Stabilization of Ni 2+ dimers in hexacyano Mo 6 cluster-based Prussian blue derivatives: experimental and theoretical investigations of magnetic properties

Herein, two new octahedral molybdenum cyanide cluster compounds, namely [{Ni(NH ) } {Ni (NH ) } ][Mo Br Q (CN) ] ·12H O, Q = S (1) and Se (2), have been synthesized as single crystals by slow diffusion of a solution of nickel chloride into aqueous ammonia solutions of a K Cs [Mo Br Q (CN) ] molybdenum cyanide cluster-based compound. Both 1 and 2 were structurally characterized by single-crystal X-ray diffraction. They are isostructural and crystallize in the cubic system (Im3[combining macron]m (no. 229); Z = 2, a = 18.147(1) Å, and V = 5976(1) Å and a = 18.188(2) Å and V = 6016(2) Å for 1 and 2, respectively). 1 and 2 are based on the association of [Mo Br Q (CN) ] (Q = S, Se) cluster anions with Ni dimer-based cubic [Ni (NH ) ] and octahedral [Ni(NH ) ] cations. The structure is based on 2-fold interpenetrated [{Ni(NH ) } {Ni (NH ) } ][Mo Br Q (CN) ] frameworks related to each other by [½, ½, ½] translation. The unit cell is based on a body-centered cubic framework of cubic [Ni (NH ) ] . The [Mo Br Q (CN) ] (Q = S, Se) cluster units are located in the middle of the edges and at the center of the faces of the cell. The [{Ni(NH ) }] cations are located at the center of the cubes of the a/2 edge. The dimers [Ni (NH ) ] are stabilized by hydrogen bonds between the cyanide ligands of the cluster unit and the hydrogen atoms of the ammonia molecules. Both compounds exhibit a weak antiferromagnetic coupling within the [Ni (NH ) ] dimer entities at low temperatures together with a paramagnetic behavior originating from the cations of the octahedral [{Ni(NH ) }] complexes.