SYNTHESIS AND SINGLE-CRYSTAL STRUCTURE OF AN UNUSUAL HEPTACOORDINATE CADMIUM(II) COMPLEX, [CD(MEDIEN)(NO3)(2)] (MEDIEN = BIS(2-AMINOETHYL)METHYLAMINE)

Molecular geometry and coordination number play the key role in explor ing the chemistry of a coordination compound. Cadmium(II) usually poss esses octahedral as well as tetrahedral geometry.(1) Pentacoordination in cadmium(II) is also described.(1,2) However, heptacoordinate cadmi um(II) complexes are not common,(3-10) and most of them are examples o f apparent seven-coordination forced by geometrical demand of polydent ate ligands.(3-7) The examples of truly seven-coordinate cadmium(II), i.e. in which the coordination of each atom is not forced by the geome try of the ligands, are very scant in the chemistry of cadmium(II). Th e crystal structure characterization of many of the cadmium(II) comple xes with chain triamines (L), such as bis(3-aminopropyl)amine (dpt), ( 2-aminoethyl)(3-aminopropyl)amine (aepn), and bis(2-aminoethyl)amine ( dien) [L=H2N1-(CH2)(n)-(NH)-H-2-(CH2)(m)-(NH2)-H-3 when n=m=3, L=dpt; n=3. m=2, L=aepn; and n=m=2, L=dien] have been reported by Cannas el a l.(2,11,12) but such characterization with N-2-alkyl-substituted triam ines has nor yet been published. Here we report the synthesis and stru ctural characterization of a rather unusual seven-coordinate cadmium(I I) complex with bis(2-aminoethyl)methylamine(medien). This belongs to that rare family of seven-coordinate cadmium(II) where geometrical dem ands did not force it into such high coordination.