Nathalie Kyritsakas

Molecular Tectonics: Control of Reversible Water Release in Porous Charge-Assisted H-Bonded Networks

The combinations of bisamidium dicationic tectons 1-2H+ and 2-2H+ bearing two OH groups as additional H-bond donor/acceptor sites with [M(CN)6](3-)2 (M = Fe, Co, Cr) anions lead to the formation of robust porous crystals (decomposition temperature in the range of 240-300 degrees C) offering channels occupied by water molecules. The release and uptake of solvent molecules takes place through a reversible single crystal-to-single crystal transformation. Importantly, the temperature of dehydration can be increased by ca 40 degrees C through the decoration of the channels by introduction of OH groups on the backbone of the organic tecton.

Molecular tectonics: on the role of counter-ions in the dimensionality of silver coordination networks

The role played by different anions (XF6− (X = P, As, Sb), BF4−) on the connectivity of coordination networks formed by a combination of different silver salts and an organic tecton based on piperazine bearing two pyridine units has been studied in the crystalline phase by X-ray diffraction on single crystal. All four weakly coordinating anions lead to the formation of analogous 2-D coordination networks. For the isostructural anions XF6− (X = P, As, Sb) the crystals are isomorphous.

Trinuclear magnetic clusters based on cyanide metal complexes: synthesis, crystal structures, and magnetic properties of four new [MnII2MIII] complexes (M = Cr, Fe, Co)

Four new cyano-bridged [MnIIMIIIMnII] heterotrinuclear complexes (MIII = Cr, Fe, Co) have been synthesized and crystallographically characterized: {[(H2O)L1Mn–NC–Cr(CN)4–CN–MnL1(H2O)]}3[Cr(CN)6]·10H2O 1, [(H2O)L2Mn–NC–M(CN)4–CN–MnL2(NCS)]·2H2O 2, [(H2O)L2Mn–NC–Fe(CN)4–CN–MnL2(H2O)](NCS)·1.5H2O 3, and [(H2O)L2Mn–NC–Co(CN)4–CN–MnL2(H2O)](NCS)·1.5H2O 4 (L1 = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, L2 = 2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene). The crystal structure of 1 consists of independent [MnCrMn] monocations whose charges are counterbalanced by [Cr(CN)6]3− anions. The crystal structure of 2 consists of neutral heterotrinuclear [MnCrMn] species, with the isothiocyanato ion coordinated to one of the manganese atoms. Compounds 3 and 4 are isomorphous. Their crystal structure consists of centrosymmetric [MnMMn] entities, uncoordinated NCS− ions, and solvent molecules. The magnetic properties of the four complexes have been investigated. Compounds 1 and 2 are new examples of systems with an irregular spin state structure, exhibiting the characteristic minimum on the the χMTversusT curves. The exchange interaction between the chromium(III) and the manganese(II) ions is antiferromagnetic (1: J = −9.8 cm−1; 2: J = −6.52 cm−1). For compound 3, the exchange interaction between manganese(II) and iron(III) was found to be ferromagnetic.

Molecular tectonics: generation of 2-D molecular networks by combination of coordination and hydrogen bonds

The combination of two organic tectons 1 and 2, based on a 1,4-phenylenediamine backbone functionalised with two pyridine units through amide junctions with HgCl2, leads to the formation of two types of 2-D networks, one of the purely metallo-organic type, based on only coordination bonds, and the other combining both coordination and hydrogen bonds.

Alkoxo-bridged copper(II) complexes as nodes in designing solid-state architectures. The interplay of coordinative and d10-d10 metal-metal interactions in sustaining supramolecular solid-state architectures

Four novel polymeric coordination networks have been obtained through self-assembly processes involving alkoxo-bridged copperII species as nodes, and anionic cyano-complexes as linkers: infinity2[{Cu2(pa)2}{M(CN)2}2](M=Ag, 1; Au, 2), (infinity)3[{Cu4(mea)4}{Au(CN)2}4.H2O]3, and (infinity)3[{Cu2(pa)2}{Ni(CN)4}](pa = deprotonated propanolamine; mea = deprotonated monoethanolamine). The supramolecular architectures of compounds 1, and 2 are sustained by argentophilic or strong aurophilic interactions. The solid-state architectures of 1 and 2, which are isomorphous, consist of infinite layers, constructed from binuclear alkoxo-bridged nodes and [M(CN)2]- spacers. The layers are stacked in an offset parallel mode, and are further interconnected through Ag...Ag or Au...Au contacts (1: Ag...Ag 3.015 A; 2: Au....Au 3.069 A). Compound 3 consists of unique fourfold interpenetrating diamondoid nets. The diamondoid topology is built of heterocubane {Cu4O4} nodes, which are connected by [Au(CN)2]- rods. The Cu-O distances within the {Cu4O4} node vary between 1.927(2) and 2.679(1) A, showing unsymmetric bridging of the copper atoms. Aurophilic interactions are established between the bridging and terminal [Au(CN)2]- metalloligands, and connect the interpenetrating nets, resulting in infinite chains of gold atoms (the Au...Au distances vary between 3.253 and 3.305 [Angstrom]). Compound 4 exhibits a 3-D network constructed from {Cu2(pa)2]2+ nodes connected by square-planar [Ni(CN)4]2- ions. Compounds 1, 2 and 4 are weakly paramagnetic. The cryomagnetic investigation of reveals a gradual increase, followed by a decrease of the chiMT product, as the temperature is lowered. A superposition of ferro- (J1=+20.8 cm(-1)) and antiferromagnetic (J2=-6.4) interactions within the tetranuclear node was found. Antiferromagnetic interactions are established between the tetranuclear nodes (theta=-2.99 K).

Molecular tectonics: modulation of size and shape of cuboid 3-D coordination networks

The pore size and shape of cuboid 3-D coordination networks may be modulated by combining rigid neutral organic tectons of different length bearing two pyridines oriented in a divergent fashion with zinc dication and SiF6 dianion behaving as a metallic node and as an inorganic tecton, respectively.

Solvent-modulated reversible conversion of a [2×2]-grid into a pincer-like complex

The triazine derived ligand reacts with one equivalent of Co(II) salts to give complexes whose architecture depends on the solvent employed: the [2 x 2]-grid like tetranuclear complex and the pincer-like mononuclear complex, obtained respectively by crystallization from nitromethane and from acetonitrile may be interconverted reversibly, the grid-pincer conversion being markedly accelerated by adding an amine.

Towards a Better Understanding of the Magnetic Interactions withinm-Phenyleneα-Nitronyl Imino Nitroxide Based Biradicals

An extensive investigation of the magnetic properties of three series of biradicals (bis-nitronyl nitroxides diNN-R, bis-imino nitroxides diIN-R and mixed INNN-R, where R is either hydrogen, a triple bond or trimethylsilylacetylenic group) has been carried out to give clear values of the intramolecular interactions through the m-phenylene coupling unit with alpha-nitronyl nitroxides (NN) or alpha-imino nitroxides (IN). An EPR study of the molecules in the isolated state is validated by ab initio calculations, which show the respective influence of spin polarisation and molecular conformation on the singlet-triplet gaps. All these results indicate that the triplet state is the ground state for such biradicals, except when the imidazolyl cycles are orthogonal to the phenyl ring. The magnetic properties of the biradicals in the solid state can be rationalised by examination of the short contacts produced between the ONCNO and ONCN groups. EPR studies on single crystals of the H-substituted series have confirmed the presence of a structural distortion for diNN-H whereas diIN-H and INNN-H do not exhibit such a peculiarity. The magnetic behaviour of diIN-H is described well by a four-spins model, with a strong intermolecular antiferromagnetic interaction of -90 K, whereas in the case of the two other compounds, a supplementary contact involves more complex interactions between the dimers. The compound diNN-tmsa exhibits a ferromagnetic intermolecular interaction of +11 K within the dimers, and this could be attributed to the relative disposition of the imidazolyl rings. Compound diNN-tr reveals a chain-like behaviour, whereas diIN-tr shows a predominant antiferromagnetic interaction within the dimers. The values for the intramolecular interactions in the solid state are in good agreement with those found for the isolated molecules.

Molecular tectonics and supramolecular chirality: rational design of hybrid 1-D and 2-D H-bonded molecular networks based on bis-amidinium dication and metal cyanide anions

Using the bis-amidinium dication 1 bearing four acidic protons disposed in a divergent fashion and capable of chelating, through H-bonds, metal cyanide anions, neutral 1- and 2-D hybrid networks were generated. Whereas in the presence of M(CN)42− (M = Ni(II), Pd(II) and Pt(II)), 1-D H-bonded networks are formed through a double dihapto mode of H-bonding between the dication and the dianion, in the case of M(CN)64− (M = Fe(II) and Ru(II)), 2-D networks based on the interconnection by the dication 1 of 1-D networks analogous to those formed in the case of [M(CN)4]2− mentioned above are obtained. Interestingly, in the case of [M(CN)6]3− (M = Cr(III)), again a 2-D H-bonded network is formed through the formation of three dihapto modes of H-bonding between the dication and the trianion. Due to this dihapto or chelate mode of H-bonding, a supramolecular chirality of the Δ′ and Λ′ type is generated within the second coordination sphere of the metallic centres. The packing of the achiral 2-D networks thus obtained leads to channels which are occupied by water molecules forming polymeric H-bonded chains.

Design and Synthesis of Sn-Porphyrin Based Molecular Gates

The design, synthesis, and structural characterization, both in solution by (1)H NMR and in the solid state by X-ray diffraction on single crystals, of a series of molecular gates based on Sn-porphyrin derivatives are presented. The molecular system is based on a porphyrin core bearing at the meso positions either phenyl or pyridyl groups as a stator, octahedral Sn(IV) cation located at the center of the porphyrin as a hinge, and different handles connected to the porphyrin through Sn-O axial bonds. The stability of the complexes in the presence of different acids is also reported.