The first dimer has a water molecule in the vicinity of the π electron cloud of two pyridine moieties of different ligands, and we label its location as pose A (see Fig. ). Another dimer was identified by positioning an H 2 O such that it interacts via a weak hydrogen bond with a C-H bond of one ligand, as indicated by the geometric alignment from the ligand-hydrogen to the lone-pair on the water molecule. We denote this dimer geometry as pose B, as shown in Fig. . Further searches for other dimers were unsuccessful, indicating that there are only two distinct, dimeric poses of an H 2 O non-covalently, directly bonded to the [Fe(bpy) 3 ] 2+ complex.