catena-Poly[disodium [[diformatotricopper(II)]-di-mu3-formato-tetra-mu2-formato]]: a new mode of bridging between binuclear and mononuclear formate-copper(II) units.

The novel title polymeric copper(II) complex, {Na2[Cu3-(CHO2)8]}n, consists of sodium cations and infinite anionic chains, in which neutral dinuclear [Cu2(O2CH)4] moieties alternate with dianionic [Cu(O2CH)4]2- units. Both metal-containing moieties are located on crystallographic inversion centers. The syn-syn bridging configuration between the mononuclear and dinuclear components yields a structure that is significantly more dense than the structures previously reported for mononuclear-dinuclear copper(II) carboxylates with syn-anti or anti-anti bridging modes.