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  • Title: Molecular conformation and supramolecular aggregation in two fused pyrazoles: pi-stacked R(2)(2)(6) dimers in 2,8,8-trimethyl-6,7,8,9-tetrahydropyrazolo[2,3-a]quinazolin-6-one, and sheets of alternating R(2(2)12) and R(6)(6)(48) rings in 3-tert-butyl-4',4'-dimethyl-1-phenyl-4,5,6,7-tetrahydro-1H-pyrazolo[3,4-b]pyridine-5-spiro-1'-cyclohexane-2',6'-dione.
    Author: Low JN, Cobo J, Mera J, Quiroga J, Glidewell C.
    Journal: Acta Crystallogr C; 2004 Apr; 60(Pt 4):o265-9. PubMed ID: 15071231.
    Abstract:
    In 2,8,8-trimethyl-6,7,8,9-tetrahydropyrazolo[2,3-a]quinazolin-6-one, C(13)H(15)N(3)O, (I), the heterobicyclic system is planar and exhibits peripheral ten pi-electron delocalization. In 3-tert-butyl-4',4'-dimethyl-1-phenyl-4,5,6,7-tetrahydro-1H- pyrazolo[3,4-b]pyridine-5-spiro-1'-cyclohexane-2',6'-dione, C(23)H(25)N(3)O(2), (II), the pyrazole ring exhibits marked bond fixation, while the reduced pyridine ring adopts a half-chair conformation. Molecules of (I) are linked into centrosymmetric R(2)(2)(6) dimers by a single C-H.N hydrogen bond [H.N = 2.50 A, C.N = 3.3397 (17) A and C-H.N = 148 degrees ], and these dimers are linked into chains by a single pi-pi stacking interaction. In (II), the combined action of one N-H.O hydrogen bond [H.O = 2.40 A, N.O = 3.2248 (15) A and N-H.O = 157 degrees ] and one C-H.O hydrogen bond [H.O = 2.48 A, C.O = 3.407 (2) A and C-H.O = 164 degrees ] links the molecules into sheets built from alternating centrosymmetric R(2)(2)(12) and R(6)(6)(48) rings; there is a weak C-H.N interaction [H.N = 2.60 A, C.N = 3.5149 (18) A and C-H.N = 154 degrees ] between molecules in adjacent sheets.
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