Copper(II), Cobalt(II), and Nickel(II) Complexes with a Bulky Anthracene-Based Carboxylic Ligand: Syntheses, Crystal Structures, and Magnetic Properties

To systematically explore the influence of the bulky aromatic ring skeleton with a large conjugated π-system on the
structures and properties of their complexes, six CuII, CoII, and NiII complexes with the anthracene-based carboxylic
ligand anthracene-9-carboxylic acid (HL1), were synthesized and characterized, sometimes incorporating different
auxiliary ligands:  [Cu2(L1)4(CH3OH)2](CH3OH) (1), [Cu4(L1)6(L2)4](NO3)2(H2O)2 (2), {[Cu2(L1)4(L3)](CH3OH)0.25}∞ (3),
[Co2(L1)4(L4)2(μ-H2O)](CH3OH) (4), {[Co(L1)2(L5)(CH3OH)2]}∞ (5), and {[Ni(L1)2(L5)(CH3OH)2]}∞ (6) (L2 = 2,2‘-bipyridine, L3 = 1,4-diazabicyclo[2.2.2]octane, L4 = 1,10-phenanthroline, and L5 = 4,4‘-bipyridine). 1 has a dinuclear
structure that is further assembled to form a one-dimensional (1D) chain and then a two-dimensional (2D) network
by the C−H···O H-bonding and π···π stacking interactions jointly. 2 takes a tetranuclear structure due to the existence
of the chelating L2 ligand. 3 possesses a 1D chain structure by incorporating the related auxiliary ligand L3, which
is further interlinked via interchain π···π stacking, resulting in a three-dimensional (3D) network. 4 also has a
dinuclear structure and then forms a higher-dimensional supramolecular network through intermolecular π···π stacking
and/or C−H···π interactions. 5 and 6 are isostructural complexes, except they involve different metal ions, showing
1D chain structures, which are also assembled into 2D networks from the different crystallographic directions by
interchain π···π stacking and C−H···π interactions, respectively. The results reveal that the steric bulk of the
anthracene ring in HL1 plays an important role in the formation of 1−6. The magnetic properties of the complexes
were investigated, and the very long intermetallic distances result in weak magnetic coupling, with the exception
of 1 and 3, which adopt the typical paddle-wheel structure of copper acetate and are thus strongly coupled.