33795-37-8Relevant articles and documents
A self-folding metallocavitand
Luecking,Chen,Rudkevich,Rebek Jr.
, p. 9929 - 9934 (2001)
The synthesis and characterization of novel metallocavitand 6 are described. This is a covalent hybrid of a deepened, self-folding cavity and a Zn-phenanthroline fragment. Host 6 features a large molecular cavity of -8×10 A dimensions, and the metal binding site is directed in toward the cavity. Binding abilities of the metallocavitand in solution was demonstrated for quinuclidine 11 and Dabco 12 using UV-vis and 1H NMR spectroscopy. Intramolecular hydrogen bonds at the upper rims of cavitand 6 resist the unfolding of the inner cavities and thereby increase the energetic barrier to guest exchange. The exchange is slow on the NMR time scale (at ambient temperatures, CD2Cl2), and kinetically stable complexes result. Both the polyaromatic cavity and metallosite participate simultaneously in the binding event. Zinc-containing deep cavities may be attractive as catalytic chambers for hydrolysis and esterification.
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Creighton et al.
, p. 4619,4623,4624 (1976)
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1H NMR spectroscopic elucidation in solution of the kinetics and thermodynamics of spin crossover for an exceptionally robust Fe2+ complex
Petzold, Holm,Djomgoue, Paul,H?rner, Gerald,Speck, J. Matth?us,Rüffer, Tobias,Schaarschmidt, Dieter
, p. 13798 - 13809 (2016/09/09)
A series of Fe2+ spin crossover (SCO) complexes [Fe(5/6)]2+ employing hexadentate ligands (5/6) with cis/trans-1,2-diamino cyclohexanes (4) as central building blocks were synthesised. The ligands were obtained by reductive amination of 4 with 2,2′-bipyridyl-6-carbaldehyde or 1,10-phenanthroline-2-carbaldehyde 3. The chelating effect and the rigid structure of the ligands 5/6 lead to exceptionally robust Fe2+ and Zn2+ complexes conserving their structure even in coordinating solvents like dmso at high temperatures. Their solution behavior was investigated using variable temperature (VT) 1H NMR spectroscopy and VT Vis spectroscopy. SCO behavior was found for all Fe2+ complexes in this series centred around and far above room temperature. For the first time we have demonstrated that the thermodynamics as well as kinetics for SCO can be deduced by using VT 1H NMR spectroscopy. An alternative scheme using a linear correction term C1 to model chemical shifts for Fe2+ SCO complexes is presented. The rate constant for the SCO of [Fe(rac-trans-5)]2+ obtained by VT 1H NMR was validated by Laser Flash Photolysis (LFP), with excellent agreement (1/(kHL + kLH) = 33.7/35.8 ns for NMR/LFP). The solvent dependence of the transition temperature T1/2 and the solvatochromism of complex [Fe(rac-trans-5)]2+ were ascribed to hydrogen bond formation of the secondary amine to the solvent. Enantiomerically pure complexes can be prepared starting with R,R- or S,S-1,2-diaminocyclohexane (R,R-trans-4 or S,S-trans-4). The high robustness of the complexes reduces a possible ligand scrambling and allows preparation of quasiracemic crystals of [Zn(R,R-5)][Fe(S,S-5)](ClO4)4·(CH3CN) composed of a 1:1 mixture of the Zn and Fe complexes with inverse chirality.
Solvent extraction of americium(iii) and europium(iii) with tridentate N,N-dialkyl-1,10-phenanthroline-2-amide-derived ligands: extraction, complexation and theoretical study
Cao, Shiwei,Wang, Jieru,Tan, Cunmin,Zhang, Xin,Li, Sa,Tian, Wei,Guo, Hangxu,Wang, Lei,Qin, Zhi
, p. 10560 - 10568 (2016/12/07)
The extraction and complexation behavior of soft-hard combined N,N-dialkyl-1,10-phenanthroline-2-amide (PTA) ligands with Am(iii) and Eu(iii) in HNO3 solution was investigated. The effects of acidity of the aqueous solution, shaking time, concentration of the extractant and temperature on the distribution ratios were studied. The extraction ability for both Am(iii) and Eu(iii) was found to decrease with an increase in the length of the substituent alkyl chains, and the highest extractability and selectivity for Am(iii) over Eu(iii) were found for the diethyl-substituted ligand. The separation factor for Am(iii) over Eu(iii) reached around 7.6 at low acidity and high salinity. UV-vis titrations revealed that the dialkyl-substituted tridentate PTAs all predominantly formed 1?:?1 complexes with Eu(iii), which agreed well with the results of slope analyses in the extraction experiments. The stability constants (KEuL) as well as the protonation constants (KH) were also determined by UV-vis titration. Computational chemistry gave a good explanation of the relationship between the alkalinity and the protonation energy of the proposed PTA ligands. Density functional theory (DFT) calculations on the optimized structures of Am(iii) and Eu(iii) complexes with C2-PTA showed that the selectivity may originate from differences in the degree of covalency of the bonds between the metal ions and the donor N atoms, which fits well with the experimental results.
