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 yl-1,3,5,8,12-penta-azacyclotetradecane)nickel(II) complexe s [NiL] (ClO4)(2) (R = Me, Et, n-Pr, n-Bu, n-octyl, n-tridecyl, n-octa decyl) has been prepared and characterised. The planar octahedral equi librium in solution has been studied in detail for R = Et. For this eq uilibrium 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) perchlorat e 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 gauch e with the sec-NH centres having the RSRS configuration. The N-Et grou p is axial. (C) 1997 Elsevier Science Ltd.