The title compound was prepared from a mixture of the elements by melting in a glassy carbon crucible (HF furnace, argon atmosphere). EuGa 2 + /- x Ge 4 x crystallizes in a new structure type (orthorhombic symmetry, space group Cmcm (no. 63), a=4.1571(3) Å, b=11.268(1) Å, c=13.155(1) Å, V=616.2(2) Å 3 , Z=4, Pearson symbol oC28) and is characterized by a 3D framework of 4-fold bonded (4b) E atoms (E=Ga,Ge) with channels parallel to the short a-axis. The europium atoms lie in the E 1 8 holes of those channels. The structure can also be described as an intergrowth of segments from BaAl 2 Si 2 and from a reconstructed diamond type of structure. The (Ga,Ge) 2 4 framework of the title compound is equivalent to that of the Si(Al) atoms in the zeolite structure of CsAlSi 5 O 1 2 . Magnetic susceptibility measurements show that EuGa 2 + /- x Ge 4 x undergoes a transition from a paramagnetic to an antiferromagnetic ordered state at about 9 K. In the paramagnetic region, an oxidation state of 2+ for europium (μ e f f ~8 μ B /Eu) was obtained. The crystal chemical formula of EuGa 2 Ge 4 is Eu 2 + [(4b)Ga 1 - ] 2 [(4b)Ge 0 ] 4 according to a charge balanced Zintl phase. This was confirmed by quantum chemical calculations (TB-LMTO, ELF). However, like several other similar compounds, e.g. alkaline earth metal clathrates, EuGa 2 + /- x Ge 4 x has a metal-like temperature dependence of the electrical resistivity with a low charge-carrier concentration in agreement with the low value of the calculated density of states.