June 3, 2002
Volume 80, Number 22
CENEAR 80 22 p. 7
ISSN 0009-2347


NANOSCIENCE

SHRINK-WRAPPED NANO-BEANPOLES
Flexible insulating ligands twist around rigid molecular wires

MICHAEL FREEMANTLE

A new class of double-helical molecules has been synthesized. The molecules consist of two platinum atoms bridged by a rodlike chain of carbon atoms--along which electrons and charge can flow--surrounded by diphosphine ligands bearing flexible carbon double helices that insulate the rods.

"The flexible sp3 carbon chains wind around the rigid sp carbon chain just like climbing beans wrap around a beanpole," explains John. A. Gladysz, chemistry professor at the Institute for Organic Chemistry, University of Erlangen-Nuremberg, in Germany. Gladysz carried out the work with colleagues there and at the University of Utah [
Angew. Chem. Int. Ed., 41, 1871 (2002)].

"The template effect of a beanpole was known to ancient agrarian societies but has never been exploited on a molecular scale," he continues.

The group used two strategies to prepare the compounds. A "directed synthesis" employed a series of organometallic reactions, including an alkene metathesis step using a ruthenium catalyst. Then, in a self-assembly process, a Pt(C[C)Pt complex was treated with diphosphines [(Ar)2P- (CH2)14P(Ar)2, where Ar = aryl].

The resulting molecules are unique in that there are no covalent or hydrogen bonds between the double-helix strands.

"There are only van der Waals attractions between the strands," Gladysz tells C&EN. "The overall process is very much like the shrink-wrapping technique used in the manufacture of insulated circuit components."

Oxford University chemistry lecturer Harry L. Anderson, an expert on insulated molecular wires, is impressed with the new compounds. "It is beautiful work and an interesting new approach to insulated molecular wires," he says. "It is remarkable that one can make structures like this so easily, and that they adopt helical conformations."



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