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)2 PO2]-·MeOH [2], (iii) [HNC5H4-N=N-C5 H4NH]2+[{CH2 (6-t-Bu-4-Me-C6H2O)2 PO2}2]2-·4CH3 CN·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·1/2;MeOH [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].