A detailed study of the non-Beer's law behavior of the absorption features of the UV spectrum of aqueous K2Pt(CN)4 and BaPt(CN)4 allows a more definitive set of excited-state assignments than previously possible for the monomer. Concentration dependence, quenching, and lifetime studies of the several room-temperature emission features allow a distinction between fluorescences and phosphorescences and a probable assignment as to the oligomers responsible. Two excited-state absorptions and a long-lived chemical transient are found.The tetracyanoplatinites, known for well over a hundred years, have been variously studied by quite a number of investigators. Our interest, however, was stimulated by recent work of Gliemann, Yersin, and co-workers,1 11"9 who studied the low-temperature emission from various salts of Pt(CN)42". They concluded that the stacking that occurs in the crystal leads to a splitting of the platinum z-axis orbitals, the emission properties being sharply dependent on the Pt-Pt distance, R. Our interest was in whether stacking association might occur in solutions and, if so, in the consequent photophysical and photochemical behavior.Emission from aqueous solutions of the Ba, Mg, and K salts is well-known,10"15 the most recent work being that of Rossiello and Furlani16 and Webb and Rossiello.17 The matter of possible oligomer formation in solution has not been directly studied, however, nor have there been any clear assignments of the emission features. Day18,19 did conclude that since the tetracyanoplatinites form insulating crystals in which the molecular units are clearly distinguishable, it seems a priori probable that the lowest crystal excited states are neutral Frenkel excitons formed from simple molecular transitions coupled by an intermolecular interaction potential. The simplest approximate treatment is by Davydov theory.20 One predicts a shift to lower energy of the transition that is polarized along the Pt-Pt axis, or the z direction, proportional to /?'3 (as observed).The absorption spectrum of Pt(CN)42" has been analyzed theoretically by various authors,21"33 but only one paper has specifically attempted a treatment of the dilute aqueous solution spectrum.29 The spectrum is complex; there are four distinct but nonsymmetric features, which may be deconvoluted into six Gaussian components.
Experimental SectionMaterials. The tetracyanoplatinate salts were prepared by a modification of a literature method.34 To platinum(II) chloride (Alfa Inorganics) was added a 20% excess of potassium cyanide dissolved in a minimum of water. The resulting solution was filtered, and the filtrate was evaporated at 60-80 °C to about half the volume (12 cm3 for 5 g of PtCl2) and allowed to cool. The resulting crystals could be recrystallized from dilute aqueous potassium cyanide. Ba [Pt(CN)4] •4 20 was prepared by adding a slight excess of barium chloride to a warm concentrated solution of the potassium salt of the complex, and filtering off any Ba(OH)2 that formed. Crystals separated on cooling and were recr...
