The similarities and differences between the behavior of carbon-bound and terminal metal-bound halogens and halide ions as potential hydrogen bond acceptors has been extensively investigated through examination of many thousands of interactions present in crystal structures. Halogens in each of these environments are found to engage in hydrogen bonding, and geometric preferences for these interactions have been established. Notably, typical H···X−M angles are markedly different for X = F than for X = Cl, Br, I. Furthermore, there are significant parallels between the behavior of moderately strong hydrogen bond acceptors X−M and the much weaker acceptors X−C. The underlying reasons for the observed geometric preferences have been established by ab initio molecular orbital calculations using suitable model systems. The results are presented within the context of their potential applications in crystal engineering and supramolecular chemistry, including relevance to nucleation in halogenated solvents. The br...

Understanding the Behavior of Halogens as Hydrogen Bond Acceptors

Syntheses, crystal structures and electronic properties of a series of copper(II) complexes with 3,5-halogen-substituted Schiff base ligands and their solutions

Raman spectroscopy is less commonly used than infrared absorption spectroscopy for the vibrational characterization of inorganic compounds, but its applications have significantly increased over the past decade due to high-performance instrumentation. This Comment describes the use of Raman spectroscopy for the characterization of inorganic compounds. We illustrate the application of Raman techniques with the spectra of a series of classic transition metal complexes recorded at variable temperature and pressure. Illustrative examples include [Ni(NH3)6]X2 compounds (X˭Cl− or [NO3]−), thermochromic square-planar or tetrahedral [CuCl4]2− complexes, the cis and trans [Cu(glycinato)2] · H2O complexes, square-planar [Pt(dithiocarbamate)2] and [Pd(dithiocarbamate)2] complexes, as well as metal-oxo and trans-dioxo complexes of metals with the d2 electron configuration, such as molybdenum(IV), rhenium(V), and osmium(VI). The variation of the symmetric metal-ligand stretching frequencies with temperature or pressur...

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Raman spectroscopy of transition metal complexes: molecular vibrational frequencies, phase transitions, isomers, and electronic structure

Synthesis and crystal structures of the flexible Schiff base complex bis(N-1,2-diphenylethyl-salicydenaminato-κ2N,O)copper(II) (methanol): A rare case of solvent-induced distortion

The structural flexibility of hybrid perovskite materials allows for phase transition and consequently thermochromic properties Here we investigate the thermochromic performance in a series of copper-based layered perovskites with organic cations having different alky chain lengths Their transition temperature is found to be dependent on the organic cations due to molecular motion and hydrogen bond interaction, providing possibilities to prepare thermochromic semiconductors near room temperature for smart window applications

Lead-free thermochromic perovskites with tunable transition temperatures for smart window applications

The tetrachlorocuprate(II) ion can crystallize in two different structures with the piperazinium dication (pipzH(2)). Both structures contain discrete CuCl42- species. A yellow compound (pipzH(2))[CuCl4]. 2H(2)O (1) is monoclinic (C2/c, Z = 4, a = 10.538(3) Angstrom, b = 7.4312(5) Angstrom, c = 17.281(4) Angstrom, beta = 111.900(10)degrees) and contains the CuCl42- ion as a distorted tetrahedron. A green compound (pipzH(2))(2)[CuCl4]. Cl-2. 3H(2)O (2) is triclinic (P (1) over bar, Z = 2, a = 9.264(3) Angstrom, b = 10.447(2) Angstrom, c = 11.366(2) Angstrom, alpha = 68.38 degrees, beta = 82.86(2)degrees, gamma = 83.05(2)degrees) and contains the CuCl42- ion with a square planar geometry. This latter compound shows thermo/photochromism, changing from green to yellow upon heating or laser irradiation.

Debora Neill

Papers

Thermochromism and Structure of Piperazinium Tetrachlorocuprate(II) Complexes.