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

Abstract

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-.4CH₃ CN.H₂O [3], (v) [K, 18-crown-6]⁺[{CH₂(6-t-Bu-4-Me-C₆H₂O)₂P(O)OH}{C H₂(6-t-Bu-4-Me-C₆H₂O)₂PO₂}]^-.2THF [4], (vi) 1.cytosine.MeOH [5], (vii) 1.adenine.½MeOH [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 N­H···O hydrogen bond [N···O 2.558(4) Å ] is observed. Compounds 6 and 7 also exhibit short N­H···O hydrogen bonds. In 1.EtOH, a 12-membered hydrogen-bonded ring motif, with one of the shortest known O­H···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].