What is the nature of bonds in FeSO4.7H20?

Question

are the h2o bound using bonds? then is it possible for iron to have more than 6 such bonds? upto my knowledge fe2+ exists in [Fe(H2O)6]2+ then where does 7h2o atoms come from?? Please help..

Answer 1

I'm not sure if you're referring to the crystalline structure or the bonding molecular orbitals, but I found this article that seems extensive enough to be helpful. In essense, the water molecules are held in a octahedral crystal around the metal sulfate molecule by hydrogen bonding, not by direct molecular bonding to the FeSO4 itself (since it is a heptahydrate):

Melanterite FeSO4·7H2O, is monoclinic and crystallizes in the space group P21/c, with a 14.0774(9), b 6.5039(4), c 11.0506(7) Å, ß 105.604(1)°, Z = 4. From the literature, we know that minerals of the melanterite group (M2+ = Co, Cu, Fe, Mg, Mn, Zn) consist of a sulfate tetrahedron, two crystallographically distinct M2+ atoms in octahedral coordination, with six H2O groups forming the coordination sphere of each M2+ atom and one interstitial H2O molecule that is not a direct ligand of an M2+ atom (Baur 1967, Fronczek et al. 2001). There are 14 unique H-bonds in the melanterite structure linking M1 octahedra to M2 octahedra via the sulfate tetrahedra, creating a flexible undulating layer of repeating SO4–M1–SO4–M2 polyhedra (Fig. 3). The first five H-bonds link the M1 and SO4 polyhedra within the layer in a pseudo-edge-sharing arrangement of bonds (Fig. 4). Likewise, the M2 and SO4 polyhedra are linked within the layer by two H-bonds in a pseudoedge- sharing arrangement and three H-bonds associated with the Ow7 H2O molecule (Fig. 4). The remaining four H-bonds, of the 14 H-bonds in melanterite, bridge the layer of polyhedra and must break for the mineral to cleave along (001) (Fig. 3).