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The employment of the [1+1] condensation approach for the preparation of new macrocyclic scaffolds (LN6 and LN3O3) towards high-performance Dy(III) single-molecule magnets (SMMs) with pseudo-D6h symmetry is described. Engineering of the macrocycles denticity from LN6 to LN3O3 leads to a mononuclear SMM with a large Ueff value of 1300 K. The experimental results are supported by ab initio calculations, which indicate relaxation of the magnetization via the second-excited state. [ABSTRACT FROM AUTHOR]

The chemistry of heterometallic metal complexes continues to attract the interest of molecular inorganic chemists mainly because of the properties that different metal ions can bring to compounds. Contrary to the plethora of 3d–4f- and 3d–3d′-metal complexes, complexes containing both 3d- and 4d-metal ions are much less studied. The choice of the bridging organic ligand is of paramount importance for the synthesis of such species. In the present work, we describe the use of the potentially tetradentate NOO′O″ Schiff bases N-(2-carboxyphenyl)salicylideneimine (saphHCOOH) and N-(4-chloro-carboxyphenyl)salicylideneimine (4ClsaphHCOOH) in CdII-MIII (M = Fe, Cr) chemistry. The complexes [Cd2Fe2(saphCOO)4(NO3)2(H2O)2] (1), [Cd2Cr2(saphCOO)4(NO3)2(H2O)2] (2), [Cd2Fe2(4ClsaphCOO)4(NO3)2(H2O)2] (3) and [CdCr2(4ClsaphCOO)4(H2O)3(EtOH)] (4) have been structurally characterized, the quality of the structure of the latter being poor but, permitting the knowledge of the connectivity and the main structural features. Complexes 1–3 are isostructural, but not isomorphous, possessing a variety of lattice solvent molecules (EtOH, MeCN, CH2Cl2, H2O). The metal topology can be described as two isosceles triangles sharing a common CdII...CdII edge. The two CdII atoms are doubly bridged by two μ-aqua groups. The MIII...CdII sides of the triangles are each asymmetrically bridged by one carboxylate oxygen atom of a 2.2111 saphCOO2−/4ClsaphCOO2− ligand. The core of the molecules is {Cd2M2(μ-Oaqua)2(μ-OR)4}6+, where the OR oxygen atoms are the bridging carboxylate oxygens. The coordination spheres of the metal ions in the centrosymmetric molecules are [Cd(Oaqua)2(Ocarboxylato)4(Onitrato)2] and [M(Nimino)2(Ocarboxylato)2(Ophenolato)2]. The biaugmented trigonal prism is the most appropriate for the description of the coordination geometry of the CdII atoms in 1 and 3, while the geometry of these metal ions in 2 is best described as distorted triangular dodecahedral. A combination of H-bonding and π–π stacking interactions give interesting supramolecular patterns in the three tetranuclear compounds. The three metal ions in 4 define an isosceles triangle with two almost equal CdII...CrIII sides. The CdII center is linked to each CrIII atom through one carboxylato oxygen of a 2.2111 4ClsaphCOO2− ligand. The core of the molecule is {CdCr2(μ-OR)2}6+, where the OR oxygen atoms are the bridging carboxylato oxygens. A tridentate chelating 1.1101 4ClsaphCOO2− ligand is bonded to each CrIII. The coordination spheres are [Cd(Oaqua)3(Oethanol)(Obridging carboxylato)2(Oterminal carboxylate)2] and [Cr(Obridging carboxylato)(Oterminal carboxylato)(Ophenolato)2(Nimino)2]. Complexes 1–4 are the first heterometallic 3d–4d complexes based on saphHCOOH and 4ClsaphCOOH. The structures are critically compared with those of previous reported ZnII-MIII (M = Fe, Cr) complexes. The IR and Raman spectra of the complexes are discussed in terms of the coordination modes of the ligands involved. UV/VIS spectra in CH2Cl2 are also reported, and the bands are assigned to the corresponding transitions. The δ and ΔEQ57Fe-Mössbauer parameters of 1 and 3 at room temperature and 80 K suggest the presence of isolated high-spin FeIII centers. Variable-temperature (1.8–310 K) and variable-field (0–50 kOe) magnetic studies for 1 and 2 indicate the absence of MIII...MIII exchange interactions, in agreement with the long distances (~8 Å) between the paramagnetic metal ions. The combined work demonstrates the ability of saphCOO2− and 4ClsaphCOO2− to give 3d–4d metal complexes. [ABSTRACT FROM AUTHOR]

One-pot reactions between the [Mn3O(O2CPh)6(py)x]+/0 triangular precursors and either CaBr2·xH2O or CaCl2·6H2O, in the presence of salicylhydroxamic acid (shaH2), have afforded the heterometallic complexes [MnIII4Ca2(O2CPh)4(shi)4(H2O)3(Me2CO)] (1) and (pyH)[MnII2MnIII4Ca2Cl2(O2CPh)7(shi)4(py)4] (2), respectively, in good yields. Further reactions but using a more flexible synthetic scheme comprising the Mn(NO3)2·4H2O/Ca(NO3)2·4H2O and Mn(O2CPh)2·2H2O/Ca(ClO4)2·4H2O "metal blends" and shaH2, in the presence of external base NEt3, led to the new complexes (NHEt3)2[MnIII4MnIV4Ca(OEt)2(shi)10(EtOH)2] (3) and (NHEt3)4[MnIII8Ca2(CO3)4(shi)8] (4), respectively. In all reported compounds, the anion of the tetradentate (N,O,O,O)-chelating/bridging ligand salicylhydroxime (shi3-), resulting from the in situ metal-ion-assisted amide-iminol tautomerism of shaH2, was found to bridge both Mn and Ca atoms. Complexes 1-4 exhibit a variety of different structures, metal stoichiometries, and Mn oxidation-state descriptions; 1 possesses an overall octahedral metal arrangement, 2 can be described as a Mn4Ca2 octahedron bound to an additional Mn2 unit, 3 consists of a Mn8 "ring" surrounding a CaII atom, and 4 adopts a rectangular cuboidal motif of eight Mn atoms accommodating two CaII atoms. Solid-state direct-current magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the Mn centers, leading to S = 0 spin ground-state values for all complexes. From a bioinorganic chemistry perspective, the reported compounds may demonstrate some relevance to both high-valent scheme (3) and lower-oxidation-level species (1, 2, and 4) of the catalytic cycle of the oxygen-evolving complex.

One-pot reactions between the [Mn3O(O2CPh)6(py)x]+/0 triangular precursors and either CaBr2·xH2O or CaCl2·6H2O, in the presence of salicylhydroxamic acid (shaH2), have afforded the heterometallic complexes [MnIII4Ca2(O2CPh)4(shi)4(H2O)3(Me2CO)] (1) and (pyH)[MnII2MnIII4Ca2Cl2(O2CPh)7(shi)4(py)4] (2), respectively, in good yields. Further reactions but using a more flexible synthetic scheme comprising the Mn(NO3)2·4H2O/Ca(NO3)2·4H2O and Mn(O2CPh)2·2H2O/Ca(ClO4)2·4H2O "metal blends" and shaH2, in the presence of external base NEt3, led to the new complexes (NHEt3)2[MnIII4MnIV4Ca(OEt)2(shi)10(EtOH)2] (3) and (NHEt3)4[MnIII8Ca2(CO3)4(shi)8] (4), respectively. In all reported compounds, the anion of the tetradentate (N,O,O,O)-chelating/bridging ligand salicylhydroxime (shi3-), resulting from the in situ metal-ion-assisted amide-iminol tautomerism of shaH2, was found to bridge both Mn and Ca atoms. Complexes 1-4 exhibit a variety of different structures, metal stoichiometries, and Mn oxidation-state descriptions; 1 possesses an overall octahedral metal arrangement, 2 can be described as a Mn4Ca2 octahedron bound to an additional Mn2 unit, 3 consists of a Mn8 "ring" surrounding a CaII atom, and 4 adopts a rectangular cuboidal motif of eight Mn atoms accommodating two CaII atoms. Solid-state direct-current magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the Mn centers, leading to S = 0 spin ground-state values for all complexes. From a bioinorganic chemistry perspective, the reported compounds may demonstrate some relevance to both high-valent scheme (3) and lower-oxidation-level species (1, 2, and 4) of the catalytic cycle of the oxygen-evolving complex.

The enantiomerically pure Schiff base ligands H2L‐S and H2L‐R yield chiral heterometallic dodecanuclear complexes of the form [Cu8Ln4(OH)8(OMe)4(O2CBut)8(L‐S or L‐R)4(H2O)4] where LnIII=Gd (1S), Tb (2S), Dy (3S, 3R), Ho (4S, 4R), Er (5S) or Y (6S, 6R) and H2L=(S or R)‐2‐{[(1‐hydroxypropan‐2‐yl)imino]methyl}‐6‐methoxyphenol. The complexes are isomorphous and crystallize in the non‐centrosymmetric polar space group C2 in enantiomeric conformation. The chirality of the Schiff base ligands originates from the respective S‐ or R‐ enantiomer of 2‐aminopropan‐1‐ol, is imparted to the complexes and to the crystals that belong to non‐centrosymmetric space group. The chirality and enantiomeric conformation of all complexes are retained in dmso solutions as confirmed by Circular Dichroism spectra which consist of mirror images, expected for enantiomeric pairs. All complexes consist of four distorted cubane‐like subunits [Cu2Ln2(μ3‐OH)2(μ3‐OMe)(μ3‐OR)], which share the LnIII ions and result in a cyclic distorted tetragonal arrangement; each edge of the {LnIII4} quadrilateral is occupied by two μ‐OH− ions that further bridge to a CuII ion. Magnetic susceptibility measurements revealed ferromagnetic interactions for 3S with LnIII=Dy and antiferromagnetic interactions for all other complexes. AC susceptibility data of 3S under 1 kOe external dc field indicate slow magnetic relaxation phenomena below 2 K. [ABSTRACT FROM AUTHOR]

The synthesis and structural characterization of new "2+1" mixed ligand fac-[Re(CO)3(OO)(L)] and Re(CO)2(OO)(L)2 complexes are reported herein. Maltol and kojic acid were chosen as bidentate OO ligands, while imidazole, isocyanocyclohexane or triphenylphosphine were selected as the monodentate ligands. The synthesis of the rhenium complexes was based on the reaction of [NEt4]2[Re(CO)3Br3] with maltol and kojic acid to generate the intermediate aqua complex fac-[Re(CO)3(OO)(H2O)], followed by the replacement of the labile aqua ligand by the monodentate ligand. Structural characterization of all Re complexes was established by NMR and IR spectroscopies, as well as two of them by single-crystal X-ray crystallography, revealing distorted octahedral geometry around the Re center. In the crystal lattice, the complexes form supramolecular networks due to the development of intermolecular interactions of the N-H⋯O, C-H⋯O and C-H⋯π type. [ABSTRACT FROM AUTHOR]

This review summarizes the structural characteristics and physicochemical properties of chiral 4f and 3d-4f complexes based on enantiopure salen-type Schiff base ligands. The chirality originates from the enantiopure diamines and is imparted to the Schiff base ligands and complexes and finally to the crystal structures. The reported enantiopure Schiff base ligands derive from the condensation of aromatic aldehydes, such as salicylaldehyde and its various derivatives, and the enantiopure diamines, (1R,2R) or (1S,2S)-1,2-diamino-cyclohexane, (1R,2R) or (1S,2S)-1,2-diamino-1,2-diphenylethane, (R) or (S)-2,2′-diamino-1,1′-binaphthalene, and 1,2-diaminopropane. [ABSTRACT FROM AUTHOR]

The study of small synthetic models for the highly selective removal of uranyl ions from seawater with amidoxime-containing materials is a valuable means to enhance their recovery capacity, leading to better extractants. An important issue in such efforts is to design bifunctional ligands and study their reactions with trans-{UO2}2+ in order to model the reactivity of polymeric sorbents possessing both amidoximate and another adjacent donor site on the side chains of the polymers. In this work, we present our results concerning the reactions of uranyl and pyrimidine-2-amidoxime, a ligand possessing two pyridyl nitrogens near the amidoxime group. The 1:2:2 {UO2}2+/pmadH2/external base (NaOMe, Et3N) reaction system in MeOH/MeCN provided access to complex [UO2(pmadH)2(MeOH)2] (1) in moderate yields. The structure of the complex was determined by single-crystal X-ray crystallography. The UVI atom is in a distorted hexagonal bipyramidal environment, with the two oxo groups occupying the trans positions, as expected. The equatorial plane consists of two terminal MeOH molecules at opposite positions and two N,O pairs of two deprotonated η2 oximate groups from two 1.11000 (Harris notation) pmadH− ligands; the two pyridyl nitrogen atoms and the –NH2 group remain uncoordinated. One pyridyl nitrogen of each ligand is the acceptor of one strong intramolecular H bond, with the donor being the coordinated MeOH oxygen atom. Non-classical Caromatic-H⋯X (X=O, N) intermolecular H bonds and π–π stacking interactions stabilize the crystal structure. The complex was characterized by IR and Raman spectroscopies, and the data were interpreted in terms of the known structure of 1. The solid-state structure of the complex is not retained in DMSO, as proven via 1H NMR and UV/Vis spectroscopic techniques as well as molar conductivity data, with the complex releasing neutral pmadH2 molecules. The to-date known coordination chemistry of pmadH2 is critically discussed. An attempt is also made to discuss the technological implications of this work. [ABSTRACT FROM AUTHOR]

The novel [Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,P´}I2] complex (1) was synthesized and investigated by a variety of spectroscopic methods (IR, 1H and 31P NMR). The molecular structure of 1, determined by single crystal X-ray diffraction, was compared with those of the analogue [Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,P´}Cl2] complex (2) and the recently reported [Ni{iCPrP)2NH-P,P´}I2] complex. Complexes 1 and 2 were tested as homogeneous catalysts for the oligomerization of ethylene, leading to the formation of C4 and, to a smaller extent, C6 products, in moderate yields.