A self-assembled cobalt molecular grid of a pyrazine-bridged bis-tridentate ligand (L(R)), where R = H (1), CH3 (2), and Br (3), was prepared and structurally characterized. Depending on the electronic effects of the substituents on the ligand, the redox of the metal center was systematically modulated, and the magnetic behavior from essentially high-spin Co(II) in 3 versus completely diamagnetic Co(III) in 1 to Co(II) spin-crossover in 2 can be achieved.