Cu(II) ion directed self-assembly of a Y8/Cu6 heterometallic coordination cage via an Y(III) metalloligand

A non-centrosymmetric yttrium [Y(III)] metalloligand, [Y(H3L)(NO3)]·2NO3·THF (1) {tris{[2-{(imidazole)methylidene}amino]-ethyl}amine = H3L}, was synthesized and subsequently used in a Cu(II) directed self-assembly process to form a Y8/Cu6- type heterometallic coordination cage [Cu6Y8L8(NO3)5(H2O)3]·7NO3·21H2O (2). The eight corners of the distorted cubic cage are defined by eight Y(III) ions while Cu(II) ions occupy the centers of six faces with two opposite Cu(II) ions considerably outside the faces. The asymmetric Y(III) metal centres due to the extra coordination of either water molecules or nitrate anions induce chirality in the cage, with equal numbers of both enantiomers present in the solid state. The cage formation in both solution and in the solid state was demonstrated by ESI-MS and single crystal X-ray diffraction. Magnetic property measurements indicate that cage 2 remains paramagnetic down to 2 K. In addition, vibrational modes, electronic structure and thermal stability of the coordination cage 2 have been further investigated and reported.