A two-dimensional, layer-stacked metal-organic framework (MOF) with a dangling acid functionality was developed as the first-ever example of carboxylic-acid-catalysed Friedel–Crafts alkylation with high reusability. Contrary to conventional hydrogen-bond-donating catalysis, a pair of oppositely oriented –COOH moieties acted as potential hydrogen-bonding sites, and efficiently worked for electronically assorted substrates. Control experiments including juxtaposing the performances of a post-metalated MOF and an unfunctionalized analogue explicitly authenticated the carboxylic-acid-mediated catalytic route.