The encapsulation of three different cobalt substituted polyoxometalates (POMs) within the mesoporous chromium(iii) terephthalate MIL-101(Cr) metal-organic framework (MOF) was studied by a simple and green impregnation method using water. The POM@MIL composite materials were fully characterized by EDX, XRPD, IR, MAS NMR and N2 porosimetry measurements. The encapsulated POMs were then extracted by an exchange procedure using a LiCl solution. (31)P NMR spectroscopy is the key experiment which indicates that the monosubstituted Keggin anion [PW11CoO39(H2O)](5-) (PW11Co) and the sandwich-type anion [(PW9O34)2Co4(H2O)2](10-) (P2W18Co4) can be encapsulated and extracted without degradation, neither of the POM nor of the MOF, while the hybrid sandwich-type POM [(PW9O34)2Co7(OH)2(H2O)4(O3PC(O)(C3H6NH3)PO3)2](14-) (Co7-Ale) evolves into P2W18Co4 inside the cavities of the mesoporous material. The PW11Co Keggin anion is the most quantitatively uploaded and the most easily extracted anion. (31)P MAS-NMR spectroscopy further suggests that this anion is more mobile inside the cavities of the MOF than the P2W18Co4 POM.

The incorporation of polyoxometalates (POMs) as structural units into ordered porous constructs such as metal-organic frameworks (MOFs) is desirable for a range of applications where intrinsic properties inherited from both the MOF and POM are utilised, including catalysis and magnetic data storage. The controlled self-assembly of targeted MOF topologies containing POM units is hampered by the wide range of oxo and hydroxo units on the peripheries of POMs that can act as coordinating groups towards linking metal cations leading to a diverse range of structures, but incorporation of organic donor units into hybrid POMs offers an alternative methodology to programmably synthesise POM/MOF conjugates. Herein, we report six coordination polymers obtained serendipitously wherein Zn 2+ and Cu 2+ link pyridine-appended Mn-Anderson clusters into two-and three-dimensional network solids with complex connectivities and topologies.2 Careful inspection of their solid-state structures has allowed us to identify common structuredirecting features across these coordination polymers, including a square motif where two Zn 2+ cations bridge two POMs. By correlating certain structural motifs with synthetic conditions we have formulated a series of design considerations for the self-assembly of coordination polymers of hybrid POMs, encompassing the selection of reaction conditions, co-ligands and linking metal cations. We anticipate that these synthetic guidelines will inform the future assembly of hybrid POMs into functional MOF materials. INTRODUCTIONPolyoxometalates ( ) that have been widely studied for their catalytic, [4][5][6][7][8][9] magnetic, 10-17 photochromic 18-21 and redox properties. [22][23][24][25][26][27][28] Given their large range of their chemical and physical properties, their incorporation into Metal-Organic Frameworks (MOFs) -network structures composed of metal clusters or metal ions connected by organic linkers -or more generally into porous frameworks has been investigated. 29,30 Creating POM/MOF conjugate materials can associate their individual properties, for instance the catalytic properties of a POM with the large surface area of a MOF, 31 or achieving a synergistic effect, for example the cooperative effect of single molecule magnets 32 or enhanced photocatalytic proton reduction. 33 To do so, two main approaches have been followed to date ( Figure 1a). The first is the impregnation of the POMs into the pores of a MOF, where POMs are either added during the MOF synthesis and trapped in the pores, [34][35][36][37][38][39][40] or they are inserted postsynthetically by soaking the MOF in a solution of the desired POM. [41][42][43][44] The second approach is to consider POMs as building blocks for porous structures, 45 with the aim of creating a bond between the POM and 3 either an organic linker (usually a multitopic carboxylic acid or N-donor ligand) [46][47][48][49] -di-(4-pyridyl)-1,4,5,8- (Figures 1b and 1c). The amido-pyridyl tris-alkoxo MnAnderson (POM-1) has been reported previously 76 and sh...

Ammonia absorption has been investigated in metal-organic frameworks (UiO-67, HKUST-1 and CPO-27-Co) using custom-built apparatus that allows simultaneous neutron powder diffraction (NPD), microwave dielectric characterisation and out-gas mass spectroscopy of solid-state materials during ammonia adsorption. Deuterated ammonia was flowed through the sample and absorption monitored using mass flow meters and mass spectroscopy. Argon gas was then flowed through the ammoniated sample to cause ammonia desorption. Changes in structure found from NPD measurements were compared to changes in dielectric characteristics to differentiate physisorbed and metal-coordinated ammonia, as well as determine decomposition of sample materials. The results of these studies allow the identification of materials with useful ammonia storage properties and provides a new metric for the measurement of gas absorption within mesoporous solids.