abstract
Two new alkaline earth copper(II) germanates were hydrothermally synthesized: CaCuGeO4 center dot H2O (1) and BaCu2Ge3O9 center dot H2O (2), and their structures determined by single crystal X-ray diffraction. Compound (1) crystallizes in space group P2(1)/c with a=5.1320(2) angstrom, b=16.1637(5) angstrom, c=5.4818(2) angstrom, beta=102.609(2)degrees, V=443.76(3) angstrom(3) and Z=4. This copper germanate contains layers of composition [CuGeO4](infinity)(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) angstrom, b=10.8606(9) angstrom, c=13.5409(8) angstrom, V=817.56(9) angstrom(3) 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 chi T plot seems to indicate the onset of interchain antiferromagentic correlations. However, no ordering temperature is detected in the susceptibility data. Published by Elsevier Inc.
keywords
FRAMEWORK; BEHAVIOR
subject category
Chemistry
authors
Brandao, P; Reis, MS; Gai, Z; dos Santos, AM
our authors
Paula Cristina Ferreira da Silva Brandão
Assistant ResearcherProjects
Photocatalytic reduction of carbon dioxide into valuable hydrocarbon products (PTDC/QUI/72584/2006)
acknowledgements
P.B. thanks FCT and FEDER (QREN-COMPETE-FCOMP 01-0124 FEDER-007461) for funding the Project PTDC/QUI/72584/2006 and collaboration project between Portugal and Brazil FCT/CAPES/2011/2012. Research at ORNL was conducted at the Quantum Condensed Matter Division and the CNMS, which are sponsored at ORNL by the Office of Basic Energy Sciences, U.S. DOE. The ORNL is managed by UT-Battelle, LLC for the U.S. DOE under Contract no. DE-AC05-00OR22725. M.S.R. acknowledge Brazilian agencies: CAPES, CNPq, FAPERJ and PROPPi-UFF.