Structural studies and redox reactivity of platinum complexes of 14-membered tetraaza macrocyclic ligands

Abstract

Pt(II) monomeric complexes of N-containing macrocycles have been synthesized and characterized in solution by 1H NMR, 13C NMR, and electrospray mass spectroscopy (ESMS) and in the solid state by X-ray crystallography. Crystals of [Pt(cyclam)](ClO4)2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) are orthorhombic, space group P21cn, a = 9.596 (3), b = 14.595 (21), c = 24.8782 (20) Å, Z = 8. The structure was solved by direct methods and was refined by the full-matrix least-squares method to R = 0.073 and Rw = 0.093 for 2976 reflections with I ≥ 2.5σ(I). Crystals of [Pt(N-methylcyclam)]-(ClO4)2•CH3CN (N-methylcyclam = 1,4,8,11 tetramethyl-1,4,8,11-tetraazacyclotetradecane = NMe4cyclam = tmc) are orthorhombic, space group Pmcn, a = 9.574 (8), b = 14.116 (5), c = 17.5456 (15) Å, Z = 4. The structure was solved by direct methods and was refined by the full-matrix least-squares method to R = 0.067 and Rw = 0.091 for 2216 reflections with I ≥ 2.5σ(I). Cyclic voltammetry and EPR spectroscopy have been used to study the redox reactivity of the Pt(II)and Pt(IV) complex ions. The solution chemistry of Pt(IV) complexes based on cyclam and N-methylcyclam was investigated by electrospray mass spectrometry. Electrospray mass spectral evidence has been obtained for the formation of [Pt(III)(cyclam)Cl2]+ and [Pt(III)(N-methylcyclam)Cl2]+ ions. Keywords: Pt macrocycles, crystallography, electrospray mass spectroscopy, cyclic voltammetry, Pt(III) complex ions, tetraaza macrocycles.