β-Diiminatolanthanoid(III) halides revisited

The crystalline compounds [LnCl₂(L)(thf)₂] [Ln = Ce (1), Tb (2), Yb (3)], [NdI₂(L)(thf)₂] (4), [LnCl(L′)₂] [Ln = Tb (5), Yb (6) (a known compound)] and [YbCl(L′′)(μ-Cl)₂Li(OEt₂)₂] (7) have been prepared [L = {N(C₆H₃Prⁱ₂-2,6)C(H)}₂CPh, L′ = {N(SiMe₃)C(Ph)}₂CH, L′′ = {N(SiMe₃)C(C₆H₄Ph-4)}₂CH]. The X-ray molecular structures of 2-7 have been established; in each, the monoanionic ligand L, L′ or L′′ is N,N′-chelating and essentially π-delocalised. Each of 1-7 was prepared from the appropriate LnCl₃, or for 4 [NdI₃(thf)₂], and an equivalent portion of the appropriate alkali metal [Li for 7, Na for 2, 3 and 5, or K for 1, 4 and 6] β-diiminate in thf; the isolation of exclusively 5 and 6 (rather than the L′ analogues of 2 or 3) is noteworthy, as is the structure of 7 which has no precedent in Group 3 or 4f metal β-diiminato chemistry.     

Exploring the coordination chemistry and reactivity of hemilabile N-alkylaminopyrazole ligands towards Pd(II)

Reaction of the N-alkylaminopyrazole (NN′N) ligands bis[(3,5-dimethyl-1-pyrazolyl)methyl]ethylamine (bdmae) and bis[(3,5-dimethyl-1-pyrazolyl)methyl]isopropylamine (bdmai) with [PdCl₂(CH₃CN)₂] in a 1:1 M/L ratio in CH₂Cl₂ produces cis-[PdCl₂(NN′N)] (NN′N = bdmae (1), bdmai (2)). The solid state structure of complex 1 was determined by X-ray diffraction studies. The bdmae ligand is coordinated through the two N_pz atoms to the metal atom, which completes its coordination with two chlorine atoms in a cis disposition.Treatment of the corresponding ligand with [PdCl₂(CH₃CN)₂] in 1:1 M/L ratio in the presence of AgBF₄ and metathesis with NaBPh₄ in CH₂Cl₂/CH₃OH (3:1) gave [PdCl(bdmae)](BPh₄) (3), and in the presence of NaBPh₄ in CH₂Cl₂/CH₃CN (3:1) gave [PdCl(bdmai)](BPh₄) (4). Complexes 1 and 2 were again obtained when complexes 3 and 4 were heated under reflux in a solution of Et₄NCl in acetonitrile. These Pd(II) compounds were characterised by elemental analyses, conductivity measurements, IR, ¹H and ¹³C{¹H} NMR, HMQC and NOESY spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed.     

Acid dissociation of 2,2′-dipyridylamine in non-aqueous medium when chelated to some Ru(II)N4 cores

[Ru(2,2′-bipyridine)₂(Hdpa)](BF₄)₂ · 2H₂O (1), [Ru(1,10-phenanthroline)₂(Hdpa)] (PF₆)₂ · CH₂Cl₂ (2) and [Ru(4,4,4′,4′-tetramethyl-2,2′- bisoxazoline)₂(Hdpa)] (PF₆)₂ (3) are synthesized where Hdpa is 2,2′-dipyridylamine. The X-ray crystal structures of 1 and 2 have been determined. Hdpa in 1 and 2 is found to bind the metal via the two pyridyl N ends. Comparing the NMR spectra in DMSO-d₆, it is concluded that 3 has a similar structure. The pK_a values (for the dissociation of the NH proton in Hdpa) of free Hdpa and its complexes are determined in acetonitrile by exploiting molar conductance. These correlate linearly with the chemical shift of the NH proton in the respective entities.     

Aromatic N-oxide bridged copper(II) coordination polymers: Synthesis, characterization and magnetic properties

The complexes [Cu₂(o-NO₂-C₆H₄COO)₄(PNO)₂] (1), [Cu₂(C₆H₅COO)₄(2,2′-BPNO)]_n (2), [Cu₂(C₆H₅COO)₄(4,4′-BPNO)]_n (3), [Cu(p-OH-C₆H₄COO)₂(4,4′-BPNO)₂·H₂O]_n (4), (where PNO = pyridine N-oxide, 2,2′-BPNO = 2,2′-bipyridyl-N,N′-dioxide, 4,4′-BPNO = 4,4′-bipyridyl-N,N′-dioxide) are prepared and characterized and their magnetic properties are studied as a function of temperature. Complex 1 is a discrete dinuclear complex while complexes 2-4 are polymeric of which 2 and 3 have paddle wheel repeating units. Magnetic susceptibility measurements from polycrystalline samples of 1-4 revealed strong antiferromagnetic interactions within the {Cu₂}⁴⁺ paddle wheel units and no discernible interactions between the units. The complex 5, [Cu(NicoNO)₂·2H₂O]_n·4nH₂O, in which the bridging ligand to the adjacent copper(II) ions is nicotinate N-oxide (NicoNO) the transmitted interaction is very weakly antiferromagnetic.     

Synthesis, structure, cytotoxic activities and DNA-binding properties of tetracopper(II) complexes with dissymmetrical N,N′-bis(substituted)oxamides as ligands

To compare the cytotoxicities and the DNA-binding properties in tetranuclear complexes with different bridging ligands, two tetracopper(II) complexes with formulae of [Cu₄(oxbe)₂Cl₂(bpy)₂]·4H₂O (1) and [Cu₄(oxbm)₂Cl₂(bpy)₂]·2H₂O (2) were synthesized, where H₃oxbe and H₃oxbm stand for N-benzoato-N′-(2-aminoethyl)oxamide and N-benzoato-N′-(1,2-propanediamine)oxamide, respectively, and bpy is 2,2′-bipyridine. Complex 1 was characterized by elemental analyses, IR and electronic spectra and single-crystal X-ray diffraction. The crystal structure reveals the presence of the circular tetranuclear copper(II) cations which are assembled by a pair of cis-oxamido-bridged dinuclear copper(II) units through carboxyl bridges. The crystal structure of complex 2 has been reported in our previous paper. However, the bioactivities were not studied. Cytotoxicities experiments reveal that both the two complexes exhibit cytotoxic effects against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549, and complex 1 has the better activities than those of complex 2. The results of the interactions between the two complexes and herring sperm DNA (HS-DNA) suggest that the two complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants of 3.93 × 10⁴ M⁻¹ (1) and 2.48 × 10⁴ M⁻¹ (2). These results indicated that the bridging ligands may play an important role in the cytotoxicities and the DNA-binding properties of tetranuclear complexes.     

Towards absolute asymmetric synthesis. Synthesis and crystal structure of stereochemically labile MCl2 (M = Co, Ni, Cu, Zn) complexes with diamine ligands

In search for new conglomerates, seven stereochemically labile complexes between MCl₂ (M = Co, Cu, Ni, Zn) and bidentate ligands, the commercially available N,N,N′-trimethylethane-1,2-diamine (trimeda) and the somewhat bulkier N-isopropyl-N,N′,N′-trimethylethane-1,2-diamine (itmeda), have been synthesized and characterized using single crystal X-ray diffraction. The trimeda and itmeda ligands exhibit chirogenic nitrogen centers and may form chiral metal complexes that are candidates for total spontaneous resolution. Copper(II) chloride forms the dimeric meso complexes [{CuCl₂(trimeda)}₂] (1) and [{CuCl₂(itmeda)}₂] (2), while [CoCl₂(trimeda)₂] (3) and [NiCl₂(trimeda)₂] (4) exhibit six-coordinate but chiral (R,R)- and (S,S)-complexes. Three examples of the chiral target complex, comprising four-coordinate stereochemically labile monomers, was successfully prepared, viz. [NiCl₂(itmeda)] (5), [ZnCl₂(itmeda)] (6), and [CoCl₂(itmeda)] (7).In all seven complexes, the λ-conformation of the five-membered trimeda-metal chelate ring corresponds to the (S)-configuration at nitrogen, and vice versa. Supramolecular interactions in 3 and 4 form hydrogen-bonded heterochiral ribbons. However, crystals of 5-7 display homochiral interactions resulting in polar phases. Weak CH-Cl interactions in 5 and 6 form homochiral layers. In 7, interactions form homochiral helices along the a-axis.     

Synthesis of new platinum(II) compounds with several bidentate and tridentate nitrogen-donor ligands. Structural analyses by H, C{H} and Pt{H} NMR spectroscopy and X-ray crystal structure

The reaction of the N-alkylaminopyrazole (NN′) ligands 1-[2-(ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[2-(tert-butylamino)ethyl]-3,5-dimethylpyrazole (deat), or (NN′N) ligands bis[(3,5-dimethylpyrazolyl)methyl]ethylamine (bdmae) and bis[(3,5-dimethylpyrazolyl)ethyl]ethylamine (ddae) with [PtCl₂(CH₃CN)₂] affords a series of square-planar Pt(II) complexes with formula [PtCl₂(NN′)] (NN′ = deae (1); deat (2)), [PtCl₂(bdmae)] (3), or [PtCl(ddae)]Cl (4). Treatment of complex 4 in the presence of AgBF₄ in CH₂Cl₂/methanol (3:1) gives [PtCl(ddae)](BF₄) (5). These Pt(II) complexes have been characterised by elemental analyses, conductivity measurements and IR, ¹H, ¹³C{¹H}, and ¹⁹⁵Pt{¹H} NMR spectroscopies. The ¹H NMR spectroscopic studies of the complexes prove the rigid conformation of the ligands when they are complexed. The solid-state structure of complex 1 was determined by single crystal X-ray diffraction methods. The deae ligand is coordinated through the N_pz and N_amino atoms to the metallic centre, which completes its coordination with two chlorine atoms in cis disposition.     

2-(1-(Dimethylamino)ethyl)phenylpalladium(II) complexes 5-functionalized with fluorous silyl tails

New fluorous-organometallics based on the chiral ligand α-methyl-N,N-dimethylbenzylamine (TMBA) were prepared by treatment of fluorous silyl bromide reagents with in situ 4-lithiated TMBA to give fluorous N,N-dimethyl(α-methyl-4-trialkylsilylbenzyl)amine ligands 1a-1c that vary in the number of fluorous tails attached to the Si atom. Ligands 1a-1c were successfully cyclo-palladated by treatment with Pd(OAc)₂/LiCl in methanol to furnish the corresponding chloride-bridged dimeric arylpalladium(II) complexes 2a-2c in good yields. The latter derivatives could be converted into monomeric Lewis-base adducts by complexation with pyridine (3a-3c), or triphenylphosphine (4a-4c). The crystal structure of triphenylphosphine complex 4a has been elucidated. To probe their fluorophilicity, the partition coefficient of each of the derivatives in the fluorous biphasic solvent (FBS) system perfluoromethylcyclohexane/n-octane has been determined.     

Crystal structures and third-order NLO properties in DMF solution of Co(II)-bpfp coordination polymers (bpfp=N,N-bis(pyridylformyl)piperazine)

Two novel Co(II) coordination polymers {[Co(H₂O)₂(CH₃OH)₂(4-bpfp)](NO₃)₂}_n1 (4-bpfp=N,N^′-bis(4-pyridylformyl)piperazine) and [Co(NCS)₂(CH₃OH)₂(3-bpfp)]_n2 (3-bpfp=N,N^′-bis(3-pyridylformyl)piperazine) have been synthesized and characterized by single crystal X-ray diffraction. Both the polymers consist of one-dimensional chains constructed by bridging bpfp ligands and Co(II) ions. The existence of O?H-O hydrogen bond in 1 and S?H-O hydrogen bond in 2 play important roles in creating interesting supramolecular structures. Their third-order nonlinear optical (NLO) properties in DMF solution have been studied by Z-scan technique. The results reveal that polymers 1 and 2 exhibit strong NLO absorption effects (α₂=9.00×10⁻¹¹ m W⁻¹ for 1; 1.41 × 10⁻¹⁰ m W⁻¹ for 2) and self-focusing performance (n₂=3.24×10⁻¹⁶ esu for 1; 3.05 × 10⁻¹⁶ esu for 2) in DMF solutions. The corresponding effective NLO susceptibilities χ⁽³⁾ values are 3.08 × 10⁻¹² esu (1) and 4.70 × 10⁻¹² esu (2). All of the values are comparable to those of the reported good NLO materials. Additionally, the TG-DTA results of the two polymers are in agreement with the crystal structures.     

Studies of mononuclear and dinuclear complexes of dibromodimethylplatinum(IV): Preparation, characterization and crystal structures

A number of complexes of the types [PtBr₂Me₂(N^?N)] (N^?N = 4,4′-di-Me-2,2′-bpy (1); 4,4′-di-t-Bu-2,2′-bpy (2); 2,2′-bpz (3); bpym (4)) and [PtBr₂Me₂(L)₂] (L = H-pz (5); 4-Me-H-pz (6); H-idz (7); H-im (8); H-bim (9); quaz (10)) are reported. Characterization by NMR (¹H, ¹³C and ¹⁹⁵Pt), IR and EI-MS is given. In addition, crystal structures of several of these complexes are described. Furthermore, interactions within these structures including intramolecular hydrogen bonding and π-π stacking interactions are reported. The reactivity of selected mononuclear complexes was investigated and yielded two dinuclear complexes [PPh₄][(PtBrMe₂)₂(μ-Br)(μ-pz)₂] (11) and [(PtBr₂Me₂)₂(μ-bpym)] (12), respectively. The latter complex is accompanied by a solid-state structure. Finally, the thermal stability of all complexes is reported.     

Mononuclear and dinuclear model hydrolases of nickel and cobalt

Reaction between the dinuclear model hydrolases [M₂(μ-OAc)₂(OAc)₂(μ-H₂O)(tmen)₂]; M = Ni (1); M = Co (2) and trimethylsilyltrifluoromethanesulphonate (TMS-OTf) under identical reaction conditions gives the mononuclear complex [Ni(OAc)(H₂O)₂(tmen)][OTf] · H₂O (3) in the case of nickel and the dinuclear complex [Co₂(μ-OAc)₂(μ-H₂O)₂(tmen)₂][OTf]₂ (4) in the case of cobalt.Reaction of (3) with urea gives the previously reported [Ni(OAc)(urea)₂(tmen)][OTf] (5), whereas (4) gives [Co₂(OAc)₃(urea)(tmen)₂][OTf] (6) previously obtained by direct reaction of (2) with urea. Both (3) and (4) react with monohydroxamic acids (RHA) to give the dihydroxamate bridged dinuclear complexes [M₂(μ-OAc)(μ-RA)₂(tmen)₂][OTf]; M = Ni (7); M = Co (8) previously obtained by the reaction of (1) and (2) with RHA, illustrating the greater ability of hydroxamic acids to stabilize dinuclear complexes over that of urea by means of their bridging mode, and offering a possible explanation for the inhibiting effect of hydroxamic acids by means of their displacing bridging urea in a possible intermediate invoked in the action of urease.     

Bridged dinucleating N-heterocyclic carbene ligands and their double helical mercury(II) complexes

A series of six 3,6-bis(imidazolium-3-yl)pyridazine derivatives with different imidazole-N substituents have been synthesized and isolated as the salts [H₂L]Cl₂ (1a)-(6a) and [H₂L](PF₆)₂ (1b)-(6b). Solid state structures have been determined crystallographically for eleven out of the twelve compounds, revealing diverse hydrogen bonding patterns that involve the imidazolium-C²H units and the anions. N-heterocyclic carbene (NHC) mercury(II) complexes [Hg₂L₂](PF₆)₄ (7)-(9) are readily formed in good yields from ligand precursors [H₂L](PF₆)₂ and Hg(OAc)₂, as long as imidazole-N substituents are not too bulky. X-ray crystallography reveals double helical bimetallic arrangements for the stable [Hg₂L₂]⁴⁺ cations. Ligand scrambling in [Hg₂L₂]⁴⁺ occurs only in the presence of free carbene precursor, presumably via an associative mechanism.     

Syntheses and characterization of titanium malonato and amino acid complexes: [Ti(cp)2(OOCCH2NMe2)] - The first structurally characterized α-amino acid titanium(III) complex

The reaction of [Ti(cp^∗)₂(BTMSA)] (1) (cp^∗ = η⁵-C₅Me₅, BTMSA = bis(trimethylsilyl)acetylene) with malonic acids ((HOOC)₂CR₂, R = H, Me) and N,N-dimethylglycine resulted in the formation of titanium(IV) dicarboxylato complexes [Ti(cp^∗)₂{(OOC)₂CR₂}] (R = H, 2; R = Me, 3) and an α-amino acid titanium(III) complex [Ti(cp^∗)₂(OOCCH₂NMe₂)] (4). The identities of complexes 2-4 were confirmed by microanalysis, ¹H and ¹³C NMR spectroscopy (2, 3), ESI-MS and CID experiments (2, 3) as well as by ESR and magnetic measurements (μ_eff = 1.81, 298 K) for 4. Single X-ray diffraction analyses of 2 and 4 exhibited monomolecular complexes in which the titanium atom is distorted tetrahedrally coordinated by two η⁵-C₅Me₅ rings and by the chelating bound malonato-κ²O,O′ (2) and N,N-dimethylglycinato-κ²O,O′ ligand (4).     

Formation of coordination polymer and molecular complex of 4,4′-bipyridyl-N,N′-dioxide of manganese and zinc

A 1D-coordination polymer [{Mn₃(C₆H₅COO)₆(BPNO)₂(MeOH)₂}(MeOH)₂]_n (1) having benzoate as the anionic ligand and 4,4′-bipyridyl-N,N′-dioxide (BPNO) as bridging ligand is synthesized by reacting benzoic acid with manganese(II) acetate tetrahydrate followed by reaction with 4,4′-bipyridyl-N N′-dioxide. The bridging bidentate BPNO ligands in this coordination polymer along with the benzoate bridges hold the repeated units. The chain like structure in one dimension by benzoate bridges are connected to each other through the μ³-η²:η¹ bridges of BPNO ligands. This coordination polymer can be transformed to a molecular complex [Mn(H₂O)₆](C₆H₅COO)_2.4BPNO (2). In this complex the BPNO remains outside the coordination sphere but they are hydrogen bonded to water molecules to form self assembled structure. The reaction of 3,5-pyrazoledicarboxylic acid (L₁H2) and BPNO with manganese(II) acetate or zinc(II) acetate led to molecular complexes with composition [M₂(L₁)₂(H₂O)₆].BPNO·xH₂O {where M = Mn(II) (3), Zn(II)(4)}. These molecular complexes of BPNO are characterised by X-ray crystallography. The complexes 3-4 are binuclear carboxylate complexes having M₂O₂ core formed from carboxylate ligands with two metal ions.     

Coordination compounds of Cd(II) with several bidentate-NN′ and tridentate-NN′N nitrogen donor ligands. Cd NMR studies of monomeric compounds containing nitrogen donor atoms

Reaction of CdCl₂ with N-alkylaminopyrazole ligands 1-[(2-ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[(2-(tert-butylamino)ethyl)]-3,5-dimethylpyrazole (deat), bis-[(3,5-dimethylpyrazolyl)methyl]ethylamine (bdmae), and bis-[(3,5-dimethylpyrazolyl)ethyl]ethylamine (ddae) in absolute ethanol yields [CdCl₂(NN′)] (NN′ = deae (1), deat (2)), [CdCl₂(bdmae)] (3), and [CdCl(ddae)]₂[CdCl₄] (4). The Cd(II) complexes have been characterised by elemental analyses, conductivity measurements, IR, ¹H, ¹³C{¹H} and ¹¹³Cd NMR spectroscopies, and X-ray diffraction methods. ¹H and ¹¹³Cd NMR experiments at variable temperature for 3 and 4 show that dynamic processes are taking place in solution. We report the measurements of ¹¹³Cd NMR chemical shift data for complexes 1-4 in solution. X-ray crystal structures for complexes 2 and 3 have been determined. The Cd(II) is coordinated to the deat ligand, in 2, by one nitrogen atom of the pyrazolyl group and one nitrogen atom of the amine. It finishes a tetrahedral geometry with two chlorine atoms. The bdmae ligand is linked to Cd(II), in 3, by two nitrogens atoms of the pyrazolyl groups and one amine nitrogen, along with two chlorine atoms, in a distorted trigonal bipyramidal geometry.     

Synthetic, structural and spectroscopic studies of complexes derived from the copper(II) perchlorate/succinamic acid/N,N′-donor tertiary reaction systems

The use of succinamic acid (H₂sucm) in Cu(ClO₄)₂·6H₂O/N,N′-donor [2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 4,4′-bipyridine (4,4′-bpy)] reaction mixtures yielded compounds [Cu₂(Hsucm)₃(bpy)₂](ClO₄)·0.5MeOH (1·0.5MeOH), [Cu₂(Hsucm)(OH)(H₂O)(bpy)](ClO₄)₂ (2), [Cu₄(Hsucm)₅(dmbpy)₄]_n(ClO₄)_3n·nH₂O ·0.53nMeOH (3·nH₂O·0.53nMeOH), [Cu₂(Hsucm)₂(dmbpy)₂(H₂O)₂](ClO₄)₂·2H₂O (4·2H₂O), [Cu₂(Hsucm)₂(phen)₂(H₂O)₂](ClO₄)₂·1.8MeOH (5·1.8MeOH), [Cu₂(Hsucm)₂(phen)₂(MeOH)₂](ClO₄)₂·MeOH (6·MeOH) and [Cu(Hsucm)₂(H₂O)(4,4′-bpy)]_n (7). The succinamate(−1) ligand exists in five different coordination modes in the structures of 1-7, i.e. the common syn, syn μ₂-κO:κO′ in 1-6, the μ₂-κ²O in 1, the μ₂-κ²O:κO′ in 1, the μ₃-κ²O:κ²O′ in 3, and the monodentate κO in 7. The primary amide group of Hsucm⁻ remains uncoordinated and participates in intra- and intermolecular hydrogen bonding interactions leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm⁻ ligands. The thermal decomposition of representative complexes was monitored by TG/DTG and DTA measurements.     

Synthesis and characterization of platinum(IV) complexes with N,S and S,S heterocyclic ligands

The reactions of [PtMe₃(OAc)(bpy)] (4) with the N,S and S,S containing heterocycles, pyrimidine-2-thione (pymtH), pyridine-2-thione (pytH), thiazoline-2-thione (tztH) and thiophene-2-thiol (tptH), resulted in the formation of the monomeric complexes [PtMe₃(-κS)(bpy)] ( = pymt, 5; pyt, 6; tzt, 7; tpt, 8), where the heterocyclic ligand is coordinated via the exocyclic sulfur atom. In contrast, in the reactions of [PtMe₃(OAc)(Me₂CO)_x] (3, x = 1 or 2) with pymtH, pytH, tztH and tptH dimeric complexes [{PtMe₃(μ-)}₂] (μ- = pymt, 9; pyt, 10; tzt, 11) and the tetrameric complex [{PtMe₃(μ₃-tpt-κS)}₄] (12), respectively, were formed. The complexes were characterized by microanalyses, ¹H and ¹³C NMR spectroscopy and negative ESI-MS (12) measurements. Single-crystal X-ray diffraction analysis of [PtMe₃(pymt-κS)(bpy)] (5) exhibited a conformation where the pymt ligand lies nearly perpendicular to the complex plane above the bpy ligand that was also confirmed by quantum chemical calculations on the DFT level of theory.     

Four new copper(II) complexes with di-substituted s-triazine-based ligands

In this paper, two di-substituted triazine-based ligands, 6-chloro-N,N,N′N′-tetrakis-pyridin-2-ylmethyl-[1,3,5]triazine-2,4-diamine (L1), and 6-chloro-N,N′-bis-pyridin-2-ylmethyl-N,N′-bis-thiophen-2-ylmethyl-[1,3,5]triazine-2,4-diamine (L2), have been prepared. Reaction of CuCl₂·2H₂O and Cu(NO₃)₂·3H₂O with L1 and L2 results in the formation of [Cu₂Cl₄(L1)]·3MeOH (compound 1), [Cu₄(NO₃)₈(L1)₂]·2.07CH₂Cl₂·0.93MeOH (compound 2), [Cu₂Cl₄(L2)₂] (compound 3) and [Cu(NO₃)₂(L2)]·CH₂Cl₂ (compound 4), respectively, which have been fully characterized and determined by single-crystal X-ray crystallography, FT-IR, elemental analysis, thermogravimetric measurement and magnetic susceptibility. The dinuclear compound 1 shows strong π-π interactions between the neighboring pyridine rings. The nitrate-π (1,3,5-triazine ring) interaction with the distance of 2.755 Å in compound 2, is the closest contact reported so far. Compounds 3 and 4 are mononuclear copper(II) compounds, in which none of thiophene rings coordinates with copper(II) ion. In addition, the different orientations of two thiophene rings in compounds 3 and 4 lead to the π-π and CH₂Cl₂-π (thiophene ring) interactions in compound 4, but not in compound 3.     

Synthesis and structure of the lithium, zirconium and hafnium N-silyl-N′-benzyl-benzamidinates

The interaction of LiN(SiMe₃)CH₂Ph with one equivalent of benzenitrile gave the N-silyl-N′-benzyl-benzamidinato-lithium compound [{Me₃SiNC(Ph)N(CH₂Ph)}Li(Et₂O)]₂ (1). The derivative zirconium and hafnium compounds were produced by the treatment of 1 with ZrCl₄ or HfCl₄ in tetrahydrofuran or diethyl ether at ambient temperature, respectively, with the general formula [Me₃SiNC(Ph)N(CH₂Ph)]₃MCl (M = Zr (2), Hf (3)). Compounds 1, 2 and 3 were also characterized by X-ray single crystal diffraction and NMR analysis.     

The reactions of 2-hydroxypyridine ligands with Re2Cl4(μ-dppm)2 (dppm=Ph2PCH2PPh2) that lead to 2-pyridonate complexes

2-Hydroxypyridine (Hhp), 2-hydroxynicotinic acid (HnicOH) and 6-hydroxypicolinic acid (HpicOH) react with Re₂Cl₄(μ-dppm)₂ (dppm=Ph₂PCH₂PPh₂) to afford the complexes Re₂(η²-hp)Cl₃(μ-dppm)₂ (1), Re₂(η²-HnicO)Cl₃(μ-dppm)₂ (2) and Re₂(μ-picO)₂(μ-dppm)₂ (3). The identities of 1 and 2 have been established by single-crystal X-ray structure determinations (Re-Re distances of 2.2602(3) and 2.2539(3) Å, respectively) and they are shown to have unsymmetrical structures with staggered rotational geometries and trans, cis coordination of the pair of μ-dppm ligands. The crystal of 2 that was used in the structure determination was found to be of composition 2Re₂(η²-HnicO)Cl₃(μ-dppm)₂ · Re₂Cl₆(μ-dppm)₂ · 2.906CH₂Cl₂. The structure of Re₂Cl₆(μ-dppm)₂ in this crystal is compared with structures reported in the literature for other crystals that contain this edge-sharing bioctahedral dirhenium(III) complex.