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I am interested in what exactly the structure of copper sulfate pentahydrate crystal is like. In the wikipedia, it consists of copper and sulfate strand with 4 water attached to each of the copper atoms in forms of ligands. Some of the oxygen atoms on the sulfate compound seem to have negative charges. For the fifth water molecule, it seems that it is held only by hydrogen bonds.

But here is my question: isn't the whole structure supposed to be quite solid, strongly bonded and devoid of unbalanced charges? Why are there negative charges on the oxygen atoms and the water molecule unfixed in position? (I'm not sure if it is really unfixed in position though)

P.S. please do not send pictures because my internet somehow cannot access them.

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    $\begingroup$ Solid and strongly bonded? Not necessarily; not all crystals are very stable, but this particular one is. Devoid of unbalanced charges? Yes, it absolutely should be and is. $\endgroup$ Commented May 5, 2023 at 6:41
  • $\begingroup$ Though simplifying, a crystal structure is a regular spatial arrangement of objects repeated (in an eventually predictable pattern) only by translations in one, or multiple directions. Similar to a stack of shoe boxes with some enclosed content, you copy-paste this whole parallelepiped again, and again. A single layer of soap molecules between water and air prefers a regular arrangement in this plane, hence builds a 2D crystal (similar to some floor tiles' layout and wallpapers). And crystal structures may undergo rapid changes (see liquid crystals in LCD displays of pocket calculators). $\endgroup$
    – Buttonwood
    Commented May 5, 2023 at 7:49
  • $\begingroup$ The original structure is in Beevers & Lipson Proc. Roy. Soc. A (London) 1934, v 146, p570. The Cu atom is 6 coordinated, four water O atoms in the plane and axially two O atoms each one from a different sulphate ion. The fifth water is held between water molecules attached to cations and O atoms of sulphate ions, i.e this water bridges between two Cu octahedra attached to two sulphate O atoms (on different Cu centres) and an O atom on one of the Cu. The Wikipedia structure does not show this v clearly. $\endgroup$
    – porphyrin
    Commented May 5, 2023 at 14:37

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