Photoluminescence Properties of Two Closely Related Isostructural Series Based on Anderson-Evans Cluster Coordinated With Lanthanides [Ln(H2O)7{X(OH)6Mo6O18}]•yH2O, X = Al, Cr

The paper describes synthesis and structural characterization of the whole series of two closely related lanthanide coordinated chromium or aluminum hexamolybdates (Anderson-Evans cluster) including twelve new members hitherto unreported: [Ln(H₂O)₇{X(OH)₆Mo₆O₁₈}]·4H₂O and [Ln(H₂O)₇{X(OH)₆Mo₆O₁₈}Ln(H₂O)₇]{X(OH)₆Mo₆O₁₈}·16H₂O where X = Al or Cr and Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y. Crystal structures of all the solids were established by powder and single crystal X-ray diffraction techniques. The two series are dictated by a different aggregation of the same set of molecular species: Lighter lanthanides favor coordination interaction between lanthanide ions and molybdate cluster forming 1D chains (Series I) while the heavier lanthanides result in the stacking of a cation, a pair of lanthanide hydrates coordinating to the cluster, and an anion, the discrete cluster is further stabilized through a large number of water molecules (Series II). Crystallization with Er³⁺ and Tm³⁺ ions results in a concomitant mixture of Series I and II. Photoluminescence of single crystals of all the chromium molybdates was dominated by a ruby-like emission including those which contain optically active ions Pr, Sm, Eu, Tb, Dy, and Tm. In contrast, aluminum analogs showed photoluminescence corresponding to characteristic lanthanide emissions. Our results strongly suggest a possible energy transfer from f levels of lanthanide ions to d levels of chromium (III) causing the quenching of lanthanide emission when coordinated with chromium molybdates. Intensity measurements showed that the emission from chromium molybdates are almost two orders of magnitude lower than naturally occurring ruby with broader line widths at room temperature.

Room temperature large-scale synthesis of layered frameworks as low-cost 4 V cathode materials for lithium ion batteries

Li-ion batteries (LIBs) are considered as the best available technology to push forward the production of eco-friendly electric vehicles (EVs) and for the efficient utilization of renewable energy sources. Transformation from conventional vehicles to EVs are hindered by the high upfront price of the EVs and are mainly due to the high cost of LIBs. Hence, cost reduction of LIBs is one of the major strategies to bring forth the EVs to compete in the market with their gasoline counterparts. In our attempt to produce cheaper high-performance cathode materials for LIBs, an rGO/MOPOF (reduced graphene oxide/Metal-Organic Phosphate Open Framework) nanocomposite with ~4 V of operation has been developed by a cost effective room temperature synthesis that eliminates any expensive post-synthetic treatments at high temperature under Ar/Ar-H2. Firstly, an hydrated nanocomposite, rGO/K2[(VO)2(HPO4)2(C2O4)]·4.5H2O has been prepared by simple magnetic stirring at room temperature which releases water to form the anhydrous cathode material while drying at 90 °C during routine electrode fabrication procedure. The pristine MOPOF material undergoes highly reversible lithium storage, however with capacity fading. Enhanced lithium cycling has been witnessed with rGO/MOPOF nanocomposite which exhibits minimal capacity fading thanks to increased electronic conductivity and enhanced Li diffusivity.

Photoluminescent chromium molybdate cluster coordinated with rare earth cations: synthesis, structure, optical and magnetic properties

The photoluminescent chromium molybdate cluster is a potential molecular building block for synthesis of new solids with promising photophysical properties.

Discrete and Polymeric Cu(II) Coordination Complexes with a Flexible bis-(pyridylpyrazole) Ligand: Structural Diversity and Unexpected Solvothermal Reactivity

Reported here is the synthesis and structural characterisation of five copper complexes derived from the bis-bidentate ligand 4,4′-methylenebis(1-(2-pyridyl)-3,5-dimethylpyrazole), L. Complex 1, [Cu2L(CH3COO)4(OH2)2]·6H2O, is a single stranded unsaturated helical species that forms a highly connected three-dimensional hydrogen-bonding network, whereas [Cu2L(NO3)4], 2, is a coordination polymer derived from [Cu2L] fragments linked together via bridging nitrate anions to yield undulating two-dimensional sheets with (6,3)-topology. Complexes 3, 4, and 5 co-crystallise within a single batch when L is reacted under solvothermal conditions with Cu(NO3)2·2.5H2O in acetonitrile, and each contains a co-ligand formed by either decomposition of the solvent or ligand. Complex 3, [Cu4(NO3)4(µ-CH3COO)2(µ-OH)2L2], forms an unusual discrete cyclic tetrameric species containing acetate co-ligands derived through acetonitrile hydrolysis; whereas complex 4, [CuL(C2O4)(NO3)], forms a one-dimensional coordination polymer containing bridging oxalate co-ligands, formed through hydrolysis and oxidation of acetonitrile. Complex 5, [Cu2L(µ-CN)2], is a two-dimensional coordination polymer with (6,3) topology where bridging between Cu(i) centres is furnished by cyanide co-ligands, suggesting a ligand decomposition pathway for its origin, and produced with concomitant reduction of the Cu(ii) starting reagent. Having initially obtained 3, 4, and 5 serendipitously each were then prepared as pure phases by careful adjustment and control of the reaction conditions (reactant stoichiometry, concentrations, and solvothermal temperature), details of which are discussed.