Nonlinear Properties in Coordination Copolymers Derived from Randomly Mixed Ligands

Random copolymerization is a core strategy of the polymer industry, enabling broad tuning of materials properties through mixing monomers with similar reactivities. In coordination polymers, analogous results have recently been achieved using combinations of isomorphic linkers copolymerized by appropriate metals; in general, the properties of the resultant coordination copolymers can be described as a linear combination of the properties of the constituent building blocks. Here we demonstrate that this need not be the case: coordination copolymerization is a powerful strategy for directing phase formation. For example, reaction of 1,4-benzenedicarboxylic acid with Zn2+typically affords phase-impure material in N,N-dimethylformamide whereas using an amino functionalized linker leads to pure high surface area material with the structure of MOF-5. However, mixed-linker copolymers derived from a combination of both linkers display surface areas comparable to that of MOF-5 synthesized in N,N-diethylformamide, indicating that even a minor linker component can direct phase selection. In a second illustration, the pore blockage of the bulky group in 9,10-bis(triisopropylsilyloxy)phenanthrene-2,7-dicarboxylate (TPDC) not only suppresses the framework interpenetration of biphenyl-based IRMOF architectures but also blocks adsorption sites, yielding a low surface area material. However, the random coordination copolymerization of Zn2+with a mixture of TPDC and 3,3′,5,5′-tetramethyl-4,4′-biphenyldicarboxylate (Me4BPDC) controls the level of framework interpenetration and the degree of pore blockage, resulting in higher surface area (up to ∼3000 m2/g) copolymers than the noninterpenetrated Zn4O(TPDC)3and interpenetrated Zn4O(Me4BPDC)3frameworks.