Padlock macrocyclic complexes. The synthesis of a range of nickel(II) complexes of N-alkyl azacyclams and the crystal structure of (3-ethyl-1,3,5,8,12-penta-azacyclotetradecane) nickel(II) perchlorate

A range of (3-alkyl-1,3,5,8,12-penta-azacyclotetradecane)nickel(II) complexes [NiL] (ClO4)(2) (R = Me, Et, n-Pr, n-Bu, n-octyl, n-tridecyl, n-octadecyl) has been prepared and characterised. The planar octahedral equilibrium in solution has been studied in detail for R = Et. For this equilibrium Delta H-0 = -19.2+/-0.5 kJ mol(-1) and Delta S-0 = -76.4+/-1.5 JK(-1) mol(-1), with K = 0.24 at 25 degrees. The crystal structure of 3-ethyl-1,3,5,8,12-penta-azacyclotetradecane) nickel(II) perchlorate has been determined. The complex is square planar and the Ni-N bond lengths are 1.959(5) and 1.906(5) Angstrom. Both six-membered chelate rings adopt a chair conformation and the five-membered rings are gauche with the sec-NH centres having the RSRS configuration. The N-Et group is axial. (C) 1997 Elsevier Science Ltd.