POTASSIUM AND SODIUM COMPLEXES OF 1,3-CALIX[4]-BIS-CROWN-6 - CRYSTAL AND MOLECULAR-STRUCTURES, H-1-NMR INVESTIGATION AND MOLECULAR-DYNAMICSSIMULATION

The crystal structures of two alkali metal complexes involving the dit opic receptor 1,3-calix[4]-bis-crown-6, Bis-C6, are reported. KBis-C6( NO3).2CH(3)CN (1) crystallizes in the monoclinic space group C2/c: a = 18.025(8), b = 17.672(9), c = 17.454(13) Angstrom, beta = 97.55(5)deg rees, V = 5511(9) Angstrom(3), Z = 4. Refinement led to a final conven tional R value of 0.091 for 1563 reflections. The structure of (1) is isomorphous to those previously observed for the free ligand and some of its mono- and binuclear cesium complexes: the conformation of the l igand is the same in all cases, which results in nearly identical pack ings and cell parameters. The potassium ion is bonded to the six oxyge n atoms of the crown-ether and two from nitrate ions. Na(2)Bis-C6(NO3) (2)(H2O)(2).CH3CN (2) crystallizes in the monoclinic space group P2(1) /c: a = 13.487(6), b = 16.758(9), c = 23.542(15) Angstrom, beta = 101. 17(4)degrees, V = 5220(8) Angstrom(3), Z = 4. Refinement led to a fina l conventional R factor of 0.14 for 2546 reflections, One sodium ion a nd one water molecule are included in each crown-ether moiety. The sod ium ion is bonded to three oxygen atoms of the crown only, two from ni trate ions and the one of the water molecule, which also forms possibl e hydrogen bonds with two ether oxygen atoms. H-1-NMR experiments show that 1:1 potassium or sodium complexes are formed in chloroform solut ion from picrate salts, they also confirm the bonding mode observed in the solid state, with no evidence of pi-interactions between the cati ons and the aromatic rings. Molecular dynamics simulations were perfor med in vacuo and in an explicit water phase on Bis-C6/NaNO3 mono- and binuclear complexes to study the influence of the nitrate counter-ion on the structural features of these complexes.