Two azido-bridged [2×2] cobalt(ii) grids featuring single-molecule magnet behaviour

Abstract

Two Co(ii) [2 × 2] grid-like clusters containing both pyridazine and azido bridges were reported to exhibit overall intramolecular ferromagnetic coupling and field-induced single-molecule magnet behavior with the effective energy barriers up to 56 K.

Strong Coupling and Slow Relaxation of the Magnetization for an Air-Stable [Co4] Square with Both Tetrazine Radicals and Azido Bridges

“…It should be noted that attempts to fit the susceptibility data of 2 with a free J 3 parameter did not improve the quality significantly and gave similar results. The obtained J Co···rad value is similar to that observed for bptz •– radical bridged [Co II 3 ] (−67.5 cm –1 ) and [Co II 4 ] (−66.8 cm –1 ) complexes and confirms the strong AF coupling between the Co­(II) metal centers and bpztz •– radicals.…”

“…The bridging M–N azido –M angle is 117.63° for 1 and 117.89° for 2 . Significant elongation of the N–N intra-tetrazine bond distances of 1.378 Å (N2–N3) and 1.400 Å (N6–N7) in 1 and 1.377 Å (N2–N3) and 1.397 Å (N6–N7) in 2 compared with the neutral tetrazine ligand (∼1.32 Å) strongly supports the formation of tetrazine radical in 1 and 2 . , It should be mentioned that the dihedral angles between the pyrazolyl and tetrazine rings of the bpztz ligand in 2 are 3.32° and 10.21°, indicating increased coplanarity compared to the previously reported diamagnetic analogues (4.19°–26.06°) . Moreover, the chelating N pz –M–N tz (N1–Co1–N2 and N3–Co2–N4) angles of 74.51° and 72.41° in 2 are significantly smaller than those for the related [Co 4 ] complexes in a trans binding mode .…”

“…It is well-known that the end-on (EO, μ 1,1 ) azido bridge would engender appreciable and predictable ferromagnetic coupling, and we recently incorporated azide ions as secondary bridges and constructed two [Co 4 ] square complexes, {[(L) 4 Co II 4 (μ 1,1 -N 3 ) 4 ]­[BPh 4 ] 4 }·sol ( 2a , L = 3,6-bis­(3,5-dimethyl-1 H -pyrazol-1-yl)­pyridazine (pzdz); 2b , L = 3,6-di­(pyridin-2-yl)­pyridazine (pydz)), in which the neutral pyridazine derivatives adopt cis -bridging modes as dictated by the EO–azido bridge (Scheme ). The ferromagnetic coupling constant was found to be approximately +4 cm –1 , and both compounds exhibit typical field-induced slow relaxation in magnetization …”

“…The ferromagnetic coupling constant was found to be approximately +4 cm −1 , and both compounds exhibit typical field-induced slow relaxation in magnetization. 10 With this prior work as a backdrop as well as the above considerations, the related tetrazine derivative of bpztz anion radical formation was thus explored in the assembly of metal complexes within the selected topology bearing azide bridging ligand to further improve the magnetic communication. Herein we report the synthesis, structures and magnetic studies of the air-stable azido-bpztz cobridged molecular squares [M II 4 (bpztz •− ) 4 (N 3 ) 4 ] (M II = Zn 2+ , 1; Co 2+ , 2).…”

Recent developments in supramolecular complexes of azabenzenes containing one to four N atoms: synthetic strategies, structures, and magnetic properties

“…, ( L15 ). 76 L14 and L15 both formed tetranuclear [2 × 2] grid complexes with Co II i.e. , ([Co II 4 ( L14 ) 4 (N 3 ) 4 ])·sol ( CoL14 ) and [( L15 ) 4 Co II 4 (N 3 ) 4 ])·sol ( CoL15) .…”