Anion Exchange Reactions of 3R 2 -MgAl-Carbonate-LDH: Comparison with the 3R 1 Analogue and Formation of 3R 2 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 3R 2 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 3R 1 polytype (Bhojaraj et al., ACS Omega 2019 , 4 , 20072-20079) in that here too the reaction occurs topotactically resulting in 3R 2 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, 3R 2 polytypes of magnesium aluminum LDH with chloride and bromide as interlayer anions.