Ca²⁺‐Driven Self‐Assembly of POMs into 2D/3D Coordination Polymers

Abstract

A number of new POM-based coordination polymers, including two-dimensional (NH 4 ) 4 {[Ca(H 2 O) 5 ][P 2 Mo 5 O 23 ]}· 3H 2 O (4) (bpy = 2,2′-bipyridine), and a rare anion-based (NH 4 ) 5 [Co III (bpy) 3 ]{[Ca(H 2 O) 4 ] 2 [Ca(H 2 O)] 6 [PMo 6 O 22 (PO 4 ) 3 ] 2 }· 17H 2 O (3), as well as three-dimensional (NH 4 ) 8 [Co III (bpy) 3 ] 2 -{[Ca(H 2 O) 3 ] 2 [P 2 Mo 5 O 23 ] 3 }·21H 2 O (2) have been prepared using a facile wet-chemistry approach and have been characterized by X-ray diffraction analysis and a variety of physicochemical methods. The self-assembly in the above compounds has been rendered by the use of Ca 2+ ions as a suitable linker in the [a] 3525 network formation. Moreover, Ca 2+ ions were also involved in the formation of an extremely rare type of POM anion {[Ca(H 2 O)] 6 [PMo 6 O 22 (PO 4 ) 3 ] 2 } 12-. The synthesis attempt without the alkaline-earth metal led, predictably, to the formation of the discrete Strandberg-based compound (NH 4 ) 3 [Co III (bpy) 3 ]-[P 2 Mo 5 O 23 ]·14H 2 O (1). Thus, the present work reports on a suitable strategy to influence complex POM-based systems towards self-organization into multidimensional structures of higher hierarchy. The obtained compounds have been shown to possess electrocatalytic activity towards the reduction of iodates(V).Some of the common strategies to obtain multidimensional POM-based coordination polymers include the binding of densely charged POM anions with various linkage units, such as functional organic ligands, transition metals, and metal complexes, as well as rare-earth metals. [9][10][11][12][13][14] The majority of the reports related to POM-based heterometallic compounds cover examples with Cu as a second metal, [15][16][17] while only a few publications mention the anions' combination with cobalt. [18,19] Co-containing compounds based on POMs have gained popularity in the development of wateroxidation catalysts and have shown better activity than the widespread copper complexes. [20,21] Another intriguing possibility is the use of alkaline-earth metals as promising templates for discovering new binding motifs with POMs. [22] With charge numbers similar to those of typical d-elements, and possessing coordination modes and sizes similar to lanthanide ions, the alkaline-earth metals offer new and largely underexplored tools for driving self-assembly in POM-based hybrids. [23] There are also a number of vanadiumbased polyanions linked by alkaline-earth metals. [24][25][26] Moreover, the influence of the size of the guest metal ions (Ca 2+ , Sr 2+ , or Ba 2+ ) on the arrangement of Pd II -oxo shells in polyoxo noble metalates has been demonstrated. [27] Inspired by the reported structure-directing template effect of the metals on the formation of POMs, we decided to study the influence of Ca 2+ and Sr 2+ ions on phosphomolybdate-based structures. According to the CCDC, most of the publications cover [P 6 Mo 18 O 73 ] 8and [P 4 Mo 6 O 28-x (OH) 3+x ] (9-x)based compounds with Ca, Sr, and (rarely) Ba. [28][29][30][31][32] Another unique hig...

Hybrid Cu-Containing Compounds Based on Lacunary Strandberg Anions: Synthesis under Mild Conditions, Crystal Structure, and Magnetic Properties

“…Recently, we have shown the feasibility and efficiency of synthesis of novel hybrid compounds based on POMs under mild conditions using an oxidative dissolution of M 0 powder or the “classical” use of metal salts. − …”

Assembly of a coordination polymer with sulphate-capped pentamolybdate units and copper: synthesis, structure, magnetic and catalytic studies

“…[62][63][64][65] Coordination polymers with pentamolybdate {Mo 5 O 15 } ions as nodes and transition-metal groups as linkers have been extensively reported in the literature, wherein the exposed atom of the hetero-atom cluster is sometimes used for additional bonding and the formation of extended assemblies. [66][67][68] The first such examples of coordination polymeric frameworks incorporating the pentamolybdate unit and a transition metal were reported by Zubieta and co-workers in 2001, with two different compounds forming one-and two-dimensional extended assemblies, formulated as [{Cu(bpy) 2 }{Cu(bpy…”

“…Coordination polymers with pentamolybdate {Mo 5 O 15 } ions as nodes and transition-metal groups as linkers have been extensively reported in the literature, wherein the exposed atom of the hetero-atom cluster is sometimes used for additional bonding and the formation of extended assemblies. 66–68 The first such examples of coordination polymeric frameworks incorporating the pentamolybdate unit and a transition metal were reported by Zubieta and co-workers in 2001, with two different compounds forming one- and two- dimensional extended assemblies, formulated as [{Cu(bpy) 2 }{Cu(bpy)(H 2 O)}(Mo 5 O 15 ){O 3 P(CH 2 ) 4 PO 3 }]·H 2 O and [{(Cu 2 (tpypz)(H 2 O) 2 }(Mo 5 O 15 )(O 3 PCH 2 CH 2 PO 3 )]·5.5H 2 O [bpy = 2,2′bipyridine and tpypyz = tetra(2-pyridyl)pyrazine], respectively. 69 Subsequent reports of coordination polymers with the {Mo 5 O 15 (PO 3 X) 2 } (X = O, C) units have included other transition-metals, such as with manganese( ii ), 62 cobalt( ii ), 70,71 nickel( ii ), 70,72,73 copper( ii ), 62,70,73–81 zinc( ii ), 82,83 and with silver( i ), 84,85 along with organic amines as additional ligands.…”