Structural Studies of cyclopentaarsines. Crystallographic Characterization of cyclo(PhAs) 5 and cyclo(p-TolAs) 5 *

Abstract

From adventitious sources, single-crystal samples of the first aromatically substituted cyclopentaarsines, cyclo(C₆H₅As)₅ and cyclo(p-CH₃C₆H₄As)₅, have been obtained and crystallographically characterized. In both cases, the structures are those expected of cyclopentane isolobal analogues, i.e., an essentially zero dihedral plane of four atoms with a fifth atom residing in a sharply angled flap plane. The flap angle is about 10° smaller for the phenyl- and p-tolyl-substituted rings than for two previously reported alkyl-substituted rings, but is 15–20° larger than the six-membered phenyl- and p- tplyl-substituted systems. For cyclo(PhAs)₅: monoclinic, P2₁/n, a = 9.770(2)Å, b = 10.385(2)Å, c = 27.941(6)Å, β = 91.85(2)°, V = 2833.5(10)ų, Z = 4, d(calcd) = 1.782 g cm⁻³, R(F) = 7.82%. For cyclo(p-TolAs)₅: monoclinic, P 2₁/c, a = 10.785(2)Å, b = 8.798(1)Å, c = 35.872(7)Å, β = 92.52(2)°, V = 3400.4(11)ų, Z = 4, d(calcd) = 1.820 g cm⁻³ R(F) = 5.13%.