FeII(pap-5NO2)2and FeII(qsal-5NO2)2Schiff-Base Spin-Crossover Complexes: A Rare Example with Photomagnetism and Room-Temperature Bistability
摘要:
We focus here on the properties of Fe complexes formed with Schiff bases involved in the chemistry of FeIII spin-transition archetypes. The neutral Fe(pap-5NO(2))(2) (1) and Fe(qsal-5NO(2))(2).Solv (2 and 2.Solv) compounds (Solv = 2H(2)O) derive from the reaction of FeII salts with the condensation products of pyridine-2-carbaldehyde with 2-hydroxy-5-nitroaniline (Hpap-5NO(2)) or 5-nitrosalicylaldehyde with quinolin-8-amine (Hqsal-5NO(2)), respectively. While the Fe(qsal-5NO(2))(2).Solv solid is essentially low spin (S = 0) and requires temperatures above 300 K to undergo a S = 0 <-> S = 2 spin-state switching, the Fe(pap-5NO(2))(2) one presents a strongly cooperative first-order transition (T-down arrow = 291 K, T? = 308 K) centered at room temperature associated with a photomagnetic effect at 10 K (TLIESST = 58 K). The investigation of these magnetic behaviors was conducted with single-crystal X-ray diffraction (1, 100 and 320 K; 2, 100 K), Mossbauer, IR, UVvis (1 and 2.Solv), and differential scanning calorimetry (1) measurements. The Mossbauer analysis supports a description of these compounds as FeII Schiff-base complexes and the occurrence of a metal-centered spin crossover process. In comparison with FeIII analogues, it appears that an expanded coordination sphere stabilizes the valence 2+ state of the Fe ion in both complexes. Strong hydrogen-bonding interactions that implicate the phenolato group bound to FeII promote the required extra-stabilization of the S = 2 state and thus determines the spin transition of 1 centered at room temperature. In the lattice, the hydrogen-bonded sites form infinite chains interconnected via a three-dimensional network of intermolecular van der Waals contacts and pp interactions. Therefore, the spin transition of 1 involves the synergetic influence of electrostatic and elastic interactions, which cause the enhancement of cooperativity and result in the bistability at room temperature.
The development of two fluorescent chemosensors for the selective detection of Zn2+ and Al3+ ions in a quinoline platform by tuning the substituents in the receptor part: elucidation of the structures of the metal-bound chemosensors and biological studies
Fluorescent Tin(IV) Complexes with Schiff Base Ligands
作者:Kentaro Takano、Takashi Shibahara
DOI:10.1246/cl.2008.70
日期:2008.1.5
Five novel fluorescent Schiff base tin(IV) complexes of the type [SnCl3(L)] were synthesized and their properties were investigated: the emission wavelengths range from bluish green to orange (λmax: 492–545 nm). DFT calculation shows that the order of the magnitudes of HOMO–LUMO gaps is consonant with that of the emission wavelengths (λmax) of the complexes, and good correlation was observed between reduction potentials in DMSO and the energies of LUMO.
Eleven Schiff base tin(IV) complexes of the type [SnCl3(L)] (HL: Schiff base) were synthesized and structurally characterized by X-ray crystallography and 1H NMR spectroscopy, and their properties were investigated. The Schiff bases are prepared from aldehydes with a benzene or a naphthalene ring and 8-aminoquinoline or its derivatives. The complexes adopt geometries close to octahedral, with three chloride ions coordinated meridionally. Eight of the eleven tin complexes show fluorescence in DMSO, and the emission range from bluish green to orange (λmax: 492–545 nm). Two solid tin complexes are fluorescent, although they are not in DMSO, and one tin complex is not fluorescent even in the solid state. The fluorescence quantum yields (Φf) of the complexes depend very much on the ligands (Φf = 0.21–0.022). The fluorescence lifetimes (τ = 0.49–1.76 ns) were measured and the results will be discussed. DFT calculation (B3LYP/Sn, LanL2DZ; others, 6-31G**) shows that the order of the magnitudes of HOMO–LUMO gaps is consonant with that of the emission wavelengths (λmax) of the complexes. All the cyclic voltammograms of the Schiff base ligands and the complexes exhibited irreversible waves and these results suggest that the reduction products of the ligands and the complexes were unstable under the time scale in CV measurements (0.1 V s−1). Relatively good correlation was observed between reduction potentials in DMSO and the energies of LUMO.
Fe<sup>II</sup>(pap-5NO<sub>2</sub>)<sub>2</sub>and Fe<sup>II</sup>(qsal-5NO<sub>2</sub>)<sub>2</sub>Schiff-Base Spin-Crossover Complexes: A Rare Example with Photomagnetism and Room-Temperature Bistability
We focus here on the properties of Fe complexes formed with Schiff bases involved in the chemistry of FeIII spin-transition archetypes. The neutral Fe(pap-5NO(2))(2) (1) and Fe(qsal-5NO(2))(2).Solv (2 and 2.Solv) compounds (Solv = 2H(2)O) derive from the reaction of FeII salts with the condensation products of pyridine-2-carbaldehyde with 2-hydroxy-5-nitroaniline (Hpap-5NO(2)) or 5-nitrosalicylaldehyde with quinolin-8-amine (Hqsal-5NO(2)), respectively. While the Fe(qsal-5NO(2))(2).Solv solid is essentially low spin (S = 0) and requires temperatures above 300 K to undergo a S = 0 <-> S = 2 spin-state switching, the Fe(pap-5NO(2))(2) one presents a strongly cooperative first-order transition (T-down arrow = 291 K, T? = 308 K) centered at room temperature associated with a photomagnetic effect at 10 K (TLIESST = 58 K). The investigation of these magnetic behaviors was conducted with single-crystal X-ray diffraction (1, 100 and 320 K; 2, 100 K), Mossbauer, IR, UVvis (1 and 2.Solv), and differential scanning calorimetry (1) measurements. The Mossbauer analysis supports a description of these compounds as FeII Schiff-base complexes and the occurrence of a metal-centered spin crossover process. In comparison with FeIII analogues, it appears that an expanded coordination sphere stabilizes the valence 2+ state of the Fe ion in both complexes. Strong hydrogen-bonding interactions that implicate the phenolato group bound to FeII promote the required extra-stabilization of the S = 2 state and thus determines the spin transition of 1 centered at room temperature. In the lattice, the hydrogen-bonded sites form infinite chains interconnected via a three-dimensional network of intermolecular van der Waals contacts and pp interactions. Therefore, the spin transition of 1 involves the synergetic influence of electrostatic and elastic interactions, which cause the enhancement of cooperativity and result in the bistability at room temperature.
The development of two fluorescent chemosensors for the selective detection of Zn<sup>2+</sup> and Al<sup>3+</sup> ions in a quinoline platform by tuning the substituents in the receptor part: elucidation of the structures of the metal-bound chemosensors and biological studies
作者:Pravat Ghorai、Kunal Pal、Parimal Karmakar、Amrita Saha
DOI:10.1039/c9dt04902a
日期:——
Two aminoquinoline-based chemosensors (HL1 and HL2) are reported for selective detection of Zn2+ and Al3+ ions.