Abstract
We recorded surface-enhanced Raman scattering (SERS) spectra ofmetal-string complexes Co 3 (dpa) 4 Cl 2 [di(2-pyridyl)amido (dpa)], Ni 3 (dpa) 4 Cl 2 andthe oxidized form of the Ni 3 complex to determine their vibrationalwavenumbers and to investigate their structures. For SERS measurements thesecomplexes were adsorbed on silver nanoparticles in aqueous solution to eliminatethe constraint of a crystal lattice and the complexes remain in thermalequilibrium. From our analysis of the vibrational normal modes we assigned theSERS lines at 242 and 276 cm -1 to Ni 3 and Co 3 symmetric-stretching modes of the symmetric form. For Co 3 (dpa) 4 Cl 2 a Raman line at 383 cm -1 was assigned tothe Co - Co stretching mode of the unsymmetric form. The wavenumber of theNi 3 symmetric-stretching mode of the oxidized form [Ni 3 (dpa) 4 ] 3+ is 274 cm -1 , greater thanthat for neutral Ni 3 (dpa) 4 Cl 2 , in agreementwith a prediction of delocalized molecular-orbital theory that an electron isremoved from an antibonding orbital after oxidation. The experimental data showthat the SERS technique serves as an excellent tool to observe the variation ofmetal-metal bonding during an oxidation or reduction reaction. Copyright ©2010 John Wiley & Sons, Ltd.