Reactivity of palladium(II) methyl complexes towards CO2: formation of carbonate complexes

Treatment of a benzene solution of (tmeda)PdMe₂ or (dppe)PdMe₂ with carbon dioxide gives the corresponding methyl bicarbonate complex, (L-L)PdMe(O₂COH). These were characterised by NMR spectroscopy and elemental analysis. Under strictly dry conditions no reaction was observed. Recrystallisation of the tmeda bicarbonate complex from acetone yields the corresponding η²-carbonate complex, which was characterised by X-ray crystallography. The reaction probably proceeds through attack by free carbonic acid on the dimethyl complex.     

Synthesis and characterisation of palladium(II) and platinum(II) compounds containing pyrazole-derived ligands: crystal structure of [PdCl2(HL)] (HL = 3-phenyl-5-(2-pyridyl)pyrazole)

Reaction of the ligands 3-phenyl-5-(2-pyridyl)pyrazole (HL¹), 3,5-bis(2-pyridyl)pyrazole (HL²), 3-methyl-5-(2-pyridyl)pyrazole (HL³) and 3-methyl-5-phenylpyrazole (HL⁴) with [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) or [PdCl₂(cod)] gives complexes with stoichiometry [PdCl₂(HL)₂] (HL = HL¹, HL², HL³), [Pt(L)₂] (L = L¹, L², L³) and [MCl₂(HL⁴)₂] (M = Pd(II), Pt(II)). The new complexes were characterised by elemental analyses, conductivity measurements, infrared and ¹H NMR spectroscopies. The crystal and molecular structure of [PdCl₂(HL¹)] was resolved by X-ray diffraction, and consists of monomeric cis-[PdCl₂(HL¹)] molecules. The palladium centre has a typical square planar geometry, with a slight tetrahedral distortion. The tetra-coordinated metal atom is bonded to one pyridine nitrogen, one pyrazolic nitrogen and two chloro ligands in a cis disposition. The ligand HL¹ is not completely planar.     

N,N,N′,N′-Tetramethylethylendiamine adducts of amido calcium bases - Synthesis of monomeric [(tmeda)Ca{N(SiMe3)2}2], [(tmeda)Ca{NiPr2}2], and dimeric Hauser base-type [(tmeda)Ca(tmp)(μ-I)]2 (tmp = 2,2,6,6-tetramethylpiperidide)

The metathetical reaction of calcium diiodide with KNR₂ in the presence of N,N,N′,N′-tetramethylethylendiamine yields the corresponding amido calcium bases [(tmeda)Ca(tmp)₂] (1), [(tmeda)Ca{N(SiMe₃)₂}₂] (3), and [(tmeda)Ca(NiPr₂)₂] (4) regardless of the stoichiometric ratio of the starting compounds. All compounds are highly air and moisture sensitive. Only in the case of NR₂ being a tmp group very few crystals of the Hauser base-type dimeric derivative [(tmeda)Ca(tmp)(μ-I)]₂ (2) with bridging iodide ions can be isolated. In all these calcium complexes the amides are bound terminally and contain planarily coordinated nitrogen atoms. The calcium complex [(tmeda)Ca(NiPr₂)₂] (4) is much more reactive than the lighter magnesium congener and therefore, it has to be stored below 0 °C in order to avoid decomposition reactions.     

The auration of 2-hydroxy-pyridine (2-pyridone): preparative and structural studies and a comparison with reactions of related aliphatic O,N-donors

In a study of the isolobal analogy between the proton H⁺ and the ligand-backed gold(I) cations [(R₃P)Au]⁺, the reaction of the mixture of 2-pyridone/2-hydroxy-pyridine tautomers with [(Ph₃P)Au]BF₄ has been investigated. It affords the 1:1 complex with the gold atom N-bonded to the 2-hydroxy-pyridine tautomer: {(Ph₃P)Au[NC₅H₄-(OH-2)]}⁺BF₄ ⁻, which is related to known salts with the 2-hydroxy-pyridinium cation such as [HNC₅H₄(OH-2)]⁺Cl⁻. The structure was derived from analytical and spectroscopic data and from a comparison with the salt [(Ph₃P)Au(pyr)]BF₄, prepared and investigated structurally as a reference compound. An analogue was also prepared with 2-dimethylamino-ethanol as a substrate, which also affords the N-bonded complex [(Ph₃P)Au([Me₂NCH₂CH₂OH)]⁺BF₄ ⁻, the structure of which has been determined. The OH group is not attached to the gold atom but engaged in hydrogen bonding with the counterion. By contrast, in the complex [(Ph₃P)Au(Me₂NCH₂CH₂NMe₂)]⁺BF₄ ⁻ synthesized similarly with tmeda and crystallized as the dichloromethane solvate, one nitrogen atom is bonded firmly to the metal atom, but the second nitrogen atom is also weakly engaged in coordinative bonding. The compound is fluxional in solution, where a site exchange is observed which is rapid on the NMR time scale. The reaction of two equivalents of [(Ph₃P)Au]BF₄ with an alkali 2-pyridinolate, prepared from the above tautomeric mixture and sodium metal or a potassium alkoxide, yields the diaurated product {N,O-[(Ph₃P)Au]₂(NC₅H₄-O-2)}BF₄. In the crystal structure determination of a sesqui-solvate with dichloromethane it has been shown that one gold atom is attached solely to the nitrogen atom and the other solely to the oxygen atom. The dinuclear cations are associated into cyclic dimers through head-to-tail aurophilic bonding. From the geometrical characteristics of the core unit of the cations the ligand can be assigned a 2-pyridinolate form featuring pyridine and phenolate donor sites.     

Cyanoscorpionates: Co(II), Mn(II), and Ni(II) complexes coordinated only through the cyano group

New complexes have been synthesized of scorpionate ligands with cyano substituents in the 4-positions of the pyrazoles and tert-butyl substituents in the 3-positions of the pyrazoles. Reaction of Co²⁺, Mn²⁺, and Ni(cyclam)²⁺ (cyclam = 1,4,8,11-tetraazacyclotetradecane) with Tp^t-Bu,4CN in a 1:2 ratio produced new octahedral metal complexes of the form (Tp^t-Bu,4CN)₂ML₄ (L₄ = (H₂O)₄, (H₂O)₂(MeOH)₂, or cyclam). Unlike the sandwich complexes previously isolated with Tp^Ph,4CN, the crystal structures showed none of the pyrazole nitrogen atoms coordinated to the metal. Rather, the metal is coordinated to one CN nitrogen atom from each ligand, with two Tp anions coordinated trans to each other around the metal center. This leaves the Tp pyrazole nitrogen atoms open for another metal to coordinate, which could to lead to heterometallic complexes, new coordination polymers, as well as the framework for supramolecular complexes.     

Interaction of [RuCl2(PR3)3] (R = Ph, p-tolyl) with some Rh(III), Ir(III) and Pt(IV) tertiary phosphine complexes

Reactions of RuCl₂(PR₃)₃ [PR₃ = PPh₃ or P(p-tolyl)₃ with several monomeric phosphine complexes of rhodium(III), iridium(III) and platinum(IV) have been studied. The reactions with mer-MCl₃(P′R₃)₃ (M = Rh, P′R₃ = PEt₂Ph, PMe₂Ph, PMe₂Ph; M = Ir, P′R₃ = PBuPh₂, PMePh₂, PEt₂Ph) involves a phosphine ligand transfer between metal atoms to afford novel dark coloured heterobimetallic complexes containing a triple chloro-bridge. The reactions of RuCl₂(PR₃)₃ with PtCl₄(P′R₃)₂ (P′R₃ = PEt₂Ph, PBu₂Ph), however, do not give evidence for the formation of dinuclear complexes containing the (RuCl₃Pt) unit, but a reduction of Pt^IV to Pt^II occurs with transfer of phosphine ligands between the two metals. The formulation of these complexes has been established by ³¹P NMR spectroscopy.     

Synthesis and characterization of Ru(II) and Ru(III) complexes of diphenylphosphinoacetic acid and their interaction with small molecules

Complexes of Ru(II) and Ru(III) with the bidentate ligand diphenylphosphinoacetic acid (POH) are reported. The ligand POH reacts with RuCl₂(PPh₃)₃ in a 1:3 ratio to give a five-coordinate complex of composition Ru(PO)₂(POH) with complete displacement of PPh₃. In a 1:2 ratio however the complex Ru(PO)₂(PPh₃) is formed. The reaction of POH with RuCl₂(DMSO)₄ in a 2:1 ratio afforded a yellow complex of composition HRu(PO)₂Cl(DMSO). In a 3:1 ratio of POH to RuCl₂(DMSO)₄ however, the complex HRu(PO)₃ was obtained. Neutral complexes of the composition Ru(PO)₂Cl(AsPh₃) and Ru(PO)₃ were obtained by the reaction of RuCl₃(AsPh₃)₂·MeOH with POH in 1:2 and 1:3 mole ratios in acetone solution, respectively. A dimeric chloro bridged complex of composition [Ru(PO)₂Cl]₂ was obtained on reaction of RuCl₃3H₂O with POH in methanol. The complexes have been characterized on the basis of elemental analysis ¹H, ¹³C{¹H} and ³¹P{¹H} NMR, EPR and electrochemical studies.The square pyramidal complexes 1 and 2 undergo facile addition reactions with CO, H₂, PPh₃ and DMSO to form octahedral species. The redox potentials Ru^III/Ru^II of the complexes become more positive with an increase in the π-acidity of the ligand coordinated to the metal ion.     

New Nanomedicine Approaches Using Gold-thioguanine Nanoconjugates as Metallo-ligands

Reactions of [MCl₂(tmeda)] (M = Cd or Hg; tmeda = N,N,N′,N′-tetramethylethylenediamine) with M′SeC₅H₃(R-3)N (R = H or Me) gave selenolate complexes of the general formula [M{SeC₅H₃(R-3)N}₂(tmeda)_n] (M/R/n = Cd/H/1 (1); Cd/Me/1 (2); Hg/H/1 (3) and Hg/Me/0 (4)). The complexes were characterized by elemental analysis, UV-Vis and NMR (¹H, ¹³C, ⁷⁷Se, ¹¹³Cd and ¹⁹⁹Hg) spectroscopy. The crystal structures of {SeC₅H₃(Me-3)N}₂, [M(SeC₅H₄N)₂(tmeda)] (M = Cd or Hg) and [Hg{SeC₅H₃(Me-3)N}₂] were established by single crystal X-ray diffraction. The complex, [Cd(SeC₅H₄N)₂(tmeda)] comprises of an octahedral cadmium atom containing three chelating, two SeC₅H₄N and one tmeda, ligands. The corresponding mercury complex adopts a severely distorted tetrahedral configuration defined by the two-monodentate selenolate and chelating tmeda. The complex, [Hg{SeC₅H₃(Me-3)N}₂] has a linear structure with monodentate selenolate ligand. The cadmium complexes undergo a two-step decomposition (TGA) leading to the formation of CdSe. Thermolysis of [Cd{SeC₅H₃(R-3)N}₂(tmeda)_n] in hexadecylamine (HDA)/tri-n-octylphosphineoxide (TOPO) yields CdSe nanoparticles, which were characterized by UV-Vis, XRD, SEM and TEM (in part).     

Synthesis of ruthenium(II) monosubstituted squarates: 1. Procedural considerations

Attempted syntheses of ruthenium(II) monosubstituted squarate complexes in acetonitrile using cis-[RuCl₂(dmso)₄] and anisole-, methoxy-, methyl- and diphenylamino-squarate ligands, respectively, resulted in the formation in each case of the monomer cis, fac-Ru(CH₃CN)Cl₂(dmso)₃ (1) with the ruthenium atom in a distorted octahedral environment. A second crop of crystals harvested from the reaction with the methoxysquarate ligand was identified as the oxalato-bridged dimer [{cis-(CH₃CN)(Cl)(dmso)₂Ru}₂(μ-C₂O₄)] (2). When cis-[RuCl₂(dmso)₄] and methylsquarate were reacted in aqueous solution instead of acetonitrile, the dimer [{fac-(Cl)(dmso)₃Ru}₂(μ-C₂O₄)] (3) was produced. The dimers 2 and 3 are formed from oxidation/ring opening of the methoxy- and methyl-squarate ligands, respectively. Use of the salts of these ligands instead of their non-ionised forms under different reaction conditions, afforded [Na] fac-[RuCl₃(dmso)₃] (4) and [(C₄H₉)₄N]₂[(C₄O₄)(C₄H₂O₄)₂] (7), respectively, which were shown to be products of competing reactions. The information acquired from these failed attempts has provided the basis for the development of a strategy to overcome these problems and lead to a successful synthetic route to ruthenium(II) monosubstituted squarates.     

New arene ruthenium complexes with planar chirality

1,2,4-Trimethyl-cyclohexadiene reacts with RuCl₃ · nH₂O in refluxing ethanol to afford quantitatively [RuCl₂(1,2,4-C₆H₃Me₃)]₂ (1), the coordination of 1,2,4-trimethylbenzene to the ruthenium atom introducing planar chirality at the η⁶-arene ligand. The dinuclear complex 1 reacts with two equivalents of triphenylphosphine (PPh₃) to give quantitatively, as a racemic mixture of enantiomers, [RuCl₂(1,2,4-C₆H₃Me₃)(PPh₃)] (2), the structure of which has been determined by a single-crystal X-ray structure analysis of (rac)-2. Similarly, 1 reacts with two equivalents of the enantiopure phosphine (1S,2S,5R)-(+)-neomenthyldiphenylphosphine (nmdpp) to afford in good yield [RuCl₂(1,2,4-C₆H₃Me₃)(nmdpp)] (3) as a mixture of diastereoisomers, from which the isomer 3a was isolated by crystallisation. A single-crystal X-ray structure analysis of 3a allowed the determination of the absolute configuration at the planar chiral η⁶-arene moiety. Finally, complex 1 reacts with one equivalent of the diphosphine ligand 1,1^′-bis(diphenylphosphino)ferrocene (dppfc) to give the heteronuclear complex [RuCl₂(1,2,4-C₆H₃Me₃) (dppfc)RuCl₂(1,2,4-C₆H₃Me₃)] (4). All complexes were fully characterised by elemental analysis, mass spectrometry, NMR and IR spectroscopies.     

Preliminary chemico-biological studies on Ru(III) compounds with S-methyl pyrrolidine/dimethyl dithiocarbamate

[RuCl₃ · nH₂O] and Na(trans-[RuCl₄(DMSO)₂]) were reacted with 1-pyrrolidinedithiocarbamate (PDT), its S-methyl ester (PDTM), and N,N-dimethylcarbamodithioic acid methyl ester (DMDTM) in water or methanol in order to obtain the corresponding Ru(III) derivatives. Once isolated and purified, the complexes were characterized by means of elemental analysis, conductivity measurements, FT-IR and ¹H NMR spectroscopy, ion electrospray mass spectrometry (ESI-MS), and thermal analyses. The crystal structure of mer-[Ru(DMDTM)(DMSO)Cl₃] has been also determined by X-ray crystallography. In vitro cytotoxic activity of all the synthesized complexes was eventually evaluated on some selected human tumor cell lines.     

Substitution of chloride by nitrosyl ligand in a scorpionate ruthenium(III) compound: A theoretical study

A theoretical study of the ruthenium(III) complex [RuCl₂(pz₂CHSO₃)(en)] and of its nitrosyl-substituted product [Ru(NO)Cl(pz₂CHSO₃)(en)]⁺ is presented, based on density functional calculations. Several isomers of each compound differing in the position of the anionic tail of a bis(3,4-dimethyl-1-yl)methanesulfonate scorpionate ligand, pz₂CHSO₃⁻, relative to the monodentate ligands have been optimized. A two-step mechanism is proposed for the ligand substitution reaction that is consistent with the computational results and the weak coordination of the sulfonate group.     

Effect of pyrazole-substitution on the structure and nuclearity of Cu(II)-pyrazolato complexes

Trinuclear Cu(II)-pyrazolates of the general formula (Bu₄N)₂[Cu₃(μ₃-Cl)₂(μ-4-R-pz)₃Cl₃] (pz=pyrazolato anion, R=Cl, Br, I, Me), 1-4, have been prepared and characterized by X-ray diffraction and/or ¹H NMR, IR, UV-Vis spectroscopy and elemental analysis. Their structure and spectroscopic properties match the ones of the parent unsubstituted complex (Bu₄N)₂[Cu₃(μ₃-Cl)₂(μ-pz)₃Cl₃], indicating that 4-substitution of the pyrazole ligands with halogen or methyl groups does not induce structural variation. In contrast, dinuclear complexes (Bu₄N)₄[Cu₂(μ-3-Me-pz)₂Cl₄]Cl₂ · 4H₂O, Cu₂(μ-Cl)(μ-3,5-Me₂-pz)(3,5-Me₂-pzH)₄Cl₂, Cu₂(μ-Cl)(μ-OH)(3-Me-5-Ph-pzH)₄Cl₂ · 3-Me-5-Ph-pzH and Cu₂(μ-Cl)₂(3,5-Ph₂-pzH)₄Cl₂, 5-8, have been prepared with 3- and 3,5-substituted pyrazoles by the same or similar synthetic protocols.     

Synthesis and structural analysis of calix[4]arene-supported iron(III) complexes

The paper describes the reactivity of calix[4]arene dialkyl- or -silylethers H₂R₂calix, R=Me (1), Bz (2), or SiMe₃ (3) (p-tert.butyl-calix[4]arene=H₄calix), towards the iron(III) complex [FeCl(NSiMe₃)₂(thf)] 4. Bis(silylation) of H₄calix was achieved using a mixture of NEt₃ and Me₃SiCl as silylating agent, which is probably the most convenient and cheapest way for the preparation of H₂(Me₃Si)₂calix 3. [FeCl(N{SiMe₃}₂)₂(thf)] 4 has been obtained from the reaction of [FeCl₃] and commercially available K[N(SiMe₃)₂] in THF. The reactions of 4 with H₂Me₂calix and H₂Bz₂calix afford mononuclear iron(III) chloro compounds [FeCl(R₂calix)] 5 (R=Me) and 6 (R=Bz). The usage of calix[4]arene silyl ether 3 leads to a dinuclear complex [Fe₂({Me₃Si}calix)₂] 7, presumably under Me₃SiCl cleavage of a mononuclear calixarene iron(III) chloro complex. The calix[4]arene ether stabilized iron(III) chloro complexes are susceptible to nucleophilic substitution reactions, as exemplified by the reaction of 5 with sodium azide yielding an azido complex [Fe(N₃)(Me₂calix)] 8. The molecular structures of 4, 5, 6, 7, and 8 in the solid state have been determined by X-ray diffraction.     

The unexpected reactions of [RuCl3(2mqn)NO] (H2mqn=2-methyl-8-quinolinol) with 2-chloro-8-quinolinol (H2cqn) and of [RuCl(2cqn)(2mqn)NO] on photoirradiation

The reaction of [RuCl₃(2mqn)NO]⁻ (H2mqn=2-methyl-8-quinolinol) with 2-chloro-8-quinolinol (H2cqn) afforded cis-1 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2cqn is trans to the NO) (complex 1), cis-1 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2mqn is trans to the NO) (complex 2) and a 1:1 mixture of cis-2 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2mqn is trans to the NO) and cis-2 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2cqn is trans to the NO) (complex 3). The reaction was compared with that of [RuCl₃(2mqn)NO]⁻ with 8-quinolinol (Hqn) or 5-chloro-8-quinolinol (H5cqn). Photoirradiation reaction of complex 1 at room temperature in deaerated CH₂Cl₂ in the presence of NO gave trans-[RuCl(2cqn)(2mqn)NO] (the Cl is trans to the NO) and complex 2 with recovery of complex 1. The reaction was contrasted with that of cis-1 [RuCl(qn)(2mqn)NO] or cis-1 [RuCl(5cqn)(2mqn)NO]. The crystal structure of complex 1 was determined by X-ray diffraction. The reactions were examined under consideration of atomic charge of the phenolato oxygen in 8-quinolinol and its derivatives calculated at the restricted Hartree-Fock/6-311G** level.     

Heteropolymetallic complexes containing 1,1′-diphenylphosphino-ferrocene

The paper explores the capability of [(dppf)Pt(H-nbu₂-DTO)]Cl (2) (dppf = 1,1′-diphenylphosphinoferrocene; H-nbu₂-DTO = di-nbutyl-dithioxamidate) to act as a starting module for heterometallic linear chains. Actually, the reaction of 2 with [RuCl₂(p-cymene)]₂ affords the heterotrimetallic complex [Cl(p-cymene) Ru(μ-nbu₂-DTO κ-N,N Ru κ-S,S Pt)Pt(dppf κ-P,P Pt) ]₂ (4). However 2, allowed to stand, provides a blue compound of formula [(dppf)Pt(H-nbu₂-DTO)]_nCl_n (3), the most reliable value of n being 6. The oxidation behavior of the new species 2-4 has also been investigated. In particular, the oxidation behavior of cyclic compound 3 is quite unusual, and suggests a large delocalization of the HOMO over the whole multicomponent molecule.     

Synthesis and characterisation of new N1-alkyl-3,5-dipyridylpyrazole derived ligands. Study of their reactivity with Pd(II) and Pt(II)

Two new pyrazole-derived ligands, 1-ethyl-3,5-bis(2-pyridyl)pyrazole (L¹) and 1-octyl-3,5-bis(2-pyridyl)pyrazole (L²), both containing alkyl groups at position 1 were prepared by reaction between 3,5-bis(2-pyridyl) pyrazole and the appropriate bromoalkane in toluene using sodium ethoxide as base.The reaction between L¹, L² and [MCl₂(CH₃CN)₂] (M = Pd(II), Pt(II)) resulted in the formation complexes of formula [MCl₂(L)] (M = Pd(II), L = L¹ (1); M = Pd(II), L = L² (2); M = Pt(II), L = L¹ (3); M = Pt(II), L = L² (4)). These complexes were characterised by elemental analyses, conductivity measurements, infrared, ¹H, ¹³C{¹H} NMR and HMQC spectroscopies. The X-ray structure of the complex [PtCl₂(L²)] (4) was determined. In this complex, Npyridine and Npyrazole donor atoms coordinate the ligand to the metal, which complete its coordination with two chloro ligands in a cis disposition.     

Intramolecular and intermolecular C-H activation at a cationic Pt center

Syntheses and C-H bond activation reactions of the novel electrophilic Pt^II complexes [(tmeda)Pt(CH₃)(OEt₂)][BAr₁], [(tmeda)Pt(CH₃)(THF)][BAr_f], and [(tmeda)Pt(CH₃)(NC₅F₅)][BAr_f] are described {[BAr_f]⁻ = [(3,5-C₆H₃(CF₃)₂)₄B]⁻} (tmeda is N,N,N′,N′-tetramethylethylenediamine), [(tmeda)Pt(CH₃)(OEt₂)][BAr_f] and [(tmeda)Pt(CH₃)(THF)][BAr_f] are unstable at room temperature, yielding methane and the Fischer carbene Pt^II hydrides, [(tmeda)Pt(=C(CH₃)(OCH₂CH₃))(H)][BAr_f] and . The methane liberated from [(tmeda)Pt(CH₃)(OEt₂-d₁₀)][BAr_f] consists of an isotopomeric mixture, (CH₄, CH₃D, CH₂D₂ and CHD₃), indicating a multiple H/D exchange reaction following the C-D activation and prior to methane loss. [(tmeda)Pt(CH₃)(THF-d₈)][BAr] liberates CH₄ and CH₃D. Methane-¹³C, cyclohexane, toluene, and benzene react with [(tmeda)Pt(CH₃)(NC₅F₅)][BAr_f] to yield methane and new organoplatinum complexes. Deuterated alkanes and arenes react with [(tmeda)Pt(CH₃)(NC₅F₅] [BAr_f] to give a mixture of methane isotopomers. The relevance of these results to the oxidation of alkanes by aqueous platinum complexes is discussed.     

Structure and properties of a novel OH bridged dimetal helical complex with 6,6-dimethyl-2,2′:6′,2″:6″,2:6,2-quinquepyridine ligand

A new monohelical OH⁻ bridged dinuclear complex [Zn₂(dmqpy)(OOCCH₃)₂(μ-OH)][ClO₄] · 0.5EtOH, where dmqpy is 6,6-dimethyl-2,2′:6′,2″:6″,2:6,2-quinquepyridine, has been synthesized and characterized by X-ray crystallography: monoclinic, space group P2₁/c, a=13.670(1), b=14.751(1), c=16.782(1) Å, β=96.59(1)°, U=3361.7(4) ų, Z=4, R=0.0601. Two Zn(II) ions are in different coordination modes, one is five-coordinate with a N₃O₂ donor set and the other is N₂O₂ four-coordinate with a distorted tetrahedral geometry, and the zinc ions are bridged by a hydroxyl group. The presence of the OH⁻ bridge is further confirmed by electrospray mass and infrared spectroscopies. The solution properties of the complex were investigated by ¹H NMR spectroscopy. The results of NMR indicate that the complex has higher symmetry in solution than in the solid state.     

Compartmental pyrazolate ligands providing two adjacent tris(pyridylalkyl)amine-type binding pockets and their dicopper(II) fluoride complexes featuring extremely short intramolecular O-H?F bridges

A set of pyrazolate-based compartmental ligands HL²-HL⁵ with pendent (pyridylalkyl)amine side arms in the 3- and 5-positions of the pyrazole has been prepared. The ligands differ by the number and lengths of the pyridylalkyl arms, and they can be described as dinucleating versions of well-known ligands such as tris(pyridylmethyl)amine (tpma) or tris(pyridylethyl)amine (tpea). Reaction of HL², HL³ or HL⁵ with Cu(BF₄)₂ · 6H₂O in the presence of base causes fluoride abstraction from the tetrafluoroborate and gives dicopper(II) complexes 1, 2, and 3a and b, respectively, which feature extremely short intramolecular F?HOMe or F?HOH bridges (d(F?O)=2.384(6)-2.507(3)). Molecular structures of all four complexes have been elucidated by X-ray crystallography and are compared to their mononuclear analogues. The influence of the intramolecular F?HO bridge on Cu-F and Cu-O bond lengths as well as on other structural characteristics is discussed.