Electronic spectra of [(CH₃)₂NH₂]₅Cd₂CuCl₁₁ crystals

Abstract

The temperature evolution of Cu 2+ ion environment in the solid solutions of ((CH 3 ) 2 NH 2 ) 5 Cd 2 CuCl 11 is studied on the basis of absorption spectroscopy data. For the detailed analysis of experimental data the special program package Crys Tool 1.0 based on quantum-mechanical models, first of all on the model of normalized spherical harmonics (NSH), has been employed. It has been found that similarly to the crystal of ((CH 3 ) 2 NH 2 ) 5 Cd 3 Cl 11 (DMACC) the investigated solid solution contains tetragonally distorted octahedral metal-halogen complexes of two types and the degree of their distortion is changed considerably at the temperatures of phase transitions (PTs). The parameters of crystal field, angular overlap model, as well as the copper-chlorine distances, show continuous changes at T 1 = 176 K that should be related to the second-order transition, whereas the jump-like anomalies of the spectral parameters at T 2 = 115 K (on cooling) are characteristic of the first-order PTs. Introduction of the copper ions into the structure of the host DMACC crystal induces the shifts of these PTs toward low temperatures by 3.5 and 5 K, respectively. The observed structural changes around T 0 = 313 K are connected with a complex co-operative effect involving weakening of the hydrogen bonds and modification of the Jahn-Teller distortion with temperature.

Dielectric and Birefringent Properties of [(CH3)2NH2]5Cd2CuCl11Solid Solutions in the Region of Their Phase Transitions

“…At the same time, as it has been found in the spectral study [5], the behaviour of the crystal's properties at high temperatures, first of all the position of the anomalies at T 0 , strongly depend on the previous thermal history of the sample. Besides, the spectral parameters showed a considerable global hysteresis in the vicinity of the mentioned temperature.…”

“…1. The second order PT, which has been clearly detected in the spectral investigations [5], manifests itself only as a weak but noticeable change of slope of above mentioned dependences around T 1 = 175 K (Fig. 1b).…”

“…The clear anomalies of the spectral parameters [5] were observed at the temperatures close to T 1 and T 2 temperatures for the "host" DMACC crystals. These anomalies were found to be characteristic of the second and the first order PTs, respectively.…”

“…Under such circumstances the solid solutions of [(CH 3 ) 2 NH 2 ] 5 Cd 2 CuCl 11 have been grown and the temperature evolution of their electronic spectra was investigated in detail [5]. The important information concerning the nature of the PTs has been obtained from the analysis of the crystal field (CF) electronic spectra.…”

Exciton–phonon interaction and Raman spectra of [(CH3)2NH2]5Cd2CuCl11 crystals

“…The divalent copper ions, with their strong coupling to the surrounding ligands, appeared to be convenient probes of symmetry and strength of the crystal field. Due to this, important information especially concerning the nature of the PTs has been obtained from investigations of the crystal field (CF) electronic spectra [6]. The temperature evolution of the copperchlorine distances, parameters of the crystal field and the angular overlap model were analyzed using a special program package 'Crys Tool 1.0' based on quantum-mechanical models.…”