title: Structural variation in copper(I) complexes with pyridylmethylamide ligands: structural analysis with a new four-coordinate geometry index, tau4.
abstract: Four Cu(I) complexes were synthesized with a family of pyridylmethylamide ligands, HL(R) [HL(R) = N-(2-pyridylmethyl)acetamide, R = null; 2,2-dimethyl-N-(2-pyridylmethyl)propionamide, R = Me(3); 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide, R = Ph(3))]. Complexes 1-3 were synthesized from the respective ligand and [Cu(CH(3)CN)(4)]PF(6) in a 2 : 1 molar ratio: [Cu(HL)(2)]PF(6) (1), [Cu(2)(HL(Me3))(4)](PF(6))(2) (2), [Cu(HL(Ph3))(2)]PF(6) (3). Complex 4, [Cu(HL)(CH(3)CN)(PPh(3))]PF(6), was synthesized from the reaction of HL with [Cu(CH(3)CN)(4)]PF(6) and PPh(3) in a 1 : 1 : 1 molar ratio. X-Ray crystal structures reveal that complexes 1, 3 and 4 are mononuclear Cu(I) species, while complex 2 is a Cu(I) dimer. The copper ions are four-coordinate with geometries ranging from distorted tetrahedral to seesaw in 1, 2, and 4. Complexes 1 and 2 are very air sensitive and they display similar electrochemical properties. The coordination geometry of complex 3 is nearly linear, two-coordinate. Complex 3 is exceptionally stable with respect to oxidation in the air, and its cyclic voltammetry shows no oxidation wave in the range of 0-1.5 V. The unusual inertness of complex 3 towards oxidation is attributed to the protection from bulky triphenyl substituent of the HL(Ph3) ligand. A new geometric parameter for four-coordinate compounds, tau(4), is proposed as an improved, simple metric for quantitatively evaluating the geometry of four-coordinate complexes and compounds.
authors.affiliation: Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Yang
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Powell
authors.forename: Robert P
authors.initials: RP
authors.lastname: Houser
mesh_terms: D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D007202:Indicators and Reagents; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*
chemical_list: D007202:Indicators and Reagents; D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D003300:Copper