Synthesis and crystal structures of two new leadII) hexa¯uoroarsenatesV) M. Trams Ïek a , E. Lork b , R. Mews b ,B.Z Ï emva a,* a Department of Inorganic Chemistry and Technology, Joz Ïef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia b Institute of Inorganic and Physical Chemistry, University of Bremen, Leobener Straûe, NW 2, Postfach 330440, D-28359 Bremen, Germany Received 22 January 2001; accepted 21 February 2001 Dedicated to the memory of ¯uorine chemist Dr. Karel Lutar 2 September 2000) Abstract In the system PbF 2 /AsF 5 /anhydrous hydrogen ¯uoride aHF) two new leadII) hexa¯uoroarsenatesV) PbHF)AsF 6 ) 2 and PbFAsF 6 were isolated. PbHF)AsF 6 ) 2 is formed when the molar ratio AsF 5 :PbF 2 is 2 or higher. It crystallizes in the space group Pbcn with a 1058:33) pm, b 1520:96) pm, c 1079:43) pm, V 1:737410) nm 3 and Z 8. The HF molecule is directly connected to the Pb center, eight ¯uorine atoms from three different AsF 6 ions Pb±F distances ranging from 2484) to 2762) pm) and one further ¯uorine at 3063) pm complete the coordination sphere. PbFAsF 6 is obtained when equimolar amounts of PbF 2 and AsF 5 react in aHF. PbFAsF 6 crystallizes in the space group P 1 with: a 466:1010) pm, b 723:7010) pm, c 747:4010) pm, a 105:93010)8, b 101:492)8, g 90:66010)8, V 0:236987) nm 3 and Z 2. The basic unit in the structure of PbFAsF 6 ) consists of a four-membered ring of two Pb and two F atoms. The Pb atoms in the ring are further connected by two AsF 6 units via cis-¯uorine bridges, thus forming a [PbFAsF 6 )] 2 cluster, which interacts by additional Pb±F bonds thus forming a ribbon-like polymer. # 2001 Elsevier Science B.V. All rights reserved. Keywords: PbHF)AsF 6 ) 2 ; PbFAsF 6 ; Crystal structure; Synthesis; Infrared; Raman spectra 1. Introduction MetalII)hexa¯uoroarsenatesV)arewidelyusedasstart- ing materials in coordination chemistry especially in sulfur dioxide as a solvent [1]. It was previously described that MAsF 6 ) 2 can be readily prepared from MF 2 and AsF 5 in aHF [2,3], but, according to our experience, depending on the purity of the starting materials and the reaction condi- tions,usuallyavarietyofphasesareformedwhichmakethe characterization of pure compounds practically impossible without crystal structure determinations. Only a few crystal structures of metalII) hexa¯uoroarsenatesV) are known to date. In MnAsF 6 ) 2 the MnII) shows the unusually high coordination number 8 in a pure ¯uorine environment [4]. The structure of SnF 2 AsF 5 consists of discrete cyclic Sn± F) 3 3 cations and octahedral AsF 6 anions [5]. The crystal structure of AgF 2 AsF 5 is built up from an in®nite, ¯uorine- bridged Ag F n n chain and AsF 6 octahedra cross- linked to these chains via further ¯uorine bridges [6]. These few examples give an impression of the great structural variety of pure metalII) hexa¯uoroarsenatesV), thus their synthesis and their crystal structure determination still pre- sent a challenge in the research work. 2. Results and discussion 2.1. Synthesis of PbHF)AsF 6 ) 2 The reaction between PbF 2 and excess of AsF 5 inaHFas solvent reaction 1) yields a colorless solution of solvated Pb 2 cations and AsF 6 anions. PbF 2 nAsF 5 ! 295K aHF PbHF x 2 2AsF 6 n 2AsF 5 ; n 2 1) A clear solution is obtained when the molar ratio between PbF 2 :AsF 5 is reached. Excess of AsF 5 is not necessary although the reaction proceeds with a higher rate in aHF made acidic with excess of AsF 5 . PbHF)AsF 6 ) 2 was obtained as a white solid after removal of excess AsF 5 and aHF. In [2] this compound was erroneously reported Journal of Fluorine Chemistry 110 2001) 123±131 * Corresponding author. Tel.: 386-1-477-3540; fax: 386-1-423-2125. E-mail address: boris.zemva@ijs.si B. Z Ï emva). 0022-1139/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0022-113901)00419-5