Copper complexes relevant to the catalytic cycle of copper nitrite reductase: electrochemical detection of NO(g) evolution and flipping of NO2 binding mode upon Cu(II) → Cu(I) reduction.
Copper complexes of the deprotonated tridentate ligand, N-2-methylthiophenyl-2'-pyridinecarboxamide (HL1), were synthesized and characterized as part of our investigation into the reduction of copper(II) o-nitrito complexes into the related copper nitric oxide complexes and subsequent evolution of NO(g) such as occurs in the enzyme copper nitrite reductase. Our studies afforded the complexes [(L1)Cu(II)Cl]n (1), [(L1)Cu(II)(ONO)] (2), [(L1)Cu(II)(H2O)](ClO4)·H2O (3·H2O), [(L1)Cu(II)(CH3OH)](ClO4) (4), [(L1)Cu(II)(CH3CO2)]·H2O (5·H2O), and [Co(Cp)2][(L1)Cu(I)(NO2)(CH3CN)] (6). X-ray crystal structure determinations revealed distorted square-pyramidal coordination geometry around Cu(II) ion in 1-5. Substitution of the H2O of 3 by nitrite quantitatively forms 2, featuring the κ(2)-O,O binding mode of NO2(-) to Cu(II). Reduction of 2 generates two Cu(I) species, one with κ(1)-O and other with the κ(1)-N bonded NO2(-) group. The Cu(I) analogue of 2, compound 6, was synthesized. The FTIR spectrum of 6 reveals the presence of κ(1)-N bonded NO2(-). Constant potential electrolysis corresponding to Cu(II) → Cu(I) reduction of a CH3CN solution of 2 followed by reaction with acids, CH3CO2H or HClO4 generates 5 or 3, and NO(g), identified electrochemically. The isolated Cu(I) complex 6 independently evolves one equivalent of NO(g) upon reaction with acids. Production of NO(g) was confirmed by forming [Co(TPP)NO] in CH2Cl2 (λ(max) in CH2Cl2: 414 and 536 nm, ν(NO) = 1693 cm(-1)).
Department of Chemistry, National Institute of Technology-Durgapur , Mahatma Gandhi Avenue, Durgapur 713 209, India.
Ram Chandra
RC
Maji
Suman Kumar
SK
Barman
Suprakash
S
Roy
Sudip K
SK
Chatterjee
Faye L
FL
Bowles
Marilyn M
MM
Olmstead
Apurba K
AK
Patra
D001665:Binding Sites; D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009569:Nitric Oxide / Q000737:chemistry*; D009572:Nitrite Reductases / Q000737:chemistry*; D010084:Oxidation-Reduction; D017550:Spectroscopy, Fourier Transform Infrared
D056831:Coordination Complexes; D008024:Ligands; D009569:Nitric Oxide; D003300:Copper; D009572:Nitrite Reductases; C052695:nitrite reductase, copper-containing