Effect of metal size on coordination geometry of N,N′,N"-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane:: synthesis and structure of [MIIL] (ClO4)2 (M = Zn, Cd and Hg)

The hexadentate ligand N,N',N'-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane (tachpyr) forms stable metal complexes from the salts M(ClO4)(2) . 6H(2)O (M = Zn2+ and Cd2+) and Hg(ClO4)(2) in methanol or ethanol. The complexes [Zn(tachpyr)] (ClO4)(2) . CH3OH (1 . CH3OH), [Cd(tachpyr)] (ClO4)(2) (2) and [Hg(tachpyr)] (ClO4)(2) (3) have been isolated. and their solid state structures have been determined and analyzed. The coordination sphere changes from octahedral to trigonal-prismatic geometry with increasing metal radius. The trigonal twist angles (alpha) are 43.7(2)degrees in compound 1 . CH3OH, range between 11.0(4)degrees and 21.7(2)degrees in compound 2 and range between 3.1 (3)degrees and 5.5(2)degrees in compound 3. To accommodate larger metal ions there is also a slight outward expansion of the triaminocyclohexane nitrogens, which leads to a reduction in the average cyclohexyl ring C-C-C-C torsion angles (beta) with concomitant flattening of the ring. The torsion angles (beta) in 1 . CH3OH are 52.3(6)degrees and 52.4(6)degrees, range between 46.1(9)degrees and 52.7(9)degrees in compound 2 and range between 45.1 (6)degrees and 52.9(7)degrees in compound 3. (C) 2000 Elsevier Science Ltd All rights reserved.