Dear readers,
I have a crystal structure of a metal string complex (interconnected metal atoms, which are wrapped by four ligands). in the center there are nickel atoms, but their number is unkown. It shows one nickel atom with 50% probability. So , 50% it exsits 50% not. And in the formula it shows Ni 8.5. There are 8.5 nickel atom. But it should be 8 or 9. Please help me to explain or treat this crystal structure.
Thanks in advance
This is may be due to disorder in structure. Use part cammond in SHELXL
First we need information on the space group, is it P-1? Or higher symmetry? Which programme did you use to solve the structure? Which solution did you try? Direct methods or Patterson or others?
Dear Nizami,
You say that the number of nickel atoms (ions?) is "unknown", but later say that they "should be 8 or 9" - which one is it? Do you already know the structure (from literature) or are you trying to determine it (if so, you can follow both Muhammad's and Axel's suggestions)?
The sum formula only tells you what the mean occupancy is for a specific atom. There are different reasons why a sum formula does not have an stoichiometric integer for all atoms. The main ones I can think of includes partial occupancy (the atom in question is not present in all such positions) and disordered structure (the atom shares the position with another atom), or possibly a combination or the two.
In addition, in minerals, it is not uncommon for atoms to exist in two different positions in the structure which could lead to non-integer values. One example is the mineral aerugite with the sum formula Ni8.5As3O16. The required charge balance for the mineral is achieved through partial occupancy (five sixths) of the nickel(II) ion in the octahedrally coordinated layer, consisting of a mixture of AsO6 and NiO6 octahedra (with the arsenic(V) also present in the tetrahedral AsO4 units).
I hope this helps.
regards,
Daniel
Thanks a lot for your responses. And sorry for late reply. The space group is R3. I am not solved this structure. it's one of our co-authors that did it. (I am new in this domain) And when I looked to results I have seen Ni8.5. We have previous work like that. So according to our previous research we are sure there could be 8 or 9. We know similar structures but not this one excactly. So I will download shelx and try to find myself :) Daniel your answer was helpful
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