Synthesis and structure of mercurous ion and dinuclear lead(II) complexes of the 28-membered selenaaza macrocycle: Dominance of the chelate ring size effect and conformational requirement over soft-soft interactions

The flexible and larger ring size macrocycle 4 (C36H46N6Se2) afforded stable complex 5 [Hg-2(PF6)(2){C36H46N6Se2}] on treatment with 1 equiv of mercuric acetate followed by addition of NH4PF6. The reaction of Pb(OCOCH3)(2).4H(2)0 with 4 followed by treatment with NH4PF6 resulted in a dinuclear lead complex (6) [Pb-2(PF6)(2)(OCOCH3)(2){C36H46N6Se2}]. The crystal structures of complexes 5 and 6 are described: C36H46F12Hg2N6P2Se2 a = 9.5106(5) Angstrom, b = 11.5222(6) Angstrom, c = 11.8161(6) Angstrom, alpha = 115.6110(10)degrees, beta = 96.5190(10)degrees, gamma = 106.2910(10)degrees, monoclinic, P (1) over bar, Z =1; C44H57F12N8O4P2Pb2Se2 a = 9.4668(5) Angstrom, b = 11.9937(6) Angstrom, c = 25.2319(14) Angstrom, alpha = 102.4130(10)degrees, beta = 97.6130(10)degrees, gamma = 94.8540(10)degrees, monoclinic, P (1) over bar, Z= 2. The crystal structure of 5 revealed that Hg-2(2+) is trapped inside the cavity of the macrocycle. The geometry around the mercurous ion is antiprismatic with Hg-2(2+) coordinating to six nitrogen atoms forming four five-membered rings, and there is no interaction between the mercurous ion and the selenium donor atoms. The single crystal X-ray crystal structure of 6 indicates a distorted octahedral geometry around each lead atom in the cavity of the macrocycle due to presence of the sterochemically active lone pair on Pb(II). The octahedral geometry around each Pb(II) is satisfied by coordination to 3 nitrogen atoms, two oxygen atoms of the chelating acetate group, and bridging of one of the oxygen atoms of the nearby acetate.