Co II and Cu II ions are two paramagnetic transition metal ions showing different relaxation rates (ν), with ν Co II >> ν Cu II . To measure the isotropic exchange constant (J) between high spin Co II ions and between Cu II ions and high spin Co II ions, we performed magnetic and EPR measurements complemented with computational calculations on pure transdiaqua-bis(picolinato-N,O)-cobalt(II) dihydrate (1), on the Cu II ion doped compound of 1 (2), and on the Cu II ion doped compound in a Zn II matrix isomorphous to 1. The temperature dependence of the Cu II EPR resonance lines of 2 induced by the fast relaxing Co II ion host as well as the evaluation of the temperature-independent Co II -Co II and Cu II -Co II isotropic exchange [a]

We report magnetic, EPR, and computational studies on two representative examples of structurally well‐characterized one dimension (1D) molecular systems: the copper complexes catena‐[bis(μ‐pyridine‐2‐carboxylato)‐copper dihydrate] and catena‐[(μ2‐pyridine‐2,6‐dicarboxylato)‐diaqua‐copper(II)], hereafter 1 and 2, respectively. Experimental and theoretical results confirmed that the structural chains in both compounds behave as magnetic chains in which the copper ions are weakly coupled by isotropic exchange. Magnetic susceptibility measurements of 1 suggested that the copper ions are antiferromagnetically coupled whereas EPR measurements suggested ferromagnetic coupling at temperature above 100 K which becomes antiferromagnetic at low temperatures. Computational calculations would indicate that the ferromagnetic‐antiferromagnetic change may be due to dCu−Oap shortening on lowering temperature temperature (a fact that was observed experimentally by XRD at low temperatures), which redistributes the small Cu(II) unpaired spin density delocalized on the apical ligand to copper. The 1D magnetic behavior of the zigzag ladder chain of 2 is less detectable than that of the single chain of 1. Magnetic susceptibility measurements in conjunction with computational calculations showed that the pathways that give rise to the 1D ladder transmit ferromagnetic exchange interactions with different strengths, with the stronger interaction being transmitted along the rungs. The role of the weaker exchange interactions transmitted along the rails on the magnetic dimensionality of 2 is analyzed.