Self-assembly of Ni(II) metallacycles (a square and a triangle) supported by tetrazine radical bridges.

Two Ni(II) molecular metallacycles of [Ni 4 (bpz*tz˙ - ) 4 (N 3 ) 4 ] (1) and [Ni 3 (bpz Ph tz˙ - ) 3 (pz Ph (Cl)tz˙ - ) 3 ]·1.3CH 3 OH·9.3H 2 O (2) (bpz*tz = 3,6-bis(3,5-dimethyl-pyrazolyl)-1,2,4,5-tetrazine; bpz Ph tz = 3,6-bis(3-phenyl-pyrazolyl)-1,2,4,5-tetrazine; and pz Ph (Cl)tz = 3-bis(3-phenyl-pyrazolyl)-6-Cl-1,2,4,5-tetrazine) are reported. The single-crystal X-ray diffraction study reveals that 1 displays a square structure while 2 shows a triangle structure due to the steric effect, both bearing tetrazine radical bridges. Furthermore, magnetic studies reveal that the Ni-radical interaction in 1 is strongly ferromagnetic with a coupling constant ( J ) of 90.8 cm -1 in the 2 J formalist, while the overall antiferromagnetic behaviour of 2 is presumably due to the compete ferromagnetic (for the Ni-radical bridging interaction with J 1 = 95.4 cm -1 ) and antiferromagnetic (for the Ni-radical terminal interaction, J 2 = -57.5 cm -1 ) couplings.