MOLECULAR COCRYSTALS OF CARBOXYLIC-ACIDS .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

The crystal structures of the adducts of triphenylphosphine oxide (TPP O) 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 r efined to residuals 0.044, 0.040 and 0.064 for 2461, 3096 and 2227 obs erved 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 bon d between the phosphoryl oxygen and the carboxylic acid proton [such a s is found with (3)], unique three-centre interactions between the wat er molecule, the carboxylic acid groups and either a single triphenylp hosphine oxide {the polymeric adamantane carboxylic acid structure, (1 ) [O-O, 2.654 Angstrom, 2.736 Angstrom, 3.000(5) Angstrom]} or two tri phenylphosphine oxides {the monomeric terephthalic acid structure, (2) [O-O, 2.567 Angstrom, 2.707 Angstrom, 2.721 (5) Angstrom]}. In contra st, with (3), the two carboxylic acid groups are involved in separate direct interactions with the two TPPO molecules [O-O, 2.574 Angstrom, 2.625(8) Angstrom].