Infrared Spectroscopy Studies of Platinum Salts Containing Tetracyanoplatinate(II). Evidence for Strong Hydrogen-Bonding Interactions in "Vapochromic" Environmental Sensor Materials

We have studied the sorption of volatile organic compounds (VOCs) by [(n-C₄H₉)₄N]₂[Pt-(CN)₄] and [Pt(p-CN-C₆H₄-C₁₀H₂₁) ₄][Pt(CN)₄] with FTIR spectroscopy. The data indicate a strong correlation exists between ν(CN) stretching frequencies in the [Pt(CN)₄]^2- ions and the hydrogen bonding ability of the VOC (as expressed by Abraham's a values). The ν(CN) stretching frequencies for each salt with sorbed VOC indicate that similar VOC-material interactions are present in both. The correlation of the IR data for [Pt(p-CN-C₆H₄-C₁₀H₂₁) ₄]-[Pt(CN)₄] with the previously reported NIR data was only successful for solvents with α > 0.15. These results suggest that vapochromic shifts in the electronic transitions of [Pt(p-CN-C₆H₄-C₁₀H₂₁) ₄][Pt(CN)₄] result not only from H-bonds between the VOC and [Pt(CN)₄]^2- but also from one or more additional mechanisms that are most important for solvents with low H-bond donor character (α < 0.15).