Ambidentate Ligand Research Articles

Diverse polymeric metal complexes formed by the ambidentate ligand 1-(4′-pyridyl)pyridin-4-one

The preparations are reported of a range of metal complexes of the ‘extended reach’ ambidentate ligand 1-(4′-pyridyl)pyridin-4-one (pypd), four of which have been shown by X-ray studies to have polymeric network structures. The compound [Cu(pypd) 2(H 2O) 4](NO 3) 2·4H 2O ( 1) forms sheets comprising [Cu(pypd) 2(H 2O) 4] units linked by a complex set of hydrogen bonds. Crystals of stoichiometry Co(pypd) 2(NCS) 2·MeOH·H 2O ( 2) contain a 1:1 co-crystallisation of [Co(pypd) 2(H 2O) 2(NCS) 2] and [Co(pypd) 2(MeOH) 2(NCS) 2] each forming hydrogen bonded chains, which are linked into sheets by further hydrogen bonds. A combination of hydrogen bonding and π–π stacking between pyridyl and pyridone rings in Nd(pypd) 2(H 2O) 2(NO 3) 3 ( 3) also generates a sheet structure. The compound [Cd(pypd) 3](ClO 4) 2·3H 2O ( 4) forms a complex 3D network.

Different coordination modes of saccharin in the metal complexes with 2-pyridylmethanol: synthesis, spectroscopic, thermal and structural characterization

The reaction of [M(sac) 2(H 2O) 4]·2H 2O, where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II), and sac is the saccharinate anion, with 2-pyridylmethanol (mpy) result in the formation of the new complexes, which have been characterized by elemental analyses, magnetic measurements, FT-IR spectroscopy, thermal analysis and X-ray diffraction methods. The [Co(sac) 2(mpy) 2] ( 3) and [Ni(sac) 2(mpy) 2] ( 4) complexes are isomorphous with the triclinic space group the two sac ligands in both 3 and 4 exhibit unusual and non-equivalent coordination. One of them coordinates to the metals through the imino nitrogen atom, while the other is bonded to the metals with the carbonyl oxygen atom behaving as an ambidentate ligand. The [Cu(sac) 2(mpy) 2] ( 5) complex is centrosymmetric and crystallizes in orthorhombic space group and both sac ligands in ( 5) are N-coordinated. [Hg 2(sac) 4(mpy) 2] ( 8) crystallizes in monoclinic space group P2 1/ n. In 8, the mpy ligands acts as a bridge between the mercury two mercury(II) centres and the complex 8 consists of one-dimensional chains in which dimeric [Hg 2(sac) 4(mpy) 2] units are sequentially bridged by bis-bidentate sac ligands forming a coordination polymer. In all cases, the metal atoms are six-coordinate. The mpy molecules act as a bidentate N- and O-donor ligand in 1– 7. Thermal decomposition of the complexes in air results in removal of mpy ligands and formation of stable metal saccharinates as intermediates, which also decompose at higher temperatures to give the corresponding metal oxides.

The Coordination Chemistry of 3,3′-Diamino-2,2′-bipyridine and Its Dication: Exploring the Role of the Amino Groups by X-ray Crystallography

The cover picture shows the pH-dependent coordination chemistry of the potentially ambidentate ligand 2,2′-bipyridine-3,3′-diamine. A dimeric 2:2 complex is formed with copper(II) chloride in which each copper ion is bound to two pyridine nitrogen atoms and two chloride ions in a distorted square-planar arrangement, with a long axial contact from a neighbouring amino group completing a distorted square-pyramidal geometry. Under acidic conditions, both pyridine nitrogen atoms are protonated preventing coordination to the copper(II) ion and as a consequence, the two amino groups together with four chloride ions are bound to the metal ion completing an octahedral coordination sphere. Details are discussed in the article by J. D. Wallis, M. Pilkington et al. on p. 1985 ff.

Complex Formation of Phosphoryl- and Thiophosphorylacylacetonitriles with Different Cations

The enols R 1 R 2 P(E)(CN)C = CR 3 OH (E = O or S) gave in solutions either neutral metal complexes ML x or M(OH) y L x . The anionic ambidentate ligands are coordinated through E and O atoms in solutions, and O, E, and N atoms in in crystals.

Organotin(IV) complexes of 4,6-dimethylpyrimidine-2-thione, Me 2PymtH. Preparation, characterization and crystal structure determination of cis-[Ph 2Sn(Me 2Pymt) 2] and [Ph 3Sn(Me 2Pymt)

The coordination mode of the ambidentate ligand 4,6-dimethylpyrimidine-2-thione (Me 2PymtH) was investigated with respect to the organotin(IV) compounds, namely Me 2SnCl 2, n-Bu 2SnCl 2, Ph 2SnCl 2 and Ph 3SnCl. An X-ray crystal structure determination carried out on cis-[Ph 2Sn(Me 2Pymt)] ( 3) and [Ph 3Sn(Me 2Pymt)] ( 4) revealed that the Me 2Pymt − ligand is N,S-coordinated in both complexes. The Sn(IV) atom is six-coordinated in 3 and five-coordinated in 4. The similarities observed in the IR, NMR ( 1H, 13C) and mass spectroscopy are indicative of a similar behavior of the ligand in all the complexes, thus suggesting a six-coordination in the dimethyltin ( 1) derivative and five-coordination in the dibutyltin ( 2) one. The complexes were characterized by means of elemental analysis, IR, NMR ( 1H, 13C) and mass spectroscopic methods.

Combination of weak covalent, hydrogen bonding, and Ag⋯π interactions in the formation of a 3D porous network Ag(pypd)2(ClO4)·CH2Cl2 by the ambidentate ligand 1-(4′-pyridyl)pyridin-4-one

An interesting diversity of linkage types — weak covalent, hydrogen bonding, and Ag⋯π interactions — is shown to be involved in the 3D porous network formed by the title compound.

Synthesis, spectroscopic characterization and X-ray crystallographic studies of trans-[PtCl2(PEt3)(PySOR)] complexes, where PySOR= (2-methylsulphinyl)-pyridine and (2-n-propylsulphinyl)pyridine

Alkylsulphinylpyridine ligands containing three potential donor centres: N, S and O atoms and two complexes of general formula trans-[PtCl2(PEt3)PySOR)] (R = Me and n Pr) were prepared and characterized by elemental analysis, i.r. spectroscopy, 1H- and 31P-n.m.r. and X-ray crystallography. The ambidentate ligands act in both situations as monodentate ligands, bonded to the metal exclusively through the nitrogen atom. The crystal structures revealed the occurrence of discrete molecules and, in both complexes, the Pt atoms are coordinated in square planar arrangements by two chloride ions, in a trans configuration, by the pyridine nitrogen atom, and by the phosphine P atom. The oxygen atoms do not take part in the complexation scheme.

Synthesis and characterization of polypyridineruthenium(II) complexes containing a linear ambidentate ligand, NCO − or NCS −, and reaction of isocyanato complexes under acidic conditions

Isocyanato and isothiocyanatopolypyridineruthenium complexes, [Ru(NCX)Y(bpy)(py) 2] n+ (bpy=2,2′-bipyridine, py=pyridine; X=O, Y=NO 2 for n=0, and Y=py for n=1; X=S, Y=NO 2 for n=0, Y=NO for n=2, and Y=py for n=1), were synthesized by the reaction of polypyridineruthenium complexes with potassium cyanate or sodium thiocyanate salt. Isocyanatoruthenium(II) complexes, [Ru(NCO)(NO 2)(bpy)(py) 2] and [Ru(NCO)(bpy)(py) 3] +, react under acidic conditions to form the corresponding ammineruthenium complexes, [Ru(NO)(NH 3)(bpy)(py) 2] 3+. The molecular structures of [Ru(NCO)(bpy)(py) 3]ClO 4, [Ru(NCS)(NO)(bpy)(py) 2](PF 6) 2 and [Ru(NO)(NH 3)(bpy)(py) 2](PF 6) 3 were determined by X-ray crystallography.

Synthesis and characterization of two tris-chelate complexes of cobalt(III) with 3,5-dimethyl-1-( N-methyl/ethyl)thiocarbamylpyrazole (HL 1, HL 2) — biologically important bidentate ligands with one ambidentate donor site

Cobalt(III) complexes, of two potentially pyrazole-derived bidentate ligands (with one ambidentate donor site), 3,5-dimethyl-1-( N-methyl/ethyl)thiocarbamylpyrazole (HL 1 for N-methyl, HL 2 for N-ethyl) have been synthesized and characterized by elemental analyses, IR, UV–Vis and 1H NMR spectral studies. The structure of Co(L 2) 3 has been determined by single-crystal X-ray diffraction studies. The complex (triclinic, space group P1̄) has a distorted octahedral structure with the ambidentate ligands coordinated to the Co(III) ion as uninegative bidentate chelating agents via the pyrazole ring nitrogen (tertiary) and the thiocarbamyl iminyl nitrogen atoms. The distortion from the regular octahedral geometry is ascribed to the stereochemical limitations imposed by the planar bidentate ligands.

Modified Bipyridines: 5,5′-Diamino-2,2′-bipyridine Metal Complexes Assembled into Multidimensional Networks via Hydrogen Bonding and π–π Stacking Interactions

A new synthetic route for the synthesis of 5,5′-diamino-2,2-bipyridine (5) based on the coupling of 2-chloro-5-aminopyridine in the presence of NiCl2 × 6 H2O/PPh3/Zn in dimethylformamide is described. The reactions of the potentially ambidentate ligand 5 with salts of the transition metals Mn, Fe, Ni, Cu, Zn, Ag, and Cd gave a variety of 13 metal–ligand complexes depending on the anion, the crystallization conditions and the metal-to-ligand ratio. The complexes obtained were characterized by thermal analyses, NMR including 113Cd-NMR, IR, and for the iron complex 57Fe-Mößbauer spectroscopy. The structure of eight of the compounds was elucidated by X-ray crystallography. All of these metal complexes show a bipyridine–metal coordination. The amino functionality was never involved in metal coordination. The intermolecular arrangement is dictated by hydrogen bonding from the amino functionality and by π–π stacking of the bipyridine rings.

Modified Bipyridines: 5,5′-Diamino-2,2′-bipyridine Metal Complexes Assembled into Multidimensional Networks via Hydrogen Bonding and π–π Stacking Interactions

A new synthetic route for the synthesis of 5,59-diamino-2,2- NMR including 113 Cd-NMR, IR, and for the iron complex 57 Fe-Mosbauer spectroscopy. The structure of eight of the bipyridine (5) based on the coupling of 2-chloro-5aminopyridine in the presence of NiCl2 × 6H 2O/PPh3/Zn in compounds was elucidated by X-ray crystallography. All of these metal complexes show a bipyridine‐metal dimethylformamide is described. The reactions of the potentially ambidentate ligand 5 with salts of the transition coordination. The amino functionality was never involved in metal coordination. The intermolecular arrangement is metals Mn, Fe, Ni, Cu, Zn, Ag, and Cd gave a variety of 13 metal‐ligand complexes depending on the anion, the dictated by hydrogen bonding from the amino functionality and by ﷿‐﷿ stacking of the bipyridine rings. crystallization conditions and the metal-to-ligand ratio. The complexes obtained were characterized by thermal analyses,

Chloride Substitution Reactions of Cycloruthenated (R)(C)-(+)-N,N-Dimethyl(1-phenylethyl)amine with Pseudohalides: Ruthenium Atom Stereochemistry.

The diastereoselectivity of chloride substitution by the pseudohalides azide, nitrite, thiocyanate, and cyanate in has been determined by a combination of (1)H and (13)C{(1)H} NMR spectroscopy, UV-visible spectroscopy, circular dichroism, infrared spectroscopy, and single-crystal X-ray crystallography. These chloride substitution reactions proceed with predominant retention of configuration at ruthenium. For the ambidentate ligands thiocyanate and nitrite, the major bonding mode is through their nitrogen donor atoms.

Synthesis, Characterization, and Diastereoselectivity of Chloride Substitution Reactions of Cycloruthenated (R)C-(+)-N,N-Dimethyl-α-(2-naphthyl) Ethylamine

The transmetalation reaction of enantiomerically pure 1, with [(η6-C6H6)RuCl2]2 in CH3CN at ambient temperature forms a mixture of two diastereomeric ruthenacycles (SRu, RC), 2a, (96%) and (RRu, RC), 2a‘, (4%) of the type in good chemical and optical yields. The diastereoselectivity of chloride substitution in 2a,a‘ by bromide, iodide, azide, cyanate, thiocyanate, nitrite, allylisonitrile, and selected nitrogen and phosphorus donor ligands has been determined by an appropriate combination of 1H, 13C{1H}, and 31P{1H} NMR spectroscopy, UV−visible spectroscopy, circular dichroism, and single-crystal X-ray crystallography. The diastereoselectivity generally increases with increasing steric bulk of the incoming ligand and proceeds with predominant retention of configuration at ruthenium. The ambidentate ligands, cyanate, thiocyanate, and nitrite all bond to ruthenium exclusively through their nitrogen donor atoms.

5,5′-Dicyano-2,2′-bipyridine silver complexes: discrete units or co-ordination polymers through a chelating and/or bridging metal–ligand interaction

The ambidentate ligand 5,5′-dicyano-2,2′-bipyridine (L) was found to function as a bi-, tri- or tetra-dentate chelate or chelate/bridging ligand in the co-ordination of silver ions. The mode of co-ordination depends on the anion and the crystallization conditions and was elucidated by single crystal X-ray diffractometry. With metal-co-ordinating anions such as NO3– and CF3SO3– a tridentate co-ordination mode of L is observed which involves the two bipyridine nitrogen donor atoms and one cyano group. The latter bridges to a neighboring silver center so that a one-dimensional co-ordination polymer results. For NO3– this co-ordination polymer forms a 21 helix. With less co-ordinating anions such as BF4– and PF6– monomeric bis-chelate complexes are obtained, where L assumes a bidentate co-ordination mode involving only the bipyridine nitrogen donor atoms. In the case of the PF6– anion a variation in the solvent of crystallization also produced a two-dimensional hexagonal co-ordination polymer where L functions as a tetradentate ligand using all four nitrogen donor atoms in chelation and bridging to the silver centers.

Kristallstrukturen, Schwingungsspektren und Normalkoordinatenanalyse von cis-[ReCl4X2]2-, X = NCS, NCSe / Crystal Structures, Vibrational Spectra and Normal Coordinate Analysis of cis-[ReCl4X2]2-, X = NCS, NCSe

The crystal structures of cis-(n-Bu4N)2[ReCl4(NCS)2] (triclinic, space group P1̅, a = 11,245( 1), b = 20.174(3), c = 21.320(8) Å, a =109.06(2), β = 96.46(2), γ = 98.22(5)°, Z = 4) and cis-(Ph4P)2[ReCl4(NCSe)2]·2CH2Cl2 (triclinic, space group P1̅, a = 10.341(2), b = 13.436(3), c = 19.616(4) Å, α = 92.70(2), β = 92.02(2), γ = 89.99( 1)°, Z= 2) have been determined by single crystal X-ray diffraction analysis. Both ambidentate ligands NCS and NCSe are bonded via the N atom. Using the molecular parameters of the X-ray determinations the low temperature (10 K) IR and Raman spectra of the (n-Bu4N) salts have been assigned by normal coordinate analysis based on a modified valence force field. The valence force constants fd(ReN) are 1,78(NCS) and 1,79(NCSe) mdyn/ Å.

Synthesis and physical studies of copper(I) complexes with the ambidentate ligand (1-piperidyl-2-diphenylphosphino)ethane. X-ray structural characterization of a copper(I) dimer

Copper(I) complexes with (1-piperidyl-2-diphenylphosphino)ethane (L) as phosphorus and nitrogen donors ligand have been synthesized. Complex 1 has been characterized by single-crystale determinationas a centrosymmetric dihalide bridged binoclear complex of general formula [LCu(μ-X) 2CuL] in space group P2 1/n with a = 9.046(2), b = 16.144(2) and 12.754(4) A ̊ , β = 93.68(2)°, Z = 2 . Both phosphorus and nitrgoen are coordinated to copper which is tetra-coordinated. The CuN bond distance is partivularly long (2.2878(2) Å) and greatly exceeds the sun of the covalent radii. Complex 2 has been only identified by chemical analysis, mass spectra and NMR spectroscopy. These data allow us to propose the [L 2Cu]PF 6 formula, with two ligands bonded to copper in a chelating mode by phosphorus and nitrogen.

Metal-binding Ability of Desferrioxamine B

The metal complex formation properties of the naturally-occurring hydroxamate-type siderophore Desferrioxamine B is surveyed with special emphasis on its solution speciation. The most likely binding-modes of the complexes formed with this ambidentate ligand are also evaluated. A brief survey of the implications of metal chelation in the therapeutic role of DFB in the treatment of metal overloads is also given.

Synthesis, IR and X-Ray Studies of a Dioxouranium(VI) Nitrate Complex with N,N′-Tetraethyl-N″ -trichloracetylphosphortriamide

A new dioxouranium(VI) nitrate complex with N,N′-tetraethyl-N″-trichloracetylphosphortriamide (HL = CCl3C(O)N(H)P(O)(NEt2)2) of composition UO2 (HL)2(NO3)2 (1) has been synthesised. The IR spectroscopic data reveal that the ambidentate ligand is coordinated to the metal center in a monodentate manner via the phosphoryl oxygen atom. The crystal and molecular structure of 1 has been determined from X-ray diffraction data (triclinic, space group P1̄ with a = 9.225(2), b = 10.360(2), c = 12.249(2) Å, α = 100.02 (1), β = 103.81(1), γ = 108.80 (1)°, Z = 1; R = 0.037 for 4092 unique reflections. The structure is made up of centrosymmetric molecules in which the neutral ligands HL are monocoordinated. Phosphoryl and carbonyl groups of the HL moieties are in the trans positions to each other. The axial vertices of the distorted hexagonal bipyramid of uranium are occupied by two oxo ligands [U-O 1.753(5) Å] while six oxygen atoms of phosphoryl and nitrate groups lie in the equatorial plane [U-O 2.347(5)-2.547(6)Å],

Metal-Organic Layer Magnets with and without Metallic Conduction

A distinguishing feature of molecular-based magnetic materials is that the vast majority of examples are insulators, and the microscopic magnetic moments are therefore localised. Maximum connectivity between centres carrying the moments is therefore desirable to maximise ordering temperatures, so ambidentate ligands are most effective. We have been studying the bimetallic tris-oxalato series AMFeIII(C2O4)3 from this point of view and the lecture will give an overview of results. We concentrate on organic cations A stabilising a hexagonal layer structure since the details of magnetic ordering are highly sensitive to changes in the packing of A between the layers. In contrast when A = BEDT-TTF the organic layer is conducting and in one case superconductivity has been found.

2-(Diphenylphosphino)-pyridine as an Ambidentate Ligand in Homo-and Hetero-binuclear Complexes of Copper, Silver, and Gold

Abstract The reaction of 2-diphenylphosphino-pyridine (1) with AgBF4 in an equimolar ratio affords the cyclic, dinuclear complex 2 with mixed P,N-coordination of the metal atoms. With two equivalents of 1 the 2:1 complexes 4a,b are formed which have the metal atoms solely Pcoordinated. The previously reported gold complex (3), an analogue of 2, or [Au(tht)2]ClO4 (tht = tetrahydrothiophen) also give the 2:1 complexes (5a,b) when treated with an excess of ligand 1. Addition of AgClO4 to a solution of 5a in acetone, or treatment of 4a with [Au(tht)2]ClO4 in dichloromethane, give the same mixed-metal complex 6, where the Au atoms are exclusively P-coordinated, while the Ag atoms are coordinated by the two pyridine nitrogen atoms. In the crystal there are also weak interactions of the perchlorate counterions with the silver atom. Addition of [Cu(MeCN)4]BF4 to compound 5b gives the Cu/Au-complex with P,P-coordinated gold and N,N-bonded copper centers. All products were characterized by standard analytical and spectroscopic techniques; the crystal structure of complex 6 was determined in a single crystal X-ray diffraction study.