MnII Ions Research Articles

Synthesis and crystal structure of two manganese-based 12-metallacrown-4 complexes: Na2(3-chloro-benzoate)2[12-MCMn(III)N(shi)-4](DMF)6 and MnNa(3-chloro-benzoate)3[12-MCMn(III)N(shi)-4](DMF)(H2O)4·4DMF·0.72H2O.

Similar synthetic schemes yield two different metallacrown (MC) complexes: bis-(μ-3-chloro-benzoato)hexa-kis-(di-methyl-formamide)-tetra-kis-(μ4-N,2-dioxido-benzene-1-carboximidato)tetra-manganese(III)disodium(I), [Mn4Na2(C7H4ClO2)2(C7H4NO3)4(C3H7NO)6] or Na2(3-chloro-benzoate)2[12-MCMn(III)N(shi)-4](DMF)6, 1, and tetra-μ-aqua-tris-(μ-3-chloro-benzoato)(di-methyl-formamide)-tetra-kis-(μ4-N,2-dioxido-benzene-1-carboximidato)penta-manganese(III)sodi-um(I) di-methyl-formamide tetra-solvate 0.72-hydrate, [Mn5Na(C7H4ClO2)3(C7H4NO3)4(C3H7NO)(H2O)4]·4C3H7NO·0.718H2O or MnNa(3-chloro-benzo-ate)3[12-MCMn(III)N(shi)-4](DMF)(H2O)4·4DMF·0.72H2O, 2, where shi3- is salicyl-hydrox-imate and DMF is N,N-di-methyl-formamide. Both complexes have the same framework consisting of four MnIII ions in the MC ring and four shi3- ligands, resulting in an overall square-shaped mol-ecule. The MnIII ions are either five- or six-coordinate with elongated bond lengths in the apical or axial direction, respectively. The structure of 1 is nearly planar, and the MC binds two Na+ ions on opposite faces of the MC central cavity. The 3-chloro-benzoate anions also bind on opposite faces of the MC and form bridges between the central Na+ ions and the ring MnIII ions. For 1 the metallacrown mol-ecule, except for the central Na+ ion, exhibits whole mol-ecule disorder over two sets of sites. Both moieties are centrosymmetric and are related to each other by a pseudo-mirror operation with opposite sense of rotation around the Na⋯Na axis. The occupancy ratio of the main disorder of the metallacrown mol-ecules and 3-chloro-benzoate anions refined to 0.9276 (9):0.0724 (9). The structure of 2 is slightly domed, and the MC binds both an MnII ion and an Na+ ion in the MC central cavity. The MnII ion is located on the convex side of the MC, while the Na+ ion binds to the concave side. Complex 2 represents the first instance of a [12-MCMn(III)N(shi)-4] mol-ecule binding both 3d transition metal and alkali metal ions in the central cavity. In addition, three 3-chloro-benzoate anions bind on the convex side of the MC and connect the MnII ion to three of the ring MnIII ions.

Synthesis and crystal structure of a penta-copper(II) 12-metallacrown-4: cis-di-aqua-tetra-kis-(di-methyl-formamide-κO)manganese(II) tetra-kis-(μ3-N,2-dioxido-benzene-1-carboximidate)penta-copper(II) di-methyl-formamide monosolvate.

The title compound, [Mn(C3H7NO)4(H2O)2][Cu5(C7H4NO3)4]·C3H7NO or cis-[Mn(H2O)2(DMF)4]{Cu[12-MCCu(II)N(shi)-4]}·DMF, where MC is metallacrown, shi3- is salicyl-hydroximate, and DMF is N,N-di-methyl-formamide, crystallizes in the monoclinic space group P21/n. Two crystallographically independent metallacrown anions are present in the structure, and both anions exhibit minor main mol-ecule disorder by an approximate (non-crystallographic) 180° rotation with occupancy ratios of 0.9010 (9) to 0.0990 (9) for one anion and 0.9497 (8) to 0.0503 (8) for the other. Each penta-copper(II) metallacrown contains four CuII ions in the MC ring and a CuII ion captured in the central cavity. Each CuII ion is four-coordinate with a square-planar geometry. The anionic {Cu[12-MCCu(II)N(shi)-4]}2- is charged-balanced by the presence of a cis-[Mn(H2O)2(DMF)4]2+ cation located in the lattice. In addition, the octa-hedral MnII counter-cation is hydrogen bonded to both MC anions via the coordinated water mol-ecules of the MnII ion. The water mol-ecules form hydrogen bonds with the phenolate and carbonyl oxygen atoms of the shi3- ligands of the MCs.

The first 3, 5, 6-trichloropyridine-2-oxyacetate bridged manganese coordination polymer with features of π⋯π stacking and halogen⋯halogen interactions: Synthesis, crystal analysis and magnetic properties

A new coordination polymer [Mn(3, 5, 6-tcpa)2(2, 2′-bipy)]n (1) has been synthesized by the hydrothermal reaction of manganese sulfate hydrate with 3, 5, 6-trichloropyridine-2-oxyacetic acid (3, 5, 6-Htcpa) and 2, 2′-bipyridine (2, 2′-bipy) coligands. The X-ray single-crystal diffraction analysis shows that the MnII center is in deformed octahedral geometry bonded by two pyridyl nitrogen atoms of 2, 2′-bipy molecule and four carboxy oxygen atoms of four different 3, 5, 6-tcpa− ligands. The 3, 5, 6-tcpa− anions play as bidentate bridging-μ2 linkers and connect neighbouring MnII ions together to form the 1D double-stranded chain structure of 1, which displays interesting chair form [Mn2(COO)2] eight-membered rings. 1 is further assembled into 3D network by the co-effects of π⋯π stacking and Cl⋯Cl halogen bonds interactions. In addition, the magnetic characterizations indicated weak antiferromagnetic coupling between MnII centers for 1.

Stable Ferromagnetic Crystal of Two‐Dimensional Manganese‐Chromium Oxalate with Supramolecular Cation

A supramolecular cation of (m‐FAni+)(tst‐DCH[18]crown‐6), where m‐FAni+ and tst‐DCH[18]crown‐6 denote m‐fluoroanilinium and trans‐syn‐trans‐dicyclohexano[18]crown‐6, respectively, was introduced into a ferromagnetic {[MnIICrIII(oxalate)3]–} layer to obtain a stable organic‐inorganic hybridized crystal. The crystal structure of (m‐FAni+)(tst‐DCH[18]crown‐6){[MnIICrIII(oxalate)3]–} was constructed by alternate stacking of a two‐dimensional honeycomb layer of {[MnIICrIII(oxalate)3]–} and the supramolecular cations. Cyclohexyl moieties of tst‐DCH[18]crown‐6 penetrated the pores of the honeycomb layers, excluding solvent molecules in the crystal. The anionic layers showed ferromagnetic order of MnII and CrIII ions with S = 5/2 and S = 3/2 spins, respectively, at 5.5 K. Although the m‐FAni+ showed disorder with respect to 180° rotation of the aryl ring, no significant anomaly was observed in the dielectric response, suggesting that the disorder is static.

Binuclear isophthaloylbis(N,N-diphenylthioureate) transition metal complexes: Synthesis, spectroscopic, thermal and structural characterization

The isophthaloylbis(N,N-diphenylthiourea) molecule (H2L ligand) reacts with CuI, CuII, MnIII, FeII, FeIII and CoII ions to form binuclear complexes with formula [M2(L-O,S)2] (M = CuII (1), NiII (2)) or [M2(L-O,S)3] (M = FeIII (4), CoIII (5)). In presence of dimethyl sulfoxide, [Mn2(L-O,S)2(dmso)2] (3) was successfully obtained and represents the first manganese complex with any thiourea derivative ligand. The ligand and the complexes were characterized by spectroscopic techniques and elemental analysis. Complexes 1, 3, 4 and 5 were structurally analyzed by single crystal X-ray diffraction data, confirming the O,S chelating coordination mode. The stoichiometries were confirmed by thermal analysis with formation of the corresponding metal oxides. The set of the performed analysis corroborated that some metal ions undergo oxidation or reduction to form stable 2:2 or 2:3 metal to ligand stoichiometric complexes with H2L.

Synthesis, crystal structures and magnetic and electrochemiluminescence properties of three manganese(II) complexes.

Three novel complexes, namely, penta-μ-acetato-bis(μ2-2-{[2-(6-chloropyridin-2-yl)hydrazinylidene]methyl}-6-methoxyphenolato)-μ-formato-tetramanganese(II), [Mn4(C13H11ClN3O2)2(C2H3O2)5.168(CHO2)0.832], 1, hexa-μ2-acetato-bis(μ2-2-{[2-(6-bromopyridin-2-yl)hydrazinylidene]methyl}-6-methoxyphenolato)tetramanganese(II), [Mn4(C13H11BrN3O2)2(C2H3O2)6], 2, and catena-poly[[μ2-acetato-acetatoaqua(μ2-2-{[2-(6-chloropyridin-2-yl)hydrazinylidene]methyl}-6-methoxyphenolato)dimanganese(II)]-μ2-acetato], [Mn2(C13H11ClN3O2)(C2H3O2)3(H2O)]n, 3, have been synthesized using solvothermal methods. Complexes 1-3 were characterized by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction. Complexes 1 and 2 are tetranuclear manganese clusters, while complex 3 has a one-dimensional network based on tetranuclear Mn4(L1)2(CH3COO)6(H2O)2 building units (L1 is 2-{[2-(6-chloropyridin-2-yl)hydrazinylidene]methyl}-6-methoxyphenolate). Magnetic studies reveal that complexes 1-3 display dominant antiferromagnetic interactions between MnII ions through μ2-O bridges. In addition, 1-3 also display favourable electrochemiluminescence (ECL) properties.

The Two Alternative Oxidation State Assignments of Manganese Ions: What S2 CW-EPR Multiline (ML) Signal Simulations Reveal?

Characterizing the photosystem II (PSII) sample, continuous wave electron paramagnetic resonance (CW-EPR) simulations of the S2 ML signal at X-band frequencies was our focus. This can help increase our understanding of how the manganese (Mn) atoms in the catalytic site of the PSII magnetically interact using ML signals. It can also be used to further the understanding of possible water-splitting mechanisms in the oxygen-evolving complex (OEC). The question that remains is how much does each manganese (Mn) ion contribute to the ML signal through its hyperfine interactions in the OEC? Currently, there are two proposals for the average oxidation states of the Mn ions, denoted the ‘high’ oxidation paradigm (HOP) and the ‘low’ oxidation paradigm (LOP). Majority of PSII researchers favour the HOP. Various experiments have been conducted to investigate the two alternative oxidation states, including EPR (Jin et al. in Phys Chem Chem Phys 16(17):7799–7812, https://doi.org/10.1039/c3cp55189j, 2014; Baituti in Hyperfine Interact 238(1), https://doi.org/10.1007/s10751-017-1440-8, 2017; Ioannidis et al. in Biochemistry, https://doi.org/10.1021/bi060520s, 2006). The S2 ML EPR signal simulation using the 55Mn hyperfine coupling constants, with one very large, one medium, and two small hyperfine values, fits the experimental data. The Mn1 has a large hyperfine coupling, which agrees well with earlier data by Jin et al. [19]. Three large fractional anisotropy observed on three Mn centers (Mn1,3,4), suggests the presence of three MnIII ions, and Mn2 center is likely to be MnIV ion, hence favouring the LOP (MnIII MnIV MnIII MnIII).

Construction and magnetic properties of hemicyclic “phoenix crown” manganese clusters: Molecular assembly from {Mn5} to {Mn10} cluster

Two high-nuclearity manganese clusters formulated as [MnIIMnIII4(L)2(Py)8(N3)2]·2Py ({Mn5} cluster) and [MnIII10(L)5(DMF)6(H2O)4]·5DMF·9H2O ({Mn10} cluster), (H6L = N,N'-bis(2-salicylhydrazide)isophthalohydrazide, N3– = azide ion, Py = pyridine, and DMF = N,N'-dimethylformamide), were synthesized and structurally characterized. The four MnIII ions and one MnII ion in {Mn5} cluster are linked by two diacylhydrazine ligands to form hemicyclic “Phoenix crown” cluster structure. The {Mn10} cluster presents a deca-nuclear skeleton, which appears to be structurally equivalent to two “Phoenix crown” {Mn5} clusters bridged by a diacylhydrazine ligand. Interestingly, the double helix structure {Mn10} clusters can be also obtained via a simply dissolving and reassembling process of the “Phoenix crown” {Mn5} clusters in the mixed solution of DMF and CH3OH. The magnetic measurements show that {Mn5} and {Mn10} clusters reveal antiferromagnetic interactions.

With complements of the ligands: an unusual S-shaped [Mn7]2 assembly from tethered calixarenes.

The reaction between MnCl2·4H2O, 2,2'-bis-p-tBu-calix[4]arene (H8L1) and 2-(hydroxymethyl)pyridine (hmpH) in a basic dmf/MeOH solution results in the formation of the complex [MnIII10MnII4(L1)3(hmp)4(μ3-O)4(μ3-OH)2(MeOH)4(dmf)6](dmf)4 (6) upon vapour diffusion of petroleum ether into the mother liquor. The crystals are in the monoclinic space group C2/c, with the asymmetric unit (ASU) comprising one half of the molecule. The structure describes a large S-shaped cluster (∼40 Å top to tail) where the unusual syn and anti conformations of the calixarene ligands results in two binding pockets each containing a [MnIII5MnII2] moiety comprised of two perpendicular, vertex-sharing [Mn4] butterflies. One butterfly possesses a [MnIII4O4] core and the second a [MnIII2MnII2O3] unit with the MnII ions in the central body positions. Magnetic susceptibility and magnetisation measurements reveal weak exchange interactions between the metal centres.

Synthesis and crystal structure of catena-poly[[bis[(2,2';6',2''-terpyridine)-manganese(II)]-μ4-penta-thio-dianti-monato] tetra-hydrate] showing a 1D MnSbS network.

The asymmetric unit of the title compound, {[Mn2Sb2S5(C15H11N3)2]·4H2O} n , consists of two crystallographically independent MnII ions, two unique terpyridine ligands, one [Sb2S5]4- anion and four solvent water mol-ecules, all of which are located in general positions. The [Sb2S5]4- anion consists of two SbS3 units that share common corners. Each of the MnII ions is fivefold coordinated by two symmetry-related S atoms of [Sb2S5]4- anions and three N atoms of a terpyridine ligand within an irregular coordination. Each two anions are linked by two [Mn(terpyridine)]2+ cations into chains along the c-axis direction that consist of eight-membered Mn2Sb2S4 rings. These chains are further connected into a three-dimensional network by inter-molecular O-H⋯O and O-H⋯S hydrogen bonds. The crystal investigated was twinned and therefore, a twin refinement using data in HKLF-5 [Sheldrick (2015 ▸). Acta Cryst. C71, 3-8] format was performed.

Controlled hierarchical self-assembly of networked coordination nanocapsules via the use of molecular chaperones.

Supramolecular chaperones play an important role in directing the assembly of multiple protein subunits and redox-active metal ions into precise, complex and functional quaternary structures. Here we report that hydroxyl tailed C-alkylpyrogallol[4]arene ligands and redox-active MnII ions, with the assistance of proline chaperone molecules, can assemble into two-dimensional (2D) and/or three-dimensional (3D) networked nanocapsules. Dimensionality is controlled by coordination between the exterior of nanocapsule subunits, and endohedral functionalization within the 2D system is achieved via chaperone guest encapsulation. The tailoring of surface properties of nanocapsules via coordination chemistry is also shown as an effective method for the fine-tuning magnetic properties, and electrochemical and spectroscopic studies support that the nanocapsule is an effective homogeneous water-oxidation electrocatalyst, operating at pH 6.07 with an exceptionally low overpotential of 368 mV.

Enzymatic formation of consecutive thymine-HgII-thymine base pairs by DNA polymerases.

From the perspective of the preparation of a DNA-based nanowire containing an array of metal ions, DNA-polymerase-catalyzed primer extension reactions were investigated and the formation of up to ten consecutive T-HgII-T base pairs was achieved by the HgII-mediated primer extension reaction in the presence of MnII ions. This enzymatic approach may be one of the promising techniques for preparing a DNA-based metal array.

Hexadecanuclear MnII2MnIII14 Molecular Torus Built from in Situ Tandem Ligand Transformations.

A mixed-valent hexadecanuclear manganese cluster, [MnII2MnIII14(trz)14(thetach)4(μ3-O)8(H2O)10](ClO4)6 (Mn16), containing two MnII and 14 MnIII ions, is constructed from mixed in situ generated ligands, 1,2,3-triazole (Htrz) and 1,3,5-tri(2-hydroxyethyl)-1,3,5-triazacyclohexane (H3thetach). Remarkably, both ligands were not initially added into the reaction system, and their formations involve the in situ ligand decomposition and subsequent condensation reactions. The core of Mn16 is an elongated torus comprised of eight Mn atoms and four [Mn2O2] subunits bridged by oxo or alkoxide. The high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) of Mn16 dissolved in CH3CN indicates its structure remains intact as +3 and +4 species. Temperature and field dependent magnetization revealed predominantly antiferromagnetic exchange interactions within the cluster. The work provides one-pot synthesis of high-nuclearity manganese clusters using the ligands generated by in situ reactions in a tandem fashion.

A cyanide-bridged FeIII-MnII heterobimetallic one-dimensional coordination polymer: synthesis, crystal structure, experimental and theoretical magnetism investigation.

A new cyanide-bridged FeIII-MnII heterobimetallic coordination polymer (CP), namely catena-poly[[[N,N'-(1,2-phenylene)bis(pyridine-2-carboxamidato)-κ4N,N',N'',N''']iron(III)]-μ-cyanido-κ2C:N-[bis(4,4'-bipyridine-κN)bis(methanol-κO)manganese(II)]-μ-cyanido-κ2N:C], {[FeMn(C18H12N4O2)(CN)2(C10H8N2)2(CH3OH)2]ClO4}n, (1), was prepared by the self-assembly of the trans-dicyanidoiron(III)-containing building block [Fe(bpb)(CN)2]- [bpb2- = N,N'-(1,2-phenylene)bis(pyridine-2-carboxamidate)], [Mn(ClO4)2]·6H2O and 4,4'-bipyridine, and was structurally characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography and powder X-ray diffraction (PXRD). Single-crystal X-ray diffraction analysis shows that CP 1 possesses a cationic linear chain structure consisting of alternating cyanide-bridged Fe-Mn units, with free perchlorate as the charge-balancing anion, which can be further extended into a two-dimensional supramolecular sheet structure via inter-chain π-π interactions between the 4,4'-bipyridine ligands. Within the chain, each MnII ion is six-coordinated by an N6 unit and is involved in a slightly distorted octahedral coordination geometry. Investigation of the magnetic properties of 1 reveals an antiferromagnetic coupling between the cyanide-bridged FeIII and MnII ions. A best fit of the magnetic susceptibility based on the one-dimensional alternating chain model leads to the magnetic coupling constants J1= -1.35 and J2 = -1.05 cm-1, and the antiferromagnetic coupling was further confirmed by spin Hamiltonian-based density functional theoretical (DFT) calculations.

New MnIIMnIII8 and MnII2MnIII10MnIV2 clusters from the reaction of methyl 2-pyridyl ketone oxime with [Mn12O12(O2CR)16(H2O)4

The syntheses, crystal structures and magnetic properties of two mixed-valence Mn clusters [MnIIMnIII8O6(mpko)3(O2CMe)11] (1) and [MnII2MnIII10MnIV2O12(mpko)6(O2CPh)12(H2O)2] (2) are reported. They were obtained from the corresponding reactions in MeCN of [Mn12O12(O2CR)16(H2O)4] (R = Me (3), Ph (4)) with eight equivalents of methyl(pyridine-2-yl)ketone oxime (mpkoH). The cores of 1 and 2 are structurally related: 1 possesses a [Mn9(µ3-O)6]14+ core with an unusual topology comprising a near-planar MnIII-centered MnIII6 hexagon with additional MnII and MnIII ions above and below the plane. Complex 2 possesses a [Mn14(µ4-O)2(µ3-O)10]18+ core that can be described as a dimer of two Mn7 incomplete-cores of 1. It is also a rare example of a Mn cluster containing three Mn oxidation states. Fits of variable-temperature, solid-state dc magnetic susceptibility data collected in a 0.1 T field in the 5.0–300 K range established that 1 and 2 possess ground state spins of S = 3/2 and S = 1, respectively, which were confirmed by ac in-phase susceptibility data.

Synthesis, structural and DFT interpretation of a Schiff base assisted Mn(III) derivative

A mononuclear MnIII derivative, [Mn(L)(SCN)(H2O)] (1) [where H2L = N,N′-bis(salicyaldehydene)-1,3-diaminopropan-2-ol] has been synthesized and systematically characterized. In 1, the central MnIII ion is linked to the NNOO donor atoms of the potentially binucleating precursor L2− and additionally coordinates one water molecule and the pseudohalide SCN−, thus yielding a distorted octahedral geometry. The UV–Vis spectra of 1 shows an intense band corresponding to a 5T2g − 5Eg transition at 545 nm; thus presuming the octahedral geometry around the Mn ion. The solid and solution EPR spectra of 1 have been simulated with an HP 53150A microwave frequency counter which has confirmed the +3 oxidation state of the metal ion. We have also conducted a DFT computational study which has confirmed that compound 1 self assembles into a two-dimensional network via O‒H⋯O, π–π, and unconventional C‒H … π(SCN) interactions involving the π-system of the thiocyanate. The room temperature magnetic susceptibility of compound 1 has yielded an effective magnetic moment (μeff) value of 4.96 B.M.

Theoretical Studies on Trinuclear {MnIII2GdIII} and Tetranuclear {MnIII2GdIII2} Clusters: Magnetic Exchange, Mechanism of Magnetic Coupling, Magnetocaloric Effect, and Magneto-Structural Correlations.

Among various applications that are proposed for {3d-4f} clusters, magnetic refrigeration based on the principle of the magnetocaloric effect (MCE) is gaining attention in recent years due to the substantially large MCE values reported for these types of molecules. While various factors play a role in controlling the MCE values, understanding the structural parameters that control the magnetic exchange play a vital role in the development of novel molecules possessing attractive MCE characteristics. In this regard, theoretical tools based on density functional methods are indispensable. In this work, we have employed density functional methods to study the magnetic properties of six {MnIIIGdIII} clusters. This comprises a trinuclear complex {MnIII2GdIII}, [Mn2GdO(Piv)2(dmem)2(NO3)3] (dmem = 2-{[2-(dimethylamino)ethyl]methylamino}ethanol) (1), along with four tetranuclear {MnIII2GdIII2} complexes, [Mn2Gd2O2(Piv)8(HO2CCMe3)2(MeOH)2] (Piv = 2,2-dimethylpropanoic acid) (2), [Mn2Gd2O2(Piv)8(HO2CCMe3)4] (3), [Mn2Gd2(OH)2(O2CPh)4(NO3)2(teaH)2] (tea = triethanolamine) (4), and [Mn2Gd2(O)(Piv)2(hep)4(NO3)4] (hep = 2-(2-hydroxyethyl)pyridine) (5), and a single-chain compound containing the {MnIII2GdIII2} core, [Mn2Ln2(OH)(OMe)(hmp)4(NO3)4(O3SC6H4CH3)2]n (hmp = 2-hydroxymethylpyridine) (6). Here we have evaluated the exchange interactions between MnIII and GdIII ions and MnIII···MnIII ions in trinuclear as well as tetranuclear complexes. Our DFT-computed exchange interaction (J) values reproduce the experimental susceptibility data well, offering confidence in the estimated J values. Our calculations yield a diverse set of J values among these complexes ranging from weak ferromagnetic to moderate antiferromagnetic {MnIII···GdIII} coupling. Using orbital overlap and NBO analysis, we have explored the mechanism of magnetic coupling and deciphered the origin of diverse J values noted among these complexes. Particularly, the importance of Jahn-Teller axes of the MnIII ions and its orientation with respect to the nature of coupling is established using the qualitative mechanism derived. The {MnIII···MnIII} coupling in all complexes are estimated to be antiferromagnetic, and the consequence of this on the {MnIII···GdIII} J values and how this influences the ground-state S values are discussed in detail. Further, we have developed magneto-structural correlations to evaluate the importance of structural parameters that control the {MnIII···GdIII} coupling. Our results reveal that Mn-O-Gd bond angles and Mn-O-Gd-O dihedral angles hold the key to the sign and magnitude of the {MnIII···GdIII} J values. Further on, utilizing the computed J values, we have estimated the MCE values for these complexes and offer insight into how these two factors are correlated. To this end, our study reveals that the incorporation of anisotropic MnIII ions in the cluster aggregation could lead to respectable MCE values if a suitable ligand design that offers a way to control the direction of the Jahn-Teller axes of MnIII ions is presented.

Ferromagnetic interactions in a dicyanamide-bridged multinuclear metal-organic framework [Pr3NH]+ [Mn(dca)3]−·H2O

Abstract A new complex [Pr3NH]+ [Mn(dca)3]− · H2O (dicyanamide = dca−) was synthesized, in which the Mn2+ cations are bridged by end-to-end dca anions to form three-dimensional [Mn(dca)3] n n − networks and tripropylammonium cations reside in the cavities of these networks. The complex has been characterized by single-crystal X-ray diffraction, infrared spectroscopy, elemental analysis, and magnetic measurements. Magnetic susceptibility data indicate ferromagnetic interactions among the MnII ions.

Construction of Paramagnetic Manganese-Chelated Polymeric Nanoparticles Using Pyrene-End-Modified Double-Hydrophilic Block Copolymers for Enhanced Magnetic Resonance Relaxivity: A Comparative Study with Cisplatin Pharmacophore.

Cationic metal-mediated self-assembly of double-hydrophilic block copolymers (DHBCs) has been of great interest for the preparation of hybrid nanoparticles for versatile applications. Among many functional transition-metal ions, manganese (MnII) is a highly attractive element due to its paramagnetic property with a high coordination number. However, MnII does not lead to the efficient self-assembly of DHBCs because of the relatively high aqueous solubility of coordinated MnII. This article reports a facile method for direct conjugation of MnII ions inside sterically stabilized polymer assemblies, composed of pyrene-end-modified DHBCs. Nitroxide-mediated radical polymerization was used to prepare the poly(ethylene glycol)- b-poly(acrylate) DHBC precursor, followed by the end-modification with pyrene maleimide via the radical-exchange reaction. Employing the self-associated DHBC as the nanoscale template, the simple addition of MnII enables a large number of polyvalent MnII ions to be immobilized at the chelating blocks of DHBCs, which can be readily monitored by the excimeric fluorescence emission change of the terminal pyrene fluorophore. The resulting MnII-loaded polymeric nanoparticles (MnII-PNPs) possess nanogel-like scaffolds, which allow for efficient water permeation at the MnII-incorporated interior for enhanced magnetic resonance contrasting effect. Additionally, by comparing the coordination properties of MnII and cisplatin, we endeavor to understand the internal structures and the relevant physicochemical features of metal-chelated nanoparticles.

Characterization of a Manganese‐Containing Nanoparticle as an MRI Contrast Agent

We present relaxivity and physicochemical data for a high relaxivity, manganese‐containing, nanoparticle‐based, and tumor selective MRI contrast agent, SN132D. The nanoparticles have a diameter of 5–6 nm, selected to give a compromise between renal excretion and tumor contrast, based on the Enhanced Permeability and Retention effect. The per manganese relaxivity (r1) is 24.8 ± 0.2 mm–1 Mn s–1 at 1.5 T and 37 °C in water, corresponding to per nanoparticle relaxivity of 347 ± 3 mm–1 s–1. The NMRD profiles in both water and serum showed a peak in r1 in the frequency range 20–40 MHz, which is characteristic of slowly moving paramagnetic systems. The r1 decreases when the temperature is increased from 25 °C to 37 °C, indicating fast exchange dynamics of the coordinated water molecules. The exchange time constant of the whole water molecule, τMO, was 6 ns. The r1 in serum is significantly higher than in water, due to an increase in medium viscosity and chelation of 18.9 ± 2.0 % of MnII ions to human serum components, most likely human serum albumin. The r1 is stable in the pH range 3–10. The per Mn relaxivity is among the highest reported for Mn‐containing systems and far higher than those of the clinically used gadolinium‐based contrast agents.