Abstract
The main goal of this study is the validation of relativistic Hirshfeld atom refinement (HAR) as implemented in Tonto for high-resolution X-ray diffraction datasets of an organo-gold(I) compound. The influence of the relativistic effects on statistical parameters, geometries and electron density properties was analyzed and compared with the influence of electron correlation and anharmonic atomic motions. Recent work in this field has indicated the importance of relativistic effects in the static electron density distribution of organo-mercury compounds. This study confirms that differences in electron density due to relativistic effects are also of significant magnitude for organo-gold compounds. Relativistic effects dominate not only the core region of the gold atom, but also influence the electron density in the valence and bonding region, which has measurable consequences for the HAR refinement model parameters. To study the effects of anharmonic motion on the electron density distribution, dynamic electron density difference maps were constructed. Unlike relativistic and electron correlation effects, the effects of anharmonic nuclear motion are mostly observed in the core area of the gold atom.
Highlights
After the famous Dirac statement (Dirac & Fowler, 1929) saying that relativistic effects are of ‘no importance in the consideration of atomic and molecular structure and ordinary chemical reactions’, it took nearly half a century to find and confirm important influences of relativistic effects on the electronic structure of compounds (Grant, 1970; Desclaux, 1973; Ziegler et al, 1981)
To Bucinskyet. al. (2016), rks_anh_rel Hirshfeld atom refinement (HAR) yielded better agreement statistics compared with non-relativistic HAR, which demonstrates that taking relativistic effects into account improves the reconstruction of electron density from the experiment (Tables 3 and S1–S3)
The quality of the models was significantly better for HAR than for IAM
Summary
After the famous Dirac statement (Dirac & Fowler, 1929) saying that relativistic effects are of ‘no importance in the consideration of atomic and molecular structure and ordinary chemical reactions’, it took nearly half a century to find and confirm important influences of relativistic effects on the electronic structure of compounds (Grant, 1970; Desclaux, 1973; Ziegler et al, 1981). The effect increases with Z2, where Z is the atomic number of the heavy element (Pyykko, 1988). It is rather small, but it can cause changes in the chemical behavior of elements within the same group (Desclaux & Pyykko, 1976). For heavy elements (with Z > 50) (Onoe, 2000) the magnitude of the relativistic effects becomes high enough to strongly influence the chemical and physical properties of crystals, which has been reported several times (Schwerdtfeger, 2002; Christensen & Seraphin, 1971; Pitzer, 1979). Well known examples include the yellow color of gold (Pyykko, 1988), the
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