Huub Kooijman

Cyclic bis-urea compounds as gelators for organic solvents

The gelation properties of bis-urea compounds derived from opti- cally pure trans-1,2-diaminocyclohexane and 1,2-diaminobenzene, with pendant aliphatic, aromatic, or ester groups, as well as the structure of the resulting gels, have been studied by differential scan- ning calorimetry, infrared spectroscopy, small-angle X-ray diffraction, and elec- tron microscopy. These compounds have been found to be very potent gelators for organic solvents, such as aliphatic and aromatic hydrocarbons, esters, ke- tones, and alcohols, at concentrations well below 1 (w/v)%. Gelation by these compounds is completely thermorever- sible, with melting temperatures up to 1208C, and many of the gels display thixotropic properties. Even at low con- centrations these compounds self-as- semble into elongated and very thin fibers, which in turn form a three-dimen- sional network in the solvent. Infrared studies showed that aggregation is ac- companied by the formation of a hydro- gen-bonded network between urea moi- eties, and a single-crystal X-ray structure of one of the compounds showed that in crystals the molecules assemble into one-dimensional chains, which are sta- bilized by the formation of eight hydro- gen bonds between the urea groups and adjacent molecules. The molecular ar- rangement in gels is most likely very similar to that in the crystal, but the complete elucidation of the molecular arrangement in gels is complicated be- cause aggregation of these compounds is prone to polymorphism. It is concluded that the very efficient aggregation of these molecules and the elongated shape of the fibers most likely arise from the highly anisotropic hydrogen-bonding properties of these molecules, which is due to the presence of two coplanar oriented urea moieties in a single mol- ecule. Since the bis-urea compounds presented in this paper are very easy to synthesize and many structural varia- tions are possible without loss of the gelation ability, they are excellent build- ing blocks for the construction of func- tional gels.

Self‐Complementarity Achieved through Quadruple Hydrogen Bonding

Highly stable dimers are formed in solution and in the solid state by a class of readily synthesized, self-complementary building blocks for supramolecular chemistry, which associate through a donor-acceptor-donor-acceptor array of four hydrogen-bonding sites. An additional intramolecular hydrogen bond in the compound whose crystal structure is shown on the right preorganizes the molecule for dimerization.

Structure-dependent in vitro cytotoxicity of the isomeric complexes [Ru(L)2Cl2] (L=o-tolylazopyridine and 4-methyl-2-phenylazopyridine) in comparison to [Ru(azpy)2Cl2]

The dichlorobis(2-phenylazopyridine)ruthenium(II) complexes, [Ru(azpy)2Cl2], are under renewed investigation due to their potential anticancer activity. The three most common isomers α-, β- and γ-[RuL2Cl2] with L=o-tolylazopyridine (tazpy) and 4-methyl-2-phenylazopyridine (mazpy) (α indicating the coordinating Cl, N(pyridine) and Nazo atoms in mutual cis, trans, cis positions, β indicating the coordinating Cl, N(pyridine) and Nazo atoms in mutual cis, cis, cis positions, and γ indicating the coordinating Cl, N(pyridine) and Nazo atoms in mutual trans, cis, cis positions) are synthesized and characterized by NMR spectroscopy. The molecular structures of γ-[Ru(tazpy)2Cl2] and α-[Ru(mazpy)2Cl2] are determined by X-ray diffraction analysis. The IC50 values of the geometrically isomeric [Ru(tazpy)2Cl2] and [Ru(mazpy)2Cl2] complexes compared with those of the parent [Ru(azpy)2Cl2] complexes are determined in a series of human tumour cell lines (MCF-7, EVSA-T, WIDR, IGROV, M19, A498 and H266). These data unambiguously show for all complexes the following trend: the α isomer shows a very high cytotoxicity, whereas the β isomer is a factor 10 less cytotoxic. The γ isomers of [Ru(tazpy)2Cl2] and [Ru(mazpy)2Cl2] display a very high cytotoxicity comparable to that of the γ isomer of the parent compound [Ru(azpy)2Cl2] and to that of the α isomer. These biological data are of the utmost importance for a better understanding of the structure–activity relationships for the isomeric [RuL2Cl2] complexes.

catena-[μ-Tris(1,2-bis(tetrazol-1-yl)ethane-N4,N4′)iron(II)] bis(tetrafluoroborate): synthesis, structure, spectroscopic and magnetic characterization of a chain-type coordination polymer spin-crossover compound

In analogy to a common synthesis of 1-substituted 5-H tetrazoles (Tetrahedron Lett. 36 (1995)1759; Beloruss. Gos. Univ., Minsk, USSR. Khim. Geterotsikl. Soedin. 11 (1985) 1521; Beloruss. Gos. Univ., Minsk, USSR. Khim. Geterotsikl. Soedin. 1 (1991) 66; BGU, Belarus. Vestsi Akad. Navuk Belarusi, Ser. Khim. Navuk 1 (1992) 73), the new bidentate ligand 1,2-bis(tetrazol-1-yl)ethane [endi] was synthesized and characterized by X-ray diffraction, NMR, IR and UV–Vis spectroscopy. By using iron(II) tetrafluoroborate hexahydrate the complexation with this ligand yields a 1-dimensional linear coordination polymer similar to the recently published chain compound (Inorg. Chem. 39 (2000) 1891) exhibiting a thermally induced spin-crossover phenomenon. Similar to the 1,2-bis(tetrazol-1-yl)propane-bridged compound, our 1,2-bis(tetrazol-1-yl)ethane-bridged compound shows a gradual spin transition, but the spin-crossover temperature T1/2≈140 K is found to be 10 K above the other T1/2. The T1/2 was determined by temperature-dependent 57Fe-Mossbauer, far FT-IR and UV–Vis spectroscopy as well as by temperature-dependent magnetic susceptibility measurements. Single crystals of the complex were grown in situ from a solution of the ligand and iron(II) tetrafluoroborate. The X-ray structure determinations of both the high spin as well as the low spin state of the compound revealed a solid state structure, which is comparable to that of catena-[Fe(1,2-bis(tetrazole-1-yl)propane)3](ClO4)2 (Inorg. Chem. 39 (2000) 1891; 2nd TMR-TOSS Meeting, 4th Spin Crossover Family Meeting, Lufthansa Training Center, Seeheim/Germany, April 30–May 2, 1999). Both the 1,2-bis(tetrazol-1-yl)propane-bridged and our compound do not show a thermal hysteresis effect (J. Am. Chem. Soc. 115 (1993) 9810; Inorg. Chim. Acta 37 (1979) 169; Chem. Phys. Lett. 93 (1982) 567). The synthesis of the complex described in the experimental section yielded a fine powdered product being poorly soluble in most common solvents. The single crystal measurements were done with crystals obtained by various diffusion methods. Most of them yielded either thin needles or small hexagonal prism crystals depending on the specific conditions.

Increase in coordination number of lanthanide complexes with 2,2′-bipyridine and 1,10-phenanthroline by using β-diketonates with electron-withdrawing groups

Abstract The coordination chemistry of Ln(hfpd)3 (hfpd=1,1,1,5,5,5-hexafluoropentane-2,4-dionate) with phen and bpy depends on the size of the Ln3+ ion and on the used solvent. The complexes [Er(hfpd)3(phen)] (7) and [Er(hfpd)3(bpy)] (14) were obtained from the synthesis of Er(CF3SO3)3 with Hhfpd, CsOH and either 1,10-phenanthroline or 2,2′-bipyridine in acetonitrile. The structure of 7 was determined by X-ray crystallography. Similar reactions, but performed in methanol, with various other lanthanide elements resulted in isolation of five different types of complexes, according to stoichiometry and spectral properties. With elements later in the lanthanide series eight-coordinated complexes of the types [Ln(hfpd)3(bpy)] (for Ln=Dy, Ho and Yb) and [Ln(hfpd)3(phen)] (for Ln=Tb, Ho and Yb), like 7, were obtained, whereas with the early lanthanide elements ten-coordinated complexes of the types [Ln(hfpd)3(bpy)2] (for Ln=La and Sm) and [Ln(hfpd)3(phen)2] (for Ln=La, Ce, Pr and Nd) were isolated. The X-ray crystal structure of [La(hfpd)3(bpy)2] (9) was determined, which provided proof for ten-coordination around the La ion. In addition to [Sm(hfpd)3(bpy)2], the synthesis with Sm and bpy and a trace of water yielded a second compound: the nine-coordinated complex [Sm(hfpd)3(H2O)(bpy)]·(bpy) (11), which was structurally characterised by X-ray crystallography. The LnN distances vary largely, depending on the used N-donor and the Ln3+ ion, and do not run parallel with the Ln3+ ionic radius.

The binding mode of the ambidentate ligand dicyanamide to transition metal ions can be tuned by bisimidazoline ligands with H-bonding donor property at the rear side of the ligand

The synthesis and crystal structures, as well as the electronic and magnetic properties, of four new compounds containing the ligands 2,2′-biimidazoline (biz) and dicyanamide (dca) with the general formula M(II)(biz)x(dca)2 (where M = Cu(II), Co(II), Ni(II) and x = 1,2) are reported. In the compound Cu(biz)(dca)2(1), the equatorial plane around the Cu(II) atom is formed by two nitrogen atoms of one biz ligand and two nitrile atoms of two dca molecules. The dca anions are connected to a neighbouring Cu atom, with the central amide nitrogen acting as the axial atom, forming in this way a 2D polymeric sheet. The compounds Cu(biz)2(dca)2 (2) and Co(biz)2(dca)2 (3), which are isostructural, contain octahedral metal ions with the basal plane occupied by four nitrogen atoms of two biz ligands and the axial positions formed by two amide nitrogen atoms of monodentate dca ligands. The compound Ni(biz)2(dca)2 (4), differs from 2 and 3, as in this case the axial positions are occupied by the nitrile nitrogen atoms of a monodentate dca ligand. The main difference between the Co and the Cu compounds is the axial M–N bond, which in the case of Cu is elongated to 2.60 A, due to the Jahn–Teller effect. The coordination of the metal atom via the amide nitrogen atoms of dca has so far rarely been observed. All four compounds also show quite different hydrogen bonding systems via the N–H groups of the biz ligands and the nitrile nitrogen atoms of the dca molecules, forming interesting 3D and 2D polymeric and sheet-like arrays. The infrared absorptions of the compounds, as well as the electronic and EPR absorptions, are in good agreement with the crystal structures obtained. Magnetic susceptibility measurements revealed that no significant (J > −1 cm−1) interactions are present between the metal atoms, as was expected, since no serious overlap of the magnetic metal orbitals takes place via the dca ligands.

Counterion Effect on the Spin-Transition Properties of the Cation [Fe(btzx)3]2+ (btzx = m-Xylylenebis(tetrazole))

The influence of the counteranion on the structure and the spin-transition properties of original 1D bis(tetrazole) Fe(II) systems, namely [Fe(btzx)(3)]X(2) (X=PF(6) (-) (1), CF(3)SO(3) (-) (2) and ClO(4) (-) (3); btzx=m-xylylenebis(tetrazole)) is studied. The X-ray crystal structures of compounds 1 and 2 are described in detail. These structures present a solvent molecule encapsulated within pockets formed by btzx ligands along the 1D coordination chains. Compound 2 is shown to be the first structurally characterised alternating HS-LS 1D spin-transition system (HS=high spin, LS=low spin). The magnetic susceptibility measurements of all three compounds are compared. The degree of completion and the transition temperature are both drastically influenced by the counterion used, while surprisingly, the cooperative nature of the transition is not affected by the choice of counterion. Compounds 1 and 2 are further studied by Mössbauer spectroscopy and their distinct LIESST properties are compared.

Tripodal tris-urea derivatives as gelators for organic solvents

Several new tripodal tris-urea derivatives are prepared and found to be efficient gelling agents for organic solvents. The structure and thermotropic properties of the gels are studied by electron microscopy, differential scanning calorimetry (DSC) and FT-IR spectroscopy. Remarkably, the range of solvents to be gelled can be tuned by the peripheral substituents.

Characterization of poly(l-lactic acid) microspheres loaded with holmium acetylacetonate

Holmium-loaded PLLA microspheres are useful systems in radioembolization therapy of liver metastases because of their low density, biodegradability and favourable radiation characteristics. Neutron activated Ho-loaded microspheres showed a surprisingly low release of the relatively small holmium complex. In this paper factors responsible for this behaviour are investigated, in particular by the use of differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy and X-ray diffraction. The holmium complex is soluble in PLLA up to 8% in films and 17% in microspheres. Interactions between carbonyl groups of PLLA, and the Ho-ion in the HoAcAc complex, explain very satisfactorily the high stability of holmium-loaded microspheres.

Methyl-, acetyl- and allyl-palladium and -platinum complexes containing the novel chiral phosphorus-imine 2-(diphenylphosphino)-benzylidene-S(-)-a-methyl-benzylamine ligand

Neutral compounds of the type [MX2(L) ] and [MX(Me) (L) ] and ionic complexes of the type [M(Me) (L) ] (O3SCF3), in which X = C1, Br, I; M =Pd, Pt; L = 2- (diphenylphosphino) -benzylidene-S( - ) -a-methyl-henzylamine, have been prepared and characterized. Singiecrystal X-ray determinations of [ PdCl2 (L) ] (la) and [ Ptl2(L) ] (3b) showed, in both cases, a chelate coordination of the PN ligand thereby forming a six-membered ring. The square planar surrounding is completed by the two halide atoms. The single crystal X-ray determination of [ PdCI(Me)CI(L) ] (4a) shows an analogous geometry with a chelating PN ligand, a chloride atom and a methyl group, which is positioned cis to the phosphorus atom, completes the square planar surrounding. The methylpalladium and -platinum complexes reacted with CO to give the corresponding acetyl complexes. The insertion rates increased in the order C! <Br <O3SCF 3- while the re~tiou is first order in metal complex and first order in CO concentration. Complexes [ Pd(r/3-allyl) (PN) ] + Y- (Y = CI, O3SCF3) with symmetric allyl groups 2-RC3H5 (R = Me, C(O)Me), 2-MeC3Me4 and asymmetrically substituted allyi groups 2-R-C3HzM% (R ~ H, Me) have been prepared. Temperature dependent ~H, 3tp{ tH} and 13C{ tH} NMR has been used to determine the influence of the chiral ligand on the structural aspects and dynamic features. It is shown that a delicate balance between counteracting steric and electronic factors determines the type of isomer, i.e. with the P atom cis or trans to the CMe2 moiety of the asymmetric allyl group.