Coordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands

Abstract

The synthesis of mixed-ligand complexes of the type [M2L(μ-L')]+, where L represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, L' is an azobenzene carboxylate co-ligand, and M = Cd(II), Ni(II) or Zn(II), is reported. A series of new complexes were synthesized, namely [M2L(μ-L')]+ (L' = azo-H, M = Cd (1), Ni (2); L' = azo-OH, M = Zn (3), Ni (4); L' = azo-NMe2, M = Zn (5), Cd (6), Ni (7); L' = azo-CO2Me, M = Cd (8), Ni (9)), and characterized by elemental analysis, electrospray ionization mass spectrometry (ESIMS), IR, UV–vis and NMR spectroscopy (for diamagnetic Zn and Cd complexes) and X-ray single crystal structure analysis. The crystal structures of 3' and 5–8 display an isostructural series of compounds with bridging azobenzene carboxylates in the trans form. The paramagnetic Ni complexes 2, 4 and 7 reveal a weak ferromagnetic exchange interaction with magnetic exchange coupling constant values between 21 and 23 cm−1 (H = −2JS1S2). Irradiation of 1 with λ = 365 nm reveals a photoisomerization of the co-ligand from the trans to the cis form.

Synthesis and Characterisation of Luminescent [CrIII2L(μ‐carboxylato)]3+ Complexes with High‐Spin S=3 Ground States (L=N6S2 donor ligand)

“… [56] The diamagnetic [Zn 2 L( μ ‐OAc)] + complex, for example, reveals intense transitions into π‐π* configured states at similar wavelengths, namely λ max =261 nm ( ϵ =13740 M −1 cm −1 ) and 288 nm ( ϵ =24464 M −1 cm −1 ). [78] …”

“…[56] The diamagnetic [Zn 2 L(μ-OAc)] + complex, for example, reveals intense transitions into π-π* configured states at similar wavelengths, namely λ max = 261 nm (ɛ = 13740 M À 1 cm À 1 ) and 288 nm (ɛ = 24464 M À 1 cm À 1 ). [78] The spectrum of 1 reveals another intense absorption maximum at 363 nm (ɛ = 2660 M À 1 cm À 1 ), which is assigned to a transition into a thiophenolate-to-Cr III charge transfer state. Analogous transitions into ligand-to-metal charge transfer (LMCT) configurations for [Cr 2 (L N2S ) 3 ] 3 + and [Cr 2 (L N4S2 )(μ-OH)(Cl) 2 ] + are observed at similar wavelengths (317 nm, 352 nm, Table 2).…”

“…The [Zn II 2 L(μ-OAc)] + complex, on the other hand, does not absorb in this region, providing strong support for the LMCT nature of the states related to these intense absorption bands. [78] The finding that the 4 LMCT configurations can feed the emissive 2 T 1 4 A 2 / 2 E 4 A 2 excited state of 1 and 2 (see excitation spectra discussed below) suggests that these complexes may also be interesting to investigate as sensitizers based on earth-abundant metal ions [79,80] or as acceptors in supramolecular architectures. [81][82][83][84] The visible region of the spectrum of 1 reveals a shoulder on the low-energy tail of the LMCT-related band at ~417 nm and a well-defined absorption band peaking at around 571 nm (ɛ = 414 M À 1 cm À 1 ).…”

Fifty Years of Inorganic Biomimetic Chemistry: From the Complexation of Single Metal Cations to Polynuclear Metal Complexes by Multidentate Thiolate Ligands

“…For R=H the complex shows two photoswitchable configurations 22 and 22'. [72] (II) 2 (L15 Me2H4 )(F 2 )] À , M=Co (II) or Ni (II) and [Cu (I) (X 2 )], X=Cl, Br, and I. [75] for bridging acetate groups.…”

Ethereal Hydroperoxides: Powerful Reagents for S-Oxygenation of Bridging Thiophenolate Functions

“…Figure 5 displays the UV spectra of 2 and 3 in a MeCN solution (200−500 nm range). The spectra of the precursor 1 and the isostructural zinc complex [Zn 2 L S (O 2 CR)](ClO 4 ) (5) 106 are shown for comparative purposes.…”