Premium
New Mechanistic Insight into Stepwise Metal‐Center Exchange in a Metal–Organic Framework Based on Asymmetric Zn 4 Clusters
Author(s) -
Meng Wei,
Li Huijun,
Xu Zhouqing,
Du Shanshan,
Li Yunxia,
Zhu Yanyan,
Han Yi,
Hou Hongwei,
Fan Yaoting,
Tang Mingsheng
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201303434
Subject(s) - chemistry , crystallography , coordination geometry , octahedron , ligand (biochemistry) , ion exchange , metal , metal ions in aqueous solution , coordination complex , inorganic chemistry , coordination number , ion , crystal structure , molecule , organic chemistry , hydrogen bond , biochemistry , receptor
Herein, a mechanism of stepwise metal‐center exchange for a specific metal–organic framework, namely, [Zn 4 (dcpp) 2 (DMF) 3 (H 2 O) 2 ] n (H 4 dcpp=4,5‐bis(4′‐carboxylphenyl)phthalic acid), is disclosed for the first time. The coordination stabilities between the central metal atoms and the ligands as well as the coordination geometry are considered to be dominant factors in this stepwise exchange mechanism. A new magnetic analytical method and a theoretical model confirmed that the exchange mechanism is reasonable. When the metathesis reaction occurs between Cu II ions and framework Zn II ions, the magnetic exchange interaction of each pair of Cu II centers gradually strengthens with increasing amount of framework Cu II ions. By analyzing the changes of coupling constants in the Cu‐exchanged products, it was deduced that Zn4 and Zn3 are initially replaced, and then Zn1 and Zn2 are replaced later. The theoretical calculation further verified that Zn4 is replaced first, Zn3 next, then Zn1 and Zn2 last, and the coordination stability dominates the Cu/Zn exchange process. For the Ni/Zn and Co/Zn exchange processes, besides the coordination stability, the preferred coordination geometry was also considered in the stepwise‐exchange behavior. As Ni II and Co II ions especially favor octahedral coordination geometry in oxygen‐ligand fields, Ni II ions and Co II ions could only selectively exchange with the octahedral Zn II ions, as was also confirmed by the experimental results. The stepwise metal‐exchange process occurs in a single crystal‐to‐single crystal fashion.