versión On-line ISSN 0717-9707
J. Chil. Chem. Soc. v.53 n.1 Concepción mar. 2008
J. Chil. Chem. Soc, 53, N° 1 (2008)
CRYSTAL STRUCTURE OF A NEW BISMUTH PERRHENATE Bi(Re04)3H20
CARLOS MUJICAa, JAIME LLANOSa, VÍCTOR SÁNCHEZa*, PAOLA BOCAZa AND RAÚL CARDOSO-GILb
aDepartamento de Química, Universidad Católica del Norte, Casilla 1280, Antofagasta, Chile, e-mail: email@example.com
bMax Planck Instituí für Chemische Physik fester Stoffe, Nóthnitzerstr. 40, 01187 Dresden, Germany
Monoaquatris(tetraoxorhenate (VII)) bismuth(III), Bi(Re04)3(H20) was prepared by reaction of (BiO)2C03/Bi2(C03)3 with concentrated HRe04 at room temperature. The pale yellow compound crystallize triclinic in the space group PI;, (No. 2); with two formula units per unit cell (a = 746.0(1) pm, b = 111. 1(2) pm, c = 990.5(2) pm, a = 100.99(3)°, p = 99.88(3)°, y = 100.17(3)° ). The main feature of the crystal structure is a distorted bicapped trigonal prism of Bi[(Re04)3;2 (Re04)2/2 (Re04)2/2 (H20)], which are connected each other through [ReOJ-tetrahedra to form a three-dimensional network. In the titled compound, the cation Bi3+ is eightfold coordinated which agree with the tendency observed in other compounds of the family.
Keywords: crystal structure, perrhenate anions, X-ray diffraction, coordination number
In previous publications we reported the synthesis and crystal structure of tetraoxorhenates (VII) of some rare earth metals like Gd, Sm, Eu, Yb, La 1"5. In these perrhenates, the coordination number of the central cation depends mainly on the size of the 3+ ion. This dependence is also observed for many others compounds based on perrhenate as a ligand, including alkalines-earth metals, transition metals and rare-earth ions as central cation 6"18. All of them with oxidation states 2+ or 3+. According to this, we hypothesized that the coordination number of bismuth 3+ should be also in agreement with the dependence mentioned above. On the other hand, the distance between the central cation and oxygen for all of the perrhenate compounds reveals the presence of ionic interaction, considering the sum of the ionic radii. In this sense we also expected an interaction with ionic character between the Re04; ligands and the central Bi atom.
Bi(Re04)3-H20 was synthesized dissolving stepwise (BiO)2C03/Bi2(C03)3 in perrhenic acid and keeping the solution below pH = 3. HReÓ4 was prepared according to the well known method by reacting H202 (Merck, 30%) with solid rhenium powder (Aldrich 99.9%). (BiO)2C03/Bi2(C03)3 was prepared mixing BiCl3 and a saturated aqueous solution of Na2C03 with permanent stirring during 24h. Subsequently, the product was washed several times, centrifuged and dried at 60°C. Well shaped, colorless crystals of Bi(Re04)3-H20 were grown by slow concentration of the acid mother solution.
A single crystal with approximate dimensions of 0.14x0.13x0.11 mm was isolated in a glove box under Argon atmosphere (02 < 1.0 ppm; H20 < 1.0 ppm) and fixed in a sealed glass capillary for x-ray single crystal analysis. Intensity data were collected on a STOE-IPDS diffractometer. The unit cell was determined from a setting of 1679 reflections in the range 4.32° < 20 < 45.0°; Numerical absorption correction was performed with optimized shape of the crystal ". The structure was solved by direct methods (SHELXS-97) in the space group PI;, (N°. 2) and subsequently refined by least-squares methods using SHELXL-977. Crystallographic details are given in Table 1.
RESULTS AND DISCUSSION
Bi(Re04)3-H20 crystallizes in a new structure type in the centrosymetric space group PI;, (N°. 2), with two formula units in the unit cell. The Bi(III)ion shows a 8-fold coordination where the H20 molecule and one Re04; anion are in capped position over rectangular faces and the other six Re04"~; ligands form the distorted trigonal prism (Fig. 1).
Three crystallographic independent positions for the Re atoms are found in the crystal structure. They bridge the Bi-polyhedra in different way and directions building up a three dimensional network: Re(l)-tetrahedra bonds three Bi atoms bridging them along  (Fig. 2a), two Re(2)-tetrahedra bonds two Bi atoms along  (Fig.2fe) and two Re(3)-tetrahedra bonds two Bi atoms along  (Fig.2c).
The mean bond length ¿(Re-O) = 172 pm in Re04; tetrahedra is approximately the same observed for rare-earth perrhenates, transition metal perrhenates and earth alkaline perhenates 1_18
The dependence of coordination number upon the Pauling's ionic radii 21 observed for the central cation in this case, agrees with the relationship for other related compounds. Namely, when the ionic radius of the metal lays in the range 0.6Á to 0.8Á the coordination number is 6 and when the ionic radii lays in the range 1.00Á to 1.20Á the coordination number is 9. In this work, the ionic radii of Bi(III) is comparable with those of Yb(III) and Ca(II) and the three of them are eightfold coordinated (CN = 8), confirming the behavior observed for other compounds of the family (Fig.3).
Taking that into account, we can infer that when the ionic radii lays approximately between 0.9 to 1.0 A the coordination number of central cation should be 8. Coordination number 7 could be observed when the ionic radii are approximately in the range 0.8 to 0.9 A, leading to different structures, but those are not observed due to the relatively instability of this coordination number.
The unsuccessfull synthesis of Pt (II) and Pd (II) perrhenates attempted in our laboratories can be explained considering the correlation shown on fig. 3. Thus, the ionic radii of both cations (0.86 A) lay in the middle range (0.8-0.9 A") expected for coordination 7, being this CN relatively unstable.
On the other hand, perrhenates of alkali metals are not included in this comparison since none of them contain H20 molecules as ligands and do not fit the correlation showed in Fig.3.
This work was supported by FONDECYT under grant 1010305
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(Received: 3 December 2007 - Accepted: 21 January 2008)