Coordination Chemistry in the Solid: Study of the Incorporation of Cu(II) into Cyclam-Containing Hybrid Materials

Nickel containing ionic liquid based ordered nanoporous organosilica: a powerful and recoverable catalyst for synthesis of polyhydroquinolines

The synthesis, characterization and catalytic application of a novel nickel containing ionic liquid based ordered mesoporous organosilica are demonstrated.

Periodic Mesoporous Organosilicas: from simple to complex bridges; a comprehensive overview of functions, morphologies and applications

Periodic Mesoporous Organosilicas (PMOs) were developed in 1999 and are basically ordered templated mesoporous organosilicas, prepared by the combination of a surfactant as template and a silsesquioxane as the organosilica precursor. They were one of the first examples of the so-called "hybrid" organic/inorganic materials. In the years that followed, an amazing variety of functional groups, morphologies and applications has been developed. Some of these high-end applications, like low-k buffer layers in microelectronics, chiral catalysts, chromatographic supports, selective adsorbents and light-harvesting devices, have clearly shown their potential. In this review, we will give a comprehensive overview of all these different functionalities and applications that have been created for Periodic Mesoporous Organosilicas.

Electron exchange columns through entrapment of a nickel cyclam in a sol-gel matrix

An electron exchange column (analogous to ion exchange columns) was developed using the unique redox properties of the nickel-tetraazamacrocyclic complexes (nickel cyclam [Ni(II)L(1)](2+)) and nickel-trans-III-meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, ([Ni(II)L(2)](2+)), and the physical and chemical stability of the ceramic materials using the sol-gel process to entrap the complexes. The entrapment by the biphasic sol-gel method is based on non-covalent bonds between the matrix and the complex; therefore the main problem was leaching. Parameters controlling the leaching were investigated. Redox cycles with the reducing agent ascorbic acid, and persulfate as the oxidizing agent were performed.

Factors affecting copper(II) binding to multiarmed cyclam-grafted mesoporous silica in aqueous solution

Single- as well as multi-anchored cyclam-functionalized silica samples have been prepared by grafting amorphous silica gel (K60) and mesostructured silica (SBA-15) with silylated cyclam precursors bearing one, two, or four triethoxysilyl groups, respectively ascribed to cyclam-mono, cyclam-di, and cyclam-tetra. Their reactivity toward copper(II) has been thoroughly investigated in aqueous solution and discussed with respect to the number of arms tethering the ligand to the silica surface and the structural ordering of the adsorbent in terms of capacity, long-term stability, and speed of access to the binding sites. Less-than-complete metal ion uptake was always observed, even in excess of cyclam groups with respect to solution-phase Cu(II), suggesting lower stability of immobilized complexes relative to those in solution. Therefore, the number of arms attaching cyclam moieties to the silica walls (one, two, or four) was found to dramatically affect the binding properties of these hybrids toward copper(II), revealing significantly larger capacities when reducing the number of arms (less rigidity constraints in the macrocycle). In parallel, multiarm tethering resulted in better chemical resistance toward degradation as evidenced by UV-visible monitoring of Cu-cyclam complexes in solution (i.e., more ligand leaching from the adsorbent for singly tethered cyclam). On the other hand, electron spin resonance (ESR) experiments did not evidence significant differences between complexes bearing one, two, or four alkyl arms, since all Cu(II)-cyclam surface complexes were found to be hexacoordinated with a strong equatorial ligand field. Comparison of amorphous gels and mesostructured materials indicates that the binding properties of the adsorbents were hardly influenced by their level of ordering, suggesting that accessibility to the binding sites was not the limiting factor. Some advantage belonging to mesostructured adsorbents was however observed with respect to the rate of access to the active centers at pH values close to neutrality (due to faster mass transport), but this was no more the case when operating at lower pH values where the formation of the Cu-cyclam complex became the rate-determining step, as pointed out by electrochemistry.

Modification of the Stöber process by a polyazamacrocycle leading to unusual core-shell silica nanoparticles

In the view of designing functional nanoparticles, the encapsulation of 1,4,7,10-tetraazacyclododecane (cyclen) within silica nanoparticles using the Stöber process was studied. In the presence of cyclen and tetraethoxysilane (TEOS), silica particles exhibiting an unusual core-shell structure were obtained. On then basis of TEM, DLS, and NMR data, we suggest that the particle core is constituted of hybrid primary nanoparticles resulting from cyclen-silica interactions, whereas the shell formation results from further condensation of unreacted silica precursors. Control experiments performed with the zinc-cyclen complex and ammonia addition suggest that cyclen-TEOS interactions arise from the activation of the silicon alkoxide hydrolysis with the polyazamacrocycle amine groups. These data are discussed in the context of silica biomineralization mechanisms, where polyamine/silica interactions have been shown to play a major role. Moreover, the possibility to control the size and the structure of these nanoparticles makes them promising materials for pharmaceutical applications.

Substituent Effect on Formation of Heterometallic Molecular Wheels: Synthesis, Crystal Structure, and Magnetic Properties

The reaction of manganese(III) Schiff bases of the type salen(2-) (N,N'-ethylenebis(salicylideneaminato)) with X-substituted (X = CH(3), Cl) pyridinecarboxamide dicyanoferrite(III) [Fe(X-bpb)(CN)(2)](-) gave rise to a series of cyanide-bridged Mn(6)Fe(6) molecular wheels, [Mn(III)(salen)](6)[Fe(III)(bpmb)(CN)(2)](6) x 7H(2)O (1), [Mn(salen)](6)[Fe(bpClb)(CN)(2)](6) x 4H(2)O x 2CH(3)OH (2), [Mn(salen)](6)[Fe(bpdmb)(CN)(2)](6) x 10H(2)O x 5CH(3)OH (3), [Mn(5-Br(salpn))](6)[Fe(bpmb)(CN)(2)](6) x 24H(2)O x 8CH(3)CN (4), and [Mn(5-Cl(salpn))](6)[Fe(bpmb)(CN)(2)](6) x 25H(2)O x 5CH(3)CN (5). Compared with [Fe(bpb)(CN)(2)](-), which always gives rise to 1D or polynuclear species when reacting with Mn(III) Schiff bases, the introduction of substituents (X) to the bpb(2-) ligand has a driving force in formation of the novel wheel structure. Magnetic studies reveal that high-spin ground state S = 15 is present in the wheel compounds originated from the ferromagnetic Mn(III)-Fe(III) coupling. For the first time, the quantum Monte Carlo study has been used to modulate the magnetic susceptibility of the huge Mn(6)Fe(6) metallomacrocycles, showing that the magnetic coupling constants J range from 3.0 to 8.0 K on the basis of the spin Hamiltonian [Formula: see text]. Hysteresis loops for 1 have been observed below 0.8 K, indicative of a single-molecule magnet with a blocking temperature (TB) of 0.8 K. Molecular wheels 2-5 exhibit frequency dependence of alternating-current magnetic susceptibility under zero direct-current magnetic field, signifying the slow magnetization relaxation similar to that of 1. Significantly, an unprecedented archlike Mn(2)Fe(2) cluster, [Mn(5-Cl(salpn))](2)[Fe(bpmb)(CN)(2)](2) x 3H(2)O x CH(3)CN (6), has been isolated as an intermediate of the Mn(6)Fe(6) wheel 5. Ferromagnetic Mn(III)-Fe(III) coupling results in a high-spin S = 5 ground state. Combination of the high-spin state and a negative magnetic anisotropy (D) results in the observation of slow magnetization relaxation in 6.

Exceptional Affinity of Nanostructured Organic–Inorganic Hybrid Materials towards Dioxygen: Confinement Effect of Copper Complexes

We report the exceptional reactivity towards dioxygen of a nanostructured organic-inorganic hybrid material due to the confinement of copper cyclam within a silica matrix. The key step is the metalation reaction of the ligand, which can occur before or after xerogel formation through the sol-gel process. The incorporation of a Cu(II) center into the material after xerogel formation leads to a bridged Cu(I)/Cu(II) mixed-valence dinuclear species. This complex exhibits a very high affinity towards dioxygen, attributable to auto-organization of the active species in the solid. The remarkable properties of these copper complexes in the silica matrix demonstrate a high cooperative effect for O(2) adsorption; this is induced by close confinement of the two copper ions leading to end-on mu-eta(1):eta(1)-peroxodicopper(II) complexes. The anisotropic packing of the tetraazamacrocycle in a lamellar structure induces an exceptional reactivity of these copper complexes. We show for the first time that the organic-inorganic environment of copper complexes in a silica matrix fully model the protecting role of protein in metalloenzymes. For the first time an oxygenated dicopper(II) complex can be isolated in a stable form at room temperature, and the reduced Cu(2) (I,I) species can be regenerated after several adsorption-desorption cycles. These data also demonstrate that the coordination scheme and reactivity of the copper cyclams within the solid are quite different from that observed in solution.

Steric Control of a Bridging Ligand for High-Nuclearity Metallamacrocycle Formation: A Highly Puckered 60-Membered Icosanuclear Metalladiazamacrocycle

A novel S4-symmetric icosanuclear manganese metalladiazamacrocycle was synthesized using a pentadentate ligand, N-3-phenyl-trans-2-propenoylsalicylhydrazide (H3L), that has a rigid and bulky terminal N-acyl group. A 20 cyclic repeat of an--(Mn-N-N)--linkage resulted in a highly puckered diaza-bridged 60-membered icosanuclear metallamacrocycle. The steric interaction between the ligands in the cyclic system leads to five consecutive Mn(III) centers in a chemically different--(Mn(A)Mn(B)Mn(C)Mn(D)Mn(E))--environment, with the chiralities of the metal centers being in a rather complicated--(LambdaLambdaDeltaLambdaLambda)(DeltaDeltaLambdaDeltaDelta)--sequence.

Neutral Molecular Pd6 Hexagons Using κ3-P2O-Terdentate Ligands

The one-step synthesis of three new P2O-terdentate carboxylic acid ditertiary phosphines 2-{(Ph2PCH2)2N}-3-(X)C6H3CO2H (X = OCH3, L1; X = OH, L2) and 2-{(Ph2PCH2)2N}-5-(OH)C6H3CO2H (L3) by a phosphorus-based Mannich condensation reaction using Ph2PCH2OH and the appropriate amine in CH3OH is reported. Compounds L1-L3 function as typical kappa2-P2-didentate ligands upon complexation to Pd(CH3)Cl(cod) (cod = cycloocta-1,5-diene), affording the neutral, mononuclear complexes Pd(CH3)Cl(L1-L3) (1-3). Metathesis of 1 with NaX (X = Br, I) gave the corresponding (methyl)bromopalladium(II) (4) and (methyl)iodopalladium(II) (5) complexes, respectively. When chloroform or chloroform/methanol solutions of 1-3 (or 5) were allowed to stand, at ambient temperatures, yellow crystalline solids were isolated in very high yields (71-88%) and were analyzed for the novel hexameric palladium(II) compounds 6-9. All new compounds reported have been fully characterized by a combination of spectroscopic (multinuclear NMR, Fourier transform IR, electrospray mass spectrometry, matrix-assisted laser desorption ionization time-of-flight mass spectrometry) and analytical methods. The self-assembly reactions are remarkably clean as monitored by 31P{1H} and 1H NMR spectroscopy. Single-crystal X-ray structures have been determined for L1, 4, 7.17CDCl3.2Et2O, 8.6CHCl3.8CH3OH, and 9.17CDCl3. In hexamers 7-9, all six square-planar palladium(II) metal centers comprise a kappa2-P2-chelating diphosphine, a kappa1-O-monodentate carboxylate, and either a chloride or iodide ligand, leading to 48-membered metallomacrocycles (with outside diameters of ca. 2.5 nm). Whereas only intramolecular O-H...N hydrogen bonding between the hydroxy group and tertiary amine has been observed in 7, strong intermolecular O-H...O hydrogen bonding of the type CO...HO(CH3)...HO, involving a methanol solvate, has been found in 8, leading to an unprecedented three-dimensional network motif.

Aggregation of [(tBu3SiS)MX]: Structures of {[Br2Fe(μ-SSitBu3)2FeBr(THF)]Na(THF)4}∞, cis-[(THF)FeI]2(μ-SSitBu3)2, [(tBu3SiS)Fe]2(μ-SSitBu3)2, and Comparative Structure and Magnetism Studies of [(tBu3SiS)MX]n (M = Fe, Co, X = Cl, n = 12; M = Fe, Ni, X = Br, n = 12; M = Fe, X = I, n = 14)

A convenient synthesis of (t)Bu(3)SiSH and (t)Bu(3)SiSNa(THF)(x)() led to the exploration of "(t)Bu(3)SiSMX" aggregation. The dimer, [((t)Bu(3)SiS)Fe](2)(mu-SSi(t)Bu(3))(2) (1(2)), was formed from [{(Me(3)Si)(2)N}Fe](2)(mu-N(SiMe(3))(2))(2) and the thiol, and its dissolution in THF generated ((t)Bu(3)SiS)(2)Fe(THF)(2) (1-(THF)(2)). Metathetical procedures with the thiolate yielded aggregate precursors [X(2)Fe](mu-SSi(t)Bu(3))(2)[FeX(THF)]Na(THF)(4) (3-X, X = Cl, Br) and cis-[(THF)IFe](2)(mu-SSi(t)Bu(3))(2) (4). Thermal desolvations of 3-Cl, 3-Br and 4 afforded molecular wheels [Fe(mu-X)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-FeX, X = Cl, Br) and the ellipse [Fe(mu-I)(mu-SSi(t)Bu(3))](14)(C(6)H(6))(n) (6-FeI). Related metathesis and desolvation sequences led to wheels [Co(mu-Cl)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-CoCl) and [Ni(mu-Br)(mu-SSi(t)Bu(3))](12)(C(6)H(6))(n) (5-NiBr). The nickel wheel disproportionated to give, in part, [((t)Bu(3)SiS)Ni](2)(mu-SSi(t)Bu(3))(2) (7), which was also synthesized via salt metathesis. X-ray structural studies of 1(2) revealed a roughly planar Fe(2)S(4) core, while 1-(THF)(2), 3-Br, and 4 possessed simple distorted tetrahedral and edge-shared tetrahedral structures. X-ray structural studies revealed 5-MX (MX = FeCl, FeBr, CoCl, NiBr) to be wheels based on edge-shared tetrahedra, but while the pseudo-D(6)(d) wheels of 5-FeCl, 5-CoCl, and 5-FeBr pack in a body-centered arrangement, those of pseudo-C(6)(v)() 5-NiBr exhibit hexagonal packing and two distinct trans-annular d(Br...Br). Variable-temperature magnetic susceptibility measurements were conducted on 5-FeCl, 5-CoCl, 5-FeBr, and 6-FeI, and the latter three are best construed as weakly antiferromagnetic, while 5-FeCl exhibited modest ferromagnetic coupling. Features suggesting molecular magnetism are most likely affiliated with phase changes at low temperatures.

Coordination chemistry in the solid: evidence for coordination modes within hybrid materials different from those in solution

Two routes of incorporation of europium(III) salts into cyclam-containing hybrid materials have been explored, to elucidate the coordination mode of EuIII in cyclam-containing hybrid materials in a study of the arrangement of cyclam moieties during the solgel process. They were 1) complexation of europium salts by N-tetrasubstituted 1,4,8,11-tetraazacyclotetradecane (cyclam) derivatives bearing four hydrolysable Si(OEt)3 groups, followed by hydrolysis and polycondensation of these complexes; and 2) hydrolysis and polycondensation of N-tetrasubstituted silylated cyclam derivatives, then incorporation of europium salts directly into the hybrid materials. The coordination mode of europium salts within solids is not the same as in solution. In solution, the complexation of EuIII with cyclam is not possible; it requires cyclam derivatives containing N-chelating substituents such as amido groups in an appropriate geometry. In contrast, the incorporation of EuIII into hybrid materials is always possible, whatever the nature of the arms of the cyclam moieties. Thus, EuIII uptake is one EuIII/two macrocycles with cyclam moieties containing N-alkyl substituents. This constitutes the first example of 4N + 4N lanthanide coordination.