Five coordinate nickel(II) isothiocyanato and chloro complexes of triazacycloalkanes

Abstract

The new nickel(II) complexes [Ni(pqr-cy)(NCS) 2], [Ni(pqr-cy)Cl]ClO 4, and Ni 2(pqr-cy) 3(ClO 4) 4·nH 2O (n = 4 or 5) have been prepared, where pqr-cy is a triazacycloalkane, NH(CH 2) pNH(CH 2) qNH(C H 2) r (p,q = 2,3; r = 2–6). The isothiocyanato complexes are six-coordinate, NCS-bridged octahedral when t (= p + q + r) is small (t≦9). but they are five-coordinate when t is large (t≧9). The five-coordination is peculiar and its origin is attributable to blocking of a coordination site by the backbone polymethylene groups of the pqr-cy ligands. Only the ligands with t=9 and 10 form the chloro complexes, which are Cl-bridged dimers and are also five-coordinate because of the same steric hindrance. It is worth noting that these five-coordinate nicke(II) complexes are isolated from aqueous solutions. The 2:3 perchlorate complexes are octahedral and available only for the ligands with t=9.