N-(Aryl)picolinamide complexes of rhodium · Synthesis, structure and, spectral and electrochemical properties

Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata-700 032, India

E-mail : samaresh _ b@hotmail. com

Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK

Manuscript received 20 December 2011, revised 30 December 2011, accepted 30 December 2011

Reaction of a series of N-(aryl)picolinamide ligands (HL-R, where H denotes the acidic proton and R (R=OCH₃, CH₃, H, Cl and N0₂) is the para substituent in the aryl fragment) with RhCI₃ ·3H₂0 in rcfluxing ethanol in the presence of a base (NEt₃) affords two groups of yellow complexes of type [Rh(HL-R)(L-R)CI₂) and [Rh(L-R)₂ (H₂0)CI]. In [Rh(HL-R)(L-R)CI₂], IIL-R is coordinated as neutral N,O-donor and L-R as monoanionic N,N-donm·, and the two chlorides are mutually trans. In [Rh(L-R)₂(H₂0)Cl] both the amide ligands arc coordinated as monoanionic N,N-donor, and the chloro and aquo ligands are mutually cis. Structures of the [Rh(HL-OCH₃)(L-OCH₃)CI₂) and [Rh(L-CI)₂(H₂0)CI] complexes have been determined by X-ray crystallography. All the complexes show characteristic ¹H NMR signals and intense LLCT transitions in the ultraviolet region. Cyclic voltammetry on the complexes shows an oxidation of the coordinated amide ligand within 0. 78-1.80 V vs SCE and a reductive response within -0.20 to -0.75 V vs SCE. DFT calculations have been done to explain the electronic spectral and electrochemical properties.