NaK 29 Hg 48 is a new silver metallic, air-sensitive ternary alkali metal amalgam with metallic properties. It crystallizes in space group Pm3n (No. 223, Z=2, a=1685.3(2) pm) and shows a superconducting phase transition at 2.5 K. Its crystal structure is characterized by novel icosahedral Hg 12 clusters centered by Na atoms and hexagonal antiprismatic Hg 12 clusters (“drums”) centered by K atoms. Both cluster types are embedded in a matrix of K atoms. With respect to the topology of the cluster centers the three-dimensional arrangement corresponds to the A15 structure type (Nb 3 Sn). The crystal structure of NaK 29 Hg 48 is closely related to that of the complex intermetallic phases A 3 Na 29 In 48 (A=K, Rb, Cs) and others. It is an unexpected electron deficient borderline case with respect to electron counting rules (Wade's rules and Zintl–Klemm concept), which were successfully applied to explain the occurence of icosahedral and hexagonal antiprismatic In 12 /Tl 12 clusters in the latter two compounds.