Enantioselective synthesis of optically active polymeric homo- and bimetallic oxalate-bridged networks [M2(ox)3]n

The synthesis of the enantiomeric forms of the two- and three-dimensional polymers: {[NBu4] [MnCr(ox)(3)]}(n) (1) (Bu = n-butyl, ox = oxalate), {[M(bpy)(3))][LiCr(ox)(3)]}(n) (M = Ni (2), Ru (4)) (bpy = 2,2'-bipyridine), {[M(bpy)(3))]-Mn-2(ox)(3)]}(n) (M = Ni (3), Ru (5)) using resolved [Cr(ox)(3)](3-) and [M(bpy)(3)](2+) (M = Ni, Ru) species as chiral building blocks, and their structural characterization are reported. The optical activity of these systems arises from the helical chirality of the tris-chelated subunits with Delta or Lambda configurations. Bimetallic two-dimensional optically active network 1 results from the stacking of similar metallo-oxalate honeycomblike layers containing [Cr(ox)(3)](3-) units of the same chirality. The assembly of homochiral species leads to optically active three-dimensional 3-connected 10-gon nets 2-5. Solid state circular dichroism (CD) measurements demonstrate the enantiomeric character of the obtained polymers. Absolute configurations of the metal centers have been assigned according to circular dichroism and X-ray diffraction data. Enantiomerically pure single crystals of the two enantiomeric forms, ([Ru-Delta(bpy)(3))][LiDeltaCrDelta(ox)(3)]H2O}(n) (4 Delta) and {[Ru-Lambda(bpy)(3))][LiLambdaCrLambda(ox)(3)]H2O}(n) (4 Lambda), have been obtained and the structures determined by X-ray diffraction studies (crystals data: cubic system, space group P2(1)3, a (Angstrom) = 15.293(8) (4 Delta), 15.289(2) (4 Lambda), Z = 4).