MnII Centers Research Articles

(2,5-Di-methyl-imidazole){N,N',N'',N'''-[porphyrin-5,10,15,20-tetra-yltetra-(2,1-phenyl-ene)]tetra-kis(pyridine-3-carboxamide)}manganese(II) chloro-benzene disolvate.

In the title compound, [Mn(C68H44N12O4)(C5H8N2)]·2C6H5Cl, the central MnII ion is coordinated by four pyrrole N atoms of the porphyrin core in the basal sites and one N atom of the 2,5-di-methyl-imidazole ligand in the apical site. Two chloro-benzene solvent mol-ecules are also present in the asymmetric unit. Due to the apical imidazole ligand, the Mn atom is displaced out of the 24-atom porphyrin mean plane by 0.66 Å. The average Mn-Np (p = porphyrin) bond length is 2.143 (8) Å, and the axial Mn-NIm (Im = 2,5-di-methyl-imidazole) bond length is 2.171 (8) Å. The structure displays inter-molecular and intra-molecular N-H⋯O, N-H⋯N, C-H⋯O and C-H⋯N hydrogen bonding. The crystal studied was refined as a two-component inversion twin.

Synthesis, crystal structure and Hirshfeld surface analysis of Mn(II) coordination compounds with ONO-donor ligands derived from ampyrone

Four manganese(II) coordination compounds, [Mn2(L1)2(NCS)2(MeOH)2] (1) [Mn(HL2)2(NCS)2(MeOH)2] (2) [Mn2(L3)2(NCS)2(MeOH)2] (3) and [Mn(HL3)2(NCS)2(MeOH)2] (4) have been synthesized from the reaction of MnCl2·4H2O, KSCN and Schiff base ligands derived from 4-aminoantipyrine (HL1= (E)-4-((2-hydroxybenzylidene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one; HL2 = (E)-4-((2-hydroxy-3-methoxybenzylidene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one and HL3 = (E)-4-((5-bromo-2-hydroxybenzylidene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one) in methanol and the products have been characterized with single crystal X-ray diffraction (SC-XRD). The detailed studies involve the synthesis, crystal structure, FT-IR spectroscopy, UV–Vis spectroscopy, bond sum valence calculations, elemental and Hirshfeld surface analyses. In the case of 1 and 3, the phenolate bridged dinuclear MnII complexes are formed by chelating two Schiff base ligands, two thiocyanates and two methanol molecules and two crystallographically equivalent MnII ions are connected together by phenolate oxygen with the Mn···Mn distance of 3.1618(4) (in 1) and 3.1910(6) Å (in 3). In the case of 2 and 4, the octahedral coordination geometry of the MnII center in these mononuclear species is formed by chelating two Schiff base ligands, two thiocyanates and two methanol molecules. The presence of intermolecular hydrogen bond in 2 leads to the formation of molecular chains within the layers. Also, the presence of efficient π···π interactions between pyrazolone and phenyl rings and intermolecular hydrogen bonding in 4 lead to the formation of molecular chains within the layers. All of the intermolecular and intramolecular interactions have been studied by Hirshfeld surface analyses.

Bis(tetra-butyl-ammonium) tetra-chlorido-manganate(II) di-chloro-methane disolvate.

The title compound, (C16H36N)2[MnCl4]·2CH2Cl2, is an ionic organic-inorganic hybride compound consisting of a tetra-butyl-ammonium cation and a tetra-chlorido-manganate(II) anion in a 2:1 stoichiometric ratio. The cation contains a central nitro-gen atom bonded to four n-butyl groups in a tetra-hedral arrangement, while the anion contains a central MnII atom tetra-hedrally coordinated by four chlorido ligands. It co-crystallized with two equivalents of di-chloro-methane solvent, CH2Cl2, to give the following empirical formula: [(C4H9)4N]2[MnCl4]·(CH2Cl2)2. The crystal structure is mainly stabilized by Coulombic inter-actions.

Electrochemical and In-situ spectroelectrochemical properties of novel mononuclear 2,4-di-tert-butyl-6-(3,4-dicyanophenoxy)phenolate substituted metallophthalocyanine compounds

In this study, the synthesis and characterization of a series of novel tetra substituted highly soluble metallophthalocyanines [M = CoII, FeIII, MnIII, NiII and ZnII] derivatives bearing 2,4-di-tert-butyl-6-(3,4-dicyanophenoxy)phenolate groups on the peripheral positions are reported. These phthalocyanine (Pc) compounds can be used as new starting materials for the synthesis of dinuclear ball-type Pcs due to the involvement of four phthalonitrile rings as closable end groups in their molecules. The assignment of the redox processes of these compounds indicated that CoII, FeIII, and MnIII centers into the Pc core increased the redox richness of the complexes, with the addition of metal-based electron transfer processes to the ring-based ones while NiPc and ZnPc show only ring-based electron transfer processes. These ball-type Pc precursor compounds exhibited a unique character also as a result of eight redox-active nitrile end groups on the peripheral tails of the Pc core. Thus, electrochemical and spectroelectrochemical properties of metallophthalocyanine complexes were analysed, also in comparison to their previously reported (5-(tert-butyl)-2-((3,4-dicyanophenoxy)methyl)phenyl)methanolate substituted analogues to determine the influence of metal centers and substituents in the periphery. Altering the metal center of the Pc ring as incorporation of a redox active metal center and changing the positions of the substituents slightly affected the potentials for nitrile and Pc ring redox processes. However, the spectral and color responses of the complexes were significantly influenced by the nature of central metal and peripheral substituents. As an important reflection, the electron transfer processes of the complexes and the connection between the electrochemically generated anionic and cationic species originated distinct spectral and color changes, identified with in-situ spectroelectrochemical measurements in solution medium. These measurements pointed out their potential applicability in the fields of the opto electronic technologies.

Coordination Number in High-Spin-Low-Spin Equilibrium in Cluster Models of the S2 State of the Oxygen Evolving Complex.

The S2 state of the Oxygen Evolving Complex (OEC) of Photosystem II (PSII) shows high-spin (HS) and low-spin (LS) EPR signals attributed to distinct structures based on computation. Five-coordinate MnIII centers are proposed in these species but are absent in available spectroscopic model complexes. Herein, we report the synthesis, crystal structure, electrochemistry, SQUID magnetometry, and EPR spectroscopy of a MnIIIMnIV3O4 cuboidal complex featuring five-coordinate MnIII. This cluster displays a spin ground state of S = 5/2, while conversion to a six-coordinate Mn upon treatment with water results in a spin state change to S = 1/2. These results demonstrate that coordination number, without dramatic changes within the Mn4O4 core, has a substantial effect on spectroscopy.

Whose Oxygen Atom Is Transferred to the Products? A Case Study of Peracetic Acid Activation via Complexed MnII for Organic Contaminant Degradation.

Identifying reactive species in advanced oxidation process (AOP) is an essential and intriguing topic that is also challenging and requires continuous efforts. In this study, we exploited a novel AOP technology involving peracetic acid (PAA) activation mediated by a MnII-nitrilotriacetic acid (NTA) complex, which outperformed iron- and cobalt-based PAA activation processes for rapidly degrading phenolic and aniline contaminants from water. The proposed MnII/NTA/PAA system exhibited non-radical oxidation features and could stoichiometrically oxidize sulfoxide probes to the corresponding sulfone products. More importantly, we traced the origin of O atoms from the sulfone products by 18O isotope-tracing experiments and found that PAA was the only oxygen-donor, which is different from the oxidation process mediated by high-valence manganese-oxo intermediates. According to the results of theoretical calculations, we proposed that NTA could tune the coordination circumstance of the MnII center to elongate the O-O bond of the complexed PAA. Additionally, the NTA-MnII-PAA* molecular cluster presented a lower energy gap than the MnII-PAA complex, indicating that the MnII-peroxy complex was more reactive in the presence of NTA. Thus, the NTA-MnII-PAA* complex exhibited a stronger oxidation potential than PAA, which could rapidly oxidize organic contaminants from water. Further, we generalized our findings to the CoII/PAA oxidation process and highlighted that the CoII-PAA* complex might be the overlooked reactive cobalt species. The significance of this work lies in discovering that sometimes the metal-peroxy complex could directly oxidize the contaminants without the further generation of high-valence metal-oxo intermediates and/or radical species through interspecies oxygen and/or electron transfer.

Interplay of Anisotropic Exchange Interactions and Single-Ion Anisotropy in Single-Chain Magnets Built from Ru/Os Cyanidometallates(III) and Mn(III) Complex.

Two novel 1D heterobimetallic compounds {[MnIII(SB2+)MIII(CN)6]·4H2O}n (SB2+ = N,N'-ethylenebis(5-trimethylammoniomethylsalicylideneiminate) based on orbitally degenerate cyanidometallates [OsIII(CN)6]3- (1) and [RuIII(CN)6]3- (2) and MnIII Schiff base complex were synthesized and characterized structurally and magnetically. Their crystal structures consist of electrically neutral, well-isolated chains composed of alternating [MIII(CN)6]3- anions and square planar [MnIII(SB2+)]3+ cations bridged by cyanide groups. These -ion magnetic anisotropy of MnIII centers. These results indicate that the presence of compounds exhibit single-chain magnet (SCM) behavior with the energy barriers of Δτ1/kB = 73 K, Δτ2/kB = 41.5 K (1) and Δτ1/kB = 51 K, Δτ2 = 27 K (2). Blocking temperatures of TB = 2.8, 2.1 K and magnetic hysteresis with coercive fields (at 1.8 K) of 8000, 1600 Oe were found for 1 and 2, respectively. Theoretical analysis of the magnetic data reveals that their single-chain magnet behavior is a product of a complicated interplay of extremely anisotropic triaxial exchange interactions in MIII(4d/5d)-CN-MnIII fragments: -JxSMxSMnx-JySMySMny-JzSMzSMnz, with opposite sign of exchange parameters Jx = -22, Jy = +28, Jz = -26 cm-1 and Jx = -18, Jy = +20, Jz = -18 cm-1 in 1 and 2, respectively) and single orbitally degenerate [OsIII(CN)6]3- and [RuIII(CN)6]3- spin units with unquenched orbital angular momentum in the chain compounds 1 and 2 leads to a peculiar regime of slow magnetic relaxation, which is beyond the scope of the conventional Glaubers's 1D Ising model and anisotropic Heisenberg model.

Trinuclear heterometallic CuII–MII (M = Mn and Co) complexes of N,O donor ligands with o-nitro benzoate anion: Structures, magnetic properties and catalytic oxidase activities

Three new heterometallic complexes [(CuL1)2Mn(o-(NO2)C6H4CO2)2] (1), and{[(CuL2)2Mn(o-(NO2)C6H4CO2)2]·2CH3CN} (2) and {[(CuL2)2Co(o-(NO2)C6H4CO2)2]·2H2O} (3) have been synthesized using [CuL1]/[CuL2] as metalloligands (where H2L1 = N,N′-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine, H2L2 = N,Ń-bis(methyl2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Structural characterization of complexes (1–3) show that contains linear trinuclear architecture, where the terminal [CuL1]/[CuL2] units are coordinated to the central MnII (for 1 and 2)/CoII (for 3) through double phenoxido bridge along with a syn-syn bridging carboxylate anion. Complexes 1 and 2 exhibit biomimetic catecholase-like activity with the turn over numbers (kcat) of 164 and 140 h−1, respectively. The mass spectral study suggest the most probable mechanism of this biomimetic oxidase reaction whereas, cyclic voltammetry measurements indicate that CuII is reducible to CuI during catalysis. Variable temperature (2–300 K) magnetic susceptibility measurements reveal that all complexes (1–3) possess an overall antiferromagnetic coupling between CuII and the hetero metal ions with J values of –7.027(2), –7.076(1) and –2.2(1) cm−1, respectively.

Three new MnII-[MoIII(CN)7]4- molecular magnets constructed from chiral bidentate chelating ligands.

Three new cyanide-bridged compounds {[Mn((S,S)-Dpen)]3[Mn((S,S)-Dpen)(H2O)][Mo(CN)7]2·4H2O·4C2H3N}n (1-SS), {[Mn((R,R)-Dpen)]3[Mn((R,R)-Dpen)(H2O)][Mo(CN)7]2·4.5H2O·4C2H3N}n (1-RR), and {[Mn(Chxn)][Mn(Chxn)(H2O)0.8][Mo(CN)7]·H2O·4C2H3N}n (2) (SS/RR-Dpen = (S,S)/(R,R)-1,2-diphenylethylenediamine and Chxn = 1,2-cyclohexanediamine) have been successfully synthesized from the self-assembly reaction of the [MoIII(CN)7]4- unit, the MnII ions, and two chiral bidentate chelating ligands. Single-crystal structure determinations show that compounds 1-SS and 1-RR containing ligands SS/RR-Dpen are enantiomers and crystallize in the chiral space group P21. On the other hand, compound 2 crystallizes in the achiral centrosymmetric space group P1̄ due to the racemization of the SS/RR-Chxn ligands during the growth of the crystals. Despite their different space groups and ligands, all three compounds exhibit similar framework structures consisting of cyano-bridged MnII-MoIII two-dimensional layers separated by the bidentate ligands. The circular dichroism (CD) spectra have further demonstrated the enantiopure character of compounds 1-SS and 1-RR. Magnetic measurements revealed that all three compounds display ferrimagnetic ordering with similar critical temperatures of about 40 K. The chiral enantiomers 1-SS and 1-RR exhibit the magnetic hysteresis loop with a coercive field of about 8000 Oe at 2 K, which is by far the highest for all known MnII-[MoIII(CN)7]4- magnets. Analyses of their structures and magnetic properties indicated that their magnetic properties depend on the anisotropic magnetic interactions between the MnII and MoIII centers, which are closely related to the C-N-M bond angles.

Reaction of a nitrosyl complex of Mn(II)-porphyrinate with superoxide: NOD activity is favoured over SOD activity.

A five-coordinated {Mn(NO)}6 complex of Mn(II)-porphyrinate, [Mn(TMPP2-)(NO)], 1 {TMPPH2 = 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin}, upon reaction with two equivalents of superoxide (O2-) in THF at -40 °C results in the corresponding MnIII-OH complex [MnIII(TMPP2-)(OH)], 2, via the formation of a putative MnIII-peroxynitrite intermediate. Spectral studies and chemical analysis suggest that one equivalent of superoxide ion is consumed to oxidize the metal center of complex 1 leading to [MnIII(TMPP2-)(NO)]+, while the subsequent equivalent reacts with [MnIII(TMPP2-)(NO)]+ to form the corresponding peroxynitrite intermediate. UV-visible and X-band EPR spectroscopic studies suggest the involvement of a MnIV-oxo species in the reaction, which forms through the O-O bond cleavage of the peroxynitrite moiety with concomitant release of NO2. The formation of MnIII-peroxynitrite is further supported by the well-established phenol ring nitration experiment. The released NO2 has been trapped using TEMPO. It should be noted that in cases of MnII-porphyrin complexes, the reaction with superoxide generally proceeds through a SOD-like pathway where the first equivalent of superoxide ion oxidizes the MnII center and itself is reduced to peroxide (O22-), while the subsequent equivalent of superoxide reduces the MnIII center with the release of O2. In contrast, here the second equivalent of superoxide reacts with the MnIII-nitrosyl complex and follows a NOD-like pathway.

Structural Origin of Enhanced Circularly Polarized Luminescence in Hybrid Manganese Bromides

AbstractChiral hybrid metal halides with a high dissymmetry factor (glum) and a superior photoluminescence quantum yield (PLQY) are promising candidates for circularly polarized luminescence (CPL) light sources. Here, we report eight new chiral hybrid manganese halides, crystallizing in the non‐centrosymmetric space group P212121 and showing intense CPL emissions. Oppositely‐signed circular dichroism (CD) and CPL signals are detected according to the R‐ and S‐configurations of the chiral alkanolammonium cations. Time‐resolved PL spectra show long averaged decay lifetimes up to 1 ms for (R‐3‐quinuclidinol)MnBr3 (R‐1). The glum of polycrystalline samples for coordinated structures (23×10−3) is more than doubled compared with the non‐coordinated ones (8.5×10−3), due to the structural variations. R‐1 exhibit both a high glum and a high PLQY (50.2 %). The effective chirality transfer mechanism through coordination bonds, with strongly emissive MnII centers, enables a new class of high‐performance CPL materials.

Structural Origin of Enhanced Circularly Polarized Luminescence in Hybrid Manganese Bromides.

Chiral hybrid metal halides with a high dissymmetry factor (glum ) and a superior photoluminescence quantum yield (PLQY) are promising candidates for circularly polarized luminescence (CPL) light sources. Here, we report eight new chiral hybrid manganese halides, crystallizing in the non-centrosymmetric space group P21 21 21 and showing intense CPL emissions. Oppositely-signed circular dichroism (CD) and CPL signals are detected according to the R- and S-configurations of the chiral alkanolammonium cations. Time-resolved PL spectra show long averaged decay lifetimes up to 1 ms for (R-3-quinuclidinol)MnBr3 (R-1). The glum of polycrystalline samples for coordinated structures (23×10-3 ) is more than doubled compared with the non-coordinated ones (8.5×10-3 ), due to the structural variations. R-1 exhibit both a high glum and a high PLQY (50.2 %). The effective chirality transfer mechanism through coordination bonds, with strongly emissive MnII centers, enables a new class of high-performance CPL materials.

Single crystal structure features of a new synthesized heteronuclear Mn/Cu complex, a precursor for heterogeneous catalytic conversion of CO

A unique hetero-nuclear complex formulated as [Cu(pydc)2Mn(H2O)5].2H2O (1) where pydc2− = pyridine-2,6-dicarboxylato has been synthesized through a facile and environment-friendly ultrasonic reaction. Complex 1 was characterized by various techniques, including single-crystal X-ray diffraction (SC-XRD). X-ray crystallographic analysis reveals that the parallelepiped green crystals of complex 1 have a monoclinic structure with space group P21/c. The CuII and MnII centers have distorted square bipyramid geometry, while extensive H-bonding interactions help to produce a three-dimensional network. The bimetallic Cu-Mn/Al2O3 catalyst was prepared by thermal decomposition of [Cu(pydc)2Mn(H2O)5].2H2O/Al2O3. Also, a reference catalyst formulated as Cu-Mn/Al2O3 was prepared via the impregnation conventional method. Characterization of catalysts was carried out using inductively coupled plasma mass spectrometry (ICP-MS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) surface area. The performance of the catalysts was evaluated for CO conversion in the low-temperature water-gas shift (LT-WGS) reaction in the temperature range of 160–240 °C. A comparison of the WGS performance of these catalysts points out the potential application of inorganic complex in LT-WGS reaction. The catalyst constructed by thermal decomposition of complex 1 shows higher activity than the reference catalyst prepared by the impregnation conventional method.

Computational studies of the magneto-structural correlations in a manganese dimer with Jahn-Teller distortions.

Inspired by the crystal structure of a MnIII dinuclear complex we obtained featuring both Jahn-Teller (JT) elongation and compression distortions, we have modelled a series of complex cations based on the disordered crystal formulation; [Mn2(L1)2(μ2-OH)2)4+ (1), [Mn2(L1)(L2)(μ2-OH)2)4+ (2), [Mn2(L2)(L1)(μ2-OH)2)4+ (3), and [Mn2(L2)2(μ2-OH)2)4+ (4) (where L1 = (1E,1'E)-5-tert-butyl-3-(((4-(((5-tert-butyl-2-hydroxy-3-((E)-(hydroxyimino)methyl)benzyl)(methyl)amino)methyl)benzyl)(methyl)amino)methyl)-2-hydroxybenzaldehyde and L2 = 3,3'-(1,4-phenylenebis(methylene))bis(methylazanediyl)bis(methylene)bis(5-tert-butyl-2-hydroxybenzaldehyde)) with different geometries to investigate the effects of the distortions on the magnetic coupling parameter. All computationally modelled dimers had a ferromagnetic interaction between the MnIII centres, with greater magnetic coupling calculated for complexes with both JT elongation and compression present. The ferromagnetic contribution to the J coupling was ascribed to the orthogonality of the singly occupied magnetic orbitals along with the cross-interaction between the unfilled Mn1(dx2-y2) and singly occupied Mn2(dx2-y2) orbitals. Constrained calculations showed that reducing the extent of the compression at Mn2 results in a concomitant increase in the dihedral angle between the JT axes, thereby reducing the relative magnitude of the magnetic coupling between MnIII centres.

Templated Growth of a Spin-Frustrated Cluster Fragment of MnBr2 in a Metal-Organic Framework.

The metal-organic framework Zr6O4(OH)4(bpydc)6 (bpydc2- = 2,2'-bipyridine-5,5'-dicarboxylate) is used to template the growth of a cluster fragment of the two-dimensional solid MnBr2, which was predicted to exhibit spin frustration. Single-crystal and powder X-ray diffraction analyses reveal a cluster with 19 metal ions arranged in a triangular lattice motif. Static magnetic susceptibility measurements indicate antiferromagnetic coupling between the high-spin (S = 5/2) MnII centers, and dynamic magnetic susceptibility data suggest population of low-lying excited states, consistent with magnetic frustration. Density functional theory calculations are used to determine the energies for a subset of thousands of magnetic configurations available to the cluster. The Yamaguchi generalized spin-projection method is then employed to construct a model for magnetic coupling interactions within the cluster, enabling facile determination of the energy for all possible magnetic configurations. The confined cluster is predicted to possess a doubly degenerate, highly geometrically frustrated ground state with a total spin of STotal = 5/2.

Geometrical variations of two manganese(II) complexes with closely related quinoline-based tripodal ligands.

Structural analyses of the compounds di-μ-acetato-κ4 O:O'-bis-{[2-meth-oxy-N,N-bis-(quinolin-2-ylmeth-yl)ethanamine-κ4 N,N',N'',O]manganese(II)} bis-(tetra-phen-yl-borate) di-chloro-methane 1.45-solvate, [Mn2(C23O2)2(C23H23N3O)2](C24H20B)·1.45CH2Cl2 or [Mn(DQMEA)(μ-OAc)2Mn(DQMEA)](BPh4)2·1.45CH2Cl2 or [1](BPh4)2·1.45CH2Cl2, and (acetato-κO)[2-hy-droxy-N,N-bis(quinolin-2-ylmeth-yl)ethanamine-κ4 N,N',N'',O](methanol-κO)manganese(II) tetra-phenyl-borate methanol monosolvate, [Mn(CH3COO)(C22H21N3O)(CH3OH)](C24H20B)·CH3OH or [Mn(DQEA)(OAc)(CH3OH)]BPh4·CH3OH or [2]BPh4·CH3OH, by single-crystal X-ray diffraction reveal distinct differences in the geometry of coordination of the tripodal DQEA and DQMEA ligands to MnII ions. In the asymmetric unit, compound [1](BPh4)2·(CH2Cl2)1.45 crystallizes as a dimer in which each manganese(II) center is coordinated by the central amine nitro-gen, the nitro-gen atom of each quinoline group, and the meth-oxy-oxygen of the tetra-dentate DQMEA ligand, and two bridging-acetate oxygen atoms. The symmetric MnII centers have a distorted, octa-hedral geometry in which the quinoline nitro-gen atoms are trans to each other resulting in co-planarity of the quinoline rings. For each MnII center, a coordinated acetate oxygen participates in C-H⋯O hydrogen-bonding inter-actions with the two quinolyl moieties, further stabilizing the trans structure. Within the crystal, weak π-π stacking inter-actions and inter-molecular cation-anion inter-actions stabilize the crystal packing. In the asymmetric unit, compound [2]BPh4·CH3OH crystallizes as a monomer in which the manganese(II) ion is coordinated to the central nitro-gen, the nitro-gen atom of each quinoline group, and the alcohol oxygen of the tetra-dentate DQEA ligand, an oxygen atom of OAc, and the oxygen atom of a methanol ligand. The geometry of the MnII center in [2]BPh4·CH3OH is also a distorted octa-hedron, but the quinoline nitro-gen atoms are cis to each other in this structure. Hydrogen bonding between the acetate oxygen atoms and hydroxyl (O-H⋯O) and quinolyl (C-H⋯O and N-H⋯O) moieties of the DQEA ligand stabilize the complex in this cis configuration. Within the crystal, dimerization of complexes occurs by the formation of a pair of inter-molecular O3-H3⋯O2 hydrogen bonds between the coordinated hydroxyl oxygen of the DQEA ligand of one complex and an acetate oxygen of another. Additional hydrogen-bonding and inter-molecular cation-anion inter-actions contribute to the crystal packing.

Electronic and magnetic signatures of low-lying spin-flip excitonic states of [formula omitted][formula omitted]-acetate

Based upon recent work on the Mn3 monomer and the Mn(taa) there is an expectation that MnIII centers can exist in local spin states with S = 2 (3d↑↑↑↑) or S = 1 (3d↑↑↑↓). While the high-spin states are usually more stable based on Hunds first rule, the Mn3 monomer, the Mn(taa) and [Mn6IIIMnIII]3+ triplesalen provide examples where the presence of S = 1 and S = 0 low-spin states is energetically favorable. In this paper we examine the possibility that such S = 1 centers, referred to as Spin-Flip Excitons (SFE) can exist in the Mn12O12(COOR)16[H2O]2 molecule (Mn12-Ac). Our results show that up to eight of these excitons can exist as metastable electronic states. We examine the relative stability per exciton as a function of the number of these excitons and determine spin-crossover paths between the Mn12-Ac zero-exciton ground state (S = 10), a four-exciton state (S = 6) and an eight-exciton state (S = 2). The magnetic anisotropy of these states decreases monotonically and significantly with the number of excitons.

Magnetic coupling in oximato bridged {MnIII6} clusters bridged by diamagnetic dicyano-metallato linkers: A theoretical perspective

Oximato bridged {MnIII6} clusters are among the best known SMMs for transition metal clusters that exhibit a very large barrier height for magnetization reversal and decent blocking temperatures. Several attempts were made to improve the magnetic properties of this family, among others, employing dicyano-metallo linkers such as [Au/Ag(CN)2]- to link two {MnIII6} clusters gained attention as this paves the way forward to construct supramolecular architecture based on {MnIII6} units and also facilitate a way to control the intercluster exchange coupling – a parameter vital to Qubit application. In this work, we have employed DFT calculations to estimate various exchange coupling constants within the {MnIII6} clusters ([MnIII6(μ3-O)2(Et-sao)6(3-py)2(MeOH)2 (M(CN)2)2] M = Au (1), Ag (2) here sao2- is the dianion of salicylaldoxime or 2-hydroxybenzaldeyhyde oxime). We have identified four different Js within the cluster based on the orientation of the Jahn-Teller axes and the MnNOM dihedral angles. The computed J values within the clusters are in the borderline of ferro and antiferromagnetic coupling, leading to a competing interaction within the cluster, and for this reason, several spin states are found to lie close to each other. The computed Js reproduce the experimental susceptibility data and yield very small/negligible {MnIII6-MI-MnIII6} intercluster interaction. The reason for such weak couplings was analysed, and a search for stronger exchange coupling was undertaken by studying in detail the J values in [{Mn(salen)(EtOH)}3{M(CN)6}] (here M = FeIII (3), CrIII (4); Salen = N,N′-bis(salicylidene)ethylenediamine) clusters. This predictive strategy suggests that incorporating a metal ion such as CrIII could be a game-changer as this promotes a very strong ferromagnetic coupling between two MnIII centers. If this prediction is attempted for oximato bridged {MnIII6} clusters, it could be very rewarding.

A single-chain magnet based on bis(end-on azido/alkoxo)-bridged linear [MnIII2MnII] repeating units

The synthesis, structural characterization and magnetic studies of the 1D coordination polymer [MnIII2MnII(L)2(N3)2(MeOH)2]n (1) is presented. Compound 1 consists of MnIII-MnII-MnIII strictly linear trinuclear repeating units with bis(end-on azido/alkoxo) bridges between the central MnII ion and each one of the terminal MnIII ions, defining two rhombic units [MnIIIMnII(μ1,1-N3)(μ-OR)]. Each repeating unit is further linked to its neighboring ones through two μ-OR groups, defining rhombic units [MnIII2(μ-OR)2], thus promoting the chain structure of 1. The magnetic studies revealed that 1 displays single-chain magnet behavior (SCM) with energy barrier Δ = 53 ± 1 K. Compound 1 is the first example of SCM based on a mixed-valence linear trinuclear unit [MnIII2MnII(μ1,1-N3)2(μ-OR)2].

Influence of Mn/Ca ratio in Mn-Ca coordination clusters: Synthesis, structure, and magnetic characterisation

Similar reactions of MnCl2·4H2O and CaCl2 with 2,6-bis(hydroxymethyl)-4-methylphenol gave heterometallic coordination clusters with very different nuclearities, depending on the Mn:Ca ratio used. With a 1:1 ratio, the hexanuclear cluster [MnIII3CaII3(μ3-Cl(HLMe)6(H2O)6]Cl2·6.74H2O (2) with a “triangle-in-triangle” topology was obtained. However, a Mn:Ca ratio of 2:1 resulted in [MnIII12MnIICaII6(μ4-O)8(μ3-Cl)3.7(μ3-η1-N3)4.3(HLMe)12(MeCN)6]Cl2∙15MeOH (3), which corresponds structurally to the replacement by Ca2+ of six of the seven MnII centers in our previously-published cluster [MnIII12MnII7(μ4-O)8 (μ3-η1-N3)8(HLMe)12(MeCN)6]Cl2. Magnetic studies showed that the three MnIII centers in 2 are moderately antiferromagnetically coupled, while the results for 3 allowed an experimental estimate of the MnIII-MnIII coupling in the original [Mn19] cluster.