STRUCTURES INVOLVING UNSHARED ELECTRON PAIR - THE CRYSTAL-STRUCTURES OF AS(OCOCH3)3 AND AS2O(OCOCH3)4

As2O(OCOCH3)4, reported now for the first time, was obtained, besides As(OCOCH3)3 by dissolving As2O3 in acetic anhydride. The crystals of A s(OCOCH3)3 (A) (monoclinic, space group Cc, Z = 4, a = 9.970(2), b = 1 3.203(2), c = 8.272(1) angstrom, beta = 117.01(2)degrees) and of As2O( OCOCH3)4 (B) (monoclinic, space group P2(1)/n, Z = 4, a = 13.966(5), b = 8.127(4), c = 12.706(4) angstrom, beta = 95.14(1)degrees) are built up from discrete molecules defined by chemical formulae As(OCOCH3)3 a nd (CH3OCO)2As-O-As(OCOCH3)2, respectively. The molecular structure of both compounds is based on the AsO3 pyramid: in (A) with the As-O bon ds of 1.841(6) angstrom and the O-As-O angle of 89.9(3)degrees as a me an, in (B) with slightly different values and with the As-O-As angle o f 127.7(4)degrees at the bridging oxygen atom. The additional weak che lating contacts are at the distances As ... O from 2.625(9) to 2.745(1 0) angstrom in (A) and from 2.72(1) to 2.84(2) in (B). The actual arse nic coordination can be described as very distorted octahedral in (A) and square-pyramidal in (B).