Coordination des cations alcalino-terreux dans leurs complexes avec des molécules macrobicycliques. I. Structure cristalline et moléculaire du cryptate de calcium C₁₈H₃₆N₂O₆.CaBr₂.3H₂O

Abstract

(Regu le 22 fOvrier 1973, acceptd le 2 mars 1973)The crystal structure of C18H36N206. CaBr2.3HzO has been determined and refined by three-dimensional least-squares techniques based on 1718 intensities measured on a PAILRED automatic diffractometer. The crystals are orthorhombic, space group P212121, with a= 19.200 (5), b = 14.518 (4), c= 9.511 (2) A and Z=4. The final R value for 1718 reflexions is 0.050. The Ca 2+ ion is bonded to the six oxygen and two nitrogen atoms of the macrobicyclic ligand and one water molecule which form an approximate tricapped trigonal prism. The calcium-bromine distances are greater than 5 A indicating that there is no interaction between the metal ion and the anions. The values of the torsion angles indicate that the cavity of the macrobicyclic ligand approaches its minimal size.

Monoamide Derivatives of EDTA Incorporating Pendent Carboxylates or Pyridyls: Synthesis, Metal Binding, and Crystal Structure of a Dinuclear Ca2+ Complex Featuring Bridging Na+ Ions

“…The bond distances and bite angles (Table ) for the chelate rings in Ca 2 (AmGly 1 ) 2 are also comparable to those found in eight‐coordinate Ca 2+ complexes with similar donor sets . Furthermore, it can be seen that the pendent carboxylate group does not coordinate to either Ca 2+ ion in the dimer.…”

The Stability of Divalent 3d‐ and Trivalent 4f‐Metal Complexes with Diazapolyoxa Macrocyclic Ligands

“…For the other divalent 3d-cations, because for the lower values of their stability constants with ethylenediamine, the same destabilization would lead to systems in which hydrolytic processes would prevail over complex formation. has not enough flexibility to adjust to the small size of the alkaline-earth cations' [21]. It is therefore expected that these difficulties will increase in the case of the much smaller divalent cations with r = 0.8 to 0.7 A.…”

“…Leaving in [2.2.2] only one dioxa bridge unaltered and substituting four CH,-0-CH, groups with four carboxylate groups the flexible EGTAis obtained. It is also an octadentate ligand and forms quite stable complexes with the 3d divalent and 4f trivalent cations [21]. -COO--0OC -CH, 7…”

The Design of Molecular Hosts, Guests, and Their Complexes

“…Crystal structures of Pedersen's 18-crown-6 (21) and Lehn's [2.2.2]cryptand (22,23) show that in their uncomplexed states they contain neither cavities nor convergently arranged binding sites. Comparisons of the crystal structure of host 4 with that of its K+ complex 5 and of host 6 with that of its K+ complex 7 indicate that the complexing act must be accompanied by host reorganization and desolvation.…”