Synthese und Struktur vier- und achtkerniger Chelatkomplexe – exohedraler Gastaustausch an Tetrahemispheraplexen

Selective Guest Encapsulation by a Cobalt-Assembled Cage Molecule

Metal-assembled resorcinarene-based cages enclose space and entrap organic molecules from water. Addition of cobalt(II) ions to a neutral, aqueous solution of a resorcinarene that has iminodiacetic acids attached to its upper rim results in the formation of cages. These cages not only entrap organic molecules, but they do so in a selective manner. Guests with optimum size, shape, and polarity are preferentially entrapped. For example, selection of p-xylene is twenty thousand times more favorable than that of m-xylene. The enthalpy of resorcinarene deprotonation and cage formation was calculated by performing calorimetry studies and ranged from -305 to -348 kJ mol(-1). The change in enthalpy of guest encapsulation varied by as much as 43 kJ mol(-1). The differences in change in free energy of guest encapsulation varied by -16 kJ mol(-1). The changes in enthalpy and free energy of guest encapsulation were used to calculate the changes in entropy, which ranged from -97 to +37 J mol(-1) K(-1). An enthalpy-entropy compensation of guest encapsulation was observed.

Inter-conversion of 15-MC-5 to 12-MC-4 manganese metallacrowns: structure and bioactivity of metallacrowns hosting carboxylato complexes

Interaction of manganese with salicylhydroxamic ligands (shi) in methanol, in the presence of pyridine, leads to the formation of a series of 15-membered metallacrown (MC) Mn(II)(L)2[15-MCMn(III)N(shi)-5](py)6 or 7, (L=formato, benzoate or alkanoato ligand, py=pyridine). In the absence of pyridine, the Mn(II)(L)2[12-MCMn(III)N(shi)-4](MeOH)6 metallacrown was isolated and structurally characterized. The crystal structure of {[Mn(II)(HCOO)2][(15-MCMn(III)N(shi)-5)(py)7]}.py.1.9CH3OH.H2O (1) contains a neutral 15-membered metallacrown ring consisting of five Mn(III) and five shi(-3) ligands. The 15-membered metallacrown ring is formed by the succession of five structural moieties of the type [Mn(III)-N-O]. The diverse in the configuration (planar or propeller) for the ring Mn(III) ions gives the metallacrown core a bending structure. The crystal structure of {[Mn(II)(C6H5COO)2][(12-MCMn(III)N(shi)-4)(CH3OH)6]}.2CH3OH (2) contains a neutral 12-membered metallacrown ring consisting of four Mn(III) and four shi(-3) ligands. The 12-membered metallacrown ring is formed by the same way of succession of four structural moieties of the type [Mn(III)-N-O], while the presence of a planar only configuration of shi ligands around ring Mn(III) ions gives to the metallacrown core a planar structure. The encapsulated Mn(II) is six and seven-coordinate for (1) and (2), respectively, and is bound to the hydroximate oxygen of the metallacrown core and two oxygen atoms from the carboxylate ligands. Antibacterial screening data showed that, among all the compounds tested, manganese metallacrowns are more active compared to the simple manganese herbicide or carboxylate complexes, with increased efficiency for [15-MCMn(III)N(shi)-5] compared to the analogous [12-MCMn(III)N(shi)-4].

Self-assembly of tetrahedral and trigonal antiprismatic clusters [Fe4(L4)4] and [Fe6(L5)6] on the basis of trigonal tris-bidentate chelators

In a one-pot reaction, the tetranuclear iron chelate complex [Fe4(L4)4] 6 was generated from benzene-1,3,5-tricarboxylic acid trichloride (4), bis-tert-butyl malonate (5a), methyllithium, and iron(II) dichloride under aerobic conditions. Alternatively, hexanuclear iron chelate complex [Fe(L5)6] 7 was formed starting from bis-para-tolyl malonate (5b) by employing identical reaction conditions to those applied for the synthesis of 6. The clusters 6 and 7 are present as racemic mixtures of homoconfigurational (delta,delta,delta,delta)/(lambda,lambda,lambda,lambda)-fac or (delta,delta,delta,delta,delta,delta)/(lambda,lambda,lambda,lambda,lambda,lambda)-fac stereoisomers. The structures of 6 and 7 were unequivocally resolved by single-crystal X-ray analyses. The all-iron(III) character of 6 and 7 was determined by Mössbauer spectroscopy.