Tetranuclear Copper(II) and Nickel(II) Cluster Complexes Derived by Self-Assembly from a Series of Tetradentate Diazine Ligands: Structural and Magnetic Studies

A series of tetranuclear copper(II) and nickel(II) complexes is described, all of which form by a strict self-assembly process involving just a single ligand and the metal salt. The ligands POAP, POAPZ, PZOAP, and 6POAP contain terminal pyridine and pyrazine residues bound to a central flexible diazine subunit (N−N) and contain two potentially bridging groups (alkoxo and diazine). In all cases but one the metals are linked by alkoxo oxygens alone, forming essentially square [M 4 (μ 2 -O) 4 ] clusters. A rectangular copper(II) complex [Cu 4 (μ 2 -N 2 ) 2 (μ 2 -O) 2 ] involves a mixture of two alkoxo and two diazine bridges. The square Cu 4 O 4 clusters exhibit ferromagnetic coupling between the metal centers, associated with the orthogonal arrangement of magnetic orbitals, while for the Ni 4 O 4 clusters the nickel(II) centers are coupled antiferromagnetically. The [Cu 4 (μ 2 -N 2 ) 2 (μ 2 -O) 2 ] cluster exhibits strong antiferromagnetic coupling through a trans Cu(N-N)Cu bridging arrangement, typical for systems of this sort. X-ray structures are reported for [Cu 4 (POAP-H) 4 (H 2 O) 2 ](NO 3 ) 4 ·4H 2 O ( 2 ), [Cu 4 (POAPZ-H) 4 (H 2 O)](NO 3 ) 4 ·3H 2 O ( 3 ), [Cu 4 (6POAP-H) 4 ](ClO 4 ) 4 ( 4 ), [Cu 4 (PZOAP-H) 4 ](NO 3 ) 4 ·3H 2 O ( 5 ), [Ni 4 (POAP-H) 4 (H 2 O) 4 ](NO 3 ) 4 ·8H 2 O ( 6 ), and [Ni 4 (PZOAP-H) 4 (H 2 O) 4 ](ClO 4 ) 4 ·5H 2 O ( 9 ). 2 crystallized in the monoclinic system, space group C 2/ c, with a = 20.479(3) Å, b = 14.920(2) Å, c = 19.671(3) Å, β = 90.591(4)°, and Z = 8. 3 crystallized in the monoclinic system, space group P 2 1 / c, with a = 14.12(1) Å, b = 14.116(3) Å, c = 29.043(4) Å, β = 94.50(3)°, and Z = 4. 4 crystallized in the monoclinic system, space group C 2/ c, with a = 22.646(4) Å, b = 25.842(5) Å, c = 12.349(5) Å, β = 110.34(2)°, and Z = 4. 5 crystallized in the monoclinic system, space group P 2/ n, with a = 14.3573(4) Å, b = 10.8910(6) Å, c = 20.5360(10) Å, β = 96.975(4)°, and Z = 4. 6 crystallized in the triclinic system, space group P 1̄, with a = 12.0509(6) Å, b = 12.7498(6) Å, c = 23.1208 Å, α = 93.1050(10)°, β = 100.1500(10)°, γ = 108.5050(11)°, and Z = 2. 9 crystallized in the orthorhombic system, space group Pbcn, with a = 14.368(4) Å, b = 25.469(7) Å, c = 18.479(5) Å, and Z = 4.