Methane Ligands Research Articles

A DFT and ab Initio Benchmarking Study of Metal−Alkane Interactions and the Activation of Carbon−Hydrogen Bonds

Density functional theory and ab initio methods have been used to calculate the structures and energies of minima and transition states for the reactions of methane coordinated to a transition metal. The reactions studied are reversible C-H bond activation of the coordinated methane ligand to form a transition metal methyl hydride complex and dissociation of the coordinated methane ligand. The reaction sequence can be summarized as L(x)M(CH(3))H <==> L(x)M(CH(4)) <==> L(x)M + CH(4), where L(x)M is the osmium-containing fragment (C(5)H(5))Os(R(2)PCH(2)PR(2))(+) and R is H or CH(3). Three-center metal-carbon-hydrogen interactions play an important role in this system. Both basis sets and functionals have been benchmarked in this work, including new correlation consistent basis sets for a third transition series element, osmium. Double zeta quality correlation consistent basis sets yield energies close to those from calculations with quadruple-zeta basis sets, with variations that are smaller than the differences between functionals. The energies of important species on the potential energy surface, calculated by using 10 DFT functionals, are compared both to experimental values and to CCSD(T) single point calculations. Kohn-Sham natural bond orbital descriptions are used to understand the differences between functionals. Older functionals favor electrostatic interactions over weak donor-acceptor interactions and, therefore, are not particularly well suited for describing systems--such as sigma-complexes--in which the latter are dominant. Newer kinetic and dispersion-corrected functionals such as MPW1K and M05-2X provide significantly better descriptions of the bonding interactions, as judged by their ability to predict energies closer to CCSD(T) values. Kohn-Sham and natural bond orbitals are used to differentiate between bonding descriptions. Our evaluations of these basis sets and DFT functionals lead us to recommend the use of dispersion corrected functionals in conjunction with double-zeta or larger basis sets with polarization functions for calculations involving weak interactions, such as those found in sigma-complexes with transition metals.

Bis{[μ-bis(diphenylarsino)methane-1:2κ2As:As′]nonacarbonyl-1κ3C,2κ3C,3κ3C-[tris(4-chlorophenyl)phosphine-3κP]-triangulo-triruthenium(0)} chloroform monosolvate

The asymmetric unit of the title triangulo-triruthenium compound, 2[Ru3(C25H22As2)(C18H12Cl3P)(CO)9]·CHCl3, consists of two mol­ecules (A and B) of the triangulo-triruthenium complex and one mol­ecule of chloro­form solvent. The bis­(diphenyl­arsino)methane ligand bridges an Ru—Ru bond and the monodentate phosphine ligand bonds to the third Ru atom. Both the phosphine and arsine ligands are equatorial with respect to the Ru3 triangle. In addition, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. The three phosphine-substituted benzene rings make dihedral angles of 73.5 (3), 57.2 (3) and 75.7 (3)° with each other in mol­ecule A, while these angles are 60.7 (3), 86.8 (3) and 54.9 (3)° in mol­ecule B. The dihedral angles between the two benzene rings are 87.3 (3) and 89.6 (3)° for the two diphenyl­arsino groups in mol­ecule A and 85.6 (3) and 87.7 (3)° in mol­ecule B. In the crystal packing, the mol­ecules are linked into a three-dimensional framework via inter­molecular C—H⋯O and C—H⋯Cl hydrogen bonds. Weak inter­molecular C—H⋯π inter­actions furture stabilize the crystal structure. The crystal studied was an inversion twin, the refined ratio of twin components being 0.480 (7):0.520 (7).

μ-Bis(diphenylarsino)methane-1:2κ2As:As′]nonacarbonyl-1κ3C,2κ3C,3κ3C-[triphenylstibine-3κSb]-triangulo-triruthenium(0)

In the title triangulo-triruthenium compound, [Ru3(C25H22As2)(C18H15Sb)(CO)9], the bis­(diphenyl­arsino)methane ligand bridges an Ru—Ru bond and the monodentate stibine ligand bonds to the third Ru atom. Both the stibine and arsine ligands are equatorial with respect to the Ru3 triangle. Additionally, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. The three stibine-substituted phenyl rings make dihedral angles of 84.3 (3), 80.4 (3) and 70.5 (3)° with each other. The dihedral angles between the two phenyl rings are 85.9 (3) and 75.2 (3)° for the two diphenyl­arsine groups. In the crystal packing, mol­ecules are linked into chains down the c axis via inter­molecular C—H⋯O hydrogen bonds. Weak inter­molecular C—H⋯π inter­actions further stabilize the crystal structure.

Fréchet‐Type Pallado‐Dendrimers Containing Bis(pyrazolyl)methane Ligands

AbstractNeutral and cationic {bis(3,5‐dimethylpyrazol‐1‐yl)methane}palladium(II) complexes of general formula [PdClX{RCH(3,5‐Me2pz)2}] (X = Cl or Me) or [PdMe(MeCN){RCH(3,5‐Me2pz)2}][BArf4], where R is a benzyl or benzyloxycarbonyl group or a poly(aryl ether) Fréchet‐type dendron, have been synthesized and fully characterized, including by X‐ray diffraction methods in some cases. These palladium complexes have been evaluated as catalyst precursors in the Heck reaction between para‐iodotoluene and methyl acrylate. The active catalytic species formed from these precursors are apparently not coordinated to the bis(pyrazolyl)methane ligands.

(Benzyldiphenylphosphine-3κP)[μ-bis(diphenylarsino)methane-1:2κ2As:As′]nonacarbonyl-1κ3C,2κ3C,3κ3C-triangulo-triruthenium(0)

The asymmetric unit of the title triangulo-triruthenium compound, [Ru3(C25H22As2)(C19H17P)(CO)9], consists of two crystallographically independent mol­ecules of the triangulo-triruthenium complex, A and B. The bis­(diphenyl­arsino)methane ligand bridges an Ru—Ru bond and the monodentate phosphine ligand bonds to the third Ru atom. Both the phosphine and arsine ligands are equatorial with respect to the Ru3 triangle. In addition, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. With regard to the three phosphine-substituted rings, the benzyl ring makes dihedral angles of 41.0 (3) and 43.9 (3)° with the other two benzene rings in mol­ecule A; these angles are 49.8 (3) and 56.8 (3)° in mol­ecule B. The dihedral angles between the two benzene rings are 76.1 (3) and 88.2 (3)° for the two diphenyl­arsino groups in mol­ecule A and 71.3 (3) and 78.1 (3)° in mol­ecule B. In the crystal packing, mol­ecules are linked into chains via inter­molecular C—H⋯O hydrogen bonds. Weak inter­molecular C—H⋯π inter­actions further stabilize the crystal structure.

Bis{[μ-bis(diphenylphosphino)methane-1:2κ2P:P′]nonacarbonyl-1κ3C,2κ3C,3κ3C-[tris(4-methoxyphenyl)arsine-3κAs]-triangulo-triruthenium(0)} dichloromethane solvate

The asymmetric unit of the title triangulo-triruthenium compound, 2[Ru3(C21H21AsO3)(C25H22P2)(CO)9]·CH2Cl2, contains one triangulo-triruthenium complex mol­ecule and one half-mol­ecule of the dichloro­methane solvent. The dichloro­methane solvent lies across a crystallographic inversion center leading to the mol­ecule being disordered over two positions of equal occupancy. The bis­(diphenyl­phosphino)methane ligand bridges an Ru—Ru bond and the monodentate arsine ligand bonds to the third Ru atom. Both the arsine and phosphine ligands are equatorial with respect to the Ru3 triangle. In addition, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. The three arsine-substituted benzene rings make dihedral angles of 82.00 (6), 76.67 (7) and 66.09 (6)° with each other. The dihedral angles between the two benzene rings are 80.12 (8) and 78.34 (7)° for the two diphenyl­phosphino groups. In the crystal packing, the mol­ecules are linked together into chains down the b axis via inter­molecular C—H⋯O hydrogen bonds. An inter­molecular C—H⋯O hydrogen bond and weak inter­molecular C—H⋯π inter­actions further stabilize the crystal structure.

μ-Bis(diphenylarsino)methane-1:2κ2As:As′]nonacarbonyl-1κ3C,2κ3C,3κ3C-[tris(4-fluorophenyl)phosphine-3κP]-triangulo-triruthenium(0)

In the title triangulo-triruthenium compound, [Ru3(C25H22(As2)(C18H12F3P)(CO)9], the bis­(diphenyl­arsino)methane ligand bridges an Ru—Ru bond and the monodentate phosphine ligand bonds to the third Ru atom. Both the phosphine and arsine ligands are equatorial with respect to the Ru3 triangle. Additionally, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. The three phosphine-substituted rings make dihedral angles of 87.76 (13), 57.43 (13) and 73.81 (12)° with each other. The dihedral angles between the pairs of rings are 69.78 (14) and 83.38 (16)° for the two diphenyl­arsino groups. In the crystal packing, mol­ecules are linked by inter­molecular C—H⋯F and C—H⋯O hydrogen bonds, forming two-dimensional planes parallel to the ab plane. These planes are also linked by inter­molecular C—H⋯O hydrogen bonds into a three-dimensional framework. Inter­molecular C—H⋯π inter­actions further stabilize the crystal structure.

μ-Bis(diphenylphosphino)methane-1:2κ2P:P′]nonacarbonyl-1κ3C,2κ3C,3κ3C-[tris(4-methylphenyl)arsine-3κAs]-triangulo-triruthenium(0)

In the title triangulo-triruthenium compound, [Ru3(C21H21As)(C25H22P2)(CO)9], the bis­(diphenyl­phos­phino)methane ligand bridges an Ru—Ru bond and the monodentate arsine ligand bonds to the third Ru atom. Both the phosphine and arsine ligands are equatorial with respect to the Ru3 triangle. Additionally, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. The three arsine-substituted phenyl rings make dihedral angles of 87.36 (10), 81.96 (10) and 73.37 (11)° with each other. The dihedral angles between the two phenyl rings are 88.08 (12) and 80.15 (10)° for the two diphenyl­phosphino groups. In the crystal packing, the mol­ecules are linked together as dimers via inter­molecular C—H⋯O hydrogen bonds. These dimers are stacked down b axis. Inter­molecular C—H⋯π and π–π inter­actions [centroid–centroid distance = 3.6383 (13) Å] further stabilize the crystal structure.

μ-Bis(diphenylarsino)methane-1:2κ2As:As′]nonacarbonyl-1κ3C,2κ3C,3κ3C-tricyclohexylphosphine-3κP-triangulo-triruthenium(0)

In the title triangulo-triruthenium compound, [Ru3(C25H22As2)(C18H33P)(CO)9], the bis­(diphenyl­arsino)methane ligand bridges an Ru—Ru bond and the monodentate phosphine ligand bonds to the third Ru atom. Both the phosphine and arsine ligands are equatorial with respect to the Ru3 triangle. In addition, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. All three cyclo­hexane rings are disordered over two positions with site occupancies of 0.628 (6) and 0.372 (6). The mean planes of these three phosphine-substituted cyclo­hexane rings make dihedral angles of 53.0 (8), 68.3 (6) and 89.9 (7)° (major components), and 46.7 (14), 41.3 (11) and 75.8 (10)° (minor components) with each other. The dihedral angles between the two phenyl rings are 85.0 (2) and 88.1 (2)° for the two diphenyl­arsino groups. Two cyclo­hexane rings adopt a chair conformation whereas the other adopts a slightly twisted chair conformation for the major components; these conformations are similiar for the minor components. Intra­molecular C—H⋯O hydrogen bonds stabilize the mol­ecular structure. In the crystal packing, the mol­ecules are linked together into chains via inter­molecular C—H⋯O hydrogen bonds down the a axis. Weak inter­molecular C—H⋯π inter­actions further stabilize the crystal structure.

μ-Bis(diphenylarsino)methane-1:2κ2As:As-nonacarbonyl-1κ3C,2κ3C,3κ3C-[(2-methoxyphenyl)diphenylphosphino-3κP]-triangulo-triruthenium(0)

In the title triangulo-triruthenium compound, [Ru3(C25H22As2)(C19H17OP)(CO)9], the bis­(diphenyl­arsino)methane ligand bridges a Ru—Ru bond and the monodentate phosphine ligand bonds to the third Ru atom. Both the phosphine and arsine ligands are equatorial with respect to the Ru3 triangle. Additionally, each Ru atom carries one equatorial and two axial terminal carbonyl ligands. The three phosphine substituted phenyl rings make dihedral angles of 74.34 (12), 68.34 (12) and 85.45 (11)° with each other. The dihedral angles between the two phenyl rings are 87.56 (11) and 60.56 (11)° for the two diphenyl­arsino groups. In the crystal packing, the mol­ecules are linked together into chains via inter­molecular C—H⋯O hydrogen bonds down the a axis. Weak inter­molecular C—H⋯π inter­actions further stabilize the crystal structure.

Remarkable Product Diversity in the “Self-Organized” Reaction of Deprotonated Acetonitrile with Chlorophosphines

This study examined the reaction of in situ deprotonated acetonitrile with different chlorophosphines ClPR(2) (5a-d) to find new nitrile functionalized bis(diphenylphosphino)methane (dppm) ligands. Depending on the steric and electronic demand of the phosphines, very different and unexpected products (1b, 6, 9b and 11) were found. In the case of aryl-substituted phosphines (ClPPh(2) (5a) and ClPMes(2) (5b)), bis(diarylphosphino)acetonitrile compounds (1a and 1b) were found. Introduction of alkyl substituents at the ClPR(2) fragment (R = (t)butyl (5c) and cyclohexyl (5d)) changes the overall reaction behavior drastically. A new heteropentafulvene type structure (6), a P/N-disubstituted acetylene (9), and a P-substituted 3-amidocrotononitrile species (11) were found. Considering the experimental simplicity of these three-component reactions, these products are complex and their formations are highly organized. Most compounds were characterized by X-ray diffraction, NMR spectroscopy, and elemental analysis.

Monofluoride Bridged, Binuclear Metallacycles of First Row Transition Metals Supported by Third Generation Bis(1-pyrazolyl)methane Ligands: Unusual Magnetic Properties

The reaction of M(BF(4))(2).xH(2)O, where M is Fe, Co, Cu, and Zn, and the ditopic, bis(pyrazolyl)methane ligand m-[CH(pz)(2)](2)C(6)H(4), L(m), where pz is a pyrazolyl ring, yields the monofluoride bridged, binuclear [M(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes. In contrast, a similar reaction of L(m) with Ni(BF(4))(2).6H(2)O yields dibridged [Ni(2)(mu-F)(2)(mu-L(m))(2)](BF(4))(2). The solid state structures of seven [M(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes show that the divalent metal ion is in a five-coordinate, trigonal bipyramidal, coordination environment with either a linear or nearly linear M-F-M bridging arrangement. NMR results indicate that [Zn(2)(mu-F)(mu-L(m))(2)](BF(4))(3) retains its dimeric structure in solution. The [Ni(2)(mu-F)(2)(mu-L(m))(2)](BF(4))(2) complex has a dibridging fluoride structure that has a six-coordination environment about each nickel(II) ion. In the solid state, the [Fe(2)(mu-F)(mu-L(m))(2)](BF(4))(3) and [Co(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes show weak intramolecular antiferromagnetic exchange coupling between the two metal(II) ions with J values of -10.4 and -0.67 cm(-1), respectively; there is no observed long-range magnetic order. Three different solvates of [Cu(2)(mu-F)(mu-L(m))(2)](BF(4))(3) are diamagnetic between 5 and 400 K, thus showing strong antiferromagnetic exchange interactions of -600 cm(-1) or more negative. Mossbauer spectra indicate that [Fe(2)(mu-F)(mu-L(m))(2)](BF(4))(3) exhibits no long-range magnetic order between 4.2 and 295 K and isomer shifts that are consistent with the presence of five-coordinate, high-spin iron(II).

Carbonyl[tris(3,5-diphenylpyrazol-1-yl-κN2)methane]copper(I) hexafluoridophosphate–dichloromethane–diethyl ether (4/3/1)

In the title compound, [Cu(C46H34N6)(CO)]PF6·0.75CH2Cl2·0.25C4H10O, the CuI atom is coordinated by three N atoms from the tridentate chelating tris­(3,5-diphenyl­pyrazol-1-yl)methane ligand (average Cu—N distance = 2.055 Å) and the C atom from a carbon monoxide ligand in a distorted tetra­hedral coordination geometry. The average N—Cu—N angle between adjacent pyrazole-ring-coordinated N atoms is 88.6°, while the average N—Cu—C angle between the pyrazole-bound N atom and the C atom of carbon monoxide is 126.3°. One of the 3-phenyl rings of the tris­(pyrazol­yl)methane ligand is disordered over two sites each with an occupancy factor of 0.50. The structure also exhibits disorder of the monosolvate that has been modeled with 0.75 CH2Cl2 and 0.25 Et2O occupancy.

Catena-Poly[[[acetonitrilecopper(I)]-bis[μ-bis(diphenylphosphino)methane-κ2P:P′]-copper(I)-μ-1,2-di-4-pyridylethene] bis(tetrafluoridoborate)

The title dinuclear copper(I) complex, {[Cu2(C2H3N)(C12H10N2)(C25H22P2)2](BF4)2}n, contains 1,2-di-4-pyridyl­ethene, bis­(diphenyl­phosphino)methane and acetonitrile ligands. The two Cu atoms, one with an N2P2 ligand set and the other with an NP2 ligand set, are bridged by two bis­(diphenyl­phosphino)methane ligands, forming an eight-membered ring.

{μ-Bis(1-methylimidazol-2-yl)methane-κ2N3:N3′}bis{[(1-methylimidazol-2-yl)methane-κ2N3,N3′]copper(I)} bis(trifluoromethanesulfonate)

The title compound, [Cu2(C9H12N4)3](CF3SO3)2, contains two CuI ions, three bis­(1-methyl­imidazol-2-yl)methane (Me2BIM) ligands, and two trifluoromethanesulfonate anions in the asymmetric unit. Each CuI ion has a distorted trigonal-planar geometry and is coordinated by two N atoms from the Me2BIM ligand and another N atom from the Me2BIM that acts as a bridging ligand, another N atom of the bridging Me2BIM being linked to the second CuI ion. The imidazole rings of Me2BIM form intra­molecular π–π stacking inter­actions [centroid–centroid distances = 3.445 (2) and 3.547 (2) Å].

Dichlorido{[(diphenylphosphino)methyl]bis(2-methylphenyl)phosphine-κ2P,P′}palladium(II)

In the title compound, [PdCl2(C27H26P2)] or PdCl2[(C6H5)2PCH2P(C6H4CH3)2], the palladium center has a distorted square-planar geometry. There are two crystallographically independent mol­ecules in the asymmetric unit. The dihedral angle between the PdP2 and PdCl2 planes is 2.95 (4)° in one independent mol­ecule and 5.15 (4)° in the other. The P—Pd—P and P—C—P bond angles are significantly distorted because of the small bite angle of the chelating (bis­phosphino)methane ligand. The steric demands of the substituted rings in the mixed ligand cause a slight elongation of the Pd—P(C6H4CH3)2 bond relative to the Pd—P(C6H5)2 bond. In one molecule the tolyl ring shows positional disorder in a 0.58 (2):0.42 (2) ratio, in the other molecule the phenyl ring shows positional disorder in a 0.838 (9):0.162 (9) ratio.

Single-Electron Transfer in Palladium Complexes of 1,4-Naphthoquinone-Containing Bis(pyrazol-1-yl)methane Ligands

A 1,4-naphthoquinone-substituted bis(pyrazol-1-yl)methane ligand (N--N) has been synthesized and transformed into its corresponding Pd(II) chelate complex [(N--N)PdCl(2)]. Both N--N and [(N--N)PdCl(2)] have been fully characterized by NMR spectroscopy, spectro-electrochemistry, and X-ray crystallography. After treatment of [(N--N)PdCl(2)] with NEt(3), the signature of a 1,4-naphthosemiquinonate radical is visible in the UV-vis- and electron paramagnetic resonance (EPR) spectrum of the reaction mixture; the free ligand N--N does not react with NEt(3) under the conditions applied. It is therefore concluded that NEt(3) first reduces the Pd(II)-ion of [(N--N)PdCl(2)] to the zero-valent state and that this reaction is followed by a single-electron transfer from the metal atom to the 1,4-naphthoquinone moiety. The complex has been specifically designed to disfavor any direct Pd-to-naphthoquinone coordination. Electron transfer thus proceeds through space or, less likely, via sigma-bonds of the ligand framework.

Copper Complexes with Neutral N4 Tripodal Ligands: Influence of the Number of Nitrogen Donors on Their Structures, Properties, and Reactivity

AbstractCopper coordination complexes of the neutral tetradentate nitrogen‐containing ligands tris(3,5‐dimethylpyrazol‐1‐ylmethyl)amine (L0N4) and tris(3,5‐diisopropylpyrazol‐1‐ylmethyl)amine (L1N4), namely the copper(II) chlorido complexes [CuII(L0N4)Cl2] (1) and [CuII(L1N4)Cl2] (2), the copper(II) nitrato complexes [CuII(L0N4)(NO3)](NO3) (3) and [CuII(L1N4)(NO3)](NO3) (4), and the copper(II) sulfato complexes [CuII(L0N4)(SO4)] (5) and [CuII(L1N4)(SO4)] (6), and the copper(I) complexes [CuI(L0N4)](PF6) (7) and [CuI(L0N4)(PPh3)](ClO4) (8), have been systematically synthesized in order to investigate the influence of the number of nitrogen donors on their structures, properties, and reactivity. All copper(II) complexes were fully characterized by X‐ray crystallography and by IR/far‐IR, UV/Vis absorption, and ESR spectroscopy. Although the structure of 7 was not determined by X‐ray crystallography, this complex and the structurally characterized copper(I) triphenylphosphane complex 8 were fully characterized by IR/far‐IR and NMR spectroscopy. A comparison of the copper(II) complexes with two tris(pyrazol‐1‐ylmethyl)amine ligands with different bulkiness of the pyrazolyl rings has allowed us to evaluate the second coordination sphere effects of the ligands. Moreover, the structures and physicochemical properties of these complexes are compared with those of related complexes containing the neutral tridentate tris(pyrazolyl)methane ligand and the neutral bidentate bis(pyrazolyl)methane ligand. Finally, the relative stability of the copper(I) complexes is discussed. The influence of the number of nitrogen donors in copper complexes is observed from these systematic results.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)

New Zinc Complexes bearing κ2-Heteroscorpionate Ligands: Influence of Second-Sphere Bonding Interactions on Reactivity and Properties

New zinc complexes (LOMe)ZnCl(2) (1) and (LOH)ZnCl(2)(2) of the heteroscorpionate ligands 1-[(3,5-di-tert-butyl-2-methoxyphenyl)(3,5-dimethyl-pyrazol-1-yl)methyl)]-3,5-dimethyl-pyrazole (LOMe) and 2,4-di-tert-butyl-6-[bis(3,5-dimethyl-pyrazol-1-yl)methyl]phenol (LOH) have been synthesized. The X-ray molecular structure of 2 was reported and compared with the one of the iron(II) complex (LOH)FeI(2) (3). The complexes 2-3 adopt a tetrahedral structure in the solid state in which the LOH ligand is kappa(2)-coordinated to the metal via the imino nitrogens of the two pyrazolyl rings. The hydroxyl phenyl group is not coordinated to the metal but found to be involved in an intermolecular hydrogen bond. The solution structures of 1 and 2 are consistent with this tetrahedral C(S) symmetric geometry. Dilution and (1)H-(1)H Nuclear Overhauser Effect Spectroscopy (NOESY) experiments revealed that the free ligands LOMe and LOH are involved in intra- and intermolecular hydrogen bonding interactions. Coordination of LOMe and LOH to ZnCl(2) was investigated by NMR titration methods. Association constants (K(a)) of (8.6 +/- 0.4) x 10(2) M(-1) and (7.8 +/- 0.3) x 10(2) M(-1) were obtained in methanol/water solutions (95:5) for LOMe and LOH, respectively. Coordination of bis(3,5-dimethyl-pyrazol-1-yl)methane (bpm) ligand to ZnCl(2) is weaker, as evidenced by the lower value of the association constant (5.3 +/- 0.3) x 10(2) M(-1). When bpm was added to solutions of 1 or 2, an equilibrium shifted toward the (bmp)ZnCl(2) species was observed. The thermodynamic parameters for this reaction were determined by VT NMR analysis. The optical properties of the ligands (LOMe, LOH) and of the corresponding zinc complexes 1 and 2 were also investigated by means of UV-vis and fluorescence spectroscopy to assess the potential use of these ligands as fluorescent sensors for Zn(2+) detection.

Spin-state splittings of iron(II) complexes with trispyrazolyl ligands

We report a computational study at the OPBE/TZP level on the chemical bonding and spin ground-states of mono-nuclear iron(II) complexes with trispyrazolylborate and trispyrazolylmethane ligands. We are in particular interested in how substitution patterns on the pyrazolyl-rings influence the spin-state splittings, and how they can be rationalized in terms of electronic and steric effects. One of the main observations of this study is the large similarity of the covalent metal–ligand interactions for both the borate and methane ligands. Furthermore, we find that the spin-state preference of an individual transition-metal (TM) complex does not always concur with that of an ensemble of TM-complexes in the solid-state. Finally, although the presence of methyl groups at the 3-position of the pyrazolyl groups leads to ligand–ligand repulsion, it is actually the loss of metal–ligand bonding interactions that is mainly responsible for shifts in spin-state preferences.