pubs.acs.org/IC Published on Web 08/26/2009 r 2009 American Chemical Society 9036 Inorg. Chem. 2009, 48, 9036–9040 DOI: 10.1021/ic901283k Soft-Hard Acid-Base Interactions: Probing Coordination Preferences of Sulfur and Selenium in Mixed Chalcophosphates in the Family APbPS 4-x Se x (A = K, Rb, Cs; x =0-4) Alexander Rothenberger, † Collin Morris, † Hsien-Hau Wang, ‡ Duck Young Chung, ‡ and Mercouri G. Kanatzidis* ,†,‡ † Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, and ‡ Materials Science Division (Bldg. 223), Argonne National Laboratory, 9700 S. Cass Ave., Argonne, Illinois 60439 Received July 3, 2009 The synthesis and structures of the three new compounds, KPbPS 1.84 Se 2.16 (1), RbPbPS 1.56 Se 2.43 (2), and CsPbPS 3.46 Se 0.54 (3), are reported. The solid state structures of 1-3 consist of two-dimensional layers of [PbP- (S/Se) 4 ] separated by alkali metal ions. The structure of 1 was solved in the orthorhombic space group Pna2 1 . Compounds 2 and 3 possess the CsSmGeS 4 structure type, crystallizing in the orthorhombic space group P2 1 2 1 2 1 . All compounds were refined as racemic twins. All chalcogen sites around the tetrahedrally coordinated P atoms show mixed S/Se occupancy; however, there is a preference for Se binding to Pb ions and S binding to alkali ions. A 31 P magic angle spinning NMR study on 1 suggests that, in mixed seleno-/thiophosphates, all of the anions [PS x Se 4-x ] 3- (x = 0, 1, 2, 3, 4) are present. The different amount of sulfur and selenium present in KPbPS 1.84 Se 2.16 (1), RbPbPS 1.56 Se 2.43 (2), and CsPbPS 3.46 Se 0.54 (3) is reflected in the solid state absorption spectra from which bandgaps of 2.2 eV were determined for 1 and 2, and a blue-shift to 2.5 eV was observed because of the higher sulfur- content in 3. Thermogravimetric analysis experiments indicated that, upon heating, compound 1 decomposes forming PbSe and sulfur together with other unidentified products. A Raman spectrum of compound 1 showed more bands than are usually observed in seleno- or thiophosphate salts and is another indicator of the mixed seleno-/thiophosphate anions found in 1. Introduction A great variety of selenophosphate anions have been synthesized, including the discrete anions [PSe 4 ] 3- , 1 [P 2 Se 6 ] 4- , 2,3 [P 2 Se 9 ] 4- , 4 and [P 8 Se 18 ] 6- 5 and the polymeric anions 1/ ¥ [P 2 Se 6 2- ], 6 1/ ¥ [PSe 6 - ], 7 and 1/ ¥ [P 5 Se 10 5- ]. 8 In order to enhance the properties of metal selenophosphates for potential use in semiconducting devices, 9 as phase-change materials in read-write devices, and as nonlinear optical materials, 6 several new directions are pursued. A promising route involves the incorporation of heavy and polarizable p-block elements into selenophosphate coordination en- vironments. In Cs 5 BiP 4 Se 12 , for example, the complex anion [Bi(P 2 Se 6 ) 2 ] 5- is held together by weak Se 333 Se interactions, and the phase can be processed to transparent fibers. These are transparent in the near- and mid-IR ranges and were found to exhibit a nonlinear optical second harmonic gen- eration response at 1 μm that is approximately twice that of the benchmark material AgGaSe 2 . 10 Less established is the modification of the chalcophosphate anions, for example, by mixing group 16 elements Q in [PQ 4 ] 3- anions or other chalcophosphate derivatives. 11,12 Whereas the thiophosphate anions [PO x S 4-x ] 3- (x =1-3) can be readily obtained by the treatment of P 4 S 10 or PSCl 3 with aqueous NaOH solutions, 13-19 similar reactions of P 2 Se 5 resulted in the *To whom correspondence should be addressed. Fax: þ1-847-491-5937. E-mail: m-kanatzidis@northwestern.edu. (1) Knaust, J. M.; Dorhout, P. K. J. Chem. Crystallogr. 2006, 36, 217–223. (2) Francisco, R. H. P.; Tepe, T.; Eckert, H. J. Solid State Chem. 1993, 107, 452–459. (3) (a) McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1995, 34, 1257– 1267. (b) McCarthy, T. J.; Kanatzidis, M. G. Chem. Mater. 1993, 5, 1061–1063. (4) Chondroudis, K.; McCarthy, T. J.; Kanatzidis, M. G. Inorg. Chem. 1996, 35, 840–844. (5) Chondroudis, K.; Kanatzidis, M. G. Inorg. Chem. 1998, 37, 2582–2584. (6) Chung, I.; Malliakas, C. D.; Jang, J. I.; Canlas, C. G.; Weliky, D. P.; Kanatzidis, M. G. J. Am. Chem. Soc. 2007, 129, 14996–15006. (7) Banerjee, S.; Malliakas, C. D.; Jang, J. I.; Ketterson, J. B.; Kanatzidis, M. G. J. Am. Chem. Soc. 2008, 130, 12270-12272. (8) Chondroudis, K.; Kanatzidis, M. G. Angew. Chem., Int. Ed. 1997, 36, 1324–1326. (9) Afzaal, M.; O’Brien, P. J. Mater. Chem. 2006, 16, 1597–1602. (10) Chung, I.; Song, J.-H.; Jang, J. I.; Freeman, A. J.; Ketterson, J. B.; Kanatzidis, M. G. J. Am. Chem. Soc. 2009, 131, 2647–2656. (11) Gagor, A.; Pietraszko, A.; Panko, V. V. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2008, 64, I33–I34. (12) Evain, M.; Queignec, M.; Brec, R.; Sourisseau, C. J. Solid State Chem. 1988, 75, 413–431. (13) Kubierschky, C. J. Prakt. Chem. 1885, 31, 93–111. (14) Yasuda, S. K.; Lambert, J. L. Inorg. Synth. 1957, 5, 102–104.