The homoleptic mononuclear compound [Co(bpp‐COOMe)₂](ClO₄)₂ (1) (bpp‐COOMe=methyl 2,6‐di(pyrazol‐1‐yl)pyridine‐4‐carboxylate) crystallizes in the monoclinic C2/c space group, and the cobalt(II) ion possesses a pseudo‐octahedral environment given by the two mer‐coordinated tridentate ligands. Direct‐current magnetic data, single‐crystal torque magnetometry, and EPR measurements disclosed the easy‐axis nature of this cobalt(II) complex, which shows single‐molecule magnet behavior when a static field is applied in alternating‐current susceptibility measurements. Diamagnetic dilution in the zinc(II) analogue [Zn(bpp‐COOMe)₂](ClO₄)₂ (2) afforded the derivative [Zn_0.95Co_0.05(bpp‐COOMe)₂](ClO₄)₂ (3), which exhibits slow relaxation of magnetization even in zero field thanks to the reduction of dipolar interactions. Theoretical calculations confirmed the overall electronic structure and the magnetic scenario of the compound as drawn by experimental data, thus confirming the spin‐phonon Raman relaxation mechanism, and a direct quantum tunneling in the ground state as the most plausible relaxation pathway in zero field.

The cis influence of a series of anionic ligands X and Y has been evaluated through the magnitude of the Pt–P coupling constants for compounds of formula trans-[PtXY(PPh₃)₂]. The order of decreasing cis influence was found to be I > Cl > SePh ∼ SPh ∼ SEt > NO₃ > AcO ∼ NO₂ > H > Me > Ph > mtc (mtc = N,N-dimethylmonothiocarbamato-S); moreover, the cis influences of the various ligands was found to be additive. The X-ray structures of three representative compounds (t-4: X = Cl, Y = NO₃; t-5: X = Cl, Y = AcO and t-12: X = Y = NO₂) have also been determined.