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Establishing an effective design principle in solid-state materials for a blue-light-excited Eu2+ -doped red-emitting oxide-based phosphors remains one of the significant challenges for white light-emitting diodes (WLEDs). Selective occupation of Eu2+ in inorganic polyhedra with small coordination numbers results in broad-band red emission as a result of enhanced crystal-field splitting of 5d levels. Rb3 YSi2 O7 :Eu exhibits a broad emission band at λmax =622 nm under 450 nm excitation, and structural analysis and DFT calculations support the concept that Eu2+ ions preferably occupy RbO6 and YO6 polyhedra and show the characteristic red emission band of Eu2+ . The excellent thermal quenching resistance, high color-rendering index Ra (93), and low CCT (4013 K) of the WLEDs clearly demonstrate that site engineering of rare-earth phosphors is an effective strategy to target tailored optical performance.

A chiral nickel histidine compound, [Ni(L-his)2]×H2O (1, L-his = anion of L-histidine), was synthesized in high yield from the reaction of Ni(OAc)2×4H2O and L-histidine in the presence of 4,4′-bipyridine under mild reaction conditions. A single-crystal X-ray diffraction analysis showed that compound 1 crystallizes in the monoclinic system, space group C2, with a chemical formula of C12H18N6NiO5, cell parameters: a = 29.416(2) A, b = 8.2667(7) A, c = 6.3137(5) A, β = 90.066(2)°, V = 1535.3(2) A3 and Z = 4. Each nickel(II) ion in 1 is six coordinated, bonded to two oxygen donors and four nitrogen donors from two crystallographically independent L-his− ligands with a tridentate coordination mode to form a monomeric species. Monomeric forms of 1 undergo self-assembly to form a three-dimensional (3D) supramolecular architecture via subtle combinations of N-H···O type hydrogen bonding interactions among the adjacent L-his−ligands and π-π stacking interactions among the imidazole rings of the L-his− ligands. The supramolecular entity exhibits an unusually high thermal stability, at temperatures of up to 360 °C and shows reversible de-/re-hydration properties.

A water-containing iron(III) complex, [FeIII(SalEen)2]ClO4·0.5H2O [1, SalEen = N-ethyl-N-(2-aminoethyl)salicylaldiminate], and an unsolvated complex, [FeIII(SalEen)2]ClO4 (2), are synthesized and structurally characterized. Complex 1 crystallizes in a polar orthorhombic space group Fdd2, whereas 2 crystallizes in a monoclinic space group P21/c. The presence or absence of water molecules results in different molecular packings, which give rise to different magnetic properties. The temperature dependent magnetic measurements show very gradual spin transitions for both 1 and 2; the iron(III) center is in the high-spin (HS) state with S = 5/2 at 350 K and is in the low-spin (LS) state with S = 1/2 below 30 K for 1 (T1/2 = 155 K) and at 120 K for 2 (T1/2 = 230 K). The crystal structures of the HS and LS states for both 1 and 2 are characterized. In addition, the structure of 1 at 150 K is also investigated. The Fe–N and Fe–O bond lengths are 0.14 and 0.03 A shorter in the LS state than those in the HS state. The octahedral distortion in the iron(III) coordination geometry, expressed as Σ and Θ parameters, is slightly larger in the HS than in the LS state.

cNational Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan, R.O.C. A reversible crystal-to-crystal structural phase transition is found in one of the polymorphs (A )o f complext-Fe(abpt)2[N(CN)2]2(abpt=4-Amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole).Thecrystalat25 K remains unchanged as triclinic space group P1 from that of the ambient temperature, but with different cell parameters: a = 8.7960(6), b = 8.8110(9), c = 10.1020(7) A, = 94.146(8), = 93.296(6) = 114.460(7), V = 707.48(10) A 3 . Thermal-dependent powder X-ray diffraction reveals a first order phase transition with transition temperature, T1/2, at 270 K, which coincides with the change in cell parameters monitored by single crystal diffraction experiment. The molecular structure does vary on the orientation of the axial ligand, N(CN)2, during the phase transition, however the FeN bond distance and the octahedron distortion parameters around Fe indicate that Fe remains at high spin state even after the phase transition which is in accord with the observed thermal-dependent magnetic measurement.