Novel alkaline earth copper germanates with ferro and antiferromagnetic S=1/2 chains

Two new alkaline earth copper(II) germanates were hydrothermally synthesized: CaCuGeO4·H2OCaCuGeO4·H2O (1) and BaCu2Ge3O9·H2OBaCu2Ge3O9·H2O (2), and their structures determined by single crystal X-ray diffraction. Compound (1) crystallizes in space group P21/cP21/c with a=5.1320(2) Å, b=16.1637(5) Å, c=5.4818(2) Å, β=102.609(2)°β=102.609(2)°, V=443.76(3) Å3 and Z  =4. This copper germanate contains layers of composition [CuGeO4]∞2− comprising CuO4 square planes and GeO4 tetrahedra with calcium and water molecules in the inter-layer space. Compound (2) crystallizes in the Cmcm space group with a=5.5593(3) Å, b=10.8606(9) Å, c=13.5409(8) Å, V=817.56(9) Å3 and Z=4. This structure contains GeO6 and CuO6 octahedra as well as GeO4 tetrahedra, forming a three-dimensional network of interconnecting six-membered ring channels. The magnetic susceptibility for both samples can be interpreted as S=1/2 chains, in agreement with the copper topology observed in the crystal structure. The susceptibility of (1) exhibits a Bonner–Fisher type behavior, resulting from antiferromagnetic intra-chain interactions without three-dimensional ordering down to 5 K—the lowest measured temperature. This observation, together with the absence of super-exchange paths between the copper chains, make this system particularly promising for the study of low dimensional magnetism. The magnetic properties of (2) show a very weak ferromagnetic near-neighbor interaction along the chain. In this compound a peak the χTχT plot seems to indicate the onset of interchain antiferromagentic correlations. However, no ordering temperature is detected in the susceptibility data.

Graphical abstractCopper chains present in CaCuGeO4·H2OCaCuGeO4·H2O and BaCu2Ge3O9·H2OBaCu2Ge3O9·H2O, two novel copper germanates synthesized hydrothermally, showing antiferromagnetic and ferromagnetic intra-chain interactions respectively.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The structure of two new chain containing copper germinates is reported. ► The calcium compound CaCuGeO4·H2OCaCuGeO4·H2O contains corner sharing square planes. ► The barium compound BaCu2Ge3O9, displays edge sharing octahedra. ► Susceptibility data show that the Ca compound is a one-dimensional antiferromagnet while Ba is a weak ferromagnet.