Crystal structures and solution behaviors of dinuclear d10-metal complexes containing anions of N,N ′-bis(pyrimidine-2-yl) formamidine

The salts of Zn(II), Cd(II) and Hg(II) react instantaneously with Kpmf (pmf(-) = anion of N, N'-bis(pyrimidine-2-yl) formamidine, Hpmf) in THF, producing bimetallic complexes of the types [M-2(pmf)(3)](X) (M = Zn(II), X = I-3(-), 1a; M = Zn(II), X = NO3-, 1b; M = Zn(II), X = ClO4-, 1c; M = Cd(II), X = NO3-, 2a; M = Cd(II), X = ClO4-, 2b) and Hg-2(pmf)(2)X-2 (X = Cl, 3a; Br, 3b; I, 3c). New tridentate and tetradentate coordination modes were observed for the pmf- ligands and their fluxional behaviors investigated by measuring variable-temperature H-1 NMR spectra. Complexes 2a and 2b, which possess only tetradentate coordination modes for the pmf- ligands in the solid state show larger free energy of activation [GRAPHICS] for the exchange than complexes 1a-c and 3a-c with tetradentate and/or tridentate coordination modes. Complexes 1a-c and 3a-c are the first dinuclear Zn(II) and Hg(II) complexes containing formamidinate ligands. Moreover, the separation between the two Hg(II) atoms are 3.4689(9), 3.4933(13) and 3.5320(10) A for complexes 3a-c, respectively, similar to the sum of van der Waals radii of two Hg(II) atoms which is 3.50(7) A. All the complexes exhibit emissions and the nature of the anions hardly change the emission wavelengths of the complexes with the same metal centers. The emission bands may be tentatively assigned as intraligand (IL) pi ->pi* transitions.