Françoise Conan

New side-bridged bismacrocycles and cross-bridged macrotricycles. Syntheses and Cu(II) complexation study

Eight new cyclen based constrained macropolycycles (4a–4d, 5a–5d) have been obtained by reductive ring cleavage of polyaminal derivatives of bis-macrocycles or macrotricyclic polyammonium salts by sodium borohydride. The mononuclear and dinuclear Cu(II) complexes of these macropolycyclic ligands were isolated as solids and investigated by UV-Vis and EPR spectroscopies. The possibility to obtain the specific formation of mononuclear complexes constitutes an original feature of these new macropolycycles.

RADICAL CATION-RADICAL ANION SALTS : MOLYBDENUM COMPLEXES CONTAINING THE TCNQ.- OR TCNE.- RADICAL ANIONS. X-RAY CRYSTAL STRUCTURE OF MO(ET2NCS2)4(TCNQ )

Abstract The reactions between the molybdenum(IV) complexes [Mo(dtc) 4 ] 1 (dtc = Et 2 NCS 2 for 1a and Me 2 NCS 2 for 1b ) and TCNQ produced the 1 : 1 derivatives [Mo(dtc) 4 ](TCNQ) 2. Subsequent reaction of 2 with TCNQ gave the 1 : 2 complexes 3 [Mo(dtc) 4 ](TCNQ) 2 . Complexes 1 reacted with TCNE under nitrogen to give the 1 : 1 compounds [Mo(dtc) 4 ](TCNE) 4 while under ambient conditions the pentacyanopropenide derivatives [Mo(dtc) 4 ](NC) 2 CC(CN)C(CN) 2 ] 5 were obtained. In solution, cyclic voltammetry and ESR studies revealed the presence for all types of complexes of the molybdenum(V) radical cation [Mo(dtc) 4 ] •− which is associated with the radical anion TCNX •− in 2 (X = Q) and 4 (X = E) and with a 1:1 mixture of neutral and anionic TCNQ species in 3 . Complex 2a has been studied by single crystal X-ray diffraction. The crystal structure consists of monomeric TCNQ •− radical anions and [Mo(dtc) 4 ] •+ cations with a triangular dodecahedral arrangement of S atoms and a point group symmetry which is approximately D 2 d .

Pentacyanopropenide group as ligand in organometallic chemistry. Crystal structure and electrochemical studies of (Et4N)[W(CO)5{(C(CN)2C(CN)C(CN)2}]

Abstract The title complex has been obtained by reaction of the tetraethylammonium pentacyanopropenide with tungsten hexacarbonyl in acetone. Its crystal structure involves discrete [W(CO)5{C3(CN)5}]− anions in which the organic fragment is N-coordinated via one of the nitrogen atoms of a cyano group borne by one of the terminal carbon atoms of the allylic skeleton. The anion presents a distorted octahedral coordination with a W–N bond length [2.168(5) A] considerably longer than the W–C bond lengths [cis-W–C in the range 1.998(7)–2.068(4) A; trans-W–C 1.962(7) A]. Cyclic voltammograms of this complex, recorded in CH2Cl2 and CH3CN (Bu4NPF6 0.1 M), display a quasi-reversible reduction and irreversible oxidation waves.

Syntheses, structural characterisation and magnetic properties of Fe(II) and Mn(II) compounds with the pentacyanopropenido ligand; structural characterisation of a substituted pyrazolo[1,5-a]pyrimidine

Reactions between the metal(II) salts [M(CH3CN)n](BF4)2 (M = Fe, n = 6; M = Mn, n = 4) and some organic anionic polynitriles were studied. With the pentacyanopropenide anion pcp− [pcp− = (NC)2CC(CN)C(CN)2−], were obtained, according to the experimental conditions, the new complexes [M(pcp)2(H2O)4] (1, M = Fe; 2, M = Mn) and [M(pcp)2] (3, M = Fe; 4 = Mn). Use of the hexacyano-3,4-diazahexadienediide anion [(NC)2CC(CN)NNC(CN)C(CN)22−] instead of pcp− did not afford polynitrile metal complexes but led to a new organic derivative 5, of formula C10N8H2. Crystallographic studies indicated that the isostructural compounds 1 and 2 involve discrete monomeric units with pcp ligands acting with a monodentate coordination mode and having the metal in a pseudooctahedral trans-MN2O4 environment; however, a rich hydrogen bond system gives rise to a 3D array. Complex 3, which presents metal in a pseudooctahedral MN6 environment, has a 3D structure arising from pcp ligands having an unprecedented μ3-coordination mode. Compound 5 is a bicyclic derivative with a pyrazolo[1,5-a]pyrimidine skeleton. In all derivatives, the organic part is essentially planar and involves a strongly delocalized π system. The magnetic properties of the inorganic complexes have been studied in the 2–300 K range. Fit of the magnetic data indicates high spin complexes with weak antiferromagnetic interactions in 2, 3 and 4 and the presence of a significant zero field splitting of the Fe(II) ion in 1.

Determination of charge transfer in molybdenum complexes of 7,7,8,8-tetracyano-p-quinodimethane with vibrational spectroscopy

Abstract The influence of charge transfer on the vibrational lines of three new molybdenum TCNQ complexes [MoO(dtc)3](TCNQ) 1a, [Mo(dtc)4](TCNQ) 2a, and [Mo(dtc)4](TCNQ)2 3a is reported (dtc=Et2NCS2). It is shown that Raman scattering is able to probe the charge state of TCNQ entities in these complexes. Infrared spectra are discussed and compared to Raman spectra. Electronic polarization of the TCNQ moieties and reduction of TCNQ° in TCNQ•− is found for all complexes. The estimated charge transferred when reduction occurs is one electron onto the TCNQ molecule whereas it is about 0.2–0.3 electron onto nitrile groups. The formation of monomers and dimers of TCNQ in these complexes is discussed in relation with specific Raman lines found in reference compounds such as TCNQ salts of alkali. These new Raman data suggest to us that TCNQ moieties form mainly dimers and monomers in complexes 1a and 2a, respectively.

Insights into water coordination associated with the Cu(II)/Cu(I) electron transfer at a biomimetic Cu centre.

The coordination properties of the biomimetic complex [Cu(TMPA)(H2O)](CF3SO3)2 (TMPA = tris(2-pyridylmethyl)amine) have been investigated by electrochemistry combined with UV-Vis and EPR spectroscopy in different non-coordinating media including imidazolium-based room-temperature ionic liquids, for different water contents. The solid-state X-ray diffraction analysis of the complex shows that the cupric centre lies in a N4O coordination environment with a nearly perfect trigonal bipyramidal geometry (TBP), the water ligand being axially coordinated to Cu(II). In solution, the coordination geometry of the complex remains TBP in all media. Neither the triflate ion nor the anions of the ionic liquids were found to coordinate the copper centre. Cyclic voltammetry in all media shows that the decoordination of the water molecule occurs upon monoelectronic reduction of the Cu(II) complex. Back-coordination of the water ligand at the cuprous state can be detected by increasing the water content and/or decreasing the timescale of the experiment. Numerical simulations of the voltammograms allow the determination of kinetics and thermodynamics for the water association-dissociation mechanism. The resulting data suggest that (i) the binding/unbinding of water at the Cu(I) redox state is relatively slow and equilibrated in all media, and (ii) the binding of water at Cu(I) is somewhat faster in the ionic liquids than in the non-coordinating solvents, while the decoordination process is weakly sensitive to the nature of the solvents. These results suggest that ionic liquids favour water exchange without interfering with the coordination sphere of the metal centre. This makes them promising media for studying host-guest reactions with biomimetic complexes.

Synthesis and crystal structure of a new salt of the complex anion [(TCNQ)3]2− [Mo2(μ2-S2)2 (S2CNME2)4] (TCNQ)3

Abstract The reaction of compounds [Mo 2 (μ 2 -S 2 ) 2 (S 2 CNR 2 ) 4 ](BF 4 ) 2 ( 1 ) (a R = Me, b R= Et) with 2 equiv. of LiTCNQ in methanol results in the formation of complexes [Mo 2 (μ 2 -S 2 ) 2 (S 2 CNR 2 ) 4 ](TCNQ) 2 ( 2 ). Further reaction of 2 with TCNQ yields the derivatives [Mo 2 (μ 2 -S 2 ) 2 (S 2 CNR 2 ) 4 ](TCNQ) 3 ( 3 ). Compounds 2 and 3 were characterized fully by microanalytical, IR and electron spin resonance studies. The single crystal structure of the green product 3a ·2 CH 3 CN was determined by X-ray diffraction methods. The TCNQ units form centrosymmetrical trimers with a slipped conformation and an interplanar distance of 3.16 A. In the [(TCNQ) 3 ] 2− anion, the bond lengths agree with an almost complete delocalization of the charge between three essentially identical TCNQ units. The trimers stack with an intertrimer distance of 3.56 A. The centrosymmetric dinuclear cation is characterized by an MoMo distance of 2.817(2) A in agreement with a metal-metal single bond. The molybdedum atoms are bridged by two μ 2 -S 2 2 ligands which presnet a quite normal bridge distances S-S of 2.001 ( 2 ) A.

Unprecedented reactivity of a Schiff base ligand in the co-ordination sphere of copper(I) complex towards β-diketones. Synthesis and X-ray characterisation of a new copper(I) complex

The reactions of the copper(I) derivative [CuL(THF)(CH 3 CN)]PF 6 ( 1 ), in which L is the di-imine/pyridine ligand 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine, with different β-diketones (2,4-pentanedione (acacH), 1,3-diphenyl-1,3-propanedione (dbm)) yielded the new Cu(I) salt [CuL′ 2 ]PF 6 ( 2 ) (L′: 2-[acetyl]-6-[1-(2,6-diisopropylphenylimino)ethyl]pyridine). These reactions of β-diketones with a di-imine/pyridine ligand co-ordinated to a Cu(I) centre constitute the first example of a partial hydrolysis of such a Schiff base within the inner sphere of a Cu centre. Compound 2 ·acaH has been characterised by X-ray crystallography.

On the Magnetic Coupling and Spin Crossover Behavior in Complexes Containing the Head-to-Tail [FeII2(μ-SCN)2] Bridging Unit: A Magnetostructural Experimental and Theoretical Study

A new dinuclear complex [{Fe(tpc-OBn)(NCS)(μ-NCS)}2] (1) based on the tripodal tpc-OBn ligand (tpc-OBn = tris(2-pyridyl)benzyloxymethane), containing bridging μ-κN:κS-SCN and terminal κN-SCN thiocyanate ligands, has been prepared and characterized by single crystal X-ray diffraction, magnetic studies, and DFT theoretical calculations. This complex represents the first example of dinuclear FeII complex with double μ-κN:κS-SCN bridges in a head-to-tail configuration that exhibits ferromagnetic coupling between metal ions (JFeFe = +1.08 cm-1). Experimental and theoretical magnetostructural studies on this kind of infrequent FeII dinuclear complex containing a centrosymmetrically [Fe2(μ-SCN)2] bridging fragment show that the magnitude and sign of the magnetic coupling parameter, JFeFe, depend to a large extent on the Fe-N-C (α) angle, so that JFeFe decreases linearly when α decreases. The calculated crossover point below which the magnetic interactions change from ferromagnetic to antiferromagnetic is found at 162.3°. In addition, experimental results obtained in this work and those reported in the literature suggest that large Ntripodal-FeII distances and bent N-bound terminal κN-SCN ligands favor the high spin state of the FeII ions, while short Ntripodal-FeII distances and almost linear Fe-N-C angles favor a stronger ligand field, which enables the FeII ions to show spin crossover (SCO) behavior.

Azacyanocarbon chemistry. Comparison of thehexacyano-3,4-diazahexa-1,5-dienediide[C10N8]2- with the correspondingradical anion[C10N8]˙-:electrochemical and EPR studies, crystallographic and electronicstructures

Electrochemical, spectrochemical and structural characterization of the tetraalkylammonium salts of the 1,1,2,5,6,6-hexacyano-3,4-diazahexa-1,5-dienediide anion [(R4N)2(C10N8): R = Et 1a; R = Bu 1b] are reported. The dianion displays two one-electron reversible oxidation processes at E′01 = -0.10 V [(C10N8)˙-/(C10 N8)2-] and E′02 = +0.59 V [(C10N8)/(C10N8)˙ -] (ref. Fc+/Fc). Solutions of the radical anion have been prepared by bulk electrolysis and fully characterized by EPR spectroscopy. Chemical oxidation of 1a by iodine in dichloromethane affords this radical anion as its tetraethylammonium salt (Et4N)(C10N8) 3a. (C10N8)2- and (C10N8)˙- have unequivocally different IR and visible spectra. Single crystal X-ray diffraction studies of 1b and 3a have been carried out. In 1b, the dianion is planar within ±0.03 A and has a crystallographically imposed symmetry but the point group is approximately C2h while in 3a the (C10N8)˙- unit, which has no crystallographically imposed symmetry, is only roughly planar. In both cases, the two –C(CN)C(CN)2 groups are in trans positions relative to the N–N bond. The crystal structure of 3a clearly shows that the anion exist as dimer units [(C10N8)2]2-. This is in agreement with the EPR spectra and the molecular orbital study carried out at the semi-empirical AM1 level which both indicate a thermally populated triplet excited state.