Unprecedented High‐Nuclear Transition‐Metal‐Cluster‐Substituted Heteropolyoxoniobates: Synthesis by {V₈} Ring Insertion into the POM Matrix and Antitumor Activities

Abstract

Reactions of hexaniobate with vanadate in the presence of Ni(2+) , Zn(2+) , or Cu(2+) have furnished three high-nuclear vanadium cluster-substituted heteropolyoxoniobates (HPNs): {Ni(en)3 }5 H{V(V) Nb8 V(IV) 8 O44 }⋅9 H2 O (1), (H2 en)Na2 [{Zn(en)2 (Hen)}{Zn(en)2 (H2 O)}2 {PNb8 V(IV) 8 O44 }]⋅11 H2 O (2), and Na{Cu(en)2 }3 {[Cu(en)2 ]2 [PNb8 V(IV) 8 O44 ]}⋅11 H2 O (3) (en=1,2-diaminoethane). Their structures have been determined and characterized by single-crystal X-ray diffraction analysis, thermogravimetric analysis (TGA), and elemental analysis. Structural analysis has revealed that compounds 1-3 contain similar {V8 }-substituted [X(V) Nb8 V(IV) 8 O44 ](11-) (X=P, V) clusters, obtained by inserting a {V8 } ring into tetravacant HPN [XNb8 O36 ](27-) . To the best of our knowledge, compounds 1-3 represent the first high-nuclear vanadium cluster-substituted HPNs, and compound 1 is the largest vanadoniobate cluster yet obtained in HPN chemistry. Nickel and zinc cations have been introduced into HPNs for the first time, which might promise a more diverse set of structures in this family. Antitumor studies have indicated that compounds 1 and 2 exhibit high activity against human gastric cancer SGC-7901 cells, SC-1680 cells, and MG-63 cells.

A {Co4O4} Cubane Incorporated within a Polyoxoniobate Cluster

“…3 Generally, the synthetic strategy utilized to obtain TM‐containing PONbs has involved choosing a metal that is base‐soluble or protected by chelating ligands 2b. 4 Examples of this interesting type of PONb include copper‐containing derivatives {Cu 24 Nb 56 }5 and {Cu 25.5 Nb 56 },5 {CuNb 11 },1b titanium‐containing derivatives {Ti 12 Nb 6 },6a {TiNb 9 },6b and {Ti 2 Nb 8 },6c and vanadium‐containing derivatives {V 4 Nb 6 },4a {V 4 Nb 10 },7a {V 3 Nb 12 },4c, 7b {PV 2 Nb 12 },7c {V 8 Nb 8 },7d {PV 6 Nb 12 },7e and {VNb 14 } 7f. Some other TM‐containing PONbs are also known, such as {MNb 9 } (M=Co, Cr, Mn, Fe, Ni),8a,b {Cr 2 Nb 10 },8c {MnNb 10 },8d {MNb 12 } (M=Co, Mn, Ni),9a,b and {Co 14 Nb 36 } 4b.…”

Modified polyoxometalate: a novel monocapped bi-supporting and reduced α-Keggin structure {PMo12O40[Cu(2,2′-bpy)]}[Cu(2,2′-bpy)(en)(H2O)]2

“…Three strategies, i.e. reduction, substitution and lacunarity, were exploited to increase the surface charge density and activate the surface O atoms of a POM, for instance, changing M VI (M = Mo or W) to M V by a strong reducing agent (Han et al, 2014;Salomon et al, 2018;Sha et al, 2007), substituting high-oxidation-state Mo VI by lower oxidation state V IV or Nb V (Guo et al, 2011;Niu et al, 2010;Shen et al, 2014;Yuan et al, 2003), or removing MO 6 octahedra to form lacunary POMs (Al-Oweini et al, 2018;Zheng et al, 2008). Thus, various functionalized 'value-added' Keggin derivatives, such as capped, supported, substituted or extended structures, were self-assembled through incorporating or grafting transition metals, lanthanides, organometallic or organic groups onto the surface of polyoxoanions (Dolbecq et al, 2010;Gumerova & Rompel, 2018;Zhao et al, 2016).…”

“…The capped POMs with discrete cluster structures have been regarded as an important family in the field of modified POMs (Chen & Hill, 1996;Xu et al, 1999). A variety of electrophilic groups, such as high-oxidation-state {VO} 2+ (Niu et al, 2010;Sha et al, 2007;Yuan et al, 2003), {MoO 2 } 2+ (Han et al, 2014;Salomon et al, 2018;Shen et al, 2014), As 3+ and Sb 3+ (Lu et al, 2010;Zhang et al, 2014Zhang et al, , 2015a, have been employed as capping units to induce and catch the reduced polyoxoanions, producing bi-or tetracapped POMs (Gumerova & Rompel, 2018). However, POM clusters decorated with divalent first-row transition metals as capping atoms, such as Ni 2+ , Ag + and Cu 2+ , have been rarely reported, to our knowledge (Hu et al, 2013;Li et al, 2018;Pang et al, 2015;Yuan et al, 2003).…”

Vanadium Polyoxoanions within Coordination Polymers Based on a Macrocyclic Nickel Complex: Structural Diversities and Single‐Crystal to Single‐Crystal Transformation

“…As a member of the POM family, inorganic–organic hybrid materials of polyoxovanadate have also been widely studied for a number of years. A number of inorganic–organic hybrids with 1D, 2D, and 3D extended structures have been obtained by using transition‐metal complexes and polyoxovanadate clusters as building blocks . We have also constructed several inorganic–organic hybrids by using the transition‐metal macrocyclic complex [ML 0 ] 2+ (L 0 = 5,5,7,12,12,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane) and polyoxometalates .…”