From infinite tubular arrays to discrete molecules and back: An example of reversible ring-opening polymerization in silver(I)-diphosphazane chemistry

The reaction of AgX with the diphosphazane ligand, PrⁱN(PPh₂)₂ (L) gives the polymeric complexes, [Ag₂(μ-X)₂(μ-L)]_n (X = NO₃1a or OSO₂CF₃1b). Single crystal X-ray analysis of 1a reveals a novel structural motif formed by interlinking of giant 40-membered rings; the diphosphazane ligand L adopts a unique ‘C_s’ geometry. These polymeric complexes exhibit a completely reversible ring-opening polymerization-depolymerization relationship with the dinuclear and mononuclear complexes, [{Ag(μ-L)(X)}₂] (X = NO₃2a, X = OSO₂CF₃2b) and [Ag(κ²-L)₂]X (X = NO₃3a, X = OSO₂CF₃3b).     

6-Halogenopyridin-2-olato complexes with the diruthenium(2+) core: Equilibria between head-to-head and head-to-tail structures

The dinuclear bis(6-X-pyridin-2-olato) ruthenium complexes [Ru₂(μ-XpyO)₂(CO)₄(PPh₃)₂] (X = Cl (4B) and Br (5B)), [Ru₂(μ-XpyO)₂(CO)₄(CH₃CN)₂] (X = Cl (6B), Br (7B) and F (8B)) and [Ru₂(μ-ClpyO)₂(CO)₄(PhCN)₂] (9B) were prepared from the corresponding tetranuclear coordination dimers [Ru₂(μ-XpyO)₂(CO)₄]₂ (1: X = Cl; 2: X = Br) and [Ru₂(μ-FpyO)₂(CO)₆]₂ (3) by treatment with an excess of triphenylphosphane, acetonitrile and benzonitrile, respectively. In the solid state, complexes 4B-9B all have a head-to-tail arrangement of the two pyridonate ligands, as evidenced by X-ray crystal structure analyses of 4B, 6B and 9B, in contrast to the head-to-head arrangement in the precursors 1-3. A temperature- and solvent-dependent equilibrium between the yellow head-to-tail complexes and the red head-to-head complexes 4A-7A and 9A, bearing an axial ligand only at the O,O-substituted ruthenium atom, exists in solution and was studied by NMR spectroscopy. Full ¹H and ¹³C NMR assignments were made in each case. Treatment of 1 and 2 with the N-heterocyclic carbene (NHC) 1-butyl-3-methylimidazolin-2-ylidene provided the complexes [Ru₂(μ-XpyO)₂(CO)₄(NHC)], X = Cl (11A) or Br (12A). An XRD analysis revealed the head-to-head arrangement of the pyridonate ligands and axial coordination of the carbene ligand at the O,O-substituted ruthenium atom. The conversion of 11A and 12A into the corresponding head-to-tail complexes was not possible.     

Assembly of 1D, 2D and 3D silver(I) coordination polymers with nitrilotriacetate and 2-aminopyrimidyl mixed ligands

Three mixed ligands coordination polymers (CPs) [Ag_1.5(apym)(nta)_0.5]_n (1), [(NH₄)Ag₂(mapym)(nta)·(H₂O)₃]_n (2), [Ag₂(dmapym)₃(Hnta)]_n (3) (apym = 2-aminopyrimidine, mapym = 4-methyl-2-aminopyrimidine, dmapym = 4, 6-dimethyl-2-aminopyrimidine, H₃nta = nitrilotriacetate) were synthesized and characterized. For 1-3, as the substituents change from H to one methyl and two methyl groups, the dimensionalities of 1-3 decrease from three-dimension (3D) to one-dimension (1D) due to the steric effect of methyl groups. For 1, the μ₂-apym ligands link the Ag(I) ions to form a 1D double-chain incorporating ligand unsupported Ag···Ag interaction. The nta³⁻ ligands extend the 1D double-chain into a 3D framework. In 2, one heptadentate nta³⁻ ligand binds four Ag(I) ions and incorporates μ₂-mapym ligand to link metal centers to form a 2D sheet which can be simplified to be a 10³ net. Complex 3 features a 1D chain structure incorporating Hnta²⁻ and monodentate dmapym ligands. The substituents on the pyrimidyl ring intensively influence the coordination environments of metal ion and the coordination modes of the carboxyl group, and thus determine the structures of the CPs. The photoluminescent properties of 1-3 were also investigated.     

Cationic ligands for Ag(I): Organometallic polymers versus unimolecular complexes

We have prepared and characterized two cationic ligands and their Ag(I) coordination compounds. For the bidentate ligand 2, 2,2-bis-pyridin-2-ylmethyl-2,3-dihydro-1H-isoindolium bromide, we obtained the organometallic polymer [AgL]_x[CF₃SO₃]_2x (4), and the unimolecular complex [AgL₂][PF₆]₃ (5). Compound 4 exists as an organometallic linear polymer with triflate anions either bonded to Ag(I) or non-bonded and sandwiched between the polymer chains. Complex 5 is the only unimolecular example in this series due to the non-interaction of anions with Ag(I) or with the cationic portion of the ligand. In the case of the tridentate cationic ligand 3-(3-pyridin-2-yl-2-pyridin-2-ylmethy-propyl)-benzyl-triethylammonium bromide (3), two dimeric Ag(I) complexes are formed, [Ag₂L₂][CF₃SO₃]₄ (6), and [Ag₂(CH₃CN₂)₂L₂][PF₆]₄ (7). Both of these dimers have essentially similar structures, with a closed-shell Ag(I)?Ag(I) interaction of approximately 3.00 Å in both cases; the pyridyl moieties of the ligands are forced into an electronically unfavourable face-to-face arrangement. The coordination spheres of the Ag(I) cations are completed by in the case of 6, and by CH₃CN solvent in the case of 7. In the extended packing diagrams, the arrangements of 6 and 7 are driven by intermolecular π-stacking and cation-anion interactions.     

One-dimensional silver(I) and mercury(II) complexes with 1,4-bis(1-benzyl-benzimidazol-2-yl)cyclohexane (N-BBzBimCH)

The crystal structures of four Ag(I) and Hg(II) complexes of the ligand 1,4-bis(1-benzyl-benzimidazol-2-yl)cyclohexane (N-BBzBimCH) have been described, that is, [Hg₂(N-BBzBimCH)Cl₄] (1), [Hg(N-BBzBimCH)Br₂] (2), [Ag(N-BBzBimCH)](NO₃)(H₂O) (3) and [Ag₂(N-BBzBimCH)(CF₃OCO)₂] (4). All these compounds show 1D polymeric structures in the solid state. In complexes 1 and 4, the chloride ions and the trifluoroacetate groups bridge the [Hg₂(N-BBzBimCH)Cl₂] and [Ag₂(N-BBzBimCH)] fragments, respectively, to generate 1D polymers. While the bromide ions in complex 2 and nitrate groups in complex 3 are only serving as terminal ligands to suffice the coordination geometry of the metal centers. In all cases, weak intermolecular interactions such as C-H?X (X = Cl, Br) contacts, hydrogen bonds, π-π interactions and C-H?π stacking play important roles to extend the 1D chain structures to 2D network. Solid state fluorescence of these compounds was also studied.     

Copper(I) and silver(I) tertiary phosphines complexes: Synthesis, X-ray structures and spectroscopic characterization

Six new complexes, [Cu₄I₄(PPh₂Cy)₄]·2H₂O (1), [CuI(PPhCy₂)₂] (2), [CuCl(PPhCy₂)₂] (3), and [CuBr(PPh₃)₃]·CH₃CN (4), [Ag(PPhCy₂)₂(NO₃)] (5), [Ag(PCy₃)(NO₃)]₂ (6) [where Ph = phenyl, Cy = cyclohexyl], have been synthesized and structurally characterized by X-ray diffraction, IR absorption spectra and NMR spectroscopic studies (except complex 4). The X-ray diffraction analysis of complex (1), pseudo polymorph of complex [Cu₄I₄(PPh₂Cy)₄], reveals a stella quadrangula structure. The four corners of the cube are occupied by copper(I) atoms and four I atoms are present at the alternative corners of the cube, further more the copper(I) atoms are coordinated to a monodentate tertiary phosphine. Complexes (2) and (3) are isostructural with trigonal planar geometry around the copper(I) atom. The crystal structure of complex (4) is a pseudo polymorph of complex [CuBr(PPh₃)₃] and the geometrical environment around the copper(I) centre is distorted tetrahedral. In the Ag^I complexes (5) and (6), the central metal atoms have pseudo tetrahedral and trigonal planar geometry, respectively. Spectroscopic and microanalysis results are consistent with the single crystal X-ray diffraction studies.     

Synthesis, structure, and catalytic activity of chiral silver(I) and copper(II) complexes with biaryl-based nitrogen-containing ligands

A series of chiral Ag(I) and Cu(II) complexes have been prepared from the reaction between AgX (X = NO₃, PF₆, OTf) or CuX₂ (X = Cl, ClO₄) and chiral biaryl-based N-ligands. The rigidity of the ligand plays an important role in the Ag(I) complex formation. For example, treatment of chiral N₃-ligands 1-3 with half equiv of AgX (X = NO₃, PF₆, OTf) gives the chiral bis-ligated four-coordinated Ag(I) complexes, while ligand 4 affords the two-coordinated Ag(I) complexes. Reaction of AgX with 1 equiv of chiral N₄-ligands 5, 7, 8 and 10 gives the chiral, binuclear double helicate Ag(I) complexes, while chiral mono-nuclear single helicate Ag(I) complexes are obtained with N₄-ligands 6 and 9. Treatment of either N₃-ligand 1 or N₄-ligand 9 or 10 with 1 equiv of CuX₂ (X = Cl, ClO₄) gives the mono-ligated Cu(II) complexes. All the complexes have been characterized by various spectroscopic techniques, and elemental analyses. Seventeen of them have further been confirmed by X-ray diffraction analyses. The Cu(II) complexes do not show catalytic activity for allylation reaction, in contrast to Ag(I) complexes, but they do exhibit catalytic activity for Henry reaction (nitroaldol reaction) that Ag(I) complexes do not.     

Synthesis and characterisation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes [Ti(IV), Zr(IV), Hf(IV), La(III), Ce(III), Yb(III), Sn(II) and Fe(II)]

The preparation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes is described. These are of formula [M{η⁵-C₅H₄(BX)}Cl₃] [M = Ti and X = CAT (2a), CAT^t (2b) or CAT^tt (2c); X = CAT^tt and M = Zr (4a) or Hf (4b)], [M{η⁵-C₅H₄(BX)}₂Cl₂] [M = Zr, X = CAT (3a) or CAT^t (3c); or M = Hf, X = CAT (3b) or CAT^t (3d)], [M{(μ-η⁵-C₅H₃BCAT)₂ SiMe₂}Cl₂] [M = Zr (5a) or Hf (5b)], [M{η⁵-C₅H₃(BCAT)₂}Cl₃] [M = Zr (6a) or Hf (6b)], [M{η⁵-C₅H₄BCAT}₃(THF)] [M = La (7a), Ce (7b) or Yb (7c)], [Sn{η⁵-C₅ H₄(BCAT^t)}Cl](8) and [Fe{η⁵-C₅H₄(BCAT^t)}₂] (9). The abbreviations refer to BO₂C₆H₄-1,2 (BCAT) and the 4-Bu^t (BCAT^t) and the (BCAT^tt) analogues. The compounds 2a-9 have been characterised by microanalysis, multinuclear NMR and mass spectra. The single crystal X-ray structure of the lanthanum compound 7a is presented.     

Supramolecular assembly of coordination networks in silver(I) triple salts containing acetylenediide and some N,O-donor ligands

Five new silver(I) triple salts: (Ag₂C₂)(AgNO₃)₄(AgL¹)₂(L¹H)₂ (1), (Ag₂C₂)(AgCF₃CO₂)₂(AgL¹)₂(L¹H)_1/2 (2), [(Ag₂C₂)(AgCF₃CO₂)₄(L²)(H₂O)] · (L²H₂) (3), (Ag₂C₂)(AgNO₃)₃(AgL³)₂ (4), and [(Ag₂C₂)(AgCF₃CO₂)₄(AgL³)₂(H₂O)₂] · H₂O (5) (L¹H = nicotinic acid, L²H = isonicotinic acid, L³H = 2-pyrazinecarboxylic acid) have been synthesized by the hydrothermal method. All five compounds contain polyhedral silver(I) cages each encapsulating an acetylenediide dianion, . In 1, C₂@Ag₈ cages in the shape of bicapped trigonal prisms are interlinked by nitrate, L¹, and L¹H ligands into a three-dimensional architecture. In 2, silver(I) columns generated from fusion of triangulated dodecahedra are linked by L¹ into a layer structure. Compound 3 provides a rare example of a (L²H₂)⁺-pillared three-dimensional structure via hydrogen bonding. In 4, nitrate ligands together with L³ link the C₂@Ag₇ cages into a three-dimensional architecture. Compound 5 also exhibits a three-dimensional architecture generated from trifluoroacetate and L³-linked C₂@Ag₈ cages.     

Two new polyoxometalate-based hybrids: Structural transformation played by a secondary bridging ligand

Two new Keggin polyoxometalate-based compounds, [Ag₄(phnz)₆(SiW₁₂O₄₀)] (phnz = phenazine) (1) and [Ag(phnz)_1.5][Ag(phnz)(pz)][{Ag₂(phnz)(pz)(H₂O)}(SiW₁₂O₄₀)] (2) (pz = pyrazine), have been hydrothermally synthesized. Compound 1 is a discrete cluster in which the [SiW₁₂O₄₀]⁴⁻ (SiW₁₂) anion symmetrically connects two dinuclear Ag₂(phnz)₃ fragments. All Ag^I in 1 adopt a trigonal geometry. By introducing the secondary bridging ligand “pz” into the above system, compound 2 was obtained. Compound 2 contains three kinds of silver complex subunits: [Ag₂(phnz)(pz)(H₂O)]²⁺, [Ag₂(phnz)₃]²⁺ and [Ag(phnz)(pz)]⁺. The first one extends to a wave-like chain with SiW₁₂ anions as bi-dentate suspenders, and the last two are counter cations. Furthermore, Ag^I ions in 2 exhibit three kinds of coordination modes. Their electrochemistry properties have also been studied.     

Tetrameric 1:1 and monomeric 1:3 complexes of silver(I) halides with tri(p-tolyl)-phosphine: A structural and biological study

Silver(I) halides react with tri(p-tolyl)phosphine (tptp, C₂₁H₂₁P) in MeOH/MeCN solutions in 1:1 or 1:3 molar ratios to give complexes of formulae {[AgCl(tptp)]₄} (1) or [AgX(tptp)₃] (X = Cl (2), Br (3), I (4)), respectively. The complexes were characterized by elemental analyses, and FT-IR far-IR, FT-Raman, TG and ¹H, ¹³C, ³¹P NMR spectroscopic techniques. Crystal structures of complexes 2-4 were determined by X-ray diffraction at room temperature (rt). The crystal structure of 1 and 4 was also determined at 100(1) and 140(2) K (lt), respectively. In complex 1 four μ3-Cl ions are bonded with four Ag(I) ions forming a cubane while the coordination sphere of silver(I) ions is completed by one P atom from a terminal tri(p-tolyl)phosphine ligand. In complexes 2-3 one terminal halogen and three P atoms from phosphine ligands form a tetrahedral arrangement around the metal ion. Complexes 1-4 were tested for in vitro cytostatic activity against sarcoma cancer cells (mesenchymal tissue) from the Wistar rat, polycyclic aromatic hydrocarbons (PAH, benzo[a]pyrene) carcinogenesis and against murine leukemia (L1210) and human T-lymphocyte (Molt4/C8 and CEM) cells. The silver(I) complexes 1-4 show strong activity.     

Copper(I) complexes with Schiff base and 1,2-bis(diphenylphosphino)ethane as ligands: Synthesis, structure and catalytic properties for the amination of aryl halide

Some copper(I) complexes of the type [Cu(L)(dppe)]X (1-4) [where L = (3-trifluoromethylphenyl)pyridine-2-ylmethylene-amine; dppe = 1,2-bis(diphenylphosphino)ethane; X = Cl⁻, CN⁻, ClO₄⁻ and BF₄⁻] have been synthesized by the condensation of 3-aminobenzotrifluoride with 2-pyridinecarboxaldehyde followed by the reaction with CuCl, CuCN, [Cu(MeCN)₄]ClO₄ and [Cu(MeCN)₄]BF₄ in presence of dppe. The complexes 1-4 were then characterized on the basis of elemental analysis, IR, UV-Vis and ¹H NMR spectral studies. The representative complex of the series 4 has been characterized by single crystal X-ray diffraction which reveal that in complex the central copper(I) ion assumes the irregular pseudo-tetrahedral geometry. The catalytic activity of the complexes was tested and it was found that all the complexes worked as effective catalyst in the amination of aryl halide.     

Syntheses, structures and photoluminescent properties of silver(I) complexes with in situ generated hexahydropyrimidine derivatives

Two new linear and V-shaped tetradentate ligands, namely 1,4-bis(2-hexahydropyrimidyl)benzene (L) and 1,3-bis(2-hexahydropyrimidyl)benzene (L^′), and their silver(I) complexes, [Ag₂L(μ-ONO₂)](NO₃) · 2H₂O (1), [Ag₂L(μ-pn)](NO₃)₂ (2), [Ag₂L(μ-pn)](ClO₄)₂ (3) and [Ag₄L^′₂(H₂O)](NO₃)₄ · 5H₂O (4) (pn=1,3-diaminopropane) have been synthesized in situ and structurally characterized by single-crystal X-ray diffraction. 1 and 2 were obtained from the same reaction solution but different crystallization conditions. 1 is an one-dimensional chain featuring cuboid tetranuclear silver(I) units interconnected through monoatomic nitrate bridges. Both 2 and 3 are ribbon-like helical compounds in which each L ligand acts in a tetradentate bridging mode to interconnect four metal atoms, and each pn ligand functions in a bidentate bridging mode to link a pair of metal atoms. 4 shows a truncated square-pyramidal tetranuclear motif arose by the V-shaped L^′ ligand. Close Ag?Ag separations (2.901-2.939 Å) assisted by bis(hexahydropyrimidine) bridges were observed in 1 and 4, indicating metal-metal interactions. Photoluminescence of 1-4 has also been observed in the solid state and solution at room temperature and low temperature, respectively.     

Solution and solid-state complexes of the potentially tetradentate pyridyl-thiazole ligand 6,6′-bis(4-methylthiazol-2-yl)-2,2′-bipyridine with Co, Ni, Cu, Cd, Hg, Cu and Ag

Reaction of the potentially tetradentate N-donor ligand 6,6′-bis(4-methylthiazol-2-yl)-2,2′-bipyridine (L¹) with the transition metal dications Co^II, Ni^II, Cu^II, Cd^II and Hg^II results in the formation of mononuclear [M(L¹)]²⁺ complexes, in which a planar ligand coordinates to the metals via all four N-donors. In contrast, reaction of L¹ with Cu^I and Ag^I monocations, affords dinuclear double stranded helicate species [M₂(L¹)₂]²⁺ (where M = Cu^I or Ag^I), in which partitioning of the ligand into two bis-bidentate pyridyl-thiazole chelating units allows each ligand to bridge both metal centres. X-Ray crystallography, electrospray mass spectroscopy and NMR spectroscopy reveal that the complexes [M_n(L¹)_m]^z+ (where n = 1, m = 1 and z = 2, when M = Co^II, Ni^II, Cu^II, Cd^II and Hg^II; n = 2, m = 2 and z = 2, when M = Cu^I), retain their solid-state structures in solution. Conversely, whilst ¹H NMR studies suggest that combination of equimolar amounts of Ag(X)(where ) and L¹ (in either nitromethane or acetonitrile) results in the formation of a helicate in solution, in the solid-state, an anion-templating effect gives rise to either mononuclear or dinuclear helicate structures [Ag_n(L¹)_n][X]_n (where n = 2 when X = OTf⁻; n = 1 when ).     

Heterocyclic thioamide derivatives of coinage metals (Cu, Ag): Synthesis, structures and spectroscopy

Heterocyclic thioamides, namely, imidazolidine-2-thione (imdzSH), 1-methyl-1, 3-imidazoline-2-thione (mimzSH), thiazolidine-2-thione (tzdSH) and 2,4-dithiouracil (dtucH₂) with silver(I)/copper(I) salts in presence of triphenyl phosphine (PPh₃) have yielded complexes of different nuclearity: mononuclear, [Ag(η¹-S-HL)(PPh₃)₂Cl] (HL = imdzSH 1, mimzSH 2, tzdSH 3), dinuclear, [Ag₂(η¹-S-tzdSH)₂(μ-S-tzdSH)₂(PPh₃)₂](NO₃)₂4, and polynuclear, {Cu(μ-S,S-dtucH₂)(PPh₃)₂X} (X = Cl 5, Br 6, I 7). All complexes have been characterized using analytical data, IR and multinuclear NMR spectroscopy (¹H, ¹³C and ³¹P) and single crystal X-ray crystallography. The thio-ligands are bonded to the metal centers as neutral sulfur donors. The geometry around each metal center is distorted tetrahedral. Complexes 5-7 represent first examples of polymers of 2,4-dithiouracil in its coordination chemistry with metal salts. The hydrogen bonding interactions lead to the formation of 1D (2, 3, 7) and 2D (1, 4-6) sheet structures.     

Syntheses, thermal analyses, crystal structures and antimicrobial properties of silver(I)-saccharinate complexes with diverse diamine ligands

Five new silver(I)-saccharinate complexes [Ag₂(sac)₂(tmen)₂] (1), [Ag₂(sac)₂(deten)₂] (2), [Ag₂(sac)₂(dmen)₂] (3), [Ag(sac)(N,N-eten)] (4), and [Ag(sac)(dmpen)]_n (5); (sac = saccharinate, tmen = N,N,N′,N′-tetramethylethylenediamine, deten = N,N′-diethylethylenediamine, dmen = N,N′-dimethylethylenediamine, N,N-eten = N,N-diethylethylenediamine and dmpen = 1,3-diamino-2,2-dimethylpropan) have been synthesized and characterized by elemental analyses, IR, thermal analyses, single crystal X-ray diffraction and antimicrobial activities. The crystallographic analyses show that all the complexes crystallize in monoclinic space group P2₁/c. In 1, the sac ligand acts as a bridge to connect the silver centres through its imino N and carbonyl O atoms forming an eight-membered bimetallic ring in a chair conformation. Complex 2 has also a dimeric structure in which the monomeric [Ag(sac)(deten)] units are linked by Ag?Ag interactions. In 3, saccharinate ligand acts as a bridging bidentate ligand between two silver(I) centres through sulfonyl group and imino N atom, forming an alternating polymeric chain through the direction [0 1 0]. In 4, the inter-molecular N-H?O hydrogen bonds form one-dimensional polymeric chains through the a axis, and these linear chains are inter-connected to each other by N-H?O hydrogen bonds, which produce a chain of edge-fused and rings along [1 0 0]. Complex 5 is a coordination polymer in which the monomeric [Ag(dmpen)(sac)]_n units are linked by Ag?Ag interactions, and the dmpen ligand acts as a bridge between the silver(I) ions, forming a two-dimensional network parallel to the (1 0 0) plane.     

Assembly of luminescent Ag(I) coordination architectures adjusted by modification of pyrimidine-based thioether ligands

Two new structurally related pyrimidine-based thioether ligands, angular ditopic ligand 1,3-bis(2-pyrimidinylthiomethyl)benzene (L²) and linear ditopic ligand 1,4-bis(2-pyrimidinylthiomethyl)benzene (L³), have been designed and prepared. Reaction of two shaped-specific ligands with different silver(I) salts affords three novel luminescent coordination architectures: discrete metallomacrocycle [Ag₄(L²)₂(NO₃)₄] · 2MeOH (3), 1D chain {[Ag₂L³(NO₃)₂] · 2CCl₃}_n (4) and 2D wire netlike structure {[AgL³(DMF)]ClO₄ · 0.25H₂O}_n (5). The results show that the nature of organic ligands, geometric requirement of metal atoms and counter anions have great influence on the structures of metal-organic frameworks.     

Extended molecular networks based on Zn and Cd imparting N-substituted imidazole

Synthesis of complexes with the formulations [M(CPI)₂Cl₂] (M = Zn, 1; M = Cd, 4) and [M(CPI)₆](X)₂ (M = Zn, X = NO₃⁻, 2; X = ClO₄⁻, 3; M = Cd, X = NO₃⁻, 5; X = ClO₄⁻, 6) have been achieved from the reactions of MCl₂, M(NO₃)₂·xH₂O and M(ClO₄)₂·xH₂O (M = Zn, Cd) with 1-(4-cyanophenyl)-imidazole (CPI). Complexes 1-6 have been characterized by elemental analyses and spectral studies (IR, ¹H, ¹³C NMR, electronic absorption and emission). Molecular structures of 1, 2, 3 and 6 have been determined crystallographically. Weak interaction studies on the complexes revealed presence of various interesting motifs resulting from C-H···N, C-H···Cl and π-π stacking interactions. The complexes under study exhibit strong luminescence at ∼450 nm in DMSO at room temperature.     

The reactivity of NbX5 (X = F, Cl) with lactons, lactams, and the synthesis of the first nucleobase-containing niobium complex

NbX₅ (X = F, 1a; X = Cl, 1b) reacted with γ-butyrolactone (but), ε-caprolactam (cap), δ-valerolactam (val) in 1:1 M ratio in chlorinated solvent, affording either the neutral coordination adducts NbCl₅L (L = but, 2a; L = val, 2b) or the ionic ones [NbX₄L₂][NbX₆] (X = F, L = but, 3a; X = F, L = val, 3b; X = F, L = cap, 3c; X = Cl, L = cap, 3d). The reaction of 1a with equimolar amount of guanine (gua) in CH₃CN resulted in the formation of the complex [NbF₄(gua)₂][NbF₆], 3e. The addition of two equivalents of organic substrate to 1 gave selectively the compounds NbCl₅L₂ (L = but, 4a; L = val, 4b) or [NbF₄L₄][NbF₆] (L = but, 5a; L = val, 5b; L = cap, 5c). The 1:2 M reaction of 1b with ε-caprolactam proceeded with C-N bond activation and afforded the derivative , 6, in high yield.     

Synthesis and characterization of sterically hindered tris(pyrazolyl)borate Ni complexes

Addition of KTp^Ph2 to a solution of NiX₂ (X = Cl, Br, NO₃, OAc and acac) or NiBr(NO)(PPh₃)₂ in THF yields the structurally characterized series [NiCl(Hpz^Ph2)Tp^Ph2] (1) and [NiXTp^Ph2] (X = Br 2, NO 3, NO₃4, OAc 5 and acac 6) including the first example of a tris(pyrazolyl)borate nickel nitrosyl complex. IR spectroscopy confirms that all the Tp^Ph2 ligands are κ³ coordinated and that the NO ligand in 3 is linearly bound. Electronic spectra are consistent with four- or five-coordinate species in solution. NMR spectroscopic studies indicate that the complexes are paramagnetic, with the exception of 3. This is confirmed by magnetic susceptibility studies, which suggest that complexes 1, 2 and 4-6 are paramagnetic with two unpaired electrons. X-ray crystallographic studies of 5 reveal a distorted trigonal bipyramidal nickel centre with a symmetrically coordinated acetate ligand.