The controlled hydrolysis of an ethylzinc guanidinate complex affording an alkylzinc cluster containing a [Zn₁₀O₄]¹²⁺ supertetrahedron core stabilized by the guanidinate ligands is described. Accompanying investigations on the reactivity of this unprecedented cluster toward alcohols resulted in the formation of a mononuclear zinc alkoxide supported by the guanidinate ligands.