The new Li2CoGeS4 compound crystallizes in the Pn space group with the wurtz-kesterite structure, according to single,crystal X-ray diffraction. The structure of Li2CoGeS4 and the high degree of phase-purity in which it is prepared are supported by high-resolution synchrotron X-ray powder diffraction. Varying the divalent ion in Li-2-II-GeS4 materials yields three different structure types, all of which are derived from hexagonal diamond. These structural variations give rise to Li+-eficompassing [II-GeS4](2-) nets with different topologies that offer diversity in lithium-ion diffusion pathways. In the first systematic study of the lithium ion conductivity in quaternary diamond-like materials, wurtz-kesterite-type Li2CoGeS4 and Li2FeGeS4 (Pn), lithium cobalt(II) silicate-type Li2MnGeS4 (Pna2(1)), and wurtz-stannite-type Li2CdGeS4 (Pmn2(1)) are presented-as environmentally stable lithium ion conductors. These materials are comprised of cubic diamond-like [CoGeS4](2-) and [FeGeS4](2-) anionic frameworks, ABW-like [MnGeS4](2-), and square lattice-like [CdGeS4](2-). As assessed using impedance spectroscopy, Li2FeGeS4 exhibits the most promising Li+ ion conductivity of 1.8(3) x 10(-4) S/cm at 100 degrees C, while Li2CdGeS4 shows the lowest activation energy for lithium ion conduction, E-A = 0.74(2) eV. (C) 2015 Elsevier B.V. All rights reserved.