Pyrite diamagnetism

Ruthenium and osmium form only disulfides. These have the pyrite structure and are diamagnetic semiconductors this implies that they contain M . RuSc2, RuTc2, OsSc2 and OsTc2 are very similar. All 6 dichalcogenides are obtained directly from the elements. 

While the diamagnetic AuSb2 is a metallic and even superconducting (27) d7 pyrite, the corresponding Cu and Ag phosphides are both diamagnetic semiconductors (33, 134). The cation, therefore, must be either mono- or trivalent. The monoclinic structure of CuP2 has recently been determined by Olofsson (135) [C h — P2i/c, all atoms in 4(e)], The phosphorus atoms form infinite puckered layers almost identical to those met... 

Hence the elongation of the anion octahedron is such that the cation is in square-planar coordination while the anion is surrounded by a deformed tetrahedron of four cations (Fig. 51). This distortion of the crystal structure from NiS(h) to PtS exactly corresponds to the transition from high-spin ds pyrite NiSa to diamagnetic PdSa by elongation of the anion octahedra. 

The disulfides have pyrite (Ru3 and Os), distorted pyrite (Pd) and Cdl2 (Pt) structures all are diamagnetic. There are various mixed sulfides such as Ta2PdS6. 

Binary halides of Ru(II) and Os(II) are not well characterized and there are no oxides. Heating the metal with S gives M 2 (M = Ru, Os) which contain [82] and adopt a pyrite structure (see Section 21.9). Most of the chemistry of Ru(II) and Os(II) concerns complexes, all of which are diamagnetic, low-spin and, with a few exceptions, octahedral. We saw in Section 20.3 that values of (for a set of related complexes) are greater for second and third row metals than for the first member of the triad, and low-spin complexes are favoured. A vast number of Ru(II) complexes are known and we can give only a brief introduction. 

Garnet-red crystals with metallic, yellowish-green reflectance, stable in air, diamagnetic. M.p. 178.5°C (undergoes deformation at 151°C). Soluble in chloroform and benzene in the cold, readily soluble in the hot solvents. Can be recrystallized ty reprecipitation with alcohol from a chloroform solution. Can be obtained from methylene chloride in this case, large crystals, similar in appearance to pyrites, are obtained. 

The anion-anion distances, S—S = 2.13A and Se-Se = 2.36A, are slightly larger than expected for covalent single bonds but the non-metallic character of these diamagnetic compounds is a proof that these are single bonds. When the distortion of the anion octahedra in PdS2 is reduced by pressure the semiconductor transforms into a metal before the pyrite structure is reached [419]. 

As is to be expected from the ionic formula Pd (S—P—P—S)" the silvery blade-like crystals of PdPS and PdPSe are diamagnetic semiconductors with band gaps of 0.7 eV and 0.15 eV, respectively. PdPS and PdPSe are completely miscible [419]. PdAsS and PdSbS as well as PdAsSe and PdSbSe crystallize in a pyrite structure and are therefore metallic, whereas PdPTe is unknown. In this context it is of interest to note that substitution of P by As in the anion chains of PdP2 is possible up to PdPAs whereas at the composition PdAs2 only the pyrite structure is obtained. We wonder whether the structural PdPS-type pyrite-type transition in Pd(P, As)S and Pd(P, As)Se solid solutions occurs near the semiconductor -> metal transition point. 

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