Extremely Long Cu···O Contact as a Possible Pathway for Magnetic Interactions in Na₂Cu(CO₃)₂

Chemical binding in a mixed copper sodium carbonate Na2Cu­(CO3)2, a layered material showing ferromagnetic intralayer exchange and weak antiferromagnetic interlayer coupling, was examined within the topological analysis of experimental (from high-resolution X-ray diffraction) and theoretical (from periodic quantum chemical calculations) electron density functions in its crystal. Together with modeling of a superexchange pathway within the LSDA and DFT+U approach, the results obtained reveal a very weak Cu···O interaction (0.5 kcal/mol worth) between the copper–carbonate layers that is nevertheless stabilizing (bonding) and may serve as a possible pathway for antiferromagnetic interactions.