The single-crystal structure of a mixed-valence heptanuclear cyanide-bridged complex Fe(II)Fe(III)6 that may be considered as a model of Prussian blue has been determined. The low-temperature magnetic properties (T < 2 K) reveal a metamagnetic behavior below 220 mK. This is the result of the intermolecular antiferromagnetic interaction between the ferromagnetically coupled high-spin clusters.