Synthesis and Characterizations of Macrocyclic Cr(III) and Co(III) 1-Ethynyl Naphthalene and 9-Ethynyl Anthracene Complexes: An Investigation of Structural and Spectroscopic Properties

Bis-Alkynyl Complexes of Fe(III) Tetraaza Macrocycles─A Tale of Two Rings

Reported herein are new Fe bis-alkynyl complexes [Fe^III(L)(C₂R)₂]BPh₄ based on tetraimine macrocycle (L = HMTI = meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene; 1a-1c; R = C₆H₅ (a), C₁₀H₉ (b), SiMe₃ (c)) and tetraamine macrocycle (L = HMC = meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane; 2a-2c). These complexes have been characterized using single-crystal X-ray diffraction, electronic absorption spectroscopy, and cyclic and differential pulse voltammetry. Spectroelectrochemical studies of 1a and 2a allowed for investigation of the Fe^II oxidation state, which revealed a strong dependence on the nature of the macrocycle for both the energies of the Fe^II to C₂Ph metal-to-ligand charge transfer (MLCT) and the ν(C≡C). The ν(C≡C) was further influenced by the oxidation state, though sensitivity to the formal metal oxidation state was much higher in the case of 2a than in 1a. These findings are rationalized on the basis of the relative energies of the formally metal-centered orbitals via density functional theory calculations.

Heterometal Grafted Metalla-ynes and Poly(metalla-ynes): A Review on Structure-Property Relationships and Applications

Metalla-ynes and poly(metalla-ynes) have emerged as unique molecular scaffolds with fascinating structural features and intriguing photo-luminescence (PL) properties. Their rigid-rod conducting backbone with tunable photo-physical properties has generated immense research interests for the design and development of application-oriented functional materials. Introducing a second d- or f-block metal fragment in the main-chain or side-chain of a metalla-yne and poly(metalla-yne) was found to further modulate the underlying features/properties. This review focuses on the photo-physical properties and opto-electronic (O-E) applications of heterometal grafted metalla-ynes and poly(metalla-ynes).

A unique series of chromium(iii) mono-alkynyl complexes supported by tetraazamacrocycles

Described herein is the synthesis and characterization of macrocyclic Cr^III mono-alkynyl complexes. By using the meso-form of the tetraazamacrocycle HMC (HMC = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane), trans-[Cr(HMC)(C₂Ph)Cl]OTf (1a), trans-[Cr(HMC)(C₂Np)Cl]OTf (2a), trans-[Cr(HMC)(C₂C₆H₄^tBu)Cl]OTf (3a), and trans-[Cr(HMC)(C₂(3,5-Cl₂C₆H₃))Cl]OTf (4a) complexes have been realized. These complexes were synthesized in high yield through the reaction of trans-[Cr(meso-HMC)(C₂Ar)₂]OTf (1b-4b) with stoichiometric amounts of methanolic HCl. Single crystal X-ray diffraction showed that the trans-stereochemistry and pseudo-octahedral geometry is retained in the desired mono-alkynyl complexes. The absorption spectra of complexes 1a-4a display d-d bands with distinct vibronic progressions that are slightly red shifted from trans-[Cr(HMC)(C₂Ar)₂]⁺ with approximately halved molar extinction coefficients. Time-delayed measurements of the emission spectra for complexes 1a-4a at 77 K revealed phosphorescence with lifetimes ranging between 343 μs (4a) and 397 μs (1a). The phosphorescence spectra of 1a-4a also exhibit more structuring than the bis-alkynyl complexes due to a strengthened vibronic coupling between the Cr^III metal center and alkynyl ligands.

Investigation of nitro-nitrito photoisomerization: crystal structure of trans-chlorido-nitro-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N,N',N'',N''')cobalt(III) chloride

The reaction cavity of the nitro group in the crystal of the title compound, [CoCl(NO2)(C10H24N4)]Cl, (I), was investigated to confirm that it offers sufficient free space for linkage isomerization to occur in accordance with the observed photochemical reactivity. The complex cation has crystallographic 2/m symmetry and the nitro and chloro ligands at the trans positions are statistically disordered. The complete cyclam ligand is generated by symmetry from a quarter of the mol-ecule. In the crystal of (I), the complex cations and Cl- ions are linked into a three-dimensional network by N-H⋯Cl(counter-ion) hydrogen bonds.