Paddlewheel 1,2,4-diazaphospholide dibismuthanes with very short bismuth-bismuth single bonds

Computational study of the photophysical properties and electronic structure of iridium(III) photosensitizer complexes with electron-withdrawing groups

A series of novel [Ir(tpy)(btp)Cl]+ complexes (Ir1-Ir4) have been reported to show excellent performance as photosensitizers. The introduction of electron-withdrawing groups increases visible light absorption and the lifetime of triplet states. To improve the photophysical properties, we theoretically design Ir5-Ir9 with electron-withdrawing groups (Cl, F, COOH, CN and NO2). Surprisingly, our findings indicate that the photosensitizer performance does not strictly increase with the electron-withdrawing ability of the substituents. In this work, the geometric and electronic structures, transition features, and photophysical properties of Ir1-Ir9 are investigated. The natural transition orbital (NTO) analysis indicates that the T1 and T2 states play a role in the photochemical pathways. Ultraviolet-visible (UV-vis) absorption spectra and charge-transfer spectra (CTS) have been investigated to show that the introduction of electron-withdrawing groups not only improves the visible light absorbing ability, but also changes the nature of electron excitation, providing a future molecular design strategy for similar series of photosensitizers. The rates of (reverse) intersystem crossing and the Huang-Rhys factors are evaluated to interpret the experimental results within the framework of Marcus theory. For complexes Ir1-Ir7, the introduction of electron-withdrawing groups leads to a lower efficiency of reverse intersystem crossing and a strong non-radiative process T2 → T1, resulting in a long triplet lifetime and excellent performance as a photosensitizer. Furthermore, some newly designed complexes (Ir7-Ir9) show great potential as thermally activated delayed fluorescence emitters, contrary to our initial expectations.

Ion-bearing stairs: alkali metal complexes of 1,2-diaza-4-phospholides

In this work, eight alkali metal complexes with 1,2-diaza-4-phospholide ligands were prepared and characterized by X-ray single-crystal structural analysis and NMR spectroscopy. Their structures showed varied coordination motifs: (i) a dimeric 1,2-diaza-4-phospholide lithium complex with exo-bidentate bridging coordination (4) consists of two lithium atoms that are linked via two μ₂-bridging, κN,κN'-coordinated ligands; (ii) the polymeric chain 1,2-diaza-4-phospholide potassium complex (5) showed an ion-bearing stair-shaped chain structure running through axis a, where the steps are η² interactions, and there is a transition platform between every two stairs; (iii) the polymeric chain 1,2-diaza-4-phospholide potassium complex (6) also presented a polymeric chain structure in the solid state but displayed a head-to-tail arrangement of two 1,2-diaza-4-phospholides; (iv) in comparison to 6, the 1,2-diaza-4-phospholide sodium complex (7) displayed a tetrameric structure, in which the sodium ions are arranged in a distorted tetrahedral fashion and each of them occupies a vertex of the tetrahedron; (v) the polymeric chain 1,2-diaza-4-phospholide potassium complex (8) presented a solvent-free chain structure, in which potassium ions each is η⁵-bonded by two 1,2-diaza-4-phospholides and η²-coordinated by another, consisting of a stair-shaped chain structure running through axis a but without significant intermolecular contacts between the adjacent stairs in comparison to that of 5; (vi) the polymeric chain 1,2-diaza-4-phospholide sodium complex (9) presented a solvent-free chain structure, in which sodium ions each is η¹(N),η²(N,N),η¹(P)-bonded by three 1,2-diaza-4-phospholides, consisting of a chain structure running through axis a; and (vii) the treatment complex 8 with elemental sulphur or selenium in the presence of crown ether gave rare thiophosphonato potassium [η³(S,P,S)-3,5-tBu₂dp-(μ-K)(S₂)([18]crown-6)] (10) or a selenophosphonato potassium [η³(Se,P,Se)-3,5-tBu₂dp-(μ-K)(Se₂)([18]crown-6)] (11). Both of the complexes crystallized in the orthorhombic space group Pnma as pale-yellow (or red) crystals. The X-ray diffraction analysis revealed 10 or 11 as a terminal complex with the η¹,η¹-X,X-coordination mode (X = S and Se). The ¹H DOSY NMR spectroscopy study of the species 8 in DMSO-d₆ suggested that polymeric complexes (4-9) in the solid state should dissociate into the related monomers in the solutions when the donor solvents were used.

Computational Study of Photochemical Relaxation Pathways of Platinum(II) Complexes

A series of functional platinum(II) complexes (Pt1-Pt3), which present high activity in four-photon absorption, in vivo imaging, and precise cancer therapy, as previously reported by the experimental work of Zhang et al. (Inorg. Chem. 2021, 60, 2362-2371), are computationally investigated in the article. We find that after the complex goes through four-photon absorption to the S₁ state, it undergoes intersystem crossing to the T₂ state and eventually reaches the T₁ state through internal conversion. On the T₁ state, both radiative and nonradiative decay to S₀ exit. The radiative decay forms the basis for the phosphorescence imaging in tissues as reported in the original paper. In addition, the nonradiative decay can simultaneously generate cytotoxic singlet oxygen by the excited energy transfer process, also known as triplet oxygen's quenching of triplet states. We conclude that the phosphorescence property as well as the photosensitizer character jointly bring high activity of in vivo imaging and photodynamic therapy to these complexes.

1,2-Diaza-4-phospholide complexes of chromium(ii): dipotassium organochromates behaving as single-molecule magnets

The 1,2-diaza-4-phospholide (dp^-) dipotassium ate complexes of chromium(ii) {[(η¹-N-3,5-tBu₂dp)₄Cr][(η⁵-(N,N,C,C,P))₂-K(η¹-O-THF)₂]₂} (5) and {[(η¹-N-3,5-Ph₂dp)₄Cr][(η⁵-(N,N,C,C,P))₂-K(η¹-O-THF)₂]₂}_∞ (6) were synthesized and characterized by X-ray single crystal structure analysis. Complex 5 with a near-square planar geometry at the chromium(ii) ion was unambiguously characterized by the high field electron paramagnetic resonance (HF-EPR) technique and magnetic measurements, revealing that it is a field-induced single-molecule magnet (SMM).

1,2,4-Triazolato paddlewheel dibismuth complexes with very short Bi(ii)–Bi(ii) bonds: bismuth(iii) oxidation of 1,2,4-triazolato anions into neutral N-1,2,4-triazolyl radicals

Bismuth(iii) oxidation of 1,2,4-triazolato anions allowed paddlewheel 1,2,4-triazolato dibismuth complexes to be isolated and the reaction involved the neutral N-1,2,4-triazolyl radicals that were evidenced by EPR analysis.

Synthesis and coordination properties of new σ2,λ3-P/N switchable chelators based on [1,2,3]-diazaphosphole

New ligands with σ²,λ³-P/N switching ability were synthesised and their coordination properties toward transition metals were studied.

A dipotassium 1,2,4-diazaphospholide dianion radical as an organometallic building block: the first 1,2-diaza-4-phosphine ruthenocene

A persistent dipotassium 3,5-diphenyl-1,2,4-diazaphospholide dianion radical {K+2[(3,5-Ph2dp)]˙2-} (2) was synthesized and investigated by EPR analysis and magnetic susceptibility measurement, and it can be used as a transfer agent for the preparation of an unusual 1,2-diaza-4-phosphine ruthenocene (4) with exclusive σ(P)-coordination. A plausible mechanism for the formation of 4 was proposed as one that involves a reactive radical intermediate {K+[(η5-CpMe5Ru)(σ(P),σ(C)-(3,5-Ph2dp)˙]-)} (K+[5A˙]-) with σ(P)-coordination due to the high spin density (SD) at the phosphorus (σ2λ3) atom.

1,2-Diaza-4-phosphaferrocenes: synthesis, structural characterization, 57Fe Mössbauer spectrum analysis, and DFT calculation

Two 1,2-diaza-4-phosphaferrocenes [(η⁵-3,5-R₂dp)Fe(η⁵-CpMe₅)] (R = tBu (3), Ph (4)) with a single η⁵ ring containing two nitrogen atoms are prepared. Mössbauer spectroscopic, electrochemical, and density functional theory (DFT) studies have provided a more detailed understanding of the electronic structures and stabilities of these complexes.

Paddlewheel 1,2,4-diazaphospholide distibines with the shortest antimony-antimony single bonds

One-electron reduction of SbCl3 with the non-innocent 1,2,4-diazaphospholide anion [3,5-R2dp](-) produced straightforwardly three unprecedented paddlewheel distibines [L2(Sb-Sb)L2] (L = η(1),η(1)-3,5-R2dp, R = tBu (4), iPr (5α, 5β), or Cy (6)) with very short Sb-Sb bond lengths (2.6691(8)-2.7451(8) Å). The novel structures were rationalized by DFT calculations.

1,2,4-Diazaphospholide complexes of lanthanum(iii), cerium(iii), neodymium(iii), praseodymium(iii), and samarium(iii): synthesis, X-ray structural characterization, and magnetic susceptibility studies

A few heteroleptic, charge-separated heterobimetallic, and polymeric alkali metalate complexes of 1,2,4-diazaphospholide lanthanum(iii), cerium(iii), neodymium(iii), praseodymium(iii), and samarium(iii) were simply prepared via the metathesis reaction of MCl3 (THF)m (m = 1-2) and K[3,5-R2dp] ([3,5-R2dp](-) = 3,5-di-substituent-1,2,4-diazaphospholide; R = tBu, Ph) in a varied ratio (1 : 3, 1 : 4, and 1 : 5, respectively) at room temperature in tetrahydrofuran. All the complexes were fully characterized by (1)H, (13)C{(1)H}, (31)P{(1)H}, IR, and X-ray single crystal diffraction analysis despite their paramagnetism (excluding La(iii) complexes). The structures of the complexes were found to feature varied coordination modes. The magnetic properties of several compounds were studied by magnetic susceptibility, and the complexes presented the magnetic moments close to or lower than the theoretical values for the free ions in the trivalent oxidation states (Pr(3+), Nd(3+)).

Chromium(III) complexes with 1,2,4-diazaphospholide and 2,6-bis(N-1,2,4-diazaphosphol-1-yl) pyridine ligands: synthesis, X-ray structural characterization, EPR spectroscopy analysis, and magnetic susceptibility studies

Three chromium(III) 1,2,4-diazaphospholide complexes were prepared: 3,5-di-tert-butyl-1,2,4-diazaphospholide chromium(III) dichloride [(η 2-3,5-tBu2dp)Cr(THF)2Cl2] (1), 3,5-di-phenyl-1,2,4-diazaphospholide chromium(III) dichloride [(η 2-3,5-Ph2dp)Cr(THF)2Cl2] (2), and 2,6-bis(N-1,2,4-diazaphosphol-1-yl)pyridine chromium(III) trichloride {[2,6-bis(N-1,2,4-diazaphosphol-1-yl)pyridine]CrCl3} (3). X-ray diffraction analysis has shown that these six-coordinate complexes each have a pseudo-octahedral configuration. Electron paramagnetic resonance (EPR) spectroscopy data for complex 1 for the paramagnetic S = 3/2 system (d 3 electron configuration) confirm a Cr(III) center in the octahedral coordination environment. The magnetic susceptibility of complex 1 followed the Curie–Weiss law well between 25 and 300 K. The magnetic moment of 1 was found to be close to the spin-only magnetic moment expected for three unpaired electrons (3.87 μB).

1,2,4-Diazaphospholide complexes of yttrium(iii), dysprosium(iii), erbium(iii), and europium(ii,iii): synthesis, X-ray structural characterization, and EPR analysis

Several structurally characterized heteroleptic, charge-separated heterobimetallic, and polymeric alkali metal ate complexes of 1,2,4-diazaphospholide Y(iii), Dy(iii), Er(iii), Eu(iii), and Eu(ii) were prepared via the reaction of MCl3 and K[3,5-R2dp] in varied ratios at 200-220 °C (M = Y, Dy, Er, Eu; R = tBu, Ph).