Manganese Analogue Research Articles

Synthesis, Characterization, and Reactivity of a (PPP) Pincer-Ligated Manganese Carbonyl Complex: Polarity Reversal Imparted by the Electrophilic Nature of a Planar Mn-P(NR2)2 Fragment.

The bonding interactions of a synthesized pincer-ligated manganese dicarbonyl complex featuring an N-heterocyclic phosphenium (NHP+) central moiety are explored. The pincer ligand [PPP]Cl was coordinated to a manganese center using Mn(CO)5Br and 254 nm light to afford the chlorophosphine complex (PPClP)Mn(CO)2Br (2) as a mixture of halide exchange products and stereoisomers. The target dicarbonyl species (PPP)Mn(CO)2 (3) was prepared by treatment of 2 with 2 equiv of the reductant KC8. Computational investigations and analysis of structural parameters were used to elucidate multiple bonding interactions between the Mn center and the PNHP atom in 3. The generation of a product of formal H2 addition, (PPHP)Mn(CO)2H (4), was achieved through the dehydrogenation of NH3BH3, affording a 2:1 mixture of 4syn:4anti stereoisomers. The nucleophilic nature of the Mn center and the electrophilic nature of the PNHP moiety were demonstrated through hydride addition and protonation of 3 to produce K(THF)2[(PPHP)Mn(CO)2] (6) and (PPClP)Mn(CO)2H (5), respectively. The observed reactivity suggests that 3 is best described as a Mn-I/NHP+ complex, in contrast to pincer-ligated dicarbonyl manganese analogues typically assigned as MnI species.

Peptide-based metalloporphyrin catalysts: unveiling the role of the metal ion in indole oxidation

Over the last decades, much effort has been devoted to the construction of protein and peptide-based metalloporphyrin catalysts capable of promoting difficult transformations with high selectivity. In this context, mechanistic studies are fundamental to elucidate all the factors that contribute to catalytic performances and product selectivity. In our previous work, we selected the synthetic peptide-porphyrin conjugate MnMC6*a as a proficient catalyst for indole oxidation, promoting the formation of a 3-oxindole derivative with unprecedented selectivity. In this work, we have evaluated the role of the metal ion in affecting reaction outcome, by replacing manganese with iron in the MC6*a scaffold. Even though product selectivity is not altered upon metal substitution, FeMC6*a shows a lower substrate conversion and prolonged reaction times with respect to its manganese analogue. Experimental and theoretical studies have enabled us to delineate the reaction free energy profiles for both catalysts, indicating different thermodynamic limiting steps, depending on the nature of the metal ion.

A P450 Harboring Manganese Protoporphyrin IX Generates a Manganese Analogue of Compound I by Activating Dioxygen

The self-sufficient cytochrome P450 102A1 (P450BM3), known for its highly efficient activation of molecular oxygen, was reconstituted with manganese protoporphyrin IX. This artificial enzyme (Mn-BM3) was found to catalyze the monooxygenation of various substrates by activating molecular oxygen. Investigation using mechanistic probes (i.e., radical clock substrates) revealed that hydroxylation by Mn-BM3 proceeds via a radical intermediate of the substrate, supporting the involvement of an “H atom abstraction/•OH recombination” mechanism, which is the commonly accepted mechanism for hydroxylation by P450s. A DFT study also indicated that the activation barrier of Mn-porphine in the rebound step is higher than that of Fe-porphine, consistent with the experimental results obtained in the radical clock experiment, wherein Mn-BM3 presents a slower rebound rate than that of heme-bound BM3.

A Highly Water- and Air-Stable Iron-Containing MRI Contrast Agent Sensor for H2 O2.

A highly water- and air-stable Fe(II) complex with the quinol-containing macrocyclic ligand H4 qp4 reacts with H2 O2 to yield Fe(III) complexes with less highly chelating forms of the ligand that have either one or two para-quinones. The reaction increases the T1 -weighted relaxivity over four-fold, enabling the complex to detect H2 O2 using clinical MRI technology. The iron-containing sensor differs from its recently characterized manganese analog, which also detects H2 O2 , in that it is the oxidation of the metal center, rather than the ligand, that primarily enhances the relaxivity.

Computational Study for CO2-to-CO Conversion over Proton Reduction Using [Re[bpyMe(Im-R)](CO)3Cl]+ (R = Me, Me2, and Me4) Electrocatalysts and Comparison with Manganese Analogues

The Nippe group has previously reported a series of imidazolium-functionalized rhenium bipyridyl tricarbonyl electrocatalysts, [Re[bpyMe(Im-R)](CO)3Cl]+ (R = Me and Me2), for CO2-to-CO conversion using H2O as the proton source [Sung, S.; Kumar, D., Electrocatalytic CO2 Reduction by Imidazolium-Functionalized Molecular Catalysts. J. Am. Chem. Soc. 2017, 139, 40, 13993−13996. 10.1021/jacs.7b07709]. These compounds feature charged imidazolium ligands in the secondary coordination sphere and exhibit higher catalytic activities as compared to the Lehn catalyst [Re(bpy)(CO)3Cl] (where bpy = 2,2′-bipyridine). However, the reaction mechanism for the CO2 reduction reaction (CO2RR) over the competing hydrogen evolution reaction (HER) is unclear. Here, we employ density functional theory (DFT) and restricted active space self-consistent field (RASSCF) methods to study the selectivity for CO2 fixation using [Re[bpyMe(ImMe)](CO)3Cl]+ (1+) in water and compare its reactivity to [Re[bpyMe(ImMe2)](CO)3Cl]+ (2+) and [Re[bpyMe(ImMe4)](CO)3Cl]+ (3+). Our results reveal that the turnover frequency (TOF) for CO2RR using 1+ is 4 orders of magnitude higher than for proton reduction, consistent with controlled potential electrolysis (CPE) experiments in which CO was the only detectable reduction product. The imidazolium moiety in the secondary coordination sphere stabilizes the metallocarboxylate species and assists the C–O cleavage through intermolecular hydrogen-bonding stabilizations. Furthermore, our calculations imply that the strongest hydrogen-bonding interactions at the C2 position in 1+ contribute to the faster reaction rate observed experimentally with respect to 2+. More significantly, the use of the energy span model demonstrates that the turnover frequency-determining transition state (TDTS) corresponds to the formation of the Re–CO2 adduct, contrasting with manganese analogues in which the C–O bond cleavage step is the TDTS. We attribute this distinction based on the electronic structures of doubly reduced active catalysts. Indeed, RASSCF calculations indicate that rhenium compounds are best described as a rhenium(I) coupled with a doubly reduced bipyridine ligand, [ReI[bpyMe(ImMe)2–](CO)3]0. In contrast, manganese analogues feature a metal center in a formal zero oxidation state antiferromagnetically coupled with an unpaired electron on the bpy, [Mn0[bpyMe(ImMe)•–](CO)3]0.

Through Bridge Spin Coupling in Homo- and Heterobimetallic Porphyrin Dimers upon Stepwise Oxidations: A Spectroscopic and Theoretical Investigation.

We have described copper(II)-iron(III) and copper(II)-manganese(III) heterobimetallic porphyrin dimers and compared them with the corresponding homobimetallic analogs. UV-visible spectra are very distinct in the heterometallic species while electrochemical studies demonstrate that these species, as compared to the homobimetallic analog, are much easier to oxidize. Combined Mössbauer, EPR, NMR, magnetic and UV-visible spectroscopic studies show that upon 2e-oxidation of the heterobimetallic complexes only ring-centered oxidation occurs. The energy differences between HOMO and LUMO are linearly dependent with the low-energy NIR band obtained for the 2e-oxidized complexes. Also, strong electronic communication between two porphyrin rings through the bridge facilitates coupling between various unpaired spins present while the coupling model depends on the nature of metal ions used. While unpaired spins of Fe(III) and the porphyrin π-cation radical are strongly antiferromagnetically coupled, such coupling is rather weak between Mn(III) and a porphyrin π-cation radical. Moreover, the coupling between two π-cation radicals are much stronger in the 2e-oxidized complexes of dimanganese(III) and copper(II)-manganese(III) porphyrin dimers as compared to their diiron(III) and copper(II)-iron(III) analogs. Furthermore, coupling between the unpaired spins of a π-cation radical and copper(II) is much stronger in the 2e-oxidized complex of copper(II)-iron(III) porphyrin dimer as compared to its copper(II)-manganese(III) analog. The Mulliken spin density distributions in 2e-oxidized homo- and heterobimetallic complexes show symmetric and asymmetric spread between the two macrocycles, respectively. In both the 2e-oxidized heterobimetallic complexes, the Cu(II) porphyrin center acts as a charge donor while Fe(III)/Mn(III) porphyrin center act as a charge acceptor. The experimental observations are also strongly supported by DFT calculations.

A gadolinium-based magnetic ionic liquid for dispersive liquid-liquid microextraction.

A hydrophobic gadolinium-based magnetic ionic liquid (MIL) was investigated for the first time as an extraction solvent in dispersive liquid–liquid microextraction (DLLME). The tested MIL was composed of trihexyl(tetradecyl)phosphonium cations and paramagnetic gadolinium chloride anions. The prepared MIL showed low water miscibility, reasonable viscosity, markedly high magnetic susceptibility, adequate chemical stability, low UV background, and compatibility with reversed-phase HPLC solvents. These features resulted in a more efficient extraction than the corresponding iron or manganese analogues. Accordingly, the overall method sensitivity and reproducibility were improved, and the analysis time was reduced. The applicability of the proposed MIL was examined through the microextraction of four sartan antihypertensive drugs from aqueous samples followed by reversed-phase HPLC with UV detection at 240 nm. The DLLME procedures were optimized for disperser solvent type, MIL mass, disperser solvent volume, as well as acid, base, and salt addition. The limits of quantitation (LOQs) obtained with the analysis of 1.2-mL samples after DLLME and HPLC were 80, 30, 40, and 160 ng/mL for azilsartan medoxomil, irbesartan, telmisartan, and valsartan, respectively. Correlation coefficients were greater than 0.9988 and RSD values were in the range of 2.48–4.07%. Under the optimized microextraction conditions and using a 5-mL sample volume, enrichment factors were raised from about 40 for all sartans using a 1.2-mL sample to 175, 176, 169, and 103 for azilsartan medoxomil, irbesartan, valsartan, and telmisartan, respectively. The relative extraction recoveries for the studied sartans in river water varied from 82.5 to 101.48% at a spiked concentration of 0.5 μg/mL for telmisartan and irbesartan and 1 μg/mL for azilsartan medoxomil and valsartan. Graphical abstract Electronic supplementary materialThe online version of this article (10.1007/s00216-020-02992-z) contains supplementary material, which is available to authorized users.

Removal of Na+ and Ca2+ with Prussian blue analogue electrodes for brackish water desalination

Desalination of brackish water sources is critical to addressing the growing global freshwater demand. One promising approach is electrically driven desalination using intercalation electrodes. While intercalation electrodes have been widely researched for energy storage applications, only a small subset of those materials is suitable for desalination. Here we report the synthesis, characterization, and in-device testing of three Prussian blue analogue intercalation compounds: copper, manganese, and zinc hexacyanoferrate with formulas KxM[Fe(CN)6]z·nH2O (M = Cu, Mn, Zn). The desalination performance for each of these materials against carbon electrodes is reported for Na+ intercalation and for Ca2+ intercalation using 1000 ppm NaCl and 1000 ppm CaCl2 feed solutions, respectively. While the copper and manganese analogs showed promising performance for Na+ and Ca2+ intercalation, the zinc compound was unstable and underwent rapid dissolution. Manganese hexacyanoferrate showed the best desalination performance in terms of salt removal capacities and salt removal rates with NaCl while copper hexacyanoferrate performed the best with CaCl2. The manganese analog proved to be the most stable intercalation material, retaining 83% and 72% of its salt removal capacity after 280 cycles in NaCl and CaCl2 feed solutions respectively.

Lithium ion storage in 1D and 2D redox active metal-organic frameworks

The lithium ion storage properties of a series of metal-organic frameworks (MOFs) with formula {[M(L)(H2O)2]H2O}n and [M(CA)(Pyz)]n (where L refers to the tetraoxolene ligands: CA = chloranilate and DHBQ = dihydroxybenzoquinone; Pyz = pyrazine; M = Fe and Mn) and exhibiting a 1D and 2D structure, respectively, have been studied. The 1D MOFs ({[M(L)(H2O)2]H2O}n) show higher reversible capacity values for lithium ion insertion with respect to 2D structures containing two organic ligands (M(CA)(Pyz)]n). The gravimetric capacity for the 1D Fe-CA MOF is 75 mAh/g at 2.16 mA/g (∼ 1 lithium atom per formula unit) higher than for the Mn complexes which is 65 mAh/g at 2.12 mA/g, though isostructural. Lithium ion insertion in the 1D Mn-CA chains takes place at 2.4 V vs. Li+/Li which is ∼700 mV higher than what is recorded for the Fe analogue. This result is most probably due to much more stable d5 electronic configuration of Mn2+ than d6 of Fe2+ in its isostructural Fe-based framework analogue of the final reduced phases. The 1D Fe-DHBQ capacity is higher than its manganese analogue 75 mAh/g at 2.5 mA/g (0.8 lithiums) against 40 mAh/g. In general, the high voltages of reaction in these 1D MOFs suggest that they involve the participation of the ligand on the redox processes along with the reduction of the transition metal if any. In fact, the potential of ion insertion changed depending on the metal. This fact along with the absence of evidence of conversion reaction by x-ray diffraction of cycled electrodes suggests that the charge delocalization may be all along the metal-ligand molecular framework participating as a whole hybrid unit in the lithium storage.

Effect of Extra-Framework Cations on Negative Linear Compressibility and High-Pressure Phase Transitions: A Study of KCd[Ag(CN)2]3.

The negative thermal expansion material potassium cadmium dicyanoargentate, KCd[Ag(CN)2]3, is studied at high pressure using a combination of X-ray single-crystal diffraction, X-ray powder diffraction, infrared and Raman spectroscopy, and density functional theory calculations. In common with the isostructural manganese analogue, KMn[Ag(CN)2]3, this material is shown to exhibit very strong negative linear compressibility (NLC) in the crystallographic c direction due to structure hinging. We find increased structural flexibility results in enhanced NLC and NTE properties, but this also leads to two pressure-induced phase transitions—to very large unit cells involving octahedral tilting and shearing of the structure—below 2 GPa. The presence of potassium cations has an important effect on the mechanical and thermodynamic properties of this family, while the chemical versatility demonstrated here is of considerable interest to tune unusual mechanical properties for application.

Crystal Structure of the Dietary Supplement Ferrous Glycine Sulfate

AbstractThe crystal structure of ferrous glycine sulfate (a ferroglycine sulfate complex with chemical formula FeSO4(C2H5NO2), a compound extensively used as an iron dietary supplement, was refined from synchrotron X‐ray powder diffraction data. The crystal structure of an (so‐far unreported) isostructural manganese analogue was also structurally detailed by a Rietveld refinement against the corresponding X‐ray powder diffraction pattern. All studied compounds crystallize in the monoclinic P21 space group, building layers of metal cations coordinated by the oxygen atoms of sulfate groups and glycine ligands. Neighboring layers are parallel packed, bonded by hydrogen bonds. The coordination polyhedra around the cations can be regarded as distorted and elongated octahedral, presumably due to severe strains present in the crystal structure of the layers.

Activity and Stability of the Tetramanganese Polyanion [Mn4(H2O)2(PW9O34)2]10— during Electrocatalytic Water Oxidation

In natural photosynthesis, the oxygen evolving center is a tetranuclear manganese cluster stabilized by amino acids, water molecules and counter ions. However, manganese complexes are rarely exhibiting catalytic activity in water oxidation conditions. This is also true for the family of water oxidation catalysts (WOCs) obtained from POM chemistry. We have studied the activity of the tetranuclear manganese POM [Mn4(H2O)2(PW9O34)2]10—(Mn4), the manganese analog of the well-studied [Co4(H2O)2(PW9O34)2]10— (Co4), one of the fastest and most interesting WOC candidates discovered up to date. Our electrocatalytic experiments indicate that Mn4 is indeed an active water oxidation catalysts, although unstable. It rapidly decomposes in water oxidation conditions. Bulk water electrocatalysis shows initial activities comparable to those of the cobalt counterpart, but in this case current density decreases very rapidly to become negligible just after 30 min, with the appearance of an inactive manganese oxide layer on the electrode.

Low-Temperature Prepared Lithium-Cobalt-Nickel-Oxide Spinels

LiMn2O4-based spinel materials have been one of the most important types of cathode materials in current lithium-ion batteries since layered LiCoO2 was used in the first commercial products by Sony Corporation in 1991. While LiCoO2 is still the preferred cathode of choice for portable electronic devices such as mobile phones, cameras, and laptop computers, the LiMn2O4-based spinels, which have low price and high power performance, are finding application in batteries for electric vehicles.1 Compared to the extensive understanding of manganese-based spinel materials, relatively little is known about the structural and electrochemical properties of cobalt-nickel-based spinel electrodes, since lithium-cobalt-nickel-oxides stabilize as a layered structure during high-temperature synthesis. However, low-temperature firing of precursor materials during the solid state synthesis of layered oxide compositions, particularly those with high cobalt content, can result in intermediate structures with quasi-spinel character.2,3 A significant advantage of these Li-Co-Ni-O (LCNO-S) spinel structures is that they offer an attractive ~3.6 V vs. lithium, i.e., approximately 600 mV higher than their manganese analogues. Moreover, unlike manganese, cobalt has a lower propensity to migrate during the electrochemical reactions. In this presentation, the low-temperature prepared LCNO-S materials will be revisited to delve into their structural and electrochemical properties.

Crystallographic and spectroscopic characterization and reactivities of a mononuclear non-haem iron(III)-superoxo complex.

Mononuclear non-haem iron(III)-superoxo species (Fe(III)-O2(-·)) have been implicated as key intermediates in the catalytic cycles of dioxygen activation by non-haem iron enzymes. Although non-haem iron(III)-superoxo species have been trapped and characterized spectroscopically in enzymatic and biomimetic reactions, no structural information has yet been obtained. Here we report the isolation, spectroscopic characterization and crystal structure of a mononuclear side-on (η(2)) iron(III)-superoxo complex with a tetraamido macrocyclic ligand. The non-haem iron(III)-superoxo species undergoes both electrophilic and nucleophilic oxidation reactions, as well as O2-transfer between metal complexes. In the O2-transfer reaction, the iron(III)-superoxo complex transfers the bound O2 unit to a manganese(III) analogue, resulting in the formation of a manganese(IV)-peroxo complex, which is characterized structurally and spectroscopically as a mononuclear side-on (η(2)) manganese(IV)-peroxo complex. The difference in the redox distribution between the metal ions and O2 in iron(III)-superoxo and manganese(IV)-peroxo complexes is rationalized using density functional theory calculations.

Influence of calcium(II) and chloride on the oxidative reactivity of a manganese(II) complex of a cross-bridged cyclen ligand.

Available data from different laboratories have confirmed that both Ca(2+) and Cl(-) are crucial for water oxidation in Photosystem II. However, their roles are still elusive. Using a manganese(II) complex having a cross-bridged cyclen ligand as a model, the influence of Ca(2+) on the oxidative reactivity of the manganese(II) complex and its corresponding manganese(IV) analogue were investigated. It has been found that adding Ca(2+) can significantly improve the oxygenation efficiency of the manganese(II) complex in sulfide oxidation and further accelerate the oxidation of sulfoxide to sulfone. Similar improvements have also been observed for Mg(2+), Sr(2+), and Ba(2+). A new monomeric manganese(IV) complex having two cis-hydroxide ligands has also been isolated through oxidation of the corresponding manganese(II) complex with H2O2 in the presence of NH4PF6. This rare cis-dihydroxomanganese(IV) species has been well characterized by X-ray crystallography, electrochemistry, electron paramagnetic resonance, and UV-vis spectroscopy. Notably, using the manganese(IV) complex as a catalyst demonstrates higher activity than the corresponding manganese(II) complex, and adding Ca(2+) further improves its catalytic efficiency. However, adding Cl(-) decreases its catalytic activity. In electrochemical studies of manganese(IV) complexes with no chloride ligand present, adding Ca(2+) positively shifted the redox potential of the Mn(IV)/Mn(III) couple but negatively shifted its Mn(V)/Mn(IV) couple. In the manganese(II) complex having a chloride ligand, adding Ca(2+) shifted both the Mn(IV)/Mn(III) and Mn(V)/Mn(IV) couples in the negative direction. The revealed oxidative reactivity and redox properties of the manganese species affected by Ca(2+) and Cl(-) may provide new clues to understanding their roles in the water oxidation process of Photosystem II.

Vibrational spectroscopic study of poldervaartite CaCa[SiO3(OH)(OH)

We have studied the mineral poldervaartite CaCa[SiO3(OH)(OH)] which forms a series with its manganese analogue olmiite CaMn[SiO3(OH)](OH) using a range of techniques including scanning electron microscopy, thermogravimetric analysis, Raman and infrared spectroscopy. Chemical analysis shows the mineral is reasonably pure and contains only calcium and manganese with low amounts of Al and F. Thermogravimetric analysis proves the mineral decomposes at 485°C with a mass loss of 7.6% compared with the theoretical mass loss of 7.7%. A strong Raman band at 852cm−1 is assigned to the SiO stretching vibration of the SiO3(OH) units. Two Raman bands at 914 and 953cm−1 are attributed to the antisymmetric vibrations. Intense prominent peaks observed at 3487, 3502, 3509, 3521 and 3547cm−1 are assigned to the OH stretching vibration of the SiO3(OH) units. The observation of multiple OH bands supports the concept of the non-equivalence of the OH units. Vibrational spectroscopy enables a detailed assessment of the molecular structure of poldervaartite.

2,3,9,10,16,17,23,24-Octakis(phenoxy/octyloxy)phthalocyaninato manganese complexes. Synthesis, structure, and nonlinear optical property

2,3,9,10,16,17,23,24-Octakis(phenoxy)phthalocyaninato manganese complex MnCl[Pc(OPh)8] (1) was prepared and spectroscopically and electrochemically characterized. For the comparative reason, 2,3,9,10,16,17,23,24-octakis(octyloxy) phthalocyaninato manganese analogue MnCl[Pc(OC8H17)8] (2) was also prepared and comparatively studied. The molecular structure of 1 with a central chloridized trivalent manganese ion has been clearly determined by single-crystal X-ray diffraction analysis. The third order nonlinear optical properties of 1 and 2 in toluene solution were studied using Z-scan technique, giving effective imaginary third order molecular hyperpolarizability of 1.44 × 10−11 and 2.27 × 10−11 esu, respectively, indicating the potential application of the phthalocyaninato manganese complexes in the optical limiting.

Cyclopentadienyl-Based Amino Acids (Cp-aa) As Phenylalanine Analogues for Tumor Targeting: Syntheses and Biological Properties of [(Cp-aa)M(CO)3](M = Mn, Re, 99mTc)

Due to an enhanced demand for amino acids, the L-type amino acid transporter 1 (LAT1) is overexpressed in many tumor cell lines. LAT1 represents therefore an attractive target for cancer therapy and diagnosis. On the basis of our reported aqueous synthesis of (Cp-R)Tc-99m(CO)(3)]-type complexes,(1-S) we describe the preparation of unnatural amino acid analogues (Cp-CH2CH(NH2)COOH)Mn(CO)(3)] and (Cp-CH(NH2)COOH)M(CO)(3)] (M = Mn, Re, Tc-99m). Starting from fully protected HC5H5-aa (aa = amino acid), (Cp-aa)Tc-99m(CO)(3)] complexes are accessible in quantitative yields and in a one-step synthesis from (TcO4)-Tc-99m](-). The rhenium and manganese analogues were prepared and structurally characterized to confirm the authenticity of the Tc-99m complex. The inhibition constant of natural phenylalanine (phe) for LAT1 is in the range 70 +/- 10 mu M. The K-i value of (Cp-CH(NH2)COOH)Mn(CO)(3)] (1a) is 53 +/- 11 mu M, whereas K-i for the ``true'' phe analogue (Cp-CH2CH(NH2)COOH)Mn(CO)(3)] (2) was surprisingly high at 277 +/- 37 mu M. Complex la caused efflux when exposed to cells, underlining its active transport by LAT1 into the cell. Tc-99m analogues of small biological lead structures such as amino acids are generally not recognized anymore by their targets, in particular by trans-membrane transporters. The bioorganometallic analogues presented here are, however, actively transported and corroborate the importance of organometallic complexes as mimics of organic lead structures in life sciences.

Mononuclear and dinuclear complexes of manganese(iii) and Iron(iii) supported by 2-salicyloylhydrazono-1,3-dithiane ligand: synthesis, characterization and magnetic properties

The coordination chemistry of 2-salicyloylhydrazono-1,3-dithiane (H2L) was studied with manganese and iron ions. The following complexes have been isolated as crystalline materials, and their crystal structures have been determined by single crystal X-Ray crystallography: MnIII(acac)(HL)2 (1) (acac = acetylacetonate), MnIII(HL)3·CH2Cl2 (2), FeIII(HL)3·2CHCl3 (3), FeII(H2L)2Cl2·2CH3OH (4), FeIII2(μ-OMe)2(HL)4·0.5CH3OH (5), FeIII2(μ-O) (HL)4·3CH2Cl2 (6). All attempts to synthesize the dinuclear μ-methoxo complex [MnIII2(μ-OMe)2(HL)4] have so far failed, even when the procedure used in the case of 2-salicyloylhydrazono-1,3-dithiolane (H2L′) ligand, which worked very efficiently, was employed. The new iron dinuclear μ-methoxo complex (5) presented in this study shows antiferromagnetic intramolecular coupling (J = −21.1 cm−1), which is in agreement with the theoretical study proposed previously for its manganese analogue.

Diaquabis(5-methylpyrazine-2-carboxylato-κ2N1,O2)cadmium

In the title compound, [Cd(C6H5N2O2)2(H2O)2], the CdII ion is coordinated in a severely distorted octa­hedral geometry. The N atoms are cis to each other, while the water O atoms and ligand O atoms are mutually trans. The crystal structure is stabilized by a network of O—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds and π–π stacking inter­actions [centroid–centroid distances = 3.730 (3) and 3.652 (3) Å] between the 5-methyl­pyrazine-2-carboxyl­ate ligands. The structure is isotypic with the manganese analog.