Coordination bonds and strong hydrogen bonds giving a framework material based on a 4-and 8-connected net in [Ca[Co(en)(oxalato)(2)](2)](n)

[Ca[Co(ethylenediamine)(oxalato)(2)](2)](n) center dot 4H(2)O gives a 3D-net based on Ca(oxalato)(4) 8-connected nodes and Co(en)(oxalato)(2) 4-connected nodes resulting in a compound that retains its structure and 19% void volume even after residual solvent has been evacuated under vacuum at 160 degrees C.