Herein, a giant Sb-rich polyoxometalate (POM) {Sb 21 Tb 7 W 56 } is reported, which contains the largest number of Sb atoms in a POM so far. The Sbrich POM has many interesting structural features and is a rare example of a soluble and water-stable giant POM. Biomedical studies indicate that the Sb-rich POM exhibits broad-spectrum antitumor activity against various cancer cell lines by reactivating the P53-dependent apoptotic processes and disrupting the mitochondrial membrane. In addition, this Sb-rich POM was capable of suppressing the growth and metastasis of a breast cancer in vivo. This work demonstrates that Sb-rich POMs are promising candidates for the development of new anticancer drugs.Cancer remains the most malignant disease worldwide with high morbidity and mortality. [1] Although the development of therapeutic modalities has never stopped, chemotherapy remains one of the most prevalent therapeutic regimens. To date, chemotherapeutics based on organic, inorganic and hybrid species have been developed. [2] However, chemotherapeutics cause severe adverse effects including multiple organ failures and myelosuppression. [3] Thus, the exploration of new anticancer drugs with higher potencies and lower systemic toxicities remains challenging and requires longterm research.Polyoxometalates (POMs) have shown promising applications in various fields due to their unique structural features and rich physical and chemical properties, e.g. oxorich surface, tunable acid-base and redox properties. [4,5] These intriguing features also endow POMs with versatile bioactivities in the combat against viruses, bacteria and tumors. [6] Antimony, one heavy pnictogen, has been medicinally used for over 100 years. [7] Due to the stereo activity of the lone electron-pair, Sb-complexes can target protein tyrosine phosphatases and increase the generation of reactive oxygen species, leading to the apoptosis of cancer cells. [8] Recently, the introduction of Sb ions into POMs creating Sb-containing POMs has attracted increasing attention, because such composite POMs synergize the advantages of POMs and Sb, and thus become promising antitumor agents. [9] For example, {Co 4 Sb 9 W 24 }, [10] {Na 0.7 M 5.3 Sb 2 W 18 } (M = Ni/Co), [11] and {SbW 8 O 30 } [12] are reported to exhibit excellent antitumor activities. However, it is noteworthy that the known antitumor Sb-containing POMs are small-tomedium nuclearity (< 50) POMs with only a few Sb atoms (� 9, Table S1), and the incorporated Sb atoms in those POMs usually serve as heteroatoms wrapped by W/Mo shells, [13] which might hinder the contact with cancer cells thus impairing the antitumor activities of Sb. So, it is of great scientific interest to investigate whether increasing the nuclearity number of Sb atoms in a POM would improve the bioactivity against cancers. However, such studies remain largely unexplored due to the lack of Sb-rich POMs.Here, a rare and giant (> 2 nm) soluble Sb-rich POM H 27 [Sb 15 Tb 7 W 3 O 29 (OH) 3 (DMF)(H 2 O) 6 (SbW 8 O 30 )(SbW 9 O 33 ) 5 ]• 30 H 2 O ...
