The encapsulation of enzymes within silica gels has been extensively studied during the past decade for the design of biosensors and bioreactors. Yeast spores and bacteria have also been recently immobilized within silica gels where they retain their enzymatic activity, but the problem of the long-term viability of whole cells in an inorganic matrix has never been fully addressed. It is a real challenge for the development of sol-gel processes. Generic tests have been performed to check the viability of Escherichia coli bacteria in silica gels. Surprisingly, more bacteria remain culturable in the gel than in an aqueous suspension. The metabolic activity of the bacteria towards glycolysis decreases slowly, but half of the bacteria are still viable after one month. When confined within a mineral environment, bacteria do not form colonies. The exchange of chemical signals between isolated bacteria rather than aggregates can then be studied, a point that could be very important for 'quorum sensing'.

Oxo alcoxo metallic clusters can be employed as inorganic nanobuilding blocks to obtain well-defined organic-inorganic hybrid materials. A better understanding of the surface reactivity of the clusters should allow optimization of the elaboration of hybrid materials through a better control of the hybrid interface. The oxo alcoxo cluster Ti(16)O(16)(OEt)32 presents a shell of labile ethoxy groups that can be selectively transalcoholyzed with preservation of the titanium oxo core, leading to new oxo alcoxo clusters Ti(16)O(16)(OEt)32-x(OR)x (R: alkyl, phenyl, styrenic, etc. groups). The reactivity of the Ti(16)O(16)(OEt)32 cluster toward aliphatic and aromatic alcohols is investigated to determine both the kinetics and the number of substituted titanium atoms, which are strongly dependent on the nature of the alcohol. Characterization of the organic modification of the cluster is performed in situ by liquid (13)C NMR measurements, using the molecular structures of two new clusters, Ti(16)O(16)(OEt)28(OnPr)4 and Ti(16)O(16)(OEt)(24)(OnPr)(8) (OnPr = propoxy groups), as references. The structures of these clusters have been established using single-crystal X-ray diffraction. Moreover, a complete spectroscopic assignment of each ethoxy group is proposed after combining crystallographic data, (13)C NMR T(1) relaxation measurements, and (1)H-(1)H, (1)H-(13)C 2D NMR experiments. Finally, the cluster is functionalized with polymerizable ligands via transalcoholysis and transesterification reactions using hydroxystyrene and acetoxystyrene.

Caught in the act: The first stable η4‐diseleno‐p‐benzoquinone complex, [Cp*Ir(η4‐C6H4Se2)], has been isolated. The X‐ray structure (see picture; Ir magenta, Se yellow) confirms the coordination of the elusive diselenobenzoquinone intermediate. The anticancer activity of this complex was compared to related oxygen and sulfur analogues; only the diseleno complex was cytotoxic, having a comparable activity to cisplatin.

Stuck in the middle: Supramolecular host–guest cages of general formula [BF4⊂(RCN)2Co2L4](BF4)3 with L being a di(benzimidazole)‐1,4‐phenylene derivative (R=Me, Et, Ph) have been prepared. An encapsulated BF4− anion (B yellow, F pale green; see structure) is locked firmly inside the cage and plays a pivotal role as a template around which the CoII ions (gray) and L ligands (ball‐and‐stick representation) self‐assemble.

Treatment of hydroquinone with [Cp*M(solvent)3][OTf]2 (M = Rh, Ir) in acetone afforded the π-bonded complexes {[Cp*M(η5-semiquinone)][OTf]} n (M = Rh (1a), M = Ir (1b)) in 95% yield. The 1H NMR spectra of 1a,b recorded in CD3OD indicate strong hydrogen bonding in solution. The crystal structures of 1a and 1b were determined and exhibit strong intermolecular hydrogen bonding, forming organometallic polymers in which the integrity of the system is maintained by hydrogen bonding between metal−semiquinone subunits. Deprotonation of 1a produced the related η4-quinone complex [Cp*Rh(η4-quinone)] (2a), which was fully characterized and its X-ray molecular structure determined. Furthermore, the electrochemical behavior of these η4-quinone π-complexes [Cp*M(η4-quinone)] (M = Rh (2a), M = Ir (2b)) was investigated and compared to that of the well-known couple quinone/hydroquinone. The latter are important species in chemistry and biology; their biological action is often linked to their electron-transfer rates and redox behavior.

Overcoming a long‐standing challenge, the o‐ and p‐dithiobenzoquinone iridium complexes [Cp*Ir‐o‐(η4‐C6H4S2)] (6) and [Cp*Ir‐p‐(η4‐C6H4S2)] (7) were rationally synthesized and fully characterized for the first time including the X‐ray molecular structure of [Cp*Ir‐p‐(η4‐C6H4S2)] (7). Our strategic approach involves the preparation of the halogenated 1,2‐ and 1,4‐dichloro arene π complexes [Cp*Ir‐o‐(η6‐C6H4Cl2)][BF4]2 (4) and [Cp*Ir‐p‐(η6‐C6H4Cl2)][BF4]2 (5), which are the key molecules for 6 and 7. Subsequent treatment of 4 and 5 with NaSH and halogen displacement provides the target thioquinonoid π complexes 6 and 7 in 88 % and 95 % yields respectively. Further, the coordination chemistry of the o‐dithiobenzoquinone iridium complex [Cp*Ir‐o‐(η4‐C6H4S2)] (6) was studied by treating 6 with [(bpy)PtCl2] in the presence of AgOTf, which provided the novel platinum complex [Pt(bpy){Cp*Ir‐o‐(η4‐C6H4S2)}][OTf]2 (10) in 91 % yield. The X‐ray molecular structure of 10 is reported and shows as outstanding features the formation of 1D supramolecular assembly, which results from π–π (d = 3.484 Å; d = 3.669 Å) and Pt···Pt (d = 3.574 Å) interactions between individual subunits.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Two novel supramolecular architectures, [[Ag(2)L(1)(2)][X](2)] with X = CF(3)SO(3)(-) (2a) or X = NO(3)(-) (2b) and [[AgL(1)(2)][X]](n) with X = BF(4)(-) (3), were constructed by self-assembly and obtained in quantitative yields, using AgX as a building block and L(1) as the bridging ligand (L(1) = 1,3-bis(benzimidazol-1-ylmethyl)benzene). The X-ray molecular structures of 2a and 3 are reported. Complex 2a was identified as a metallomacrocycle in which one ligating triflate anion is coordinated to each of the two unsaturated Ag(I) ions. 2a crystallizes in monoclinic unit cell P2(1)/n with a = 9.728(6) A, b = 17.303(4) A, c = 13.268(3) A, beta = 92.52(4) degrees, V = 2231(2) A(3), and Z = 2. Remarkably, the X-ray structure of 2a shows a layered network structure consisting of infinite metallomacrocycles held together through pi-pi interactions between benzimidazole rings. In dramatic contrast, the product 3 prepared from AgBF(4) and L(1) lacks metal-counterion bonding, leading to a supramolecular 3D network with the following three outstanding features: (i) in one dimension, metallomacrocycles containing two Ag centers and two bridging ligands form infinite, double-stranded chains; (ii) neighboring chains are arranged by two distinct pi-pi interactions, one between substituted benzene rings and the other between benzimidazole rings, leading to a 3D structure; (iii) cavities within the 3D network contain BF(4)(-) counteranions. 3 crystallizes in monoclinic unit cell C2/c with a = 25.33(3) A, b = 11.655(6) A, c = 18.466(8) A, beta = 123.00(8) degrees, V = 4572(8) A(3), and Z = 4. Interestingly, electrospray mass spectroscopy suggests in either case that the identified elemental subunit [AgL(1)(2)](+) is the key building block which self-assembles and subsequent anion templation provides either the macrocycles 2a, b or the inorganic polymer 3. Remarkably, in dichloromethane solvent ligand-to-metal stoichiometries of 2:1 in 3 and 1:1 in 2a, b are obtained even with excess ligand, showing the power of metal-anion interactions in determining the overall supramolecular structure. Anion metathesis, showing supramolecular structural rearrangements from 2a to 2b and more spectacularly from 3 to 2b, smoothly occurred. The crucial effect and the nature of coordinating counteranions (BF(4)(-), CF(3)SO(3)(-), NO(3)(-)) on the supermolecule design are presented and discussed.

We report the first synthesis of π-bonded rhodio and iridio-o-benzoquinones [Cp*M(o-benzoquinone)] (M = Rh (3a); M = Ir (3b)) following a novel synthetic procedure. These compounds were fully characterized by spectroscopic methods; in particular the X-ray molecular structure of 3b was determined. Compounds 3a,b were used as chelating organometallic linkers for the design of a new family of chiral octahedral bimetallic complexes, 4−9. The X-ray molecular structure of [(bpy)2Ru(3b)][OTf]2 (5) is presented and shows that the organometallic linker 3b is chelating the ruthenium center. In particular, the carbocycle of the organometallic linker 3b adopts a η4-quinone form, where the Cp*Ir is also bonded to only four carbons. Further our strategy to design new assemblies with organometallic linkers is successfully achieved. These assemblies hold promise for new properties relative to those made from organic bidentate ligands.