Interactions of Alkali and Alkaline-Earth Metals in Water-Soluble Heterometallic FeIII/M (M = Na+, K+, Ca2+)‑Type Coordination Complex

A water-soluble hexadentate ligand H4bedik was reproduced and employed to synthesize the corresponding mononegative [FeIIIbedik]− complex core. In the complex formation process, NaOH, KOH, and Ca­(OH)2 bases were used in order to have the corresponding cations as the counterpart of the mononegative complex core. Thus, formed complexes were designated as complex 1·H2O, Na+ ion as the countercation; complex 2, K+ ion as the countercation; and complex 3·H2O, 1/2 Ca2+ ion as the countercation. Complexes were characterized by IR and mass spectrometric techniques. Additionally, the complexes were structurally characterized by single crystal X-ray diffraction analysis. In complex 1·H2O, where the Na+ ion was present as a countercation, a two-dimensional (2D) zigzag layer structure was formed along the bc plane. The two adjacent layers were parallel to each other and propagated along the same direction, and the adjacent layers were connected to each other by H-bonding. Thus, a three-dimensional (3D) network was found. A K+ ion-containing complex 2 formed a one-dimensional (1D) linear network that propagated along the b axis. H-bonding driven 3D layers were also found in complex 2. Akin to complex 1·H2O, complex 3·H2O also formed a 2D layers structure; however, the structure was planar and not zigzag as observed in complex 1·H2O. In complex 3·H2O, two adjacent parallel layers were propagated along two opposite directions. Thermogravimetric analyses indicated that the stability of the complexes and the [FeIIIbedik]− complex core depended on the nature of the countercation. Longitudinal (r 1) and transverse relaxivity (r 2) measurements of aqueous solutions of the complexes have been performed. The value was cation-dependent and thus emphasized different interactions between [FeIIIbedik]− units in the presence of different cations.