New 1-D and 3-D thiocyanatocadmates modified by various amine molecules and Cl−/CH3COO− ions: synthesis, structural characterization, thermal behavior and photoluminescence properties

Abstract

Under ambient conditions, reactions of CdCl₂/Cd(CH₃COO)₂, SCN⁻ and various organic amine molecules in strongly acidic solutions afforded the five new thiocyanatocadmates [H₂(abpy)][CdCl₂(SCN)₂] (abpy = azobispyridine) 1, [H(apy)][Cd(SCN)₃] (apy = 4-aminopyridine) 2, [H(ba)]₂[CdCl₂(SCN)₂] (ba = tert-butylamine) 3, [H₂(tmen)][Cd₃Cl₆(SCN)₂] (tmen = N,N,N′,N′-tetramethylethylenediamine) 4, and [H(dba)]₂[Cd₂(CH₃COO)₂(SCN)₄] (dba = dibutylamine) 5. In compound 2 only, the CH₃COO⁻ ions in Cd(CH₃COO)₂ were completely displaced by SCN⁻, producing a chained thiocyanatocadmate [Cd(SCN)₃]⁻. In the other four compounds, the Cl⁻ or CH₃COO⁻ ions appeared in the final inorganic anion frameworks. In compound 1, the Cl⁻ ions doubly bridge the Cd²⁺ centers, forming a one-dimensional (1-D) infinite chain, and the SCN⁻ group exists in a terminal form, whereas in compound 3, the reverse situation is observed. Due to a trans-mode arrangement for two terminal Cl⁻ or SCN⁻ ions around each Cd²⁺ center, the inorganic anion chains in compounds 1 and 3 both show a linear shape. In compound 4, Cd²⁺ and Cl⁻ first aggregate to form a 1-D endless chain with a composition of Cd₃Cl₆, which can be described as a linear arrangement of the open double cubanes. SCN⁻ serves as the second connector, propagating the Cd₃Cl₆ chain into a three-dimensional (3-D) network with the occluded H₂(tmen)²⁺ cations. In compound 5, the SCN⁻ groups doubly bridge the Cd²⁺ centers, forming a 1-D zigzag-shape chain. The formation of the zigzag chain likely derives from chelation of the CH₃COO⁻ group to the Cd²⁺ center. The thermal behavior and the photoluminescence properties of the title compounds were also investigated.