The inﬂuence of N -alkylation and chain length in the coordination ability of diamines towards silver(I) in dimethylsulfoxide Clara Comuzzi *, Veronica Novelli, Roberto Portanova, Marilena Tolazzi * Dipartimento di Scienze e Tecnologie Chimiche, Universita ` di Udine, Via del Cotoniﬁcio 108, I-33100 Udine, Italy Received 27 September 2001; accepted 16 October 2001 Abstract The thermodynamic functions for the complexation of Ag(I) by the following diamines: N ,N -dimethyldiethylenediamine (N ,N - dmen), N ,N -dimethyl-1,3-propanediamine (N ,N -dmtn) and N ,N ,N ?,N ?-tetramethyl-1,3-propanediamine (tmtn) have been determined in dimethylsulfoxide (dmso) by potentiometric and calorimetric techniques at 298 K and 0.1 mol dm 3 ionic strength (NEt 4 ClO 4 ). Only mononuclear complexes are formed (AgL j  , j /1, 2) where the ligands act as monodentate or chelate agents. All the complexes are enthalpy stabilized whereas the entropy changes counteract the complexation. The different basicities and steric requirements of both the ligands and complexes formed together with the size of the chelate rings are taken into account to discuss the results presented here. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Silver(I); N -methylated polyamines; Complexes; Dimethylsulfoxide; Thermodynamics 1. Introduction In the last few years there has been a great deal of interest in the field of complex formation of metal ions with neutral N-donors in water [1  /8] as well as in nonaqueous or mixed solvents [9 /17]. The aim of these works has been to improve the knowledge of the coordination chemistry of soft and hard metal ions with these ligands, to investigate the strong influence of different basicities and steric properties of the ligands on the stability and nature of the complexes and to design ligands for selective complexation of metal ions. These studies have now also attracted renewed inter- est as the coordination properties of open chain poly- amines towards different cations have been taken as models allowing direct comparison with corresponding macrocyclic systems [18]. In particular many papers have reported data con- cerning Group 11 metal complexation with these ligands [1,3,7,12,16,17]. These data have shown that the co- ordination properties of amines towards these ions may be modulated through the number and the basicity of nitrogen atoms present in the ligand, the different chelate ring sizes the ligands can form, the different N- functionalization and the nature of the solvent. In this context and as an extension of previous works, we report here the results of a thermodynamic study on the complex formation of Ag(I) with the following diamines in the aprotic solvent dimethylsulfoxide (dmso): N ,N -dimethyldiethylenediamine (N ,N -dmen), N ,N -dimethyl-1,3-propanediamine (N ,N -dmtn) and N ,N ,N ?,N ?-tetramethyl-1,3-propanediamine (tmtn). The ligands have been chosen in order to provide further information on how the different alkylation and/ or the different size of the potential chelate rings formed may affect their coordination ability toward metal ions. For this purpose also a comparison with data previously reported on Ag(I) complex formation with similar diamines possessing the same skeleton, but differently methylated, i.e. ethylenediamine (en) [12c], N ,N ?-di- methylethylenediamine (dmen) [12e], N ,N ,N ?N ?-tetra- methylethylenediamine (tmen) [12e] and 1,3- propanediamine (tn) [12c], will be carefully taken into account. Potentiometric and calorimetric measurements have been used to obtain the free energy and enthalpies of the * Corresponding authors. Tel.:  /39-0432-558852/558882; fax:  /39- 0432-558803. E-mail addresses: comuzzi1@dstc.uniud.it (C. Comuzzi), tolazzi@dstc.uniud.it (M. Tolazzi). Polyhedron 21 (2002) 1337  /1342 www.elsevier.com/locate/poly 0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII:S0277-5387(02)00970-1