Growth and structure of K2NixCo(1–x)(SO4)2 · 6H2O single crystals

Resumo

Single crystals of the K₂Ni_xCo_(1–x)(SO₄)₂ · 6H₂O composition are grown by spontaneous flux crystallization. More exact chemical formulas of the single crystals are determined based on the diffraction data as K₂Co(SO₄)₂ · 6H₂O (I), K₂(Co_0.657Ni_0.343)(SO₄)₂ · 6H₂O (II), K₂(Co_0.226Ni_0.774)(SO₄)₂ · 6H₂O (III), K₂(Co_0.216Ni_0.784)(SO₄)₂ · 6H₂O (IV), and K₂Ni(SO₄)₂ · 6H₂O (V). The substitution of nickel atoms for cobalt atoms in structure I results in a shortening of all (Co,Ni)–O interatomic distances. With increasing Ni concentration, the (Co,Ni)–O2 distance shortens to a lesser degree than the (Co,Ni)–O1 and (Co,Ni)–O3 distances and, as a consequence, the distortion of (Co,Ni)O₆ octahedra decreases. NiO₆ polyhedra are less distorted than CoO₆ octahedra. The analysis of difference syntheses of electron density shows that the number of uninterpretable peaks on the maps of mixed crystals II, III, and IV, as well as on the map of K₂Co(SO₄)₂ · 6H₂O, is larger with respect to those of structure K₂Ni(SO₄)₂ · 6H₂O.