A Systematic Evaluation of the Interplay of Weak and Strong Supramolecular Interactions in a Series of Co(II) and Zn(II) Complexes Tuned by Ligand Modification

A systematic investigation on a designed series of 21 transition metal complexes has been carried out with the intention to explore and assess the relative strength and the way in which intermolecular interactions, namely, weak and strong hydrogen-bonding and π–π interactions, cooperate and direct molecular association during crystallization. The complexes were prepared using the general M^II/X^–/L or HL′ (M^II = Co^II, Zn^II; X^– = Cl^–, Br^–, I^–, NO₃^–, NO₂^–, ClO₄^–; L = 1-methyl-4,5-diphenylimidazole; and HL′ = 4,5-diphenylimidazole) reaction system and were characterized by single-crystal X-ray crystallography. Although the two ligands are structurally similar, the crystal packing organization of their complexes is markedly different. In structures with L, the 3D assembly is based only on weak C–H···X, C–H···π, and intramolecular π···π stacking interactions, whereas in those with HL′, it is the recurring N–H···X motifs that clearly dominate and guide the molecular self-assembly. The formation of such synthons has been activated by choosing appropriate anions X, acting as terminal ligands or counterions. In parallel, the conformational flexibility of the two ligands serves a dual purpose: (i) L contributes to the stabilization of complexes via intramolecular π···π stacking interactions, and (ii) HL′ facilitates the synthon formation by adopting appropriate conformations, even at the expenses of the stabilizing intramolecular π···π stacking

A Mn^II₆Mn^III₆ Single-Strand Molecular Wheel with a Reuleaux Triangular Topology: Synthesis, Structure, Magnetism, and DFT Studies

The use of the anion of 3-methyl-1,3,5-pentanetriol (mpt^3–) in manganese carboxylate chemistry has afforded the new Mn^II/III₁₂ cluster [Mn^II₆Mn^III₆(mpt)₆(CH₃CO₂)₁₂(py)₆]·3CH₃CN (<b>1</b>·3CH₃CN). Complex <b>1</b> was isolated in moderate yield by the reaction of Mn­(CH₃CO₂)₂·4H₂O and H₃mpt in a 2.6:1 molar ratio in a solvent mixture of acetonitrile and pyridine. The structure of <b>1</b> consists of alternating [Mn^II₂(CH₃CO₂)₃(py)]⁺ and [Mn^III₂(μ-OR)₂(CH₃CO₂)­(py)]³⁺ dimeric units (three of each dimer), linked at each end by two alkoxo and one acetate bridges; the mpt^3– ligands adopt the η²:η²:η²:μ₄ coordination mode. The overall metal topology of this new Mn₁₂ wheel resembles a guitar plectrum, or a Reuleaux triangle. Complex <b>1</b> displays an unprecedented structural topology, being the first example of a Mn^II₆Mn^III₆ wheel constructed from alternating homovalent dimers and the only known Mn₁₂ loop with the trigonal symmetry of a Reuleaux triangle (all other reported loops were ellipsoids). Variable-temperature, solid-state direct- and alternating-current magnetization studies were carried out on complex <b>1</b>, revealing the presence of antiferromagnetic exchange interactions between the metal ions in the molecule, which lead to a spin ground-state value <i>S</i> = 0; the exchange coupling parameters <i>J</i> were calculated using density functional theory employing a hybrid B3LYP functional