Borschevsky, A.

Ilias, M.

Pershina, V.

GSI Repository

Electronic Structure, Properties and Volatility of Chlorides and Oxychloridesof Group-4 Elements Zr, Hf, and Element 104, RfV. Pershina1, A. Borschevsky2, and M. Iliasˇ31GSI, Darmstadt, Germany; 2HIM, Mainz, Germany; 3Department of Chemistry, Faculty of Natural Sciences, MatejBel University, Tajovske´ho 40, SK-974 00 Banska´ Bystrica, SlovakiaVolatility of halides, oxyhalides and oxides of elementsat the beginning of the 6d-series, i.e., of Rf through Hshas been studied using gas-phase separation techniques [1].While the understanding of nature of molecule-surface in-teractions has been gained in group 6 through 8, such anunderstanding in group 4 and 5 has never been achieved.Neither have the experimentally observed trends in volatil-ity of the halides, Zr < Hf > Rf and Nb < Ta > Db, beenexplained.Recently, we have studied volatility of the group-5 bro-mides, MBr5 (M = Nb, Ta, and Db), on the basis of calcu-lated molecular properties and a model of dispersion inter-action [2]. We have shown that the properties of these com-pounds change smoothly in the group, so that the volatilityshould also change smoothly. In this work, we undertakea similar study for the group-4 chlorides. With this aimin view, we have calculated the electronic structures andproperties of MCl4 (M = Zr, Hf, and Rf).The calculations were performed with the use of the2-component relativistic X2C DFT method implementedin the DIRAC12 program package [3]. The uncontractedtriple-zeta relativistic basis sets of Dyall were used [4]. Theobtained results, for the B88/P86 exchange-correlation po-tential (Table 1), show an increase in the bond lengths and adecrease in the ionizations potentials in the group, thoughthe polarizabilities show a “zig-zag” behaviour. The lat-ter are much reduced by relativity, with the effect increas-ing with Z. Using these properties and a model of disper-sion interaction [5], adsorption enthalpies,−ΔHads, of thechlorides on a quartz surface were determined (Table 1).Table 1: Equilibrium bond lengths, Re (in A˚), dissociationenergies, De (in eV, from Ref. [6]), ionization potentials,IP (in eV), polarizabilities, α (in a.u.), and adsorption en-thalpies, ΔHads (in kJ/mol), of MCl4 (M = Zr, Hf, and Rf)on quartzRe De IP α ΔHadsZrCl4 2.336 20.34 11.00 103.6 106.5HfCl4 2.316 20.80 11.00 99.3 103.0RfCl4 2.370 19.40 10.96 101.2 102.7The obtained −ΔHads are indicative of the followingtrend in the adsorption strength: Zr > Hf > Rf. Usinga correlation of −ΔHads with the sublimation enthalpies,ΔHsub of 104.2 kJ/mol was predicted for RfCl4. Thus,according to the calculations, RfCl4 should be the mostvolatile compound in its group, in agreement with previousTable 2: Equilibrium bond lengths, Re (in A˚), dissociationenergies, De (in eV), ionization potentials, IP (in eV), anddipole moments, μ (in D), of MOCl2 (M = Zr, Hf, and Rf)Re(M-Cl) Re(M=O) De IP μZrOCl2 2.386 1.741 21.76 10.76 3.67HfOCl2 2.352 1.753 21.01 10.63 4.33RfOCl2 2.385 1.822 19.40 10.35 5.20predictions [7]. The obtained trend is, however, in contra-diction with the experimental observations [1].To check the possible (at the presence of oxygen in thechromatography column) formation of the oxychlorides, aswell as their volatility, we have also performed the elec-tronic structure calculations for MOCl2 (M = Zr, Hf, andRf). The obtained total energy differences between MOCl2and MCl4 are indicative of the following trend in the oxy-chloride formation: Zr > Hf > Rf. This means that theassumed earlier preference of Hf to form the oxychlorideshould not take place. The other properties of interest aresummarized in Table 2. The MOCl2 are shown to be sta-ble as a bent structure, though the difference in the totalenergy with respect to the flat one is very small. The Rfcompound should be less stable than those of Zr and Hf,similarly to MCl4. The central atom - ligand separation in-creases from Hf to Rf, which also leads to an increase inthe dipole moments. Such an increase in μ should result ina decrease in the volatility of MOCl2 with Z as adsorptionon a quartz surface due an increase in the dipole moment- surface charge interactions. Thus, volatility of the oxy-chlorides should change as Zr < Hf < Rf. This trend is,however, also in disagreement with the experimental obser-vations [1]. Thus, the experimentally determined reversedtrend in group 4 cannot find its theoretical explanation; nei-ther can the one in group 5 be interpreted.References[1] A. Tu¨rler and V. Pershina, Chem. Rev. 113, 1237 (2013)[2] V. Pershina and J. Anton, J. Chem. Phys. 136, 034308 (2012)[3] DIRAC12 program package (http://diracprogram.org/)[4] K. G. Dyall, Theor. Chem. Acc. 129, 603 (2011)[5] V. Pershina and T. Bastug, Chem. Phys. 311, 139 (2005)[6] J. Anton et al., Chem. Phys. Lett. 380, 95 (2003)[7] V. Pershina and B. Fricke, In: Heavy Elements and RelatedNew Phenomena, W. Greiner and R. K. Gupta, Eds., WorldScientific, Singapore, 1999, Vol. 1, p. 194.NUSTAR-SHE-08 GSI SCIENTIFIC REPORT 2013132 doi:10.15120/GR-2014-1-NUSTAR-SHE-08

Electronic Structure, Properties and Volatility of Chlorides and Oxychlorides of Group-4 Elements Zr, Hf, and Element 104, Rf

http://repository.gsi.de/record/67847/files/NUSTAR-SHE-08.pdf

Electronic Structure, Properties and Volatility of Chlorides and Oxychlorides of Group-4 Elements Zr, Hf, and Element 104, Rf

Abstract

Similar works

Full text

Available Versions

GSI Repository