Binuclear nickel(II) and cobalt(II) complexes of the novel binucleating ligand 3,6-bis(1′-pyrazolyl)pyridazine. Crystal and molecular structure and magnetism of bis[µ-3,6-bis(1′-pyrazolyl)pyridazine-N1(Ni1)N2′(Ni1)N2(Ni2)N2″(Ni2)]bis[diaquanickel(II)] tetrachloride dihydrate

Abstract

Reaction of the ligand 3,6-bis(1′-pyrazolyl)pyridazine (ppd) with nickel(II) and cobalt(II) salts produces binuclear derivatives in which the two pseudo-octahedral metal centres are bound simultaneously between two adjacent ligands in a doubly bridged structure. The complex [Ni₂(ppd)₂(H₂O)₄]Cl₄·2H₂O (1) crystallizes in the triclinic space group P with a= 7.133 9(7), b= 10.331 0(6), c= 10.820 9(5)Å, α= 85.503(4), β= 89.939(6), γ= 75.479(6)°, and Z= 1. Refinement based on 4 505 unique reflections gave R= 0.0353. The binuclear cation [Ni₂(ppd)₂(H₂O)₄]⁴⁺ is essentially planar with in-plane Ni–N distances of 2.1 30(2), 2.035(2), 2.059(2), and 2.1 21(2)Å, axial Ni–O distances of 2.044(2) and 2.048(2)Å, and N–Ni–N angles of 98.6(1), 77.8(1), 77.9(1), and 105.8(1)°. Variable-temperature magnetic susceptibility measurements on (1) indicate significant antiferromagnetic exchange between the nickel(II) centres with –J= 14.8 cm^–1. Analogous cobalt(II) compounds are also produced and in one case, [Co₂(ppd)₂(OH)(H₂O)₂][ClO₄]₃·1.5H₂O, a triply bridged structure is proposed involving an additional hydroxide bridge.