Coexistence of Spin Canting and Metamagnetism in a One-Dimensional Mn(II) Compound Bridged by Alternating Double End-to-End and Double End-On Azido Ligands and the Analog Co(II) Compound

Two new compounds of general formula [M(N3)2(dmbpy)] in which dmbpy = 5,5′-dimethyl-2,2′-bipyridine, and M = Mn(II) or Co(II), have been solvothermally synthesized and characterized structurally and magnetically. The structures consist of zig-zag polymeric chains with alternating bis-µ(azide-N1)2M and bis-µ(azide-N1,N3)2M units in which the cis-octahedrally based coordination geometry is completed by the N,N’-chelating ligand dmbpy. The molecular structures are basically the same for each metal. The Mn(II) compound has a slightly different packing mode compared to the Co(II) compound, resulting from their different space groups. Interestingly, relatively weak interchain interactions are present in both compounds and this originates from π–π stacking between the dmbpy rings. The magnetic properties of both compounds have been investigated down to 2 K. The measurements indicate that the manganese compound shows spin-canted antiferromagnetic ordering with a Néel temperature of TN = 3.4 K and further, a field-induced magnetic transition of metamagnetism at temperatures below the TN. This finding affords the first example of an 1D Mn(II) compound with alternating double end-on (EO) and double end-to-end (EE) azido-bridged ligands, showing the coexistence of spin canting and metamagnetism. The cobalt compound shows a weak ferromagnetism resulting from a spin-canted antiferromagnetism and long-range magnetic ordering with a critical temperature, TC = 16.2 K.

Understanding the biogeochemical mechanisms of metal removal from acid mine drainage with a subsurface limestone bed at the Motokura Mine, Japan

Subsurface limestone beds (SLBs) are used as a passive treatment technique to remove toxic metals from acid mine drainage (AMD). In this study, we investigated the mechanisms and thermodynamics of metal (manganese, copper, zinc, cadmium, and lead) precipitation in the SLB installed at the Motokura Mine. Field surveys in 2017 and 2018 showed that the pH of the SLB influent (initially 5–6) increased to approximately 8 in the drain between 24 and 45 m from the inlet. This increase was caused by limestone dissolution and resulted in the precipitation of hydroxides and/or carbonates of copper, zinc, and lead, as expected from theoretical calculations. Manganese and cadmium were removed within a pH range of approximately 7–8, which was lower than the pH at which they normally precipitate as hydroxides (pH 9–10). X-ray absorption near-edge structure analysis of the sediment indicated that δ-MnO2, which has a high cation-exchange capacity, was the predominant tetravalent manganese compound in the SLB rather than trivalent compound (MnOOH). Biological analysis indicates that microorganism activity of the manganese-oxidizing bacteria in the SLB provided an opportunity for δ-MnO2 formation, after which cadmium was removed by surface complexation with MnO2 (≡ MnOH0 + Cd2+ ⇄ ≡ MnOCd+ + H+). These findings show that biological agents contributed to the precipitation of manganese and cadmium in the SLB, and suggest that their utilization could enhance the removal performance of the SLB.

The superoxide dismutase mimetic GC4419 enhances tumor killing when combined with stereotactic ablative radiation

The penta-aza macrocyclic manganese compound GC4419 is in phase 3 clinical trials as a modifier of mucositis in H&N cancer treated by radio-chemotherapy based upon its properties as a superoxide dismutase mimetic. In studies to address the potential for tumor radioprotection, a significant anti-tumor effect was identified in tumors generated from the non-small cell lung cancer (NSCLC) cell line H1299, when GC4419 was combined with radiation. This effect was directly related to the size of the radiation dose as demonstrated by greater efficacy in tumor growth delay when biologically equivalent irradiation regimens using a limited number of dose fractions was substantially more effective compared to regimens where the fraction number was higher and dose per fraction decreased. Furthermore, a TCD50 assay using H1299 tumors that tested the combination of GC4419 with radiation revealed a Dose Enhancement Factor of 1.67. Based upon these results the hypothesis that GC4419 was generating cytotoxic levels of hydrogen peroxide during the superoxide dismutation process. Peroxide flux did increase in cells exposed to GC4419 as did the expression of the oxidative stress markers 4-HNE and 3-NT. H1299 cells that overexpressed catalase were then challenged as tumors by the combination of radiation and GC4419 and the tumoricidal effect was nearly eliminated. The enhanced radiation response was not specific to NSCLC as similar findings were observed in human head and neck squamous cell carcinoma and pancreatic ductal adenocarcinoma xenografts. RNA sequencing analysis revealed that GC4419, in addition to generating high levels of hydrogen peroxide in irradiated cells, alters inflammatory and differentiation signaling in the tumor following irradiation. Together, these findings provide abundant evidence that the radioprotector GC4419 has dual functionality and will increase tumor response rates when combined with agents that generate high levels of superoxide like stereotactic ablative body radiotherapy (SAbR). Combining SAbR with GC4419 may be an effective strategy to enhance tumor response in general but may also allow for fully potent radiation doses to tumors that might not necessarily be able to tolerate such doses. The potential for protection of organs at risk may also be exploitable.

Structural Diversity of Nickel and Manganese Chloride Complexes with Pyridin-2-One

Reactions of NiCl2·6H2O and pyridin-2-one (C5H5NO = Hhp) afforded novel molecular complexes, i.e., mononuclear [NiCl2(Hhp)4] (1), dinuclear [NiCl2(Hhp)(H2O)2]2.2Hhp (3) and [Ni2Cl4(Hhp)5]·2MeCN (4), and an ionic complex [Ni(Hhp)6]Cl2 (2). Single-crystal X-ray analyses revealed two modes of Hhp ligation in these complexes: a monodentate coordination of carbonyl oxygen in all of them and an additional µ2-oxygen bridging coordination in the dinuclear complex 4. Three bridging molecules of Hhp span two nickel(II) ions in 4 with a 2.9802 (5) Å separation of the metal ions. Complex 3 is a chlorido-bridged nickel dimer with a planar Ni2(µ-Cl)2 framework. Hydrogen bonds and parallel stacking arrangements of the Hhp molecules govern the connectivity patterns in the crystals, resulting in 1D structures in 1 and 5 or 2D in 3. A single manganese compound [MnCl2(Hhp)4] (5), isostructural to 1, was isolated under the similar conditions. This is in contrast to four nickel(II) chloride complexes with Hhp. Thermal analyses proved the stability of complexes 1 and 3 in argon up to 145 °C and 100 °C, respectively. The decomposition of 1 and 3 yielded nickel in argon and nickel(II) oxide in air at 800 °C.

μ-4,4′-Bipyridine-κ2N:N′-bis[tetraaqua(4,4′-bipyridine-κN)dimanganese(II)] bis(4-aminobenzoate) bis(perchlorate)–4,4′-bipyridine–water (1/2/4): a supramolecular system constructed by π–π and hydrogen-bond interactions

The title dinuclear manganese compound, [Mn2(C10H8N2)3(H2O)8](C7H6NO2)2(ClO4)2·2C10H8N2·4H2O, (I), has an inversion center located midway between the MnIIions. Each MnIIion has a distorted octahedral coordination environment, defined by two mutuallycisN atoms from two different 4,4′-bipyridine (4,4′-bipy) ligands and four O atoms from four water molecules. The asymmetric unit contains cationic [Mn(4,4′-bipy)1.5(H2O)4]2+, one isolated 4,4′-bipy molecule, one 4-aminobenzoate ion, one disordered perchlorate ion and two uncoordinated water molecules. In the dinuclear manganese cationic unit, one 4,4′-bipy acts as a bidentate bridging ligand between two MnIIions, while the other two act only as monodentate terminal ligands, giving rise to a `Z-type' [Mn2(4,4′-bipy)3(H2O)8] host unit. These host units are linked to each otherviaface-to-face π–π stacking interactions between monodentate terminal 4,4′-bipy ligands, generating a zigzag chain. The corners of these chains, defined by Mn(OH)4units, are surrounded by the solvent water molecules and the carboxylate O atoms of the 4-aminobenzoate ions, and all of these are connected to each otherviastrong O—H...O hydrogen-bond interactions, leading to a three-dimensional grid network with a large cavity running along thebaxis of the unit cell. The isolated 4,4′-bipy molecules, the 4-aminobenzoate and perchlorate anions and the water molecules are encapsulated in the cavities by numerous hydrogen-bond interactions.