Investigation by Chemical Substitution within 2p-3d-4f Clusters of the Cobalt(II) Role in the Magnetic Behavior of [vdCoLn] 2 (vd = Verdazyl Radical).

1,5-Dimethyl-3-(3'-(hydroxymethyl)-2'-pyridine)-6-oxotetrazane (H 3 vdpyCH 2 OH) or its oxidized verdazyl form (vdpyCH 2 OH) reacted with transition metal and/or lanthanide acetates to yield [(vdpyCH 2 O) 2 Co 2 Ln 2 (acO) 8 ] (Ln = Y(III): I Co,Y ; Gd(III): I Co,Gd ), [(vdpyCH 2 O) 2 M 3 (acO) 4 ] (M = Zn(II): II Zn ; Co(II): II Co ) and [(vdpyCH 2 OH)Zn(acO) 2 ] ( III Zn ) through self-assembly implying a complex- as -ligand intermediate. Single-crystal diffraction reveals that I MT,Ln are composed of 2p-3d-4f centrosymmetric clusters with verdazyl radicals at the two ends coordinated to the transition-metal ion in a tridentate mode and to the {Ln 2 (acO) 4 } lanthanide central core in a monodentate mode through its alkoxo moiety. In I Co,Gd , the transition-metal ions adopt an irregular octahedral environment, and the {Ln 2 (acO) 4 } core adopts a paddlewheel motif, whereas in I Co,Y , the transition metal is pentacoordinated, and the central core contains only two acetate bridges. Going from I Co,Y to II Co , the central {Y 2 (acO) 4 } core is replaced by an axially compressed octahedral cobalt(II) center, whereas the outer parts of the molecule remain still. The dc magnetic studies revealed that the alternate π-stacking of the verdazyl radicals in II Zn led to the formation of alternate antiferromagnetically coupled 1D chains with J vd-vd = -8.2(1) cm -1 and J vd-vd ' = -7.6(1) cm -1 (-2 J convention). In I Co,Y , a complex fitting procedure allowed us to retrieve a complete set of magnetic parameters to take into account both the magnetic anisotropy of the cobalt(II) centers and intra- and inter-molecular exchange effects. For I Co,Y , it led to g Co = 2.13(4), D Co = 100(2) cm -1 , E Co = 19.9(5) cm -1 , J Co-vd = +26.5(4) cm -1 , and J vd-vd = -7.95(4) cm -1 . ac magnetic susceptibility of I Co,Y , I Co,Gd and II Co did not reveal any slow relaxation of the magnetization even when a dc external magnetic field up to 2000 Oe was applied.