TY - JOUR
T1 - Mechanism for the formation of substituted manganese(V) cyanidonitrido complexes
T2 - Crystallographic and kinetic study of the substitution reactions of trans-[MnN(H2O)(CN)4]2- with monodentate pyridine and bidentate pyridine-carboxylate ligands
AU - Van Der Westhuizen, Hendrik J.
AU - Meijboom, Reinout
AU - Schutte, Marietjie
AU - Roodt, Andreas
PY - 2010/10/18
Y1 - 2010/10/18
N2 - Dissolution of [(CH3)N]2Na[MnN(CN) 5]·H2O in water results in the rapid dissociation of the trans-CN- ligand to form trans-[MnN(H2O)(CN) 4]2-(aq), which reacts with monodentate pyridine ligands such as 3-methyl and 4-methyl pyridine to form the corresponding mono-substituted complexes, of which the molecular structures obtained from X-ray crystallography, trans-[MnN(3-pic)(CN)4]2- and trans-[MnN(4-pic)(CN)4]2-, are reported. [MnN(H 2O)(CN)4]2-(aq) also reacts with bidentate nucleophiles such as pyridine-2-carboxylate (pico) and quinoline-2-carboxylate (quino), yielding the corresponding [MnN(η2-pico)(CN) 3]2- and [MnN(η2-quino)(CN) 3]2- complexes as determined by X-ray crystallography. The formation kinetics of pyridine-2-carboxylate and three different pyridine-2,x-dicarboxylate ligands (x= 3, 4, 5) are reported, and two consecutive reaction steps are proposed, defined as the formation of the [MnN(η1-pico)(CN)4]3- and [MnN(η2-pico)(CN)3]3- complexes, respectively. Only the second steps could be spectrophotometrically observed and kinetically investigated. The first reaction is attributed to the rapid aqua substitution of [MnN(H2O)(CN)4]2-, thermodynamically unfavored and too fast to observe by conventional rapid third generation stopped-flow techniques. The second, slower reaction is attributed to cyanido substitution, with overall formation rate constants (25 °C; k 1'; M-1 s-1) and corresponding activation parameters (ΔHk1'†, kJ mol-1, ΔSk1'†, J K-1 mol-1) for the following entering bidentate nucleophiles: pyridine-2-carboxylate: (1.15 ± 0.04) × 10-3,102 ± 1, and 48 ± 3; pyridine-2,3-dicarboxylate: (1.1 ± 0.1) × 10-3,93 ± 2, and 20 ± 4; pyridine-2,4-dicarboxylate (8.5 ± 0.5) × 10-4,123 ± 5, and 115 ± 14; pyridine-2,5-dicarboxylate: (1.08 ± 0.04) × 10-3,106 ± 1, and 60 ± 2. A dissociative activation for the cyanido substitution process is proposed.
AB - Dissolution of [(CH3)N]2Na[MnN(CN) 5]·H2O in water results in the rapid dissociation of the trans-CN- ligand to form trans-[MnN(H2O)(CN) 4]2-(aq), which reacts with monodentate pyridine ligands such as 3-methyl and 4-methyl pyridine to form the corresponding mono-substituted complexes, of which the molecular structures obtained from X-ray crystallography, trans-[MnN(3-pic)(CN)4]2- and trans-[MnN(4-pic)(CN)4]2-, are reported. [MnN(H 2O)(CN)4]2-(aq) also reacts with bidentate nucleophiles such as pyridine-2-carboxylate (pico) and quinoline-2-carboxylate (quino), yielding the corresponding [MnN(η2-pico)(CN) 3]2- and [MnN(η2-quino)(CN) 3]2- complexes as determined by X-ray crystallography. The formation kinetics of pyridine-2-carboxylate and three different pyridine-2,x-dicarboxylate ligands (x= 3, 4, 5) are reported, and two consecutive reaction steps are proposed, defined as the formation of the [MnN(η1-pico)(CN)4]3- and [MnN(η2-pico)(CN)3]3- complexes, respectively. Only the second steps could be spectrophotometrically observed and kinetically investigated. The first reaction is attributed to the rapid aqua substitution of [MnN(H2O)(CN)4]2-, thermodynamically unfavored and too fast to observe by conventional rapid third generation stopped-flow techniques. The second, slower reaction is attributed to cyanido substitution, with overall formation rate constants (25 °C; k 1'; M-1 s-1) and corresponding activation parameters (ΔHk1'†, kJ mol-1, ΔSk1'†, J K-1 mol-1) for the following entering bidentate nucleophiles: pyridine-2-carboxylate: (1.15 ± 0.04) × 10-3,102 ± 1, and 48 ± 3; pyridine-2,3-dicarboxylate: (1.1 ± 0.1) × 10-3,93 ± 2, and 20 ± 4; pyridine-2,4-dicarboxylate (8.5 ± 0.5) × 10-4,123 ± 5, and 115 ± 14; pyridine-2,5-dicarboxylate: (1.08 ± 0.04) × 10-3,106 ± 1, and 60 ± 2. A dissociative activation for the cyanido substitution process is proposed.
UR - http://www.scopus.com/inward/record.url?scp=78549276247&partnerID=8YFLogxK
U2 - 10.1021/ic101274q
DO - 10.1021/ic101274q
M3 - Article
AN - SCOPUS:78549276247
SN - 0020-1669
VL - 49
SP - 9599
EP - 9608
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 20
ER -