Showing papers by "Brian W. Skelton published in 2001"

Oxidative Addition of the Imidazolium Cation to Zerovalent Ni, Pd, and Pt: A Combined Density Functional and Experimental Study

Abstract: Oxidative addition of different imidazolium cations to zerovalent group 10 metals, to afford heterocyclic carbene complexes, has been investigated by both density functional theory (DFT) and experimental studies. The theoretical analysis shows that addition of imidazoliums to Pt0 and Ni0 is more exothermic than to Pd0, and Ni0 is predicted to react with a much lower barrier than either Pt0 or Pd0. Strongly basic supporting ligands on the metal, as well as cis-chelating ligands, increase the exothermicity of the reaction and also lower the activation barrier. The addition of 2-H imidazoliums is easier and more exothermic than addition of 2-alkylimidazoliums, and a halo-imidazolium is expected to further lower the barrier to oxidative addition and increase the exothermicity. The DFT results show that all three of the metals should be able to oxidatively add imidazolium cations under appropriate conditions. Experimental studies confirmed that oxidative addition is possible, and a number of Pt− and Pd−carbene...

Palladium carbene complexes derived from imidazolium-linked ortho-cyclophanes

Abstract: Reaction of imidazolium-linked ortho-cyclophanes with nickel(II) and palladium(II) salts in the presence of acetate base led to the formation of complexes where a metal centre is bound by a pair of heterocyclic carbenes which themselves are part of a cyclophane skeleton These cyclophane–metal complexes have been characterised by NMR spectroscopy and (for five complexes) X-ray diffraction studies The complexes are highly active as promoters of Heck and Suzuki couplings, with preliminary studies showing Heck reactions with turnover numbers approaching 107 p

Simple Syntheses, Structural Diversity, and Tishchenko Reaction Catalysis of Neutral Homoleptic Rare Earth (II or III) 3,5-Di-tert-butylpyrazolates-The Structures of [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln=La, Nd, Yb, Lu), and [Eu4(tBu2pz)8]

Abstract: The homoleptic rare-earth pyrazolate complexes [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln = La, Nd, Sm, Lu), [Eu4(tBu2pz)8] and the mixed oxidation state species [Yb2(tBu2pz)5] (tBu2pz = 3,5-di-tert-butylpyrazolate) have been prepared by a simple reaction between the corresponding rare-earth metal and 3,5-di-tert-butylpyrazole, in the presence of mercury, at elevated temperatures. In addition, [Yb2(tBu2pz)6] was prepared by redox transmetallation/ligand exchange between ytterbium, diphenylmercury(II) and tBu2pzH in toluene, whilst the same reactants in toluene under different conditions or in diethyl ether gave [Yb2(tBu2pz)5]. The complexes of the trivalent lanthanoids display dimeric structures [Ln2(tBu2pz)6] (Ln = La, Nd, Yb, Lu) with chelating eta2-terminal and eta2:eta2-bridging pyrazolate coordination. The considerably smaller Sc3+ ion forms monomeric [Sc(tBu2pz)3] of putative D3h molecular symmetry, with pyrazolate ligands solely eta2-bonded. [Eu4(tBu2pz)8] is a structurally remarkable tetranuclear EuII complex with two types of europium centres in a linear array. The outer two are bonded to one terminal and two bridging pyrazolates, and the inner two are coordinated by four bridging ligands. Unprecedented mu-eta5:eta2 pyrazolate ligation is observed, with each outer Eu2+ sandwiched between two eta5-bonded pyrazolate groups, which are also eta2-linked to an inner Eu2+. The two inner Eu2+ ions are linked together by two equally occupied components of each of two symmetry related, disordered pyrazolate groups with one component eta4:eta2 bridging and one eta3:eta2 bridging. [La2(tBu2pz)6] has also been shown to be a Tishchenko reaction catalyst with several organic substrates.

Systematic Structural Coordination Chemistry of p-tert-Butyltetrathiacalix(4)arene: 1. Group 1 Elements and Congeners

Abstract: Determinations of the crystal structures of complexes of the alkali metal ions with, in the case of Li, the dianion and, in the cases Na-Cs, the monoanion of p-tert-butyltetrathiacalix[4]arene have shown that both the sulfur atoms which form part of the macrocyclic ring, as well as the pendent phenolic/phenoxide oxygen donor atoms, are involved in coordination to these metals. Although the Li and Na complex structures are similar to those of the corresponding complexes of p-tert-butylcalix[4]arene, there is no similarity in the structures of the Cs complexes, with the present structure showing no evidence of polyhapto Cs(+)-pi interactions. Instead, the complex crystallizes as a ligand-bridged (S-, O-donor) aggregate of three Cs ions, solvent molecules, and four calixarenes, somewhat like the Rb complex, though here four Rb ions are present, and higher in aggregation than the K+ complex, where two K+ ions are sandwiched between two calixarene moieties. The triethylammonium complex of the thiacalixarene monoanion, though formally analogous in that it involves a monocation, has a simpler structure than any of the alkali metal derivatives, based formally on proton coordination (H-bonding). However, interestingly, it can be isolated in both solvated (dmf, dmso) and unsolvated forms, as indeed can the "free", p-tert-butyltetrathiacalix[4]arene ligand itself.

A unique heteropentanuclear CuII2CoIICoIII2 complex, synthesised from metallic Cu and Co acetate in the presence of triethanolamine. Magnetic properties and a strong H-bond stabilised lattice

Abstract: Reaction of zerovalent copper with cobalt(II) acetate and triethanolamine (H3Tea) in DMF solution in air yields the unique pentanuclear mixed-valence complex [CuII2CoIICOIII2(O2CMe)4(H2Tea)2(Tea)2]·2(HO2CMe), 1, which has been characterized by a range of spectroscopic methods and structurally by X-ray crystallography. In the centrosymmetric unit of 1 five metal ions are linked together by eight oxygen atoms of the four triethanolamine ligands and by two acetate anions in the sequence Cu(II)–Co(III)–Co(II)–Co(III)–Cu(II), with the metal–metal separations being 2.823(2) and 2.964(1) A for Cu(II)···Co(III) and Co(III)···Co(II), respectively. Discrimination between Co(II) and Co(III) atoms is based on bond length considerations; the Co(III) is low spin. The lattice hydrogen-bonded network involving the non-coordinating acetic acid molecules links the pentanuclear units together and results in the formation of an extended one-dimensional structure. Magnetic measurements for 1 showed a marked decrease of the χT value at low temperature, indicative of antiferromagnetic interactions between magnetic centres. A fit was attempted assuming an effective S = 1/2 ground state for Co(II) and an Ising-type anisotropy, considering only intramolecular interactions. The obtained value for Jz of 36 cm−1 must originate from the efficient role of the diamagnetic Co(III) in transmitting the interaction between Cu(II) and Co(II) below 40 K.

Bridged 1-Methylbisimidazoles as Building Blocks for Mixed Donor Bi- and Tridentate Chelating Ligands

Abstract: Novel biand tridentate imidazole chelate ligands consisting of varying donor sets were prepared using an efficient oneor two-step procedure. Ketoand methylene-bridged bisimidazoles 1, 2 served as versatile starting materials for the introduction of additional donor groups, thus allowing the facile variation of donor sets within a bisimidazole ligand framework.

Rare Earth Complexes of Bulky 2,6-Diphenylphenolates Containing Additional, Potentially Buttressing 3,5-Substituents

Abstract: The rare earth aryloxide complexes, [Yb(OArtBu)3(THF)]·THF, [Sc(OArtBu)3(THF)]·THF, [Yb(OArMe)3(THF)], and [Sm(OArPh)3(THF)2] (OArR = 2,6-diphenyl-3,5-di-R-phenolate), have been prepared by redox transmetallation/ligand exchange between the rare earth metal, bis(pentafluorophenyl)mercury, and HOArR in tetrahydrofuran. This reaction also provided [Yb(OArPh)3(DME)]·3/2THF by incorporation of adventitious 1,2-dimethoxyethane. A similar reaction between Yb metal, diphenylmercury, and HOArMe gave [Yb(OArMe)2(THF)3]. The homoleptic complexes [Yb(OArPh)3] and [Sc(OArH)3] have been prepared by direct reaction of the rare earth element with HOArR in a sealed tube in the presence of mercury at elevated temperatures (200−250 °C) and the latter was converted into [Sc(OArH)3(THF)] by treatment with THF. X-ray crystal structure determinations of [Yb(OArtBu)3(THF)]·THF, [Sc(OArtBu)3(THF)]·THF, and [Yb(OArMe)3(THF)] show the complexes to be monomeric and four coordinate with a trigonal pyramidal stereochemistry. These structures provide clear evidence that groups meta to the phenolate donor can modify the coordination behaviour of the 2,6-diphenylphenolate ligand. In [Yb(OArPh)3(DME)]·3/2THF a distorted square pyramidal stereochemistry is observed. The divalent complex [Yb(OArMe)2(THF)3] exhibits a distorted trigonal bipyramidal arrangement of the oxygen donor atoms with apical THF ligands. The homoleptic scandium 2,6-diphenylphenolate has three oxygen atoms in a triangular array with additional π-η1-Ph···Sc interactions above and below the ScO3 plane [C−Sc−C = 154.2(8)°], providing a new type of binding of this aryloxide ligand.

Carboxymethylated cage amines: Coordination and lactamization

Abstract: Depending upon the position and degree of substitution, carboxymethyl derivatives of cage amines of the "sarcophagine" (3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane) type vary considerably in the stability of their lactamized forms. For 1,8-diamino-3-carboxymethylsarcophagine, L(1), only indirect evidence for some involvement of a lactamized form of its Ni(II) complex has been obtained. Crystal structure determinations for [Cu(H(2)L(1))](NO(3))(3.5)Cl(0.5) x 2.5H(2)O and [Ni(HL(1))]Cl(3) x 3H(2)O show distorted octahedral coordination of all six endocyclic N-donor atoms in both cases. For related diaminosarcophagine derivatives with either two (1,8; L(2)) or three (1,1,8; L(3)) carboxymethyl substituents on the exocyclic N atoms, crystallographic studies have shown a dilactam form for the ligands in their Ni(II) and Cu(II) complexes which is of almost identical conformation to that of the diprotonated "free" ligand in [H(2)L(3)][ZnCl(4)] x 6H(2)O. The lactamized ligands appear to strongly favor square planar four-coordination, and the Co(II) complex of L(2) shows a remarkable lack of reactivity toward oxygen. Kinetic studies indicate that the hydrolytic stability of the lactam rings is comparable to that of uncoordinated analogues.

Syntheses, structural studies and solution properties of iron complexes of some amide-substituted calixarenes

Abstract: Iron(III) complexes of 5,11,17,23-tetra-tert-butyl-24-hydroxy-26,27,28-tris(diethylcarbamoylmethoxy)calix[4]arene (II) and 5,11,17,23,29,35-hexa-tert-butyl-36,39-dihydroxy-37,38,40,41-tetrakis(diethylcarbamoylmethoxy)calix[6]arene (IV) have been synthesised, and a single crystal structure determination has been carried out on [Fe(II − H)](FeCl4)2; the iron in the complex cation is bound to all seven O atoms of the calixarene with the shortest Fe–O distance to the phenolate O atom. The voltammetric properties of these complexes and the previously described Fe(III) complex of 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-bis(diethylcarbamoylmethoxy)calix[4]arene (I) have been studied. The results suggest that the complexes of I and II undergo a reduction which is metal-centred, and an oxidation which is ligand-centred.

Alkali metal and magnesium enamides from metallation of the alkyl ligands [(2-Pyr)(SiMe3)CH2 and [6-Me-(2-Pyr)(SiMe3)CH2]: a solid state and ab initio study

Abstract: The alkali metal complexes [rNa·(pmdta)]2, 1, [rK·(pmdta)]2, 2, [rNa·(tmeda)]2, 3, [r′Li·(pmdta)], 4, and the magnesium complex, [(r)2Mg·(hmpa)2], 5, formed on metallation of the monosilylated ligands [(2-Pyr)(SiMe3)CH2] (= rH) and [6-Me-(2-Pyr)(SiMe3)CH2] (= r′H), rather than being metal alkyls, are all metal enamides in the solid state, as evidenced by single crystal X-ray diffraction studies. Even in the presence of the bi- and tri-dentate donors tmeda (= N,N,N′,N′-tetramethylethylenediamine) and pmdta (= N,N,N′,N′,N″-pentamethyldiethylenetriamine) the heavier alkali metal complexes are found to be dimeric. The Li complex is monomeric and adopts the enamide configuration despite the presence of additional steric bulk on introduction of a Me group on the 6-position of the pyridyl ring. This preference for an enamide configuration, rather than that of carbanion or aza-allyl, has been studied by ab initio MO calculations. These confirmed that as the coordination environment of the metal increases the enamide form rather then the aza-allylic form becomes the most energetically favoured configuration.

Some Chemistry of Diynyl-Tungsten Complexes

Abstract: Reactions between W(CCCA≡CH)(CO)3Cp (1) and {Mo(CO)2Cp}2,Pt (η-C2H4)(PPh3)2 and 1,4-I2C6H4 [the latter catalysed by Pd0/CuI] have given M2{μ-HC2CA≡C[W(CO)33Cp]}(CO)4Cp2(2), Pt{η2-HC2CA≡C[W(CO)3-Cp]}(PPh3)2 (3) and 1,4-{[W(CO)3Cp]CA≡CCA≡C}2C6H4 (5), respectively. The adduct Co2{μ-PhC2CA≡C[W(CO)3-Cp]}(μ-dppm)(CO)4(6) was obtained from W(CA≡CCA≡CPh)(CO)3Cp (4) and Co2(μ-dppm)(CO)6. Substitution of one CO ligand in W(CA≡CCA≡CSiMe3)(CO)3Cp (7), prepared from the CuI-catalysed reaction of WCl(CO)3Cp with HCA≡CCA≡CSiMe3in tetrahydrofuran/NHEt2, by bis(diphenylphosphino)methane/Me3NO gave W(CA≡CCA≡CSiMe3)(CO)2(dppm-P)Cp (8). Treatment of (7) with RuCl(PPh3)2Cp afforded {Cp(OC)3W}CA≡CCA≡C-{Ru(PPh3)2Cp} (9), which reacts at the W–CA≡C– triple bond with tetracyanoethylene (tcne) to give{Cp(OC)33W}{C[=C(CN)2]C[=C(CN)2]CA≡C}{Ru(PPh3)2Cp} (10), and with Fe2(CO)9 to form the cluster Fe22W{μ3-C2CA≡C[Ru(PPh3)Cp]}(CO)8Cp (11). The molecular structures of (1), (2), (6), (8), (10) and (11) have been determined by single-crystal X-ray diffraction.

Inter- and intra-molecular pathways in polyamine synthesis from diamines

Abstract: Characterisation, largely through crystal structure determinations of their metal complexes, of the polyamine products of several reactions between (in all but one case) polyalcohol benzenesulfonates and 1,2- and 1,3-diamines, confirmed that intramolecular reaction pathways are important only in the 1,2-diamine reactions. Even under conditions where the amine reactants are in large excess, however, it is possible to obtain products resulting from alkylation of a diamine by more than one molecule of sulfonate (or, in one case, of a bromochloroalkane). In metal ion complexes formed by the new ligands there are examples of only partial coordination of the N-donor sites, giving species which might be suitable for further, selective functionalisation at the unbound centres. Conversion of the complexes into macrocyclic derivatives also suited to further functionalisation is straightforward.

Syntheses and crystal structures of binuclear gold(I), silver(I) and copper(I) complexes containing bulky pyridyl functionalised alkyl ligands

Abstract: Treatment of (CO)AuCl, CuCl or AgNO3 with 2-LiC(SiMe3)2-Py-6-CH2R gives the binuclear metal compounds [M2(μ-2-C(SiMe3)2-6-CH2RPy)2] [R = H, M = Au (1), Cu (2) and Ag (3); R = Me3Si, M = Cu (4)]. The dimeric structures of complexes 1, 2 and 4 have been established by single-crystal X-ray diffraction studies. The complexes are centrosymmetric with each ligand bridging the two metal centres which are in close proximity to each other [M⋯M 2.690(2) A in 1, 2.436(1) A in 2 and 2.431(1) A in 4].

Proton Controlled Supramolecular Assembly: A Comparative Structural Study of Bis(2-guanidinobenzimidazolo)nickel(II) with Bis(2-guanidinobenzimidazole)nickel(II) Nitrate and 2-guanidinobenzimidazole

Abstract: Previously studies have shown that when 2-guanidinobenzimidazole complexes with a number of transition metal ions it tautomerises so that, in contrast to the free ligand structure, no intermolecular hydrogen bonding between bound ligands occurs. In the present study it is demonstrated that ligand deprotonation to yield bis(2-guanidinobenzimidazolo)nickel(II) restores much of the original hydrogen bonding capability of the uncomplexed ligand. The structure of this neutral complex is compared to the previously reported structure of its diprotonated derivative, bis(2-guanidinobenzimidazole)nickel(II) nitrate, as well as to the structure of the uncomplexed ligand. In contrast to the dicationic species, the neutral complex exists in two enantiomeric forms that assemble to form an extended supramolecular lattice, containing channels through its structure. The walls of the channels are made up of ‘strings’ of complex molecules and are held in position by hydrogen bonding between the bound ligands and di...

Functionalization of cage amines with pendant aromatic and heteroaromatic substituents

Abstract: Structural studies have confirmed that it is possible to exploit the relatively low nucleophilicity of the "external" amino substituents on the CoIII complex of 1,8-diaminosarcophagine ("sarcophagine" = sar = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]-icosane) in acylation and alkylation reactions leading to a variety of functionalized cage amine complexes. With the appropriate choice of solvent, all these reactions can be conducted with high efficiency, and the new complexes display properties foreshadowing the application of cage systems in, for example, electroactive polymers.

Solid-state and solution studies of bis-carboxylate binding by bis-amidinium calix[4]arenes

Abstract: Bis-amidinium calix[4]arene receptors were shown to coordinate bis-carboxylate anions in DMSO solution; the crystal structure of the malonate salt of one of the receptors revealed a number of different amidinium–carboxylate interactions, demonstrating the propensity of these species to form complex hydrogen bonding networks.

Syntheses of Bis(aryloxo)halogenoytterbium(III) Complexes: [Yb(OAr)2X(THF)2] (X = Cl, Br, I; OAr = OC6H2–2,6‐tBu2–4‐R; R = H, Me, tBu) and the X‐Ray Crystal Structures of [Yb(OC6H2–2,6‐tBu2‐4‐Me)2I(THF)2] and [Yb(OC6H3‐2,6‐tBu2)2OH(THF)]2

Abstract: Oxidation of [Yb(OArR)2(THF)3] (OArR = OC6H2–2,6-tBu2-4-R; R = H, Me, tBu) with HgX2 or with (CH2X)2 (X = Cl, Br, I) in THF yields [Yb(OArR)2X(THF)2], whilst [Yb(OArMe)2Cl(THF)2] was also obtained by oxidation of the appropriate Yb(II) aryloxide with C2Cl6 in THF. An X-ray crystal structure determination has shown [Yb(OArMe)2I(THF)2] to be a five coordinate monomer, in which ytterbium has distorted square pyramidal stereochemistry with mutually trans OArMe and THF ligands in the square plane and an apical iodide. Attempts to grow single crystals of [Yb(OArH)2Cl(THF)2] yielded [Yb(OArH)2OH(THF)]2, shown to be an hydroxo-bridged dimer with five-coordinate ytterbium by X-ray crystallography. Organoamido- und Aryloxo-Lanthanoide. 26 Synthese von Bis(aryloxo)halogenoytterbium(III)-Komplexen: [Yb(OAr)2X(THF)2] (X = Cl, Br, I, OAr = OC6H2–2,6-tBu2-4-R; R = H, Me, tBu) und die Kristallstrukturen von [Yb(OC6H2-2,6-tBu2-4-Me)2I(THF)2] und [Yb(OC6H3-2,6-tBu2)2OH(THF)]2 Die Umsetzung von [Yb(OArR)2(THF)3] (OArR = OC6H2-2,6-tBu2-4-R; R = H, Me, tBu) mit HgX2 (X = Cl, Br, I) oder mit (CH2X)2 in THF fuhrt zu [Yb(OArR)2X(THF)2]. [Yb(OArMe)2Cl(THF)2] ist ebenso durch Oxidation des entsprechenden Yb(II)-Aryloxides mit C2Cl6 in THF erhaltlich. Nach Auskunft einer Einkristallstrukturanalyse liegt [Yb(OArMe)2I(THF)2] als Monomer mit funffach koordiniertem Ytterbium vor. Die Anordnung der Liganden um das Ytterbiumatom entspricht einer verzerrten quadratischen Pyramide, mit trans-standigen OArMe- und THF-Liganden in der Basisflache und dem Iod-Atom in der apikalen Position. Versuche, Einkristalle von [Yb(OArH)2Cl(THF)2] zu zuchten, fuhrten zur Bildung von [Yb(OArH)2OH(THF)]2, in denen eine OH-verbruckte dimere Einheit vorliegt, so dass Ytterbium ebenfalls die Koordinationszahl 5 erreicht.

Reactions of Ru(CCPh)(PPh3)2Cp* with tetracyanoethene: cycloaddition, formation of unusual η2-CNR complexes and oligomerisation via bridging cyanocarbon ligands

Abstract: Thermolysis of Ru{η3-C(CN)2CPhCC(CN)2}(PPh3)Cp* (2), obtained from Ru(CCPh)(PPh3)2Cp* and tetracyanoethene, has given the three complexes Ru{η1,η2(C,N)-C(CN)C(CN)CPhC(CN)(CN)}(PPh3)Cp* (3), {Ru(PPh3)Cp*}{μ-N:η3-NCC(CN)CPhCC(CN)2}{μ-η1:N-C(CN)C(CN)CPhC(CN)2}{RuCp*} (4) and {Ru[η3-C(CN)2CPhCC(CN)2]Cp*}3 (5). All four complexes have been characterised by single-crystal X-ray structure determinations and contain isomeric forms of the C4(CN)4Ph ligand. Unusual features of the molecular structures are (i) the presence of a side-on (η2) CN group in 3; (ii) formation of a second isomer of the polycyanocarbon ligand by CN migration to an adjacent carbon, in 3 and 4; (iii) the use of one or more CN groups to bridge ruthenium centres in 4 and 5; and (iv) the complete loss of PPh3 ligands during the formation of the trimer 5. Although there are three crystallographically distinct RuCp* groups in 5, only one Cp* resonance is found in solution NMR spectra, suggesting that oligomer formation by facile CN–Ru bond breaking and making is occurring.

Macrocyclic ligand design. A synthetic, solvent extraction, computational and NMR study of the effect of cryptand flexibility on sodium ion affinity

Abstract: The rigidity of a series of cryptands incorporating an N2O6-donor has been shown to have a marked effect on the ability of such species to complex sodium ions. X-Ray and associated computational investigations, including molecular mechanics, semi-empirical (AM1) and ab initio (density functional) studies, coupled with the results of sodium picrate extraction experiments and NMR studies, have been employed to probe the conformational aspects influencing sodium ion complexation along the ligand series. It is concluded that the ease with which a cryptand is able to adopt an endo–endo conformation is an important factor affecting the occurrence of inclusive metal-ion binding in these systems.

Complexes of late transition metals containing the mixed donor ligands 2,6-(RSCH2)2C5H3N (R = Ph, Me): Crystal structures of [{Cu(2,6-(PhSCH2)2C5H3N)(μ-X)}2] (X = Cl, Br) and [Ni(2,6-(PhSCH2)2C5H3N)Br2]

Abstract: A range of NiX2 and CuX (X = halide) complexes containing the tridentate NS2 ligands 2,6-bis(methylthiomethyl)pyridine (L1) and 2,6-bis(phenylthiomethyl)pyridine (L2) were prepared. Reaction of CuX with 1 molar equivalent of L1 or L2 afforded the binuclear species [{CuL(μ-X)}2] (L = L1, X = Cl; L = L2, X = Cl, Br, I). These compounds have been characterised by IR and 1H NMR spectroscopies, mass spectrometry and microanalysis. Crystal structure determinations of [{CuL2(μ-X)}2] (X = Cl, Br) confirm the dimeric nature of these complexes through bridging halide centres, with the NS2 ligands coordinated through their pyridyl nitrogens and one of the sulfur atoms in a bidentate manner. Reaction of NiX2 with 1 molar equivalent of L1 or L2 afforded mononuclear species for [NiLX2] (L = L1, X = I; L = L2, X = Br, I) and binuclear species for [NiLX2]2 (L = L1, X = Cl, Br; L = L2, X = Cl). These compounds have limited solubility and were characterised through IR and UV-Vis reflectance spectroscopies and microanalysis. The crystal structure determination of [NiL2Br2] confirms the compound to be monomeric with a five-coordinate, square pyramidal nickel centre.

Isolation and detailed characterization of the trans-[(H2O)2FeCl4](-) anion: stabilization of novel iron(III) species by large organic cations.

Abstract: 1,2-Diaminoethane (en) and FeCl3 give (enH2) [FeCl5(H2O)] (1) in concentrated HCl, extending the aquapentachloroferrate(III) series. For 1: C2H12N2Cl5OFe, orthorhombic, P2(1)2(1)2(1), a = 14.531(6) A, b = 10.772(4) A, c = 6.888(2) A, Z = 4. Diazabicyclo[2.2.2]octane dihydrochloride (DABCO-2HCl) and FeCl3 in concentrated HCl form a tetrachloroferrate(III) derivative whose subsequent ethanol treatment (restricted water access) results in the formation of a compound of composition (DABCOH2)2 [FeCl4(H2O)2]Cl3 (2). This contains the trans-[FeCl4(H2O)2](-) anion, in which the trans-Fe-O distances are 2.049(4) A. For 2: C12H32N4Cl7O2Fe, orthorhombic, Pnma, a = 16.378(3) A, b = 7.3323(6) A, c = 19.431(3) A, Z = 4. A combination of 57Fe Mossbauer spectroscopy and ac susceptibility data confirm uncanted 3D antiferromagnetic ground states with T(Neel) approximately 3.4 K for (enH2)[FeCl5(H2O)] and approximately 2.0 K for [DABCOH2]2[FeCl4(H2O)2]Cl3.