Single-Crystal-to-Single-Crystal Cluster Transformation in a Microporous Molybdoarsenate(V)-Metalorganic Framework.

Nour Dissem,Amor Haddad,María Dm Vivanco,Estibaliz Ruiz-Bilbao,Garikoitz Beobide,Leire San Felices,Oscar Castillo,Beñat Artetxe,Juan M Gutiérrez-Zorrilla,Luis Lezama

doi:10.1021/acs.inorgchem.1c02276

Abstract

The hybrid compound [Cu(cyclam)(H2O)2]0.5[{Cu(cyclam)}1.5{B-H2As2Mo6O26(H2O)}]·9H2O (1) (cyclam = 1,4,8,11-tetraazacyclotetradecane) was synthesized in aqueous solution by reacting the {Cu(cyclam)}2+ complex with a mixture of heptamolybdate and an arsenate(V) source. Crystal packing of 1 exhibits a supramolecular open-framework built of discrete covalent molybdoarsenate/metalorganic units and additional [Cu(cyclam)(H2O)2]2+ cations, the stacking of which generates squarelike channels parallel to the z axis with an approximate cross section of 10 × 11 Å2 where all the hydration water molecules are hosted. Thermal evacuation of solvent molecules yields a new anhydrous crystalline phase, but compound 1 does not preserve its single-crystalline nature upon heating. However, when crystals are dehydrated under vacuum, they undergo a structural transformation that proceeds via a single-crystal-to-single-crystal pathway, leading to the anhydrous phase [{Cu(cyclam)}2(A-H2As2Mo6O26)] (2). Total dehydration results in important modifications within the inorganic cluster skeleton which reveals an unprecedented solid-state B to A isomerization of the polyoxoanion. This transition also involves changes in the CuII bonding scheme that lead to covalent cluster/metalorganic layers by retaining the open-framework nature of 1. Compound 2 adsorbs ambient moisture upon air exposure, but it does not revert back to 1, and the hydrated phase [{Cu(cyclam)}2(A-H2As2Mo6O26)]·6H2O (2h) is obtained instead. Structural variations between 1 and 2 are reflected in electron paramagnetic resonance spectroscopy measurements, and the permanent microporosity of 2 provides interesting functionalities to the system such as the selective adsorption of gaseous CO2 over N2.

Highlights

The construction of polyoxometalate (POM)-based openframeworks allows the combination of the intrinsic properties of these nanometric metal-oxo clusters[1−3] with the inherent features of porous materials, such as high internal surface area.[4,5] these systems represent promising candidates for applications in fields like gas sorption and separation, ion-exchange, sensing, and catalysis.[6]
This procedure usually lacks predictability, and it avoids a previous rational design. Another elegant strategy involves the preparation of structural analogues of the well-known metalorganic frameworks (MOFs) by either connection of metal polysubstituted POMs through bridging organic ligands or the combination between metallic nodes and organically derivatized POMs that act as linkers.[11]
[H2As2Mo6O26]4−.31−34 Here we report on the hybrid [Cu(cyclam)(H2O)2]0.5[{Cu(cyclam)}1.5{BH2As2Mo6O26(H2O)}]·9H2O (1) framework, which is able to undergo a nonreversible SCSC transformation induced by the evacuation of guest solvent molecules to afford the anhydrous

Summary

Introduction

The construction of polyoxometalate (POM)-based openframeworks allows the combination of the intrinsic properties of these nanometric metal-oxo clusters (e.g., redox properties, magnetism, luminescence...)[1−3] with the inherent features of porous materials, such as high internal surface area.[4,5] these systems represent promising candidates for applications in fields like gas sorption and separation, ion-exchange, sensing, and catalysis.[6].

Results

Conclusion