Crystals of [Co(diox)2(4-NO2-py)2] (1) and [Co(diox)2(4-CN-py)2](2) where diox are the o-Dioxolene 3,5-di-tbutylsemiquinonate (SQ •-)and/or 3,5-di-t-butylcatecholate (Cat 2-)ions, 4-NO2-py is 4-nitro-pyridine, 4-CN-py is 4-cyano-pyridine, are among the few known crystals presenting both thermal-induced and photoinduced ls-[M +3 (SQ •-)(Cat 2-)] hs-[M 2+ (SQ •-)2]valence tautomerism interconversion (VTI). In 2 the thermal-induced VTI is cooperative, characterizing an abrupt conversion and in 1 it is non-cooperative. In this work, crystals of [Co(diox)2(4-NO2-py)2]•benzene (1BZ), [Co(diox)2(4-NO2-py)2]•toluene (1TL), [Co(diox)2(4-CN-py)2]•benzene (2BZ) and [Co(diox)2(4-CN-py)2]•toluene (2TL) have been prepared and analyzed by single crystal X-ray diffraction in order to investigate how solvation modulates thermal-induced VTI. The solvate crystals, like the nonsolvated ones, present essentially reversible thermal-induced and photoinduced VTI. 1TL crystal presents the same monoclinic symmetry and the same intermolecular hydrogen-bonded network of 1 and both present a non-cooperative thermal-induced VTI. 1BZ crystal has triclinic symmetry and present a cooperative and abrupt VTI with a thermal hysteresis of ~30 K. In contrast to 2, thermal-induced VTI in 2BZ and 2TL is non-cooperative despite the fact that 2, 2BZ and 2TL crystals exhibit the same monoclinic symmetry and the same intermolecular hydrogen-bonded network. In 2BZ and 2TLbenzene and toluene molecules as well as the tbutyl groups of the o-dioxolene molecules convert gradually from being dynamically disordered at about 300 K to a static disorder state below 150 K. The layer separation distance of interacting [Co(diox)2(4-X-py)2], X=CN and NO2, molecules in all solvate crystals is ~15 Å whereas in the 2, which presents cooperative VTI, it is ~12 Å. An order-disorder component might account to the stabilization of the metastable hs-Co 2+ state in 2BZ and in 2TL but no disorder was found in the 1TL crystals. Therefore, the lack of cooperativeness in the thermal-induced VTI in these crystals seems to be due to the large distance between the layers of interacting molecules. Cooperativeness in the VTI of 1BZ crystal is likely to be related with the unique molecular bond scheme network that connects neighboring active [Co(diox)2(4-NO2-py)2] molecules through the o-Dioxolene oxygen atoms bonded directly to the Co ion.

A Co /porphyrinate-based macrocycle in the presence of a 3,5-diphenylpyridine axial ligand functions as an endotopic ligand to direct the assembly of [2]rotaxanes from diazo and styrene half-threads, by radical-carbene-transfer reactions, in excellent 95 % yield. The method reported herein applies the active-metal-template strategy to include radical-type activation of ligands by the metal-template ion during the organometallic process which ultimately yields the mechanical bond. A careful quantitative analysis of the product distribution afforded from the rotaxane self-assembly reaction shows that the Co /porphyrinate subunit is still active after formation of the mechanical bond and, upon coordination of an additional diazo half-thread derivative, promotes a novel intercomponent C-H insertion reaction to yield a new rotaxane-like species. This unexpected intercomponent C-H insertion illustrates the distinct reactivity brought to the Co /porphyrinate catalyst by the mechanical bond.

We herein present the synthesis and X-ray structures of five copper(II) complexes of formulae [Cu(bpca)(CF3SO3)(H2O)]·H2O (1), [Cu(bpca)(Phpr)(H2O)]·3/2H2O (2), {[Cu(bpca)]2[Cu(opba)(H2O)]}·H2O (3), {[Cu(bpca)]2(H2opba)}2·6H2O (4) and [Cu(bpca)(EtH2opba)]n (5), where bpca = bis(2-pyridylcarbonyl)amidate, Phpr = 3-phenylpropionate, CF3SO3(−) = triflate (anion of the trifluoromethanesulphonic acid), H4opba = N,N′-1,2-phenylenebis(oxamic acid), and EtH3opba = monoethyl ester derivative of the H4opba. 1 and 2 are mononuclear copper(II) complexes where the copper atom is five-coordinate in distorted square pyramidal surroundings with a tridentate bpca and a water molecule (1)/carboxylate oxygen (2) building the basal plane and a triflate oxygen (1)/water molecule (2) filling the apical position. 3 is a neutral tricopper(II) complex where the [Cu(opba)(H2O)]2− unit acts as a bis-bidentate ligand toward two peripheral [Cu(bpca)]+ fragments. The three crystallographically independent copper(II) ions in 3 are five-coordinate with two nitrogen and two oxygen atoms (inner copper atom)/three bpca-nitrogen and an oxamate oxygen (outer copper atom) building the basal plane plus a water molecule (inner copper)/an oxamate oxygen (outer copper) in the apical position (inner copper atom) of somewhat distorted square pyramidal surroundings. 4 is a centrosymmetric tetracopper(II) compound where four [Cu(bpca)]+ fragments are assembled by two H2opba2− groups adopting an unusual bidentate/bis-monodentate bridging mode. The two crystallographically independent copper(II) ions in 4 are also five-coordinate having the three bpca-nitrogens in basal positions, the other two sites of the distorted square pyramid being filled by two oxygens of either a bidentate oxamate (at one copper centre) or two bis-monodentate oxamates (at the other copper atom). 5 is a zigzag chain of [Cu(bpca)(H2O)]+ units which are connected through the EtH2opba− ligand adopting a bidentate/monodentate bridging mode across the monodeprotonated oxamate group. Each copper(II) ion in 5 is six-coordinate in an elongated octahedral CuN3O3 chromophore. The magnetic properties of 3–5 were investigated in the temperature range 1.9–300 K. 3 exhibits an intermediate intramolecular antiferromagnetic interaction [J = -65.8(2) cm(-1) with the Hamiltonian H = -J(S(Cu1)·S(Cu2) + S(Cu2)·S(Cu3))] which leads to a low-lying spin doublet at low temperatures. A weak antiferromagnetic coupling between the inner copper(II) ions occurs in 4 [J = -2.36(2) cm(-1), H = -JS1·S2)] and a very small intrachain antiferromagnetic interaction is observed in 5 [J = -0.17(1) cm(-1) with H = -J∑(i)S(i)·S(i+1)]. These values are analyzed by means of simple orbital symmetry considerations and compared with those previously reported for parent systems.

Bi-stable molecular systems presenting valence tautomerism are associated with the development of new functional materials, which can be used for applications in organic electric conductors, optoelectronic and molecular magnetic devices. The properties of these materials can be adjusted with slight chemical changes and can be induced by external stimuli. Typical examples of valence tautomer compounds are coordination complexes of Co and o-dioxolene ligands, notably quinone like ones. In the search for a new class of cobalt complexes presenting valence tautomerism we report herein the synthesis and characterization of five new coordination compounds of cobalt and 2-hydroxy-1,4-naphthoquinone (lawsone or shortly Law). Complexes [Co(Law)2(im)2]·C6H5CH3 (1), [Co(Law)2(py)2]·CH3OH (2), [Co(Law)2(phen)]·(C4H8O)2 (3), [Co(Law)2(2,2-bpy)]·C6H5CH3 (4) and [Co(Law)2(2,2-bpy)] (5) were synthesized and fully characterized by X-ray diffraction and EPR techniques in a wide range of temperatures and under illumination. Despite presenting similar molecular and geometry packing of the valence tautomer complexes of cobalt and o-dioxolenes, neither structural nor electronic evidence of valence tautomerism could be found in the Co and lawsone complexes.

A unique bistable copper-metallacyclic complex is used as an elegant molecular switch for the reversible formation of emulsions by simple pH variation. This switch may have several exciting applications in biphasic processes such as catalysis and separation science technologies.

Five new complexes of formula K 4 [Pd 2 (mpba) 2 ] · 4H 2 O (1), {[K 4 (H 2 O)(dmso)][Pd 2 (mpba) 2 ]} (2), {[Cu(bpca)] 4 [Pd 2 (mpba) 2 ]} · 6H 2 O (3), {[Cu(bpca)] 2 [Pd(opba)]} · 1.75dmso · 0.25H 2 O (4), {[Cu(bpca)] 2 [Pd(opba)]} n · ndmso (5) [H 4 mpba =1,3-phenylenebis(oxamic acid), H 4 opba = 1,2-phenylenebis(oxamic acid), Hbpca = bis(2-pyridylcarbonyl)amide, and dmso = dimethyl sulfoxide] have been prepared and investigated by infrared spectroscopy, thermal analysis, single crystal X-ray diffraction, and magnetic susceptibility techniques. The structure of 2 consists of a [Pd 2 (mpba) 2 ] 4− anionic entity in which the palladium(II) cations are coordinated by two mpba ligands resulting in a dipalladium(II) unit that acts as a ligand toward potassium(I) cations leading to a neutral three-dimensional network. Compound 3 is a neutral hexanuclear complex where the dinuclear [Pd 2 (mpba) 2 ] 4− unit adopts a tetrakis(bidentate) coordination mode toward four [Cu(bpca)] + end-cap entities. This compound can be viewed as a "dimer of trimers" in which two Cu II −Pd II −Cu II trinuclear units are connected by two mpba ligands. Compounds 4 and 5 have in common the presence of a [Pd(opba)] 2− unit, which acts as a bis(bidentate) ligand toward two [Cu(bpca)] + entities to afford neutral heterotrinuclear Cu II −Pd II −Cu II motifs that are interlinked through weak double (4) and single (5) out-of-plane copper(II) to carbonyl(bpca)-oxygen atoms leading to uniform linear (4) and zigzag (5) chains of heterobimetallic trinuclear units. The investigation of the magnetic properties of 3−5 in the 1.9−300 K temperature range reveals the presence of very weak antiferromagnetic interactions between the copper(II) ions. The nature and magnitude of these magnetic interactions are discussed in terms of orbital symmetry considerations. ■ INTRODUCTIONIn the last years, several building blocks have been described in the literature as examples to design molecular materials with predictable properties. 1 The major challenge that scientists face today is the control and understanding of the methods involved in the self-assembly process to obtain the desired species. 2 In this respect, and by restricting ourselves to the research fields of coordination chemistry and materials science, the metalloligand or building block approach is one of the most rewarding synthetic strategies. Indeed, the appropriate choice of the tailormade metalloligand will determine the molecule-based architecture that can be engineered as well as the desired physical properties therein. 3−5 The richness and variety of magnetic systems based on the use of cyanide-bearing complexes 6−8 or bis-and tris(oxalate)chromate(III) 9−20 as building blocks illustrate the possibilities and broad applicability of this strategy in building new multifunctional chemical objects.Part of our research activity was focused on the building blocks based on oxamate/oxamate-containing complexes and paid special attention to their assembling processes as well as to the main factors that can...

A 5,15‐bis(1,1′‐biphenyl)porphyrin‐based molecular clip covalently connected to a ditopic aliphatic ester loop moiety yields a semi‐rigid macrocycle with a well‐defined cavity. The resulting macrocycle fits the structural requirements for the preparation of porphyrinates capable of promoting formation of C−C bonds. To demonstrate the usefulness of porphyrin‐based macrocycles, an active‐metal‐template synthesis of rotaxanes through a redox non‐innocent carbene transfer reaction is described. Coordination of CoII ions into the porphyrin subunit followed by addition of appropriate monodentate nitrogen‐based additives to function as axial ligands enables the radical carbene transfer reactions to styrene derivatives to occur exclusively through the cavity of the macrocycle to afford cyclopropane‐linked rotaxanes in excellent 95 % yield. Investigation of the product distribution afforded from the rotaxane assembly reaction reveals how the redox cooperative action between the carbene species and the CoII ions can be manipulated to gain control over the radical‐type mechanism to favor the productive rotaxane forming process.

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