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1. Light‐responsive and Protic Ruthenium Compounds Bearing Bathophenanthroline and Dihydroxybipyridine Ligands Achieve Nanomolar Toxicity towards Breast Cancer Cells †

   https://doi.org/10.1111/php.13508  

   Oladipupo, Olaitan E. ; Brown, Spenser R. ; Lamb, Robert W. ; Gray, Jessica L. ; Cameron, Colin G. ; DeRegnaucourt, Alexa R. ; Ward, Nicholas A. ; Hall, James Fletcher ; Xu, Yifei ; Petersen, Courtney M. ; et al ( November 2021 , Photochemistry and Photobiology)

   We report new ruthenium complexes bearing the lipophilic bathophenanthroline (BPhen) ligand and dihydroxybipyridine (dhbp) ligands which differ in the placement of the OH groups ([(BPhen)₂Ru(n,n′‐dhbp)]Cl₂withn = 6 and 4 in 1_Aand 2_A, respectively). Full characterization data are reported for 1_Aand 2_Aand single crystal X‐ray diffraction for 1_A. Both 1_Aand 2_Aare diprotic acids. We have studied 1_A, 1_B, 2_A, and 2_B(B = deprotonated forms) by UV‐vis spectroscopy and 1 photodissociates, but 2 is light stable. Luminescence studies reveal that the basic forms have lower energy³MLCT states relative to the acidic forms. Complexes 1_Aand 2_Aproduce singlet oxygen with quantum yields of 0.05 and 0.68, respectively, in acetonitrile. Complexes 1 and 2 are both photocytotoxic toward breast cancer cells, with complex 2 showing EC₅₀light values as low as 0.50 μM with PI values as high as >200vs. MCF7. Computational studies were used to predict the energies of the³MLCT and³MC states. An inaccessible³MC state for 2_Bsuggests a rationale for why photodissociation does not occur with the 4,4′‐dhbp ligand. Low dark toxicity combined with an accessible³MLCT state for¹O₂generation explains the excellent photocytotoxicity of 2.

    

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2. Characterization of the Ligand Field in Pseudo‐Octahedral Ni(II) Complexes of Pincer‐Type Amido Ligands: Magnetism, Redox Behavior, Electronic Absorption and High‐Frequency and ‐Field EPR Spectroscopy

   https://doi.org/10.1002/ejic.202300446  

   Ortiz, Robert J. ; Shepit, Michael ; van Lierop, Johan ; Krzystek, J. ; Telser, Joshua ; Herbert, David E. ( August 2023 , European Journal of Inorganic Chemistry)

   The description of π‐donor amido moieties as ‘weak‐field’ ligands can belie the influence of metal‐ligand covalency on the overall ligand field of coordination complexes, which can in turn influence properties including the magnetic ground state and those of their excited states. In this contribution, the ligand fields of pseudo‐octahedral Ni(II) complexes supported by diarylamido pincer‐type amido ligands – three previously reported examples supported by asymmetric (2‐R‐phenanthridin‐4‐yl)(8‐quinolinyl)amido ligands (R = Cl, CF₃,tBu;^RL¹) along with a new congener bearing a symmetricbis(8‐quinolinyl)amido ligand (BQA;L²) – were investigated in two ways. First, high‐frequency and ‐field electron paramagnetic resonance spectroscopy (HFEPR), SQUID magnetometry, and electronic absorption spectroscopy were used to determine the ligand field parameters. Second, the ability to electrochemically address ligand‐based oxidations despite metal‐centered SOMOs in the parentS=1 paramagnets was investigated, supported by time‐dependent density functional theory (TDDFT) identification of strong intervalence charge‐transfer (IVCT) transitions attributed to electronic communication between two N_amidomoieties mediated by a Ni(II) bridge. These findings are discussed in the broader context of 3d transition metal coordination complexes of weak‐field π‐donor ligands.

    

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3. From 0 to II in One‐Electron Steps: A Series of Ruthenium Complexes Supported by TropPPh 2

   https://doi.org/10.1002/ange.201605687  

   Yang, Xiuxiu ; Gianetti, Thomas L. ; Harbort, Joshua ; Wörle, Michael D. ; Tan, Lilin ; Su, Cheng‐Yong ; Jurt, Pascal ; Harmer, Jeffrey R. ; Grützmacher, Hansjörg ( August 2016 , Angewandte Chemie)

   We report the synthesis of a series of ruthenium complexes supported by the phosphine olefin ligand tropPPh₂(trop=5‐H‐dibenzo‐[a,d]cyclohepten‐5‐yl) in the oxidation states 0, +I, and +II, formed via successive one‐electron oxidization steps from Ru⁰(tropPPh₂)₂. The bidentate character of the tropPPh₂ligand and its steric hindrance force the complexes to adopt uncommon geometries, which were investigated by X‐ray diffraction analysis. EPR data of the mononuclear Ru^Icomplex reveal couplings of the unpaired spin with the ruthenium and two phosphorus nuclei, as well as the olefinic protons which show that the spin is mainly localized on the Ru^Icenter.

    

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4. Crystal structures of [Cu(phen)(H 2 O) 3 ( M F 6 )]·H 2 O ( M = Ti, Zr, Hf) and [Cu(phen)(H 2 O) 2 F] 2 [HfF 6 ]·H 2 O

   https://doi.org/10.1107/S2056989021000645  

   Nisbet, Matthew L. ; Poeppelmeier, Kenneth R. ( February 2021 , Acta Crystallographica Section E Crystallographic Communications)

   null (Ed.)

   The crystal structures of three bridged bimetallic molecular compounds, namely, triaqua-2κ 3 O -μ-fluorido-pentafluorido-1κ 5 F -(1,10-phenanthroline-2κ 2 N , N ′)copper(II)titanium(IV) monohydrate, [Cu(TiF 6 )(phen)(H 2 O) 3 ]·H 2 O (phen is 1,10-phenanthroline, C 12 H 8 N 2 ), (I), triaqua-2κ 3 O -μ-fluorido-pentafluorido-1κ 5 F -(1,10-phenanthroline-2κ 2 N , N ′)copper(II)zirconium(IV) monohydrate, [Cu(ZrF 6 )(phen)(H 2 O) 3 ]·H 2 O, (II), and triaqua-2κ 3 O -μ-fluorido-pentafluorido-1κ 5 F -(1,10-phenanthroline-2κ 2 N , N ′)copper(II)hafnium(IV) monohydrate, [Cu(HfF 6 )(phen)(H 2 O) 3 ]·H 2 O, (III), and one molecular salt, bis[diaquafluorido(1,10-phenanthroline-κ 2 N , N ′)copper(II)] hexafluoridohafnate(IV) dihydrate, [CuF(phen)(H 2 O) 2 ] 2 [HfF 6 ]·2H 2 O, (IV), are reported. The bridged bimetallic compounds adopt Λ-shaped configurations, with the octahedrally coordinated copper(II) center linked to the fluorinated early transition metal via a fluoride linkage. The extended structures of these Λ-shaped compounds are organized through both intra- and intermolecular hydrogen bonds and intermolecular π–π stacking. The salt compound [Cu(phen)(H 2 O) 2 F] 2 [HfF 6 ]·H 2 O displays an isolated square-pyramidal Cu(phen)(H 2 O) 2 F + complex linked to other cationic complexes and isolated HfF 6 2− anions through intermolecular hydrogen-bonding interactions. 

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5. Photocytotoxicity and photoinduced phosphine ligand exchange in a Ru( ii ) polypyridyl complex

   https://doi.org/10.1039/d1sc05647f  

   Steinke, Sean J. ; Gupta, Sayak ; Piechota, Eric J. ; Moore, Curtis E. ; Kodanko, Jeremy J. ; Turro, Claudia ( February 2022 , Chemical Science)

   Two new tris-heteroleptic Ru( ii ) complexes with triphenylphosphine (PPh 3 ) coordination, cis -[Ru(phen) 2 (PPh 3 )(CH 3 CN)] 2+ (1a, phen = 1,10-phenanthroline) and cis -[Ru(biq)(phen)(PPh 3 )(CH 3 CN)] 2+ (2a, biq = 2,2′-biquinoline), were synthesized and characterized for photochemotherapeutic applications. Upon absorption of visible light, 1a exchanges a CH 3 CN ligand for a solvent water molecule. Surprisingly, the steady-state irradiation of 2a followed by electronic absorption and NMR spectroscopies reveals the photosubstitution of the PPh 3 ligand. Phosphine photoinduced ligand exchange with visible light from a Ru( ii ) polypyridyl complex has not previously been reported, and calculations reveal that it results from a trans -type influence in the excited state. Complexes 1a and 2a are not toxic against the triple negative breast cancer cell line MDA-MB-231 in the dark, but upon irradiation with blue light, the activity of both complexes increases by factors of >4.2 and 5.8, respectively. Experiments with PPh 3 alone show that the phototoxicity observed for 2a does not arise from the released phosphine ligand, indicating the role of the photochemically generated ruthenium aqua complex on the biological activity. These complexes represent a new design motif for the selective release of PPh 3 and CH 3 CN for use in photochemotherapy. 

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