Molecules composed of two weakly magnetically coupled [MnIII4] clusters

With the help of a bis(beta-diketonate) ligand, a family of robust molecules is formed, all consisting of two [Mn(III)4] subunits that interact slightly magnetically with each other, through two bridging pyrazine ligands.     

Reversibly reducible cis-dichloroplatinum(II) and cis-dichloropalladium(II) complexes of bis(1-methylimidazol-2-yl)glyoxal

Complexes cis-MCl2(big), big=bis(1-methylimidazol-2-yl)glyoxal, M=Pt, Pd, were prepared and characterized through electrochemistry, spectroscopy, and for M=Pt, by X-ray structure analysis. The seven-membered chelate ring formed through N,N' coordination of the ligand big shows a boat conformation in agreement with density functional theory (DFT) calculation results. No significant intermolecular interactions were observed for the platinum compound. Both the PdII and PtII complexes undergo reversible one-electron reduction in CH2Cl2/ 0.1 M Bu4NPF6; the reduced palladium compound disintegrates above -30 degrees C. Electron paramagnetic resonance (EPR), UV-vis, and IR spectroelectrochemistry studies were employed to study the monoanions. The anion radical complex [cis-PtCl2(big)]*- exhibits a well-resolved EPR spectrum with small but well-detectable g anisotropy and an isotropic 195Pt hyperfine coupling of 12.2 G. DFT calculations confirm the spin concentration in the alpha-semidione part of the radical complex with small delocalization to the bis(imidazolyl)metal section. The results show that EPR and electroactive moieties can be linked to the cis-dichloroplatinum(II) group via imidazole coordination.     

Boron templated catechol phosphines as bidentate ligands in silver complexes

Reaction of 3-[(diphenylphosphinyl)methyl]benzene-1,2-diol () and 4-[(diphenylphosphinyl)methyl]benzene-1,2-diol () with AgOTf or B(OH)(3) produced the bis-phosphine complexes , , or the borates , , respectively. All products were characterised by analytical and spectroscopic data and single-crystal X-ray diffraction studies. The anionic assembly was shown to act as a template-based chelate ligand toward Ag(+) by forming a neutral complex of composition [()Ag] with AgOTf. Spectroscopic and single-crystal X-ray diffraction studies revealed the presence of a kinetically very stable and conformationally rigid chelate that is best described as a bis-phosphine silver complex with a distinctly non-linear P-Ag-P array and two further secondary Ag-O interactions. Reaction of with AgOTf proceeded in a 2 : 2 molar ratio to give a dimeric product which was, on the basis of spectroscopic data, formulated as a macrocycle of composition [()(2)Ag(2)]. The different molecular sizes of and was underlined by PGSE NMR measurements which gave further evidence for the formation of solvent adducts between the chelate complex and DMF. Analysis of the (1)H,(109)Ag HMQC NMR spectra of provided evidence for a dependence of the (3)J(Ag,H) coupling on torsional angles which resembles a Karplus-type relationship.     

S(T) = 22 [Mn10] supertetrahedral building-block to design extended magnetic networks

The controlled organization of high-spin complexes, eventually single-molecule magnets, is a great challenge in molecular sciences to probe the possibility to design sophisticated magnetic systems to address a large quantity of magnetic information. The coordination chemistry is a tool of choice to make such materials. In this work, high-spin S(T) = 22 [Mn(10)] complexes, such as [Mn(III)(6)Mn(II)(4)(L(1))(6)(μ(4)-O)(4)(μ(3)-N(3))(4)(CH(3)CN)(11)(H(2)O)]·(ClO(4))(2)·(CH(3)CN)(8.5) (1), have been assembled using (i) 1,3-propanediol derivatives as chelating ligands to form the [Mn(10)] core units and (ii) dicyanamide or azide anions as linkers to synthesize the first 2D and 3D [Mn(10)]-based networks: [Mn(III)(6)Mn(II)(4)(L(2))(6)(μ(3)-N(3))(4)(μ(4)-O)(4)(CH(3)OH)(4)(dca)(2)] (2) and [Mn(III)(6)Mn(II)(4)(L(3))(6)(μ(3)-N(3))(4)(μ(4)-O)(4)(N(3))(2)]·(CH(3)OH)(4) (3). The synthesis of these compounds is reported together with their single-crystal X-ray structures and magnetic properties supported by DFT calculations. In the reported synthetic conditions, the stability of the [Mn(10)] complex is remarkably good that allows us to imagine many new materials combining these high-spin moieties and other diamagnetic but also paramagnetic linkers to design for example ordered magnets.     

Mononuclear Fe(II) single-molecule magnets: a theoretical approach

The single-molecule magnet behavior found in mononuclear tetracoordinate Fe(II) complexes with trigonal monopyramidal coordination due to large magnetic anisotropy has been analyzed using theoretical methods based on CASSCF-RASSI calculations. We focus our study on the dependence of such magnetic properties on the geometrical parameters of the complexes (asymmetry of the ligands and the out-of-plane shift of the Fe(II) cation with respect to the three equatorial nitrogen atoms) and the influence of the basicity of the N ligands. Low basicity, larger shifts, and larger distortions of the FeN(4) central framework decrease the D value and increase the E value. Also, we predict similar magnetic properties for similar pentacoordinate complexes adding an axial ligand that will increase the chemical stability of such systems.     

Zr2N2Se: The First Zirconium(IV) Nitride Selenide by the Oxidation of Zirconium(III) Nitride with Selenium

The oxidation of zirconium(III) nitride (ZrN) with suitable amounts of selenium (Se) in the presence of sodium chloride (NaCl) as flux yields small yellow brownish platelets of the first zirconium(IV) nitride selenide with the composition Zr₂N₂Se. The new compound crystallizes in the hexagonal space group P6₃/mmc (no. 194) with a = 363.98(2) pm, c = 1316.41(9) pm (c/a = 3.617) and two formula units per unit cell. The crystallographically unique Zr⁴⁺ cations are surrounded by three selenide and four nitride anions in the shape of a capped trigonal antiprism. The Se^2– anions are coordinated by six Zr⁴⁺ cations as trigonal prism and the N^3– anions reside in tetrahedral surrounding of Zr⁴⁺ cations. These [NZr₄]¹³⁺ tetrahedra become interconnected via three edges each to form $\rm^{2}_{\infty}$ {[(NZr_4/4)₂]²⁺} double layers parallel to the (001) plane, which are held together by monolayers of Se^2– anions.     

Family of carboxylate- and nitrate-diphenoxo triply bridged dinuclear Ni(II)Ln(III) complexes (Ln = Eu, Gd, Tb, Ho, Er, Y): synthesis, experimental and theoretical magneto-structural studies, and single-molecule magnet behavior

Seven acetate-diphenoxo triply bridged M(II)-Ln(III) complexes (M(II) = Ni(II) and Ln(III) = Gd, Tb, Ho, Er, and Y; M(II) = Zn(II) and Ln(III) = Ho(III) and Er(III)) of formula [M(μ-L)(μ-OAc)Ln(NO(3))(2)], one nitrate-diphenoxo triply bridged Ni(II)-Tb(III) complex, [Ni(μ-L)(μ-NO(3))Tb(NO(3))(2)]·2CH(3)OH, and two diphenoxo doubly bridged Ni(II)-Ln(III) complexes (Ln(III) = Eu, Gd) of formula [Ni(H(2)O)(μ-L)Ln(NO(3))(3)]·2CH(3)OH have been prepared in one pot reaction from the compartmental ligand N,N',N"-trimethyl-N,N"-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H(2)L). Moreover, Ni(II)-Ln(III) complexes bearing benzoate or 9-anthracenecarboxylate bridging groups of formula [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN have also been successfully synthesized. In acetate-diphenoxo triply bridged complexes, the acetate bridging group forces the structure to be folded with an average hinge angle in the M(μ-O(2))Ln bridging fragment of ~22°, whereas nitrate-diphenoxo doubly bridged complexes and diphenoxo-doubly bridged complexes exhibit more planar structures with hinge angles of ~13° and ~2°, respectively. All Ni(II)-Ln(III) complexes exhibit ferromagnetic interactions between Ni(II) and Ln(III) ions and, in the case of the Gd(III) complexes, the J(NiGd) coupling increases weakly but significantly with the planarity of the M-(O)(2)-Gd bridging fragment and with the increase of the Ni-O-Gd angle. Density functional theory (DFT) theoretical calculations on the Ni(II)Gd(III) complexes and model compounds support these magneto-structural correlations as well as the experimental J(NiGd) values, which were found to be ~1.38 and ~2.1 cm(-1) for the folded [Ni(μ-L)(μ-OAc)Gd(NO(3))(2)] and planar [Ni(H(2)O)(μ-L)Gd(NO(3))(3)]·2CH(3)OH complexes, respectively. The Ni(II)Dy(III) complexes exhibit slow relaxation of the magnetization with Δ/k(B) energy barriers under 1000 Oe applied magnetic fields of 9.2 and 10.1 K for [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN, respectively.     

Triangular nickel complexes derived from 2-pyridylcyanoxime: an approach to the magnetic properties of the [Ni3(μ3-OH){pyC(R)NO}3]2+ core

A series of nickel complexes with nuclearity ranging from Ni(3) to Ni(6) have been obtained by treatment of a variety of nickel salts with the 2-pyridylcyanoxime ligand. The reported compounds have as a common structural feature the triangular arrangement of nickel cations bridged by a central μ(3)-oxo/alkoxo ligand. These compounds are simultaneously the first nickel derivatives of the 2-pyridylcyanoxime ligand and the first examples of isolated, μ(3)-O triangular pyridyloximate nickel complexes. Magnetic measurements reveal antiferromagnetic interactions promoted by the μ(3)-O and oximato superexchange pathways and comparison of the experimental structural and magnetic data with DFT calculations give an in-depth explanation of the factors that determine the magnetic interaction in this kind of system.     

Heterohexanuclear (Cu3Fe3) Complexes of Substituted Hexaazatrinaphthylene (HATN) Ligands: Twofold BF4− Association in the Solid and Stepwise Oxidation (3e) or Reduction (2e) to Spectroelectrochemically Characterized Species

New tris(ferrocenylcopper) compounds [(μ₃‐dqp){Cu(dppf)}₃][X]₃ (dppf=1,1′‐bis(diphenylphosphinoferrocene), dqp=hexamethyl‐, hexachloro‐ or un‐substituted diquinoxalino[2,3‐a:2′,3′‐c]phenazine=hexaazatrinaphthylene (HATN), X^?=BF₄^? or PF₆^?) undergo at least two different, reversible one‐electron reductions and three very closely spaced one‐electron oxidations. While the latter are attributed to the stepwise ferrocene→ferrocenium conversions, the first electron addition occurs in the ligand bridge to yield EPR detectable radical complexes. X‐band EPR measurements at 9.5 GHz showed a partially resolved hyperfine structure, while high‐frequency EPR measurements at 95 or 115 GHz revealed a small but variable axial g tensor anisotropy. All reversible steps were investigated by optically transparent thin‐layer electrode (OTTLE) spectroelectrochemistry (UV/Vis/NIR regions), revealing very low energy transitions for the reduced forms in agreement with the frontier MO arrangement. A crystal structure of the compound with unsubstituted dqp shows notable deviation from the trigonal symmetry and the close association of two tetrafluoroborate anions with the complex trication along the quasi‐trigonal axis to yield [(μ₃‐dqp){Cu(dppf)}₃(BF₄)₂]BF₄.     

Borate‐Driven Gatelike Scaffolding Using Mesoporous Materials Functionalised with Saccharides

We report the development of an MCM‐41 mesoporous support that is functionalised with saccharides at the pore outlets and contains the dye [Ru(bipy)₃]²⁺ in the pores (solid S1 ; bipy=2,2′‐bipyridyl). For this hybrid system, the inhibition of mass transport of the dye from the pore voids to the bulk solution in the presence of borate is demonstrated in water at neutral pH. The formation of the corresponding boroester derivative is related to the selective reaction of borate with the appended saccharides. This control is selective and only anion borate, among several anions and cations, can act as a molecular tap and inhibit the delivery of the entrapped guest. Additionally, the S1 –borate system behaves as pH‐controlled gatelike scaffolding. This pH‐responsive release can be achieved in an acidic pH (due to hydrolysis of the boroester), whereas the system remains closed at neutral pH. Molecular dynamic simulations using force‐field methods have been made to theoretically study the open/close borate‐driven mechanism. A mesoporous silica structure was constructed for this purpose, taking the plane (1?11) of the β‐cristobalite structure as a base on which hexagonal nanopores and anchored saccharide derivatives were included. The final model shows a highly flexible nanopore diameter of approximately 12.5 Å of similar size to the [Ru(bipy)₃]²⁺ complex (ca. 12 Å). However, the anchoring of borate to the appended saccharides results in a remarkable reduction of the pore size (down to ca. 6.4 Å) and a significant constraint in the flexibility and mobility of the saccharides. The theoretical calculations are in agreement with the experimental results and enable visualisation of the functional borate‐driven dye‐delivery‐inhibition outcome.