Molecular cocrystals of carboxylic acids Part 24: cocrystals involving triphenylphosphine oxide: structures of the unique adduct hydrates of triphenylphosphine oxide with adamantane carboxylic acid and terephthalic acid, and the anhydrous adduct with o-phthalic acid 1

Abstract

Abstract The crystal structures of the adducts of triphenylphosphine oxide (TPPO) with the carboxylic acids adamantane carboxylic acid (ACA) {the 1:1 monohydrate, [(TPPO)(ACA)(H2O)], (1)}, terephthalic acid (PPA) {the 4:1 dihydrate, [(TPPO)4(PPA)(H2O)2], (2)} and o-phthalic acid (OPA) {the 2:1 anhydrate, [(TPPO)2(OPA)], (3)} have been determined and refined to residuals 0.044, 0.040 and 0.064 for 2461, 3096 and 2227 observed reflections, respectively. The adducts (1) and (2) represent the first reported hydrated examples of TPPO-carboxylic acid adducts and in addition have, instead of the expected single directed hydrogen bond between the phosphoryl oxygen and the carboxylic acid proton [such as is found with (3)], unique three-centre interactions between the water molecule, the carboxylic acid groups and either a single triphenylphosphine oxide {the polymeric adamantane carboxylic acid structure, (1) [O–O, 2.654 Å, 2.736 Å, 3.000(5) Å]} or two triphenylphosphine oxides {the monomeric terephthalic acid structure, (2) [O–O, 2.567 Å, 2.707 Å, 2.721(5) Å]}. In contrast, with (3), the two carboxylic acid groups are involved in separate direct interactions with the two TPPO molecules [O–O, 2.574 Å, 2.625(8) Å].