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The capability of bis(dioxolene) ligands to access multiple redox states makes them ideal candidates to tune the electronic properties of metal complexes, for example to achieve valence tautomerism (VT). In this study, a family of dinuclear cobalt complexes have been isolated with the bridging bis(dioxolene) thean− ligand in the cat2−‐cat2−, cat2−‐SQ⋅− and SQ⋅−‐SQ⋅− states (cat2−=catecholate, SQ⋅−=semiquinonate): [{CoIII(tpa)}2(theacat−cat)](PF6)2 (1), [{CoIII(tpa)}2(theacat−SQ)](PF6)3 (2), and [{CoIII(tpa)}2(theaSQ−SQ)](PF6)4 (3) (theaH4=2,3,6,7‐tetrahydroxy‐9,10‐dimethyl‐9,10‐dihydro‐9,10‐ethanoanthracene, tpa=tris(2‐pyridylmethyl)amine). Multi‐technique analysis confirms that 1, 2 and 3 adopt low spin‐CoIII containing {CoIII‐cat‐cat‐CoIII}, {CoIII‐cat‐SQ‐CoIII} and {CoIII‐SQ‐SQ‐CoIII} states, respectively. Compound 1 undergoes thermally‐induced {CoIII‐cat‐cat‐CoIII} ⇌ {CoIII‐cat‐SQ‐CoII} VT in the solid‐ and solution‐states above 300 K, involving high spin‐CoII. This interconversion is contrary to expectations, as tpa typically stabilizes low spin‐CoIII‐catecholate. Compound 2 is mixed‐valence class II/II–III, indicating a localized electronic structure, with electron transfer faster than the EPR and solvent rearrangement timescales, but slower than the infrared timescale. Compound 3 exhibits strong antiferromagnetic exchange. The overlap between the dioxolene π‐orbitals in thean− increases the accessibility of the cat2−‐SQ⋅− state, resulting in VT for 1. This study demonstrates that thean− can be isolated in multiple oxidation states in metal complexes, which is promising for applications in magnetic materials. [ABSTRACT FROM AUTHOR]

Heteroleptic lanthanoid (Ln = Eu, Gd, Tb, Dy, Ho and Yb) complexes featuring hydro‐tris(1‐pyrazolyl)borate (Tp−) ligands combined with the bidentate O‐donor ligands tropolonate (trop−) or 3,5‐di‐tertbutylseminquinonate (dbsq⋅−) have been synthesized and investigated. Despite the similarity of the bidentate O‐donor trop− and dbsq⋅− ligands, and the lanthanoid coordination geometries, the complexes [LnTp2dbsq] (Ln‐dbsq) and [LnTp2trop] (Ln‐trop) exhibit markedly different redox and photophysical properties. The electrochemistry of Ln‐dbsq is dominated by processes associated with the readily redox‐active dbsq⋅− moiety. In contrast, the relative redox inactivity of Ln‐trop allows for the observation of the Eu(III) to Eu(II) reduction process. Photophysical measurements reveal no sensitized emission for the Ln‐dbsq family, while the trop− antenna ligand is able to sensitize emission in the visible range for Eu(III) and Ho(III), and in the near‐infrared for Ho(III) and Yb(III). [ABSTRACT FROM AUTHOR]

Herein we describe the synthesis of a library of new mercury complexes, including some dimers and polymeric species. Initially, a phosphonium salt, [PPh3CH2C(O)C6H4–m-OCH3]Br (S), was synthesized from triphenylphosphine (PPh3) and BrCH2C(O)C6H4-m-OCH3 in acetone. We then reacted this phosphonium salt with an appropriate base to acquire a new phosphorus ylide monodentate, PPh3=C(H)C(O)C6H4-m-OCH3 (Y). Finally, we treated the synthesized ligand with mercury halides in dry CH3OH to form C-coordinated complexes of the form [HgX(PPh3C(H)C(O)C6H4-m-OCH3) (μ-X)]2 [X = Cl (1), Br (2), I (3)], [(PPh3=C(H)C(O)C6H4-m-OCH3)Hg(NO3)2]n (4). We characterized these compounds using CHN analysis, FT-IR, NMR (1H, 13C and 31P) and density functional theory. We elucidated the structure of 2 by single-crystal X-ray diffraction. The results establish that 1, 2 and 3 have dimeric structures, while a polymeric structure is suggested for 4. The antioxidant activity of all compounds in DMSO was assessed using a DPPH free radical scavenging method. Also, the nature of metal-ligand (C→Hg) bonding in 1, 2 and 3 have been investigated using natural bond orbital (NBO) and energy-decomposition analyses (EDA). [ABSTRACT FROM AUTHOR]

Pleysteinite, [(H 2 O) 0.5 K 0.5 ] 2 Mn 2 Al 3 (PO 4) 4 F 2 (H 2 O) 10 ⚫ 4H 2 O, is the aluminium analogue of benyacarite, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in specimens of altered zwieselite, in association with nordgauite, fluellite, rockbridgeite, pyrite and columbite. Pleysteinite occurs as isolated and small aggregates of colourless, stubby prisms that are typically 10 to 30 µ m wide and up to 100 µ m long. The crystals are flattened on {010} and bounded by {111} , {100} and {001} planes. The calculated density is 2.34 g cm -3. Optically, pleysteinite crystals are biaxial (+), with α=1.566(2) , β=1.580(2) , γ=1.600(2) (measured in white light) and 2 V (meas.) = 80(1) ∘. The empirical formula from electron microprobe analyses and structure refinement is [(H 2 O) 0.50 K 0.50 ] 2 (Mn 1.20 Mg 0.49 Fe 0.272+ Zn 0.05) ∑2.01 (Al 1.63 Fe 0.203+ Ti 0.194+) ∑2.02 (Al 0.56 Ti 0.444+) (PO 4) 4.02 [F 0.58 O 0.31 (OH) 0.11 ] 2 (H 2 O) 10 ⚫ 3.92H 2 O. Pleysteinite has orthorhombic symmetry, with space group Pbca and unit-cell parameters a = 10.4133(8) Å, b=20.5242(17) Å, c=12.2651(13) Å, V=2621.4(4) Å 3 and Z=4. The crystal structure was refined using single-crystal data to wR obs=0.054 for 1692 reflections with I>3σ(I). The crystal structure contains corner-connected linear trimers of Al-centred octahedra that share corners with PO 4 tetrahedra to form 10-member rings parallel to (010). K + cations and water molecules are located in the rings. Additional corner-sharing of the PO 4 tetrahedra with Mn(H 2 O) 4 O 2 octahedra occurs along [010] to complete the 3D framework structure. [ABSTRACT FROM AUTHOR]

Whiteite-(CaMnFe), CaMn 2+ Fe 22+ Al 2 (PO 4) 4 (OH) 2 ⋅ 8H 2 O, is a new whiteite-subgroup member of the jahnsite group from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in vugs in an altered feldspar area of a specimen composed predominantly of rockbridgeite, with hureaulite and relic triphylite. Other associated minerals in small vugs in the specimen were strengite and laueite. Whiteite-(CaMnFe) occurs as sprays and clusters of colourless to pale yellow, rod-like crystals, with diameters of typically 10 to 50 µ m and lengths up to ∼ 500 µ m. The crystals are flattened on {001} and elongated along [010]. The measured density is 2.80(2) g cm -3. Optically, whiteite-(CaMnFe) crystals are biaxial (+), with α=1.608(3) , β=1.612(3) , γ=1.624(3) and 2 V (meas.) = 59(1) ∘. The empirical formula from electron microprobe analyses and structure refinement is (Ca 0.70 Mn 0.30)Mn(Fe 1.232+ Mn 0.49 Mg 0.29 Zn 0.06) (Al 1.88 Fe 0.123+)(PO 4) 3.96 (OH) 2 (H 2 O) 8. Whiteite-(CaMnFe) is monoclinic, P2 /a , a=14.925(5) , b=7.0100(14) , c=10.053(2) Å, β=111.31(2) ∘ , V=979.9(4) Å 3 and Z=2. The crystal structure was refined using single-crystal data to wRobs=0.052 for 1613 reflections with I>3σ(I). Site occupancy refinements confirm the ordering of dominant Ca, Mn and Fe 2+ in the X , M 1 and M 2 sites, respectively, of the general jahnsite-group formula XM 1 M 2 2 M 3 2 (H 2 O) 8 (OH) 2 (PO 4) 4. [ABSTRACT FROM AUTHOR]

The effect of core geometry constraints of hydrogenase H-cluster analogues on reduction chemistry have been explored by a combination of structural, electrochemical and IR spectroelectrochemical (IR-SEC) studies. A series of phosphido-bridged diiron hexacarbonyl complexes, Fe2(µ2-PPh2(CH2) x PPh2)(CO)6, x = 2 (2P) and 4 (4P) and previously reported with x = 3 (3P) and the unlinked bis-diphenylphosphido (DP) analogues were investigated. The X-ray structures of the neutral complexes demonstrate the effect of the linking group on the Fe2P2 core geometry with P–Fe–Fe–P torsion angles of 95 (2P), 101 (3P), 108 (4P) and 109° (DP) and a twisting of the Fe(CO)3 fragments from an eclipsed geometry (2P , 3P and DP) for 4P. For all four compounds the primary reduction process involves two close-spaced one-electron reactions (E1 and E2) with a systematic trend to more negative reduction potentials with a shorter link between the bridging phosphorus atoms. This reflects the greater constraint that the bridging group places on the adoption of a planar 2Fe2P geometry. The sensitivity of the core geometry is greater for E2 than E1 and this impacts the stability of the monoanion with respect to disproportion (K disp(298 K) = 0.02 (2P), 2.4 (3P) and 3540 (4P and DP)). 4P has a stable dianion and gives reversible cyclic voltammetry at 298 K and is quasi-reversible at 253 K, whereas the response of 2P is irreversible at 298 K, with two distinct daughter products, but becomes quasi-reversible at 253 K. IR-SEC measurements enabled elucidation of the spectra and time evolution of the reduction products. These results are consistent with a bimolecular reaction giving a distinct reduced product modelled as a dimeric, 4Fe species. The sensitivity of the reduction chemistry of the bridged diiron compounds underpins their utility as catalytic proton reduction catalysts and the systematic trends delineated in this investigation provide the framework for charting the path of their redox-coupled chemical reactions. Integration of IR spectroelectrochemical and electrochemical simulation of the series of phosphido-bridged diiron hexacarbonyl complexes, Fe2(µ2-PPh2(CH2) x PPh2)(CO)6, x = 2 (2P) and (4P) and previously reported x = 3 (3P) and bis-diphenylphosphido (DP) analogues have allowed delineation of the impact of constraints on the 2Fe2P core geometry on the reduction chemistry. The sensitivity of the reduction chemistry of the bridged diiron compounds underpins their utility as catalytic proton reduction catalysts and the systematic trends delineated in this investigation provide the framework for charting the path of their redox-coupled chemical reactions. [ABSTRACT FROM AUTHOR]