X-RAY CRYSTALLOGRAPHIC STRUCTURES OF TWO POLYMORPHIC FORMS OFCIS-6-CARBOXY-2,10-DIOXA-1-PHOSPHABICYCLO-[4.4.0JDECANE 1-OXIDE

Abstract

The title compound, cis-6-carboxy-2,10-dioxa-l-phosphabicyclo[4.4.O]decane 1-oxide (4), crystallizes in two different crystalline forms: 4a, monoclinic, F'2,/c, a = 7.7702(5) A, b = 7.111513) 8, c = 17.8577(10), p = 99.146(5)", V = 974.46(10) A3, Z = 4, D,,,, = 1.501 Mg m-', Cu Ka, A = 1.54178 A, p = 2.51 mm-I, F(000) = 464, T = 298(2) K, R = 0.041 and 4b; orthorhombic, P2,2,2,, a = 7.9188(8) A, b = 10.8147(6) A, c = 11.261(2), V = 964.4(3) A', Z = 4, D,,,, = 1.515 Mg ~n -~, Cu Ka, A = 1.54178 A, p = 2.54 mm-', F(oo0) = 464, T = 295(2)K, R = 0.046. In each form the structures are found to consist of two cis-fused six-membered rings, with each ring in the chair conformation. Both structures exhibit intermolecular hydrogen bonding of the form H. . . H -O -m with 4a in the form ofdimers and 4b in the form of helical chains. All corresponding bond lengths and angles are statistically the same for 4a and 4b. A significant difference in the orientation of the carboxy group in 4a and 4b was observed. This orientation of the carboxy group was investigated using molecular calculations at the PM3 level.