Haemocyanin
Haemocyanin is, like haemerythrin, an alternative for oxygen transport. It is used by a number of molluscs and arthropods.
The protein contains two copper atoms, which are ca. 350 pm apart from each other. In the oxidized form, they coordinate two oxygen atoms, which leads to the antiferromagnetic coupling of the copper centers.
Coordination environement of the copper center