Doubly Thiocyanato(S,N)-Bridged Dinuclear Complexes of Mercury(II) from the Use of 2-pyridyl Oximes as Capping Ligands

Abstract

The reactions between Hg(SCN) 2 and the 2-pyridyl oximes, 2-pyridine aldoxime (paoH), methyl 2-pyridyl ketone oxime (mepaoH), pyridine-2-amidoxime (NH 2 paoH) and di-2-pyridyl ketone oxime (dpkoxH), have been investigated. The products in Me 2 CO or Me 2 CO/MeOH are the dinuclear complexes [Hg 2 (SCN) 4 (paoH) 2 ] (1), [Hg 2 (SCN) 4 (mepaoH) 2 ] (2), [Hg 2 (SCN) 4 (NH 2 paoH) 2 ] (3) and [Hg 2 (SCN) 4 (dpkoxH) 2 ] (4), whose structures have been determined by single-crystal X-ray crystallography. The molecular structures consist of centrosymmetric dinuclear molecules in which the two Hg II ions are bridged by two bidentate bridging 1 : 1 :: (: 1,3) SCNgroups forming a planar (1, 2) or non-planar (3, 4), 8-membered metallacyclic ring. The Hg II centers are each chelated by a N(2-pyridyl), N(oxime)-bidentate ligand and are bound to one terminal S-bonded thiocyanato group. Due to the very long Hg II-N (bridging SCN-) distances in 3, this complex can also be described as pseudodimer. The second 2-pyridyl ring of each dpkoxH ligand in 4 remains uncoordinated. The 2D lattice of 1 and 2 is built through H-bonding and-stacking interactions. Hydrogen bonds and S...S interactions generate 3D networks in 3 and 4. The IR spectra of the complexes are discussed in terms of the coordination modes of the ligands involved (SCN-, 2-pyridyl oximes). 1 H NMR spectra in d 6-DMSO indicate that the complexes decompose in solution.

Modeling the Solvent Extraction of Cadmium(II) from Aqueous Chloride Solutions by 2-pyridyl Ketoximes: A Coordination Chemistry Approach

“…This paper describes our results from the synthetic investigation of the general reaction system CdCl 2 ∙2H 2 O/phpaoH and from the full structural and spectroscopic characterization of the products; the implication of our study with respect to the solvent extraction of Cd(II) from aqueous chloride solutions by 2-pyridyl ketoximes have also been critically discussed. The present work can be considered as a continuation of our interest in several aspects of Cd(II) chemistry [15,16,17,18,19,20] and the coordination chemistry of 2-pyridyl oximes (aldo-, keto-, and amidoximes) [20,21,22,23,24,25,26,27,28,29,30,31,32,33]. Our previous experience on the latter area shows that phpaoH behaves similarly with methyl 2-pyridyl ketoxime (mepaoH; the substituent on the oxime carbon atom is a methyl group) [21,30] in 3d- and mixed 3d/4f-metal complexes, and this justifies partly the choice of phpaoH for our model studies.…”

Dinuclear Lanthanide(III) Complexes from the Use of Methyl 2-Pyridyl Ketoxime: Synthetic, Structural, and Physical Studies

“…The medium-intensity band at 1116 cm −1 in the spectrum of free mepaoH has been assigned to the v (OH) oxime mode [ 21 ]; this band has been shifted to lower wavenumber (~1090 cm −1 ) in the spectra of the six complexes due to coordination of the oxime nitrogen [ 21 ]. The in-plane pyridyl deformation of free mepaoH at 632 cm −1 shifts upwards in the spectra of the complexes (~685 cm −1 ) confirming the involvement of the ring N-atom in coordination [ 18 , 24 , 32 ]. The spectra of 1 – 5 are almost identical supporting similar structures of the complexes [Ln 2 (O 2 CMe) 4 (NO 3 ) 2 (mepaoH) 2 ] (Ln = Nd, Eu, Gd, Tb, Dy).…”

“…Restricting further discussion to the former family of ligands, the emphasis of our efforts (only selected references from our work are given below) has been on (a) the optical and magnetic properties of the resulting homo- and heterometallic dinuclear [ 18 , 19 , 20 , 21 ] and polynuclear [ 22 , 23 , 24 , 25 , 26 , 27 ] complexes, (b) the metal-mediated/promoted/assisted reactivity of these ligands [ 28 , 29 , 30 ], and (c) the modeling of the solvent extraction of toxic metal ions from aqueous solutions by 2-pyridyl ketoximes [ 31 , 32 ]. A literature survey reveals that a plethora of homometallic complexes of paoH, mepaoH, phpaoH, and ClpaoH ( Figure 1 ), in their neutral or anionic forms, have been prepared and studied with transition [ 22 , 23 , 24 , 25 , 27 , 28 , 29 , 31 , 32 ] and actinide [ 21 ] metal ions. In contrast, with the exception of [LnCl 3 (phpaoH) 3 ] (Ln = Nd [ 33 ], Sm [ 34 ]), such complexes are not known in lanthanide (Ln) chemistry.…”