THE CRYSTAL-STRUCTURES OF EU5GE3 AND EUIRGE2

Eu5Ge3 and EuIrGe2 were prepared from the elements in tantalum tubes, and their crystal structures were determined from single crystal X-ray data. Eu5Ge3 adopts the structure of Cr5B3: I4/mcm, a = 799.0(1)pm, c = 1536.7(1)pm, Z = 4, wR2 = 0.0421 for 669 F-2 values and 16 variable s. The structure of Eu5Ge3 contains isolated germanium atoms and germa nium atom pairs with a Ge-Ge distance of 256.0 pm. Eu5Ge3 may be descr ibed as a Zintl phase with the formulation [5Eu(2+)](10+)[Ge](4-)[Ge-2 ](6-). Magnetic investigations of Eu5Ge3 show Curie-Weiss behaviour ab ove 50 K with a magnetic moment of mu(exp) = 7.6(1) mu(B) which is clo se to the free ion value of mu(eff) = 7.94 mu(B) for Eu2+. EuIrGe2 is isotypic with CeNiSi2: Cmcm, a = 445.5(2) pm, b = 1737.4(4) pm, c = 42 6.6(1) pm, Z = 4, wR2 = 0.0507 for 295 F-2 values and 18 variables. Th e structure of EuIrGe2 is an intergrowth of ThCr2Si2-like slabs with c omposition EuIr2Ge2 and AlB2-like slabs with composition EuCe2 in an A B stacking sequence. Both slabs are distorted when compared to the sym metry of the prototypes. The Ge-Ge distance of 256.6 pm in the AlB2-li ke fragment is comparable to that in Eu5Ge3.