Crystal and molecular structure of 2,9-di-(methylnitronato)-3,5,10,12-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,11-dienenickel(II) di-triethylammonium diperchlorate,C16H28N6O4Ni·2(C2H5)3NH·2ClO4

The crystal and molecular structure of 2,9-di-(methylnitronato)-3,5,10,12-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,11-dienenickel(II) di-triethylammonium diperchlorate (2c) has been determined of the basis of X-ray diffraction data. The crystals are monoclinic, space groupP2₁/c,Z=2; cell constants=11.478(3),b=15.177(3),c=11.431(3) Å,=99.34(2)°. The structure was refined (full matrix, least squares) with 3408 unique reflections givingR=0.0616. An octahedral configuration of the Ni(II) coordination sphere was found to consist of the macrocycle N₄ atoms occupying the equatorial plane of the octahedron with the O-atoms of the nitronato groups in the apical positions. The triethylammonium cations are hydrogen-bonded to the remaining O-atoms of the nitronato groups.     

Intermetallic interactions in face-to-face homo- and heterodinuclear bismacrocyclic complexes of copper(II) and nickel(II)

New face-to-face heterodinuclear complexes containing copper(II) and nickel(II) in identical tetraazamacrocyclic environments have been synthesized and characterized using ESI mass-spectrometry, X-ray diffraction, spectroscopic methods, and elemental analysis. These new bismacrocyclic systems were compared with the respective mono- and bismacrocyclic and [2]catenane homonuclear complexes. Interactions between the metal centers were monitored by magnetic and electrochemical measurements. Magnetic data indicate that all copper compounds studied behave as weakly interacting magnets. In the case of copper [2]catenane, the extent of magnetic interactions decreased when a benzocrown moiety was introduced between the macrocyclic units. On the basis of electrochemical data, the interactions between the metal centers were found to be substantially larger for the nickel complexes than for the corresponding copper ones. Interlocking of a benzocrown ether to form [2]catenane led to a nonequivalence of the metal centers and to the increase of donor abilities of the catenane compared to the respective bismacrocyclic complex. This is reflected by the shift of the first formal potential to less positive values. Intermetallic interactions for the heteronuclear nickel/copper complexes were found intermediary compared to the homonuclear ones. They were strengthened by shortening the spacer between the two tetraazamacrocyclic subunits which is a convenient way of fine-tuning the interactions. The increase of intermetallic interactions led to the increased stability of the intermediate mixed-valence states indicated by the higher values of comproportionation constants.     

Novel [2]catenane structures introducing communication between transition metal centers via pi...pi interactions

[2]Catenane systems containing copper(II) and nickel(II) as metal centers have been self-assembled using tetraazamacrocyclic complexes and benzo-24-crown-8 as building blocks. A variety of methods, including X-ray crystallography, ESI mass spectrometry, (13)C and (1)H NMR, and electrochemistry, were applied to characterize these new face-to-face bismacrocyclic systems. Weak pi...pi interactions introduced by interlocking transition metal complexes with benzocrown moieties were shown to increase the communication (cooperativity) of metal centers. Introduction of the benzocrown increases the stability of the mixed valence state of the macrocyclic complex, which is reflected in high values of conproportionation constants. Moreover, this effect was found to be stronger than that obtained by shortening the length of the spacer between the two tetraazamacrocyclic subunits in the parent bismacrocycles. The extent of communication is larger for the nickel catenane than for the copper one.     

Fine-tuning of properties of bismacrocyclic dinuclear cyclidene receptors by N-methylation

N-Methylated bismacrocyclic Cu and Ni complexes were synthesised and structurally characterised in the solid state. Their properties in solution were analysed by using NMR and ESR spectroscopies and electrochemical methods. Face-to-face biscyclidenes linked through polymethylene chains form rectangular boxlike cations. These moieties can host some small guest molecules (water, pi-electron donating compounds) and are stabilised by a shell of neighbouring counterions. For the bismacrocyclic dinuclear complexes containing two nickel or two copper ions, the intramolecular interactions between the metallic centres are strengthened through methylation of the macrocyclic components, as compared with the nonmethylated species. We report the electron coupling created by two unpaired electrons coming from two copper centres observed by ESR spectroscopy. Methylation weakens the electron-acceptor properties of the complexes, which leads to less effective binding of the pi-electron-donating guests. It also increases the stability of the lower oxidation states. In the case of the copper complexes, both Cu(II)/Cu(I) and Cu(II)/Cu(III) reversible one-electron transfers are seen in the voltammograms. These changes in properties are interpreted as the consequences of steric repulsion between the methyl substituents and the macrocyclic ring.     

Crystal and molecular structure of meso-2,9-dicyano-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene,C18H30N6

meso-2,9-Dicyano-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene (1) has been investigated by X-ray structural methods. The crystals are monoclinic, space groupP2₁/n, with cell dimensions=7.319(1),b=7.442(1),c=17.359(3)Å, and=98.30(1)°;Z=2. The structure was solved by direct methods and refined by a full-matrix, least-squares procedure against 1339 observed reflections givingR=0.0627. The [133133]_i macro-chair (m ¹ C ₄) was assigned to the macrocycle of1. The occurrence of intramolecular bifurcated hydrogen bonding NHN=C was postulated.     

Tetraimine macrocyclic transition metal complexes as building blocks for molecular devices

The synthetic strategy initiated by Busch and further developed in recent years resulted in an impressive variety of new azamacrocyclic ligand superstructures. In this contribution, we have reviewed papers containing general synthetic strategies, structural and electronic properties and results of electrochemical studies for a long series of neutral and charged macrocyclic tetraimine complexes of transition metals leading to a new type of homo- and heteronuclear[2]catenanes as examples of switchable molecular machines. The whole series consists of neutral and charged mono-, bis- and trismacrocycles and appropriate reference neutral molecules and many of their derivatives. The bismacrocyclic moieties are constructed from simpler tetraazamacrocyclic fragments. When two of them are linked through polymethylene chains, they form face-to-face biscyclidenes—rectangular box-like moieties. They can host some small guest molecules (water, π-electron-donating compounds) and are stabilized by hydrogen bonds with solvent molecules or a shell of neighboring counterions. Neutral thiol derivatives are used as recognition sites of monolayers self-assembled on electrode surfaces to be employed in devices based on donor–acceptor interactions.Our catenanes consist of bismacrocyclic transition metal complexes linked by aliphatic chains and interlocked with a substituted crown ether. We have proved that under external stimuli – electrochemical pulses – the heteronuclear catenane exhibits controlled intramolecular relocation of the crown ether between two positions. The relocation is possible due to π?π interactions between the aromatic fragments of the crown ether and the transition metal (Ni, Cu) coordinating macrocyclic rings.Our model tetraimine complexes of transition metals can also be used to solve the problem of controlling directional relative movement of molecular fragments present in complex supramolecules. On the way to this aim we have synthesized trismacrocyclic derivatives which are now appropriately modified to serve as components of complex catenanes.     

Nickel(II) complexes of the macrocyclic ligand 5-nitromethyl-5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene containing a pendant nitro group

The reaction of MeNO2 in the presence of Et3N with the nickel(II) complex of C-meso-5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene gives the nickel(II) complex of the 5-nitromethyl derivative containing a pendant nitro group. The complex is octahedral with the nitro group coordinated to nickel(II) via the aci-nitro tautomer. Although the complex contains one water molecule, six-coordination occurs by interaction with a neighbouring CH NO2- group in a polymeric structure. Recrystallisation from aqueous ammonia gives a blue paramagnetic complex with lattice ammonia. Addition of HClO4 to the blue paramagnetic hydrate gives the orange-brown diperchlorate salt with a pendant nitro group. This salt displays a planar octahedral equilibrium in aqueous solution, NiL+2H2O NiL(H2O)2, with K=0.28 at 40degC. The thermodynamic parameters for this equilibrium are DeltaH=-59+2kJmol-1and DeltaS=-200+5JK-1mol-1. The nitro group can be reduced with Zn/HCl to give the amino derivative. The configurations of the complexes are considered and the spectroscopic results discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Magnetism and crystal structures of CuMn and CuNi ordered bimetallic chains

The syntheses, crystal structures and magnetic properties of the new bimetallic compounds {CuL_α[Ni(NCS)₄(H₂O)₂]} (1) and {CuL_α[Mn(NCS)₄(H₂O)₂]} (2), where L = N-dl-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene, are reported. Both structures consist of well-separated and magnetically equivalent layers which are composed of thiocyanate-bridged Cu(II)–Mn(II) or Cu(II)–Ni(II) binuclear units and create infinite polymeric zig-zag-like chains in the crystal lattices. The [Ni(NCS)₄(H₂O)₂] and [Mn(NCS)₄(H₂O)₂] molecular fragments have a distorted octahedral symmetry. The geometry of the Cu(II) unit is octahedral with the apical positions occupied by bridging thiocyanate ligands and the basal ones by four nitrogen atoms from the macrocyclic ring. The shortest intramolecular M–M distances are: 6.342 Å (Cu–Ni) and 6.421 Å (Cu–Mn). Magnetic susceptibility and magnetization measurements for the examined compounds have been carried out over the range 1.8–300 K. The data suggest antiferromagnetic interactions through the thiocyanate bridge. Finally, the magnitudes of the Cu(II)–M(II) interactions (M = Ni and Mn) have been compared and qualitatively rationalised.