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Toward Heteronuclear Molecular Re(I)-Cu(II) Boxes: Structural, Luminescent, and Magnetic Properties.

ABSTRACT: The bifunctional ligands of isonicotinic acid (Py-4-COOH) and 4-pyrid-4-ylbenzoic acid (Pybz-4-COOH) instead of polypyridines were therefore reacted with (Re(CO)4)3(C3N3S3) (C3N3S3 = cyanurate trianion), resulting in the formation of two trinuclear [(Re(CO)3)3(C3N3S3)(Py-4-COOH)3] (1) and [(Re(CO)3)3(C3N3S3)(Pybz-4-COOH)3] (2), respectively. In the meantime, both complexes 1 and 2 are connected by three bifurcated hydrogen bonds between their carboxylic acid moieties Py-4-COOH and Pybz-4-COOH to form the supramolecular trigonal-prismatic and -antiprismatic structures, respectively. It is noted that complex 1 can further react with copper(II) nitrate upon deprotonation to give nonanuclear [(Re(CO)3)3(C3N3S3)(Py-4-COO)3]2Cu3(H2O)9 (3), where two trinuclear [(Re(CO)3)3(C3N3S3)(Py-4-COO)3] moieties are connected by three penta-coordinate copper(II) ions, each coordinating to two carboxylates and three water molecules, to form the trigonal-prismatic structure. Surprisingly, addition of pyrazine (pz) in the synthetic process of complex 3 resulted in serendipitous isolation of a rare example of octadecanuclear {[(Re(CO)3)3(C3N3S3)(Py-4-COO)3]2Cu3(H2O)6(pz)2}2 (4), which can be regarded as a dimer of complex 3, connected by two bridging pz ligands. Interestingly, both complexes 3 and 4 are heteronuclear molecular Re(I)-Cu(II) boxes, constructed by a complex-as-a-ligand strategy. Furthermore, complexes 1 and 2 can exhibit respective low-energy luminescence at ca. 561 and 534 nm at room temperature upon photoexcitation, and complex 3 is found to display antiferromagnetic coupling of -127.68 and -134.70 cm-1, possibly due to multiple hydrogen bonds inducing significant Cu(II)···Cu(II) coupling.

SUBMITTER: Tzeng BC

PROVIDER: S-EPMC8656206 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:We report a complex with a rare Cu(II)-O-Cu(II) structural motif that is stable at room temperature, which allows its in-depth characterization by a variety of spectroscopic methods. Interest in such compounds is fueled by the recent discovery that a Cu(II)-O-Cu(II) species on the surface of Cu-ZSM-5 is capable of oxidizing methane to methanol, and this in turn ties into mechanistic discussions on the methane oxidation at the dicopper site within the particulate methane monooxygenase. For the synthesis of our Cu2O complex we have developed a novel, neutral ligand system, FurNeu, exhibiting two N-(N',N'-dimethylaminoethyl)(2-pyridylmethyl)amino binding pockets connected by a dibenzofuran spacer. The reaction of FurNeu with CuCl yielded [FurNeu](Cu2(μ-Cl))(CuCl2), 1, demonstrating the geometric potential of the ligand to stabilize Cu-X-Cu moieties. A Cu(I) precursor with weakly coordinating anions was chosen in the next step, namely [Cu(NCCH3)4]OTf, which led to the formation of [FurNeu](Cu(NCCH3))2(OTf)2, 3. Treatment of 3 with O2 or PhIO led to identical green solutions, whose UV-vis spectra were markedly different from the one displayed by [FurNeu](Cu)2(OTf)4, 4, prepared independently from FurNeu and Cu(OTf)2. Further investigations including PhIO consumption experiments, NMR and UV-vis spectroscopy, HR-ESI mass spectrometry, and protonation studies led to the identification of the green product as [FurNeu](Cu2(μ-O))(OTf)2, 5. DOSY NMR spectroscopy confirmed its monomeric character. Over longer periods of time 5 decomposes to give [Cu(picoloyl)2], formed through an oxidative N-dealkylation reaction followed by further oxidation of the ligand. Due to its slow decomposition reaction, all attempts to crystallize 5 failed. However, its structure in solution could be determined by EXAFS analysis in combination with DFT calculations, which revealed a Cu-O-Cu angle that amounts to 105.17°. Moreover, TDDFT calculations helped to rationalize the UV-vis absorptions of 5. The reactivity of complex 5 with 2,4-di-tert-butylphenol, DTBP, was also investigated; the initially formed biphenol product, TBBP, was found to further react in the presence of excessive O2 to yield 2,4,7,9-tetra-tert-butyloxepino[2,3-b]benzofuran, TBOBF, via an intermediate diphenoquinone. It turned out that 5, or its precursor 3, can even be employed as a catalyst for the oxidation of DTBP to TBBP or for the oxidation of TBBP to TBOBF.

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Toward Heteronuclear Molecular Re(I)-Cu(II) Boxes: Structural, Luminescent, and Magnetic Properties.

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