Synthesis, crystal structure, fluorescence, electrochemical property, and SOD-like activity of an unexpected nickel(II) complex with a quinazoline-type ligand

Photocatalytic hydrogen evolution over a nickel complex anchoring to thiophene embedded g-C3N4

Evolution of hydrogen from water by utilizing solar energy and photocatalysts is one of the most promising ways to solve energy crisis. However, designing a cost-effective and stable photocatalyst without any noble metals is of vital importance for this process. Herein, an extremely active molecular complex cocatalyst NiL₂(Cl)₂ is successfully designed. After being covalently linked to thiophene-embedded polymeric carbon nitride (TPCN), the hybrid catalyst NiL₂(Cl)₂/TPCN exhibits extraordinary H₂ production activity of 95.8 μmol h^-1 without Pt (λ ≥ 420 nm), together with a remarkable apparent quantum yield of 6.68% at 450 nm. In such a composite catalyst, the embedded π-electron-rich thiophene-ring not only extends the π-conjugated system to enhance visible light absorption, but also promotes the charge separation through electron-withdrawing effect. It turns out that the CN covalent bonds formed between NiL₂(Cl)₂ and TPCN skeleton accelerate the transfer of electrons to the Ni active sites. Our finding reveals that the strategy of embedding π-electron-rich compounds to graphitic carbon nitride provides potentials to develop excellent photocatalysts. The strong covalent combination of molecular complexes cocatalyst onto organic semiconductors represents an important step towards designing noble-metal-free photocatalysts with superior activity and high stability for visible light driven hydrogen evolution.

A Fluorescence-Detected Coordination-Induced Spin State Switch

The response of the spin state to in situ variation of the coordination number (CISSS) is a promising and viable approach to smart sensor materials, yet it suffers to date from insensitive detection. Herein, we present the synthetic access to a family of planar nickel(II) complexes, whose CISSS is sensitively followed by means of fluorescence detection. For this purpose, nickel(II) complexes with four phenazine-based Schiff base-like ligands were synthesized and characterized through solution-phase spectroscopy (NMR and UV-vis), solid-state structure analysis (single-crystal XRD), and extended theoretical modeling. All of them reveal CISSS in solution through axial ligating a range of N- and O-donors. CISSS correlates nicely with the basicity of the axial ligand and the substitution-dependent acidity of the nickel(II) coordination site. Remarkably, three out of the four nickel(II) complexes are fluorescent in noncoordinating solvents but are fluorescence-silent in the presence of axial ligands such as pyridine. As these complexes are rare examples of fluorescent nickel(II) complexes, the photophysical properties with a coordination number of 4 were studied in detail, including temperature-dependent lifetime and quantum yield determinations. Most importantly, fluorescence quenching upon adding axial ligands allows a "black or white", i.e. digital, sensoring of spin state alternation. Our studies of fluorescence-detected CISSS (FD-CISSS) revealed that absorption-based CISSS and FD-CISSS are super proportional with respect to the pyridine concentration: FD-CISSS features a higher sensitivity. Overall, our findings indicate a favored ligation of these nickel(II) complexes in the excited state in comparison to the ground state.

Metal-Dependent Cytotoxic and Kinesin Spindle Protein Inhibitory Activity of Ru, Os, Rh, and Ir Half-Sandwich Complexes of Ispinesib-Derived Ligands

Ispinesib is a potent inhibitor of kinesin spindle protein (KSP), which has been identified as a promising target for antimitotic anticancer drugs. Herein, we report the synthesis of half-sandwich complexes of Ru, Os, Rh, and Ir bearing the ispinesib-derived N,N-bidentate ligands (R)- and (S)-2-(1-amino-2-methylpropyl)-3-benzyl-7-chloroquinazolin-4(3H)-one and studies on their chemical and biological properties. Using the enantiomerically pure (R)- and (S)-forms of the ligand, depending on the organometallic moiety, either the S_M,R or R_M,S diastereomers, respectively, were observed in the molecular structures of the Ru- and Os(cym) (cym = η⁶-p-cymene) compounds, whereas the R_M,R or S_M,S diastereomers were found for the Rh- and Ir(Cp*) (Cp* = η⁵-pentamethylcyclopentadienyl) derivatives. However, density functional theory (DFT) calculations suggest that the energy difference between the diastereomers is very small, and therefore a mixture of both will be present in solution. The organometallics exhibited varying antiproliferative activity in a series of human cancer cell lines, with the complexes featuring the (R)-enantiomer of the ligand being more potent than the (S)-configured counterparts. Notably, the Rh and Ir complexes demonstrated high KSP inhibitory activity, even at 1 nM concentration, which was independent of the chirality of the ligand, whereas the Ru and especially the Os derivatives were much less active.

A Newly Synthesized Heterobimetallic NiII-GdIII Salamo-BDC-Based Coordination Polymer: Structural Characterization, DFT Calculation, Fluorescent and Antibacterial Properties

A unprecedented hetero-bimetallic 3d-4f BDC-salamo-based coordination polymer, [(L)Ni(BDC)Gd(NO3)(DMF)] was prepared and validated via elemental analyses, IR and UV–Visible absorption spectra, DFT calculation, and X-ray crystallography. The six-coordinated Ni1 ion lies at the N2O2 donor site of the L2− moiety, and one DMF O atom and carboxylate O atom occupy, collectively, the axial positions, and form a twisted octahedron. The nine-coordinated Gd1 ion consists of three oxygen atoms (O12, O13, and O14) of two carboxylate groups, two oxygen atoms (O8 and O9) derived from one bidentate nitrate group, and an O2O2 coordination site (O1, O2, O6, and O5) of the L2− unit, forming a twisted three-capped triangular prism coordination geometry. Compared to the ligand (H2L), the fluorescence intensity decreases due to the coordination of metal ions. Meanwhile, the antibacterial activities are researched.

Four rare structurally characterized hetero-pentanuclear [Zn4Ln] bis(salamo)-type complexes: syntheses, crystal structures and spectroscopic properties

Four new hetero-pentanuclear 3d–4f complexes [Zn₄(L)₂La(NO₃)₂(OEt)(H₂O)] (1), [Zn₄(L)₂Ce(NO₃)₂(OMe)(MeOH)] (2), [Zn₄(L)₂Pr(NO₃)₂(OEt)(EtOH)] (3) and [Zn₄(L)₂Nd(NO₃)₂(OMe)(MeOH)] (4) were synthesized by the reactions of a newly synthesized octadentate bis(salamo)-based tetraoxime ligand (H₄L) with Zn(OAc)₂·2H₂O and Ln(NO₃)₃·6H₂O (Ln = La, Ce, Pr and Nd), respectively, and characterized via elemental analyses, FT-IR, UV-Vis spectroscopy and single crystal X-ray crystallography. The X-ray crystallographic investigation revealed that all Zn^II ions were located in N₂O₃ coordination spheres, and possessed a trigonal bipyramid coordination environment. The Ln^III ion lay in an O₈ coordination sphere, and adopted a distorted square antiprismatic coordination environment. Furthermore, supramolecular interactions and fluorescence properties were investigated.

Four new hetero-pentanuclear 3d–4f complexes 1–4 were synthesized and characterized. Supramolecular interactions and fluorescence properties of complexes 1–4 were investigated.

A New Half-Salamo-Based Homo-Trinuclear Nickel(II) Complex: Crystal Structure, Hirshfeld Surface Analysis, and Fluorescence Properties

A new homo-trinuclear Ni(II) half-salamo-based complex [Ni3(L)2(μ-OAc)2(OAc)2(CH3OH)2]·2CH3OH was synthesized via the reaction of a tridentate ligand HL (2-[O-(1-ethyloxyamide)]oxime-4-bromophenol) and Ni(OAc)2·4H2O, and characterized using elemental analyses, IR spectra, UV-Vis absorption spectra, X-ray crystallography, and Hirshfeld analysis. Interestingly, single-crystal X-ray analysis showed that the two acetate molecules were bonded simultaneously with the Ni(II) atoms by mono-dentate chelating and bidentate bridging coordination modes, respectively, and the resulting hexa-coordinate geometries were ultimately formed. Furthermore, the Hirshfeld analysis of the complex was studied. Compared with HL, the complex fluorescence intensity was significantly lowered, indicating that the Ni(II) ions have fluorescence quenching characteristics.

Antimicrobial activities of self-assembled copper(ii), nickel(ii), and cobalt(iii) complexes combined with crystallographic, spectroscopic, DFT calculations and Hirshfeld surfaces analyses

Three 2-D and 3-D Cu(ii), Ni(ii), and Co(iii) complexes were obtained by reaction of HL1 with different metal salts. The complexes were characterized by single-crystal X-ray crystallography and spectroscopic methods, as well as Hirshfeld surface analysis and DFT studies.

Luminescent and electrochemical properties of four novel butterfly-shaped hetero-pentanuclear [Zn4Ln] complexes constructed from a bis(salamo)-type ligand

Four novel butterfly-shaped hetero-pentanuclear 3d-4f complexes [Zn₄(L)₂Sm(H₂O)₄]3NO₃·2EtOH (1) [Zn₄(L)₂Eu(NO₃)₂(MeOH)(EtOH)]NO₃·H₂O (2), [Zn₄(L)₂Gd(H₂O)₄]3NO₃·MeOH·EtOH (3) and [Zn₄(L)₂Tb(NO₃)(EtOH)(H₂O)₂]NO₃·MeOH·EtOH (4) were synthesized by the reactions of a bis(salamo)-type tetraoxime ligand (H₄L) with Zn(OAc)₂·2H₂O and Ln(NO₃)₃·6H₂O (Ln = Sm, Eu, Gd and Tb), respectively. The structures of complexes 1-4 were fully characterized by elemental analyses, FT-IR, UV-Vis spectroscopy and single crystal X-ray crystallography, and their luminescence properties were also discussed. In addition, cyclic voltammograms were used to characterize electrochemical properties of the Zn(II)-Ln(III) (Ln = Sm, Eu, Gd and Tb) complexes.

Homo- and heterometallic Cu(II)-M(II) (M = Ca, Sr and Ba) bis(salamo)-based complexes: Syntheses, structures and fluorescent properties

Four homo/heterometallic complexes [Cu₃(L)(μ₂-OAc)₉(CH₃OH) ₉]·3CHCl₃ (1), [Cu₂(L)Ca(μ₂-NO₃)₉] (9), [{Cu₂(L)Sr(μ₂-NO₃)₉}₉]·CH₃CH₂OH (11) and [Cu₂(L)Ba(μ₂-OAc)₉(OAc)] (14), containing an acyclic naphthalenediol-based ligand H₄L, were synthesized and characterized by elemental analyses, IR, UV-Vis, fluorescence spectra, TG-DTA and X-ray crystallography. The complex 1 was obtained by the reaction of H₄L with 11 equivalents of Cu(OAc) ₉·2H₂O. The heterometallic complexes 9, 11, 14 were acquired by the reaction of H₄L with 9 equivalents of Cu(OAc)₉·2H₂O or Cu(NO₃)₉·2H₂O and 1 equivalent of M(OAc)₉ (M = Ca, Sr and Ba). Owing to the different coordination cavities of the N₂O₂ and O₆ of the completely deprotonated (L)^14- unit, the crystal structures showed the N₂O₂ sites were occupied by Cu(II) atoms, alkaline earth metal(II) atoms occupied the O₆ site of the ligand (L)^14- unit, respectively. Furthermore, the fluorescence properties and TG-DTA analyses were discussed.

Unusual constructions of two Salamo-based copper(II) complexes

wo unusual Cu(II) complexes [{Cu(L¹)}₂] (1) and [Cu₂(L²)] (2), with an asymmetric salamo-type bisoxime ligand H₂L¹ were synthesized and characterized by elemental analyses, UV-Vis, fluorescent spectra, Hirshfeld surface analyses and single-crystal X-ray diffraction analyses. For the complex 1, two Cu(II) ions are penta-coordinate by N₂O₂ donor atoms from the (L¹)^2- unit and one bridged phenol oxygen atom from another (L¹)^2- unit. Complex 1 does not have intermolecular hydrogen bonds, formed an isolated zero dimensional structure. Meanwhile, for the complex 2, an unexpected ligand H₄L² was synthesized by aldol condensation reaction of H₂L¹ and acetone upon coordination, then the new ligand and Cu(II) ions combined, formed a highly symmetrical structure, and two Cu(II) ions of the complex 2 have tetra-coordinate environment. With the help of intermolecular hydrogen bonding CH⋯O interactions, a self-assembled infinite 1D supramolecular structure was formed. Meanwhile, the photophysical spectra and Hirshfeld surface analyses of the complexes 1 and 2 were also measured and discussed.

A heterotrimetallic Ni(II)–Dy(III) bis(salamo)-based complex: synthesis, structure and fluorescent property

A discrete heterotrinuclear complex [{Ni2LDy(OAc)3(CH3OH)}2] · 2CH3OH · 3CH2Cl2, with a naphthalenediol-based acyclic bis(salamo) ligand H4L, has been synthesized and structurally characterized using elemental analyses, IR, UV/Vis and fluorescence spectra and single crystal X-ray diffraction. The crystal structure shows two crystallographically independent but chemically identical molecules (moleculesIandII). All the Ni(II) atoms are hexa-coordinated with slightly distorted octahedral geometries. The central Dy atoms are nona-coordinated with slightly distorted tricapped trigonal prism geometries. An infinite 3D supramolecular structure is formed via intermolecular hydrogen bonding and C–H…π interactions.

Unprecedented Fluorescent Dinuclear CoII and ZnII Coordination Compounds with a Symmetric Bis(salamo)-Like Tetraoxime

Two unprecedented homometallic Co^II and Zn^II coordination compounds, [M₂(L)(OCH₃)][M₂(L)(OAc)] (M^II = Co^II (1) and Zn^II (2)), with a novel symmetric bis(salamo)-like tetraoxime ligand H₃L were synthesized and characterized by elemental analyses, infrafred (IR), ultraviolet–visible spectroscopy (UV-Vis), fluorescent spectra and single-crystal X-ray diffraction analyses. The unit cell of the two coordination compounds contains two crystallographically and chemically independent dinuclear coordination compounds. In the two coordination compounds, three metal ions are five-coordinated, formed two square pyramidal and a trigonal bipyramidal geometries, and the other metal ion is a hexacoordinate octahedral configuration. In addition, the coordination compound 1 forms a 3D supramolecular structure, and the coordination compound 2 forms a 0D dimer structure by the inter-molecular hydrogen bond interactions. Meanwhile, the fluorescence spectra of the coordination compounds 1 and 2 were also measured and discussed.

Synthesis and Fluorescence Properties of Structurally Characterized Heterobimetalic Cu(II)⁻Na(I) Bis(salamo)-Based Complex Bearing Square Planar, Square Pyramid and Triangular Prism Geometries of Metal Centers

A novel heterotrinuclear complex [Cu₂(L)Na(µ-NO₃)]∙CH₃OH∙CHCl₃ derived from a symmetric bis(salamo)-type tetraoxime H₄L having a naphthalenediol unit, was prepared and structurally characterized via means of elemental analyses, UV-Vis, FT-IR, fluorescent spectra and single-crystal X-ray diffraction. The heterobimetallic Cu(II)–Na(I) complex was acquired via the reaction of H₄L with 2 equivalents of Cu(NO₃)₂·2H₂O and 1 equivalent of NaOAc. Clearly, the heterotrinuclear Cu(II)–Na(I) complex has a 1:2:1 ligand-to-metal (Cu(II) and Na(I)) ratio. X-ray diffraction results exhibited the different geometric behaviors of the Na(I) and Cu(II) atoms in the heterotrinuclear complex; the both Cu(II) atoms are sited in the N₂O₂ coordination environments of fully deprotonated (L)⁴⁻ unit. One Cu(II) atom (Cu1) is five-coordinated and possesses a geometry of slightly distorted square pyramid, while another Cu(II) atom (Cu2) is four-coordination possessing a square planar coordination geometry. Moreover, the Na(I) atom is in the O₆ cavity and adopts seven-coordination with a geometry of slightly distorted single triangular prism. In addition, there are abundant supramolecular interactions in the Cu(II)–Na(I) complex. The fluorescence spectra showed the Cu(II)–Na(I) complex possesses a significant fluorescent quenching and exhibited a hypsochromic-shift compared with the ligand H₄L.

Synthesis and Fluorescence Properties of a New Heterotrinuclear Co(II)-Ce(III)Complex Constructed from a bis(salamo)-Type Tetraoxime Ligand

[Co₂(L)Ce(OAc)₃(CH₃CH₂OH)]·1.5CH₃OH∙0.5CH₂Cl₂, a heterotrinuclear Co(II)-Ce(III) bis(salamo)-type complex with a symmetric bi(salamo)-type ligand H₄L and an acyclic naphthalenediol moiety, was designed, synthesized and characterized by elemental analyses, FT-IR, UV-Vis and fluorescence spectroscopy and X-ray crystallography. The X-ray crystallographic investigation revealed the heterotrinuclear complex consisted of two Co(II) atoms, one Ce(III) atom, one (L)^4‒ unit, three μ₂-acetate ions, one coordinated ethanol molecule, one and half crystallization methanol molecule and half crystallization dichloromethane molecule. Two Co(II) atoms located in the N₂O₂ coordination spheres, are both hexacoordinated, with slightly distorted octahedral geometries. The Ce(III) atom is nine-coordinated and located in the O₆ cavity possesses a single square antiprismatic geometry. In addition, supramolecular interactions exist in the Co(II)-Ce(III) complex. Two infinite 2D supramolecular structures are built via intermolecular O-H···O, C-H···O and C-H···π interactions, respectively.

Unprecedented Hexanuclear Cobalt(II) Nonsymmetrical Salamo-Based Coordination Compound: Synthesis, Crystal Structure, and Photophysical Properties

A novel hexanuclear Co(II) coordination compound with a nonsymmetrical Salamo-type bisoxime ligandH4L, namely [{Co3(HL)(MeO)(MeOH)2(OAc)2}2]·2MeOH, was prepared and characterized by elemental analyses, UV–vis, IR and fluorescence spectra, and X-ray single-crystal diffraction analysis. Each Co(II) is hexacoordinated, and possesses a distorted CoO6 or CoO4N2 octahedrons. The Co(II) coordination compound possesses a self-assembled infinite 2D supramolecular structure with the help of the intermolecular C–H···O interactions. Meanwhile, the photophysical properties of the Co(II) coordination compound were studied.