1H and INEPT 15N and 109Ag NMR studies of the structural and dynamic features in solution of some silver(I) and copper(I) complexes with polydentate N4-donor ligands, (R),(S)-1,2-(6-R-py-2-CH=N)2-Cy and 1,2-(6-R-py-2-CH=N)2Et (Cy = cyclohexene, Et = Ethane, R = H or Me)