Journal of Nuclear and Radiochemical Sciences,Vol. 3, No. 1, pp. 133–136, 2002

133

Relativistic Quantum Chemistry of the Superheavy Elements. Closed-Shell Element 114
as a Case Study.
Peter Schwerdtfeger∗,a and Michael Sethba
Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealandb
Department of Chemistry, University of Calgary, Calgary, Canada T2N 1N4
Received: October 23, 2001; In Final Form: March 18, 2002
The chemistry of superheavy element 114 is reviewed. The ground state of element 114 is closed shell [112]7s2 7p21/2
and shows a distinct chemical inertness (low reactivity). This inertness makes it rather difficult to study the atom-ata-time chemistry of 114 in the gas or liquid phase.

1. Introduction
The synthesis of the latest (proton-even) superheavy elements
114,1 116,2 and 1183 have been reported recently by the Dubna
and Lawrence-Berkeley groups.4 However, the unambiguous
identification of these elements by spectroscopic methods still
remains a challenge as the recent withdrawal from the observation of the α-decay chain of isotope 293 118 shows.5 One disadvantage was that the α-decay chain of 293 118 does not end
in the region of known isotopes.3 Furthermore, the very small
cross sections which lie in the picobarn region for such elements
implicate a very small production rate of one atom per day orless.6 The decay signal (usually by α decay or nuclear fission)
has then to be singled out against a background of signals fromother nuclear processes. Transfer of mass to the lighter nucleus
in the collision (quasi-fission) may also inhibit the fusion process.7 Another disadvantage is that the isotopes of superheavy
elements of high nuclear charge Z are close to the proton dripline making it increasingly more difficult to identify such newelements. The next generation of superheavy elements also requires less stable isotopes which implies the use of a radioactive
beam facility. There is further evidence that magic nuclei above
lead do not exist8 and it will become increasingly more difficult
to obtain elements with a lifetime in the second range or above.9
An important additional way for the positive identification ofsuperheavy elements is by atom-at-a-time chemistry. Atom-ata-time chemistry is currently the only experimental tool to gain
valuable insight into the chemical behavior of superheavy elements.9 Experiments have been carried out on element 106(seaborgium) by Schädel’s group at the GSI in Darmstadt10 andpreparations are currently underway to study 107–109, 112, andeven 114.11 The recently synthesized isotope 288 114 has a αdecay half-life in the second range.1 Before such experiments
are carried out the chemical behavior has to be at least estimatedfrom extrapolation of known chemistry of the lighter congeners
in the periodic table.12
It is now well known that the chemistry of the heavier elements can be quite different compared to the lighter elements inthe same group of the periodic table.13 Table 1 shows a comparison of physical properties of Group 11 compounds.14 It isevident that from these trends the chemistry of superheavy element 111 (eka-Au) cannot be deducted with great certainty
from their lighter congeners. This is mainly due to relativistic effects which become increasingly more important for theheavier elements. Relativity can influence the chemical andphysical properties of the heavier elements significantly leading
to well known “Group-anomalies”.15 Relativistic quantum theory is therefore the only way to accurately predict the physicaland chemical behavior of superheavy elements.16 We note thatwhilst relativistic effects are important for both the inner shell∗Corresponding author. E-mail: schwerd@ccu1.auckland.ac.nz.
FAX: (64-9) 3737422.

and the valence shell region, quantum electrodynamic (QED)
effects such as the electron and photon self-energy can safely
be neglected in the valence shell region.17 The Breit interaction
consisting of the magnetic (Gaunt) and retardation term should
be included for very accurate calculations. For properties like Kshell ionization potentials (K-IP) of superheavy elements QED
effects can be of the order of 1% of the total K-IP.18
A number of different techniques are in use to account for
both relativistic and electron correlation effects. The most accurate way is a fully relativistic treatment at the Dirac-HartreeFock (DHF) level19 including Breit interactions and other QED
effects followed by well known correlation techniques such as
coupled cluster theory (i.e. CCSD(T)).20 A number of twocomponent techniques by eliminating the small component areused as well and a review has been given recently by Barysz andSadlej.21 The two-component (spin-orbit coupled) all-electron
Hamiltonian is the ideal starting point for introducing spin-orbit
coupled pseudopotentials.22 Finally, scalar relativistic techniques are used as well at both the all-electron and the pseudopotential level.23 The various relativistic Hamiltonians can be usedin density functional theory.24 We mention that our group has
shown that the scalar relativistic pseudopotential approximation
produces results almost as accurate as all-electron calculations25
and we expect the same for two-component techniques, if thepseudopotential parameters have been adjusted carefully to thevalence spectrum of the Dirac-Hamiltonian.
2. Chemistry of Element 114
Table 2 shows a comparison between calculated ionization
potentials and excitation energies of element 114 at different
levels of theory. The most accurate values are from Kaldor andco-workers Fock-space relativistic coupled cluster calculations
using the Dirac-Fock-Breit solutions as a starting point.26 Our
DHF CCSD(T) calculations obtained earlier27 are slightly below Kaldor et al.’s results. The results obtained by Liu et al.28
using either the Nash pseudopotential29 plus CCSD(T) or the
Bejing four-component density functional program (BDF) arealso close to Kaldor et al.’s data. Balasubramanian’s results30 are
about 2 eV too low compared to the others. The pseudopotential
used was the same as in Liu’s calculations, hence we assume
that either the basis set or the electron correlation procedure applied was insufficient. Furthermore, calculations with the same
pseudopotential by Nash et al. gave 8.51 eV for the first ionization potential of 114 and 5.43 eV for the 2 P1/2 /2 P3/2 splitting of
114+ .31 We also mention that early Hartree-Fock-Slater calculations carried out by Keller et al. gave 8.5 and 16.8 eV for the
first and second ionization potential of 114.32
The most common oxidation states of group 14 elements
are +2 and +4. However, the stability of the higher oxidation state in p-block elements decreases with increasing nuclear
charge in one group which is often termed as the “inert pair ef-

c 2002 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 6/30/2002

134 J.Nucl.Radiochem.Sci.,Vol. 3, No. 1, 2002

Schwerdtfeger

TABLE 1: A comparison of properties of Group 11 elements.

Property
ColourSpecific resistivity / 10−8 Ωm
Thermal conductivity / J·cm−1 s−1 K−1Electronic heat capacity / 10−4 J·K−1 mol−1
Melting point / ◦ C
Boiling point / ◦ C
Atomic volume / cm3 mol−1
Electronegativities
Cohesive energies / kJ·mol−1
Energy of O2 -chemisorption / eV
Desorption temperature of CO on metal / K
Common oxidation states
MF fluorides (solid)
Superconductors

Cu
bronze
1.72
3.85
6.926
1083
2567
7.12
1.9
330
5.4
190–210I, II
unknownmany

Ag
silver
1.62
4.18
6.411
961
2212
10.28
1.9
280
6.0
40–80
I
AgF
rare

Au
yellow
2.4
3.1
6.918
1064
3080
10.21
2.4
370
3.6
170–180
I, III
unknown
rare

TABLE 2: Electron affinity (EA), ionization potentials (IP), and electronic excitation energies (EE) for element 114 from various relativistic
calculations. All values are given in eV.

Property
DHFa
10
2 2
3
10
2 2
1
2
EA 6d 7s p1/2 ( P0 ) → 6d 7s p1/2 p3/2 ( P3/2 )0.00
IP1 6d 10 7s2 np21/2 (3 P0 ) → 6d 10 7s2 p11/2 (2 P1/2 )
8.36
16.55
IP2 6d 10 7s2 p11/2 (2 P1/2 ) → 6d 10 7s2 (1 S0 )IP3 6d 10 7s2 (1 S0 ) → 6d 10 7s1 (2 S1/2 )35.52
EE 6d 10 7s2 p11/2 (2 P1/2 ) → 6d 10 7s2 p13/2 (2 P3/2 )
4.77
4
3
d5/2
7s2 (2 D5/2 )2.09
EE 6d 10 7s1 (2 S1/2 ) → 6d3/2a
DHF CCSD(T) from our group.27b
Fock-space coupled cluster calculations by Landau et al.26c
PP MRCI calculations by Balasubramanian.30d
PP CCSD(T) calculations by Liu et al.28eFour-component density functional calculations by Liu et al.28

DHF + Bb
0.00
8.54
16.87
35.74
4.88

PPc

PPd

BDFe

6.31

8.45
16.74
36.40

8.26
16.62
35.43

3.18
1.94

TABLE 3: Molecular properties of di- and tetravalent 114 compounds from scalar relativistic pseudopotential calculations at the MP2level of theory. For the hydrides DHF structures are listed as well. Bond distances re in Å, H-(114)-H angles αe in degrees (for the(114)X4 molecules is the tetrahedral angle), and decomposition energies ∆U0 in kJ·mol−1 (corrected for spin-orbit coupling) for the reactions (114)X4 → (114)X2 + X2 and (114)X2 → (114) + X2 .

Compound(114)H2(114)H4(114)F2(114)F4(114)Cl2(114)Cl4

MethodSRPP/MP2
DHF
SRPP/MP2
DHF
SRPP/MP2
SRPP/MP2
SRPP/MP2
SRPP/MP2

re
1.865
1.872
1.750
1.780
2.128
2.136
2.498
2.477

Relativistic
αe
89.7
93.1
109.5
109.5
97.1
109.5
99.7
109.5

fect”.33, 34 From a one-center expansion within a Dirac-HartreeFock (DHF) scheme Grant and Pyper obtained heats of formation for di- and tetravalent 114 compounds which revealed rather
low stability for the higher oxidation state.35 This was recently
supported by more accurate spin-orbit coupled relativistic pseudopotential calculations for the hydrides, chlorides, and fluorides of element 114, (114)X2 , and (114)X4 (X = H, F, Cl).27 Allcompounds are relativistically destabilized towards either decomposition, (114)X4 → (114)X2 + X2 or (114)X2 → (114) + X2 .
In all cases the (114)X4 decomposition is exothermic. Thus, element 114 is chemically more inert than the lighter elements Pb,
Sn, or Ge.
Table 3 shows calculated bond parameters and decomposition energies of (114)X4 and (114)X2 compounds (X = H, F, andCl) at various levels of theory. The basis sets used have been
described elsewhere.27 The calculations show that relativistic
effects are significant. For (114)Cl4 , which could be a candidatefor gas phase separation techniques, the higher oxidation stateis destabilized by ca. 400 kJ·mol−1 ! Hence, the only oxidation
state accessible for element 114 will be +2 in agreement withthe prediction of Keller et al. more than 30 years ago.32

∆U0
−288
−151

+331
−15
+150
−46

re
1.987
2.001
1.930
1.964
2.154
2.106
2.591
2.514

Nonrelativistic
αe
90.7
92.7
109.5
109.5
94.3
109.5
96.0
109.5

∆U0

−44

+32
+833
+585
+543
+340

Relativistic effects in bond distances are smaller and less than
0.1 Å. For (114)F4 relativistic effects lead to a slight increasein bond length which could be, however, due to inaccuracies
in the pseudopotential or electron correlation procedure applied.
Spin-orbit effects in bond distances and angles are small as well.
Because of the spin-orbit contraction of the 7p1/2 orbital, spinorbit coupling should decrease bond distances and increase bondangles. This is indeed calculated, i.e. for (114)H2 we obtain∆SO re = −0.037 Å, ∆SO αe = +1.8◦ . We mention that the bonddistance of (114)H4 has been predicted earlier by Pyykkö and
Desclaux to be 1.787 Å using a simple one-center Dirac-Fockapproximation.36
114 is a closed-shell atom with an electronic configuration
7s2 7p21/2 . We therefore expect a rather low reactivity to form
diatomic compounds in the gas phase. Indeed, all diatomic 114
compounds calculated by Liu et al. have lower dissociation energies compared to the corresponding lead compounds.28 Similar
results were obtained by Nash and Bursten.31 Here spin-orbit
effects are very large as a careful comparison between one- andtwo-component methods by Liu et al. showed.28 In fact due
to the increased chemical inertness, spin-orbit effects increase

Relativistic Quantum Chemistry of the Superheavy Elements
2.5
re [Å]

Group 14 Fluorides

2

Group 14 Hydrides

1.5

Row

1
2

3

4

5

6

7

Figure 1. Experimental (from CX to PbX (X = H, F), Reference 37)
and calculated bond distances (at the scalar relativistic CCSD(T) level
if not available) for Group 14 diatomic hydrides and fluorides.

the bond distance in all diatomic (114)X compounds.28 Hence,
we do not expect a change in trend in bond distances down theGroup 14 element compounds as shown clearly in Figure 1. Dissociation energies De of (114)X compounds decrease dramatically due to spin-orbit effects and for all diatomic (114)X compounds calculated so far De is lower than 200 kJ·mol−1 .28
3. Conclusion
Scalar relativistic and spin-orbit effects lead to an increased
chemical inertness of superheavy element 114 making it rather
difficult to form compounds in the gas phase. The behavior of
114 in solution is not known, however, and further theoretical
calculations are needed to study the chemistry of 114 in solution. Nevertheless, we expect that charged complexes of 114 insolution are less stable compared to their lighter congeners in
the periodic table.
Acknowledgment. This work was supported by the Marsden
Fund managed by the Royal Society of New Zealand (contract
number 96-UOA-PSE-0081) and the Auckland University Research Committee.
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