Tuning of the spin states in trinuclear cobalt compounds of pyridazine by the second simple bridging ligand

Three novel trinuclear cobalt(II) compounds of pyridazine, [CO3(mu-OH)(2)(P-pdz)(4)(pdz)(2)(NO3)(2)(H2O)(2)]-(NO3)(2)(.)(THF)(.)2(MeOH) (1), [Co-3 (mu-OH)(2)(mu-pdz)(4)(pdz)(4) (NO3)(2)] (.) [Co-3 (mu-OH)(2)(P-pdz)(4)(MeOH)(4)(NO3)(2)](.)(NO3)(4) (2), and [Co-3(P-pdz)(4)(mu-NCS)(2)(pdz)(2)(NCS)(4)](.)2MeOH (3) (pdz = pyridazine), have been synthesized and characterized. The structures of all three compounds consist of centrosymmetric trimer building blocks bridged by the two nitrogen atoms of the pyridazine ligands and the second small bridging anions (hydroxide in I and 2, and end-on thiocyanate in 3). The two-atom bridging modes of the pyridazine ligand in 1 and 2 are unusual: each bridging pyridazine ligand affords two nitrogen donors to two metal ions with different bond lengths. This results in two kinds of spin states for the cobalt(II) atoms in 1. Magnetic measurements show a typical antiferromagnetic interaction between the high-spin metals in 3, but an unusual magnetic coupling through two high- and one low-spin cobalt atoms within the trimer in 1. An irregular spin states structure is also observed in 1 at low temperature. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).