Bond Characterization of Metal Squarate Complexes [M^II(C₄O₄)(H₂O)₄; M = Fe, Co, Ni, Zn]

Abstract

Tetraaqua metal squarate complexes, M(C 4 O 4 )(H 2 O) 4 , (M ) Fe, Co, Ni, Zn), are known to have a polymeric chain structure with C 4 O 4 2as a bridge (µ-2) ligand between two metal ions in the trans position. Each metal ion is bonded to two C 4 O 4 2and four water molecules. They are all isostructural with space group C2/c. A complete Ewald sphere of data is measured at 120 K up to 2θ of 100-120°using Mo KR radiation for each complex. Such carefully measured intensities are used to investigate the detailed electron density distribution in order to understand the chemical bonding and the d-orbital splitting of the metal ions subjected in such a ligand field. Results on the electron density distribution will be presented in the form of deformation density and of Laplacian maps. Deformation density will be presented in terms of experimental ∆F x-x , ∆F m-a (multipole model), and of theoretical ∆F derived from the HF and DFT calculations. The interesting bent bond feature on the four-membered ring ligand C 4 O 4 2is explicitly demonstrated by the deformation density distribution and the bond path of the cyclic carbon-carbon bond. The asphericity in electron density distribution around the metal ion is also clearly illustrated in these compounds both in the deformation density and in Laplacian of the density. The comparison on the series of 3d-transition metal complexes will be made not only by the deformation density distribution and by the Laplacian of the density but also by the d-orbital population and by the associated topological properties at the bond critical point. The total number of d-electrons from the experiments are 6. 05, 6.88, 7.89, and 8.40, respectively, for Fe(II), Co(II), Ni(II), and Zn(II) ions in these compounds. A comparison between experiment and theory is made for the Ni complex.

Atomic interactions in ethylenebis(1-indenyl)zirconium dichloride as derived by experimental electron density analysis

“…In this respect, the Zr-C2 interaction differs from the image of intermediate interactions in molecules, which consist of the main group atoms (Bader, 1990). Similar observations for the metal-ligand bonds in the coordination compounds based on the experimental Laplacian were also reported by Smith et al (1997), Wang et al (1997), Hwang & Wang (1998), Lee et al (1999) and Macchi & Sironi (2003).…”

Experimental charge-density study on the nickel(II) coordination complex [Ni(H3 L)][NO3][PF6] [H3 L = N,N′,N′′-tris(2-hydroxy-3-methylbutyl)-1,4,7-triazacyclononane]: a reappraisal

“…The values of (r b ) for the Ni-N and Ni-O bonds may be compared with other recent studies on nickel(II) complexes, e.g. for trans-[Ni(NH 3 ) 4 (NO 2 ) 2 ], Ni-N = 0.65 (2), 0.76 (2) e Å À3 (Iversen et al, 1997); for [Ni(C 4 N 4 H 2 ) 2 ], Ni-N = 0.94 e Å À3 (Hwang & Wang, 1998); [Ni(C 4 O 4 )(OH 2 ) 4 ], Ni-O = 0.44, 0.47 e Å À3 (Lee et al, 1999); and a square-planar nickel(II) Schiff base complex, Ni-O = 0.581 (5), Ni-N = 0.522 (5), 0.644 (6), 0.711 (6) e Å À3 (Kožíšek et al, 2004). Our values of (r b ) are at the lower end of these, but are sufficiently large to suggest a significant shared interaction.…”

“…In view of these problems, and in light of subsequent experimental charge density studies on nickel(II) and cobalt(II) coordination compounds (Iversen et al, 1997;Hwang & Wang, 1998;Lee et al, 1999Lee et al, , 2002Ptasiewicz-Bak et al, 1999;Kožíšek et al, 2004), which showed very different features, we decided to re-investigate the charge density in complex (1), using a recent release of the XD software (Version 4.10). This version of XD has been shown in a number of studies (Lee et al, 2002;Macchi et al, 2001Macchi et al, , 2002Macchi & Sironi, 2003;Farrugia et al, 2003;Farrugia & Evans, 2005) to provide reliable charge densities from experimental data on transition metal complexes that are in good agreement with the densities from accurate quantum calculations.…”

μ‐1,3‐ (trans) and μ‐1,2‐ (cis) Bonding in Squarato‐Bridged Dinuclear Copper(II) and Nickel(II) Complexes Derived from Polypyridyl Amines

“…[7,19] Polymeric structures via µ-1,2-and µ-1,3-coordination have also been reported. [11,12,22,25] More recently, the trinuclear complex, [Cu 3 (pmap) 3 (µ 1,2,3 -C 4 O 4 )](ClO 4 ) 4 · 2H 2 O {pmap = bis[2-(2-pyridyl)ethyl][(2-pyridyl)methyl]-amine} with the µ-1,2,3-coordination mode has been structurally and magnetically characterized. [1] The different bonding modes in squarato-bridged metal(II) complexes are depicted in Scheme 1.…”