Paramagnetic trinuclear complexes, trans-[Pt 2 M-(piam) 4 (NH 3 ) 4 ](ClO 4 ) x (t-M; piam = pivalamidate, M = Mn, Fe, Co, Ni, and Cu, x = 2 or 3), aligned as Pt−M−Pt were successfully synthesized and characterized. The dihedral angles between the Pt and M coordination planes in t-M are approximately parallel, showing straight metal−metal bonds with distances of approximately 2.6 Å. Except for t-Fe, the trinuclear complexes are dimerized with close contact (approximately 3.9 Å) between the end Pt atoms to form Pt−M−Pt•••Pt−M−Pt alignments with high-spin M(+2) containing five (t-Mn), three (t-Co), two (t-Ni), and one (t-Cu) unpaired electrons localized on M atoms. Several physical measurements and calculations revealed that the dimerized structures were maintained in MeCN, where cyclic voltammograms for t-M exhibited two-step oxidation and reduction attributed to Pt−Mvia mixed-valent states. Magnetic susceptibility measurements for t-M showed antiferromagnetic interaction, t-Mn: J = −0.9 cm −1 , t-Co: J = −3.5 cm −1 , t-Ni: J = −7.3 cm −1 , and t-Cu: J = 0.0 cm −1 , between the two M centers with distances of 9.0 Å through Pt•••Pt bonds.