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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 {[CdCl 2 (dpkoxH)∙2H 2 O]} n ( 1 ∙2H 2 O), {[CdBr 2 (dpkoxH)]} n ( 2 ) and {[CdI 2 (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 η 1 :η 1 :η 1 :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 (η 1 - X)(μ - X) 2 (N pyridyl ) 2 (N oxime )} (X = Cl, Br, I). The trans -donor-atom pairs in 1 ∙2H 2 O 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 ∙2H 2 O 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 ∙2H 2 O and 2 are different compared with their [ZnX 2 (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 ( 1 H, 13 C, and 113 Cd 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 [CdI 2 (DMSO) 4 ].

The present work describes the reactions of CdI 2 with 2-pyridyl aldoxime (2paoH), 3-pyridyl aldoxime (3paoH), 4-pyridyl aldoxime (4paoH), 2-6-diacetylpyridine dioxime (dapdoH 2 ) and 2,6-pyridyl diamidoxime (LH 4 ). The primary goal was to contribute to understanding the molecular basis of the very good liquid extraction ability of 2-pyridyl ketoximes with long aliphatic chains towards toxic Cd(II) and the inability of their 4-pyridyl isomers for this extraction. Our systematic investigation provided access to coordination complexes [CdI 2 (2paoH) 2 ] ( 1 ), {[CdI 2 (3paoH) 2 ]} n ( 2 ), {[CdI 2 (4paoH) 2 ]} n ( 3 ) and [CdI 2 (dapdoH 2 ) ] ( 4 ). The reaction of CdI 2 and LH 4 in EtOH resulted in a Cd(II)-involving reaction of the bis(amidoxime) and isolation of [CdI 2 (L'H 2 )] ( 5 ), where L'H 2 is the new ligand 2,6-bis(ethoxy)pyridine diimine. A mechanism of this transformation has been proposed. The structures of 1 , 2 , 3 , 4· 2EtOH and 5 were determined by single-crystal X-ray crystallography. The complexes have been characterized by FT-IR and FT-Raman spectra in the solid state and the data are discussed in terms of structural features. The stability of the complexes in DMSO was investigated by 1 H NMR spectroscopy. Our studies confirm that the excellent extraction ability of 2-pyridyl ketoximes is due to the chelating nature of the extractants leading to thermodynamically stable Cd(II) complexes. The monodentate coordination of 4-pyridyl ketoximes (as confirmed in our model complexes with 4paoH and 3paoH) seems to be responsible for their poor performance as extractants.

The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO 3 ) 3 · n H 2 O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln 2 (O 2 CMe) 4 (NO 3 ) 2 (mepaoH) 2 ] (Ln = Nd, 1 ; Ln = Eu, 2 ; Ln = Gd, 3 ; Ln = Tb, 4 ; Ln = Dy, 5 ); the acetato ligands derive from the Ln III -mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O 2 CMe) 3 ·4H 2 O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy 2 (O 2 CMe) 6 (mepaoH) 2 ] ( 6 ). Treatment of 6 with one equivalent of HNO 3 gave 5 . The structures of 1 , 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2 - 4 display similar structural characteristics with 1 and 5 . The structures of 1 - 5 consist of dinuclear molecules in which the two Ln III centers are bridged by two bidentate bridging ( η 1 : η 1 : μ 2 ) and two chelating-bridging ( η 1 : η 2 : μ 2 ) acetate groups. The Ln III atoms are each chelated by a N , N '-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5 , the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate Ln III centers in 1 , 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the Tb III atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0-300 K range reveal weak antiferromagnetic intramolecular Gd III… Gd III exchange interactions in 3 ; the J value is -0.09(1) cm -1 based on the spin Hamiltonian Ĥ = -J(Ŝ Gd1 ·Ŝ Gd2 ).

We report here that the halogen bond driven self-assembly of 1,3,5-trifluorotriiodobenzene with tetraethylammonium and -phosphonium bromides affords 1:1 co-crystals, wherein the mutual induced fit of the triiodobenzene derivative and the bromide anions (halogen bond donor and acceptors, respectively) elicits the potential of these two tectons to function as tritopic modules (6,3). Supramolecular anionic networks are present in the two co-crystals wherein the donor and the acceptor alternate at the vertexes of the hexagonal frames and cations are accommodated in the potential empty space encircled by the frames. The change of one component in a self-assembled multi-component co-crystal often results in a change in its supramolecular connectivity and topology. Our systems have the same supramolecular features of corresponding iodide analogues as the metric aspects seem to prevail over other aspects in controlling the self-assembly process., Competing Interests: The authors declare no conflict of interest.