Comparison of the crystal structures of Co2(X2O7)·2H2O,X=P and As

摘要

Crystals of Co2(X2O7)·2H2O,X=P/As were synthesized under hydrothermal conditions. Their crystal structures were determined by single crystal X-ray diffraction:a=6.334(1)/6.531(2),b=13.997(2)/14.206(4),c=7.637(1)/7.615(2)Å, β=94.77(2)/94.74(2)°, space group P21/n,R=0.032/0.046,Rw=0.028/0.034 for 2423/2042 reflections and 131/119 variables. Within the twoXO4tetrahedra connected via a common corner to anX2O7group the average 〈P-O〉 bond lengths are approximately equal (1.540 and 1.543 Å), but 〈As-O〉 differs significantly (1.685 and 1.696 Å). A comparison with the isotypic Mn and Mg pyrophosphates shows a correlation between the ratio 〈Me-O〉/〈X-O