Cu(0) nanoclusters derived from poly(propylene imine) dendrimer complexes of CU(II)

A family of diaminobutane core, poly(propylene in-Line) dendrimers coordina ted to Cu(II), DAB-Am-n-Cu(II)(x) (n = 4, 8, 16, 32, 64, x = n/2), was stud ied by means of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopies. The geometry of the dipropylene triamine (dpt)-Cu(II) end-group complexes for all dendrimer gen erations is reported for the first time and is found to be that of a square -based pyramid with each Cu ion bound to three nitrogen atoms (Cu-N distanc e similar to2.03 Angstrom) of the dpt end group of the dendrimer. An oxygen atom residing 1.96 Angstrom from the Cu ion also occupies the equatorial p lane, and the pyramid is completed by an axial oxygen at similar to2.65 Ang strom. In addition, we report for the first time that reduction of the Cu(I I)-dendrimer complexes with NaBH4 yields DAB-Am-n-Cu(0)(cluster) species. T ransmission electron microscopy (TEM) studies of the reduced species demons trate that there is a systematic decrease in the size of the generated Cu c lusters with increasing dendrimer generation. Additionally, it was found th at the size of the nanoclusters is a function of the n/x ratio of the DAB-A m-n-Cu(II)(x) precursor, with highly monodisperse, extremely small nanoclus ters (r(cluster) = 8.0 +/-1.6 Angstrom) obtained with n = 64 and x = 16. EX AFS and XANES measurements on the reduced DAB-Am-n-Cu(0)(cluster) corrobora te the TEM data, and provide additional information on the possible encapsu lation of the Cu nanoclusters by the dendrimers.