Molecular complexes of Ca, Sr, and Ba with the reduced forms of 3,6-di-tert-butyl-o-benzoquinone as ligands (catecholate, 3,6-Cat2–, or semiquinone 3,6-SQ–‧) were synthesized and structurally characterized. Trinuclear complexes [M3(3,6-Cat)3(thf)6] (1, M = Ca; 2, M = Sr) or tetranuclear complex [Ba4(3,6-Cat)4(thf)6] (3) crystallize from tetrahydrofuran (thf) solutions. In the structures of 1 and 2 metal atoms form a nearly right triangle with two µ3-bridging 3,6-Cat ligands; in 3, the metal atoms form a tetrahedron contracted along a twofold axis, and all the catecholates are µ3-bridging. In nonpolar media the complexes 1–3 lose coordinated thf, upon which 1 is converted into complex [Ca4(3,6-Cat)4(thf)4] (4), structurally similar to 3. Complex 1 is oxidized by one equivalent of the quinone to yield mixed-ligand complex [Ca3(3,6-SQ)2(3,6-Cat)2(thf)4] (5), structurally similar to 1. Successive oxidation by the quinone leads to dissociation to mononuclear species, [Ca(3,6-SQ)2(thf)3] (5), which possesses pentagonal-bipyramidal coordination with two semiquinolate ligands lying in an equatorial plane. Solution behavior of the complexes is studied by NMR (for catecholates) and EPR (for semiquinolates) spectroscopy.