Structural investigations of silver(I) and copper(I) complexes with neutral nitrogen (N4) donor ligands: x-ray crystal and molecular structure of the dimer [Ag2{.mu.-(R)(S)-1,2-(py-2-CH:N)2Cy}2](O3SCF3)2 and proton, carbon-13, and INEPT silver-109 and nitrogen-15 NMR solution studies