Patrick Franz

Nickel(II)-, cobalt(II)-, copper(II)-, and zinc(II)-phthalate and 1-methylimidazole coordination compounds: synthesis, crystal structures and magnetic properties

Three new coordination polymers [M(Pht)(1-MeIm)2]n (where M=Cu (1), Zn (2), Co (3); Pht2−=dianion of o-phthalic acid; 1-MeIm=1-methylimidazole) and two compounds [M(1-MeIm)6](HPht)2 · 2H2O (M=Co (4), Ni (5)) have been synthesized and characterized by X-ray crystallography. The structures of 1–3 (2 is isostructural to 3) consist of [M(1-MeIm)2] building units connected by 1,6-bridging phthalate ions to form infinite chains. In complex 1, each copper(II) center adopts a square coordination mode of N2O2 type by two O atoms from different phthalate ions and two N atoms of 1-MeIm, whereas in 3 two independent metal atoms are tetrahedrally (N2O2) coordinated to a pair of Pht ligands and a pair of 1-MeIm molecules. There are only van der Waals interactions between the chains in 1, while the three-dimensional network in 3 is assembled by C–H⋯O contacts. In contrast to polymers 1–3 the structures of 4 and 5 (complexes are also isostructural) are made up of the [M(1-MeIm)6]2+ cation, two hydrogen phthalate anions (HPht−) and two H2O solvate molecules. The coordination around each metal(II) atom is octahedral with six nitrogen atoms of 1-MeIm. Extended hydrogen bonding networks embracing the solvate water molecules and a phthalate residue as well as the weak C–H⋯O interactions stabilize the three-dimensional structures. Magnetic studies clearly show that the magnetic ions do not interact with each other. Furthermore, in compound 4 we have another example of a highly anisotropic Co2+ ion with a rhombic g-tensor and large zero-field-splitting. The complexes were also characterized by IR and 1H NMR spectroscopy, thermogravimetric analysis, and all data are discussed in the terms of known structures.

Synthesis, structure and properties of {M4O4} cubanes containing nickel(II) and cobalt(II)

A survey of the crystal structures containing simple {M4O4} cubane units is reported. It shows that the average M-M distance in these complexes is relatively constant for a given metal ion M. The structures are all distorted from the idealised cube to a T(d) structure, and most show a further distortion which, however, usually maintains some elements of symmetry. A system for classifying the different types of ligand in these complexes is proposed. Two new cubanes of cobalt(II) and nickel(II) with the ligand (R,R)-bis-1,2-(1-methylbenzimidazol-2-yl)ethane-1,2-diol, (R,R)- or its enantiomer have been isolated and the crystal structure of the cobalt(II) complex confirms the cubane structure. Electronic, CD and (1)H NMR spectra and magnetic susceptibility data are reported. The magnetic data for these and other compounds in the literature are discussed in terms of the structural parameters.

1,2-Bis(2-benzimidazolyl)-1,2-ethanediol, a chiral, tridentate, facially coordinating ligand

The ligand 1,2-bis(1H-benzimidazol-2-yl)-1,2-ethanediol, 1, and its methylated derivative 2 are readily synthesized from tartaric acid, and act as chiral, facially coordinating tridentate ligands, forming complexes of composition ML2 with octahedral transition metals. The copper(II) complexes show distorted 4 + 2 coordination with benzimidazoles occupying the equatorial sites and alcohol functions weakly binding in the axial sites. Nickel(II) complexes in three different states of protonation show regular octahedral geometry with the alcohols mutually cis. Deprotonation of the coordinated alcohol produces little structural change but the monodeprotonated complex forms a hydrogen bonded dimer. Magnetic measurements show the hydrogen bonded bridge to offer a pathway for weak antiferromagnetic coupling. UV-Visible spectroscopy shows the ligand to have a field intermediate between water and pyridine. The diastereoselectivity of complexation depends on the geometry: nickel(II) shows a weak preference for the homochiral complex, whereas copper(II) forms almost exclusively homochiral complexes.

Chapter 9:Variable-pressure luminescence and Raman spectroscopy of molecular transition metal complexes: spectroscopic effects originating from small, reversible structural variations

The past ten years have seen a significantly increasing number of published crystal structures for molecular transition metal complexes at variable pressure, providing quantitative information on structural variations. Spectroscopic measurements at variable pressure have been reported over the past 60 years for a variety of complexes, but luminescence measurements were mostly limited to intense signals until early in this century. The combination of variable-pressure structure variations with spectroscopic trends can lead to detailed new insight on a variety of aspects of electronic structure. This approach holds promise for the in-depth study of many categories of functional materials.