Palladium(II) co-ordination by linear N-methylated polyamines: a solution and solid-state study

L'articolo riporta lo studio delle proprietà coordinative di alcuni leganti poliamminici nei confronti dello ione Pd(II). Palladium(II) co-​ordination by the tertiary polyamines 2,​5,​8-​trimethyl-​2,​5,​8-​triazanonane, 2,​5,​8,​11-​tetramethyl-​2,​5,​8,​11-​tetraazadodecane, 2,​5,​9,​12-​tetramethyl-​2,​5,​9,​12-​tetraazatridecane, 2,​6,​9,​13-​tetramethyl-​2,​6,​9,​13-​tetraazatetradecane, 2,​5,​8,​11,​14-​pentamethyl-​2,​5,​8,​11,​14-​pentaazapentadecane, 2,​5,​8,​11,​14,​17-​hexamethyl-​2,​5,​8,​11,​14,​17-​hexaazaoctadecane and by the new compd. 2,​5,​8,​11,​14,​17,​20,​23-​octamethyl-​2,​5,​8,​11,​14,​17,​20,​23-​octaazatetracosane has been investigated by means of potentiometric (0.1 M NMe4Cl aq. soln., 298.1 K) and spectrophotometric measurements. The species present in soln. and their stability consts. have been detd. The first five amines form only mononuclear complexes, while the last two can give both mono- and bi-​nuclear complexes in aq. soln. The thermodn. data show that the complexes with N-​methylated polyamines are tremendously less stable than their non-​methylated counterparts. The UV​/VIS spectra of the complexes exhibit a marked red shift of the L M charge-​transfer bands with respect to the complexes of the non-​methylated ligands. As a consequence of the reduced thermodn. stability, both mono- and bi-​nuclear complexes show a particular acid-​base behavior with respect to those of the non-​methylated amines. Such complexes can easily bind a proton or a hydroxide anion in aq. soln., with consequent detachment of a coordinated nitrogen. The crystal structures of two binuclear complexes were detd. In both the metals show distorted square-​planar arrangements of the donors.