Gas sorbing materials that are both reversible and highly selective are attracting attention due to their use in chemical sensing and chemical storage applications. The development of vapochromic materials, which exhibit pronounced color changes upon exposure to volatile organic compounds (VOCs), is advantageous because these materials can be used as visual indicators for hazardous chemicals. Stacked square-planar d8 metal complexes prove especially effective as vapochromic sensors, because the colors of these materials are strongly dependent on metal-metal separation. Intercalation of VOCs into these materials can perturb the metal-metal interactions, causing a dramatic color change. Unfortunately, most of the known vapochromic systems lack either the tunability necessary for systematic study, or suffer from the inability to produce X-ray diffraction quality crystals before and after vapor exposure. At present, the notion that one might predict vapochromic properties of materials prior to synthesis seems a distant possibility. Nevertheless, it is reasonable to envision the identification of trends and development guidelines for preparing vapochromic materials, particularly for a specific metal-ligand system.
With these difficulties in mind, we became interested in characterizing the vapochromic properties of Pt(tpy)X+ salts. As found for Pt(Me2bzimpy)Cl+ (Me2bzimpy = 2,6-bis(N-methylbenzimidazoly-2-yl)pyridine), the vapochromic properties of Pt(tpy)X+ (X- = Cl-, Br- or I-) are readily modulated by changes in the counter-anion, the ancillary ligand position, as well as substitutions on the tridentate ligand. Equally as important, the structures of several Pt(tpy)X+ salts have been characterized by X-ray crystallography, which establishes the feasibility of using Pt(tpy)X+ salts for investigating the factors which govern the vapochromic process. This dissertation primarily focuses on investigating the vapochromic behavior of Pt(tpy)X+ (X = Cl-, Br- and I-) salts with group 15 hexafluoride (PF6-, AsF6- and SbF6-) and ClO4- anions with aims of elucidating the mechanism by which these compounds respond to VOCs. Chapters 2 and 3, herein, provide a detailed investigation [Pt(tpy)X](YF6) structures with and without acetonitrile. Conclusions from this study not only provide the first detailed look at how changes in the counter-anion and ancillary ligand influence the structures of Pt(tpy)X+ salts, but, also examines the structures of these materials to understand the physical origin of the attenuation of the vapochromic response resulting from these changes. Chapter 4 examines the vapochromic response of [Pt(tpy)Cl](ClO4) to water. Of significant interest is the observation of an intermediate species in the conversion of [Pt(tpy)Cl](ClO4).H2O to [Pt(tpy)Cl](ClO4), which speaks of the complexity in the vapochromic response. In keeping with the theme of using Pt(tpy)X+ salts for sensing applications, Chapter 5 describes the colorimetric and luminescence response of [Pt(tpy)Cl](PF6) to aqueous solutions of perchlorate. Chapter 6 shifts gears to the synthesis, spectroscopy, crystal structures, and photochemistry of Pt(tpy)X3+ salts (X- = Cl- and Br-). The significance of this chapter is the successful synthesis and detailed spectroscopic characterization of two Pt(IV) complexes where terpyridine is bonded in a tridentate fashion. The research described in this chapter has more significant implications on the understanding of Pt(IV) spectroscopy as well as the use of these and related materials as catalysts.