Very strong C-H•••O, N-H•••O, and O-H•••O hydrogen bonds involving a cyclic phosphate

Very short C-H . . .O, N-H . . .O, and O-H . . .O hydrogen bonds have been generated utilizing the cyclic phosphate [CH2(6-t-Bu-4-Me-C6H2O)(2)]P(O)OH (1). X-ray structures of (i) I (unsolvated, two polymorphs), 1-EtOH, and 1-MeOH, (ii) [imidazolium](+)[CH2(6-t-Bu-4-Me-C6H2O)(2)PO2]-.MeOH [2], (iii) [HNC5H4-N=N-C5H4NH](2+)[CH2(6-t-Bu-4-Me-C6H2O)(2)PO2}(2)](2-).4CH(3)CN .H2O [3], (v) [K. 18-crown-6](+)[{CH2(6-t-Bu-4-Me-C6H2O)(2)P(O)OH}]CH2(6-t-Bu-4-Me-C6H2O)(2)PO2}](-). 2THF [4], (vi) 1-cytosinc-MeOH [5]. (vii) 1(.)adenine(.1)/2MeOH [6], and (viii) 1(.)S-(-)-proline [7] have been determined. The phosphate 1 in both its forms is a hydrogen-bonded dimer with a short O-H . . .O distance of 2.481(2) [triclinic form] or 2.507(3) Angstrom [monoclinic form]. Compound 2 has a helical structure with a very short C-H . . .O hydrogen bond involving an imidazolyl C-H and methanol in addition to N-H . . .O hydrogen bonds. A helical motif is also seen in 5. In 3, an extremely short N-H . . .O hydrogen bond [N . . .O 2.558(4) A] is observed. Compounds 6 and 7 also exhibit short N-H . . .O hydrogen bonds. In 1(.)EtOH, a 12-membered hydrogen-bonded ring motif, with one of the shortest known O-H . . .O hydrogen bonds [O . . .O 2.368(4) Angstrom], is present, 1(.)MeOH is a similar dimer with a very short O(-H). . .O bond [2.429(3) Angstrom]. In 4, the deprotonated phosphate (anion) and the parent acid are held together by a hydrogen bond on one side and a coordinate/covalent bond to potassium on the other: the O-H . . .O bond is symmetrical and very strong [O . . .O 2.397(3) Angstrom].