Check cavity fit for target and competing ions. Review hydration penalties, donor match, and temperature. Choose stronger complexes with clearer, faster lab planning today.
| Crown Ether | Target Ion | Competitor Ion | Cavity (Å) | Likely Preference |
|---|---|---|---|---|
| 18-crown-6 | K+ | Na+ | 2.60 | K+ often shows stronger size fit |
| 15-crown-5 | Na+ | K+ | 1.70 | Na+ can gain a size advantage |
| 12-crown-4 | Li+ | Na+ | 1.20 | Li+ may benefit from tighter fit |
Ion diameter = 2 × ionic radius
Relative mismatch = |cavity diameter − ion diameter| ÷ cavity diameter
Size score = exp(−7 × relative mismatch²)
Charge score = 1 + [0.22 × (charge ÷ ionic radius)]
Hydration score = exp[−hydration energy ÷ (180 + 0.20 × temperature)]
Solvent score = max(0.45, 1.30 − solvent polarity ÷ 12)
Denticity score = 0.70 + donor atoms ÷ 10
Relative binding index = size score × charge score × hydration score × solvent score × denticity score × donor match × softness match × flexibility factor × steric factor
Selectivity coefficient = target binding index ÷ competing binding index
This model is a practical screening tool. It does not replace measured stability constants or full quantum and thermodynamic analysis.
Crown ethers are classic host molecules. They bind metal ions through donor atoms. Their selectivity depends on fit, charge, and solvation. A good screening tool helps compare ions fast. It also supports route selection during synthesis, extraction, and sensing work.
Cavity size is usually the first filter. A crown ether often prefers ions with a close diameter match. Too small means steric crowding. Too large means weak contact. Strong selectivity usually appears when the guest sits inside the cavity with balanced strain and favorable donor alignment.
Hydration energy matters because metal ions are stabilized by solvent. Highly hydrated ions are harder to remove from solution. Even with a good size match, strong hydration can lower complexation efficiency. That is why selectivity can shift between water, mixed solvents, and less polar media.
Charge density influences electrostatic attraction. Smaller ions with the same charge often show stronger local interactions. Yet they may also pay a larger dehydration penalty. Donor matching helps balance this effect. Oxygen rich crowns often favor hard cations, while softer systems can shift preferences in modified hosts.
This calculator combines cavity fit, denticity, hydration effects, charge contribution, solvent influence, flexibility, and steric correction. It creates a relative binding index for a target ion and a competing ion. The selectivity coefficient then shows which ion should be preferred under the chosen inputs.
Use this model for screening, ranking, and early design. It is helpful before experiments or when comparing possible hosts. It is not a substitute for measured equilibrium constants. Still, it gives a structured way to think about host guest behavior and supports clearer laboratory decisions.
It compares target ion binding against competing ion binding. A value above 1 favors the target. A much larger value suggests stronger discrimination by the selected crown ether.
No. It is a relative screening value. It helps rank options quickly. Experimental log K values still require laboratory measurement or advanced modeling.
Highly hydrated ions are strongly stabilized in solution. The host must overcome that stabilization. Strong hydration often lowers apparent complexation efficiency.
Real systems rarely contain one ion only. Competition affects extraction, sensing, transport, and separation performance. Comparing two ions gives a more practical selectivity picture.
It is a user supplied adjustment. It reflects how well the ion and donor environment complement each other. Higher values raise relative binding strength.
It lets you account for softer or harder interaction tendencies. It is useful when substituted crowns or unusual ions shift behavior beyond simple size matching.
Yes. Choose the custom option or edit the cavity and donor fields directly. That allows quick screening of new hosts, derivatives, or literature based structures.
Export when you want screening records, shareable summaries, or project documentation. CSV works well for data logs. PDF works well for reports and review notes.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.