When two paramagnetic transition metal ions are present in the same molecular entity, the magnetic properties can be totally different from the sum of the magnetic properties of each ion surrounded by its nearest neighbors. These new properties depend on the nature and the magnitude of the interaction between the metal ions through the bridging ligands. If both ions have an unpaired electron (e.g. Cu2+ ions), then the molecular state of lowest energy is either a spin singlet or a spin triplet. In the former case, the interaction is said to be antiferromagnetic, in the latter case ferromagnetic. The nature and the order of magnitude of the interaction can be engineered by judiciously choosing the interacting metal ions and the bridging and terminal ligands, and, thus, by the symmetry and the delocalization of the orbitals centered on the metal ions and occupied by the unpaired electrons (magnetic orbitals). The first success in this “molecular engineering” of bimetallic compounds was in the synthesis of a Cu2+VO2+ heterobimetallic complex in which the interaction is purely ferro-magnetic. The same strategy could be utilized for designing molecular ferromagnets, one of the major challenges in the area of molecular materials. Another striking result is the possibility of tuning the magnitude of the interaction through a given bridging network by modifying the nature of the terminal ligands, which, in some way, play the role of “adjusting screws”. By careful selection of the bridging and terminal ligands, a very large antiferro-magnetic interaction can be achieved, even if the metal ions are far away from each other. Some sulfur-containing bridges are especially suitable in this respect.

Dinuclear Complexes with Predictable Magnetic Properties

A computational study of the exchange coupling is presented for a selected sample of carboxylato-bridged dinuclear copper(II) compounds. Model calculations have been used to examine the influence of several factors on the coupling constants: a) the electron-withdrawing power of the bridging ligands; b) the nature of the axial ligands; c) the number of bridging carboxylato groups; d) some structural distortions frequently found in this family of compounds; and e) the coordination mode of the carboxylato bridge. Coupling constants calculated for some complete structures, as determined by X-ray diffraction, are in excellent agreement with experimental data, confirming the ability of the computational strategy used in this work to predict the coupling constant for compounds for which experimental data are not yet available.

Exchange Coupling in Carboxylato‐Bridged Dinuclear Copper(II) Compounds: A Density Functional Study

Designed materials offer noteworthy applications which are often architecture dependent. Despite knowing such a fact, one of the major challenges faced by the scientific community is to find ways to predict and, if possible, control the resultant architecture of a network. If such an exercise is fruitful, it creates enormous opportunities to synthesize exotic materials with tailor-made applications. Any network is composed of individual molecules and the transition from a single molecule to a network can be achieved through several routes taking advantage of synthetic chemistry. There exists a molecular building block at the heart of such a transition which mediates such a process from a single molecule to a network. Although a large number of building blocks have created assorted materials, utilization of a well-defined coordination complex as the building block (i.e., metalloligand) is unique for the construction of a designed architecture. A coordination complex as the building block offers structural rigidity that places the auxiliary functional groups to a pre-organized conformation. Such auxiliary functional groups could then coordinate a secondary metal ion or be involved in the self-assembly via weak interactions, such as hydrogen bonds. This review focuses on the recent progress achieved through assorted molecular building blocks towards generating ordered networks. Broadly, two classes of metalloligands will be discussed: those offering hydrogen bond sensitive functional groups and those tendering coordination bond responsive groups. Nevertheless, the result is the construction of networks of a highly-ordered nature in both cases. The present review is expected to provide new strategies for constructing functional materials through metalloligands for challenging and practical applications.

Molecularly designed architectures – the metalloligand way

Coordination chemistry of N,N′-bis(coordinating group substituted)oxamides: a rational design of nuclearity tailored polynuclear complexes

Two nickel(II) complexes of formula (H3dien)2[Ni2(ox)5]·12H2O (1) and [Ni2(dien)2(H2O)2(ox)]Cl2 (2) (dien = diethylenetriamine and ox = oxalate dianion) have been synthesized and characterized by single-crystal X-ray diffraction. 1 crystallizes in the orthorhombic system, space group Abnn, with a = 15.386(4) A, b = 15.710(4) A, c = 17.071(4) A, and Z = 4. 2 crystallizes in the monoclinic system, space group P21/c, with a = 10.579(1) A, b = 7.258(1) A, c = 13.326(1) A, β = 93.52(3)°, and Z = 2. The structures of 1 and 2 consist of dinuclear oxalato-bridged nickel(II) units which contain bidentate oxalate (1) and tridentate dien in the fac-conformation (2) as terminal ligands. Both features, oxalato as a peripheral ligand and dien in the fac-conformation (instead of its usual mer-conformation), are unprecedented in the coordination chemistry of nickel(II). The nickel atom is six-coordinated in both compounds, the chromophores being NiO6 (1) and NiN3O3 (2). The Ni−O(ox) bond distances at the bridge (2.072(4)...

Influence of the Peripheral Ligand Atoms on the Exchange Interaction in Oxalato-Bridged Nickel(II) Complexes: An Orbital Model. Crystal Structures and Magnetic Properties of (H3dien)2[Ni2(ox)5]·12H2O and [Ni2(dien)2(H2O)2(ox)]Cl2

Exchange coupling in dinuclear copper(II) complexes with oxalato, oxamidato and oxamato ligands

Etude du complexe Cu 2 (amoxa)(CH 3 COO) 2 . Cristallisation dans le systeme monoclinique, groupe P2 1 /n et affinement jusqu'a R=0,033. Coordination pyramidale a base carree deformee autour de Cu. Variation avec la temperature de la susceptibilite magnetique. Spectre RPE

G. Franchini

Papers

Exchange coupling in dinuclear copper(II) complexes with oxalato, oxamidato and oxamato ligands

Magnetic properties and crystal structure of a linear-chain copper(II) compound with bridging acetate and oxamidate ligands

Magnetic Properties and Crystal Structure of a Linear-Chain Copper(II) Compound with Bridging Acetate and Oxamidate Ligands.