Isolation and X-ray crystal structures of {Li-2[mu(2)-As(SiMe(3))(2)][mu(3)-As(SiMe(3))(2)](THF)}(2) and [(Me(3)Si)(2)AsLi(THF)(2)](2)

The lithium arsenides {Li-2[mu(2)-As(SiMe(3))(2)][mu(3)-As(SiMe(3))(2)](THF)}(2), (I) (THF = tetrahydrofuran) and [(Me(3)Si)(2)AsLi(THF)(2)](2) (II) were isolated and their solid-state structures determined by X-ray methods. Compound I crystallizes in the monoclinic system, space group P2(1)/c, with a = 10.147(1) Angstrom, b = 19.665(2) Angstrom, c = 16.768(2) Angstrom, beta = 107.78(1)degrees and Z = 2. The core structure consists of an [LiAs](4) ladder-like framework with four antiparallel adjacent As-Li rungs. The two lithium atoms of the central ring each bridge three arsenic centers while the two lithium atoms belonging sorely to the outer rings each span two arsenic atoms and are coordinated to one THF molecule. Monoclinic crystals of compound II belong to space group C2/c, with a = 17.877(4) Angstrom, b = 14.077(3) Angstrom, c = 19.006(4) Angstrom, beta = 109.16(2)degrees and Z = 4. The structure consists of a centrosymmetric dimer containing a four-membered As-Li-As-Li ring wherein each lithium atom is coordinated to two molecules of THF.