The adsorption behavior of 4-biphenylisocyanide (BPNC) has been studied by means of surface-enhanced Raman scattering (SERS). BPNC has been found to adsorb on silver and gold via the carbon lone pair electrons assuming a standing geometry with respect to the surfaces. The presence of the ν(CH) band in the SERS spectra indicated a vertical orientation of the biphenyl ring of BPNC on Ag and Au. Neither a substantial red shift nor a significant band broadening of the ring breathing modes implied that a direct ring π orbital interaction with metal substrates should be quite low. On the basis of the electromagnetic surface selection rule, we attempted to explain the orientation of the adsorbate on Ag and Au surface by determining the relative enhancement factor of each vibrational band. The band analysis indicated that BPNC should have a slightly more vertical orientation on silver than on gold. The frequency of the ν(NC) band on gold increased by ∼10 cm -1 than that on silver surface. Such a higher blue shift of the ν(NC) stretching vibration in the gold sol SER spectrum may be due to a higher electronegativity of gold.

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Treatment of CuI with 2 equiv of LiC6H3-2,6-Mes2 (Mes = C6H2-2,4,6-Me3) in Et2O/THF solution affords the species [Li(THF)4][2,6-Mes2H3C6Cu2I2] (1), which was characterized by 1H, 7Li, and 13C NMR spectroscopy and by X-ray crystallography. An analogous reaction involving CuI and 1 equiv of LiC6H3-2,6-Trip2 (Trip = C6H2-2,4,6-i-Pr3) gives the contact ion-pair species (Et2O)Li{ICuC6H3-2,6-Trip2} (2), which was characterized similarly. Compounds 1 and 2 represent very rare instances of well-characterized organohalocuprate species. The unique structure of the anion in 1 features two copper iodides bound to the ipso-carbon of the m-terphenyl ligand −C6H3-2,6-Mes2. The organic group interacts almost equally strongly with each copper, and there is a very short Cu−Cu distance of 2.391(3) Å. The copper in compound 2 is bound in an almost linear fashion by an iodide and an ipso-carbon atom from the ligand −C6H3-2,6-Trip2. The iodide is also bound to a lithium ion (which is solvated by two ethers) such that there is an unusually narrow interligand angle Li−I−Cu = 95.5(2)° at the iodide.

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