Investigation of low-hydrated metal(II) nitrates. Syntheses and crystal structures of Zn(NO3)2· H2O and M(II)(NO3)2· 2 H2O (M = Mg, Mn, Co, Ni)

Abstract

AbstractCrystals of Zn(NO3)2· H2O and Mn(NO3)2· 2 H2O were synthesized by heating melts of the respective penta- or hexahydrates. Single crystal X-ray diffraction of the two highly hygroscopic phases reveals new sheet-structure types: Zn(NO3)2· H2O [Pbca,a= 9.722(1),b= 5.865(1),c= 17.799(3) Å (120 K),Z= 8,R1= 0.025]; Mn(NO3)2· 2 H2O [P212121,a= 5.921(1),b= 8.835(1),c= 22.882(3) Å (120 K),Z= 8,R1= 0.020]. Zn(NO3)2· H2O is built of only one kind of complicated, corrugated sheets held together by hydrogen bonds, while Mn(NO3)2· 2 H2O is built of alternating sheets with Mn in 6- and 7-fold coordination, respectively, again interconnected by hydrogen bonds. While in Zn(NO3)2· H2O the hydrogen bond system is quite clear-cut, this is not the case in Mn(NO3)2· 2 H2O. Contrary to expectation, the thermal expansion is not clearly largest perpendicular to the sheets in both compounds.In the well known structures of the nitrate dihydrates of Mg, Co and Ni new refinements allowed to locate the hydrogen atoms.Together with Mn(II) nitrate monohydrate and the dihydrates of Mg, Co, Ni, Zn and Cd the two new nitrates form an interesting group of sheet structures.