2 research outputs found
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<sup>II</sup>/X<sup>–</sup>/L or HL′ (M<sup>II</sup> = Co<sup>II</sup>,
Zn<sup>II</sup>; X<sup>–</sup> = Cl<sup>–</sup>, Br<sup>–</sup>, I<sup>–</sup>, NO<sub>3</sub><sup>–</sup>, NO<sub>2</sub><sup>–</sup>, ClO<sub>4</sub><sup>–</sup>; 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<sup>II</sup><sub>6</sub>Mn<sup>III</sup><sub>6</sub> 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<sup>3–</sup>) in manganese carboxylate chemistry has afforded the new Mn<sup>II/III</sup><sub>12</sub> cluster [Mn<sup>II</sup><sub>6</sub>Mn<sup>III</sup><sub>6</sub>(mpt)<sub>6</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>12</sub>(py)<sub>6</sub>]·3CH<sub>3</sub>CN (<b>1</b>·3CH<sub>3</sub>CN). Complex <b>1</b> was isolated in
moderate yield by the reaction of MnÂ(CH<sub>3</sub>CO<sub>2</sub>)<sub>2</sub>·4H<sub>2</sub>O and H<sub>3</sub>mpt 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<sup>II</sup><sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>3</sub>(py)]<sup>+</sup> and [Mn<sup>III</sup><sub>2</sub>(μ-OR)<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)Â(py)]<sup>3+</sup> dimeric units (three of each dimer), linked
at each end by two alkoxo and one acetate bridges; the mpt<sup>3–</sup> ligands adopt the η<sup>2</sup>:η<sup>2</sup>:η<sup>2</sup>:μ<sub>4</sub> coordination mode. The overall metal
topology of this new Mn<sub>12</sub> 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<sup>II</sup><sub>6</sub>Mn<sup>III</sup><sub>6</sub> wheel constructed from alternating
homovalent dimers and the only known Mn<sub>12</sub> 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