A rare example of a double metamagnetic transition leading to 2D and 3D long-range order in the two-dimensional pyrazine- and azido-bridged cobalt(II) compound [Co(pyz)(N 3 ) 2 ].

The synthesis, characterization, crystal structure and detailed magnetic properties of a pyrazine (pyz) and azido (N 3 ) bridged cobalt(II) compound of formula [Co(N 3 ) 2 (pyz)] (1) are reported. Compound 1 shows a layered structure formed by Co(II) chains with double μ-N 3 (κN 1 ,N 1 ) bridges that are further connected by μ-(pyrazine-κN 1 ,N 4 ) bridges. The layers present weak van der Waals interactions between azido terminal groups. The magnetic properties show the presence of a metamagnetic behaviour in 1 with two critical fields of 200 and 400 mT at low temperatures. AC magnetic measurements show the presence of a long-range 2D ferromagnetic order at T c ≈ 8.0-7.0 K for dc fields above 200 mT and a long-range 3D ferromagnetic order at T c ≈ 4.5 K for dc fields above 400 mT.