Comparison of heteronuclear coupling constants for isostructural nitrogen coordination compounds of Cd-111/113 and Hg-199

The complexation of Cd(II) by the tripodal ligand tris[(2-pyridyl)methyl]am ine and dipodal ligand bis[(2-pyridyl)methyl]amine was investigated by solu tion-state NMR and X-ray crystallography. Cadmium coordination compounds ex hibiting rarely observed solution-state NMR H-1-Cd-111/113 satellites were characterized. The eight-coordinate complex [Cd(TMPA)(2)](ClO4)(2). toluene (1) crystallizes in the triclinic space group P1 with a = 9.629(2) Angstro m, b = 11.020(2) Angstrom, c = 11.641(2) Angstrom, alpha = 114.069(13)degre es, beta = 97.492(13)degrees, gamma = 91.034(14)degrees, and Z = 1. The ave rage Cd-N-amine distance is 2.53(4) Angstrom and the average Cd-N-pyridyl d istance is 2.54(6) Angstrom. The complex [Cd(BMPA)(NCCH3)(OH2)(OClO3)][Cd(B MPA)(2)](ClO4)(3).(CH3CN) (2) crystallizes in the triclinic space group P ( 1) over bar with a = 10.446(2) Angstrom, b = 16.653(3) Angstrom, c = 17.736 (3) Angstrom, alpha = 62.479(9)degrees, beta = 80.606(14)degrees, gamma = 8 4.66(2)degrees, and Z = 2. In the pseudo-octahedral monocation, the nitroge n-containing ligands occupy equatorial positions with Cd-N distances of 2.3 21(8), 2.283(7), and 2.263(8) Angstrom for the amine, pyridyl (average) and acetonitrile nitrogens, respectively. Significant axial interactions occur with Cd-O bond distances of 2.313(7) Angstrom (water) and 2.478(7) Angstro m (perchlorate). In the pseudo-trigonal prismatic dication, the average Cd- N-amine distances is 2.395(5) Angstrom and the average Cd-N-pyridyl distanc e is 2.362(8) Angstrom. The solid-state structures and solution-state NMR t rends were very similar to recently reported isovalent complexes of Hg(II), providing an exceptional opportunity tb compare coupling constants of coor dination compounds. Implications for the use of Cd-111/113 and Hg-199 NMR a s metallobioprobes are discussed.