Combinational Post Synthetic Modifications for Single Crystal to Single Crystal Transformations

Abstract

Metal-organic framework, [Ni3(btc)2(bipy)3(H2O)2]·xDMF (1; btc = benzene-1,3,5-tricarboxylic acid, bipy = 4,4’-bipyridine and DMF = N,N-dimethylformamide) was prepared via de-novo reaction. [Ni3(btc)2(pz)3(H2O)2] (2; pz = pyrazine), [Ni6(btc)4(pz)4.75(H2O)5.5] (3), via two different methods of single crystal transformation which are ligand exchange and heat treatment. By soaking 1 in pz DMF solution, all bipy linkers in 1 were completely exchanged by the shorter pz pillaring linkers to form 2. Also, the structure of 2 was transformed to 3 by heat treatment. The single crystal diffraction studies reveal that 1 and 2 are constructed with 2-P sheets linked by bipy and pz, respectively. Dinuclear nickel clusters, [Ni2(COO)2] as a secondary building unit (SBU), are doubly linked using two btc ligands to form an 1-periodic (1-P) noded ribbon structure. The 1- P noded ribbons are further connected via mononuclear Ni2 centers to form a corrugated 2-periodic (2-P) sheet of a 3,4-c bex topology. The 2-P sheets are pillared via bipy or pz linkers to form a 3- periodic (3-P) network. The 3-P networks are considered as a rare 3,4,6-c net of sqc130 topology consisting of the dinuclear nickel cluster as a 6-c node, the mononuclear Ni ion as a 4-c node, and btc ligand as a 3-c node. The two structures have the same topology, but those structure have a little different relative connectivity. In transformation process of 3, the pz linkers of 2 were partially removed by heat treatment, which leaded the rearrangement of coordinated environment of Ni metal. It formed more stable structure at that composition. All single crystal transformations could transform back to original by post-synthetic ligand insertion and exchange.