Inorg. Chem. 2009, 48, 11513–11517 11513 DOI: 10.1021/ic901229d Quaternary Neptunium Compounds: Syntheses and Characterization of KCuNpS3, RbCuNpS3, CsCuNpS3, KAgNpS3, and CsAgNpS3 Daniel M. Wells,† Geng Bang Jin,† S. Skanthakumar,‡ Richard G. Haire,§ L. Soderholm,‡ and James A. Ibers*,† †Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, ‡Chemical Science and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, and §Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 Received June 25, 2009 The five quaternary neptunium compounds KCuNpS3, RbCuNpS3, CsCuNpS3, KAgNpS3, and CsAgNpS3 (AMNpS3) have been synthesized by the reaction of Np, Cu or Ag, S, and K2SorRb2S3 or Cs2S3 at 793 K (Rb) or 873 K. These isostructural compounds crystallize as black rectangular plates in the KCuZrS3 structure type in space group Cmcm of the orthorhombic system. The structure comprises MS4 (M=Cu or Ag) tetrahedra and NpS6 octahedra that edge share 2 - to form ¥[MNpS3 ] layers. These layers are separated by the alkali-metal cations. The Np-S bond lengths vary from 2.681(2) to 2.754(1)A˚. When compared to the corresponding isostructural Th and U compounds these bond distances obey the expected actinide contraction. As the structure contains no S-S bonds, formal oxidation states of þ1/þ1/þ4/-2 may be assigned to A/M/Np/S, respectively. From these results a value of 2.57 for the bond-valence 4þ 2- parameter r0 for Np -S has been derived and applied to the estimation of the formal oxidation states of Np in the binary NpxSy compounds whose structures are known. Introduction these aspects of Np chemistry, soft chalcogen-containing The solid-state chemistry of Np is thought to be inter- ligands have been used extensively in actinide organometallic and separations chemistry,6 and actinide chalcogenides have mediate between those of U and Pu, but the dearth of well- 7 characterized examples of Np compounds remains an im- been investigated as potential fuels for future fast reactors. A pediment to the full understanding of its chemistry. This is fundamental understanding of Np chalcogenide solid-state especially true for the non-oxide, non-neptunyl compounds chemistry is clearly relevant and is needed for these potential where the stability of Np in multiple oxidation states is higher applications. and such properties as superconductivity1,2 and non-Fermi Even though many binary neptunium chalcogenides have liquid behavior3,4 have been observed. Np is produced both been characterized by powder X-ray diffraction methods, only the cubic NpQ (Q=S, Se, or Te) compounds have been by the irradiation of U and as a byproduct in the production 8 of important Pu isotopes. Understanding its chemistry is characterized by single-crystal X-ray diffraction methods. Most of the other known NpxQy compounds resemble the essential for efficient separations of spent nuclear fuel, 4þ addressing high-level radioactive waste, and production of corresponding UxQy compounds and usually contain Np , 5237 but some resemble the corresponding LnxQy compounds special Pu isotopes. Np has also been highlighted as a 3þ 5,9 “burnable” isotope for future reactor fuels.5 In addition to (Ln = rare-earth metal) and presumably contain Np . Other than the NpxQy compounds, NpTQ (T=O, As, or Sb; 10-14 *To whom correspondence should be addressed. E-mail: ibers@chem. Q = S, Se, or Te), the superconducting Chevrel phase northwestern.edu. Phone: +1 847 491 5449. Fax: +1 847 491 2976. (1) Damien, D.; de Novion, C. H.; Gal, J. Solid State Commun. 1981, 38, – – (6) Nash, K. L. Solvent Extr. Ion Exch. 1993, 11, 729 768. 437 440. (7) Allbutt, M.; Dell, R. M. J. Nucl. Mater. 1967, 24,1–20. (2) Aoki, D.; Haga, Y.; Matsuda, T. D.; Tateiwa, N.; Ikeda, S.; Homma, (8) Wastin, F.; Spirlet, J. C.; Rebizant, J. J. Alloys Compd. 1995, 219, 232– Y.; Sakai, H.; Shiokawa, Y.; Yamamoto, E.; Nakamura, A.; Settai, R.; 237. Onuki, Y. J. Phys. Soc. Jpn. 2007, 76, 063701/1–063701/4. (9) Thevenin, T.; Pages, M.; Wojakowski, A. J. Less-Common Met. 1982, (3) Stewart, G. R.; Kim, J. S.; Sykora, R. E.; Haire, R. G. Physica B 2006, 84, 133–137. 378-380,40–43. (10) Zachariasen, W. H. Acta Crystallogr. 1949, 2, 291–296. (4) Arko, A. J.; Joyce, J. J.; Havela, L. In The Chemistry of the Actinide (11) Charvillat, J. P.; Wojakowski, A.; Damien, D. Proc. Int. Conf. and Transactinide Elements, 3rd ed.; Morss, L. R., Edelstein, N. M., Fuger, J., Electron. Struct. Actinides, 2nd 1976, 469–473. Eds.; Springer: Dordrecht, The Netherlands, 2006; Vol. 4, pp. 2307-2379. (12) Blaise, A.; Charvillat, J. P.; Salmon, P.; Wojakowski, A. Proc. Int. (5) Yoshida, Z.; Johnson, S. G.; Kimura, T.; Krsul, J. R. In The Chemistry Conf. Electron. Struct. Actinides, 2nd 1976, 475–481. of the Actinide and Transactinide Elements, 3rd ed.; Morss, L. R., Edelstein, N. (13) Blaise, A.; Collard, J. M.; Fournier, J. M. J. Phys., Lett. 1984, 45,L- M., Fuger, J., Eds.; Springer: Dordrecht, The Netherlands, 2006; Vol. 2,pp 571–L-576. 699-812. (14) Wojakowski, A. J. Less-Common Met. 1985, 107, 155–158. r 2009 American Chemical Society Published on Web 08/25/2009 pubs.acs.org/IC 11514 Inorganic Chemistry, Vol. 48, No. 24, 2009 Wells et al. 1,15 37 Np1þxMo6Se8, and the recently synthesized compound science for its simplicity. The method has found applica- 16 NpCuSe2 are known. The results of magnetic measurements tions in crystallography, solid-state physics, mineralogy, and suggest that the compounds NpTQ (T=As or Sb, Q=S, Se, biology.37 Extending this simplistic bonding model to acti- 11,13 1,15 3þ or Te) and Np1þxMo6Se8 contain Np , but that the nide chemistry may help explain the stability of the many compounds NpOQ (Q = S and Se) contain Np4þ.17,18 On the oxidation states found in the early actinides and expand our basis of powder X-ray diffraction measurements the NpTQ understanding of the localization or itineracy of the 5f compounds are isostructural to the corresponding U com- electrons. The model has been extended to neptunyl, nþ 38,39 pounds, whereas the Np1þxMo6Se8 compound is isostructural NpO2 , compounds. Here we use the structural results to the corresponding Ln compounds. NpCuSe2 is isostructural on the title Np compounds to calculate the bond-valence 16 4þ 2- to known LnCuSe2 compounds. parameter r0 for Np -S and then probe oxidation states The five quaternary compounds KCuNpS3,KAgNpS3, in the known binary NpxSy compounds. RbCuNpS3, CsCuNpS3,andCsAgNpS3 presented here crys- 19 tallize in the KCuZrS3 structure type. This highly stable Experimental Section structure is unusual in its ability to accommodate both rare- General Syntheses. The following reagents were used as earth and actinide elements in a wide variety of combinations obtained from the manufacturer: K (Cerac, 98%), Rb (Strem, of alkali- or alkaline-earth metals (A = K, Rb, Cs, Sr, or Ba) 99%), Cs (Aldrich, 99.5%), Cu (Aldrich, 99.5%), Ag (Aldrich, and mono- or divalent transition metals (M=Cu, Ag, Au, Mn, 99.99%), and S (Mallinckrodt, 99.6%). Brittle 237Np chunks 20-30 Co, Zn, Cd, Hg). For the actinides of formula AMAnQ3, (ORNL, 99.99%) were crushed and used as provided. The 40 the examples at this time are limited to combinations of A=K, reactive fluxes used in these syntheses, K2S, Rb2S3, and 31-36 Rb,Cs;M=Cu,Ag,Au;An=ThorU. Formal Cs2S3, were prepared by stoichiometric reactions of the elements þ þ þ - oxidation states here can be described as A1 M1 An4 (S2 ) . in liquid NH3. 3 Caution! 237 R γ Thus, before this work no corresponding Np compounds were Np is an - and -emitting radioisotope and as such known and no Pu compounds are currently reported. it is considered a health risk. Its use requires appropriate infra- structure and personnel trained in the handling of radioactive The bond-valence model, though empirical, has become materials. To minimize the risk of reaction-vessel failures, all popular throughout solid-state chemistry and material reaction vessels in this work consisted of primary and secondary containment. Primary containment was supplied by standard carbon-coated fused-silica ampules. Secondary containment com- (15) de Novion, C. H.; Damien, D.; Hubert, H. J. Solid State Chem. 1981, prised a combination of mechanical containment that consisted of 39, 360–367. (16) Wells, D. M.; Skanthakumar, S.; Soderholm, L.; Ibers, J. A. Acta stainless steel tubing with tongue and groove caps and chemical Crystallogr., Sect. E: Struct. Rep. Online 2009, 65, i14. containment that was provided by a larger second fused-silica (17) Collard, J. M.; Blaise, A.; Boge, M.; Bonnisseau, D.; Burlet, P.; ampule. Further precautions were taken by heating all reactions in Fournier, J. M.; Larroque, J.; Beauvy, M. J. Less-Common Met. 1986, 121, a computer-controlled high-temperature furnace equipped with 313–318. both standard and runaway controllers. The furnace was located (18) Amoretti, G.; Blaise, A.; Boge, M.; Bonnisseau, D.; Burlet, P.; inside a negative-pressure hood. Collard, J. M.; Fournier, J. M.; Quezel, S.; Rossat-Mignod, J.; Larroque, J. J. Magn. Magn. Mater. 1989, 79, 207–224. Syntheses. KCuNpS3 was prepared from a reaction mixture (19) Mansuetto, M. F.; Keane, P. M.; Ibers, J. A. J. Solid State Chem. of 0.086 mmol Np, 0.086 mmol Cu, 0.043 mmol K2S, and 1992, 101, 257–264. 0.258 mmol S. KAgNpS3 was prepared from a reaction mixture (20) Wu, P.; Christuk, A. E.; Ibers, J. A. J. Solid State Chem. 1994, 110, of 0.084 mmol Np, 0.084 mmol Ag, 0.042 mmol K2S, and 337–344.