Polyoxovanadates: High-Nuclearity Spin Clusters with Interesting Host-Guest Systems and Different Electron Populations. Synthesis, Spin Organization, Magnetochemistry, and Spectroscopic Studies Achim Mu 1 ller,* ,² Roberta Sessoli, ‡ Erich Krickemeyer, ² Hartmut Bo 1 gge, ² Jochen Meyer, ² Dante Gatteschi,* ,‡ Luca Pardi, § Jo 1 rg Westphal, ² Kai Hovemeier, ² Ralf Rohlfing, ² Joachim Do 1 ring, ² Frank Hellweg, ² Christian Beugholt, ² and Marc Schmidtmann ² Fakulta ¨t fu ¨r Chemie, Lehrstuhl fu ¨r Anorganische Chemie I, Universita ¨t Bielefeld, D-33501 Bielefeld, Germany, and Dipartimento di Chimica, Universita ` di Firenze, I-50144 Firenze, Italy ReceiVed March 27, 1997 X The compounds Cs 12 [V IV 18 O 42 (H 2 O)]‚14H 2 O(1a), K 12 [V IV 18 O 42 (H 2 O)]‚16H 2 O(1b), Rb 12 [V IV 18 O 42 (H 2 O)]‚19H 2 O (1c), K 9 [H 3 V IV 18 O 42 (H 2 O)]‚14H 2 O‚4N 2 H 4 (1d), K 11 [H 2 V IV 18 O 42 (Cl)]‚13H 2 O‚2N 2 H 4 (2a), K 9 [H 4 V IV 18 O 42 (Br)]‚- 14H 2 O‚4N 2 H 4 (2b), K 9 [H 4 V IV 18 O 42 (I)]‚14H 2 O‚4N 2 H 4 (2c), K 10 [H 3 V IV 18 O 42 (Br)]‚13H 2 O‚0.5N 2 H 4 (2d), K 9 - [H 4 V IV 18 O 42 (NO 2 )]‚14 H 2 O‚4N 2 H 4 (3), Cs 11 [H 2 V IV 18 O 42 (SH)]‚12H 2 O(4), K 10 [HV IV 16 V V 2 O 42 (Cl)]‚16H 2 O(5a), Cs 9 [H 2 V IV 16 V V 2 O 42 (Br)]‚12H 2 O(5b), K 10 [HV IV 16 V V 2 O 42 (Br)]‚16H 2 O(5c), Cs 9 [H 2 V IV 16 V V 2 O 42 (I)]‚12H 2 O(5d), K 10 [HV IV 16 V V 2 O 42 (I)]‚16H 2 O(5e), K 10 [HV IV 16 V V 2 O 42 (HCOO)]‚15H 2 O(6), (NEt 4 ) 5 [V IV 10 V V 8 O 42 (I)] (7), and Na 6 - [H 7 V IV 16 V V 2 O 42 (VO 4 )]‚21H 2 O(8) have been characterized by elemental analyses, redox titrations, IR and EPR spectroscopy, and magnetic susceptibility measurements, as well as by single crystal X-ray structure analyses. The anions containsas a common structural featuresan approximately spherical {V 18 O 42 } shell, which can act as a unique host system for neutral and anionic guests. Remarkably, the electron population of these clusters cansdepending on the specific reaction conditionssbe varied in a wide range between 10 and 18 3d electrons without changing the overall structure. The related magnetic properties in connection with the phenomenon of electron-dependent spin organization on a spherical cluster shell have been discussed in detail. Introduction Vanadium in its higher oxidation states tends to form polynuclear, anionic metal-oxygen clusters with an extraordi- nary variety of the relevant topology and electronic structures. 1 This variety can be attributed to the multitude of possibilities to link basic building blocks which correspond to {V n+ O x } polyhedra (x ) 4, 5, 6) like tetrahedra, tetragonal pyramids, or octahedra. The resulting structures range from quite compact forms, like in the case of V 10 O 28 6- , to open ribbon-, basket-, shell-, and cagelike host systems, 2 suitable for the uptake of neutral 3-6 as well as ionic guests. 7-16 In addition, also two- dimensional layered materials 17,18 as well as three-dimensional host structures 19 have been described in recent years. Apart from their interesting structural variety, polyoxovana- dates show remarkable, facile redox processes so that the species can exist with quite different electron populations. The corre- sponding clusters are of special interest for different aspects of bioinorganic and magnetochemistry but also for research in homogeneous and heterogeneous catalysis. 20 Whereas it is usually unproblematical today to determine the basic geometric structure even of rather complex polyvanadates, the determination of the electronic structure can be very complicated. This refers in particular to the problem of distinguishing for instance between cluster shells of the type V IV m V V n and V IV m-x V V n+x for large m and n and small values of x mainly if the calculation of the charge on the cluster anion is not possible due to difficulties in determining the degree of protonation and the number of cations with sufficient accuracy. To avoid errors, application of different physical apart from analytical methods is often indispensable. In order to confirm the obtained results the knowledge of magnetic susceptibility and EPR data is of utmost importance. In this paper, compounds with structurally equivalent {V 18 O 42 } shells but remarkably ² University of Bielefeld. ‡ University of Florence. § National High Magnetic Field Laboratory, Tallahassee, FL. X Abstract published in AdVance ACS Abstracts, October 1, 1997. (1) Pope, M. T.; Mu ¨ller A. Angew. Chem., Int. Ed. Engl. 1991, 30, 34. (2) Klemperer, W. G.; Marquart, T. A.; Yagi, O. M. Angew. 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Chem. 1997, 36, 5239-5250 S0020-1669(97)00364-9 CCC: $14.00 © 1997 American Chemical Society