Molecular and Electronic Structure of Octahedral o-Aminophenolato and o-Iminobenzosemiquinonato Complexes of V(V), Cr(III), Fe(III), and Co(III). Experimental Determination of Oxidation Levels of Ligands and Metal Ions

Abstract

The coordination chemistry of the ligands 2-anilino-4,6-di-tert-butylphenol, H[L(AP)], and N,N"'-bis[2-(4,6-di-tert-butylphenol]diethylenetriamine, H(2)[(L(AP))N(L(AP))], has been studied with the first-row transition metal ions V, Cr, Fe, and Co. The ligands are noninnocent in the sense that the aminophenolato parts, [L(AP)](-) and [L(AP)-H](2)(-), can be readily oxidized to their o-iminobenzosemiquinonato, [L(ISQ)](-), and o-iminobenzoquinone, [L(ISB)], forms. The following neutral octahedral complexes have been isolated as crystalline materials, and their crystal structures have been determined by X-ray crystallography at 100 K: [Cr(III)(L(ISQ))(3)] (1), [Fe(III)(L(ISQ))(3)] (2), [Co(III)(L(ISQ))(3)] (3), [V(V)(L(ISQ))(L(AP)-H)(2)] (4), [V(V)(L(AP)-H)(2)(L(AP))] (5), and [V(V)O[(L(AP))N(L(AP)-H)]] (6). From variable-temperature magnetic susceptibility measurements and X-band EPR spectroscopy it has been established that they possess the ground states: 1, S = 0; 2, S = 1; 3, S = (3)/(2); 4, S = (1)/(2); 5, S = 0; 6, S = 0. The o-iminobenzosemiquinonato radicals (S(rad) = (1)/(2)) couple strongly intramolecularly antiferromagnetically to singly occupied orbitals of the t(2g) subshell at the respective metal ion but ferromagnetically to each other in 3 containing a Co(III) ion with a filled t(2g)(6) subshell. It is demonstrated that the oxidation level of the ligands and metal ions can be unequivocally determined by high-quality X-ray crystallography in conjunction with EPR, UV-vis, and Mössbauer spectroscopies. The spectro- and electrochemistry of these complexes have also been studied in detail. Metal- and ligand-based redox chemistry has been observed. The molecular and electronic structures are compared with those of their o-semiquinonato analogues.

Understanding cage effects in the n-alkane conversion on zeolites

“…At temperatures higher than those typically used in hydroprocessing, FER-type zeolites change category from topologies with a negative Gibbs free energy of adsorption for long-chain n-alkanes to those with a positive Gibbs free energy of adsorption for long-chain n-al- [6,16,17]); (b) Henry coefficient, K H , in MFI-type silica simulated for n-alkanes at these reciprocal temperatures, (c) intrinsic reaction rate constants, k, as calculated from measured kK H (a) and simulated K H (b). In all figures the legend is as follows: n-C 8 (1), n-C 10 (Q), n-C 12 ( ), n-C 14 (+), n-C 16 (2), n-C 18 (F), and n-C 20 ("). The linear regression parameters for the correlations in Fig.…”

“…The addition of ethanol displaces the most volatile compounds in the gasoline pool to meet front-end volatility specifications. Previous attempts at compensating for a similar shift in composition [1] coincided with the commercialization of the Selectoforming process [2]. This light-naphtha reforming process selectively hydrocracks short-chain n-pentane and n-hexane, removing them from the gasoline pool to yield liquid petroleum gas (LPG).…”

“…The resulting high-octane gasoline is compatible with high-compression engines and their concomitant advantage of increased mileage. In principle, these improved-mileage automobiles afforded an adequate response to the high gasoline prices of the 1970s [2]. At the time of for the cage effect have focused exclusively on the effect of zeolite topology on the barrier to adsorption [22][23][24][25][26][27][28][29][30][31].…”

Enhancing p -xylene selectivity during m -xylene transformation using mildly pre-coked ZSM-5 catalyst

“…However, the introduction of Mobil's selective toluene disproportionation process "MSTDP" in 1988 represented a clear technological improvement [1]. It should be mentioned that toluene alkylation with methanol over ZSM-5 was the first test reaction used by Chen [2] to demonstrate para-selectivity [1,2].…”

“…The shape selective conversion of xylenes over ZSM-5 has been investigated in detail by several workers [1][2][3][4][5][6][7][8][9][10][11][12]. Modifications of ZSM-5 by various compounds have been employed to enhance p-xylene selectivity from xylene transformation process [13][14][15][16].…”