Chromium hexacyano complexes: The crystal structures of the cyano elpasolites (NMe4)(2)ACr(CN)(6) (A = K, Cs) and of the cubic barium compound Ba-3[Cr(CN)(6)](2) center dot 20 H2O

The crystal structures of the cyano elpasolites (NMe4)(2)KCr(CN)(6) (a = 15 27.3(1), b = 888.1(1), c = 1539.0(1) pm, beta = 109.92(1)degrees; C2/c, Z = 4) and (NMe4)(2)CsCr(CN)(6) (a = 1278.9(1) pm; Fm (3) over bar m, Z = 4), as well as of the cubic compound Ba-3[Cr(CN)(6)](2). 20H(2)O (a= 1631.0(1)p m; Im (3) over bar m, Z = 4) were determined by X-ray methods with single c rystals. Reasons for the enlarged distances within the [Cr(CN)(6)](3)(-)-oc tahedron of the K compound (Cr-C: 209.3 pm) compared to the observations wi thin both cubic complexes (206.1 resp. 206.9 pm) are discussed in context w ith the tolerance factors of cyano elpasolites. As is the case there concer ning the cyano bridges Cr-CN-A towards the alkali ions the novel structure type of the barium compound, too, exhibits nearly linear bridging towards B a. It contributes, however, only four N ligands to the ninefold [BaN4O5] co ordination; part of the aqua ligands show disorder (Ba-N: 287.5, Ba-O: 281/ 293 pm).