Unprecedented intramolecular pancake bonding in a {Dy₂} single-molecule magnet

Abstract

The first example of unique coordination induced intramolecular pancake bonding was achieved through the reduction of two bis(pyrazolyl)-tetrazine ligands.

Enhancing Magnetic Communication between Metal Centres: The Role of s‐Tetrazine Based Radicals as Ligands

“…The complex [Dy III 2 ( μ ‐(bpytz .− ) 2 )(THMD) 4 ] ( 18 ), recently published by our group, represents the first example of an intramolecular pancake bond between two reduced tetrazine moieties coordinated to metal centres [71] . As shown in Figure 11 (top) due to the unique coordination of the two radical species, the proximity of the central radical tetrazine centres is close, leading to the stabilization of a π‐dimer connecting two Dy III metal centres.…”

“…The complex [Dy III 2 (m-(bpytzC À ) 2 )(THMD) 4 ]( 18), recently published by our group, represents the first example of an intramolecular pancake bond between two reduced tetrazine moieties coordinated to metal centres. [71] As shown in Figure 11 (top) due to the unique coordination of the two radical species, the proximity of the central radicalt etrazine centres is close, leading to the stabilization of a p-dimer connecting two Dy III metal centres.T he tetrazine rings face one another at a distance of 2.73( 5) which is considerably longer than as ingle 19), in which one neutralb pytz moiety acts as ad iamagnetic linker between two Dy III ions, bridging the metal centres in a syn-anti fashion (Figure 11,b ottom). The cT product at room temperature at 1000 Oe is equal to 27.53 cm 3 Kmol À1 for 18 and 27.83 cm 3 Kmol À1 for 19,w hich are close to the expected values for two non-interacting Dy III (M J = 15/2, cT = 14.17 cm 3 Kmol À1 ).…”

“…Figure 12. DFT spin densityp lots of 20.T he green and red isodensity surfaces indicate negative and positives pin phases, respectively.F igure was adapted from ref [71]…”

Pancake Bonding Seen through the Eyes of Spectroscopy

“…Table 1 summarizes the calculated bond distances (R calc ), experimental bond distances (R exp ), calculated bond dissociation energies (BDE calc ), experimental bond dissociation energies (BDE exp ), local stretching force constants (k a ), local mode vibrational frequencies (ω a ), bond strength orders (BSO n), electron densities (ρ b ), and energy densities (H b ) for the targeted CC bonds of of targeted contacts bonds of dimers 1-6 and rings of 1-3. Table 2 summarizes symmetry, singlet and triplet C⋯C contact distance (R(CC)), energy values of SOMOs (E SOMO ), and triplet/singlet (ΔE ST ) for all species investigated in this work (1)(2)(3)(4)(5)(6). Figure 2 shows the equilibrium geometries for the HCNTeTeN 3 dimer (C 2 )in singlet and triplet states.…”

“…More recently the term "pancake bonding" has primarily been used to describe the formation of stabilizing parallel π-π interactions between two or more open-shell free radicals, those of which are typically planar and/or consist of light-atoms [2][3][4]. Such interactions have received a considerable amount of interest as they allow one to synthesize novel radical-based materials, via electron or hole through-space delocalization, that exhibit unique magnetic [5], optical [6], and electronic properties (i.e. conductive polymers, organic conductors) [7].…”