Structures of vanadium(III)-ethylenediamine-N,N'-diacetato-N,N'-di-3-propionato complexes. Critical role of pπ-dπ donation in determining the coordination number.

Li[V(eddadp)]·3H(2)O (1a) and Cs[V(eddadp)]·2H(2)O (1b) were characterized by X-ray crystallography. 1a crystallizes in the monoclinic space group Cc with a = 11.467(7) Å, b = 13.398(8) Å, c = 12.529(8) Å, ß = 114.85(4)°; V = 1746.7(2) Å(3), and Z = 4; 1b crystallizes in the monoclinic space group P2(1)/n with a = 10.265(5) Å, b = 11.673(6) Å, c = 15.507(8) Å, ß = 104.29(2)°, V = 1800.6(2) Å(3), and Z = 4. The solution structure of 1 has been ascertained to be predominantly six-coordinated with a hexadentate eddadp which is based on a comparison of the electronic and Raman spectra of aqueous solutions of 1 with those in the solid state.

Syntheses, solid state and solution structures of the palladium(II) complexes of malonamide-derived open-chain and macrocyclic ligands.

The crystal structures of the palladium(II) complexes of the open-chain and macrocyclic ligands PdL(1).3H(2)O, PdL(2).6H(2)O and PdL(3).5H(2)O have been determined (H(2)L(1) = 1,4,8,11-tetraazaundecane-5,7-dione, H(2)L(2) = 1,4,8,11-tetraazacyclotetradecane-5,7-dione, H(2)L(3) = 1,4,8,11-tetraazacyclotridecane-5,7-dione). The coordination polyhedra of the palladium(II) ions in all complexes are formed by two deprotonated amide and two amine donors with Pd-N distances being similar in PdL(1) and PdL(2) and substantially shorter in PdL(3). A detailed analysis of the (1)H NMR spectra of the macrocyclic complexes supports the formation in aqueous solution of only N-meso isomers of both compounds in agreement with the X-ray data. The spectra of the palladium(II) macrocyclic complexes are shifted downfield as a whole as compared to those of the nickel(II) analogues with the shifts being essentially non-uniform. The latter feature can be related to the differences in magnetic anisotropy of the M-N bonds. The maxima of d-d absorption bands of the palladium(II) complexes demonstrate weaker dependence on the macrocycle size as compared to those of the nickel(II) analogues. Both macrocyclic compounds PdL(2).6H(2)O and PdL(3).5H(2)O are characterized by lamellar crystal structures consisting of interleaved layers formed by macrocyclic units and by water molecules with similar metal complex layers and different 2D water sheets. A columnar crystal structure is inherent for PdL(1).3H(2)O with the water molecules present as discrete (H(2)O)(3) clusters.

Distortional isomerism with copper(I) complexes of 3,7-diazabicyclo[3.3.1]nonane derivatives.

Two structural forms of the tetradentate bispidine ligand (3,7-diazabicyclo[3.3.1]nonane, pyridine-substituted at C2 and C4), coordinated to CuI, are known: a pentacoordinate square pyramidal structure with an acetonitrile completing the coordination sphere, and a tetracoordinate distorted tetrahedral structure, where one of the pyridine groups is dissociated. Similar structures are observed in crystals of the CuI complexes of another tetradentate and two pentadentate bispidine ligands. The structural dynamics in the CuI coordination sphere of the four ligands are probed by 1H-NMR spectroscopy, supported by approximate density functional theory (DFT) calculations. DFT and NMR spectroscopy indicate that there is an additional isomeric form, and experimental as well as computational data lead to the conclusion that the potential energy surfaces are very flat with various shallow minima.

Crystal and molecular structures of related nickel(II) complexes of open-chain and macrocyclic oxamide-based ligands and the peculiarities of water aggregates in their crystal lattices.

A comparison of the molecular structure of related nickel(II) complexes of the open-chain and 13-membered macrocyclic oxamide-derived ligands NiL(1).4H2O and NiL(2).3H2O revealed that the formation of an additional 6-membered chelate ring in the complex results in rather small changes in the molecular structure of the ligands and the bite angles around the metal ion. Two deprotonated amide and two amine donors form an approximately square planar environment for the nickel(II) in both complexes and the only essential consequence of ligand cyclization is the contraction of the nickel-nitrogen distances by 0.012 and 0.021 A for the Ni-N(amide) and Ni-N(amine) bonds, respectively. The packing modes of NiL(1) and NiL(2) in the crystalline state are essentially different--lattice water molecules form isolated monomolecular 2D sheets separating and gluing the metallocomplex layers in the former complex, while they are included in the formation of hybrid metallocomplex-water layers connected by van der Waals interactions in the latter. Analysis of the 1H NMR spectra reveals that the solid state conformation of the macrocyclic complex is retained in aqueous solution.

Oxidative N-dealkylation in cobalt-bispidine-H2O2 systems.

The reaction of the Co(II) complex with the rigid bispidine ligand L1 with two tertiary amine and two pyridine donors, [Co(II)(L1)(OH2)2]2+, with H2O2 and O2 produces [Co(II)(L2)(OH2)2]3+, where L2 is demethylated at one of the amine donors, and CH2O.

Helically chiral ferrocene peptides containing 1'-aminoferrocene-1-carboxylic acid subunits as turn inducers.

We present a detailed structural study of peptide derivatives of 1'-aminoferrocene-1-carboxylic acid (ferrocene amino acid, Fca), one of the simplest organometallic amino acids. Fca was incorporated into di- to pentapeptides with D- and L-alanine residues attached to either the carboxy or amino group, or to both. Crystallographic and spectroscopic studies (circular dicroism (CD), IR, and NMR) of about two dozen compounds were used to gain a detailed insight into their structures in the solid state as well as in solution. Four derivatives were characterized by single-crystal X-ray analysis, namely Boc-Fca-Ala-OMe (16), Boc-Fca-D-Ala-OMe (17), Boc-Fca-beta-Ala-OMe (18), and Boc-Ala-Fca-Ala-Ala-OMe (21) (Boc=tert-butyloxycarbamyl). CD spectroscopy is an extremely useful tool to elucidate the helical chirality of the metallocene core. Unlike in all other known ferrocene peptides, the helical chirality of the ferrocene is governed solely by the chirality of the amino acid attached to the N terminus of Fca. Depending on the degree of substitution of both cyclopentadiene (Cp) rings, different hydrogen-bonding patterns are realized. (1)H NMR and IR spectroscopy, together with the results from X-ray crystallography, give detailed information regarding not only the hydrogen-bonding patterns of the compounds, but also the equilibria between different conformers in solution. Differences in chemical shifts of NH protons in dimethyl sulfoxide ([D(6)]DMSO) and CDCl(3), that is, the variation ratio (vr), is used for the first time as a measure of the hydrogen-bonding strength of individual COHN bonds in ferrocenoyl peptides. In dipeptides with one intramolecular hydrogen bond between the pendant chains, for example, in dipeptide 16, an equilibrium between hydrogen-bonded and open forms is observed, as testified by a vr value of around 0.5. Higher peptides, such as tetrapeptide 21, are able to form two intramolecular hydrogen bonds stabilizing one single conformation in CDCl(3) solution (vr approximately 0). Due to the low barrier of Cp-ring rotation, new and unnatural hydrogen-bonding patterns are emerging. The systematic work described herein lays a solid foundation for the rational design of metallocene peptides with unusual structures and properties.

Encapsulation of cyanometalates by a tris-macrocyclic ligand tricopper(II) complex: syntheses, structural variation, and magnetic exchange coupling pathways.

The reaction of [M(CN)(6)](3-) (M = Cr(3+), Mn(3+), Fe(3+), Co(3+)) and [M(CN)(8)](4-/3-) (M = Mo(4+/5+), W(4+/5+)) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu(3)(L)](6+)) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu(3)(L)](6+) forms the isostructural host-guest complexes [[[Cu(3)(L)(OH(2))(2)][M(CN)(6)](2)][M(CN)(6)]][M(CN)(6)]30 H(2)O with one bridging, two partially encapsulated, and one isolated [M(CN)(6)](3-) unit. The octacyanometalates of Mo(4+/5+) and W(4+/5+) are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)(8)](4-) were obtained. The Mo(4+) and W(4+) complexes were crystallized in two different structural forms: [[Cu(3)(L)(OH(2))](2)[Mo(CN)(8)]](NO(3))(8)15 H(2)O with a structural motif that involves isolated spherical [[Cu(3)(L)(OH(2))](2)[M(CN)(8)]](8+) ions and a "string-of-pearls" type of structure [[[Cu(3)(L)](2)[M(CN)(8)]][M(CN)(8)]](NO(3))(4) 20 H(2)O, with [M(CN)(8)](4-) ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the CuCu pairs in the [Cu(3)(L)](6+) "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr(3+), exchange coupling of Mn(3+) and Fe(3+) is very small, and the octacoordinate Mo(4+) and W(4+) systems have a closed-shell ground state.

Coordination chemistry of a new rigid, hexadentate bispidine-based bis(amine)tetrakis(pyridine) ligand.

The hexadentate bispidine-based ligand 2,4-bis(2-pyridyl)-3,7-bis(2-methylenepyridine)-3,7-diazabicyclo[3.3.1]nonane-9-on-1,5-bis(carbonic acid methyl ester), L(6m), with four pyridine and two tertiary amine donors, based on a very rigid diazaadamantane-derived backbone, is coordinated to a range of metal ions. On the basis of experimental and computed structural data, the ligand is predicted to form very stable complexes. Force field calculations indicate that short metal-donor distances lead to a buildup of strain in the ligand; that is, the coordination of large metal ions is preferred. This is confirmed by experimentally determined stability constants, which indicate that, in general, stabilities comparable to those with macrocyclic ligands are obtained with the relative order Cu(2+) > Zn(2+) >> Ni(2+) < Co(2+), which is not the typical Irving-Williams behavior. The preference for large M-N distances also emerges from relatively high redox potentials (the higher oxidation states, that is, the smaller metal ions, are destabilized) and from relatively weak ligand fields (dd-transition, high-spin electronic ground states). The potentiometric titrations confirm the efficient encapsulation of the metal ions since only 1:1 complexes are observed, and, over a large pH range, ML is generally the only species present in solution.

Catalytic transesterification of dialkyl phosphates by a bioinspired dicopper(II) macrocyclic complex.

For a number of phosphoryltransfer enzymes, including the exonuclease subunit of DNA polymerase I, a mechanism involving two-metal ions and double Lewis-acid activation of the substrate, combined with leaving group stabilization, has been proposed. Inspired by the active site structure of this enzyme, we have designed as a synthetic phosphoryl transfer catalyst the dicopper(II) macrocyclic complex LCu(2). Crystal structures of complexes [(L)Cu(2)(mu-NO(3))(NO(3))](NO(3))(2) (1), [(L)Cu(2)(mu-CO(3))(CH(3)OH)](BF(4))(2) (2), and [(L)Cu(2)(mu-O(2)P(OCH(3))(2))(NO(3))](NO(3))(2) (3) illustrate various possibilities for the interaction of oxoanions with the dicopper(II) site. 1 efficiently promotes the transesterification of dimethyl phosphate (DMP) in CD(3)OD, k(cat) = 2 x 10(-)(4) s(-)(1) at 55 degrees C. 1 is the only available catalyst for the smooth transesterification of highly inert simple dialkyl phosphates. From photometric titrations and the pH dependence of reactivity, we conclude that a complex [(L)Cu(2)(DMP)(OCH(3))](2+) is the reactive species. Steric bulk at the -OR substituents of phosphodiester substrates O(2)P(OR)(2)(-) drastically reduces the reactivity of 1. This is explained with -OR leaving group stabilization by Cu coordination, an interaction which is sensitive to steric crowding at the alpha-C-atom of substituent R. A proposed reaction mechanism related to that of the exonuclease unit of DNA polymerase I is supported by DFT calculations on reaction intermediates. The complex [(L)Cu(3)(mu(3)-OH)(mu-CH(3)O)(2)(CH(3)CN)(2)](ClO(4))(3) (4) incorporates a [Cu(OH)(OCH(3))(2)(CH(3)CN)(2)](-) complex anion, which might be considered as an analogue of the [PO(2)(OCH(3))(2)(OCD(3))](2)(-) transition state (or intermediate) of DMP transesterification catalyzed by LCu(2).

Biphenyl derived oxovanadium(IV) and copper(II) salen-type complexes--structure and redox tuning.

A series of vanadyl(IV) salen (N,N'-bis(salicylidene)ethylenediaminato)-type complexes (1-4) bearing phenyl or 2-hydroxyphenyl moieties have been prepared and characterized by means of mass spectrometry, infra-red, electron paramagnetic resonance (EPR), UV/Vis spectroscopy, cyclovoltammetry and X-ray crystallography. Their structures have been compared to their copper(II) analogs 5-8. Hydrogen intralinkages have been observed in the crystal structure of 5. The pendant hydroxy groups fine-tune the redox properties of the complexes. The catalytic activity in the oxygenation of ethyl phenyl sulfide to the corresponding sulfoxide was investigated. Results indicate that complex 1 bearing hydroxyphenyl subunits and a phenylene bridge is the most selective under these reaction conditions, with the smallest amount of the over-oxidized product, sulfone.

Structural variety and magnetic properties of tetranuclear nickel(II) complexes with a central mu4-azide.

Using a set of pyrazolate-based dinucleating ligands with thioether sidearms and a set of different carboxylates, seven tetranuclear nickel(II) complexes of types [L2Ni4(N3)3(O2CR)2](ClO4) (1) and [L2Ni4(N3)(O2CR)4](ClO4) (2) featuring an unprecedented central mu4-1,1,3,3-azide could be isolated and fully characterized. X-ray crystal structures are discussed for 1a,b,e and 2b. The mu4-1,1,3,3-azide is symmetric in all cases except 1a but exhibits distinct binding modes with significantly different Ni-N(azide)-Ni angles and Ni-NNN-Ni torsions in type 1 and 2 complexes, which indicates high structural flexibility of this novel bridging unit. Also, IR-spectroscopic signatures and magnetic properties are distinct for type 1 and 2 complexes. Magnetic data for 1a,b,d,e and 2a,b were investigated and analyzed in a three-J approach. The only model that gave a satisfactory fit for all type 1 complexes includes one dominant antiferromagnetic coupling and two ferromagnetic interactions (one large and one smaller), indicating some degree of frustration. On the basis of magneto-structural correlations for end-on and end-to-end azide linkages, it is reasonable to assign the antiferromagnetic interaction to the intradimer exchange along the pyrazolate and the end-to-end linkage of the mu4-azide. Overall, the magnitude of the coupling constants differs significantly for the two distinct types of compounds, 1 or 2, and depends on the individual geometric details of the Ni4 array and the mu4-1,1,3,3-azide.

Structures and magnetic properties of tetranuclear nickel(II) complexes with unusual mu3-1,1,3 azido bridges.

Pyrazolate-based dinucleating ligands with thioether-containing chelate arms have been used for the synthesis of a family of novel tetranuclear nickel(II) complexes [L2Ni4(N3)3(O2CR)](ClO4)2 that incorporate three azido bridges and one carboxylate (R = Me, Ph). Molecular structures have been elucidated by X-ray crystallography in four cases, revealing Ni4 cores with a unique topology in which two of the azido ligands adopt an unusual mu3-1,1,3 bridging mode. The compounds were further characterized by mass spectrometry, IR spectroscopy, and variable-temperature magnetic susceptibility measurements. Magnetic data analyses indicate a combination of significant intramolecular ferromagnetic and antiferromagnetic exchange interactions that give rise to an overall S(T) = 0 ground state. The sign and the magnitude of the individual couplings have been rationalized in the framework of the common magnetostructural correlations for end-to-end and end-on azido linkages, suggesting that these correlations also remain valid for the respective fragments of multiply bridging mu3-1,1,3 azido ligands.

Synthesis of a novel dinucleating aminocarboxylate macrocycle and structures of its dinuclear complexes with di- and trivalent transition and lanthanide metal ions.

The synthesis of the new ligand L1(H4L1= 3,8,16,21-tetrakis(carboxylmethyl)-3,8,16,21,27,28-hexaazatricyclo[21.3.1.1(10,14)]octacosa-1(27),10,12,14(28),23,25-hexaen-5,18-diine) is reported. The solid-state structures of the four homodinuclear chelate complexes, [Zn2(L1)(H2O)2] x 6H2O, [Fe2(L1)(mu-O)] x 4H2O, [La2(L1)(NO3)2(H2O)2] x 6H2O and Na[Eu2(L1)(mu-AcO)3] x 3H2O, were determined by single-crystal X-ray structural analysis.

Synthesis, structure and magnetism of a new ferromagnetic hexanuclear nickel cluster with a dicubane-like core.

A new ferromagnetic nickel(II) hexameric structure based on the versatile N,O3-ligand 2,2',2"-nitrilotribenzoic acid has been prepared and characterised by X-ray crystallography and magnetic measurements; the compound represents a rare example of a nickel cluster with a dicubane-like core having only oxygen bridges.

"Bent bonds" between bismuth and carbon atoms as a result of C-H activation in Mo-Bi complexes.

The reaction of molybdocenedihydride with two equivalents of [Bi(OtBu)(3)] proceeds via alcohol elimination and provides the compound [Cp(2)Mo{Bi(OtBu)(2)}(2)] (1), which contains two Mo--Bi metal bonds, in good yields. If the two reagents are employed in a 1:1 ratio continuative condensation reactions occur. These initially lead to [{Cp(2)Mo}(2){mu-Bi(OtBu)}(2)] (2), which, however, is very unstable in solution and decomposes via additional alcohol elimination: Complex-induced proximity effects facilitate the cleavage of C--H bonds within the cyclopentadienyl ligands by the residual alkoxide ligands, so that spontaneously two further equivalents of alcohol are released, thereby yielding two isomeric compounds 3 and 4 with Cp ligands bridging Mo--Bi metal bonds: The first isomer (3) contains two mu(2)-eta(5):eta(1)-C(5)H(4) ligands, the second isomer (4) contains one bridging mu(3)-eta(5):eta(1):eta(1)-C(5)H(3) ligand. The binding of these ligands to molybdenum and bismuth atoms at the same time is made possible through "bent bonds" between the bismuth and certain carbon centres. These unusual bonding situations were analysed by means of calculations based on density functional theory (DFT), the atoms in molecules (AIM) theory, natural bond order (NBO) considerations and the electron localisation function (ELF). According to the results the bonds can be understood in terms of carbanionic centres interacting with bismuth cations (i.e. closed-shell interactions). The formation of these bonds and the thermodynamics/kinetics involved on going from 2 to 3 and 4 were also studied by theoretical methods, so that the product formation is rationalised. The crystal structures of all four new compounds were determined. These structures but also the properties and mechanisms of formation are discussed against the background of the corresponding results obtained while studying the system [(Me)Cp(2)MoH(2)]/[Bi(OtBu)(3)].

A (H2O)4/crown ether network spanned between organometallic complex metal fragments.

[Mo(eta3)-C3H5)(CO)2(bipy*)Cl] undergoes trigonal twist rearrangements in solution, so that three isomers are coexisting. It was used as a starting material leading to a dinuclear complex containing a hydrogen-bonded network of H(2)O and crown-ether molecules between two Mo(eta3-C3H5)(CO)2(bipy*) moieties.

On, off and intermediate coordination of a bridgehead triarylamine donor in tripodal complexes: towards the tuning of coordinative bond distance.

A series of first row transition metal complexes of the tripodal ligand 2,2',2"-nitrilotribenzoic acid H3L has been prepared and characterised by X-ray crystallography: Mononuclear [M(L)]- species [Cu(H2O)4]3[Cu(L)(H2O)]6.25H2O (2), [Co(H2O)6][Co(L)(H2O)].8H2O (4), [Zn(H2O)6][Zn(L)(H2O)].8H2O (5) and a neutral [M(L)] complex [Fe(III)2(L)(H2O)3].5H2O (8) are formed as well as dimeric [M(L)]2 2- species (HNEt3)2[Cu(L)]2.2CH3CN (1), (HNEt3)3[Ni(L)]2(ClO4).H2O (3), (HNEt3)2[Fe(II)(L)]2.2CH3CN (6) and (HNEt3)2[Fe(III)2(L)2(mu-O)](7). The complexes display a unique variation in the M-N distance (2.09 A for Cu(II) to 3.29 A for Fe(III)) to the bridgehead triphenylamine donor and are classified into compounds with "On","Off" and "Intermediate" N-coordination. The trigonal-bipyramidal coordination polyhedron changes towards tetrahedral in the intermediate and octahedral in the Off-state. The M-N distance of individual complexes is reversibly tuned by external chemical input such as changes of metal ion oxidation state (Fe(II)/Fe(III)) or variation of the axial coligand as a consequence of solvent or pH variation. Possible reasons for the exceptional tolerance of the M-N bond to distance variations are discussed under consideration of gas phase DFT calculations of [Zn(L)]-.

The first oligopeptide derivative of 1'-aminoferrocene-1-carboxylic acid shows helical chirality with antiparallel strands.

The unnatural organometallic amino acid 1'-aminoferrocene-1-carboxylic acid (Fca) induces a turn structure in a tetrapeptide with anti-parallel strands which is stabilized by two intra-molecular hydrogen bonds in the solid state and in solution.

Biphenyl derived Schiff-base vanadium(V) complexes with pendant OH-groups--structure, characterization and hydrogen peroxide mediated sulfide oxygenation.

A series of mononuclear oxovanadium(v) complexes of tridentate Schiff bases HL(1)-HL(4) and H(2)L(5)-H(2)L(8) derived from 6-phenylsalicylaldehyde and 6-(2-hydroxyphenyl)salicylaldehyde and four different amines was synthesized. The systematically selected ligands contain aliphatic or aromatic nitrogen, or alkoxy- and phenoxy-oxygen as third donor atom. The complexes were characterised by spectroscopic methods in solution and the solid state. Single-crystal X-ray analyses were performed with VO(2)L(1)(), VO(2)L(3)x1/2EtOH (), VO(2)L(4)(), VO(OiPr)L(7)xiPrOH, VO(OiPr)L(8) and H(2)L(8). For all compounds the vanadium(v) cores contain distorted tetragonal pyramidal geometry around the dioxo- and oxovanadium site at which the N(2)O- and NO(2)-donor ligands bind equatorially. Complexes and display intramolecular hydrogen bonding of the pendant hydroxyphenyl group to a coordinated oxygen trans to a nitrogen atom and therefore serve as suitable models for the native site of vanadium dependent haloperoxidases. Variable-temperature (1)H NMR spectra revealed significant hydrogen bond interaction in acetonitrile solution. In situ prepared catalysts are active for hydrogen peroxide mediated oxygenation of ethyl phenyl sulfide and showed complete conversion of the substrate to ethyl phenyl sulfoxide, together with small amounts of the corresponding sulfone, as detected by GC/MS after 10 min. The complex of H(2)L(7) turned out to be most efficient while HL(1) and HL(2) were completely inactive. Catalysis is supported by the pendant OH group in the complex of HL(3), the catalyst is twice as active as the complex of HL(4).