Physical Chemistry Laboratory, Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan.
Phys Chem Chem Phys. 2010 Apr 7;12(13):3156-63. doi: 10.1039/b920411c. Epub 2010 Feb 19.
Effects of metal substrate on the bonding nature of isocyanide group of two aryl isocyanides, 1,4-phenylene diisocyanide (PDI) and 4-methylphenyl isocyanide (MPI), and tilt angle of MPI were examined by measuring sum frequency generation (SFG) spectra of the self-assembled monolayers (SAMs) of these molecules on Au, Pt, Ag, and Pd surfaces. The SFG peaks due to "metal bonded" and "free"-NC groups were resolved by comparing the SFG spectra of PDI with IR spectra obtained by DFT calculations and previous results of vibrational spectroscopy. Based on the peak positions of the "metal bonded"-NC, it is clarified that while PDI and MPI were adsorbed at top sites on Au, Ag, and Pt surfaces, they adsorbed at bridge sites on the Pd surface. The tilt angles of MPI were determined from the intensity ratio between the SFG peaks of C-H symmetric and asymmetric stretching vibrational modes of the CH(3) group. The tilt angles of the MPI SAMs were in the order of Pt < Pd < Ag < Au, reflecting the bonding nature between the -NC group and the substrate atoms.
通过测量两种芳基异氰化物（1,4-亚苯基二异氰酸酯（PDI）和 4-甲基苯基异氰酸酯（MPI））在 Au、Pt、Ag 和 Pd 表面上自组装单分子层（SAM）的和频产生（SFG）谱，研究了金属衬底对异氰酸酯基团的键合性质和 MPI 的倾斜角度的影响。通过比较 PDI 的 SFG 谱与 DFT 计算得到的 IR 谱和先前的振动光谱结果，解析了“金属键合”和“游离”-NC 基团的 SFG 峰。基于“金属键合”-NC 的峰位置，澄清了 PDI 和 MPI 分别在 Au、Ag 和 Pt 表面上以顶位吸附，而在 Pd 表面上以桥位吸附。MPI 的倾斜角度是从 CH(3)基团的 C-H 对称和不对称伸缩振动模式的 SFG 峰的强度比确定的。MPI SAM 的倾斜角度顺序为 Pt < Pd < Ag < Au，反映了-NC 基团与衬底原子之间的键合性质。
