STRUCTURAL STUDIES OF CYCLOPENTAARSINES - CRYSTALLOGRAPHIC CHARACTERIZATION OF CYCLO(PHAS)(5) AND CYCLO(P-TOLAS)(5)

From adventitious sources, single-crystal samples of the first aromati cally substituted cyclopentaarsines, cyclo(C6H5As)(5) and cyclo(p-CH3C 6HAs)(5), have been obtained and crystallographically characterized. I n both cases, the structures are those expected of cyclopentane isolob al analogues, i.e., an essentially zero dihedral plane of four atoms w ith a fifth atom residing in a sharply angled flap plane. The flap ang le is about 10 degrees smaller for the phenyl- and p-tolyl-substituted rings than for two previously reported alkyl-substituted rings, but i s 15-20 degrees larger than the six-membered phenyl-and p-tolyl-substi tuted systems. For cyclo(PhAs)(5): monoclinic, P2(1)/n, a = 9.770(2)An gstrom, b = 10.385(2)Angstrom, c = 27.941(6)Angstrom,beta = 91.85(2)de grees, V = 2833.5(10)Angstrom(3), Z = 4, d(calcd) = 1.782 g cm(-3), R( F) = 7.82%. For cyclo(p-TolAs)(5): monoclinic, P2(1)/c, a = 10.785(2)A ngstrom, b = 8.798(1)Angstrom, c = 35.872(7) Angstrom, beta = 92.52(2) degrees V = 3400.4(11)Angstrom(3), Z = 4, d(calcd) = 1.820 g cm(-3), R (F) = 5.13%.