Low dimensional solids based on Mo₆ cluster cyanides and Mn²⁺, Mn³⁺ or Cd²⁺ metal ions: Crystal chemistry, magnetic and optical properties

Five new cluster compounds based on [Mo₆Brⁱ ₈(CN)^a ₆]^2- and [Mo₆Brⁱ ₆Qⁱ ₂(CN)^a ₆]^n- (Q = S, Se, n = 3, 4) cluster units have been synthesized and characterized. Structures were determined by X-ray single crystal diffraction techniques and measurements of relevant magnetic susceptibility and optical properties were carried out. [trans-Mn(H₂O)₂][Mo₆Br₈(CN)₆] (1) crystallizes in the orthorhombic system (Imma space group) and contains 2D square-net-layers built-up from [Mo₆Brⁱ ₈(CN)^a ₆]^2- and [trans-M(H₂O)₂]²⁺ moieties. Cs_x[trans-(Mn^II _xMn^III _1-x)(H₂O)₂][Mo₆Br₆Q₂(CN)₆] (Q = S (2) and Se (3)) crystallize in the Imma space group as well; their structures are strongly related to that of 1 with a 2D square net of cluster units and transition metals. They are based on [Mo₆Brⁱ ₆Qⁱ ₂(CN)^a ₆]^3- (Q = S, Se) cluster units whose charge is counter balanced by Cs⁺ as well as Mn²⁺ and Mn³⁺ in high spin states. It is evidenced that the x content of the Cs⁺ counter-cation is equal to that of Mn²⁺ in order to maintain-along with (1 - x) Mn³⁺-23 valence electrons per cluster and a 3- charge for the cluster unit. The two oxidation states Mn²⁺ and Mn³⁺ were confirmed by electron energy loss spectroscopy (EELS) measurements. (H₃O)H[cis-Cd(H₂O)₂][Mo₆Br₆Q₂(CN)₆]-H₂O (Q = S (4) and Se (5)) crystallize in the trigonal system (P3₁21 space group) and are based on [Mo₆Brⁱ ₆Qⁱ ₂(CN)^a ₆]^4- (Q = S, Se) cluster units. In contrast to compounds 1-3, owing to the cis-position of the two water molecules around the transition metal, 4 and 5 exhibit a close-packed 3D structure based on an interpenetrated framework of cluster-based chains. In particular, it contains infinite chains alternating [Mo₆Brⁱ ₆Qⁱ ₂(CN)^a ₆]^4- and H⁺ protons as linkers. Magnetic and optical properties are also reported as well as theoretical calculations to support the structural analysis and physical properties. Structural analogies with [Re₆Qⁱ ₈(CN)^a ₆]^4- based compounds are discussed.