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ACS Appl Mater Interfaces ; 9(39): 33934-33940, 2017 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-28898044


Developing efficient sodium-ion-storage mechanisms to increase the energy capacity in organic electrodes is a critical issue even after this period of prolonged effort. Uric acid (UA), a simple organic compound with three carbonyl groups is demonstrated to be electrochemically active in the insertion/extraction of Na ions. Theoretical calculations and experimental characterizations reveal that the sodium-ion storage by UA is a result of the stepwise mechanisms of p-π conjugation and the carbon anion. Aside from C═O, the functional group C═C(NH-)2 also provides an efficient Na-storage activated site in which the lone-pair electrons is stabilized through the planar-to-tetrahedral structural transition and low-energy orbital hybridization of N atoms. For further improvement of the electrochemical performance, a uric acid and carbon nanotube (UA@CNT) composite is prepared via a vacuum solution impregnation method. When employed as an anode material for sodium-ion batteries, the UA@CNT composite exhibits high specific capacity, excellent rate capability, and long cycling life even at high current densities. A reversible capacity of over 163 mA h g-1 is maintained even after 150 cycles at a current density of 200 mA g-1. The present study paves a way to develop reversible high-capacity organic electrode materials for sodium-ion batteries by a carbon-anion stabilization mechanism.

Inorg Chem ; 53(12): 6022-33, 2014 Jun 16.
Artigo em Inglês | MEDLINE | ID: mdl-24901836


Eleven new mononuclear manganese(III) complexes prepared from two hexadentate ligands, L1 and L2, with different degrees of steric bulk in the substituents are reported. L1 and L2 are Schiff bases resulting from condensation of N,N'-bis(3-aminopropyl)ethylenediamine with 3-methoxy-2-hydroxybenzaldehyde and 3-ethoxy-2-hydroxybenzaldehyde respectively, and are members of a ligand series we have abbreviated as R-Sal2323 to indicate the 323 alkyl connectivity in the starting tetraamine and the substitution (R) on the phenolate ring. L1 hosts a methoxy substituent on both phenolate rings, while L2 bears a larger ethoxy group in the same position. Structural and magnetic properties are reported in comparison with those of a previously reported analogue with L1, namely, [MnL1]NO3, (1e). The BPh4(-) and PF6(-) complexes [MnL1]BPh4, (1a), [MnL2]BPh4, (2a), [MnL1]PF6, (1b'), and [MnL2]PF6, (2b), with both ligands L1 and L2, remain high-spin (HS) over the measured temperature range. However, the monohydrate of (1b') [MnL1]PF6·H2O, (1b), shows gradual spin-crossover (SCO), as do the ClO4(-), BF4(-), and NO3(-) complexes [MnL1]ClO4·H2O, (1c), [MnL2]ClO4, (2c), [MnL1]BF4·H2O, (1d), [MnL2]BF4·0.4H2O, (2d), [MnL1]NO3, (1e), and [MnL2]NO3·EtOH, (2e). The three complexes formed with ethoxy-substituted ligand L2 all show a higher T1/2 than the analogous complexes with methoxy-substituted ligand L1. Analysis of distortion parameters shows that complexes formed with the bulkier ligand L2 exhibit more deformation from perfect octahedral geometry, leading to a higher T1/2 in the SCO examples, where T1/2 is the temperature where the spin state is 50% high spin and 50% low spin. Spin state assignment in the solid state is shown to be solvate-dependent for complexes (1b) and (2e), and room temperature UV-visible and NMR spectra indicate a solution-state spin assignment intermediate between fully HS and fully low spin in 10 complexes, (1a)-(1e) and (2a)-(2e).

Angew Chem Int Ed Engl ; 51(50): 12597-601, 2012 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-23129209


Mind the gap: A complete, cooperative spin transition for a mononuclear Mn(III) complex is reported with an 8 K hysteresis window. Raman spectra collected at a single temperature in warming and cooling modes confirm the electronic bistability within the hysteresis loop. The source of the cooperativity is a disconnection in the hydrogen-bonded 1D chains that connect adjacent cations owing to an order-disorder transition in the PF(6)(-) counterion.