Crystal engineering and magnetic properties of a 2D cyano-bridged NiIIFeII network formed through reduction of ferricyanide

Reaction of potassium ferricyanide with a mixture of nickel(II) chloride hexahydrate and trans-1,2-diaminocyclohexane (L) produces both a ferrocyanide ([NiIIL2]2[FeII(CN)6] · 5H2O (1)) and a ferricyanide ([NiII(L)2]3[FeIII(CN)6]2 · 2H2O (2)) compound. Clearly, the formation of 1 is accompanied by the reduction of ferricyanide to ferrocyanide. Interestingly, the relative amounts of the formation of 1 and 2 depends on the nickel(II):diamine ratio and the volume of the reaction mixture. It has been established from spectrophotometric titration that trans-1,2-diaminocyclohexane is responsible for the reduction of [Fe(CN)6]3− to [Fe(CN)6]4−. The ferrocyanide analogue, 1, can also be prepared by mixing potassium ferrocyanide with the nickel(II)-diamine solution. Among the six cyanides of each hexacyanoferrate(II), four coordinate to four different nickel(II) centers to form cyano-bridged two-dimensional square grids. The remaining two cyanides form strong hydrogen bonds with two hydrogens of one water of crystallization to result in squares, which can be considered as appended to the two-dimensional grids. The hydrogen bonds involving the hydrogens of amine groups of one 2D grid and the oxygens forming the appended squares of another 2D grid generate the third dimension of the structure. Variable-temperature (2–300 K) magnetic susceptibility measurements reveal that the nickel(II) centers in 1 are practically non-correlated.

Reaction of potassium ferricyanide with a mixture of nickel(II) chloride and trans-1,2-diaminocyclohexane (L) produces both a ferrocyanide ([NiIIL2]2[FeII(CN)6] · 5H2O (1)) and a ferricyanide ([NiII(L)2]3[FeIII(CN)6]2 · 2H2O (2)) compound. From spectrophotometric titration, it has been established that the diamine is responsible for the reduction of ferricyanide to ferrocyanide. The factors that affect the formation of the two compounds as well as crystal engineering and magnetic properties of the ferrocyanide analogue, 1, have been described. The structure of 1 consists of a two-dimensional cyano-bridged square grid network which is self-assembled into three-dimensions due to hydrogen bonding interactions.Figure optionsDownload as PowerPoint slide