Oxalate, squarate and croconate complexes with bis(2-pyrimidylcarbonyl)amidatecopper(II): synthesis, crystal structures and magnetic properties

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

“…The broadening or the split of the perchlorate band in these complexes most probably results from the reduction of the symmetry of the ClO 4 -ion to C 3v or to C 2v . It may also be attributed to the interaction of the ClO 4 -ions with the lattice water in 1 or with aqua water molecules in 2 and 3 (see Crystal Structure section). The IR spectra of the complexes also display strong to medium intensity bands in the 1550-1440 cm -1 region.…”

“…[4] In this compound, a J value of 1.3 cm -1 was interpreted on the basis of accidental orthogonality of magnetic orbitals. [4] In a continuous effort to understand the factors that might affect the coordination mode of bonding in the squarato-bridged metal(II) complexes and how this is related to the magnetic exchange pathways in theses complexes, the present study was undertaken to explore the structural and magnetic properties of a novel series of dinuclear squaratobridged Cu II and Ni II compounds based on polypyridylamine ligands. The structures of these ligands and their abbreviations are illustrated in Scheme 2.…”

“…The presence of four donor oxygen atoms and the richness of the electron density on the squarate dianion enhance its capability to simultaneously bind more than one metal ion, hence acting as a bridging ligand. The bridging squarato ligand affords three types of coordination modes known as µ-1,3-(trans), [2][3][4]6,16,22] µ-1,2-(cis), [2,5,8,9,13,14,16,18] and µ- ronment in 2 is achieved by the three N-atoms of the MeDPA ligand, by an oxygen atom of a bridging squarato ligand and, at longest distances, by two oxygen atoms from coordinated water molecules. In the nickel complex 3, the geometry is attained by the four N-atoms of TPA and by two oxygen atoms supplied by a coordinated water molecule and by a bridging squarato ligand.…”

“…5 Å in the cis-(µ-1,2) bonding to 8 Å in the trans-(µ-1,3) bonding. The magnetic measurements on structurally characterized squarato-bridged dinuclear nickel(II) and copper(II) complexes reveal weak antiferromagnetic interactions between the paramagnetic centers [2,4,18] (|J| = 0.4-1.7 cm -1 in Ni II and |J| = 0-26 cm -1 for Cu II complexes, J is the singlettriplet exchange constant). In general, the dinuclear copper(II) complexes with the µ-1,3-squarato bonding are usually antiferrromagnetically coupled with |J| values in the range of 0-8.6 cm -1 .…”

One‐Dimensional Oxalato‐Bridged Metal(II) Complexes with 4‐Amino‐1,2,4‐triazole as Apical Ligand

“…The strongest antiferromagnetic coupling (values of J ranging from -260 to -400 cm -1 ) [12,20,21] result when the oxalato bridge is symmetrically coordinated with two short bonds to each copper() center in such a way that it is coplanar with the singly occupied molecular orbitals (SOMOs) of the copper atoms. But when one copper-bridge distance is long (i. e., oxalato bridge is asymmetrically coordinated), the two metal-centered magnetic orbitals are parallel to each other and perpendicular to the bridging ligand (Scheme 1), the interaction between the d magnetic orbitals through the oxalato ligand is poor, and a weak anti-or ferromagnetic (when the overlap is zero, accidental orthogonality) [9][10][11]14,20,[22][23][24][25] coupling results, as occurs in 1.…”