[NH_4]_2Mn_3(H_20)_4[Mo(CN)7]_2 centre dot 4H_2O:Tuning Dimensionality and Ferrimagnetic Ordering Temperature by Cation Substitution

摘要

[NH_4]_2Mn_3(H_2O)_4[Mo(CN)_7]_2 centre dot 4H_2O (1) has been synthesized by slow diffusion of aqueous solutions containing K_4[Mo(CN)_7] centre dot 2H_2O,[Mn-(H_2O)_6](NO_3)_2,and (NH_4)NO_3.Compound 1 crystallizes in the monoclinic C2/c space group.The basic motif of the three-dimensional structure consists of a Mo1-Mn1 gridlike sheet parallel to the be plane.Two of these sheets are connected through CN-Mn2-NC linkages to form a bilayer reminiscent of the K_2Mn_3(H_20)_6-[Mo(CN)_7]_2 centre dot 6H_20 (2) two-dimensional structure.In 1,[NH_4]~+ cations allow these bilayers to be connected through direct Mo1-CN-Mn1 bridges to form a three-dimensional network,whereas in 2,they are isolated by (H_2O)K~+ cations.As shown by the magnetic measurements,this increase of dimensionality by counterion substitution induces an enhancement of the ferrimagnetic critical temperature from 39 K in 2 to 53 K in 1.