Anion Exchange Reactions of 3R2-MgAl-Carbonate-LDH: Comparison with the 3R1 Analogue and Formation of 3R2 Polytype of MgAl-LDH with Other Interlayer Anions

Anion exchange reactions with several monovalent anions and a divalent sulfate anion could be successfully carried out on 3R2 polytype of magnesium aluminum LDH containing interlayer carbonate ions by refluxing the carbonate-LDH in 1-butanol with ammonium salt of the desired anion. The reaction was similar to what was observed in the case of 3R1 polytype (Bhojaraj et al., ACS Omega2019, 4, 20072-20079) in that here too the reaction occurs topotactically resulting in 3R2 polytypes of LDHs in the cases of chloride and bromide anions. However, the reaction is much slower here demanding longer reaction times and/or higher amounts of ammonium salt of the anion. These exchange reactions pave the way for the synthesis of well-defined, hitherto unknown, 3R2 polytypes of magnesium aluminum LDH with chloride and bromide as interlayer anions.