Self-Assembled Dinuclear, Trinuclear, Tetranuclear, Pentanuclear, and Octanuclear Ni(II) Complexes of a Series of Polytopic Diazine Based Ligands: Structural and Magnetic Properties

Abstract
The nickel coordination chemistry of a series of polytopic diazine (N−N) based ligands has been examined. Self-assembly reactions lead to examples of dinuclear, trinuclear, tetranuclear, pentanuclear, and octanuclear complexes, all of which exhibit magnetic exchange coupling, with antiferromagnetic and ferromagnetic examples. Structural details are presented for [(L1)2Ni2(H2O)2](NO3)4·3H2O (1), [(L2)2Ni3(H2O)2](NO3)6·8H2O (2), [(L3)4Ni4(H2O)8] (NO3)4·8H2O (3), [(L4)2Ni5(H2O)10(NO3)](NO3)7·8H2O (4), and [(L5)4Ni8(H2O)8](BF4)8·16H2O (5). Compound 1 crystallizes in the monoclinic system, space group P21/c, with a = 14.937(1) Å, b = 18.612(2) Å, c = 20.583(2) Å, β = 108.862(2)°, Z = 4. Compound 2 crystallizes in the orthorhombic system, space group P21212, with a = 21.771(4) Å, b = 13.700(2) Å, c = 20.017(3) Å, Z = 4. Compound 3 crystallizes in the tetragonal system, space group P43, with a = 12.9483(7) Å, c = 33.416(3) Å, Z = 4. Compound 4 crystallizes in the triclinic system, space group P1̄, with a = 12.6677(8) Å, b = 18.110(1) Å, c = 19.998(1) Å, α = 100.395(1)°, β = 109.514(1)°, γ = 109.686(1)°, Z = 2. Compound 5 crystallizes in the monoclinic system, space group P21/n, with a = 21.153(5) Å, b = 35.778(9) Å, c = 21.823(5) Å, β = 97.757(6)°, Z = 4. The linear trinuclear Ni(II) complex (2) has a cis-N−N single bond bridge, and a water bridge linking the central Ni(II) to each external Ni(II) center in each of two similar trinuclear subunits, and exhibits intramolecular ferromagnetic exchange (J = 5.0 cm-1). A novel octanuclear metallacyclic ring structure exists in 5, with trans-N−N single bond bridges linking adjacent Ni(II) centers, leading to quite strong intramolecular antiferromagnetic exchange (J = −30.4 cm-1).

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