Near-Infrared Electronic Spectroscopy and Emitting-State Properties of K₂PdCl₄and K₂PdBr₄

Abstract

Near-infrared luminescence is observed from single crystals of K 2 PdCl 4 and K 2 PdBr 4 between 13 500 cm -1 and 9000 cm -1 (740 nm and 1100 nm). The emission spectrum of K 2 PdBr 4 shows vibronic structure involving both the totally symmetrical a 1g mode and the non-totally symmetrical b 1g mode (D 4h point group). The luminescence spectrum of K 2 PdCl 4 is less resolved, but shows similar vibronic structure. The maxima of the weak lowest energy absorption bands are at 14 800 cm -1 (molar absorptivity ) 0.42 M -1 cm -1 ) and 14 645 cm -1 (molar absorptivity ) 0.38 M -1 cm -1 ) at 8 K for K 2 PdCl 4 and K 2 PdBr 4 , respectively. The Stokes shifts for K 2 PdCl 4 and K 2 PdBr 4 are 3865 and 3420 cm -1 . A gap of approximately 700 (K 2 PdCl 4 ) or 950 cm -1 (K 2 PdBr 4 ) separates the emission and absorption spectra. This energy gap and the vibronic structure are analyzed with a model involving the E g × b 1g Jahn-Teller effect in the 3 E g excited state of the square-planar [PdCl 4 ] 2and [PdBr 4 ] 2complexes. The Huang-Rhys parameters S a1g and S b1g are 6.7 and 0.2 for K 2 PdCl 4 , leading to bond elongations of 0.12 Å for each of two opposing Pd-Cl bonds and of 0.09 Å for each of the other two bonds. The corresponding values for K 2 PdBr 4 are 7.6 (S a1g ), 0.4 (S b1g ), 0.12 Å, and 0.07 Å.

Synthesis, Structure, and Optical Properties of Pt(II) and Pd(II) Complexes with Oxazolyl- and Pyridyl-Functionalized DPPM-Type Ligands: A Combined Experimental and Theoretical Study

“…26−28 However, this is not the case for complexes that exhibit emission from highly distorted MC states. 27 At these temperatures, broad and featureless emission is almost always observed. For the complexes presented here, the emission bandwidths (full width at half-maximum (fwhm)) are 3750 cm −1 (5a), 3150 cm −1 (5b), 3500 cm −1 (2a), and 3200 cm −1 (2b).…”

Vibronic structure in the luminescence spectra of tetragonal d2 and d8 complexes analyzed by wavepacket dynamics on two-dimensional potential surfaces

“…Square planar chloride complexes of the two metals show luminescence spectra involving a distortion along an asymmetric stretching coordinate (b 1g in idealized D 4h symmetry) that is VLJQLILFDQWO\ ODUJHU IRU SODWLQXP Q 304 = 2.85) than for SDOODGLXP Q 270 = 1.18). 20,21 Our analysis of the spectra in Fig. 1 reveals a first case of very similar excited state distortions for corresponding platinum and palladium complexes and reveals a fundamental difference between distortions along stretching and bending modes.…”

Palladium speciation in UV‐transparent glasses

“…The distortion reduces the energy difference between the d z 2 and the d x 2 −y 2, what leads to the observed redshift in the position of the 1 A 1g → 1 B 1g transition. 55,56 In other examples, the absence of the 1 B 1g absorption band was also indicative for structural distortion. 57 From pure water to HCl solution, the d-d transition bands are increasingly red-shifted with increasing dopant concentration.…”