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A theoretical study of the geometrical properties of tellurite complexes
As the first part of a theoretical study of the geornetticai variations in the oxygen coordination of Te(XV) we have investigated the protonation of the tellurite km. TeO:-. to hydrogen telltito HTeO; or Te020H_ For pm-pose of comparison. we also present a similar study of the sulfite system. SO:-. HSOF and S020H-_ Geomevy optimizations were carried out using frozen orbital JZCP techniques on the RHF SCF level. The overall xziations in Te-0 and S-O bond lengths upon protonation are found to be smaller for TeO?than for SO:-_ Te020His. however. found to be considerably more stable than HTcO; while in the suititr system.the isomers are found to be almost equal in encrw_ The large Te-0 bond variations found in crystal structures for tellurium(fV)-ox_vgen compounds can in part be explained by the preference for the TeO;’ ion to coordinate via the oxygens.
1. Introduction The arrangement of oxygens around tellurium (IV) is often irregular and diflicult to describe in terms of simple geometrical polyhedra [l-3]. There are two main types of coordination: (1) Three-coordination in the form of a trigonal pyramid like the TeO$- ion in K,TeOs [4]. (2) Four-coordination in the form of a distorted trigonal bipyramid with the two oxygen atoms in the axial positions and the other two at two of the three equational -comers (e.g. in the structure of a-Te&). In KzTeOs [4] the three Te-0 bond distances are l-82 A and the fourth coordinated oxygen is at . a distance of 3-91 A. In the four-fold coordination compound, a-TeO? [S], the four.Te-0 bonds all lie between 1.9 and 2.1 A. -There ares many tellurite(IV) compounds in which the oxygen coordination is intermediate between these two,. and some with an everrlarger oxygen coordination 161. The telluriter-scan also be linked to each other to form long chains, sheets or .networks, but always via Te-0-Te bridges. This range of. Te-0 bond distances is of. great importance for the structural
and physical properties of the tellurite compounds (see refs. [l-3] and references therein). A study of the corresponding sulfur(IV)-oxygen compounds reveals both similarities and differences with the tellurium(IV) system. The variations in S-O bond distances are smaller for the sulfites, which also show little tendency to polymerize. A common coordination figure of the sulfur(IV)-oxygen compounds is the pyramidal one with a three-fold axis_ The SO,‘- ion can also bind to sulfur atoms of other groups but, contrary to TeOz- , via a sulfur-sulfur bond. This results in dimers or maybe small chains of sulfur(IV)-oxygen compounds but never sheets or networks as in the tellurium analogs. As a fiiSt part of a theoretical investigation of the irregul& oxygen coordination of tellurium(IV). we here present molecular orbital calculations on the TeOz- . HTeOy and T&&OHions. We have chosen to study the variations in the Te-0 bond -lengths upon protonation of the TeOz- ion, both with the proton attached to. the tellurium atom (HTeO;) and to one of the oxygens (TeOzOH-) as illustrated in fig l- The hydrogen. ion can be thought of as serving as a simple model of a
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counter ion or another tellurium from. a neighbouring tellurite group. Neither HTeO; nor TeO,OHhave been isolated and characterized experimentally, presumably due to the strong preference for polymerization in the tellurite system. In the sulfite system there are indications that the isomers HSO; and SOlOHcould exist in equilibrium in solution. We have in a previous theoretical study [7] found them to be of nearly equal energy, but only HSO; has so far been identified (in the single-crystal structure of CsHSO, [8]). In the present investigation the relative stability of HTeO; and TeOzOH- is discussed and compared
with corresponding results for HSO; and SOQH -_ We h&e approached the problem on the RHF SCF level. Experience from the .similar sulfite system [9] show3 that this is justif&. MC SCF calculations on SO,‘reveal no configurations of importance other than the Hat-tree-Fock one. In order to be able to. make the calculations on the tellurite compounds. we have employed the frozen orbital effective core potential (ECP) method [lo]. This reduces the calculations, in terms of computer resources, to the size of the corresponding sulfite ones. The frozen orbital ECP has been shown to yield quantitatively reliable results on a number of reasonably heavy molecules and ions, e-g. TeOz [IllGeometry optimizations have been performed on all the ions. MC SCF calculations have also been made on the TeO,OHion to investigate the stability of the RHF results for the Te-OH bond. For the purpose of comparison we also present parallel results for the sulfite system. In our previous study on the SO:system [7] the S-O bond distances were found to be some 0.04 A longer than those determined experimentally_ This problem, which was of no consequence for the conclusions in that work, has now been resolved 191.
2. Computational details
Fig. 1. Molecular structure and labelling of the atoms for the ions (a) TeO:-. (b) HTeO,- and (c) Te020H-_
In the present study we have employed RHF SCF and in a few cases MC SCF methods (using the CAS SCF approach [12]). All the calculations on the tellurium compounds were performed using the frozen orbital effective core potential (ECP) method suggested by Pettersson et al. [lo]. The ECP on tellurium contained the interactions involving the Is to 3d orbitals in parameterized form and the 4s, 4p and 4d orbitals in frozen form (with the frozen orbitals expanded in the valence .basis set). The valence basis set for tellurium, which originates in the 15s. 11~; 6d primitive set of Stromberg et al. [133, consisted of five s-, five p- and four d-type cartesian GTOs. The four d-functions were. contracted to three and one diffuse s-function was added. The values -of the d-exponents have been slightly modified from-
Table 1 Valence basis set and ECP param&crs Exponent
for Te Coefficient
-:
s
P
6.1861661 2.3474688 1.0818695 016750814
7_3155235 29091475 1.2078910 030356198
0.10377344 0.039
0_09901190
-d 3.7631988
1.4995293 OJ892133 0.189
d 0397642 OS36180 1.0 1.0
ECP parameters =’ 2 cn
24 1130.9164 172-77709 161-7373502 35.763416 31.088038 22505465 45.698230 12213086 5.583607 1238.15663 47-709763 8.701212
AI Az ~43
A, A, At.
0.347420 0194541 0.179019 2.979726 1549026 0.150985
=’ Notation as in ref. [lo]. The coefficients for tbe frozen orbitals are available from the authors upon request.
the original basis set, in order to describe a 5d orbital of proper shape. This is in analogy with the findings on the sulfite ion. where a 3d orbital of proper shape seems to be necessary for a proper description of the ion [9]_ Table 2 Calculated bord distances (A), angles (de&. hydrogen sulfites. X stands for Te or S
TeOf_ SC+I-rko; HSO;
TeO,OHSO?OH -
chai=esx
The ECP parameters and the valencebasis set.1 for tellurium are prtiented in tible I.’ -,f‘. f. : _ -;.__ For oxygen, the nine s- and five p-type b+isset~ of Huzinaga [14], contracted for four s and three.. p, was used with the inclusion of one diffuse p Function (0.064) while van Duijneveldt’s ;[l>] 3s primitive set, contracted to 2s, was employed for hydrogen_ In the calculations on the sulfite system, the basis set of Roos and Siegbahn [16] with the addition of one diffuse s- (0.064) and three d-functions with exponents 8.35, 2.22 and 0.67 was used on sulfur- The lOs, 6p and 3d set was contracted.to 7s. 4p and Id. The choice of basis sets for the sulfite system has been thoroughly investigated in another work [9]_ The geometry optirnizations on X02and HXOY were carried out using ordinary grid techniques. with geometries constrained :o Cj,. symmetry in all cases. The geometries of XOzOH(v&h its large number of degrees of freedom) were sought using the force-field method. with one plane of symmetry which contained the X atom and the OH group.
3. Results
and discussion
3.1. The tellwire ion, TeOj The
calculated
tellurite ion, TeO:-,
and total energies (au)
bond distance and angle for the are presented in table 2.
for tie rellurires. sulfites, hydrogen
r_x-0
6O-X-O
TX-H
4x
90
1.857 1.520 1.805 1.433
106.2 107.0 114.6 113.9
1.665 1.323
1.18 0.79 1.57 1.03
-1.06 - 0.93 - 0.85 - 0.69
- 0.02 0.04
%-0,
%-0,
rO,-H
e X-O.-H
e 0:-x-o,
e O.-S-O,
1.954 1.659
1.815 1.462
0.960 0.962
118.8 115.7
995 lC2.1
109.3 111.0
4x
40,
902
qH
E 101
T&-OH-
1.30
-0.89
so,Olyl-
0.90
-0-77
-0.91 -0.77
o-41 O-41
-486.01595 -62Z45999
4H
rellurites and
E 101 - 48528337 l0 -621.71186 -485_94080 w - 62246456
”
n) The charges are obtain& from a Mull&en population analysis. b, Tbe total energies displayed here are obtained using an ECP on Te. and are not directly comparable
with all electron en&es.
I
I
I
9
cy
0
d
‘9
I
I
I 02
6
0
I
I
1 0x9
0
F
I
I
1
9
L\!
(9
f
I
0
0
0
I
I
z I
Our calculations are in fairly go& agreement with experiment [4], but yield in. general a Te-0 bond _ioo .long .-by_ a few -hundredths of an Angstrom. This problem is discussed in detail in another study [4]_ It should be noted, however, that without using a d basis set whi&can properly describe an atomic 5d function the computed bond lengths come out, as in the case of SO:191, yet another few hundredths of an Angstrom longer. The discrepancy between calculated and measured Te-0 bond distances can at least in part be attributed to relativistic effects; in any case this is of little consequence for the aim of this investigation, since we are here interested in differences in geometries rather than an absolute geometric description_ The bonding in TeOiis similar to that in SO:-, which is described in ref. [7]. The highest occupied molecular orbital is a Te-0 antibonding orbital. As can be seen from the population analysis (cf. table 2) the bond is of more ionic character in TeOzthan in SO:-. The charge on Te is found to. be +1_18 but on S only +0.79. It is interesting to note that the spacing between the occupied orbitals in the orbital-energy diagram in fig. 2 is generally smaller in TeO:than in SO;-. This indicates more ionic character in the tellurite ion than in the sulfite one. These results are in accordance with the difference in electronegativity between tellurium and sulfur. 3.2. The TeO,OH -
protonated
tellwires
HTe03-
end
The optimized geometries for HTeO; (with the proton bound to Te) and TeOzOH(protonated on the oxygen) are presented in table 2, together with recent results for the sulfite. analogs HSOF and SO,OH-. The most striking result is the difference in the relative stability for the two isomers in the tellurite and sulfite systems respectively_ TeOzOH- is found to be more. stable than HTeO; by as much as 47 kcal/mol. Caution is necessary since both correlation and .relativistic effects might influence this energy difference_ The relativistic effect on the binding energy between tellurium and hydrogen is, however, probably only of the order of a few
kcal/mol, as indicated .by the resultsof Lee -&d McLean. [17] on AgH. Correlation. contributions~ might well be substantial, but -it .is unlikely --&at they would d&&ally change .the. present result since the X-H bond is reasonably well described on the SCF level a7,9] and below). For the hydrqgen sulfites, on-the other hand, the proton&ion at either site (oxygen or sulfur) is found to be equally favourable, HSO; being only 3 kcal/moi lower in. energy than SOzOH_ This difference in the behaviour of TeOz: and SO:could explain,. to some extent, the different structural behaviour of. sulfites and tellurites, .as will be discussed below_ Another significant result is that the geometry variations when protonating the telltite are much smaller than for the sulfite ion. The changes (cf. table 3) in the Te-0 bond length are only = 60% of the variations in the S-O bond. This can in part be understood if we look at the type of orbital which determines the geometry_ The mechanism behind the shortening of the X-O bond upon protonation on the X atom is that the HOMO of X0,‘-, which is an X-O antibonding orbital, becomes moreliie a non-bonding oxygen orbital in HXO;_ The X-H bond is constituted by the lower-lying orbitals 3a, and 4a, (see fig. 2 and ref. [7])_ When one of the oxygens is protonated, the X-OH bond is lengthened and the other two X-O bonds shortened_ The shortening of the X-O bond is caused by a mechanism similar to that in HXOF , while the lengthening of the X-OH bond stems primarily from orbitals which have become antibonding in this region of space. This mechanism is valid for both the sulfites and the tellurites, but the magnitudes of the effects are different_ Since the bonds are of more ionic character in the tellurite than the sulfite, as discusSed in the previous section, the geometry of the tellurite ion is less affected by protonation than that of the sulfite. 3.3. Differences in suI@?teand tellurite coordi_nation The energy difference between the isomers of the hydrogen tellmites shows that the hydrogen coordination via the oxygens is strongly favoured in the TeOz- ion If the positive tellurium part of another tellurite group is substituted for the proton one can understand the ability for tellurite(iV)
A. Szr@nberg a oL / GeonleIricolproperries of ~ellurirecomplexes
234
I Table 3 Cifferences in bona lengths (A) between tellurites and s&ites respectively HXO,- + 4 XOzOH‘ Ar2d--o,
Arx-0,
X=Te
0.149
x=s
0.226
0.010 0.029
x0;--
+
Ar,_,,
to Te-0-Te-0 chains or sheets. The different bridging and terminal Te-0 bond distances can then be expected to be spread at least as much as they are in.the theoretical model obtained for TeO,OH-. -181-1.95 A. The wider possibilities of variations of Te-0 bonding in the more complicated chain or sheet structures result in even a larger range, as is found experimentally_ The calculations -on the sulfite ion, SO:-,show that this ion may as well coordinate via the sulfur as via the oxygen. When binding hydrogen or other sulfite groups, coordination has mainly been found to occur via the sulfur atoms. The geometry variations obtained are of the same order as calculated for HSO;, that is quite symmetric and of modest magnitude as. e.g., in CSHSO~ [S] and S102-. Because of .t.hisfundamental difference in coordination between the tellurites and sulfites, different types of structures occur in the two systems. In order to further illustrate this difference in coordination for SO:and TeOz-. we have performed geometry optirnizations on the X0,, X0; and X0, ions to get an estimate of the adiabatic ionization potential * of the X0:ion and the electron affinity of X0? (cf. table 4)_ The adiabatic ionization potential for TeO,‘- was found to be 42 kcal/mol larger than that for SO,‘-_ These results indicate that it is more difficult to remove an electron from TeO,‘- than from SO,‘- in a stabilizing field excerted by solute ions in accordance with our previous deduction that it is easier for the sulfite-S than for the tellurite_Te to form a bond
difference in energy between the ground state and the ionized state at their respectiveequilibrium geometries.
C--,
A&O,
Ar,_,-
- 0.042 -0.058
-0.052 -o.oFz t
HXO;
..
positive counterpart_ Interestingly, -the optimum geometries of the theoretical SOT and SO; ions compare favourably with the experimental geometry of the S20:ion. e.g.. in (NH,)&Os [18] (r,_ o = 1.495 and 1.454 A). 3.4. MC SCF resuifs for Te020H
-
There is always a possibility that some strong dissociative mechanism is present that might invaiidate comparisons of RHF calculations with experiment. In a previous study of the sulfite ion [9] it was shown that no-important MC effects influenced the system, nevertheless we felt that the stability of the long Te-OH bond -in TeO,OHdeserved further investigation.- Therefore we have carried out MC SCF calculations on the TeO?OHion using CAS SCF technique. The active space contained fourteen active electrons in ten active orbitals, which rendered 2510
Table 4 Optimized geometries and energies for XOJ. X0;. x0,-
TCOZ TeO; T&gTeOF SO?
so; so;so;
” An adiabatic ionizalion potential (or elatron affinity) is the
--X$-
+.xo201i-
_. 0.097 0.139
polymerization
._
X0,‘-
rx_o(‘%
B,_,_,(deg)
E,,,(au)
1.767 1.836 1.857 1.814
113.6 1115 106.2 1128
-410.48990 =’ - 41057903 p’ - 48528337 =’ -48536225 =’
1.398 1.486 1520 1.447
119.7 115.0 107.0 :114.0
- 546.98945 - 547.02978 -621.71186 - 621.85787
and
a) The total energies displayed here are ob&ned using.& ECP on Tc. and are not directly comparable with all. electron energies. :
configurations_ The-orbitals chosen for the active space were Te-OH and Te-0 bonding and antibonding orbitals. No dominant configurations beside. the Hartree-Fock one were found. The -Te-OH bond distance, which was the. only geometrical parameter optimized, was found to be 2.012-A. This lengthening by 0.057 A is due to the inclusion of antibonding configurations_ It is quite usual that bond distances obtained on the MC SCF level come out too long. In order to get a correct result extensive CI calculations are usually required_
should thus not be compared to that of So,bd?~ but rather to those of HSO;) SO;, or SOT. which explains the small variations of the S-O bonds in e.g. S_Oj?- compared to the variations in ihe Te0-Te-0 networks. In order to further investigate the ~~tellurium(IV)-oxygen coordination and to be able to compare the different bond distances with crystal data, larger and more complicated ligands than H f will have to be employed, e.g., another tellurite group_ The CAS SCF calculations on Te020Hconfirmed that the SCF approximation is satisfactory for the needs of the present study:
4_ Conclusions The hydrogen tellurite ion with the hydrogen bound to an oxygen (TeO,OH-) is = 50 kcal/mol more stable than the other possible isomer, HTeO; _ Neither of the hydrogen tellurites has however been identified experimentally or structure determined. The TeO,OHion with its long Te-OH bond will, due to strong hydrogen bonding. have a rather high tendency to dissociate to TeO, in water solution_ This may provide an explanation for the immediate percipitation of TeO, on acidification of TeO:solutions. The preference for the tellurite ion to coordinate via the oxygen. especially to other tellurite ions. is manifested in the ability of tellurium(IV)oxygen compounds to form Te-0-Te-0 chains. These polymerized structures contain short and long Te-0 bond distances as indicated by the calculated geometry of TeO,OH-_ The higher ionization potential obtained for TeO:than for SO_:is also an indication of the relative unwillingness of Te in the tellurite ion to form covaIent bonds to positive counterparts in solutions or solids. The sulfite-sulfite interactions occur, in practice, mostly via sulfur-sulfur bonds. This can be understood-from the differences in relative energies of the HSOY-SO,OHand HTeO;-TeO,OHsystems, as explained in the text. These compounds will then tend to form dimers, and their geometries
References [l] J. ikeman. Z. Krist 127 (196s) 319. [Z] zg7k&lvist. Thesis. University of
G6!eborg.
Sweden
[3] M. TrWxl. J. Solid State Chem 35 (1980) 90. [41 L. Andersen. A. Strktberg and D. Str&nberg. Acta Ciyt.. submitted fok publication. [5] 0. Lindqvist. Acra Chctn Stand. 22 (1968) 977. 161 V-M. Kocak. C_ Platte and M. Triknel. Acta Cr\.~t. B35 (1979) 1439. 171 A. Striimberg. 0. Gropen. U_ Wahlgren and 0. Lindqvist. Inorg. Chem 22 (1983) 1129. 181 L-G. Johansson 0. Lindavist and N-G. Vannerbere Acta Ctyst_ 836 (19SO) 2523. [9] A. Str6mberg. U. Wahigren. L Petterson and P-E-M. Siegbahn. Chem_ Phys_ 89 (1984) 323_ [lo] L.G.M. Petterson. U. Wahlgren and 0. Gropen. Chem. Phyr 80 (1983) 7. Illj A. Stramberg. 0. Gropen and U. Wahlgren. J_ Chem Phys_ 80 (1984) 1593. [12] B. Roos. P_ Taylor and PEM. Siegbahn. Chun. Phys_ 48 (1980)157; P-EM. Siegbahtt. J. Almli%_ A He&erg and B. Roar J. Chem. Phys. 74 (1981) 23&l. [13] A. StrZimberg. O_ Gropen and U. Wahlgren J_ Comput. Chem. 4 (1953) 181. 1141 S. Htuinaga. Intcmal Report, Unixrsity of Alberta. Edmonton_ Canada (1971). cl51 F.B. van Duijneveldt IBM J_ Res_ Develop_ 20 (1971) 945. 1161 B. Roos and P. Siegbahn. Theoret Chim Acta 17 (1970) 209. 1171 Y-S. Lee and AD_ McLean_ J. Chem Phys. 76 (19S2) 735. [IS] 5. Bag+. Acta 0y.t. B27 (1971) 517.
1. Introduction The arrangement of oxygens around tellurium (IV) is often irregular and diflicult to describe in terms of simple geometrical polyhedra [l-3]. There are two main types of coordination: (1) Three-coordination in the form of a trigonal pyramid like the TeO$- ion in K,TeOs [4]. (2) Four-coordination in the form of a distorted trigonal bipyramid with the two oxygen atoms in the axial positions and the other two at two of the three equational -comers (e.g. in the structure of a-Te&). In KzTeOs [4] the three Te-0 bond distances are l-82 A and the fourth coordinated oxygen is at . a distance of 3-91 A. In the four-fold coordination compound, a-TeO? [S], the four.Te-0 bonds all lie between 1.9 and 2.1 A. -There ares many tellurite(IV) compounds in which the oxygen coordination is intermediate between these two,. and some with an everrlarger oxygen coordination 161. The telluriter-scan also be linked to each other to form long chains, sheets or .networks, but always via Te-0-Te bridges. This range of. Te-0 bond distances is of. great importance for the structural
and physical properties of the tellurite compounds (see refs. [l-3] and references therein). A study of the corresponding sulfur(IV)-oxygen compounds reveals both similarities and differences with the tellurium(IV) system. The variations in S-O bond distances are smaller for the sulfites, which also show little tendency to polymerize. A common coordination figure of the sulfur(IV)-oxygen compounds is the pyramidal one with a three-fold axis_ The SO,‘- ion can also bind to sulfur atoms of other groups but, contrary to TeOz- , via a sulfur-sulfur bond. This results in dimers or maybe small chains of sulfur(IV)-oxygen compounds but never sheets or networks as in the tellurium analogs. As a fiiSt part of a theoretical investigation of the irregul& oxygen coordination of tellurium(IV). we here present molecular orbital calculations on the TeOz- . HTeOy and T&&OHions. We have chosen to study the variations in the Te-0 bond -lengths upon protonation of the TeOz- ion, both with the proton attached to. the tellurium atom (HTeO;) and to one of the oxygens (TeOzOH-) as illustrated in fig l- The hydrogen. ion can be thought of as serving as a simple model of a
OjOl-0104/85/$03_3~ 0 Elsevier Science Publishers B-V_ (North-Hdland Physics Publishing Division)
counter ion or another tellurium from. a neighbouring tellurite group. Neither HTeO; nor TeO,OHhave been isolated and characterized experimentally, presumably due to the strong preference for polymerization in the tellurite system. In the sulfite system there are indications that the isomers HSO; and SOlOHcould exist in equilibrium in solution. We have in a previous theoretical study [7] found them to be of nearly equal energy, but only HSO; has so far been identified (in the single-crystal structure of CsHSO, [8]). In the present investigation the relative stability of HTeO; and TeOzOH- is discussed and compared
with corresponding results for HSO; and SOQH -_ We h&e approached the problem on the RHF SCF level. Experience from the .similar sulfite system [9] show3 that this is justif&. MC SCF calculations on SO,‘reveal no configurations of importance other than the Hat-tree-Fock one. In order to be able to. make the calculations on the tellurite compounds. we have employed the frozen orbital effective core potential (ECP) method [lo]. This reduces the calculations, in terms of computer resources, to the size of the corresponding sulfite ones. The frozen orbital ECP has been shown to yield quantitatively reliable results on a number of reasonably heavy molecules and ions, e-g. TeOz [IllGeometry optimizations have been performed on all the ions. MC SCF calculations have also been made on the TeO,OHion to investigate the stability of the RHF results for the Te-OH bond. For the purpose of comparison we also present parallel results for the sulfite system. In our previous study on the SO:system [7] the S-O bond distances were found to be some 0.04 A longer than those determined experimentally_ This problem, which was of no consequence for the conclusions in that work, has now been resolved 191.
2. Computational details
Fig. 1. Molecular structure and labelling of the atoms for the ions (a) TeO:-. (b) HTeO,- and (c) Te020H-_
In the present study we have employed RHF SCF and in a few cases MC SCF methods (using the CAS SCF approach [12]). All the calculations on the tellurium compounds were performed using the frozen orbital effective core potential (ECP) method suggested by Pettersson et al. [lo]. The ECP on tellurium contained the interactions involving the Is to 3d orbitals in parameterized form and the 4s, 4p and 4d orbitals in frozen form (with the frozen orbitals expanded in the valence .basis set). The valence basis set for tellurium, which originates in the 15s. 11~; 6d primitive set of Stromberg et al. [133, consisted of five s-, five p- and four d-type cartesian GTOs. The four d-functions were. contracted to three and one diffuse s-function was added. The values -of the d-exponents have been slightly modified from-
Table 1 Valence basis set and ECP param&crs Exponent
for Te Coefficient
-:
s
P
6.1861661 2.3474688 1.0818695 016750814
7_3155235 29091475 1.2078910 030356198
0.10377344 0.039
0_09901190
-d 3.7631988
1.4995293 OJ892133 0.189
d 0397642 OS36180 1.0 1.0
ECP parameters =’ 2 cn
24 1130.9164 172-77709 161-7373502 35.763416 31.088038 22505465 45.698230 12213086 5.583607 1238.15663 47-709763 8.701212
AI Az ~43
A, A, At.
0.347420 0194541 0.179019 2.979726 1549026 0.150985
=’ Notation as in ref. [lo]. The coefficients for tbe frozen orbitals are available from the authors upon request.
the original basis set, in order to describe a 5d orbital of proper shape. This is in analogy with the findings on the sulfite ion. where a 3d orbital of proper shape seems to be necessary for a proper description of the ion [9]_ Table 2 Calculated bord distances (A), angles (de&. hydrogen sulfites. X stands for Te or S
TeOf_ SC+I-rko; HSO;
TeO,OHSO?OH -
chai=esx
The ECP parameters and the valencebasis set.1 for tellurium are prtiented in tible I.’ -,f‘. f. : _ -;.__ For oxygen, the nine s- and five p-type b+isset~ of Huzinaga [14], contracted for four s and three.. p, was used with the inclusion of one diffuse p Function (0.064) while van Duijneveldt’s ;[l>] 3s primitive set, contracted to 2s, was employed for hydrogen_ In the calculations on the sulfite system, the basis set of Roos and Siegbahn [16] with the addition of one diffuse s- (0.064) and three d-functions with exponents 8.35, 2.22 and 0.67 was used on sulfur- The lOs, 6p and 3d set was contracted.to 7s. 4p and Id. The choice of basis sets for the sulfite system has been thoroughly investigated in another work [9]_ The geometry optirnizations on X02and HXOY were carried out using ordinary grid techniques. with geometries constrained :o Cj,. symmetry in all cases. The geometries of XOzOH(v&h its large number of degrees of freedom) were sought using the force-field method. with one plane of symmetry which contained the X atom and the OH group.
3. Results
and discussion
3.1. The tellwire ion, TeOj The
calculated
tellurite ion, TeO:-,
and total energies (au)
bond distance and angle for the are presented in table 2.
for tie rellurires. sulfites, hydrogen
r_x-0
6O-X-O
TX-H
4x
90
1.857 1.520 1.805 1.433
106.2 107.0 114.6 113.9
1.665 1.323
1.18 0.79 1.57 1.03
-1.06 - 0.93 - 0.85 - 0.69
- 0.02 0.04
%-0,
%-0,
rO,-H
e X-O.-H
e 0:-x-o,
e O.-S-O,
1.954 1.659
1.815 1.462
0.960 0.962
118.8 115.7
995 lC2.1
109.3 111.0
4x
40,
902
qH
E 101
T&-OH-
1.30
-0.89
so,Olyl-
0.90
-0-77
-0.91 -0.77
o-41 O-41
-486.01595 -62Z45999
4H
rellurites and
E 101 - 48528337 l0 -621.71186 -485_94080 w - 62246456
”
n) The charges are obtain& from a Mull&en population analysis. b, Tbe total energies displayed here are obtained using an ECP on Te. and are not directly comparable
with all electron en&es.
I
I
I
9
cy
0
d
‘9
I
I
I 02
6
0
I
I
1 0x9
0
F
I
I
1
9
L\!
(9
f
I
0
0
0
I
I
z I
Our calculations are in fairly go& agreement with experiment [4], but yield in. general a Te-0 bond _ioo .long .-by_ a few -hundredths of an Angstrom. This problem is discussed in detail in another study [4]_ It should be noted, however, that without using a d basis set whi&can properly describe an atomic 5d function the computed bond lengths come out, as in the case of SO:191, yet another few hundredths of an Angstrom longer. The discrepancy between calculated and measured Te-0 bond distances can at least in part be attributed to relativistic effects; in any case this is of little consequence for the aim of this investigation, since we are here interested in differences in geometries rather than an absolute geometric description_ The bonding in TeOiis similar to that in SO:-, which is described in ref. [7]. The highest occupied molecular orbital is a Te-0 antibonding orbital. As can be seen from the population analysis (cf. table 2) the bond is of more ionic character in TeOzthan in SO:-. The charge on Te is found to. be +1_18 but on S only +0.79. It is interesting to note that the spacing between the occupied orbitals in the orbital-energy diagram in fig. 2 is generally smaller in TeO:than in SO;-. This indicates more ionic character in the tellurite ion than in the sulfite one. These results are in accordance with the difference in electronegativity between tellurium and sulfur. 3.2. The TeO,OH -
protonated
tellwires
HTe03-
end
The optimized geometries for HTeO; (with the proton bound to Te) and TeOzOH(protonated on the oxygen) are presented in table 2, together with recent results for the sulfite. analogs HSOF and SO,OH-. The most striking result is the difference in the relative stability for the two isomers in the tellurite and sulfite systems respectively_ TeOzOH- is found to be more. stable than HTeO; by as much as 47 kcal/mol. Caution is necessary since both correlation and .relativistic effects might influence this energy difference_ The relativistic effect on the binding energy between tellurium and hydrogen is, however, probably only of the order of a few
kcal/mol, as indicated .by the resultsof Lee -&d McLean. [17] on AgH. Correlation. contributions~ might well be substantial, but -it .is unlikely --&at they would d&&ally change .the. present result since the X-H bond is reasonably well described on the SCF level a7,9] and below). For the hydrqgen sulfites, on-the other hand, the proton&ion at either site (oxygen or sulfur) is found to be equally favourable, HSO; being only 3 kcal/moi lower in. energy than SOzOH_ This difference in the behaviour of TeOz: and SO:could explain,. to some extent, the different structural behaviour of. sulfites and tellurites, .as will be discussed below_ Another significant result is that the geometry variations when protonating the telltite are much smaller than for the sulfite ion. The changes (cf. table 3) in the Te-0 bond length are only = 60% of the variations in the S-O bond. This can in part be understood if we look at the type of orbital which determines the geometry_ The mechanism behind the shortening of the X-O bond upon protonation on the X atom is that the HOMO of X0,‘-, which is an X-O antibonding orbital, becomes moreliie a non-bonding oxygen orbital in HXO;_ The X-H bond is constituted by the lower-lying orbitals 3a, and 4a, (see fig. 2 and ref. [7])_ When one of the oxygens is protonated, the X-OH bond is lengthened and the other two X-O bonds shortened_ The shortening of the X-O bond is caused by a mechanism similar to that in HXOF , while the lengthening of the X-OH bond stems primarily from orbitals which have become antibonding in this region of space. This mechanism is valid for both the sulfites and the tellurites, but the magnitudes of the effects are different_ Since the bonds are of more ionic character in the tellurite than the sulfite, as discusSed in the previous section, the geometry of the tellurite ion is less affected by protonation than that of the sulfite. 3.3. Differences in suI@?teand tellurite coordi_nation The energy difference between the isomers of the hydrogen tellmites shows that the hydrogen coordination via the oxygens is strongly favoured in the TeOz- ion If the positive tellurium part of another tellurite group is substituted for the proton one can understand the ability for tellurite(iV)
A. Szr@nberg a oL / GeonleIricolproperries of ~ellurirecomplexes
234
I Table 3 Cifferences in bona lengths (A) between tellurites and s&ites respectively HXO,- + 4 XOzOH‘ Ar2d--o,
Arx-0,
X=Te
0.149
x=s
0.226
0.010 0.029
x0;--
+
Ar,_,,
to Te-0-Te-0 chains or sheets. The different bridging and terminal Te-0 bond distances can then be expected to be spread at least as much as they are in.the theoretical model obtained for TeO,OH-. -181-1.95 A. The wider possibilities of variations of Te-0 bonding in the more complicated chain or sheet structures result in even a larger range, as is found experimentally_ The calculations -on the sulfite ion, SO:-,show that this ion may as well coordinate via the sulfur as via the oxygen. When binding hydrogen or other sulfite groups, coordination has mainly been found to occur via the sulfur atoms. The geometry variations obtained are of the same order as calculated for HSO;, that is quite symmetric and of modest magnitude as. e.g., in CSHSO~ [S] and S102-. Because of .t.hisfundamental difference in coordination between the tellurites and sulfites, different types of structures occur in the two systems. In order to further illustrate this difference in coordination for SO:and TeOz-. we have performed geometry optirnizations on the X0,, X0; and X0, ions to get an estimate of the adiabatic ionization potential * of the X0:ion and the electron affinity of X0? (cf. table 4)_ The adiabatic ionization potential for TeO,‘- was found to be 42 kcal/mol larger than that for SO,‘-_ These results indicate that it is more difficult to remove an electron from TeO,‘- than from SO,‘- in a stabilizing field excerted by solute ions in accordance with our previous deduction that it is easier for the sulfite-S than for the tellurite_Te to form a bond
difference in energy between the ground state and the ionized state at their respectiveequilibrium geometries.
C--,
A&O,
Ar,_,-
- 0.042 -0.058
-0.052 -o.oFz t
HXO;
..
positive counterpart_ Interestingly, -the optimum geometries of the theoretical SOT and SO; ions compare favourably with the experimental geometry of the S20:ion. e.g.. in (NH,)&Os [18] (r,_ o = 1.495 and 1.454 A). 3.4. MC SCF resuifs for Te020H
-
There is always a possibility that some strong dissociative mechanism is present that might invaiidate comparisons of RHF calculations with experiment. In a previous study of the sulfite ion [9] it was shown that no-important MC effects influenced the system, nevertheless we felt that the stability of the long Te-OH bond -in TeO,OHdeserved further investigation.- Therefore we have carried out MC SCF calculations on the TeO?OHion using CAS SCF technique. The active space contained fourteen active electrons in ten active orbitals, which rendered 2510
Table 4 Optimized geometries and energies for XOJ. X0;. x0,-
TCOZ TeO; T&gTeOF SO?
so; so;so;
” An adiabatic ionizalion potential (or elatron affinity) is the
--X$-
+.xo201i-
_. 0.097 0.139
polymerization
._
X0,‘-
rx_o(‘%
B,_,_,(deg)
E,,,(au)
1.767 1.836 1.857 1.814
113.6 1115 106.2 1128
-410.48990 =’ - 41057903 p’ - 48528337 =’ -48536225 =’
1.398 1.486 1520 1.447
119.7 115.0 107.0 :114.0
- 546.98945 - 547.02978 -621.71186 - 621.85787
and
a) The total energies displayed here are ob&ned using.& ECP on Tc. and are not directly comparable with all. electron energies. :
configurations_ The-orbitals chosen for the active space were Te-OH and Te-0 bonding and antibonding orbitals. No dominant configurations beside. the Hartree-Fock one were found. The -Te-OH bond distance, which was the. only geometrical parameter optimized, was found to be 2.012-A. This lengthening by 0.057 A is due to the inclusion of antibonding configurations_ It is quite usual that bond distances obtained on the MC SCF level come out too long. In order to get a correct result extensive CI calculations are usually required_
should thus not be compared to that of So,bd?~ but rather to those of HSO;) SO;, or SOT. which explains the small variations of the S-O bonds in e.g. S_Oj?- compared to the variations in ihe Te0-Te-0 networks. In order to further investigate the ~~tellurium(IV)-oxygen coordination and to be able to compare the different bond distances with crystal data, larger and more complicated ligands than H f will have to be employed, e.g., another tellurite group_ The CAS SCF calculations on Te020Hconfirmed that the SCF approximation is satisfactory for the needs of the present study:
4_ Conclusions The hydrogen tellurite ion with the hydrogen bound to an oxygen (TeO,OH-) is = 50 kcal/mol more stable than the other possible isomer, HTeO; _ Neither of the hydrogen tellurites has however been identified experimentally or structure determined. The TeO,OHion with its long Te-OH bond will, due to strong hydrogen bonding. have a rather high tendency to dissociate to TeO, in water solution_ This may provide an explanation for the immediate percipitation of TeO, on acidification of TeO:solutions. The preference for the tellurite ion to coordinate via the oxygen. especially to other tellurite ions. is manifested in the ability of tellurium(IV)oxygen compounds to form Te-0-Te-0 chains. These polymerized structures contain short and long Te-0 bond distances as indicated by the calculated geometry of TeO,OH-_ The higher ionization potential obtained for TeO:than for SO_:is also an indication of the relative unwillingness of Te in the tellurite ion to form covaIent bonds to positive counterparts in solutions or solids. The sulfite-sulfite interactions occur, in practice, mostly via sulfur-sulfur bonds. This can be understood-from the differences in relative energies of the HSOY-SO,OHand HTeO;-TeO,OHsystems, as explained in the text. These compounds will then tend to form dimers, and their geometries
References [l] J. ikeman. Z. Krist 127 (196s) 319. [Z] zg7k&lvist. Thesis. University of
G6!eborg.
Sweden
[3] M. TrWxl. J. Solid State Chem 35 (1980) 90. [41 L. Andersen. A. Strktberg and D. Str&nberg. Acta Ciyt.. submitted fok publication. [5] 0. Lindqvist. Acra Chctn Stand. 22 (1968) 977. 161 V-M. Kocak. C_ Platte and M. Triknel. Acta Cr\.~t. B35 (1979) 1439. 171 A. Striimberg. 0. Gropen. U_ Wahlgren and 0. Lindqvist. Inorg. Chem 22 (1983) 1129. 181 L-G. Johansson 0. Lindavist and N-G. Vannerbere Acta Ctyst_ 836 (19SO) 2523. [9] A. Str6mberg. U. Wahigren. L Petterson and P-E-M. Siegbahn. Chem_ Phys_ 89 (1984) 323_ [lo] L.G.M. Petterson. U. Wahlgren and 0. Gropen. Chem. Phyr 80 (1983) 7. Illj A. Stramberg. 0. Gropen and U. Wahlgren. J_ Chem Phys_ 80 (1984) 1593. [12] B. Roos. P_ Taylor and PEM. Siegbahn. Chun. Phys_ 48 (1980)157; P-EM. Siegbahtt. J. Almli%_ A He&erg and B. Roar J. Chem. Phys. 74 (1981) 23&l. [13] A. StrZimberg. O_ Gropen and U. Wahlgren J_ Comput. Chem. 4 (1953) 181. 1141 S. Htuinaga. Intcmal Report, Unixrsity of Alberta. Edmonton_ Canada (1971). cl51 F.B. van Duijneveldt IBM J_ Res_ Develop_ 20 (1971) 945. 1161 B. Roos and P. Siegbahn. Theoret Chim Acta 17 (1970) 209. 1171 Y-S. Lee and AD_ McLean_ J. Chem Phys. 76 (19S2) 735. [IS] 5. Bag+. Acta 0y.t. B27 (1971) 517.