Joining of Trinuclear Heterometallic Cu^II₂–M^II (M = Mn, Cd) Nodes by Nicotinate to Form 1D Chains: Magnetic Properties and Catalytic Activities

Abstract

In the present work, four new heterometallic coordination complexes, {[(CuL) 2 Mn(nic and [(CuL) 2 Cd(nic) 2 ]•2CH 3 OH (4) (where H 2 L = N,N′-bis(α-methylsalicylidene)-1,3-propanediamine and nic = nicotinate ion), have been synthesized and characterized by single-crystal X-ray crystallography. In complexes 1 and 2, the nicotinate ion acts as a bifunctional linker (N,O donor) and joins the linear trinuclear nodes to form 1D polymeric chains. However, in complexes 3 and 4, the nicotinate ion uses only the oxygen atoms of the carboxylic acid (O donor) to bind to the metal centers, forming discrete linear trinuclear units, while the pyridyl nitrogen (N donor atom) remains free. The dc magnetic susceptibility measurements show that the Cu II and Mn II ions are antiferromagnetically coupled in both 1 and 3, with exchange coupling constants (J Mn−Cu ) of −20.57 ± 0.08 and −9.38 ± 0.08 cm −1 , respectively. Among the four complexes, 1 and 3 show catechol oxidase and phenoxazinone synthase like catalytic activities. The turnover numbers (k cat ) of complexes 1 and 3 for catecholase activity are 1121 and 720 h −1 , respectively, at an optimum pH of 8.0 and for phenoxazinone synthase activity are 429 and 398 h −1 , respectively, at an optimum pH of 9.7. The higher k cat values of 1 for both reactions are attributable to a water molecule coordinated to the central Mn II atom that facilitates the substrate−catalyst binding. An ESI-mass spectral analysis indicates that trinuclear heterometallic species, e.g., [(CuL) 2 Mn(nic)(H 2 O)] + for 1 and [(CuL) 2 Mn-(nic)] + for 3, are the active species that bind to the substrate, and on that basis, probable mechanisms through the formation of radical intermediates have been proposed.

Copper(II) complexes with a benzimidazole functionalized Schiff base: Synthesis, crystal structures, and role of ancillary ions in phenoxazinone synthase activity

“…The development of the electronic bands at 433 and 430 nm for 1 and 2 is a signature for the production of phenoxazinone compound in solution, which is well established in the scientific literature. [67,68] Controlled experiments were also performed using 2-AP and 2-AP in the presence of benzimidazole functionalized ligand L separately under identical reaction conditions (Figure S13) up to 2 h; however, yields of control reactions were very little and can be ignored. The production of oxidation product in control reactions reveal that auto-oxidation of 2-AP under ambient reaction condition.…”

Cu(II)-Based Nanofibrous Metallogel for Phenoxazinone Synthase-like Activity

“…This observation suggests the formation of a catalyst–substrate aggregate in a preequilibrium stage, followed by irreversible oxidation of the substrate in the rate-determining step of the catalytic cycle. The Michaelis–Menten model − , is the suitable analytical tool to address such kind of reaction kinetics having saturation rate dependency on the concentration of the substrate. The corresponding Lineweaver–Burk plot , (Figure S18) was then analyzed to have the kinetic parameters V max (1.27 × 10 –2 M min –1 ) and K M (6.2 × 10 –4 M) for this heterogeneous catalytic process.…”

“…The Michaelis–Menten model − , is the suitable analytical tool to address such kind of reaction kinetics having saturation rate dependency on the concentration of the substrate. The corresponding Lineweaver–Burk plot , (Figure S18) was then analyzed to have the kinetic parameters V max (1.27 × 10 –2 M min –1 ) and K M (6.2 × 10 –4 M) for this heterogeneous catalytic process. Here, it is worth mentioning that determination of exact numbers of surface active sites for this xerogel catalyst is rather impracticable, and hence, the TON or TOF has not been mentioned here.…”

Cerium-Doped Manganese Oxide Catalyst for the Oxidative Coupling Synthesis of Fluorescent 2-Amino-1,9-dimethyl-3H-phenoxazin-3-one Using Atmospheric Oxygen

“…Phenoxazinone compounds are synthesized in nature via an enzyme-promoted process. , As a multicopper oxidase, laccase can oxidize 2-aminophenols to form dimeric structures, such as 2-amino-3 H -phenoxazin-3-one (APXO). , Therefore, a variety of copper, , cobalt, , and manganese complexes , that mimic the structure of enzymes have been designed and utilized as catalysts for the transformation. In addition to this, several palladium- and ruthenium-based catalysts have also been developed, using H 2 O 2 as an oxidant .…”