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

Abstract

Five new cluster compounds based on [Mo₆Brⁱ₈(CN)^a₆]²⁻ and [Mo₆Brⁱ₆Qⁱ₂(CN)^a₆]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 [Mo₆Brⁱ₈(CN)^a₆]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 [Mo₆Brⁱ₆Qⁱ₂(CN)^a₆]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 [Mo₆Brⁱ₆Qⁱ₂(CN)^a₆]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 [Mo₆Brⁱ₆Qⁱ₂(CN)^a₆]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 [Re₆Qⁱ₈(CN)^a₆]⁴⁻ based compounds are discussed.