Properties and Reactivity of Hydroxides of Group 13 Elements In, Tl

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Properties and Reactivity of Hydroxides of Group 13 Elements In, Tl, and Nh from Molecular and Periodic DFT Calculations Valeria Pershina* GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, D-64291 Darmstadt, Germany

Miroslav Iliaš†,‡,§ Downloaded via GUILFORD COLG on July 17, 2019 at 19:33:29 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

†

Helmholtz-Institut Mainz, Johannes Gutenberg-Universität, 55099 Mainz, Germany GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, D-64291 Darmstadt, Germany § Department of Chemistry, Faculty of Natural Sciences, Matej Bel University, Tajovského 40, 97401 Banská Bystrica, Slovakia ‡

ABSTRACT: Adsorption energies, Eads, of gaseous hydroxides of In, Tl, and the superheavy element Nh on surfaces of Teflon and gold are predicted using molecular and periodic relativistic DFT calculations. The ambition of the work is to assist related “one atom at a time” gas-phase chromatography experiments on the volatility of NhOH. The obtained low values of Eads(MOH), where M = In, Tl, Nh, on Teflon should guarantee easy transportation of the molecules through the Teflon capillaries from the accelerator to the chemistry setup. Straightforward band-structure DFT calculations using the revPBE-D3(BJ) functional have given an Eads(MOH) value of 161.4 kJ/mol on the Au(111) surface, being indicative of significant molecule−surface interaction. The MOH− gold surface binding is shown to take place via the oxygen atom of the hydroxide, with the oxygen−gold charge density transfer increasing from InOH to NhOH. The trend in Eads(MOH) is shown to be InOH < TlOH < NhOH, caused by increasing molecular dipole moments and decreasing stability of the hydroxides in this row. A trend in Eads of the atoms of these elements on gold is, however, opposite, In > Tl > Nh, caused by the increasing relativistic contraction and stabilization of the np1/2 AO with Z. These opposite trends in Eads(MOH) and Eads(M) in group 13 lead to almost equal Eads(Nh) and Eads(NhOH) values, making identification of Nh, as a type of species, difficult by measuring its adsorption enthalpy on gold.

1. INTRODUCTION Investigations of chemical properties of new man-made superheavy elements (SHEs) is an exciting and challenging area of physicochemical science.1,2 SHEs whose properties are now in the focus of the experimental studies are 112 (Cn), 113 (Nh) and 114 (Fl),3−9 having sufficiently long-lived isotopes.10 A special interest in the chemistry of these elements is explained by the expectation of unusual behavior caused by strong relativistic effects on their valence electron shells: due to the relativistic stabilization and contraction of the 7s and 7p1/2 AOs, the reactivity of these elements is expected to be significantly reduced with respect to that of their lighter homologues Hg, Tl, and Pb, respectively. However, if Cn with a closed-shell ground state (6d107s2) and Fl with a quasiclosed-shell ground state (7s27p1/22) were believed to be noblegas-like elements,11 Nh, having one unpaired electron (7s27p1/2), was expected to be quite reactive.12 Experimentally, the reactivity or volatility of SHEs is studied as an adsorption process on the surface of some materials using special gas−solid chromatography techniques.13−15 According to those techniques, the adsorption temperature, Tads, of the © XXXX American Chemical Society

species on the surface of a chromatography column, made out of quartz or supplied with gold-plated detectors, is measured. (The column is either kept at a fixed temperature or has a negative temperature gradient from room one to that much below zero, ∼−180 °C.) The adsorption enthalpy, ΔHads, is deduced from this Tads value using adsorption models and Monte Carlo simulations.13 The Tads and ΔHads values of SHEs are then compared to the related quantities of their lighter homologues in the chemical groups and with those of Rn, a noble gas. Using these techniques, the volatility or reactivity of Cn and Fl has meanwhile been investigated. These elements were shown to indeed be very volatile but still more reactive than noble gases.3−7 Experiments on volatility of Nh are on the way.8,9 Isotopes 284,285Nh are α-decay products of 288,289Mc produced in a nuclear reaction of the 48Ca beam with the 243 Am target.10 The 284Nh has a half-life of about 1 s. Feasibility experiments on the volatility of its nearest Received: April 1, 2019

A

DOI: 10.1021/acs.inorgchem.9b00949 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

The method of calculations is described in section 2, while results and their discussion are in section 3. Conclusions are given in section 4.

homologue Tl have meanwhile been performed using a quartz chromatography column with and without gold foils.16 It was shown that, in a He/H2 carrier gas mixture, Tl strongly interacts with the gold surface at Tads = 747 ± 16 °C, giving ΔHads = −270 ± 10 kJ/mol. In a pure oxygen flow, presumably volatile TlOH is formed, even over the gold surface. ΔHads(TlOH) = −146 ± 3 kJ/mol, which is much smaller than the corresponding ΔHads(Tl) on gold. The first experiments on the volatility of Nh were reported with the use of isothermal gas-phase chromatography.8 Five decay chains, characteristic of 284Nh, were registered on gold detectors of the chromatography column kept at room temperature. The adsorption behavior of Nh was found to be comparable to that of Hg and At. −ΔHads > 60 kJ/mol was determined as a lower limit.8 The chemical form of Nh could, however, not be established: it was not clear if Nh was in the atomic state or in the form of the hydroxide, by analogy with Tl, because humidity could not be excluded in the setup. In another gas-phase chromatography experiment, no decay chains of Nh were, however, observed after a chemical preseparation that should have excluded formation of NhOH.9 Traditionally, our work has been aiming at predictions of chemical properties and behavior of SHEs, lately in gas-phase chromatography experiments.2,17 For Nh, the probability of its delivery from the target chamber to the chemistry setup through Teflon capillaries was estimated using an atom-slab adsorption model and Dirac−Coulomb (DC) calculations of atomic properties.12 Bonding of Tl and Nh with gold was also studied by us with the help of relativistic DFT calculations for their gold-containing dimers.18−20 Furthermore, the adsorption energy, Eads, of Nh on the Au(111) surface was calculated using the periodic Amsterdam Modeling Suite BAND21 and DFT cluster approaches.22,23 Eads of Tl and Nh on a hydroxylated quartz surface has also been determined using the BAND program. 24 In all of the systems under consideration, Nh was found to be chemically less reactive than Tl, however, to form a significantly strong bond with Au and silicon oxide due to the involvement of both the 7p1/2 and 7p3/2 AOs. Electronic structures and properties of MOH (M = Tl, Nh) were predicted by us using the 4c-DFT and 2c-DFT approaches.19,20 It was found that the M−OH bond strength decreases from Tl to Nh, while dipole moments (μ) and polarizabilities (α) of MOH increase in this direction. Such an increase in α and μ of MOH is due to the enlargement of molecular size, caused by relativistic and orbital expansion of the np3/2 AOs taking part in the chemical bond formation in addition to the np1/2 AOs. It was, therefore, concluded that Eads(MOH) should also increase from Tl to Nh due to the increasing molecular dipole−surface interaction.20 There are some works of other authors on relativistic calculations for hydrides and halides of Nh, whose overview can be found in ref 2. As a continuation of the study on the volatility of group 13 species, in this work, we predict Eads of the MOH (M = In, Tl, Nh) molecules on surfaces of Teflon and gold. Accordingly, calculations of molecular properties and straightforward relativistic periodic calculations of Eads(MOH) on gold were performed. The probability of the safe transportation of the hydroxides through Teflon capillaries to the chemical setup was estimated using an adsorption model.

2. METHODS AND DETAILS OF THE CALCULATIONS Calculations of molecular properties of the MOH species (M = In, Tl, Nh) were performed with the Amsterdam Modeling Suite ADF25,26 using revPBE27 and revPBE-D3(BJ)28,29 functionals (only for In and Tl). The ADF method uses the zeroth-order regular approximation (ZORA) two-component (2c) Hamiltonian30,31 incorporating spin− orbital effects (SO ZORA).32 This method solves Kohn−Sham equations self-consistently. The accuracy of the ZORA approximation for the treatment of heavy elements was assessed in several earlier publications.32−35 The ADF package was utilized for geometry optimization,36 as well as for obtaining the static dipole polarizabilities (α),37,38 both average and anisotropic.39 Dipole moments were obtained as the expectation value over the Slater determinant. The basis sets were a combination of numerical atomic orbitals and Slatertype orbitals (STO). The TZ2P sets40 were found to be sufficiently good for the required accuracy. These ADF calculations were performed with all electrons. Calculations of Eads of MOH on gold were performed with the use of the Amsterdam Modeling Suite BAND.41,42 Several exchangecorrelation functionals were tested, namely PW91,43,44 PBE,45,46 revPBE,27 and the dispersion-corrected revPBE-D3(BJ),28,29 with ZORA30,31 and SO ZORA32 Hamiltonians. As the latter has not been developed for elements heavier than U, the dispersion corrections for the elements of the seventh row are taken as those for its lighter sixthrow homologue, as is foreseen in the method.42 The frozen core approximation was utilized with the smallest frozen core, as advised.42 This means that, for Nh, orbitals from 1s through 5d are frozen, while those from 6s through 5f are explicitly included in the calculations of integrals. The TZP40 sets were used for the computational efficiency of BAND. They give practically the same Eads values as the TZ2P40 sets (see below). (The accuracy of the calculations should, thus, be sufficient for reliable predictions of ΔHads, because experimental values are not very accurate due to low statistics of events and applied ideal models.) The real space integration parameter q, which governs the precision of the numerical integration, i.e., the relative precision 10−q in the integrals, was taken as 5. The k-space integration was carried out accurately using the quadratic tetrahedron method. The total number of unique k points was 5. Mulliken population analysis47 was used to investigate bonding between MOH (M = In, Tl, Nh) and the surface. The structure of the real gold surface used in the gas-phase experiments is unknown. To simulate the adsorption process, the Au(111) surface was chosen as the most probable: theoretical and experimental studies on the morphology of thin gold films came to the conclusion that this modification, coming from the fcc crystal lattice, is the most stable: i.e., it has the lowest energy.48,49 The adsorption process of single species was modeled by (4 × 4)MOH/Au(111) supercells (sc), which guarantee noninteraction between the adsorbed molecules. The gold slab consisted of four layers of Au atoms: i.e., 64 gold atoms in the unit supercell. The Au atoms of the lowest level were kept fixed in their positions obtained via the Au bulk geometry optimization (frozen), while all the Au atoms in the three upper layers, as well as all the atoms in the adsorbed MOH molecules, were relaxed. Several adsorption positions of the MOH molecules on the Au supercells were considered: “top” (with the M atom on the top of the upper surface Au atom), “bridge” (with M between the two upper Au atoms), “hollow 1” (with M on top of the gold atoms in the second layer), and “hollow 2” (on top of the gold atoms on the third layer) (see below). Geometry optimization was performed for all of the systems of interest at the scalar-relativistic (SR) level. The spin− orbit (SO) effects were taken into account as single-point calculations for the SR optimized structures. Both the non-spin-polarized and the spin-polarized noncollinear approaches were used. B


Article

Inorganic Chemistry According to the BAND methodology, the program gives the formation energy, Ef, of a system with respect to isolated atoms. The adsorption energy, Eads, was calculated using the equation

through Teflon capillaries from the target chamber to the chemistry setup. (Straightforward DFT calculations fail for such weak interactions.) For that purpose, the following equation for Eads coming from a model of molecule−slab longrange interactions51 was used

Eads(MOH−Au/sc) = −[Ef (MOH−Au/sc) − Ef (MOH) − Ef (sc)]

(1)

3 (ε − 1) 16 (ε + 2)

αmol

As required, Ef(MOH) and other properties of the MOH molecules were calculated using the periodic BAND approach within the SR and SO approximations.

Eads(d) = −

3. RESULTS AND DISCUSSION 3.1. Gold Bulk. Before calculating Eads(MOH) on gold, computations of the cohesive energy, Ecoh, of bulk gold were performed using (typical for gold) PW91 and revPBE-D3(BJ) exchange-correlation functionals. (As was established earlier, revPBE underestimates the Ecoh value of gold.21) Results of the calculations show that the revPBE-D3(BJ) functional gives the best Ecoh(Au) value and the lattice parameter (a) of the fcc gold bulk (Table 1). One can see that the use of the TZP and

−

where ε = 2.04 is a dielectric constant of Teflon, α and μ are parameters of the molecule, and d is the molecule−surface separation (Figure 1). According to the model of mobile adsorption, −ΔHads = Eads(d) + 0.5RT.13

Table 1. Calculated Lattice Parameter, a (in Å), and Cohesive Energy, Ecoh (in eV/atom), of Bulk fcc Gold for Different Functionals and Basis Sets in the SR + SO Approximation, as Well as Experimental Values

Figure 1. MOH molecule adsorbed on an inert surface by long-range forces.

PW91

a

TZP

TZ2P

TZP

TZ2P

exptl

a Ecoh

4.168 3.09

4.157 3.16

4.081 3.886

4.077 3.88

4.065 3.81

1 IPmol

+

1 IPsurf

)d

3

2 1 (ε − 1) μmol 8 (ε + 2) d3

(2)

The main difficulty in estimating Eads via eq 2 comes from the fact that the MOH molecules are highly asymmetric and their orientation with respect to the surface is unknown. We can, therefore, try to give only estimates of Eads on the basis of some assumptions, for which purpose, x, y, and z components of μ and diagonal tensor components of α have been calculated (Table 3).

revPBE-D3(BJ)

property

(

a

Reference 50.

TZ2P basis sets gives very close values of Ecoh(Au), so that they should give very similar Eads values, as was tested by earlier calculations for other systems.21 Therefore, for efficiency of the calculations for large (4 × 4)MOH/Au(111) supercells within the required accuracy (see above), the TZP basis sets were found to be sufficiently good and more economical. 3.2. Properties of the MOH (M = In, Tl, Nh) Molecules and Estimates of Their Transportation to the Chemistry Setup. Properties of the gaseous MOH (M = In, Tl, Nh) molecules, calculated with the use of both revPBE (in order to be in line with the previous calculations20) and revPBE-D3(BJ) functionals are given in Table 2. One can see that the dispersion corrections to the revPBE functional for InOH and TlOH have practically no influence on the molecular properties, so that the revPBE data for NhOH can safely be used for estimates of its volatility. The μ and anisotropies of α increase from the In to Nh hydroxide with increasing molecular size. Using the data of Table 2, we have tried to estimate the probability of the transportation of the MOH molecules

Table 3. Components of Polarizabilities, α (in au), and of Dipole Moments, μ (in D), Estimated Molecule−Surface Separations, d(MOH-surf.) (in Å), and Related Adsorption Energies, Eads (in kJ/mol), of the MOH (M = In, Tl, Nh) Molecules on the Surface of Teflon α

μ

molecule

xx

yy

zz

x

y

z

d(mol− surf)

Eads

InOH TlOH NhOH

49.3 43.9 42.5

54.2 50.4 49.6

43.3 34.2 29.3

2.07 2.64 2.86

0.46 1.04 1.31

0 0 0

2.501 2.790 2.935

25 16 14

Thus, e.g., for the most probable orientation of the molecule, such as that shown in Figure 1, the influence of μ (0 in the z direction) is minimal, so that α(MOH) decreasing with Z in the group should mainly define the trend. For reasonable (as a lower limit) values of x between 2 and 3 Å, Eads(MOH) values between 15 and 25 kJ/mol are obtained via eq 2 (Table 3),

Table 2. Calculated ADF Properties of the MOH (M = In, Tl, Nh) Molecules: Equilibrium Bond Lengths, Re (Å), M−OH Dissociation Energies, De (in eV), ∠M−O−H angles (in deg), Vibrational Frequencies, ωe (in cm−1), Dipole Moments, μ (in D), Average and Anisotropic Polarizabilities, α (in au), and the First Ionization Potentials, IP (in eV) molecule

functional

Re(M−O)

Re(O−H)

∠ MOH

De

μ

IP

αav

αanis

InOH

revPBE revPBE-D3(BJ) revPBE revPBE-D3(BJ) revPBE

2.064 2.065 2.174 2.174 2.304

0.973 0.973 0.974 0.974 0.977

120.4 120.3 116.2 115.9 106.6

4.041 4.109 3.272 3.337 2.047

2.130 2.133 2.839 2.840 3.148

8.885

48.91 48.91 42.84 42.84 40.47

43.31 43.40 123.37 123.29 219.69

TlOH NhOH

C

9.009 9.158


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Inorganic Chemistry

Figure 2. A (4 × 4)MOH/Au(111) supercell simulating adsorption of MOH on the Au(111) surface in the “hollow 2” position of M: top and side views.

Figure 3. A (4 × 4)MOH/Au(111) supercell simulating adsorption of MOH on the Au(111) surface in the “bridge” position of M: top and side views.

Figure 4. A (4 × 4)MOH/Au(111) supercell simulating adsorption of M on the Au(111) surface in the “top” position on M: top and side views.

only positive Eads values were obtained using the revPBED3(BJ) functional, which shows that the use of the dispersioncorrected term is very important for adsorption of neutral molecules on surfaces such as gold. The calculated molecule− surface separation distances and Ef values using this functional for the (4 × 4)TlOH/Au(111) system in various adsorption positions of the TlOH molecule on the Au(111) supercell are given in Table 4. The obtained geometries of MOH on the gold surface show that in all of the cases (i.e., for all of the different initial adsorption positions, Figures 2−4) the final positions of the adsorbed TlOH are far from the original ones. The molecule is moved away from the surface and becomes pointed to it by the oxygen atom, while the Tl−Au/sc distance is the longest. The atoms of the upper gold layer are also shifted from their original positions toward the molecule and rearranged. The obtained Eads(TlOH) of 146.6 kJ/mol (see below) is in excellent agreement with the experimental value of 146 ± 3 kJ/ mol,16 and it is independent of the final adsorption position.

which means that for such molecule−surface separations the molecules should be well transported through the capillaries at room temperature. Eads(NhOH) should be smaller than Eads(TlOH) due to the larger molecular size of the Nh hydroxide (Table 3). This means that if TlOH is observed experimentally in the chromatography column after the transportation, NhOH should also be registered there, provided it is synthesized. 3.3. Adsorption of the MOH (M = In, Tl, Nh) Molecules on the Au(111) Surface. As was mentioned above, adsorption of the MOH molecules on the Au(111) surface at zero coverage was modeled by the (4 × 4)MOH/ Au(111) supercells. To test the sensitivity of Eads with respect to the adsorption position of MOH, we considered several typical positions of M of the molecule above the gold atoms, as described above (see section 2). The initial “top”, “bridge”, and “hollow 2” positions of M are shown in Figures 2−4. Out of the considered exchange-correlation functionals, both revPBE and PW91 did not give molecule−surface binding. The D


Article

Inorganic Chemistry Table 4. Calculated SR Parameters of the TlOH Molecule Adsorbed on the Au(111) Surface: z Coordinates of the M and O Atoms and of the Upper Au Surface Atom (in Å), the M−Surface Distance, dz(Tl−Au) (in Å), and the formation energies, Ef (in eV), of the (4 × 4)TlOH/Au(111) Supercells in Various Adsorption Positions of TlOH param

“hollow 1”

“hollow 2”

bridge

top

z(Tl) z(O) z(H) z(Au)a dz(Tl−Au) Ef

3.190 2.415 2.647 0.119 3.075 −233.34

3.207 2.426 2.734 0.123 3.087 −233.31

3.019 2.505 2.669 0.229 2.790 −233.37

3.195 2.490 2.929 0.107 3.088 −233.33

Figure 5. A unit cell, showing a final adsorption position of the NhOH molecule on the Au(111) surface.

a

The initial (x, y, z) coordinates of the top Au atom are (0, 0, 0).

Therefore, further calculations of Eads of all the species of interest were performed using the revPBE-D3(BJ) functional. The obtained resultsoptimized molecule−surface geometries and Ef(MOH) and Eads(MOH), where M = In, Tl, Nhare summarized in Table 5. The final adsorption position of the NhOH molecule on the Au(111) surface in the 3D representation is also shown in Figure 5.

Au(111)/sc separation is shorter than the M−Au(111)/sc and H−Au(111)/sc separtions, while the M−Au(111)/sc distance is the longest (Figure 5), altogether indicating that the interaction takes place via the oxygen atom of MOH. (This also means that the orientation of the molecules toward the surface, as shown in Figure 1, is realistic.) The surface Au atoms are also rearranged and moved toward the molecule (Table 5). Overall, the MOH−gold surface separation slightly increases from the In to the Nh species. The MOH−Au/sc formation energies are very similar for the In, Tl, and Nh systems, at both the SR and SO levels. Eads(MOH) values, both SR and SO, however, decrease from InOH to NhOH. The reason for that is decreasing Ef(MOH) in the row In−Tl−Nh, being in line with decreasing De(M− OH) in this direction (Table 2). The increasing Eads(MOH) from In to Nh is also related to the increasing molecular dipole moments in this row (Table 2), confirming the preliminary conclusions made on the basis of molecular calculations.20 The SO effects, being of no importance for Eads of InOH and TlOH, only slightly decrease Eads(NhOH). To analyze the molecule−surface bonding, Mulliken effective charges47 for the free and adsorbed MOH (M = In, Tl, Nh) molecules were calculated (Table 6). One can see that QM and QH in the free and adsorbed state of MOH are almost equal, while the negative QO decreases when the molecule is deposited on the surface, being indicative of the charge transfer from the oxygen atom of MOH to the nearest Au atoms of the surface. As a result, the MOH molecules on the surface are no longer neutral but positively charged (Table 6). The total molecular charge increases from InOH to NhOH due to the increasing oxygen−gold charge density transfer and, therefore, increasing bonding in this direction. Obtained Eads values of the MOH (M = In, Tl, Nh) molecules on gold are summarized in Table 7 and shown in Figure 6, together with Eads values of atoms of these elements.21 Experimental ΔHads values of group Tl and TlOH are also shown there for comparison.16 (The experimental ΔHads obtained from the measured Tads on the surface of aunknown structure should be used for comparison with the theoretically considered ideal cases, of course, with caution. However, if experimental ΔHads values for the lighter homologues of the SHEs are reproduced by the calculations, predicted ΔHads of the heaviest species should be rather reliable, provided experiments are conducted under the same conditions.)

Table 5. BAND Calculated Parameters of the MOH (M = In, Tl and Nh) Molecules: Bond Lengths in the Free Molecules and Those in the Adsorbed Ones on the Surface, Re (Å), z coordinates of M, O, and H (in Å), Formation Energies, Ef (in eV), of the (4 × 4)MOH/Au(111) Supercells, and Adsorption Energies, Eads (in eV) on the Au(111) Surfacea system free molecule

molecule− Au(111)sc

param

InOH

TlOH

NhOH

Re(M−O) Re(O−H) ∠(M−O−H) Ef(SR) Ef(SO) Re(M−O)

2.092 0.974 120 −11.98 −11.97 2.23

2.201 0.975 115 −11.63 −11.65 2.449

2.354 0.975 106 −11.37 −11.59 2.708

Re(O−H) ∠(M−O−H) z(M) z(O) z(H) z(Au) Ef(mol−Au/sc) (SR) Ef(mol−Au/sc) (SO) Eads(SR) Eads(SO)

0.980 122 2.701 2.500 2.766 0.200 −233.61 −243.72 −1.44 −1.45

0.978 113 3.019 2.505 2.670 0.229 −233.37 −243.47 −1.54 −1.52

0.977 111 3.327 2.454 2.635 0.237 −233.45 −239.85 −1.89 −1.67

For the (4 × 4)Au(111) supercell: Ef(SR) = −220.198 eV; Ef(SO) = −230.298 eV.

a

As a result of the geometry optimization, all of the atoms of the molecules are shifted away from their original positions. Thus, e.g., for NhOH, original (x, y, z) coordinates (in Å) are Nh (1.41, 0.83, 2.00), O (−0.58, −0.33, 2.00), and H (−1.26, −1.02, 2.00), while the final coordinates are Nh (2.10, 0.42, 3.33), O (−0.44, 0.25, 2.45) and H (−0.88, −0.61, 2.64) (Table 5). Thus, all of the molecules undergo quite a distortion upon adsorption: the M−OH (M = In, Tl, Nh) bond gets significantly longer, and the O−H bond slightly increases. Also, the M−O−H angle changes. The O− E


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Inorganic Chemistry

Table 6. Mulliken Effective Charges of the Free and Adsorbed MOH (M = In, Tl, Nh) Molecules on the Au(111) Surface system

charge

InOH

TlOH

NhOH

free molecule

QM,O,H Qmol QM,O,H Qmol

In0.54O−0.78H0.24 0 In0.48O−0.66H0.21 0.03

Tl0.51O−0.72H0.21 0 Tl0.53O−0.67H0.21 0.07

Nh0.59O−0.81H0.21 0 Nh0.60O−0.67H0.18 0.11

adsorbed molecule

Table 7. Summary of the Predicted Adsorption Energies, Eads (in kJ/mol), of M and MOH (M = In, Tl, Nh) on Teflon and Gold, along with Experimental −ΔHadsa species

theor/exptl

method

surface

M

theor

DC/model ADF BAND

MOH

exptl theor

chromatogr ADF/model ADF BAND chromatogr

Teflon gold gold gold Teflon gold gold

exptl

In 22

∼24 139.9

Tl

Nh

ref.

20 213b/255c 256d 270 ± 10 ∼16 146.6 146 ± 3

14 119b 146d (168 ± 8)e ∼14 161.4 (161)e

12 21 21 16 this work this work 16

Estimates of the experimental values are given in parentheses. bPW91, in a “hollow 2” position on the regular Au(111) surface. crevPBE-D3(BJ), in a “hollow 2” position on the regular Au(111) surface. dPW91, on the Au(111) surface in a vacancy. eEstimated by taking into account the difference between the calculated and experimental values for the Tl systems. (According to the model of mobile adsorption, the difference between −ΔHads and Eads at room temperature is 2 kJ/mol, see above.) a

in the energy of the np1/2 AO, which is very much pronounced with Z. The trend in Eads(MOH) is caused by the decreasing stability and increasing dipole moments of the molecules, caused by the destabilization and expansion of the np3/2 AO (which is both orbital and indirect relativistic effects) and is, therefore, opposite and less pronounced. These different trends lead to almost equal Eads(Nh) and Eads(NhOH) values, which will make specification of Nh difficult in measuring its adsorption properties. (Anyhow, as they have such high ΔHads values, Nh or NhOH should be registered right at the beginning of the chromatography column at room temperature, independently of its chemical form.) This case is a clear demonstration of opposite actions of relativistic and orbital effects on the adsorption properties of group 13 elements and their compounds.

4. CONCLUSIONS The adsorption properties of the gaseous hydroxides of In and Tl and the superheavy element Nh on the surfaces of Teflon and gold (111) are predicted on the basis of relativistic molecular and periodic DFT calculations. Estimated Eads values of the MOH (M = In, Tl, Nh) molecules on Teflon using molecular ADF calculations and an adsorption model show that these species should be easily transported through the capillaries to the chemistry setup. Straightforward calculations of Eads values of the MOH molecules on the Au(111) surface using the BAND suite are indicative of the relatively strong interaction of the hydroxides with gold. This was obtained using the revPBE-D3(BJ) functional, while revPBE, PW91, etc. did not give binding. The calculated Eads(MOH) values were shown to be practically independent of the adsorption position of the molecule. Excellent agreement between the calculated and measured Eads values is achieved for TlOH, giving credit to the predicted Eads(NhOH) value of 161.4 kJ/mol. The trend in Eads(MOH) was shown to be InOH < TlOH < NhOH, caused by the decreasing stability of the molecular species in this row, increasing dipole moments, and, as a result, increasing charge density transfer from O of MOH to the Au atoms of the surface. The trend in the adsorption energies of the group 13

Figure 6. Adsorption enthalpies of atoms M = Tl, Nh on the Au(111) surface: calculated in a “hollow 2” position (crosses and a long dashed line), in a vacancy (tilted crosses and dashed-dotted line),21 and experimental values (dashed line; the filled circle is the experimental value for Tl and the open circle is an estimated value for Nh), and of MOH (M = In, Tl, Nh) present calculations (stars and solid line) and experimental value for TlOH (filled square).

Thus, low values of Eads of M and MOH (M = In, Tl, Nh) on the surface of Teflon should guarantee their transportation through the capillaries. However, for the open-shell atoms, this will very probably not take place, because they will react with any impurity in the setup that cannot be excluded. For adsorption on gold, Eads(TlOH) is much smaller than Eads(Tl), and excellent agreement between the calculated and experimental values for the former gives credit to the present Eads(NhOH) value of 161.4 kJ/mol, which is somewhat larger than Eads(MOH), where M = In, Tl. The most interesting finding is a different trend in Eads(MOH) in group 13 than in Eads(M). The trend in Eads(M), a decrease in the row In > Tl > Nh, is caused by the relativistic stabilization and contraction of the np1/2 AO with Z in the group, leading to its smaller participation in the M−Au bonding.21 The trend in Eads(M) follows, therefore, the trend F


Article

Inorganic Chemistry

element flerovium (element 114) is a volatile metal. Inorg. Chem. 2014, 53, 1624−1629. (6) Yakushev, A.; Eichler, R. Gas-phase chemistry of element 114, flerovium. EPJ Web Conf. 2016, 131, No. 07003. (7) Türler, A.; Eichler, R.; Yakushev, A. Chemical studies of elements with Z⩾ 104 in gas phase. Nucl. Phys. A 2015, 944, 640− 689. (8) Dmitriev, S. N.; Aksenov, N. V.; Albin, Y. V.; Bozhikov, G. A.; Chelnokov, M. L.; Chepygin, V. I.; Eichler, R.; Isaev, A. V.; Katrasev, D. E.; Lebedev, V. Y.; Malyshev, O. N.; Petrushkin, O. V.; Porobanuk, L. S.; Ryabinin, M. A.; Sabel’nikov, A. V.; Sokol, E. A.; Svirikhin, A. V.; Starodub, G. Y.; Usoltsev, I.; Vostokin, G. K.; Yeremin, A. V. Pioneering experiments on the chemical properties of element 113. Mendeleev Commun. 2014, 24, 253−256. (9) Aksenov, N. V.; Steinegger, P.; Abdullin, F. S.; Albin, Y. V.; Bozhikov, G. A.; Chepigin, V. I.; Eichler, R.; Lebedev, V. Y.; Madumarov, A. S.; Malyshev, O. N.; Petrushkin, O. V.; Polyakov, A. N.; Popov, Y. A.; Sabel’nikov, A. V.; Sagaidak, R. N.; Shirokovsky, I. V.; Shumeiko, M. V.; Starodub, G. Y.; Tsyganov, Y. S.; Utyonkov, V. K.; Voinov, A. A.; Vostokin, G. K.; Yeremin, A. V.; Dmitriev, S. N. On the volatility of nihonium (Nh, Z = 113). Eur. Phys. J. A 2017, 53, 158. (10) Oganessian, Y. T.; Utyonkov, V. K. Superheavy nuclei from 48Ca-induced reactions. Nucl. Phys. A 2015, 944, 62−98. (11) Pitzer, K. S. Are elements 112, 114, and 118 relatively inert gases? J. Chem. Phys. 1975, 63, 1032−1033. (12) Pershina, V.; Borschevsky, A.; Eliav, E.; Kaldor, U. Atomic properties of element 113 and its adsorption on inert surfaces from ab initio Dirac-Coulomb calculations. J. Phys. Chem. A 2008, 112, 13712−13716. (13) Zvára, I. The Inorganic Radiochemistry of Heavy Elements: Methods for Studying Gaseous Compounds; Springer: 2008. (14) Türler, A.; Gregorich, K. E., In The Chemistry of Superheavy Elements, 2nd ed.; Schädel, M., Shaughnessy, D., Eds.; SpringerVerlag: Berlin, Heidelberg, 2014; pp 261−308. (15) Gäggeler, H. W.; Türler, A., In The Chemistry of Superheavy Elements, 2nd ed.; Schädel, M., Shaughnessy, D., Eds.; SpringerVerlag: Berlin, Heidelberg, 2014; pp 415−483. (16) Serov, A.; Eichler, R.; Dressler, R.; Piguet, D.; Türler, A.; Vögele, A.; Wittwer, D.; Gäggeler, H. W. Adsorption interaction of carrier-free thallium species with gold and quartz surfaces. Radiochim. Acta 2013, 101, 421−425. (17) Pershina, V. Electronic structure and properties of superheavy elements. Nucl. Phys. A 2015, 944, 578−613. (18) Pershina, V.; Borschevsky, A.; Anton, J.; Jacob, T. Theoretical predictions of trends in spectroscopic properties of homonuclear dimers and volatility of the 7p elements. J. Chem. Phys. 2010, 132, 194314. (19) Pershina, V.; Anton, J.; Jacob, T. Electronic structures and properties of MAu and MOH, where M = Tl and element 113. Chem. Phys. Lett. 2009, 480, 157−160. (20) Pershina, V.; Iliaš, M. Electronic structure and properties of MAu and MOH, where M = Tl and Nh: New data. Chem. Phys. Lett. 2018, 694, 107−111. (21) Pershina, V. Reactivity of Superheavy Elements Cn, Nh, and Fl and Their Lighter Homologues Hg, Tl, and Pb, Respectively, with a Gold Surface from Periodic DFT Calculations. Inorg. Chem. 2018, 57, 3948−3955. (22) Fox-Beyer, B. S.; van Wüllen, C. Theoretical modelling of the adsorption of thallium and element 113 atoms on gold using twocomponent density functional methods with effective core potentials. Chem. Phys. 2012, 395, 95−103. (23) Rusakov, A. A.; Demidov, Y. A.; Zaitsevskii, A. Estimating the adsorption energy of element 113 on a gold surface. Cent. Eur. J. Phys. 2013, 11, 1537−1540. (24) Pershina, V. A Theoretical Study on the Adsorption Behavior of Element 113 and Its Homologue Tl on a Quartz Surface: Relativistic Periodic DFT Calculations. J. Phys. Chem. C 2016, 120, 20232− 20238.

atoms on gold, caused by relativistic stabilization of the np1/2 AO in the group, is opposite, In > Tl > Nh, so that ΔHads(Nh) and ΔHads(NhOH) become very similar. This will make identification of Nh, as a type of species, difficult by its deposition on gold. This case is a nice demonstration of opposite actions of relativistic and orbital effects on adsorption properties of group 13 elements.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for V.P.: [email protected]. ORCID

Valeria Pershina: 0000-0002-7478-857X Miroslav Iliaš: 0000-0002-8038-6489 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are thankful to leading experimentalists in this area, A. Yakushev (GSI, Darmstadt), R. Eichler (PSI, Switzerland), and P. Steinegger (JINR, Dubna), for valuable discussions of the experimental results. M.I. thanks the HIM for financial support through the Visiting Scholar Agreement and the support of the Slovak Research and Development Agency and the Scientific Grant Agency, Nos. APVV-15-0105 and VEGA 1/0737/17, respectively. A part of the calculations was performed at the Computing Centre of the Slovak Academy of Sciences using the supercomputing infrastructure acquired in Project Nos. ITMS 26230120002 and 26210120002 (Slovak infrastructure for high-performance computing) supported by the Research and Development Operational Programme funded by the ERDF.

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REFERENCES

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H


Properties and Reactivity of Hydroxides of Group 13 Elements In, Tl

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