COMMUNICATIONS dihydroxynaphthalene or 3,4-dihydroxybenzoate (extinction of blue qualify for Zintl phases when a broader definition is used. The l fluorescence at em 440 nm upon oxidation to the quinone). Nor- latter includes compounds of transition metals with filled or adrenaline reacts similarly to adrenaline down to pH 5. Adreno- empty d shells, that is the late transition metals of the Ni, Cu, chrome (2) is unstable and polymerizes to brown and finally insoluble [2] black products upon prolonged standing in solution. and Zn groups, and the early transition elements of the Ti, V, [14] a) M. Simmel, M. Turunen, J. Piironen, T. Vaara, VTT Symp. 1991, 122, and Cr groups at maximum formal oxidation states.[3] There 145 ± 161; b) R. J. Wodzinski, A. H. J. Ullah, Adv. Appl. Microbiol. are only two Zintl compounds containing a transition metal 1996, 42, 263 ± 302. with partially filled d shell, both based on manganese, [15] B.-L. Liu, A. Rafiq, Y.-M. Tzeng, A. Rob, Enzyme Microbiol. Technol. 1998, 22, 415 ± 424. (AE)14MnPn11 (AE alkaline-earth metal, Pn pnictogen) [4] [16] A. H. J. Ullah, D. M. Gibson, Prep. Biochem. 1987, 17, 63 ± 91. and Sr21Mn4Sb18 . Perhaps only they should be called true [17] Several kits for the titration of inorganic phosphate based on the ™transition metal Zintl phases∫ although the name is contra- reaction with ammonium molybdate are available commercially. dictory in itself. All but two of the d0 compounds contain Methyl-umbelliferyl phosphate and 4-nitrophenyl phosphate are isolated tetrahedra [MPn ]nÀ (M Nb, Ta, W, Ti).[5] The two general fluorogenic and chromogenic substrates for phosphatases 4 but do not enable phytases to be distinguished from other phospha- exceptions are Na5HfAs3 with dimers of edge-sharing tetra- 10À tases, in contrast to assays based on phytic acid. See also R. P. hedra of [Hf2As6] and Rb5TaAs 4Tl2 with [TaAs4] tetrahe- Haughland, Handbook of Fluorescent Probes and Research Chem- dra, where two Tl atoms bridge opposite edges, (m-Tl)- icals, 6th ed., Molecular Probes, Eugene, OR (USA), 1995. [As TaAs ](m-Tl)5À.[6] Here we report a new d0 transition [18] A. Archelas, R. Furstoss, Curr. Opin. Chem. Biol. 2001, 5, 112 ± 119. 2 2 [19] X.-J. Chen, A. Archelas, R. Furstoss, J. Org. Chem. 1993, 58, 5528 ± metal Zintl phase, Cs7NbIn3As4 , which contains an unprece- À 7À 5532. dented anion, [{In3As4Nb} As] , a cubane made of three [20] C. A. G. M. Weijers, A. L. Botes, M. S. van Dyk, J. A. M. de Bont, indium, four arsenic, and one niobium atom and a ™handle∫ Tetrahedron: Asymmetry 1998, 9, 467± 473. composed of an arsenic atom that is multiply bonded to the [21] a) An earlier endpoint assay measured the unreacted epoxide by niobium corner. reaction with excess 4-(p-nitrobenzyl)pyridine at 808C for 30 min to l The title compound was initially made in an attempt to give a colored product ( max 560 nm). This assay only works with reactive epoxides (e.g. oxiranes, styrene oxide, n-hexane oxide, indene synthesize the recently reported Cs5In3As4 at temperatures oxide). R. Serrentino, P. G. Gervati, Boll. Soc. Ital. Biol. Sper. 1980, 56, higher than the original 5008C.[7] The reaction was carried out 2393 ± 2397; b) For a version of the assay using microtiter plates and in niobium containers at 8008C, at which temperature the filter paper, see: F. Zocher, M. M. Enzelberger, U. T. Bornscheuer, B. Hauer, R. D. Schmid, Anal. Chim. Acta 1999, 391, 345 ± 351; c) see also arsenic apparently attacked the container and formed the ref. [11] for fluorogenic and chromogenic substrates for epoxide quaternary compound Cs7NbIn3As4. Later it was synthesized hydrolases. in high yield using the corresponding elements in stoichio- [22] J. L. Reymond, T. Koch, J. Schrˆder, E. Tierney, Proc. Natl. Acad. Sci. metric ratio at the same temperature.[8] USA 1996, 93, 4251 ± 4256. The overall structure of Cs NbIn As is quite simple and [23] M. T. Reetz, M. H. Becker, H.-W. Klein, D. Stˆckigt, Angew. Chem. 7 3 5 [9] 1999, 111, 1872 ± 1875; Angew. Chem. Int. Ed. 1999, 38, 1758 ± 1761. unremarkable, an ionic assembly of isolated anions of 7À [24] M. T. Reetz, K. M. K¸hling, A. Deege, H. Hinrichs, D. Belder, Angew. [NbIn3As5] immersed in a ™sea∫ of cesium cations that Chem. 2000, 112, 4049 ± 4052; Angew. Chem. Int. Ed. 2000, 39, 3891 ± screen them from each other (inter-anion dmin 5.009(4) ä). 3893. What is remarkable is the structure and bonding of the anion (Figure 1). Its geometry can be viewed in a few different ways. The more obvious approach is to recognize the cubane shape made of one Nb, three In, and four As atoms, [NbIn3As4], and its ™handle∫ of a fifth arsenic atom attached to the niobium À 7À Cubane with a Handle: [{In3As4Nb} As] in Cs7NbIn3As5** Franck Gascoin and Slavi C. Sevov* Compared to the large number of main group Zintl compounds there are only a few that contain transition metals.[1] This is not surprising since the traditional definition of Zintl phases automatically excludes transition metals. However, many such compounds with transition metals can [*] Prof. S. C. Sevov, F. Gascoin Figure 1. Structure of the cubane with a ™handle∫ [{As(InAs) }NbAs]7À Department of Chemistry and Biochemistry 3 (ORTEP drawing; thermal ellipsoids at the 95 % probability level). The University of Notre Dame unusually short distance of the handle is shown. The remaining distances Notre Dame, IN 46556 (USA) [ä] are: Nb-As2 2.484(2), Nb-As3 2.526(2), Nb-As4 2.535(2), In1-As2 Fax : (1) 219-631-6652 2.834(2), In1-As3 2.794(2), In1-As5 2.908(2), In2-As2 2.864(2), In2-As4 E-mail: [email protected] 2.789(2), In2-As5 2.894(2), In3-As3 2.845(2), In3-As4 2.822(2), In3-As5 [**] This work was supported by the National Science Foundation (CHE- 2.858(2). The angles [8] at Nb and As5 are in the range 107.26(7)± 112.82(7) 0098004). We also thank the Petroleum Research Fund, administered and 79.32(5) ± 80.27(5), respectively. The angles around As2, As3, and As4 by the ACS, for partial support of this research. fall in the range 78.15(6) ± 82.09(5)8. The angles at the indium atoms that Supporting information for this article is available on the WWW under involve As5, 98.34(5) ± 99.28(6)8, are larger that those that do not, http://www.wiley-vch.de/home/angewandte/ or from the author. 91.25(5) ± 92.20(5)8. 1232 ¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1433-7851/02/4107-1232 $ 20.00+.50/0 Angew. Chem. Int. Ed. 2002, 41,No.7 COMMUNICATIONS corner of the cube (Figure 1). Cubane is quite a popular shape bonding in the above compounds and in [{As(InAs)3} especially for combinations of four transition metal (M) and NbÀAs]7À is based on the p interactions between the empty [10] four chalcogen (Ch) atoms, M4Ch4 . Recently reported was dxz and dyz orbitals on the transition metal and the filled pp also a main group cation with the same geometry, orbitals on the arsenic center. Furthermore, while the two 4 [11] [Bi4Te 4] . In all of these systems the two atom types arsenidines [L3Ta AsPh] and [L3Nb AsTol] are bent at the alternate at the cubane corners providing equidistant MÀCh arsenic and indicate sp2 hybridization (maximum bond order edges. In [NbIn3As4], however, the cubane is uneven as one of 2), the naked arsenide ligand can be viewed as sp- vertex is occupied by a niobium instead of an indium atom hybridized where both px and py orbitals are available for (Figure 1). Thus, three of the cubane edges are NbÀAs bonds p interactions. This is the only arsenic atom in À À 7À p that are shorter (dav 2.520 ä) than the In As bonds of the [{As(InAs)3}Nb As] that is capable of interactions with remaining nine edges (dav 2.842 ä). This leads to substantial the Nb d orbitals, since the arsenic atoms of the tridentate distortion of the cube such that the niobium corner becomes ligand are ™forced∫ to be sp3-hybridized. This results in the closer to the cubane center than the other corners, and the rest very short distance of 2.390(2) ä, and the bonding can be of the cubane is compressed around the NbÀAs5 body schematically represented as a hybrid of (h3-L)MAs $ diagonal (Figure 1). All angles at As5 are, for example, (h3-L)MAsÀ $ (h3-L)M2ÀAs2À. For comparison, the aver- 8 À 7À noticeably smaller than 90 , while those at Nb and the As5-In- age Nb As distance of 2.50 ä in the tetrahedral [NbAs4] ion As angles are larger than 908. The InÀAs distances are longer is longer because all four arsenic atoms are capable of p [5] than those of four-bonded indium atoms in Cs5In3As4 , interactions. According to molecular orbital analysis the [7, 12] 0 K4In4As6, and Na3InAs2 (dav 2.70 ä), but are closer to bond order for each bond in tetrahedral d species such as the the distances of similarly three-bonded indium atoms in latter is 2.25 (nine available bonding molecular orbitals), [7] Cs5In3As4 (dav 2.90 ä). The elongation is very likely due to while it is 3.00 for tetrahedral species in which only one of the the stronger repulsion between the lone pair at the three- ligands has pp orbitals such as the single arsenic center in À 7À [16] bonded indium and the one or more lone pairs at the arsenic [{As(InAs)3}Nb As] .