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 [{[Co<sub>2</sub>(L)(N<sub>3</sub>)<sub>4</sub>]·2DMF}<sub><i>n</i></sub> (<b>1</b>) and [Mn<sub>2</sub>(L)(H<sub>2</sub>O)<sub>0.5</sub>(N<sub>3</sub>)<sub>8</sub>]<sub><i>n</i></sub> (<b>2</b>) (L = 1,4-bis(4-carboxylatopyridinium-1-methyl)benzene) were synthesized and structurally and magnetically characterized. In compound <b>1</b>, the anionic uniform Co(II) chains with mixed (μ-EO-N<sub>3</sub>)<sub>2</sub>(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 <b>2</b> features the magnetic Δ-chain formed from isosceles triangular units with single μ-EE-N<sub>3</sub> and double (μ-EO-N<sub>3</sub>)(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 <b>2</b> indicate the presence of spin frustration characteristic of Δ-chains with antiferromagnetic interactions.