Magnetic Systems with Mixed Carboxylate and Azide Bridges: Slow Relaxation in Co(II) Metamagnet and Spin Frustration in Mn(II) Compound

Two coordination polymers formulated as [{[Co₂(L)(N₃)₄]·2DMF}_n (1) and [Mn₂(L)(H₂O)_0.5(N₃)₈]_n (2) (L = 1,4-bis(4-carboxylatopyridinium-1-methyl)benzene) were synthesized and structurally and magnetically characterized. In compound 1, the anionic uniform Co(II) chains with mixed (μ-EO-N₃)₂(μ-COO) triple bridges (EO = end-on) are cross-linked by the cationic bis(pyridinium) spacers to generate 2D coordination layers. It was demonstrated that the triple bridges mediate ferromagnetic coupling and that the compound represents a new example of the rare systems exhibiting the coexistence of antiferromagnetic ordering, metamagnetism, and slow magnetic dynamics. Compound 2 features the magnetic Δ-chain formed from isosceles triangular units with single μ-EE-N₃ and double (μ-EO-N₃)(μ-COO) bridges (EE = end-to-end). The Δ-chains are interlinked by long organic ligands into a 3D framework with novel net topology and 3-fold interpenetration. The magnetic properties of 2 indicate the presence of spin frustration characteristic of Δ-chains with antiferromagnetic interactions.