Synthesis, structure and magnetic property of a 2D grid-like copper(II) complex with end-on azido and pyrazine bridges

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)(N3)2]

The synthesis, characterization, crystal structure and detailed magnetic properties of a pyrazine (pyz) and azido (N₃) bridged cobalt(II) compound of formula [Co(N₃)₂(pyz)] (1) are reported. Compound 1 shows a layered structure formed by Co(II) chains with double μ-N₃(κN¹,N¹) bridges that are further connected by μ-(pyrazine-κN¹,N⁴) 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.

The vibrational spectroscopy of the coordinated azide anion; a theoretical study

The vibrational behaviour of the azide anion in a variety of environments has been examined by DFT methods. The frequency is sensitive to polar, dipolar and quadrupolar fields. The frequency is also dependent on the metal to which it is bonded and thus to the details of that bonding. Several azides within one molecule can be strongly vibrationally coupled, a coupling which carries with it a transfer of spectral activity. It is suggested that whilst absolute vibrational frequencies carry little immediately accessible information, a combination of infrared and Raman data for the antisymmetric stretch region might give limited structural insights.