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) 1 (unsolvated, two
polymorphs), 1·EtOH, and 1·MeOH, (ii) [imidazolium]+[CH2(6-t-Bu-4-Me-C6H2O)2PO2]-·MeOH [2], (iii)
[HNC5H4−NN−C5H4NH]2+[{CH2(6-t-Bu-4-Me-C6H2O)2PO2}2]2-.4CH3CN·H2O [3], (v) [K, 18-crown-6]+[{CH2(6-t-Bu-4-Me-C6H2O)2P(O)OH}{CH2(6-t-Bu-4-Me-C6H2O)2PO2}]-·2THF [4], (vi) 1·cytosine·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) Å
[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) Å] 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) Å], is present. 1·MeOH is a similar dimer with
a very short O(−H)···O bond [2.429(3) Å]. 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) Å].