J.V. Heras

Chemistry of Rh(I) complexes based on mesogenic 3,5-disubstituted pyrazole ligands. X-ray crystal structures of 3,5-di(4-n-butoxyphenyl)pyrazole (Hpzbp2) and [Rh(μ-pzR2)(CO)2]2 (R = C6H4OCnH2n+1, n = 10, 12) compounds. Part II

Abstract Four new 3,5-disubstituted pyrazoles Hpz R2 containing long-chain 4- n -alkyloxyphenyl substituents [R=C 6 H 4 OC n H 2 n +1 ; n =4 ( 1 ), 6 ( 2 ), 12 ( 5 ), 14 ( 6 )] have been prepared and characterised. All of them showed mesomorphic behaviour, the stability and the range of the mesophases increasing with the length of the chain on the pyrazole. The X-ray structure of Hpz bp2 ( 1 ) showed a highly linear molecular shape. Related results were deduced for the remained Hpz R2 and the structural consequences agree with the observed mesomorphic properties. The mesogenic pyrazoles Hpz R2 ( 1 – 6 ) were used as ligands towards [RhCl(CO) 2 ] and [Rh(CO) 2 ] fragments. [RhCl(CO) 2 (Hpz R2 )] complexes ( 7 – 12 ) showed some physical properties dependant on the long-chained pyrazoles, and related to different molecular arrays in the solid state. In all cases these compounds evolved to [Rh(μ-pz R2 )(CO) 2 ] 2 in solution. The pyrazolate Rh(I) complexes [Rh(μ-pz R2 )(CO) 2 ] 2 ( 13 – 18 ) had the usual boat conformation, as deduced by the crystal structure of two of these derivatives [ n =10 ( 16 ), 12 ( 17 )]. The packing arrangement has both layer and columnar characteristics. No mesophases have been detected for any of the Rh(I) complexes.

3-[4-Phenoxyphenyl]pyrazole (Hpzpp) and 3-[4-butoxyphenyl]pyrazole (Hpzbp) in rhodium chemistry crystal structures of 3-[4-phenoxyphenyl]pyrazole, [Rh(μ−pzpp)(COD)]2⋅12CH2C12 and [Rh(μ-pzbp)(COD)]2

Abstract The novel pyrazoles containing 3-[4-phenoxyphenyl] (pp) and 3-[4-butoxyphenyl] (bp) substituents, Hpzpp and Hpzbp, have been synthetized and characterized, and the crystalline structure of 3-[4-phenoxiphenyl]pyrazole (Hpzpp) is also reported. Rh(I) compounds [Rh(Cl)(HpzR)(LL)] and [Rh(μ-pzR)(LL)]2 (LL = NBD, COD, 2CO; R = pp, bp) have been prepared in order to explore the influence of the alkoxy- or aryloxyphenyl substituents on the pyrazol ring of some features such as the presence of dynamic processes or the preference of determined isomers in the complexes. The molecular structures of complexes [Rh(Cl)(HpzR)(LL)] and [Rh(μ-pzR)(LL)]2 (LL = NBD, COD, 2CO; R = pp, bp) have been studied by IR and 1H and 13C NMR spectroscopies. 1H NMR spectra of compounds [Rh(Cl)(HpzR)(LL)] (LL = NBD, COD, 2CO; R = pp, bp) indicate that the presence of a metallotropic equilibrium only depends on the steric characteristics of the ancillary ligands. On the other hand, complexes [Rh(μ-pzR)(CO)2]2 (R = pp, bp) are formed as a mixture of the head-to-head (H-H) and head-to-tail (H-T) configurational isomers. By contrast, [Rh(μ-pzR)(LL)]2 (LL = NBD, COD; R = pp, bp) have been obtained as only one isomer in both the solid state and the solution. The crystalline structures of complexes [ Rh ( μ − pz pp ) ( COD ) ] 2 ⋅ 1 2 CH 2 C1 2 and [Rh(μ-pzbp)(COD)]2 have been solved, showing the presence of the H-T configurational isomer in both cases. The 1H NMR spectra of [Rh(μ-pzR)(LL)]2 (LL = NBD, COD, 2CO; R = pp, bp) show that the ortho protons of the C6H4 group of the substituents on the pyrazol ring are considerably deshielded. Furthermore, the X-ray structures of [ Rh ( μ − pz pp ) ( COD ) ] 2 ⋅ 1 2 CH 2 C1 2 and [Rh(μ-pzbp)(COD)]2 complexes show an Rh-H(ortho) distance of ca. 2.7 A, characteristic of a weak preagostic interaction.

Mesogenic Pd(II) complexes based on 3-substituted pyrazol ligands

Abstract A new family of linear Pd(II) complexes based on pyrazoles containing long-chain substituents at the third position has been prepared and their mesomorphic properties studied. The crystalline structure of one of these compounds is described as a representative example of a very elongated and straight molecule.

Polymorphism and metal–metal interactions on [Rh(Cl)(CO)2(HpzR)] complexes

The novel pyrazoles containing 3-[4- n -hexyloxyphenyl] (hp), 3-[4- n -octyloxyphenyl] (op) and 3-[4- n -decyloxyphenyl] (dp) substituents, Hpz R (R=hp, op, dp; 1 – 3 ), and their corresponding Rh(I) compounds [Rh(Cl)(LL)(Hpz R )] (LL=2,5-norbornadiene NBD, 1,5-cyclooctadiene COD, 2CO; R=hp, op, dp; 4 – 12 ) have been prepared and characterised. The influence of the pyrazol substituent on the properties of the Rh(I) complexes has been analysed. Two crystalline polymorphs (yellow and red) have been isolated for [Rh(Cl)(CO) 2 (Hpz dp )] ( 12 ) in contrast to the single red crystalline form isolated for the related complexes [Rh(Cl)(CO) 2 (Hpz R )] (R=hp, op; 10 and 11 ). X-ray crystal structures of the red forms of 10 – 12 as well as the yellow one of 12 have been solved. The red compounds display one-dimensional stacking of square-planar molecules with metal–metal interactions along the c -axis. The yellow form consists of dimeric unities held together by Cl bridges, and without the one-dimensional metal–metal contacts. In both cases an intramolecular hydrogen bond was present, being stronger in the yellow form than in the red one. Thermochromic behaviour has also been observed for these dicarbonyl complexes. No liquid crystals properties were found for the new compounds, however, the double melting behaviour observed for 10 – 12 could be closely related to mesomorphism.

Bridged 3,5-disubstituted pyrazolate ligands as support of metallomesogens containing [Pd(η3-C3H5)]+ fragments: X-ray crystal structure of [Pd(η3-C3H5)(μ-pzR2)]2·CH2Cl2 (R=C6H4OC12H25). Part III

Abstract The mesomorphic properties of two new long-chain 3,5-(4-n-alkoxyphenyl)pyrazoles HpzR2 (R=C6H4OCnH2n+1, n=16, 18) have been studied and compared with those of related compounds containing shorter chains (n=4, 6, 8, 10, 12, 14). For liquid crystal purposes, the derivative with 14 carbon atoms in the chain behaves as the best compound on the basis of the lowest melting point and the widest stability range of the mesophases. New Pd(II) complexes of formula [Pd(η3-C3H5)(μ-pzR2)]2 (R=C6H4OCnH2n+1, n=8, 10, 12, 14, 16, 18) (1–6) containing the mesomorphic ligands as pyrazolate-bridging groups have been prepared and characterised. In solution, three conformational isomers (two symmetric and one asymmetric corresponding to different orientations of the allyl groups) have been found. In the solid state, the X-ray crystal structure of 3 (n=12) evidenced the asymmetric isomer. The structure shows a bowlic core drawn on the basis of the boat-like conformation of the six-membered ring Pd(NN)2Pd. However, a rod-like shape could also be considered by taking the molecular dimensionality into account (47.80 A in length×4.75 A in wide). The Pd-complexes 2–6 were found to have liquid crystal properties exhibiting enantiotropic smectic phases consistent with the molecular characteristics. Moreover, the molecular packing of 3 is described as the layer-like type in which the molecules are parallel to the c-axis but tilted off the layer, this fact appearing similar to the molecular ordering in the smectic fluid phases.

Bulky pyrazole as ligands in rhodium(I) complexes. Crystal structure of chlorodicarbonyl (3-p-methoxyphenylpyrazole)rhodium(I)

Abstract A new family of complexes containing bulky pyrazoles substituted in the 3 or the 3 and 5 positions, [RhCl(L2)(HpzR′,R″)] (L2  NBD, 2CO; R′  But, Ph, p-CH3OC6H4 (An), R″  H; R′  But, Ph, R″  CH3; R′  R″  H, CH3), has been obtained. A dynamic behaviour has been observed only in complexes with the less demanding pyrazole ligands, relating with a metallotropic equilibrium when R′  R″  H, Me, or a diolefin reorientation when R′  But, Ph, An, R″  H. The X-ray crystal structure of [RhCl(CO)2(HpzAn)] has been solved, showing a molecular stacking with a RhRh separation of 3.398(3) A along the one-dimensional chain.

Luminescent liquid crystal materials based on unsymmetrical boron difluoride β-diketonate adducts

A strategic design based on the use of asymmetrically 1,3-alkyloxyphenyl substituted β-diketonate ligands towards the BF2 group allowed us to find unsymmetrical compounds that, in addition to a high photoluminescent quantum yield, possess a liquid crystal behaviour, which is related to the presence of the banana-shaped liquid crystal mesophases B1.

Pyridylpyrazole derivatives. A new type of mesogenic bidentate ligands inducing mesomorphism on their related PdX2 complexes

Abstract A new family of 3,5-bis(4-n-alkyloxyphenyl)-1-(pyridin-2-yl)-1H-pyrazole ligands (pypzR2) and their complexes of formula c-[PdCl2(pypzR2)] have been synthesised and their mesomorphism was investigated . The effectiveness of the asymmetric molecular design in promoting thermotropic mesophases is greater for complexes than for the related ligands, although the latter exhibit mesophases at lower temperatures. These complexes are the first example of metallomesogens containing N,N′-bidentate ligands co-ordinated to PdCl2.

Copper Complexes with New Pyridylpyrazole Based Ligands

We report the synthesis, characterization, and crystal structures of new ligands of the pyridinylpyrazole type, i.e., 3,5-bis(4-butoxyphenyl)-1-(pyridin-2-yl)-1H-pyrazole (L1) and 3,5-bis(4-phenoxyphenyl)-1-(pyridin-2-yl)-1H-pyrazole (L2) (Scheme 1), and the study of their coordination behavior towards CuI and CuII. The versatility of this type of ligand, which can give access to different coordination spheres about the metal center, depending on the nature of the copper starting material used in the preparation of the complexes (Scheme 2), is illustrated. Thus, pseudo-tetrahedral CuI as well as six-coordinated tetragonal and distorted tetragonal pyramidal CuII derivatives were obtained for [Cu(L)2]PF6, [Cu(Cl)2(L)2] (L=L1, L2), and [Cu(Cl)(L1)2]PF6, respectively. We also present a crystallographic support of a distorted octahedral cis-bis(tetrafluoroborato-κF)copper(II) compound found for [Cu(BF4)2(L1)2] (3).

Pyrazolium salts as a new class of ionic liquid crystals

New alkyloxyphenyl substituted pyrazolium salts [H2pzR(n)][A] (R(n) = C6H4OCnH2n+1; n = 8, 10, 12, 14, 16, 18; [A] = Cl−, BF4−, ReO4−, SbF6−, CF3SO3−, CH3-p-C6H4SO3−) have been synthesised and characterised. Those containing Cl−, BF4−, ReO4− and SbF6− anions behave as liquid crystal compounds exhibiting smectic A (SmA) mesophases. Because the precursor neutral pyrazoles [HpzR(n)] were not liquid crystals, their protonation and strategic choice of the counter-anion was found useful to achieve mesomorphism and to modulate the transition temperatures, so giving rise to a new class of ionic liquid crystals. The X-ray crystal structures of selected derivatives as representative examples of each type of compound have been resolved. In most of the cases, for X-ray purposes, the salts were designed to contain one methoxyphenyl-substituted pyrazolium cation. Different structural features have been found depending on the nature of the anion. Dimeric units held through hydrogen bonds are arranged in chains which pack in a layer-like array for compounds [H2pzR(10)][BF4], [H2pzR(1)][OTf] and [H2pzR(1)][PTS], but 2D structures were found for [H2pzR(1)][Cl] and [H2pzR(1)][ReO4]. Relationships between the solid and the mesophase structures are proposed. The absence of mesomorphism for CF3SO3− and CH3-p-C6H4SO3− derivatives is also explained on the basis of the main structural features.