The nature, strength, and reactivity of the sorption sites of single crystals of the microporous gallophosphate cloverite were studied in situ by IR microscopy. Two kinds of structural hydroxyl groups of high (Ga-OH groups) and moderate (P-OH groups) Bronsted acid strength were identified. Upon sorption of polar molecules, however, a partial opening of the Ga-O bond next to the structural hydroxyl group occurs, leading to a concerted Bronsted (Ga-OH) and Lewis (Ga ion) type interaction of the sorption site with the probe molecule. This change in coordination of the Ga ion upon sorption of polar molecules leads to an unusual reactivity. Methanol, for example, reacts with different surface species in cloverite, which lead to different reaction products. While the weakly hydrogen-bonded molecules interacting with the P-OH groups desorbed unreacted at 300 K, the molecules sorbed at the Ga-OH groups reacted to either dimethyl ether (characteristic for Bronsted acid sites) or formaldehyde (characteristic for Lewis acid sites). The stability of the cloverite structure was found to be strongly dependent on the coordination of the Ga ions. While the microporous structure is stable, when the structural rearrangement of the Ga ions is confined to a 5-fold (as it occurs in the as-synthesized form or after sorption of larger polar molecules) or a 4-fold (activated form, in inert atmosphere) coordination, it collapses upon sorption of small polar molecules which force the Ga ion in an octahedral (6-fold) coordination. This occurs, for example, with sufficient concentrations of water at 300 K and with ammonia at elevated temperatures.