The influence of lanthanide ionic radii on the formation and stability of the complexes: Synthesis, chemical properties and characterization of [(b-SiW 9 O 34 ) 2 (H 2 OM) 3 CO 3 ] 13 M = Eu 3+ and Gd 3+ Roushan Khoshnavazi ⇑ , Leila Bahrami, Sahar Gholamyan Department of Chemistry, University of Kurdistan, P.O. Box 66135-416, Sanandaj, Iran article info Article history: Received 10 October 2010 Received in revised form 1 January 2011 Accepted 3 January 2011 Available online 22 January 2011 Keywords: Polyoxometalates Sandwich type complexes Na 2 CO 3 solution Single crystal structure determination abstract This study has investigated the reaction of A-b-SiW 9 O 10 34 with M = Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ and Gd 3+ in aqueous Na 2 CO 3 solution and found that sandwich-type polyoxometalates of [(b-SiW 9 O 34 ) 2 (H 2 OM) 3 CO 3 ] 13 are formed only with Eu 3+ and Gd 3+ . The complexes were synthesized at room temperature and isolated as K + /Na + salt, but single crystal structure determination was carried out on (NH 4 ) 12 Na [(b-SiW 9 O 34 ) 2 (H 2 OGd) 3 CO 3 ]16.5H 2 O (CH 87 Gd 3 N 12 NaO 90.50 Si 2 W 18 ). The complex crystallizes in triclinic system, space group P-1 with a = 11.997 Å, b = 19.618 Å, c = 21.619 Å, a = 64.332°, b = 82.876°, c = 86.992° and Z = 2. The crystal structure of the complex consist of two lacunary A-b-SiW 9 O 10 34 Keggin moieties which are linked by a (H 2 OGd) 3 CO 3 belt. The results prove the retention of the isomeric form of the starting lacunary anion A-b-SiW 9 O 10 34 upon the preparation of the complexes. The title new com- plexes are less stable than of [(b-SiW 9 O 34 ) 2 (H 2 OM) 3 CO 3 ] 13 M=Y 3+ and Yb 3+ analogue because of the larger ionic radii of Eu 3+ and Gd 3+ . Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Polyoxometalates (POMs) as water-soluble metal oxide cluster with nanosizes and abundant topologies, have attracted interests for their various geometry topologies and their potential applica- tions such as catalysis, magnetism, photochemistry, electrochemis- try and biological chemistry. The evolution of POMs chemistry depends on the synthesis of novel POMs possessing unique struc- tures and properties and their systemic synthesis is still a chal- lenge in the POMs chemistry [1–9]. For almost a decade, some researches have been done on the lanthanide-containing com- pounds. These studies were motivated by their interesting lumi- nescent properties and by their ability to provide potentially applicability in material science [10–12]. Hence, the strategy of incorporation of the lanthanide ions in polyoxometalates struc- tures was successfully applied some years ago and some promising complexes were obtained. Such lanthanide-polyoxometalates derivatives have a tremendous structural variety and interesting properties in different fields; for example catalysis, magnetic, luminescent and material science [13–18]. However, the Keggin- and Dawson-type polyoxometalates and their mono vacant lacu- nary, are the major precursor of these fields. These structures are as discrete anions or polymeric polyoxometalates containing lan- thanide cations [13–18]. The trivacant polyoxotungstates, [XW 9 O 34 ] n (X = P 5+ , Si 4+ , As 5+ , ...) have potential to support lan- thanide clusters. [XW 9 O 34 ] n is derived from the Keggin structure and has six oxygen atoms available for bonding (in the A form) and seven (in the B form) [19–21]. The first complex of Keggin trilacunary derivative with lanthanide ions, [(PW 9 O 34 ) 2 Ce 3 O 3 (OH 2 ) 2 }] 12 was reported by Knoth [22]. In 2003, lanthanide com- plexes of [(XW 9 O 34 ) 2 Ln 3 O 3 (OH 2 ) 2 }] 15 where Ln = Ce 3+ , La 3+ and X=P 5+ , As 5+ were reported [23]. These complexes have sand- wich-type structure consist of two A-[PW 9 O 34 ] 9 units connected by a belt containing three oxygen atoms, alternating with the three lanthanide atoms. Hill synthesized the first example of sandwich- type polyoxometalates, [(A-PW 9 O 34 ) 2 (H 2 OY) 3 CO 3 ] 11 that encap- sulates a dianion (CO 2 3 ) in the center [24]. We have synthesized [(A-AsW 9 O 34 ) 2 (H 2 OM) 3 CO 3 ] 11 (M = Y 3+ , Sm 3+ , Yb 3+ ) [25], [(A-b-Si W 9 O 34 ) 2 (H 2 OM) 3 CO 3 ] 13 (M = Y 3+ , Yb 3+ ) [26] and then [(A-b-G eW 9 O 34 ) 2 (H 2 OM) 3 CO 3 ] 13 (M = Y 3+ , Sm 3+ , Yb 3+ ) [27] as the first lan- thanide derivatives of this category. These complexes were formed by the reaction of A-XW 9 O n 34 with M 3+ in an aqueous Na 2 CO 3 solu- tion in modest yield and in high purity. We showed that the [(A-b-S iW 9 O 34 ) 2 (H 2 OM) 3 CO 3 ] 13 (M = Y 3+ , Yb 3+ ) complexes are specially, thermally and hydrolytically stable [26]. Herein the reaction of A-b-SiW 9 O 10 34 with M = Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ and Gd 3+ in aqueous Na 2 CO 3 solution are studied. The results of research show that sandwich-type polyoxometalates of [(b-SiW 9 O 34 ) 2 (H 2 OM) 3 0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2011.01.018 ⇑ Corresponding author. Tel./fax: +98 871 6624133. E-mail addresses: khoshnavazi@yahoo.com, r.khoshnavazi@uok.ac.ir (R. Khoshnavazi). Journal of Molecular Structure 990 (2011) 57–62 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc