Kinetic study of reaction of [ReN(H2O)(CN)4]2− with quinoline-2-carboxylate and pyridine-2,3-dicarboxylate anions

Abstract

The kinetics of the reaction between [ReN(H 2 O)(CN) 4 ] 2-with different j 2 N,O-donor ligands (quin -and 2,3-dipic -, respectively) have been studied in the pH 4-12 range in aqueous solution. Two consecutive reaction steps with the formation of the [ReN(g 1 -quin)(CN) 4 ] 3-and [ReN(l 2 -quin) (CN) 3 ] 2-complexes, respectively, were spectrophotometrically observed and kinetically investigated. The same reaction mechanism is proposed for these two ligands. The first fast reaction (for quin -) is attributed to the aqua substitution of [ReN(H 2 O)(CN) 4 ] 2-with forward and reverse rate constants of 1.96(5) 9 10 -1 M -1 s -1 and 5.6(3) 9 10 -2 s -1 , while a rate of 2.64(3) M -1 s -1 was observed for the reaction between the conjugate base [ReN(OH)(CN) 4 ] 3-and quin -at 40.2°C. Due to small absorbance changes, it was difficult to obtain any good quality data for the fast reactions for 2,3-dipic -. The second, slower reaction is attributed to cyano substitution with rate constants (k 3 K 1 ) of 4.17(4) 9 10 -3 for quin -and 4.68(7) 9 10 -3 M -1 s -1 for 2,3-dipic -, at 80.02°C, respectively. The acid dissociation constant for the aqua complex was spectrophotometrically determined as 11.58(3) and 11.54(2) and kinetically as 11.51(8) and 11.41(1), at 80.4°C, respectively. Negative DS 6 ¼ values of -83.5(2) and -144.1(2) J K -1 mol -1 as well as the DH 6 ¼ of 71.4(3) and 47.3(3) kJ mol -1 , for the slow quin -and 2,3-dipic -reactions, respectively, point to an ordered transition state where bond formation is responsible for the major driving force of the reaction. The DH 6 ¼ ¼ 39:6ð2Þ kJ mol À1 and DS 6 ¼ ¼ À142:8ð1Þ J K À1 mol À1 for the fast forward reaction of quin -is indicative of expected associative activation in the transition state.

Synthesis and Photoluminescence of Tetracyanidonitridorhenium(V) Complexes with Five-Membered N-Heteroaromatic Ligands and Photoluminescence-Intensity Change

“…A nitridorhenium­(V) complex possesses a coordination site (axial site) at the trans position of the nitrido, and the site is influenced strongly by the trans effect of the nitrido. − Therefore, the site is labile, the sixth ligand is not necessary, and the five- and six-coordinate complexes are both stable . In addition, some types of the both five- and six-coordinate complexes show luminescence. − In the tetracyanidonitridorhenium­(V) complex, the emission quantum yield of the five-coordinate complex is low (Φ em < 0.01) and, thus, the complex is almost nonemissive by naked eyes .…”