Heterometallic trinuclear {CdII—MII—CdII} pivalates (M = Mg, Ca, or Sr): ways of assembly and structural features

Conditions for chemical assembly of new heterometallic trinuclear pivalates [Cd2M(piv)6L2] (M = Mg, Ca, or Sr; piv is pivalate) were found. Reactions with the nonchelating ligand 2,4-lutidine (lut) gave the crystals of heterometallic complexes [Cd2M(piv)6(lut)2] (M = Mg (1), Ca (2), and Sr (3)). With the chelating ligand 1,10-phenanthroline (phen), only the homometallic dimer [Cd2(piv)4(phen)2] (4) was obtained under these conditions. Yet heterometallic trinuclear complexes with 1,10-phenanthroline ([Cd2Mg(piv)6(H2O)(phen)2] (5), [CaCd2(piv)6(phen)2] (6), and [Cd2Sr(piv)6(phen)2]∙2MeCN (7)) were synthesized by reactions of phen with complexes 1—3. For all the complexes obtained, the molecular and crystal structures as well as the details of their molecular architecture were determined. The thermal behavior of aqua complex 5 was studied by TG and DSC. The complex eliminated the water molecule between 130 and 180 °C with a high endothermic effect (Q = 101 kJ mol–1) due to (1) intramolecular hydrogen bonds that stabilize its molecular architecture and (2) subsequent structural rearrangements.