SXRD does not show anion or counter ion in its structure. How would we know that which counter ion is attached at outer sphere to balance to positive charge of the metal ion because in some cases the ligand is neutral (e.g pyrazine) and charge of the metal ion is not balanced so a counter ion is needed to balance it but SXRD does not show this ion.
That denpens on the type of the anion. For example, the presence of NO3- could be readily detected by IR.
As Song-De Han suggested, IR would be useful. I think that in combination with elemental analysis, you should be able to deduce the counterion from the IR and your synthesis conditions. .
Or you can use some analytic experiments to detect some usual anions.
like:
Hydroxyl ions (OH-)
Adding copper sulfate solution, generating blue hydroxide, contains (OH-).
Chloride ion (Cl-)
After adding nitric acid, the silver nitrate solution, the white precipitate AgCl.Precipitation is not soluble in dilute nitric acid, can dissolve in ammonia, [Ag (NH3) 2]+.
Bromide ion (Br-)
Can react with silver nitrate, produce light yellow AgBr precipitation, insoluble in dilute nitric acid.
Iodine ion (I-)
1 can react with silver nitrate, produce yellow AgI precipitation, not soluble in dilute nitric acid.
2 with the chlorine reaction, generate I2, the starch solution turns blue.
Sulfate ion (SO42-)
The addition of hydrochloric acid to the BaCl2 solution, which is not soluble in dilute hydrochloric acid of the white precipitate.
The concentrated solution of sulfite (SO32 -) and acid reaction to produce colorless irritating smell of gas (sulfur dioxide) and the gas can fade fuchsin solution. Can react with Ba (OH) 2 solution, generate white BaSO3 precipitation, the precipitation is dissolved in hydrochloric acid, generate a colorless gas (sulfur dioxide) with pungent smell.
Sulfur ion (S2-)
Reaction with Pb (NO3) 2 solution to generate black PbS precipitation.
Carbonate ions (CO32-)
With BaCl2 solution reaction, the formation of white BaCO3 precipitation, the precipitation is dissolved in nitric acid (or hydrochloric acid), the formation of colorless and tasteless, can make clear the CO2 gas in the turbid water.
Dilute HCl directly to see if there is no gas generation; then clarify whether the gas generated by the lime water test is CO2, if it is, it contains CO32-.
Nitrate ion (NO3-)
Adding copper, sulfuric acid 1 heating concentrated solution or crystal, emit red brown gas.
2 brown ring experiment: the acidification of dilute solution is heated, the gas produced by the ferrous sulfate, the formation of brown material.
Phosphate ion (PO43-)
Adding AgNO3 solution to produce yellow precipitate, then add dilute nitric acid, precipitation dissolution.
It must be possible to narrow down the possibilities by considering the reagents that you added during the synthesis:
- What were the counterions on your metal source? Chloride? Sulphate? Nitrate? etc. This is the most likely possibility.
- Did you add anything else which could act as a counterion? For example, it is common to add monocarboxylic acid "modulators" to the synthesis mixture. These modulators, when deprotonated, can also balance the positive charge. The presence of organic anions like these can easily be detected by dissolving your MOF in an acidic (or basic) deuterated medium and measuring its proton and/or carbon NMR spectrum.
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