Search for: All records

Electrochemical stability and delocalization of states critically impact the functions and practical applications of electronically active polymers. Incorporation of a ladder-type constitution into these polymers represents a promising strategy to enhance the aforementioned properties from a fundamental structural perspective. A series of ladder-type polyaniline-analogous polymers are designed as models to test this hypothesis and are synthesized through a facile and scalable route. Chemical and electrochemical interconversions between the fully oxidized pernigraniline state and the fully reduced leucoemeraldine state are both achieved in a highly reversible and robust manner. The protonated pernigraniline form of the ladder polymer exhibits unprecedented electrochemical stability under highly acidic and oxidative conditions, enabling the access of a near-infrared light-absorbing material with extended polaron delocalization in the solid-state. An electrochromic device composed of this ladder polymer shows distinct switching between UV- and near-infrared-absorbing states with a remarkable cyclability, meanwhile tolerating a wide operating window of 4 volts. Taken together, these results demonstrate the principle of employing a ladder-type backbone constitution to impart superior electrochemical properties into electronically active polymers. 

The geometry of cobalt( ii ) ions in the axially distorted octahedral cation in [Co(MeCN) 6 ](BF 4 ) 2 ( 1 ) was compared to the trigonal prismatic cation in [CoTp py ]PF 6 ( 2 ) which revealed significant differences in magnetic anisotropy. Combined experimental and ab initio CASSCF/NEVPT2 calculations support the observed zero field SMM behaviour for 2 , with easy axis anisotropy, attributed to the rigidity of the trigonal prismatic ligand. Strong transverse anisotropy for 1 leads to significant quantum tunnelling processes. 

The combined experimental and theoretical investigation of the magnetic properties of the cobalt( ii ) NHC complexes (NHC = N-heterocyclic carbene); [Co(CH 2 SiMe 3 ) 2 (IPr)] ( 1 ), [CoCl 2 (IMes) 2 ] ( 2 ) and [Co(CH 3 ) 2 (IMes) 2 ] ( 3 ) revealed a large easy plane anisotropy for 1 ( D = +73.7 cm −1 ) and a moderate easy axis anisotropy for 2 ( D = −7.7 cm −1 ) due to significant out-of-state spin–orbit coupling. Dynamic magnetic measurements revealed slow relaxation of the magnetization for 1 ( U eff = 22.5 K, τ 0 = 3 × 10 −7 s, 1000 Oe) and for 2 ( U eff = 20.2 K, τ 0 = 1.73 × 10 −8 s, 1500 Oe). The molecular origin of the slow relaxation phenomena was further supported by the retention of AC signal in 10% solutions in 2-MeTHF which reveals a second zero field AC signal in 1 at higher frequencies. Compound 3 was found to be an S = 1/2 system. 

TCNQ (7,7,8,8-tetracyanoquinodimethane) anion-radical derivatives were used to fine tune the magnetic properties of the [Co II (Fctp) 2 ] 2+ (Fctp = 4′-(2-ferrocenyl)-2,2′:6′2′′-terpyridine) cation in the solid state. The cocrystallization of [Co II (Fctp) 2 ] 2+ with TCNQ˙ − yielded the two pseudo-polymorphic products [Co II (Fctp) 2 ] (TCNQ) 2 ( 1 ) and [Co II (Fctp) 2 ] (TCNQ) 2 ·MeCN ( 2 ) whereas the analogous reaction with TCNQF˙ − (TCNQF = 2-fluoro-7,7,8,8-tetracyanoquinodimethane) exclusively yielded [Co II (Fctp) 2 ] (TCNQF) 2 ·MeCN ( 3 ). Compound 1 exhibits slow relaxation of magnetization under an applied DC field with U eff = 19.1 K and τ 0 = 9.8 × 10 −6 s. Compounds 2 and 3 are isostructural but exhibit different spin-crossover behavior with transition temperatures of T 1/2 = 336 K and 226 K, respectively. Investigations of the solid state structures by DFT calculations indicate that the differences in magnetic properties of the cationic moiety, [Co II (Fctp) 2 ] 2+ , are induced by supramolecular interactions between [Co II (Fctp) 2 ] 2+ and tunable TCNQ˙ − /TCNQF˙ − anion-radical derivatives. 

Structural, magnetic and theoretical studies of three octahedral mononuclear Dy III complexes with triphenylphosphine oxide and halide ligands are reported. The Cl − and Br − analogues exhibit SMM behavior with energy barriers of 49.1 K and 70.9 K, respectively under a small dc field. Ab initio calculations were performed, the results of which predict higher energy barriers for iodide containing SMMs.