Modification of Network and Pore Dimensionality in Metal–Organic Frameworks Containing a Secondary Phosphine Functionality

Three new metal–organic frameworks containing a triphenylphosphine moiety, namely, [Zn 3 (tpp) 2 (DMF) 2 ]· n DMF ( 1 ), [Zn 3 (tpp) 2 (4,4′-bpy) 2 ]· n DMF ( 2 ), and [Zn 3 (tpp) 2 (3,3′-bpy)]· n DMF ( 3 ), were synthesized using 4,4′,4″-phosphanetriyltribenzoic acid (H 3 tpp) as a tritopic linker. The absence or presence of additional N-donor linker molecules in the reaction mixture lead to the formation of (3,6)-c layered, (3,8)-c pillared layered, or (3,4,6)-c frameworks. Compound 1 is composed of a trinuclear zinc secondary building unit (SBU) and the tpp 3– anion arranged in a layered (3,6)-c network with kgd topology. There are DMF guest molecules coordinated to the terminal Zn atoms of the trinuclear inorganic SBU. The addition of the neutral N-donor molecules 3,3′-bipyridine (3,3′-bpy) and 4,4′-bipyridine (4,4′-bpy) as second organic linker molecule lead to an increase of dimensionality of the networks. Compound 2 is a (3,4,6)-nodal three-dimensional MOF. Its structure consists of two equivalent interpenetrated nets with the point symbol (5 2 ·6 4 )(5 2 ·6) 2 (5 4 ·6 6 ·7 2 ·8·9 2 ) containing solvent filled pockets. The free electron pair of the phosphorus atom of the triphenylphosphine moiety is pointing toward the zero-dimensional pores. The structure of 3 can be described as layers of 1 which are connected by 3,3′-bipyridine as pillar into a three-dimensional (3,8)-c network with the point symbol (4 3 ) 2 (4 6 ·6 18 ·8 4 ). The non-interpenetrated structure of 3 contains a solvent filled three-dimensional pore system. All three materials exhibit uptake of CO 2 at 195 K after removal of the guest DMF molecules. This is particularly surprising for 2, with its zero-dimensional pores in the single-crystal structure and absence of N 2 adsorption at 77 K. Compound 3 shows a large gate opening effect for CO 2 adsorption at 195 K.