Tetravalent Metal Ion Guests in Polyoxopalladate Chemistry: Synthesis and Anticancer Activity of [MO 8 Pd 12 (PO 4 ) 8 ] 12− (M = Sn IV , Pb IV ) Peng Yang, †,△ Tian Ma, † Zhongling Lang, ‡ Sonja Misirlic-Dencic, § Andjelka M. Isakovic, § Attila Be ́ nyei, # Mirjana B. C ̌ olovic ́ , ∥ Ivanka Markovic, § Danijela Z. Krstic ́ , ⊥ Josep M. Poblet, ‡ Zhengguo Lin,* ,†,∇ and Ulrich Kortz* ,† † Department of Life Sciences and Chemistry, Jacobs University, Campus Ring 1, 28759 Bremen, Germany ‡ Departament de Química Física i Inorga ̀ nica, Universitat Rovira i Virgili, c/Marcel·lí Domingo 1, 43007 Tarragona, Spain § Institute of Medical and Clinical Biochemistry, Faculty of Medicine, ∥ Department of Physical Chemistry, “Vinč a” Institute of Nuclear Sciences, and ⊥ Institute of Medical Chemistry, Faculty of Medicine, University of Belgrade, Belgrade, Serbia # University of Debrecen, Department of Physical Chemistry, Egyetem té r 1, 4032 Debrecen, Hungary ∇ Key Laboratory of Cluster Science, Ministry of Education of China, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, P.R. China * S Supporting Information ABSTRACT: The first two examples of polyoxopalladates(II) (POPs) containing tetravalent metal ion guests, [MO 8 Pd 12 (PO 4 ) 8 ] 12− (M = Sn IV , Pb IV ), have been prepared and structurally characterized in the solid state, solution, and gas phase. The interactions of the metal ion guests and the palladium-oxo shell were studied by theoretical calculations. The POPs were shown to possess anticancer activity by causing oxidative stress inducing caspase activation and consecutive apoptosis of leukemic cells. ■ INTRODUCTION At the cutting edge of polyoxometalate (POM) chemistry, polyoxo-noble-metalates (PONMs) represent an emerging class of molecular noble metal-oxo nanoclusters, usually prepared via self-condensation of square-planar (Pd II O 4 or Au III O 4 ) building units in aqueous media, and terminated by external heterogroups (e.g., AsO 4 3− , PO 4 3− , and SeO 3 2− ) capping the discrete assemblies. 1,2 Polyoxopalladates(II) (POPs), as the most significant subset of PONMs, have witnessed an impressive development ever since the pioneering discovery in 2008 of the first POP, [Pd 13 O 8 (AsO 4 ) 8 H 6 ] 8− (Pd 13 ), 1b primarily engineered with a view to their salient physiochemical properties as well as broad applications, especially in noble metal-based catalysis. 3−7 Among the multitude of POP structures, the guest metal-encapsulated, cuboid-shaped [MO 8 Pd 12 L 8 ] n− 3b−f,5a,b and the star-shaped [MO 10 Pd 15 L 10 ] n− 4,5a (M = guest metal ion, L = heterogroup), constitute the dominant motifs. It has been well-established that the guest M covers as many as 30 different metal ions with charges ranging from +1 to +3 and ionic radii across the periodic table. Particularly, in previous work we had predicted that tetravalent cations (e.g., Sn IV and Pb IV ) are also potential candidates for encapsulation inside the Pd 12 host. 5b To enrich the host−guest chemistry of POPs and to try and unravel the associated formation mechanism, the incorporation of tetravalent metal ions into POPs is promising from a structural perspective, but perhaps also relevant en route to biofunctional materials. Albeit supported by computational studies, it proved to be experimentally rather challenging to incorporate tetravalent metal ions into POP shells. Here we report on two POP nanocubes incorporating the tetravalent metal ions Sn IV and Pb IV . ■ EXPERIMENTAL SECTION Materials and Physical Measurements. All reagents were purchased from commercial sources and used without further purification. The 31 P NMR spectra of the obtained compounds were recorded on a 400 MHz JEOL ECX instrument at room temperature, using 5 mm tubes for 31 P with resonance frequency 162.14 MHz. The chemical shift is reported with respect to the reference 85% H 3 PO 4 . The FT-IR spectra were recorded on KBr disk using a Nicolet-Avatar 370 spectrometer between 400 and 4000 cm −1 . Received: April 17, 2019 Article pubs.acs.org/IC Cite This: Inorg. Chem. XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.inorgchem.9b01129 Inorg. Chem. XXXX, XXX, XXX−XXX Downloaded via NOTTINGHAM TRENT UNIV on August 14, 2019 at 20:34:56 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.