPh₃] (1) was synthesized by PdCl₂ catalyzed reaction between Ph₃SnCl and disodium-1,3-propanedithiolate which in turn was prepared from 1,2-propanedithiol and sodium in refluxing THF. Reaction of 1 with Ru₃(CO)₁₂ in refluxing THF affords the mononuclear complex trans-[Ru(CO)₄(SnPh₃)₂] (2) and the dinuclear complex [Ru₂(CO)₆(μ-κ²-SCH₂CH₂CH₂S)] (3) in 20 and 11% yields, respectively, formed by cleavage of Sn-S bond of the ligand and Ru-Ru bonds of the cluster. Treatment of pymSSnPPh₃ (pymS = pyrimidine-2-thiolate) with Ru₃(CO)₁₂ at 55-60 °C also gives 2 in 38% yield. Both 1 and 2 have been characterized by a combination of spectroscopic data and single crystal X-ray diffraction analysis.     

Heterometal cubane-type WFe3S4 and related clusters trigonally symmetrized with hydrotris(3,5-dimethylpyrazolyl)borate

The scope of formation and structures of tungsten-iron-sulfur clusters has been explored using reactions based on [(Tp*)WS₃]¹⁻ (1) as the ultimate precursor. The reaction system 1/FeCl₂/NaSEt/S affords the cubane cluster [(Tp*)WFe₃S₄Cl₃]¹⁻ (2), which with NaSEt is converted to [(Tp*)WFe₃S₄(SEt)₃]¹⁻ (3).Clusters 2 and 3 contain the cubane [WFe₃(μ₃-S)₄]³⁺ core.Complex 1 with FeCl₂/NaSEt forms [(Tp*)WFe₂S₃Cl₂(SEt)]¹⁻ (4) with the cuboidal [WFe₂(μ₂-S)₂(μ₃-S)(μ₂-SR)]²⁺ core.Treatment of 2 with excess Et₃P yields the edge-bridged double [(Tp*)₂W₂Fe₆S₈(PEt₃)₄] (5) with the [W₂Fe₆(μ₃-S)₆(μ₄-S)₂] core. Reaction of 2 with excess leads a mixture of products, from which [(Tp*)₂W₂Fe₅S₉Na(SH)(MeCN)]³⁻(6) was identified.This cluster, as closely related [(Tp)₂Mo₂Fe₆S₉(SH)₂]³⁻, exhibits a core topology [W₂Fe₅Na(μ₂-S)₂(μ₃-S)₆(μ₆-S)] very similar to the P^N cluster of nitrogenase. All reactions were carried out in acetonitrile. The structures of 2-6 were established crystallographically as Et₄N⁺ salts. In the cubane series, substitution of tungsten for molybdenum decreases the [MFe₃S₄]^3+/2+ redox potential by ca. 0.20 V but has a negligible effect on electron distribution. This work expands the small set of previously known weak-field W-Fe-S clusters, demonstrates the existence of tungsten-containing edge-bridged double cubanes and clusters with the P^N core topology, and introduces a new cuboidal core structure as found in 4 (Tp = hydrotris(pyrazolyl)borate, Tp* = hydrotris(3,5-dimethylpyrazolyl)borate).     

Versatile reaction of the potential host system [(Me3Sn) 4Ru(CN) 6]∞ with 4-thiopyridone/4-mercaptopyridine in water

Single crystals of three derivatives of the structurally still incompletely characterized coordination polymer [(Me₃Sn)₄Ru(CN)₆] 1b have been prepared and subjected to crystallographic studies: [1b · 4H₂O]=2b forms stacks of puckered _∞²[Ru{μ-CNSn(Me₃)NC}₂] sheets interlinked by hydrogen bonds in making use of two additional CNSn(Me₃)OH₂ ligands and quasi-zeolitic water. Mild drying of 2b leads to the “missing link” between 1b and 2b, [1b · 2H₂O], 3b. The structure of [1b · 2tp] (tp=4-thiopyridone) consists of a three-dimensional, negatively charged host framework comprising (via Sn-S bonds) one “aromatic” thione linkage and a [Me₃Sn · tp]⁺guest ion involving a more zwitterionic form of tp. Slow uptake of Me₃SnCl from the gas phase by an aqueous solution of K₄[Ru(CN)₆] and tp afforded the novel assembly [1b · 2H₂O · 0.8pms · 0.2pds] (pms/pds=4,4^′-dipyridylmono-/disulfide), the supramolecular architecture of which resembles that of 2b. Bridging pms or pds molecules occupy equivalent interlayer sites, and the pms/pds ratio is likely to vary. At least three further assemblies containing again 1b and either tp or pds/pms have likewise been isolated, however, not as single crystals.     

fac-/mer-[RuCl3(NO)(P-N)] (P-N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Complex fac-[RuCl₃(NO)(P-N)] (1) was synthesized from the reaction of [RuCl₃(H₂O)₂(NO)] and the P-N ligand, o-[(N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) was obtained by photochemical isomerization of (1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl₃(NO)(P-N)] (3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex (2) a thermally induced isomerization occurs and complex (1) is regenerated.The complexes were characterized by NMR (³¹P{¹H}, ¹⁵N{¹H} and ¹H), cyclic voltammetry, FTIR, UV-Vis, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} NMR revealed the presence of singlet at 35.6 for (1) and 28.3 ppm for (2). The ¹H NMR spectrum for (1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for (2) was observed only one singlet at 3.29 ppm. FTIR Ru-NO stretching in KBr pellets or CH₂Cl₂ solution presented 1866 and 1872 cm⁻¹ for (1) and 1841 and 1860 cm⁻¹ for (2). Electrochemical analysis revealed a irreversible reduction attributed to Ru^II-NO⁺ → Ru^II-NO⁰ at −0.81 V and −0.62 V, for (1) and (2), respectively; the process Ru^II → Ru^III, as expected, is only observed around 2.0 V, for both complexes.Studies were conducted using ¹⁵NO and both complexes were isolated with ¹⁵N-enriched NO. Upon irradiation, the complex fac-[RuCl₃(NO)(P-N)] (1) does not exchange ¹⁴NO by ¹⁵NO, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) does. Complex mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′) was obtained by direct reaction of mer,trans-[RuCl₃(NO)(P-N)] (2) with ¹⁵NO and the complex fac-[RuCl₃(¹⁵NO)(P-N)] (1′) was obtained by thermal-isomerization of mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′).DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex (1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for (2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for (1) is based on NO (52.9%) and is less extent on Ru (38.4%), for (2) NO (58.2%) and Ru (31.5%).     

Cobalt(III) complexes with linear hexadentate N6 or N4S2 donor set atoms providing pyridyl-amide-amine/thioether coordination

Two new cobalt(III) complexes of symmetric hexadentate ligand with N₆ [1,10-bis(2-picolinamide)-4,7-diazadecane (pycdpnen)] and N₄S₂ [1,8-bis(2-picolinamide)-3,6-dithiaoctane (pycdadt)] donor set atoms have been synthesized as perchlorate salts and characterized by spectroscopic methods. All two ligands with strong-field pyridylcarboxamido N donor stabilize Co(III) as demonstrated by the facile oxidation of the cobalt center. The structures of [Co(pycdpnenH₋₂)](ClO₄) (1) and [Co(pycdadtH₋₂)](ClO₄) · H₂O (2) investigated by COSY, HMBC, HMQC and NOESY NMR studies show that compounds 1 and 2 have the same geometrical configuration. The X-ray analysis reveals that complex 2 crystallizes in a orthorhombic space group Pccn. The cation [Co(pycdadtH₋₂)]⁺ is distorted octahedral with the two pyridyl groups in cis position.     

Synthesis and characterization of isopropylamine complexes of lanthanide(II) diiodides: Molecular structure of TmI2(PrNH2)4 and EuI2(PrNH2)4

It was found that the lanthanide diiodides LnI₂ (1) (Ln = Nd, Sm, Eu, Dy, Tm, Yb) are dissolved in isopropylamine (IPA) without redox transformations. Stability of the formed solutions decreases in a row Eu ≈ Yb > Sm > Tm > Dy > Nd. Removing of a solvent in vacuum leaves complexes LnI₂(IPA)_x (2) (Nd, x = 5; Sm, Eu, Dy, Tm, Yb, x = 4) as crystalline colored solids. Stability of 2-Nd,Dy,Tm is higher than that of known THF or DME coordinated salts. Divalent state of metal in the products is confirmed by data of UV-Vis spectroscopy, magnetic measurements and their chemical behavior. Structure of 2-Eu and 2-Tm was established by X-ray diffraction analysis. Oxidation of 2-Nd,Dy in IPA affords amine-amides (PrⁱNH)Ln(IPA)_y (3) (Nd, y = 4; Dy, x = 3). n-Propylamine also dissolves the iodides 1-Sm,Eu,Dy,Tm,Yb but stability of the solutions is significantly lower. 1-Nd vigorously reacts with PrⁿNH₂ even at −30 °C which hampers the formation of the solution.     

Synthesis, characterisation and solution behaviour of fluoroalkyl phosphoryl complexes of tin tetrachloride

The synthesis, characterisation and solution behaviour of a series of octahedral complexes SnCl₄·2L (L = R₂NP(O)(OCH₂CF₃)₂; R = Me (1); Et (2) or L = P(O)(OCH₂R_f)₃; R_f = CF₃ (3); C₂F₅ (4)) are described. Complexes 1-4 were prepared from SnCl₄ and 2 equiv. of the ligand, L, in anhydrous CH₂Cl₂ solution. The adducts have been characterised by multinuclear (¹H, ³¹P and ¹¹⁹Sn) NMR, IR spectroscopy and elemental analysis. In dichloromethane solution, the NMR data showed the presence of a mixture of cis and trans isomers for 1 and 2 and only the cis isomer for 3 and 4. The difference could be interpreted in terms of the electronic effects of the substituents on the phosphorus atom of the ligand. In addition, the solution structure of the complexes studied by variable temperature ³¹P-{¹H} and ¹H NMR in the presence of excess ligand indicated that the ligand exchange on the cis isomer dominates the chemistry. The metal-ligand exchange barriers were estimated to be 13.38 and 11.39 kcal/mol for 1 and 3, respectively. The results are discussed and compared with those previously reported for the related hexamethylphosphoramide adduct, SnCl₄·2HMPA.     

Hydrogen-bonding assemblies constructed from metalloligand building blocks and H2O

New hydrogen-bonding assemblies were synthesized from the reaction of a metalloligand, [Cu(2,4-pydca)₂]²⁻ (L^Cu) (2,4-pydca = 2,4-pyridinedicarboxylate), with a Fe^II ion or an imidazole in an aqueous medium and crystallographically characterized. The obtained compounds, [Fe(H₂O)₆][Cu(2,4-pydca)₂] (1) and [Cu(2,4-pydca)(imidazole)₂] · 2H₂O (2), have metalloligand dimer units, [Cu₂(2,4-pydca)₄]⁴⁻ and [Cu₂(2,4-pydca)₂(imidazole)₄], respectively, each of which assembles by π-π (1) and hydrogen-bonding (2) interactions to form 1-D metalloligand arrays. The 1-D metalloligand arrays are linked by rich hydrogen-bonding interactions via H₂O molecules.     

Complexes of the {ReOX2} (X = Cl, Br) core with single amino acid chelate derivatives

The reactions of 1 equiv. of the ligand 3-(ethoxycarbonylmethyl-pyridin-2-ylmethyl-amino)-propionic acid methyl ester (2) with the Re(V) starting materials [ReOX₃(PPh₃)₂] (X = Cl, Br) in refluxing chloroform yielded the Re(V)-oxo dihalide complexes [ReOX₂{(C₅H₄NCH₂)N(CH₂CO₂)(C₂H₄CO₂CH₃)}] (X = Cl, 3; X = Br, 4). The complexes were characterized by elemental analysis, NMR and IR spectroscopy, cyclic voltammetry and X-ray crystallography. Complex 3 displays distorted octahedral coordination geometry with the tridentate ligand coordinating facially to the Re(V) center. The carboxylate oxygen atom occupies an axial site trans to the ReO bond. The two chlorine atoms consequently adopt a cis configuration.     

Reactions of the fac-[Re(CO)3] and [ReO] moieties with substituted benzothiazoles

The reaction of 2-(2-aminophenyl)benzothiazole (Habt) with [Re(CO)₅Br] led to the isolation of the rhenium(I) complex fac-[Re(Habt)(CO)₃Br] (1). With trans-[ReOCl₃(PPh₃)₂], the ligand Habt decomposed to form the oxofree rhenium(V) complex [Re(itp)₂Cl(PPh₃)] (2) (itp = 2-amidophenylthiolate). From the reaction of trans-[ReOBr₃(PPh₃)₂] with 2-(2-hydroxyphenyl)benzothiazole (Hhpd) the complex [Re^VOBr₂(hpd)(PPh₃)] (3) was obtained. Complexes 1-3 are stable and lipophilic. ¹H NMR and infrared assignments, as well as the X-ray crystal structures, of the complexes are reported.     

Synthesis, isolation and spectroscopic characterization of Dawson polyoxotungstate-supported, organometallic complex, [{(C6H6)Ru}P2W15V3O62]: The two positional isomers

The Dawson polyoxotungstate (POM)-based, organometallic ruthenium(II) complex, [{(C₆H₆)Ru}P₂W₁₅V₃O₆₂]⁷⁻, was synthesized as two materials, i.e. 1 · 2Bu₄NCl and 1 · 1Bu₄NCl (1 = (Bu₄N)₇[{(C₆H₆)Ru}P₂W₁₅V₃O₆₂]), which contained two positional isomers a and b as major or minor species. In isomer a with the overall C_s symmetry, the (C₆H₆)Ru²⁺ group was supported on one vanadium(V) octahedral site (two V-O-V bridging oxygens and one OV terminal oxygen) of the three edge-shared vanadium(V) octahedra (V₃ site, B-site) in the Dawson POM-support [1,2,3-P₂W₁₅V₃O₆₂]⁹⁻, whereas in the other isomer b with the overall C_3v symmetry, the (C₆H₆)Ru²⁺ group was supported on the center of the V₃ site in the Dawson POM-support. Material 1 · 2Bu₄NCl was prepared by a stoichiometric reaction in CH₂Cl₂ at ambient temperature of the Dawson POM-support (Bu₄N)₉[1,2,3-P₂W₁₅V₃O₆₂] with the precursor [(C₆H₆)RuCl₂]₂, whereas material 1 · 1Bu₄NCl was prepared by a stoichiometric reaction in CH₃CN under refluxing conditions. The temperature-varied ³¹P NMR spectra revealed that b was thermodynamically more stable thana.     

Pyridine and phosphine reactions with [CPh3][B(C6F5)4]

Trityl borate salts [4-RPyCPh₃][B(C₆F₅)₄] (R = H 1, ^tBu 2, Et 3, NMe₂4) and [R₃PCPh₃][B(C₆F₅)₄] (R = Me 5, ⁿBu 6, Ph[1] 7, p-MeC₆H₄8) are readily prepared via equimolar reaction of the appropriate pyridine or phosphine and trityl borate [CPh₃][B(C₆F₅)₄]. The analogous reactions of PⁱPr₃ affords the product [(p-ⁱPr₃P-C₆H₄)Ph₂CH][B(C₆F₅)₄] (9) while the corresponding reactions of Cy₃P and ^tBu₃P gave the cyclohexadienyl derivatives [(p-R₃PC₆H₅)CPh₂][B(C₆F₅)₄] (R = Cy 10, ^tBu 11). X-ray structures of 5 and 9 are reported.     

Novel long bipyridine-type linking ligands containing an intervening naphthalene fragment: [Zn(L)(NO3)2], [Zn(L)(NO3)2], and [Cd(L)1.5(NO3)2] (L = (4-py)-CHN-C10H6-NCH-(4-py); L = (3-py)-CHN-C10H6-NCH-(3-py))

Novel bipyridine-type linking ligands L¹ ((4-py)-CHN-C₁₀H₆-NCH-(4-py)) and L² ((3-py)-CHN-C₁₀H₆-NCH-(3-py)), a pair of isomers due to possessing different pairs of terminal pyridyl groups, were prepared by the Schiff-base condensation. In ligand L¹, the N?N separation between the terminal pyridyl groups is 16.0 Å, with their nitrogen donor atoms at the para positions (4,4′). The corresponding N?N separation in ligand L² is 14.2 Å, with the nitrogen donor atoms at the meta positions (3,3′). 1-D zigzag-chain coordination polymers [Zn(L¹)(NO₃)₂] (1) and [Zn(L²)(NO₃)₂] (2) were prepared by reactions of Zn(NO₃)₂ · 6H₂O with ligands L¹ and L², respectively, by solution diffusion. Polymer 3, [Cd(L¹)_1.5(NO₃)₂], prepared from Cd(NO₃)₂ · 4H₂O and L¹, exhibits a 1-D ladder structure, whose repeating ladder unit consists of four Cd metals and four L¹ ligands to create a large 76-membered ring with dimensions of 20.8 × 20.8 Å. All products were structurally characterized by X-ray diffraction.     

Manganese(III) complexes of N2O2 donor 5-bromosalicylideneimine ligands: Combined effects of electron withdrawing substituents and chelate ring size variations on electrochemical properties

A series of mononuclear manganese(III) complexes of formulae [Mn(L)(X)(H₂O)] (1-13) and [Mn(L)(X)] (14-17) (X = ClO₄, F, Cl, Br, I, NCS, N₃), derived from the Schiff bases of 5-bromosalicylaldehyde and different types of diamine (1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopropane and 1,4-diaminobutane), have been synthesized and characterized by the combination of IR, UV-Vis spectroscopies, cyclic voltammetry and by X-ray crystallography. The redox properties of all the manganese(III) complexes show grossly identical features consisting of a reversible or quasireversible Mn^III/Mn^II reduction. Besides Mn^III/Mn^II reduction, the complexes 4, 5, 10, 13 and 16 also show reversible or quasireversible Mn^III/Mn^IV oxidation. A linear correlation has been found for the complexes 5, 7, 11 and 13 [Mn(L²)(X)(H₂O)] (X = F, Cl, Br, I) when E_1/2 [Mn^III/Mn^II] is plotted against Mulliken electronegativities (χ_M). The effect of the flexibility of the ligand on redox potential has been studied. It has been observed that the manganese(II) state is stabilized with increasing flexibility of the ligand environment. The crystal structure of 6 shows an octahedral geometry.     

Bioinspired FeIIICdII and FeIIIHgII complexes: synthesis, characterization and promiscuous catalytic activity evaluation

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe^IIICd^II(L)(μ-OAc)₂]ClO₄·0.5H₂O (1) complex containing the unsymmetrical ligand H₂L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe₂^IIIHg₂^II(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) and [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe^III₂Hg^II₂(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) can be converted to (3) by the fixation of atmospheric CO₂ since the crystal structure of the tetranuclear organometallic complex [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) with an unprecedented {Fe^III(μ-O_phenoxo)₂(μ-CO₃)Fe^III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe^III-bound hydroxo group on the CO₂ molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe^III centers in 3 are antiferromagnetically coupled (J = − 7.2 cm^− 1) and that the Fe^III-OR-Fe^III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe^III…Hg^II distance could be responsible for the lower catalytic effectiveness of 2.     

Reaction of [MCl2(CH3CN)2] (M = Pd(II), Pt(II)) compounds with N1-alkylpyridylpyrazole-derived ligands

Palladium(II) and platinum(II) complexes with N-alkylpyridylpyrazole-derived ligands, 2-(1-ethyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L¹) and 2-(1-octyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L²), cis-[MCl₂(L)] (M = Pd(II), Pt(II)), have been synthesised. Treatment of [PdCl₂(L)] (L = L¹, L²) with excess of ligand (L¹, L²), pyridine (py) or triphenylphosphine (PPh₃) in the presence of AgBF₄ and NaBPh₄ produced the following complexes: [Pd(L)₂](BPh₄)₂, [Pd(L)(py)₂](BPh₄)₂ and [Pd(L)(PPh₃)₂](BPh₄)₂. All complexes have been characterised by elemental analyses, conductivity, IR and NMR spectroscopies. The crystal structures of cis-[PdCl₂(L²)] (2) and cis-[PtCl₂(L¹)] (3) were determined by a single crystal X-ray diffraction method. In both complexes, the metal atom is coordinated by one pyrazole nitrogen, one pyridine nitrogen and two chlorine atoms in a distorted square-planar geometry. In complex 3, π-π stacking between pairs of molecules is observed.     

Mixed-ligand tris chelated complexes of Mo(IV) and W(IV): A comparative study

Two hitherto unknown mixed-ligand tris chelated complexes containing 2-aminothiophenolate, [Et₄N]₂[M^IV(NH-(C₆H₄)-S)(mnt)₂] (M = Mo, 1a; W, 2a) and two mixed-ligand tris chelate complex containing N,N-diethyldithiocarbamate, [Et₄N]₂[M^IV(Et₂NS₂)(mnt)₂] (M = Mo, 1b; W, 2b) have been synthesized and characterized structurally. Although these complexes are supposed to be quite similar to the well-known symmetric tris chelate complexes of maleonitriledithiolate (mnt), [Et₄N]₂[M^IV(mnt)₃] (M = Mo, 1c; W, 2c), but display both trigonal prismatic and distorted trigonal prismatic geometry in their crystal structure indicating the possibility of an equilibrium between these two structural possibilities in solution. Unlike extreme stability of 1b, 2b, 1c and 2c, both 1a and 2a are highly unstable in solution. In contrast to one reversible reduction in case of 1b and 2b, 1a and 2a exhibited no possible reduction up to −1.2 V and two sequential oxidation steps which have been further investigated with EPR study. Differences in stability and electrochemical behavior of 1a, 1b, 2a and 2b have been correlated with theoretical calculations at DFT level in comparison with long known 1c and 2c.     

Formation and stabilization of five-coordinate iron(II) verdoheme analogues by axial weakly coordinating anion ligation. X-ray crystal structures of [(OEOPFe)2O](X)2 (X = AsF6, SbF6)

The effect of weakly coordinating anions, , as axial ligands on the formation and coordination chemistry of verdoheme analogues have been examined. Two new five-coordinate and stable iron(II) verdoheme analogues, [OEOPFe^IIX], where OEOP is the monoanion of octaethyloxoporphyrin and X = AsF₆ and SbF₆, have been isolated. The compounds have been characterized by different spectroscopic methods as well as elemental analysis. ¹H NMR spectroscopy and magnetic moment measurements show that the [OEOPFe^IIX] are paramagnetic and iron is five-coordinate. Exposure of dichloromethane solutions of [OEOPFe^IIX] (X = AsF₆ (2), SbF₆ (3)) to dioxygen result in their transformation into the μ-oxo bridged compounds, [(OEOPFe)₂O](X)₂ (X = AsF₆ (4), SbF₆ (5)). The structures of 4 and 5 have been determined by X-ray diffraction analysis, both are structurally similar with a P2₁/c space group in the monoclinic crystal system.     

Self-assembly and third-order optical properties of HgI2 with linear and angular bipyridine ligands

Two bis(pyridyl) ligands: N,N′-bis(4-pyridyl)-1,4-benzenedicarboxamide (bpba) and N,N′-bis(3-pyridylformyl)imidazolidine-2-thione (bpit) have been designed and synthesized. Self-assembly of the linear ligand bpba and angular ligand bpit with HgI₂ results in a one-dimensional zigzag polymer {[HgI₂(bpba)] · 1.5CH₃OH}_n (1) and a binuclear metallamacrocycle [HgI₂(bpit)]₂ · 3H₂O (2), respectively. Single crystal X-ray diffraction analyses reveal that in the crystal structure of 1 the linear ligand bpba is in transoid conformation, while in the crystal structure of 2 the angular ligand bpit coordinates with HgI₂ in cisoid conformation, the different geometries of the two ligands attribute to forming the dissimilar frameworks of two HgI₂ adducts. The determination of third-order nonlinear optical (NLO) properties of 1 and 2 in DMF solution shows that adducts 1 and 2 possess strong NLO self-focusing effect. The hyperpolarizability γ values of 1 and 2 are calculated to be 2.10 × 10⁻²⁹ and 3.24 × 10⁻²⁹ esu, respectively, which are comparable to those of some NLO materials. And the result indicates that the heavier atoms Hg and I together with the polymeric aggregation play an important role in determining their NLO properties.