The coordination chemistry of 2-pyridyl ketoximes continues to attract the interest of many inorganic chemistry groups around the world for a variety of reasons. Cadmium(II) complexes of such ligands have provided models of solvent extraction of this toxic metal ion from aqueous environments using 2-pyridyl ketoxime extractants. Di-2-pyridyl ketone oxime (dpkoxH) is a unique member of this family of ligands because its substituent on the oxime carbon bears another potential donor site, i.e., a second 2-pyridyl group. The goal of this study was to investigate the reactions of cadmium(II) halides and dpkoxH in order to assess the structural role (if any) of the halogeno ligand and compare the products with their zinc(II) analogs. The synthetic studies provided access to complexes {[CdCl₂(dpkoxH)∙2H₂O]}_n (1∙2H₂O), {[CdBr₂(dpkoxH)]}_n (2) and {[CdI₂(dpkoxH)]}_n (3) in 50–60% yields. The structures of the complexes were determined by single-crystal X-ray crystallography. The compounds consist of structurally similar 1D zigzag chains, but only 2 and 3 are strictly isomorphous. Neighboring Cd^II atoms are alternately doubly bridged by halogeno and dpkoxH ligands, the latter adopting the η¹:η¹:η¹:μ (or 2.0111 using Harris notation) coordination mode. A terminal halogeno group completes distorted octahedral coordination at each metal ion, and the coordination sphere of the Cd^II atoms is {Cd^II(η¹ − X)(μ − X)₂(N_pyridyl)₂(N_oxime)} (X = Cl, Br, I). The trans-donor–atom pairs in 1∙2H₂O are Cl_terminal/N_oxime and two Cl_bridging/N_pyridyl; on the contrary, these donor–atom pairs are X_terminal/N_pyridyl, X_bridging/N_oxime, and X_bridging/N_pyridyl (X = Br, I). There are intrachain H-bonding interactions in the structures. The packing of the chains in 1∙2H₂O is achieved via π-π stacking interactions, while the 3D architecture of the isomorphous 2 and 3 is built via C-H∙∙∙C_g (C_g is the centroid of one pyridyl ring) and π-π overlaps. The molecular structures of 1∙2H₂O and 2 are different compared with their [ZnX₂(dpkoxH)] (X = Cl, Br) analogs. The polymeric compounds were characterized by IR and Raman spectroscopies in the solid state, and the data were interpreted in terms of the known molecular structures. The solid-state structures of the complexes are not retained in DMSO, as proven via NMR (¹H, ¹³C, and ¹¹³Cd NMR) spectroscopy and molar conductivity data. The complexes completely release the coordinated dpkoxH molecule, and the dominant species in solution seem to be [Cd(DMSO)₆]²⁺ in the case of the chloro and bromo complexes and [CdI₂(DMSO)₄].

The oxime group is important in organic and inorganic chemistry. In most cases, this group is part of an organic molecule possessing one or more donor sites capable of forming bonds to metal ions. One family of such compounds is the group of 2-pyridyl (aldo)ketoximes. Metal complexes of 2-pyridyl oximes continue to attract the intense interest of many inorganic chemistry groups around the world for a variety of reasons, including their interesting structures, physical and biological properties, and applications. A unique member of 2-pyridyl ketoximes is di-2-pyridyl ketoxime (dpkoxH), which contains two 2-pyridyl groups and an oxime functionality that can be easily deprotonated giving the deprotonated ligand (dpkox⁻). The extra 2-pyridyl site confers a remarkable flexibility resulting in metal complexes with exciting structural and reactivity features. Our and other research groups have prepared and characterized many metal complexes of dpkoxH and dpkox⁻ over the past 30 years or so. This work is an attempt to build a “periodic table” of dpkoxH, which is near completion. The filled spaces of this “periodic table” contain metal ions whose dpkoxH/dpkox⁻ complexes have been structurally characterized. This work reviews comprehensively the to-date published coordination chemistry of dpkoxH with emphasis on the syntheses, reactivity, relationship to metallacrown chemistry, structures, and properties of the metal complexes; selected unpublished results from our group are also reported. The sixteen coordination modes adopted by dpkoxH and dpkox⁻ have provided access to monomeric and dimeric complexes, trinuclear, tetranuclear, pentanuclear, hexanuclear, heptanuclear, enneanuclear, and decanuclear clusters, as well as to a small number of 1D coordination polymers. With few exceptions ({M^IILn^III₂} and {Ni^II₂Mn^III₂}; M = Ni, Cu, Pd, and Ln = lanthanoid), most complexes are homometallic. The metals whose ions have yielded complexes with dpkoxH and dpkox⁻ are Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Re, Os, Ir, Au, Hg, lanthanoids (mainly Pr and Nd), and U. Most metal complexes are homovalent, but some mixed-valence Mn, Fe, and Co compounds have been studied. Metal ion-assisted/promoted transformations of dpkoxH, i.e., reactivity patterns of the coordinated ligand, are also critically discussed. Some perspectives concerning the coordination chemistry of dpkoxH and research work for the future are outlined.

In an attempt to fill in the empty Zn position in the “Periodic Table” of 1-methylbenzotriazole (Mebta), reactions between Zn(II) sources and this ligand were carried out. The detailed synthetic studies provided access to complexes [ZnX₂(Mebta)₂] (X = Cl, 1; X = Br, 3; X = I, 4), (MebtaH)₂[ZnCl₄] (2), tet-[Zn(NO₃)₂(Mebta)₂] (5), oct-[Zn(NO₃)₂(Mebta)₂] (6), and [Zn(Mebta)₄](Y)₂ [Y = ClO₄, 7; Y = PF₆, 8]. Solid-state thermal decomposition of 2 leads to 1 in quantitative yield. The structures of 3, 4, 5, 6, and 7 were determined by single-crystal crystallography. The structures of the remaining complexes were proposed based on spectroscopic evidence. In all compounds, Mebta behaves as monodentate ligand using the nitrogen of the position 3 as donor. Complexes 1–4, 7, and 8 are tetrahedral. Complexes 5 and 6 are isostoichiometric and their preparation in pure forms depends on the reaction conditions; in the former the Zn^II atom has a tetrahedral geometry, whereas in the latter the metal ion is octahedral. This case of rare isomerism arises from the monodentate (in 5) vs. bidentate (in 6) coordination of the nitrato groups. Extensive π–π stacking interactions and non-classical H bonds build interesting 3D architectures in the structurally characterized complexes. The compounds were characterized by IR, far-IR, and Raman spectroscopies in the solid state, and the data were interpreted in terms of the structures (known or proposed) of the complexes and the coordination modes of the organic and inorganic ligands involved. The solid-state structures of the complexes are not retained in solution, as proven by NMR (¹H, ¹³C[¹H]) spectroscopy and molar conductivity data. The thermal decomposition study of 1 and 3 leads to stable intermediates with 1:1 stoichiometry, i.e., ZnX₂(Mebta). Based on far-IR spectra, polymeric tetrahedral structures are possible with simultaneous presence of terminal and bridging X⁻ groups. Liquid-phase ab initio (MP2) and gas-phase DFT calculations, performed on Mebta and the nitrato complexes, respectively, shed light on the tendency of Mebta for N3-coordination, and the existence and relative stabilities of 5 and 6.

A motivating class of compounds with interest in the research field of biological active metallopharmaceuticals for cancer treatment is based on organometallic complexes of Sn(IV), exhibiting advantages such as improved cellular uptake and body excretion, lower toxicity, and fewer side effects compared to platinum-based drugs. In this study, the mononuclear organotin coordination complex [(CH₃)₂SnCl₂(mebta)₂] was synthesized and characterized using vibrational spectroscopy (IR, Raman), ¹H NMR, ¹³C{¹H} NMR, and X-ray crystallography. Its antiproliferative properties were thoroughly assessed across an aggressive triple-negative human breast cancer cell line. Notably, comparative studies with precursor materials verified that the observed biological activity is intrinsic to the complex itself. This study highlights the compound’s ability to induce cell fate by disrupting essential cellular functions, such as proliferation. By exploring the antiproliferative effects of organotin(IV) derivatives, we introduce a novel class of Sn complexes with 1-methylbenzotriazole (mebta), demonstrating significant potential as promising antitumor agents in the field of organotin compounds.

Metal complexes of benzotriazole-type ligands continue to attract the intense interest of many inorganic chemistry groups around the world for a variety of reasons, including their aesthetically beautiful structures, physical properties and applications. 1-methylbenzotriazole (Mebta) is the N-substituted archetype of the parent 1H-benzotriazole. The first attempt to build a “periodic table” of Mebta, which includes its complexes with several metal ions, is described in this work. This, at first glance, trivial ligand has led to interesting results in terms of the chemistry, structures and properties of its metal complexes. This work reviews the to-date published coordination chemistry of Mebta with Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(I), Cu(II), Zn(II), Pd(II), Au(I) and {U^VIO₂}²⁺, with emphasis on their preparations, reactivity, structures and properties. Unpublished results from our group comprising other Co(II), Ni(II), Cu(II) and Zn(II) complexes, as well as Cd(II), Hg(II), Ag(I), In(III) and Sn(IV) ones are briefly reported. Mebta can also provide access to 1D and 3D heterometallic thiocyanato-bridged Co(II)/Hg(II) and Ni(II)/Hg(II) compounds. In almost all cases, Mebta behaves as a monodentate ligand with the nitrogen of position 3 of the azole ring as the donor atom. However, there are two copper complexes in which this molecule adopts a bidentate bridging coordination behavior. Our efforts to complete the “periodic table” of Mebta are continued.

The oxime group is important in organic and inorganic chemistry. In most cases this group is part of an organic molecule possessing one or more donor sites capable of forming bonds to metal ions. One family of such compounds is the group of 2-pyridyl (aldo)ketoximes. Metal complexes of 2-pyridyl oximes continue to attract the intense interest of many inorganic chemistry groups around the world for a variety of reasons, including their aesthetically beautiful structures, physical and biological properties, and applications. A unique member of 2-pyridyl ketoximes is di-2-pyridyl ketoxime (dpkoxH), which contains two 2-pyridyl groups and an oxime functionality that can be easily deprotonated giving the deprotonated ligand (dpkox-). The extra 2-pyridyl site confers a remarkable flexibility resulting in metal complexes with exciting structural and reactivity features. Our and other research groups have prepared and characterized many metal complexes of dpkoxH and dpkox- over the past 30 years or so. This work is an attempt to build a “periodic table” of dpkoxH which is near completion. The filled spaces of this “periodic table” contain metal ions whose dpkoxH/dpkox- complexes have been structurally characterized. This work reviews comprehensively the to-date published coordination chemistry of dpkoxH with emphasis on the syntheses, reactivity, relationship to metallacrown chemistry, structures and properties of the metal complexes; selected unpublished results from our group are also reported. The sixteen coordination modes adopted by dpkoxH and dpkox- have provided access to monomeric and dimeric complexes, trinuclear, tetranuclear, pentanuclear, hexanuclear, heptanuclear, enneanuclear and decanuclear clusters, as well as to a small number of 1D coordination polymers. With few exceptions ({MIILnIII2} and {NiII2MnIII2}; M = Ni, Cu, Pd and Ln = lanthanoid), most complexes are homometallic. The metals whose ions have yielded complexes with dpkoxH and dpkox- are Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Re, Os, Ir, Au, Hg, lanthanoids and U. Most metal complexes are homovalent, but some mixed-valence Mn, Fe and Co compounds have been studied. Metal ion-assisted/promoted transformations of dpkoxH, i.e. reactivity patterns of the coordinated ligand, are also critically discussed. Some perspectives concerning the coordination chemistry of dpkoxH and research work for the future are outlined. Our efforts to complete the “periodic table” of di-2-pyridyl ketoxime are continued.