Paola Paoli

Thermodynamic and structural aspects of transition metal compounds. Polynuclear complexes of aza-macrocycles

A. Introduction 51 B. Macrocycles and macrobicycles able to incorporate several metal ions 52 C. Bis(macrocycles) 71 D. Bridged macrocyclic metal complexes 73 Acknowledgements 83 References 83

A Macrocyclic Ligand as Receptor and ZnII‐Complex Receptor for Anions in Water: Binding Properties and Crystal Structures

Binding properties of 24,29-dimethyl-6,7,15,16-tetraoxotetracyclo[19.5.5.0(5,8).0(14,17)]-1,4,9,13,18,21,24,29-octaazaenatriaconta-Δ(5,8),Δ(14,17)-diene ligand L towards Zn(II) and anions, such as the halide series and inorganic oxoanions (phosphate (Pi), sulfate, pyrophosphate (PPi), and others), were investigated in aqueous solution; in addition, the Zn(II)/L system was tested as a metal-ion-based receptor for the halide series. Ligand L is a cryptand receptor incorporating two squaramide functions in an over-structured chain that connects two opposite nitrogen atoms of the Me(2)[12]aneN(4) polyaza macrocyclic base. It binds Zn(II) to form mononuclear species in which the metal ion, coordinated by the Me(2)[12]aneN(4) moiety, lodges inside the three-dimensional cavity. Zn(II)-containing species are able to bind chloride and fluoride at the physiologically important pH value of 7.4; the anion is coordinated to the metal center but the squaramide units play the key role in stabilizing the anion through a hydrogen-bonding network; two crystal structures reported here clearly show this aspect. Free L is able to bind fluoride, chloride, bromide, sulfate, Pi, and PPi in aqueous solution. The halides are bound at acidic pH, whereas the oxoanions are bound in a wide range of pH values ranging from acidic to basic. The cryptand cavity, abundant in hydrogen-bonding sites at all pH values, allows excellent selectivity towards Pi to be achieved mainly at physiological pH 7.4. By joining amine and squaramide moieties and using this preorganized topology, it was possible, with preservation of the solubility of the receptor, to achieve a very wide pH range in which oxoanions can be bound. The good selectivity towards Pi allows its discrimination in a manner not easily obtainable with nonmetallic systems in aqueous environment.

Selective recognition of carboxylate anions by polyammonium receptors in aqueous solution. Criteria for selectivity in molecular recognition

The interaction in aqueous solution of the polyammonium receptor 1,4,7,10,13,16,19-heptaazacyclohenicosane (8, [21]aneN7) with the carboxylic species, 1,2-benzenedicarboxylic (1), 1,3-benzenedicarboxylic (2), 1,2,3-benzenetricarboxylic (3), 1,3,5-benzenetricarboxylic (4), cis,cis-1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic (5), cis,trans-1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic (6), and citric (7) acids has been followed by potentiometry and cyclic voltammetry at 298.1 K in 0.15 mol dm–3 NaClO4, as well as by NMR spectroscopy. The analysis of the potentiometric and electrochemical data show the formation of 1:1 adducts. A novel method based on both potentiometry and cyclic voltammetry to establish selectivity patterns in systems presenting different protonation possibilities is introduced. Preorganization of the substrates in a shape complementary to the receptor yields interesting features such as the selective recognition of 5 over its epimer 6 and recognition of the dicarboxylic species 1 and 2 over the tricarboxylic ones 6 and 7.

Efficient fluorescent sensors based on 2,5-diphenyl[1,3,4]oxadiazole: a case of specific response to Zn(II) at physiological pH.

The coordination properties and photochemical responses of three fluorescent polyamine macrocycles, 9,12,15,24,25-pentaaza-26-oxatetracyclo[21.2.1.0(2,7).0(17,22)]hexaicosa-2,4,6,17,19,21,23,25(1)-octaene (L1), 9,12,15,18,27,28-hexaaza-29-oxatetracyclo[24.2.1.0(2,7).0(20,25)]enneicosa-2,4,6,20,22,24,26,28(1)-octaene (L2), and 9,12,15,18,21,30,31-heptaaza-32-oxatetracyclo[27.2.1.0(2,7).0(23,28)]diatriconta-2,4,6,23,25,27,29,31(1)-octaene (L3), toward Cu(II), Zn(II), Cd(II), and Pb(II) are reported. Each ligand contains the 2,5-diphenyl[1,3,4]oxadiazole (PPD) moiety inserted in a polyamine macrocycle skeleton. The stability constants were determined by means of potentiometric measurements in aqueous solution. L1 forms mononuclear complexes only with Cu(II). L2 and L3 form stable mononuclear species with all of the metals, while L3 is able to form dinuclear Cu(II) species. The fluorescence of all ligands was totally quenched by the presence of Cu(II). L2 behaves as an OFF-ON sensor for Zn(II) under physiological conditions, even in the presence of interfering species such as Cd(II) and Pb(II). This ligand combines selective binding of Zn(II) with a highly specific fluorescent response to Zn(II) due to the chelating enhancement of fluorescence (CHEF) effect. The interaction of Zn(II), Cd(II), and Pb(II) with L3 does not produce an appreciable enhancement of fluorescence at the same pH. The different behavior is attributed to the cavity size of the macrocycle and to the number of amine functions. L2 possesses the best arrangement of these two characteristics, allowing a full participation of all of the amine functions in metal coordination, as shown by the crystal structures of [CuL2(ClO(4))](ClO(4))·H(2)O and [ZnL2Br]Br·H(2)O species; this prevents the PET effect and supplies the higher CHEF effect. The interaction between L2 and Zn(II) can also be observed with the naked eye as an intense sky blue emission.

Structure and vibrational spectroscopy of methanesulfonic acid hydrazide: an experimental and theoretical study

A comprehensive study of the molecule of methanesulfonic acid hydrazide (MSH) is presented. The X-ray structure shows that in the crystal two centrosymmetrically oriented MSH molecules are held together by N–H···N hydrogen bonding interactions. This feature is unprecedented for the known arylsulfonic hydrazide analogues. The energetics of the various MSH staggered conformers and the stabilisation due to dimerisation are evaluated by HF abinitio calculations. Moreover, the pathways that interconvert the conformers as well as their enantiomers are outlined. The transition states between conformers correspond to the eclipsed conformation about the S–N linkage while those between enantiomers require planarisation of the N atom bound to sulfur. Some interconversions require two steps and two barriers to be bypassed. The IR and Raman spectra of MSH have been recorded and a normal coordinate analysis (NCA) has been carried out. The assignments have been double-checked through the abinitio calculated frequencies. The latter techniques also allow evaluation of the normal modes of vibration due to interacting MSH monomers, which can be experimentally detected.

Interaction of lead(II) with highly-dentate linear and cyclic polyamines

The interaction of Pb2+ with the macrocyclic amines 1,4,7,10,13,16-hexaazacyclooctadecane (L1), 1,4,7,10,13,16,19-heptaazacyclohenicosane (L2), 1,4,7,10,13,16,19,22-octaazacyclotetracosane (L3), 1,4,7,10,13,16,19,22,25-nonaazacycloheptacosane (L4), 1,4,7,10,13,16,19,22,25,28-decaazacyclotriacontane (L5), 1,4,7,10,13,16,19,22,25,28,31-undecaazacyclotritriacontane (L6) and 1,4,7,10,13,16,19,22,25,28,31,34-dodecaazacyclohexatriacontane (L7) belonging to the [3k]aneNg series and with their related open-chain, terminally methylated polyamines 1,14-bis(methylamino)-3,6,9,12-tetraazatetra-decane (L8), 1,17-bis(methylamino)-3,6,9,12,15-pentaazaheptadecane (L9), 1,20-bis(methylamino)-3,6,9,12,15,18-hexaazaicosane (L10) and 1,23-bis(methylamino)-3,6,9,12,15,18,21-heptaazatricosane (L11) has been studied by potentiometry at 298.1 K in 0.15 mol dm–3 NaClO4. The cyclic amines L1 and L2 form only mononuclear complexes, while L3–L5 can form both mono- and bi-nuclear species. The largest amines of this series L6 and L7 form bi- and tri-nuclear lead(II) complexes. Of the open-chain ligands, L8 forms only mononuclear complexes, while L9–L11 form both mono- and bi-nuclear species. The crystal structure of the solid compound [Pb2L5][ClO4]4 has been solved by X-ray diffraction analysis [space group P21/n, Z= 2, a= 9.052(9), b= 11.400(9), c= 18.689(8)A, β= 94.42(6)°, R= 0.082 and R′= 0.068]. It shows that both Pb2+ ions are tightly co-ordinated to four nitrogens of the macrocycle (Pb–N ranging from 2.27 to 2.71 A). A fifth nitrogen and three oxygens of two perchlorate anions are weakly interacting at much larger distances (Pb–N 3.04; Pb–O 2.98, 3.38, 3.41 A). The complex cation is situated around a crystallographic symmetry centre. The arrangement of the eight atoms around the lead ion is rather asymmetric leaving a zone free from co-ordinated donor atoms which is believed to be occupied by a lone pair of electrons.

A new versatile solvatochromic amino-macrocycle. From metal ions to cell sensing in solution and in the solid state

A new fluorescent NBD-polyaza-macrocycle sensor (L) was synthesized. The coordination of Cu(ii) and Zn(ii) in acetonitrile switches on the fluorescence with different emission wavelengths. Cu(ii) complexes showed solid-state fluorescence. Both L and Cu-complex interact with human cell line (U937) highlighting the cell membrane by fluorescence microscopy.

New branched macrocyclic ligand and its side-arm, two urea-based receptors for anions: synthesis, binding studies and crystal structure

The synthesis and characterization of the two new hosting molecules for anions 4(N),10(N)-bis-[2-(4-nitrophenylureido)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L1) and 1-((diethylcarbamoyl)methyl)-3-(4-nitrophenyl)urea (L2) are reported. L1 is a branched tetraazamacrocycle bearing two p-nitrophenylureido groups as side-arms, whereas L2 has the same linear chain and binding moiety of L1 side-arm. The best synthetic routes for use in obtaining L1 were explored, affording the synthesis of the new intermediate 4, a versatile building block for further functionalized branched macrocyclic hosts. The binding properties of both ligands towards the halides series and acetate anions (G) were investigated by NMR and UV-Vis spectroscopy in a dimethyl sulfoxide–0.5% water solution. Both ligands interact with F−, Cl− and AcO− while Br− and I− did not. The NMR experiments proved that the binding occurs via H-bond to the ureido fragments. Fluoride anion is basic enough to deprotonate the ureido group of both ligands, thus preventing the determination of the addition constants to both ligands; this was instead possible for Cl− and AcO−. L1 forms G–L species of 1 : 1 ([GL1]) and 2 : 1 ([G2L1]) stoichiometry while L2 forms only the 1 : 1 [GL2] species. The higher value of the formation constant of the [AcOL1]−vs. the [AcOL2]− species (log K = 5.5 vs. 2.8 for the reaction AcO− + L = AcOL−) suggested that both side-arms of L1 cooperate in binding acetate; this does not occur with Cl−. The results confirmed that this tetraaza-macrocyclic base acts as a preorganizing scaffold for side-arms when they are linked to it via an amide function. The crystal structure of L2·H2O is also reported.

Di-and tri-palladium(II) polyazacycloalakane complexes. A case of deprotonated secondary nitrogen in solution and in solid state

Crystal structures of di- and tri-nuclear palladium(II) complexes with the azamacrocycles[18]aneN6 and [21]aneN7 have been solved by X-ray analysis; in the case of the trinuclear complex deprotonation of a secondary amino group occurs, both in solution and in the solid state.

CRYSTAL STRUCTURES OF COMPLEXES OF AMMONIUM AND POTASSIUM HEXAFLUOROPHOSPHATE WITH DIBENZO-18-CROWN-6. MOLECULAR MECHANICS STUDIES ON THE UNCOMPLEXED MACROCYCLE

Abstract Crown ether complex formed by the dibenzo-18-crown-6 (DB18C6) macrocycle with ammonium and potassium hexafluorophosphate have been prepared and their crystal structures have been determined by single crystal X-ray analyses. The ammonium compound consists of a 2:1 mixture of NH4 (DB18C6)PF6 and free DB18C6 ligand (compound 1). Crystals are monoclinic, space group P21/c with a=12.638(2), b=13.118(4), c=20.927(9) A , β=106.21(2)°, V=3331(2) A 3 and Z=4 (R=0.0457) . The ammonium cation interacts with the six oxygen atoms of the crown ether and with two fluorine atoms of a PF6− anion. The potassium derivative (compound 2) consists of K(DB18C6)PF6 units. Crystals are monoclinic, space group P2/c, with a=15.744(8), b=7.945(3), c=37.59(2) A , β=94.27(4)° , V=4689(4) A 3 and Z=8 (R=0.0786) . The potassium atoms of the three independent complexes are linked to the six oxygen atoms of the DB18C6 ligand and to fluorine atoms of two PF6− anions. Molecular mechanics calculations were performed on the uncomplexed DB18C6 molecule by using the MM2 force field.