A heteroleptic diradical Cr(iii) complex with extended spin delocalization and large intramolecular magnetic exchange

Successive chemical reductions of the heteroleptic complex [(tpy)Cr III(tphz)] 3+(tpy = terpyridine; tphz = tetrapyridophenazine) give rise to the mono- and di-radical redox isomers, [(tpy)Cr III(tphz? -)] 2+and [(tpy? -)Cr III(tphz? -)] +, respectively. As designed, the optimized overlap of the involved magnetic orbitals leads to extremely strong magnetic interactions between theS= 3/2 metal ion andS= 1/2 radical spins, affording well isolatedS T= 1 andS T= 1/2 ground states at room temperature. </p

Using Redox-Active πbridging Ligand as a Control Switch of Intramolecular Magnetic Interactions

Intramolecular magnetic interactions in the dinuclear complexes [(tpy)­Ni­(tphz)­Ni­(tpy)]^<i>n</i>+ (<i>n</i> = 4, 3, and 2; tpy, terpyridine; tphz, tetrapyridophenazine) were tailored by changing the oxidation state of the pyrazine-based bridging ligand. While its neutral form mediates a weak antiferromagnetic (AF) coupling between the two <i>S</i> = 1 Ni­(II), its reduced form, tphz^•–, promotes a remarkably large ferromagnetic exchange of +214(5) K with Ni­(II) spins. Reducing twice the bridging ligand affords weak Ni–Ni interactions, in marked contrast to the Co­(II) analogue. Those experimental results, supported by a careful examination of the involved orbitals, provide a clear understanding of the factors which govern strength and sign of the magnetic exchange through an aromatic bridging ligand, a prerequisite for the rational design of strongly coupled molecular systems and high <i>T</i>_C molecule-based magnets

A low spin manganese(IV) nitride single molecule magnet

Structural, spectroscopic and magnetic methods have been used to characterize the tris(carbene) borate compound PhB(MesIm)(3)Mn equivalent to N as a four-coordinate manganese(IV) complex with a low spin (S = 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e. its single-molecule magnet (SMM) properties, is revealed under an applied dc field. Multireference quantum mechanical calculations indicate that this SMM behavior originates from an anisotropic ground doublet stabilized by spin-orbit coupling. Consistent theoretical and experiment data show that the resulting magnetization dynamics in this system is dominated by ground state quantum tunneling, while its temperature dependence is influenced by Raman relaxation

Molecular tectonics : functionalization of cationic building blocks for the design of self-assembled architectures with tunable properties

La conception rationnelle de réseaux moléculaires organisés à l'état cristallin a été envisagée par un processus itératif d'auto-assemblage entre des briques de construction moléculaires préprogrammées et complémentaires appelées tectons. L'association dThe rational design of organized molecular networks in the crystalline state has been adressed by an iterative self-assembly process between complementary and preprogrammed molecular building blocks called tectons. The association of H-bond donor bisami

Gold Complexes with Tridentate Cyclometalating and NHC Ligands: A Search for New Photoluminescent Gold(III) Compounds

Many square-planar Pt(II) complexes are strongly photoluminescent, particularly when they contain cyclometalating and/or NHC ligands which produce strong ligand fields. In this work we investigated the possibility of obtaining isoelectronic Au(III) complexes with favorable luminescence properties. Toward this end, the coordination chemistry of gold with three different (potentially) tridentate ligands was explored: 1,3-bis(1-hexyl-2′-benzimidazoyl)benzene (L1H), 2,6-bis(3-butylimidazol-1-ium)pyridine (L2H22+), and 2,6-bis(3-hexylbenzimidazol-1-ium)pyridine (L3H22+). Pt(II) or Pd(II) complexes are known for all of these ligands or closely related analogues, and hence we anticipated that similar Au(III) complexes would be synthetically accessible as well. This turned out to be the case only for L1, despite exploration of different synthetic routes including (i) direct complexation of Au(III), (ii) transmetalation from Ag(I) precursor complexes, and (iii) transmetalation from suitable Hg(II) precursors. Only the mercury procedure was successful (at least in the case of L1); transmetalation from silver or direct complexation yields other reaction products containing Au(I) in most cases. Likewise, with ligands L2 and L3 mainly complexes of Au(I) were obtained: i.e., the propensity of gold for low oxidation states is a major obstacle to obtaining the desired Au(III) compounds. Several new complexes of Au(I) and Au(III) were characterized crystallographically. Our results provide insight into the differences between the coordination chemistry of isoelectronic Pt(II) and Au(III) with tridentate cyclometalating and NHC ligands

A cyanido-bridged two-dimensional network based on a RuIII schiff base complex and MnII ions: Synthesis, crystal structure and magnetic properties

The reaction between (Bu4N)[Ru(salen)(CN)2] and MnCl2 yielded a bidimensional (2D) network [{Ru(salen)(CN)2}2Mn(CH3CN)].H2O (1) incorporating square pyramidal MnII centers. The single crystal X-ray structure, heat capacity and magnetic properties of 1 are herein reported. From the magnetic measurements, antiferromagnetic interactions were detected between RuIII (s = 1/2) and MnII (S = 5/2) ions through the cyanido bridges (J) in the 2D framework as well as antiferromagnetic interplane interactions (J0). These interactions were estimated using a three-dimensional model in the frame of the mean field approximation (J/kB = -0.86(2) K and J0/kB = -0.067(6) K, gRu = 2.33(5)). Furthermore, a three dimensional antiferromagnetic order was evidenced by dc susceptibility measurements with a Néel temperature of 2.6 ± 0.1 K that was also confirmed by heat capacity measurements

From Tectons to Composite Crystals

International audienc

Highly Twisted Arenes by Scholl Cyclizations with Unexpected Regioselectivity

The Scholl reaction with quinquephenyl derivatives has been shown to have an unexpectedly strong preference for forming twisted, helicene aromatic polycycles, instead of their flat counterparts. This tendency is so strong that it will overcome even severe steric hindrance, and the procedure can be used in the efficient synthesis of hexa-tert-butylhexabenzotriphenylene from a simple biaryl starting material

Twisted Polycyclic Arenes by Intramolecular Scholl Reactions of C3- Symmetric Precursors

With the aim of opening an efficient access to large and sterically crowded polycyclic arenes as well as improving insight into the geometrical preferences of the Scholl reaction, a versatile synthesis strategy has been developed to form a family of flexible yet strongly crowded substrates for multiple dehydrocyclizations. Their intramolecular Scholl reactions lead with high selectivity either to considerably twisted species where the initial C3 symmetry is maintained, or to strongly rearranged products where the formation of multiple [6]helicene fragments is avoided by the formation of unusual hexa[7]circulene moieties under loss of the C3 symmetry

Fused Helicene Chains: Towards Twisted Graphene Nanoribbons

International audienceBy taking advantage of an unexpected regioselectivity of intramolecular Scholl reactions on pentaphenylenecompounds that favors distorted [5]helicenes over their flat counterparts, a new synthetic approach to twisted graphenenanoribbons has been designed based on side-fused di-tertbutyl-[5]helicene fragments. Syntheses of both small monomers and dimers have been achieved and their structures have been studied. An iterative synthetic strategy has been developed for the formation of longer flexible precursors, which relies on the step-by-step elongation of mono-functionalized oligomeric chains. The flexible trimer and tetramer have, thus, been synthesized and submitted to intramolecular Scholl reactions, which revealed important purification and characterization issues