In inorganic chemistry, metal–metal bonds describe attractive interactions between metal centers.  The simplest examples are found in bimetallic complexes.  Metal–metal bonds can be "supported", i.e. be accompanied by one or more bridging ligands, or "unsupported".  They can also vary according to bond order. The topic of metal–metal bonding is usually discussed within the framework of coordination chemistry, but the topic is related to extended metallic bonding, which describes interactions between metals in extended solids such as bulk metals and metal subhalides.