Second-sphere Coordination Complexes Research Articles

Dehydrohalogenation reactions in second-sphere coordination complexes.

The latest advances of solid-state dehydrohalogenation and halogenation reactions of hydrogen bonded halometallate salts from the second sphere coordination perspective are reported. Since the second sphere englobes many different materials, our focus has been limited to outer sphere adducts where protonated organic cations act as outer sphere hydrogen bond donors and transition metal anions act as first sphere hydrogen bond acceptors. This is our attempt to analyze dehydrohalogenation/hydrohalogenation reactions viewed as transformations from the second sphere coordination to first sphere coordination of a complex and vice versa. The examples describe a unique solid-state chemistry and reactivity in outer sphere adducts where C-H, N-H and M-X chemical bonds are cleaved and new M-N and H-X bonds are formed (where M = Cu, Zn, Co, Pt, Pd, Hg and X = Cl, Br). The transformations are induced by external stimuli, mainly by mechanochemical and thermal methods. Different reactivities have been observed depending on the lability of the transition metals, the position of the reacting functional groups in the cations and the relative position of organic cations and metal anions. The reverse hydrohalogenation reactions (i.e., from the first sphere coordination to second sphere coordination) via the gas-solid chemisorption process occur even if the materials are non-porous implying a rather dynamic behaviour of these materials. Moreover, due to the implicit changes in the coordination sphere of transition metal ions, dehydrohalogenation/halogenation reactions allow structure-function correlation to be established, for instance involving optical, sensing and magnetic aspects.

Coordination Chemistry of a Molecular Pentafoil Knot.

The binding of Zn(II) cations to a pentafoil (51) knotted ligand allows the synthesis of otherwise inaccessible metalated molecular pentafoil knots via transmetalation, affording the corresponding “first-sphere” coordination Co(II), Ni(II), and Cu(II) pentanuclear knots in good yields (≥85%). Each of the knot complexes was characterized by mass spectrometry, the diamagnetic (zinc) knot complex was characterized by 1H and 13C NMR spectroscopy, and the zinc, cobalt, and nickel pentafoil knots afforded single crystals whose structures were determined by X-ray crystallography. Lehn-type circular helicates generally only form with tris-bipy ligand strands and Fe(II) (and, in some cases, Ni(II) and Zn(II)) salts, so such architectures become accessible for other metal cations only through the use of knotted ligands. The different metalated knots all exhibit “second-sphere” coordination of a single chloride ion within the central cavity of the knot through CH···Cl– hydrogen bonding and electrostatic interactions. The chloride binding affinities were determined in MeCN by isothermal titration calorimetry, and the strength of binding was shown to vary over 3 orders of magnitude for the different metal-ion–knotted-ligand second-sphere coordination complexes.

Syntheses, structures and properties of four second-sphere coordination complexes via metal halide anion and naphthalene-based ligand

Second-sphere coordination refers to any intermolecular interactions with the ligands directly bound to the primary coordination sphere of a metal ion. Four supramolecular complexes, 0.5[L·2H]2+·0.5[MCl4]2−·[CH3OH]·0.5[CH2Cl2] (M = Co, crystal 1; M = Mn, crystal 2), 0.5[L·2H]2+·0.5[ZnBr4]2−·[CH3OH]·0.5[CH2Cl2] (crystal 3), and 0.5[L·2H]2+·0.5[Cu2Br4]2−·H2O (crystal 4), based on naphthalene-based ligand N,N,N′,N′-tetra-p-methylnaphthyl-ethanediamine (L), have been synthesized. X-ray analysis reveals that 1–3 are isostructural, in which the methanol molecules are bridges, connecting the protonated L and metal chloride anions via N–H⋯O and O–H⋯Cl (Br) interactions to construct the host framework, and forming X-shaped cavity accessible for the inclusion of weakly polar guest molecules of dichloromethane. Dichloromethane is connected with the host framework through van der Waals forces. In 4, a dinuclear anion [Cu2Br4]2− is connected with the ligand through N–H⋯Br interactions, in which the water molecules are accommodated between chains formed by the ligand and [Cu2Br4]2−. Structure stability, thermal analysis, and photoluminescent properties were studied for 1–4.

Inclusion of an anion guest within a molecular host formed by (4,6-dimethyl-1,3-phenylene)bis( N , N -dibenzylmethane) and [CuCl4]2−/[TeCl6]2− through second-sphere coordination

In this work, we have utilized the second-sphere coordination approach toward the construction of supramolecular inclusion solids Cl · 2H2O ⊂ [H2L1]0.5 · [CuCl4]0.5 (Crystal 1) and Cl ⊂ [H2L1] · [TeCl6]0.5 (Crystal 2). The chloride anions can be encapsulated inside the host assemblies formed by the diamine molecule (4,6-dimethyl-1,3-phenylene)bis(N,N-dibenzylmethane) (L1) and the metal complexes ([CuCl4]2− and [TeCl6]2−) via second-sphere coordination. The complexes have been structurally characterized by X-ray crystallography, indicating that weak C–H ··· Cl hydrogen-bonding synthons play a significant role in the construction of second-sphere coordination complexes. 2-D networks are formed in both complexes by the interconnection of 1-D networks through multiple C–H ··· Cl hydrogen-bonding interactions with [CuCl4]2− and [TeCl6]2−. The guest chlorides are encapsulated inside the host cages through N–H ··· Cl hydrogen bonds.

Selective Isolation of Component Myristicine from Ligustium sinense oliv by Second-Sphere Coordination Inclusion Crystallization

The first ligand of [CoCl4 ]2 - and the second ligand of protonated N,N,N',N'-tetra-p-methyl- benzyl-ethylenediamine were used to construct a second-sphere coordination complex as the host framework. Myristicine was selectively isolated from the volatile oil of Ligustium sinense oliv by the inclusion crystalline method as the guest molecules. IR,NMR,X-ray diffraction were used to determine the structure of the inclusion complex,and the host-guest molar ratio in the complex was found to be 2∶ 1. The myristicine was isolated from the inclusion complex via Kugelrohr vacuum distillation technique and was characterized by IR, NMR and GC. According to the result of GC,the content of myristicine in the volatile oil of Ligustium sinense oliv is 60. 4% ,and the purity of isolated myristicine reaches 100% .

Layered structures constructed by second-sphere coordination via N–H ··· Cl and C–H ··· Cl hydrogen bonding: synthesis and crystal structures of tribenzylamine and [MCl6] (M = Sn, Re, and Te)

A series of second-sphere coordination complexes of tribenzylamine (L 1 ) and [MCl6] (M = Sn, Re, Te) have been synthesized and characterized by spectroscopic techniques (IR, NMR) and single-crystal X-ray diffraction. The main driving force for the encapsulation of [MCl6] and recognition with L 1 is the second-sphere coordination of metal halides by the amide protons of the ligand via hydrogen bonding (N–H ··· Cl–M and C–H ··· Cl–M); new layered structures are described. Thermal stability and irreversible behavior of second-sphere coordination complexes [L 2 ] · 0.5[TeCl6]2− · HCl · (H3O)+ · 0.5H2O (L 2 = N,N,N′,N′-tetrabenzyl-ethylenediamine) in contact with water vapor are also described.

Second-sphere coordination complex via hydrogen bonding: Synthesis, characterization, X-ray crystal structure determination and packing of hexaamminecobalt(III) chloride di( para-nitrobenzoate)

A reddish orange coloured crystalline solid of hexaamminecobalt(III) chloride di( para-nitrobenzoate) was obtained when hexaamminecobalt(III) chloride was reacted with the sodium salt of para-nitrobenzoic acid (1:3 molar ratio) in hot aqueous medium. This cobalt(III) complex salt has been characterized by elemental analyses and spectroscopic techniques (e.g. UV/visible, IR and NMR). Single-crystal X-ray structure determination of the title complex salt revealed that it contains the cationic cobaltammine ([Co(NH 3) 6] 3+) and mixed anions (Cl −, NO 2C 6H 4COO −), which are held together by electrostatic forces attractions through second-sphere coordination, i.e. N–H⋯O (carboxylate and nitro) and N–H⋯Cl hydrogen bonds, resulting in a three-dimensional network.

Second-sphere coordination complexes via hydrogen bonding: Synthesis, characterization of [Co(NH 3) 6](XO 3) 3· nH 2O (X=Br, I) and single crystal X-ray structure determination of [Co(NH 3) 6](BrO 3) 3·0.5H 2O

Single crystals of [Co(NH 3) 6](BrO 3) 3·0.5H 2O and peach coloured precipitate of [Co(NH 3) 6](IO 3) 3·3H 2O were obtained by reacting hexaamminecobalt(III) chloride with appropriate silver halate in 1:3 molar ratio in hot aqueous medium. These hexaamminecobalt(III) complexes have been characterized by spectroscopic studies (e.g. UV–vis and IR). Single crystal X-ray structure determination of title complex salt revealed the presence of discrete ions, i.e. cation [Co(NH 3) 6] 3+, three anions, BrO 3 − and half water molecule in the solid state. Crystal lattice is stabilized by electrostatic forces of attractions and hydrogen bonding interactions (N–H⋯O −, O–H⋯O −). The formation of salts of definite composition with halate ions and solubility product data suggest that purely inorganic hexaamminecobalt(III) cation may be used as an anion receptor for these weakly coordinating inorganic oxo-anions.

Second-sphere coordination complexes via hydrogen bonding: Synthesis, spectroscopic characterization, crystal structures and packing of cis-diazidobis(ethylenediamine)cobalt(III) cations with complex fluoroanions

Crystals of cis-diazidobis(ethylenediamine)cobalt(III) tetrafluoroborate nitrate [ cis-Co(en) 2(N 3) 2] 2 (BF 4) (NO 3) I and cis-diazidobis(ethylenediamine)cobalt(III) hexafluorosilicate, [ cis-Co(en) 2(N 3) 2] 2(SiF 6) II have been obtained by slowly mixing the separately dissolved cis-diazidobis(ethylenediamine)cobalt(III) nitrate with sodium salt of tetrafluoroborate and hexafluorosilicate in aqueous medium in 1:1 and 2:1 molar ratio, respectively. Elemental analyses and spectroscopic techniques (IR, UV/visible, 1H and 13C NMR) were studied for characterizing the complex salts. Single crystal X-ray structure determinations revealed supramolecular assemblies via hydrogen bonding network between ionic groups and NH 2 group of coordinated ethylenediamine molecules, i.e. second-sphere coordination.

Role of second-sphere coordination in anion binding: Synthesis, characterization and X-ray structure of hexaamminecobalt(III) chloride hydrogen phthalate trihydrate and sodium hexaamminecobalt(III) benzoate monohydrate

In an effort to utilize [Co(NH 3) 6] 3+cation as a new host for carboxylate ions, orange coloured crystalline solids of composition [Co(NH 3) 6]Cl(C 8H 5O 4) 2·3H 2O ( 1) and Na[Co(NH 3) 6](C 7H 5O 2) 4·H 2O ( 2) were obtained by reacting hot aqueous solutions of hexaamminecobalt(III) chloride with potassium hydrogen phthalate and sodium benzoate in 1:3 molar ratio, respectively. The title complex salts were characterized by elemental analyses and spectroscopic studies (IR, UV/Visible and NMR). Single crystal X-ray structure determinations revealed the formation of second-sphere coordination complexes based on hydrogen bond interactions. In complex salt 1 only two out of three ionisable chloride ions present in [Co(NH 3) 6]Cl 3 were replaced by two C 8 H 5 O 4 − ions whereas in complex salt 2 all the three ionisable chloride ions present in [Co(NH 3) 6]Cl 3 were replaced and the final product was an adduct with another mole of sodium benzoate in solid state. The crystal lattice is stabilized by electrostatic forces of attraction and predominantly N–H⋯O interactions.

Second-sphere coordination complex via hydrogen bonding: synthesis, characterization and X-ray crystal structure of hexaamminecobalt(III)chloride dimethanesulphonate, [Co(NH 3) 6]Cl(CH 3SO 3) 2

The reaction of hexaamminecobalt(III)chloride with sodium salt of methanesulphonic acid in aqueous medium (1:3 molar ratio) leads to formation of hexaamminecobalt(III)chloride dimethanelsulphonate, [Co(NH 3) 6]Cl(CH 3SO 3) 2. This cobalt(III) complex has been characterized by elemental analyses and spectroscopic techniques (e.g. UV/Visible, IR and NMR). Single crystal X-ray structure determination of [Co(NH 3) 6]Cl(CH 3SO 3) 2 revealed supramolecular hydrogen bonding network between ionic groups (i.e. oxygen atoms of CH 3SO 3 − and Cl −) and NH group of coordinated NH 3 molecules, i.e. N–H⋯O and N–H⋯Cl − interactions resulting in bilayer formation, the bilayers being anchored by Cl − ions.

Use of metal carbonyls in the formation of [H 5O 2+·15-crown-5][MOCl 4(H 2O) -], (M=Mo, W), and a second sphere coordination complex in [ mer-CrCl 3(H 2O) 3·15-crown-5

The reactions of M(CO) 6 (M=Mo, W) with HCl (g) in the presence of 15-crown-5 and H 2O in toluene have been explored. These reactions were promoted with the use of UV radiation and formed liquid clathrates almost immediately upon reaction. For each metal species, oxidation of the metal center from either [0] to [+3] in the case of Cr or from [0] to [+5] in the case of both Mo and W occurred. For chromium, a new isomer of CrCl 3(H 2O) 3 was generated in the second-sphere coordination complex, [ mer-CrCl 3(H 2O) 3·15-crown-5] ( 1), which crystallized from the liquid clathrate layer in the reaction mixture. For molybdenum and tungsten the isostructural complexes, [H 5O 2 +·15-crown-5][MOCl 4(H 2O) −], (M=Mo ( 2), M=W, ( 3)) rapidly formed where the H 5O 2 + oxonium ion was stabilized within the liquid clathrate layer. The structures of each of these complexes were established by X-ray crystallography. Complex 1 crystallizes in the monoclinic space group P2 1/ n with a=9.261(3), b=16.182(3), c=12.899(5) Å, β=107.87(1)°, V=1839 Å 3 and D calc.=1.568 g cm −3 for Z=4. Refinement based on 3217 observed reflections led to a final R value of 0.085. Complex 2 crystallizes in the monoclinic space group P2 1/ n with a=12.840(3), b=12.053(1), c=13.290(2) Å, β=94.26(3)°, V=2051 Å 3 and D calc.=1.720 g cm −3 for Z=4. Refinement based on 3208 observed reflections led to a final R value of 0.051. Complex 3 is isostructural with 2 with a=12.805(2), b=12.024(1), c=13.293(2) Å, β=94.25(1)°, V=2041 Å 3 and D calc.=2.015 g cm −3 for Z=4. Refinement based on 2543 observed reflections led to a final R value of 0.045.

Supramolecular assemblies based on calixarenes

Abstract