Octanuclear and Nonanuclear Supramolecular Copper(II) Complexes with Linear “Tritopic” Ligands: Structural and Magnetic Studies

The structures and magnetic properties of self-assembled copper(II) clusters and grids with the “tritopic” ligands
2poap (a), Cl2poap (b), m2poap (c), Cl2pomp (d), and 2pomp (e) are described [ligands derived by reaction of
4-R-2,6-pyridinedicarboxylic hydrazide (R = H, Cl, MeO) with 2-pyridinemethylimidate (a−c, respectively) or
2-acetylpyridine (d, R = Cl; e, R = H)]. Cl2poap and Cl2pomp self-assemble with Cu(NO3)2 to form octanuclear
“pinwheel” cluster complexes [Cu8(Cl2poap-2H)4(NO3)8]·20H2O (1) and [Cu8(Cl2pomp-2H)4(NO3)8]·15H2O (2), built
on a square [2 × 2] grid with four pendant copper arms, using “mild” reaction conditions. Similar reactions of
Cl2pomp and 2pomp with Cu(ClO4)2 produce pinwheel clusters [Cu8(Cl2pomp-2H)4(H2O)8](ClO4)8·7H2O (3) and
[Cu8(2pomp-2H)4(H2O)8](ClO4)8 (4), respectively. Heating a solution of 1 in MeOH/H2O produces a [3 × 3] nonanuclear
square grid complex, [Cu9(Cl2poap-H)3(Cl2poap-2H)3](NO3)9·18H2O (5), which is also produced by direct reaction
of the ligand and metal salt under similar conditions. Reaction of m2poap with Cu(NO3)2 produces only the [3 ×
3] grid [Cu9(m2poap-H)2(m2poap-2H)4](NO3)8·17H2O (6) under similar conditions. Mixing the tritopic ligand 2poap
with pyridine-2,6-dicarboxylic acid (picd) in the presence of Cu(NO3)2 produces a remarkable mixed ligand, nonanuclear
grid complex [Cu9(2poap-H)4(picd-H)3(picd-2H)](NO3)9·9H2O (7), in which aromatic π-stacking interactions are important
in stabilizing the structure. Complexes 1−3 and 5−7 involve single oxygen atom (alkoxide) bridging connections
between adjacent copper centers, while complex 4 has an unprecedented mixed μ-(N−N) and μ-O metal ion
connectivity. Compound 1 (C76H92N44Cu8O50Cl4) crystallizes in the tetragonal system, space group I4̄, with a =
21.645(1) Å, c = 12.950(1) Å, and Z = 2. Compound 2 (C84H88N36O44Cl4Cu8) crystallizes in the tetragonal system,
space group I4̄, with a = 21.2562(8) Å, c = 12.7583(9) Å, and Z = 2. Compound 4 (C84H120N28O66Cl8Cu8) crystallizes
in the tetragonal system, space group I41/a, with a = 20.7790(4) Å, c = 32.561(1) Å, and Z = 4. Compound 7
(C104H104N46O56Cu9) crystallizes in the triclinic system, space group P1̄, with a = 15.473(1) Å, b = 19.869(2) Å,
c = 23.083(2) Å, α = 88.890(2)°, β = 81.511(2)°, γ = 68.607(1)°, and Z = 2. All complexes exhibit dominant
intramolecular ferromagnetic exchange coupling, resulting from an orthogonal bridging arrangement within each
polynuclear structure.