kpeerakit
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Orderness of many metals' salt crystals
Chinese scientists has created a single crystal of cobalt nickel sulfate twelvehydrate by mixing equal molar of CoSO4 and NiSO4 :
CoSO(4).7H(2)O + NiSO(4).6H(2)O = CoNi(SO(4))(2).12H(2)O + H(2)O
and then reported its X-rays crystal structure. I wonder why the solid forms in ordered pattern of two metal ions. It is sorted as a single compound,
not a solid solution.
And I wonder what if we mix three metal sulfate solutions and crystallize it into a single crystal, because, for three differene metal centers it may
be arranged in many forms. I wonder how do atoms "know" where or what position to be formed.
Ref: G. Su et al. (2003). Cryst. Res. Technol. 38, No.12, 1087-1092.
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JohnWW
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That instance is rather surprising, because of the close similarities in ionic radius, electronegativity, and ligand preferences of Co(II) and
Ni(II). One would, as the result, have expected a product with the same crystal structure and a continuous range of compositions over the entire range
of 0-100% Ni(II). The situation is quite different from, for example, the crystallization of "alums" formed by the sulfates (and possibly chromates,
and selenates) in equimolar proportions and with 12H2O, having the same crystal structure of a wide range of univalent cations (Na+, K+, Rb+, Cs,
NH4+, Ag+, Tl+) paired with trivalent cations (Al+++, Ga+++, In+++, Sc+++, Y+++, La+++ and other lanthanides, V+++, Cr+++, Fe+++, and possibly some
others) from strongly acid aqueous solutions.
In crystallizations of double salts, the products are usually those with minimum energy, and the most tightly internally bound, under the particular
conditions.
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kpeerakit
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Thank you. That means different particles like to be together.
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kpeerakit
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Nature use what to distinguish between the same and the difference? Think of different isotopes of the same element, or the nearly same species. Does
it depend on statistics?
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DJF90
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JohnWW: I think you're missing the point here.
The active ligands would be the water molecules; sulfate is pretty damn shit in this respect. You should have a crystal structure containing sulfate,
hexaaquacobalt (II) and hexaaquanickel (II) as elucidated from the molecular formula provided.
I suspect that the different aqua ions occupy different interstital sites (Oh vs Td), and the arrangement will therefore depend on the LFSE, much like
spinels. Recall Co3O4 is a "normal spinel" whilst Fe3O4 is an "inverse" spinel due to differences in LFSE for having the M(II)/M(III) in the Oh or Td
sites.
I suspect this is a similar case, as there is again a difference in the number of d-electrons, and hence different LFSE. The aquaions will therefore
be arranged so that the LFSE is maxed out and the crystal structure is most stable.
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