A microporous Cu2+ MOF based on a pyridyl isophthalic acid Schiff base ligand with high CO2 uptake

Abstract

A new Cu2+ complex that was isolated from the initial use of 5-((pyridin-4-ylmethylene)amino)isophthalic acid (PEIPH2) in 3d metal-organic framework (MOF) chemistry is reported. Complex {[Cu3(PEIP)2(5-NH2-mBDC)(DMF)]·7DMF}∞ denoted as Cu-PEIP·7DMF was isolated from the reaction of Cu(NO3)2·2.5H2O with PEIPH2 in N,N-dimethylformamide (DMF) at 100 °C and contains both the PEIP2- ligand and its 5-NH2-mBDC2- fragment. After the structure and properties of Cu-PEIP were known an analogous complex was prepared by a rational synthetic method that involved the reaction of Cu(NO3)2·2.5H2O, 5-((pyridin-4-ylmethyl)amino)isophthalic acid (PIPH2-the reduced analogue of PEIPH2) and 5-NH2-mBDCH2 in DMF at 100 °C. Cu-PEIP comprises two paddle-wheel [Cu2(COO)4] units and exhibits a 3D-framework with a unique trinodal underlying network and point symbol (4.52)4(42·54·64·83·92)2(52·84). This network consists of pillared kgm-a layers containing a hexagonal shaped cavity with a relatively large diameter of ∼8-9 Å surrounded by six trigonal shaped ones with a smaller diameter of ∼4-5 Å and thus resembles the structure of HKUST-1. Gas sorption studies revealed that Cu-PEIP exhibits a 1785 m2 g-1 BET area as well as high CO2 sorption capacity (4.75 mmol g-1 at 273 K) and CO2/CH4 selectivity (8.5 at zero coverage and 273 K).