Investigation of the Zinc Chloride / Methyl(2-pyridyl)ketone Oxime Reaction System: A Mononuclear Complex and an Inverse 12-Metallacrown-4 Cluster

Abstract

The reactions of methyl(2-pyridyl)ketone oxime, (py)C(Me)NOH, with zinc chloride have been investigated. An excess of the ligand in EtOH/MeCN affords the mononuclear complex [ZnCl 2 {(py)C(Me)NOH} 2 ] (1) in moderate yield. The metal ion is coordinated by two chloro ligands and two N, N'-chelating (py)C(Me)NOH molecules. The six-coordinate molecule is the ciscis-trans isomer considering the positions of the coordinated chlorine, pyridyl and oxime nitrogen atoms, respectively. The reaction between equimolar quantities of ZnCl 2 , (py)C(Me)NOH and LiOH · H 2 O in EtOH/MeCN leads to the tetranuclear cluster [Zn 4 (OH) 2 Cl 2 {(py)C(Me)NO} 4 ] (2) in high yield. The molecule lies on a crystallographic inversion center and has an inverse 12-metallacrown-4 topology. Two triply bridging hydroxides are accommodated within the metallacrown ring. Each (py)C(Me)NO − ligand adopts the 2.111 coordination mode (Harris notation), chelating one Zn II ion and bridging a Zn II 2 pair. Two metal ions are in a distorted O 2 N 4 octahedral environment, whereas the other two are in a severely distorted tetrahedral O 3 Cl environment. Complex 2 joins a small family of structurally characterized zinc(II) metallacrown complexes. The IR data are discussed in terms of the nature of bonding and the structures of the two complexes.

In search of molecules displaying ferromagnetic exchange: multiple-decker Ni12 and Ni16 complexes from the use of pyridine-2-amidoxime

“…This shift is attributed to the coordination of the oximate nitrogen. 37 The band is strong in the spectrum of the Ni 16 cluster, because it also has a ν 3 (F 2 ) [ν d (SO)] character due to the ionic sulfates (T d symmetry). Somewhat to our surprise, the 1566 cm −1 band is shifted to a higher wavenumber in the complexes (1577 cm −1 in 1•5MeOH, 1580 cm −1 in 2•10H 2 O• 26MeOH), overlapping with an aromatic stretch.…”

“…This shift may be indicative of the oximate nitrogen coordination. 37 Extensive studies on Schiff-base complexes (which also contain a CvN bond) have shown 38 that a change in the s character of the nitrogen lone pair occurs upon coordination such that the s character of the nitrogen orbital, which is involved in the CvN bond, increases; this change in hybridization produces a greater CvN stretching force constant relative to the free neutral ligand. The in-plane deformation band of the 2-pyridyl ring of free pyaoxH 2 at 632 cm −1 shifts upwards in 1•5MeOH (646 cm −1 ) and 2•10H 2 O•26MeOH (645 cm −1 ), confirming the involvement of the ring-N atom in coordination.…”

Mononuclear and Dinuclear Manganese(II) Complexes from the Use of Methyl(2‐pyridyl)ketone Oxime

“…The 1.011 ligation mode is the exclusive one for the metal complexes containing the neutral ligand [22, 24, 30]. …”

“…Thus, (py)C(R)NOH behave as N , N ' -chelating ligands (see Scheme 2) making necessary the employment of additional inorganic or organic anions to complete the coordination sphere of the metal centre or to balance the charge of the complex cation. A variety of mono anions have been used for this reason, for example, PhCO 2 − [21], Cl − [22, 23], Br − [24], and NO 3 − [25]. Recently, we have started a research program to explore the use of the sulfate ion, SO 4 2− , in 3d-metal/2-pyridyl oxime chemistry, instead of the abovementioned mono anionic ligands.…”

Synthesis and Structural Characterization of a New Tetranuclear Nickel(II) Sulfato Complex Containing the Anionic Form of Di-2-Pyridyl Ketone Oxime

“…Somewhat to our surprise, the 1568 cm −1 band is shifted to a higher wavenumber in the complex (1598 cm −1 ), overlapping with an aromatic stretch. This shift may be indicative of the oxime nitrogen coordination [94]. Extensive studies on Schiff base complexes (which also contain a C=N bond) have shown [95] that a change in the s character of the nitrogen lone pair occurs upon coordination such that the s character of nitrogen orbital involved in the C=N bond increases; this change in hybridization produces a greater C=N stretching force constant relative to the free neutral ligand.…”