Oxime-functionalized diazamesocyclic derivates and their metal complexes: Effect of the ligand backbones and anions on the generation of novel monomeric and mono-μ-Cl dimeric Cu complexes

Two oxime-functionalized diazamesocyclic derivates, namely, N,N′-bis(acetophenoneoxime)-1,4-diazacycloheptane (H₂L¹) and N,N′-bis(acetophenonoxime)-1,5-diazacyclooctane (H₂L²), have been prepared and characterized. Both ligands (obtained in the hydrochloride form) can form stable metal complexes with Cu^II and Ni^II salts, the crystal structures of which were determined by X-ray diffraction technique. The reactions of H₂L¹ with Cu(ClO₄)₂ and Ni(ClO₄)₂ afford a penta-coordinated mononuclear complex [Cu(H₂L¹)Cl] · ClO₄ (1) and a four-coordinated monomeric [Ni(HL¹)] · ClO₄ (2), in which the ligand is monodeprotonated. The ligand H₂L² also forms a quite similar mononuclear [Ni(HL²)] · ClO₄ complex with Ni(ClO₄)₂, according to our previous work. However, reactions of different Cu^II salts [Cu(ClO₄)₂, CuCl₂ and Cu(NO₃)₂ for 3, and CuSO₄ for 4] with H₂L² in the presence of NaClO₄ yield two unusual mono-μ-Cl dinuclear Cu^II complexes [Cu₂(HL²)₂Cl] · (ClO₄) (3), and [Cu₂(H₂L²)(HL²)Cl] · (ClO₄)₂ · (H₂O)(4). These results indicate that the resultant Cu^II complexes (1, 3 and 4) are sensitive to the backbones of diazamesocycles and even auxiliary anions.     

Imidazole derivatives of binuclear copper (II) and nickel (II) complexes incorporating bis(1,4,7-triazacyclononan-1-yl) ligands

A series of new binuclear copper (II) and nickel (II) complexes of the macrocyclic ligands bis(1,4,7-triazacyclononan-1-yl)butane (L^but) and bis(1,4,7-triazacyclononan-1-yl)-m-xylene (L^mx) have been synthesized: [Cu₂L^butBr₄] (1), [Cu₂L^but(imidazole)₂Br₂](ClO₄)₂ (2), [Cu₂L^mx(μ-OH)(imidazole)₂](ClO₄)₃ (3), [Cu₂L^but(imidazole)₄](ClO₄)₄ · H₂O (4), [Cu₂L^mx(imidazole)₄](ClO₄)₄ (5), [Ni₂ L^but(H₂O)₆](ClO₄)₄ · 2H₂O (6), [Ni₂L^but(imidazole)₆](ClO₄)₄ · 2H₂O (7) and [Ni₂L^mx (imidazole)₄(H₂O)₂](ClO₄)₄ · 3H₂O (8). Complexes 1, 2, 7 and 8 have been characterized by single crystal X-ray studies. In each of the complexes, the two tridentate 1,4,7-triazacyclononane rings of the ligand facially coordinate to separate metal centres. The distorted square-pyramidal coordination sphere of the copper (II) centres is completed by bromide anions in the case of 1 and/or monodentate imidazole ligands in complexes 2, 4 and 5. Complex 3 has been formulated as a monohydroxo-bridged complex featuring two terminal imidazole ligands. Complexes 6-8 feature distorted octahedral nickel (II) centres with water and/or monodentate imidazole ligands occupying the remaining coordination sites. Within the crystal structures, the ligands adopt trans conformations, with the two metal binding compartments widely separated, perhaps as a consequence of electrostatic repulsion between the cationic metal centres. The imidazole-bearing complexes may be viewed as simple models for the coordinative interaction of the binuclear complexes of bis (tacn) ligands with protein molecules bearing multiple surface-exposed histidine residues.     

Bis(O2S2 macrocycle) complexes of palladium(II)

Two isomeric dibenzo-O₂S₂ macrocycles L¹ and L² have been synthesised and their coordination chemistry towards palladium(II) has been investigated. Two-step approaches via reactions of 1:1-type complexes, [cis-Cl₂LPd] (1a: L = L¹, 1b: L = L²), with different O₂S₂ macrocycle systems (L¹ and L²) have led to the isolation of the following bis(O₂S₂ macrocycle) palladium(II) complexes in the solid state: [Pd(L¹)₂](ClO₄)₂ (2a) and a mixture of [Pd(L¹)₂](ClO₄)₂ (2a) + [Pd(L²)₂](ClO₄)₂ (2b).     

Synthesis and characterization of imidazolate-bridged polynuclear copper complexes

Copper(II) complexes of N4-donor ligands containing imidazole moieties, 4-[bis(1-methylimidazole-2-yl-methyl)aminomethyl]imidazole (Him-im₂) and 4-[bis(1-methylimidazole-2-yl-methyl)aminoethyl]imidazole (Hhis-im₂), were prepared, and [Cu(Him-im₂)Cl]ClO₄ (1) and [Cu(Hhis-im₂)Cl]ClO₄ (2) were structurally characterized by the X-ray diffraction method. Complexes 1 and 2 have a mononuclear structure with a coordinated chloride ion. The geometry of the Cu(II) center in 1 was found to be 5-coordinate trigonal-bipyramidal, whereas that of 2 was square-pyramidal. Complexes 1 and 2 showed different absorption and EPR spectra in MeOH, indicating that these compounds in solution maintain the structures revealed in the solid state. On the other hand, the reaction of Him-im₂ with Cu(ClO₄)₂ · 6H₂O under basic conditions gave a tetranuclear Cu(II) complex, [Cu₄(im-im₂)₄](ClO₄)₄ (3), whereas using the ligand Hhis-im₂ gave two kinds of polynuclear complexes [Cu₄(his-im₂)₄](ClO₄)₄ (4) and [Cu₆(his-im₂)₆](ClO₄)₆ (5) exhibiting discretely different structures. X-ray crystal structure analysis of the polynuclear complexes revealed their cyclic structures bridged by the imidazolate moiety. The geometry difference of the Cu(II) centers between 1 and 2 is thus concluded to determine the structures of tetranuclear complexes 3 and 4, respectively. Temperature dependent magnetic susceptibility measurements of complexes 3, 4, and 5 have shown an antiferromagnetic exchange interaction with a coupling constant of J = −32.5, −27.1 and −22.8 cm⁻¹, respectively.     

Bioinspired FeIIICdII and FeIIIHgII complexes: synthesis, characterization and promiscuous catalytic activity evaluation

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe^IIICd^II(L)(μ-OAc)₂]ClO₄·0.5H₂O (1) complex containing the unsymmetrical ligand H₂L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe₂^IIIHg₂^II(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) and [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe^III₂Hg^II₂(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) can be converted to (3) by the fixation of atmospheric CO₂ since the crystal structure of the tetranuclear organometallic complex [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) with an unprecedented {Fe^III(μ-O_phenoxo)₂(μ-CO₃)Fe^III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe^III-bound hydroxo group on the CO₂ molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe^III centers in 3 are antiferromagnetically coupled (J = − 7.2 cm^− 1) and that the Fe^III-OR-Fe^III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe^III…Hg^II distance could be responsible for the lower catalytic effectiveness of 2.     

Diastereoisomerically pure pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2-bipyridine: structural, electrochemical and spectral studies

Pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2^′-bipyridine of composition [(bpy)₂Ru(pzdc)Ru(bpy)₂](ClO₄) · H₂O (1) and [(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2) have been obtained in high yield and have been separated to their homochiral (ΛΛ/ΔΔ) rac (1a, 2a) and heterochiral (ΛΔ/ΔΛ) meso (1b, 2b) diastereoisomers. The distinctive structural features of these diastereoisomers have been characterized by 1-D and 2-D ¹H NMR spectroscopy. The X-ray crystal structure of rac-[(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2a) has been determined. The electrochemical and electronic spectral studies have established that there remain difference in properties and hence difference in intermetallic communication between the diastereoisomeric forms in each case.     

Polynuclear nickel (II) and copper (II) complexes of hexaazamacrocycles incorporating pairs of diethylenetriamine subunits separated by aromatic spacers

A series of Ni(II) and Cu(II) complexes of the hexaaza macrocycles, 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1^11,15]triaconta-1(29),11(30),12,14,25,27-hexaene (L¹) and 3,6,9,16,19,22-hexaazatricyclo[22.2.2.2^11,14]triaconta-1(26),11(29),12,14(30),24(28),25-hexaene (L²), have been prepared and the crystal structures determined for [Ni₂L¹(O₂CCH₃)₂(H₂O)₂](ClO₄)₂ (1), [Ni₂L²(DMF)₆](ClO₄)₄ · 2H₂O (2), {[Cu₂L²Br(O₂CCH₃)](ClO₄)₂}_n (3), [Cu₂L²(μ-CO₃)(H₂O)₂]₂(ClO₄)₄ · 8H₂O (4), [Cu₂L²(O₂CCH₃)₂](BF₄)₂ (5), and [Cu₂L¹(μ-imidazolate)Br]₂Br₄ · 6H₂O (6). In these complexes, two metal centers are bound per ligand; in 1 and 3-6, the N₃ subunits of L¹ or L² coordinate meridionally to the metal centers, whilst in 2, each N₃ subunit in L² adopts a facial mode of coordination. The binuclear cations in 1 and 2 have chair-like conformations, with the distorted octahedral Ni(II) coordination spheres completed by terminal water and a bidentate acetate ligand in 1 and three DMF ligands in 2. The Cu(II) centers in 3-6 generally reside in square planar environments, although a weakly binding ligand enters the coordination sphere in some cases, generating a distorted square pyramidal geometry. The binuclear [Cu₂L²]⁴⁺ units in 3, 4 and 5 adopt similar bowl-shaped conformations, stabilized by H-bonding interactions between pairs of amine groups from L² and a perchlorate or tetrafluoroborate anion. In 3, the binuclear units are linked through acetate groups, bridging in a syn-anti fashion, to produce a zig-zag polymeric chain structure, whilst 4 incorporates a tetrameric cation consisting of two binuclear units linked via a pair of carbonate bridges. Compound 6 features an imidazolate bridge between the two Cu(II) centers bound by L¹. Pairs of [Cu₂L¹(μ-imidazolate)]³⁺ units are then weakly linked through a pair of bromide anions.     

Syntheses, crystal structures and magnetic properties of trinuclear and [3 × 1 + 1 × 2] pentanuclear complexes derived from a compartmental ligand: Role of solvent on nuclearity and number of components

Reaction of [Cu^IIL⊂(H₂O)] (H₂L = N,N′-ethylenebis(3-ethoxysalicylaldimine)) with nickel(II) perchlorate in 1:1 ratio in acetone produces the trinuclear compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂ (1). On the other hand, on changing the solvent from acetone to methanol, reaction of the same reactants in same ratio produces the pentametallic compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)]·2MeOH (2A), which loses solvated methanol molecules immediately after its isolation to form [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)] (2B). Clearly, formation of 1 versus 2A and 2B is solvent dependent. Crystal structures of 1 and 2A have been determined. Interestingly, compound 2A is a [3 × 1 + 1 × 2] cocrystal. The cryomagnetic profiles of 1 and 2B indicate that the two pairs of copper(II)···nickel(II) ions in the trinuclear cores in both the complexes are coupled by almost identical moderate antiferromagnetic interaction (J = −22.8 cm⁻¹ for 1 and −26.0 cm⁻¹ for 2B).     

Dinickel(II), dizinc(II) and dilead(II) complexes of a pyridazine-containing Schiff-base macrocycle

The study of the mid-late first row transition metal co-ordination chemistry of the pyridazine-containing Schiff-base macrocycle L1 [derived from the (2 + 2) condensation of 3,6-diformylpyridazine and 1,3-diaminopropane] has been completed. Transmetallation reactions of [Pb₂(4 + 4)](ClO₄)₄ (1) under appropriate conditions have led to the formation of the following complexes, [Ni₂L1(NCS)₂(SCN)₂] (3), [{Pb₂L1}₂(μ³-OH)₂](ClO₄)₆ (4), and [Zn₂L1(CH₃CN)₄](ClO₄)₄ (5 · 4CH₃CN), all of which have been structurally characterised. The analogous triflate salt of 5, [Zn₂L1](CF₃SO₃)₄ (6), can only be obtained by template reaction, as transmetallation of 1 with Zn(CF₃SO₃)₂ · 6H₂O gave 5, albeit in reduced yield. Attempts to synthesise pure [Fe₂L1(CH₃CN)₄](ClO₄)₄ (7) using the transmetallation procedure, from either [Pb₂(4 + 4)](ClO₄)₄ or [Zn₂L1(CH₃CN)₄](ClO₄)₄, were unsuccessful. The electrochemical studies carried out on [Zn₂L1](ClO₄)₄ (5) revealed multiple reduction processes and associated oxidations, but no processes corresponding to oxidation of 5.     

Hydrolytic cleavage of double-strand DNA by the water-soluble dicobalt(III) complexes of 1,4,7-Triazacyclononane-N-acetate

Three water-soluble dicobalt(III) complexes, [Co₂L₂(µ-OH)₂](ClO₄)₂·5H₂O (1), [Co₂L₂(µ-OH)₂](ClO₄)₂·CH₃OH·H₂O(2); [Co₂L₂(µ-OH)₂](ClO₄)₂·4H₂O(3) (L = 1,4,7-triazacyclononane-N-acetate monoanion), were prepared to serve as nuclease mimics. The complexes were characterized by X-ray, IR and UV-vis spectroscopy as well as ESI-MS. Three complexes exhibit similar structures, just with different solvent molecules. The electrospray mass spectrum of 1 in solution indicates that dinuclear ion [Co₂L₂(µ-OH)₂-H⁺] ⁺ (4) is the active species. In the absence of any reducing agent, the complexes cleave plasmid pBR322 DNA was performed and its hydrolytic mechanism was demonstrated with radical scavengers, anaerobic reaction and T4 ligase. The kinetic aspects of DNA cleavage under pseudo- or true-Michaelis-Menten conditions are also detailed, kinetic parameters (k_cat, K_M) were calculated to be 3.57 h^− 1, 6.92 × 10^− 4 M; 0.28 h^− 1, 1.9 × 10^− 5 M for 4, respectively.     

Copper(II) complexes with monocarboxylate ligands bearing different substituent groups: Synthesis and spectroscopic studies

In our continuing efforts to explore the effects of substituent groups of ligands in the formation of supramolecular coordination structures, seven new Cu^II complexes formulated as [Cu₂(L¹)₄(DMF)₂] (1), {[Cu₂(L¹)₄(Hmta)](H₂O)_0.75}_∞ (2), [Cu₂(L²)₄(2,2′-bipy)₂] (3), [Cu₂(L³)₄(H₂O)₂] (4), [Cu₂(L³)₄(Hmta)]_∞ (5), [Cu₂(L³)₄(Dabco)]_∞ (6) and [Cu₂(L³)₄(Pz)]_∞ (7) with three monocarboxylate ligands bearing different substituent groups HL¹-HL³ (HL¹ = phenanthrene-9-carboxylic acid, HL² = 2-phenylquinoline-4-carboxylic acid, HL³ = adamantane-1-carboxylic acid, Hmta = hexamethylenetetramine, 2,2′-bipy = 2,2′-bipyridine, Dabco = 1,4-diazabicyclo[2.2.2] octane and Pz = pyrazine), have been prepared and characterized by X-ray diffraction. In 1, 2 and 4-7, each Cu^II ion is octahedrally coordinated, and carboxylate acid acts as a syn-syn bridging bidentate ligand. While each Cu^II ion in 3 is penta-coordinated in a distorted square-pyramidal geometry. 1 and 4 both show a dinuclear paddle-wheel block, while 2, 5, 6 and 7 all exhibit an alternated 1D chain structure between dinuclear paddle-wheel units of the tetracarboxylate type Cu₂-(RCO₂)₄ and the bridging auxiliary ligands Hmta, Dabco and Pz. Furthermore, 3 has a carboxylic unidentate and μ_1,1-oxo bridging dinuclear structure with the chelating auxiliary ligand 2,2′-bipy. Moreover, complexes 1-6 were characterized by electron paramagnetic resonance (EPR) spectroscopy.     

Phosphodiester hydrolysis and specific DNA binding and cleavage promoted by guanidinium-functionalized zinc complexes

Two new Zn(II) complexes containing guanidinium groups, [Zn(L¹)Cl₂](ClO₄)₂ · H₂O · CH₃OH (1) and [Zn(L²)Cl₂](ClO₄)₂ · 0.5H₂O (2), were synthesized and characterized (L¹ = 5,5′-di[1-(guanidyl)methyl]-2,2′-bipyridyl bication and L² = 6,6′-di[1-(guanidyl)methyl]-2,2′-bipyridyl bication). Both complexes are able to catalyze bis(p-nitrophenyl) phosphate (BNPP) hydrolysis efficiently. Obtained kinetic data reveal that both 1 and 2 show nearly 300- and 600-fold rate enhancement of BNPP hydrolysis, respectively, compared to their simple analogue without the guanidinium groups [Zn(bpy)Cl₂] (bpy = 2,2′-bipyridy) (3). Enhanced acceleration for cleavage of BNPP could be attributed to cooperative interaction between the Zn(II) ion and the guanidinium groups by electrostatic interaction and H-bonding. Studies on inhibition of sequence-specific endonucleases (DraI and SmaI) by complexes show that 1 and 2 are able to recognize nucleotide sequence, -TTT^AAA-, and highly effectively cleave the plasmid DNA in the presence of hydrogen peroxide, while 3 has no specific binding to the DNA target sequences and only shows low DNA cleavage activity.     

Dinuclear terephthalato-bridged nickel(II) complexes. Structural characterization and magnetic properties

The dinuclear terephthalato-bridged nickel(II) complexes [Ni₂(cyclen)₂(μ-tp)](ClO₄)₂ (1) [Ni₂(trpn)₂(μ-tp)(H₂O)₂](ClO₄)₂ (2) and [Ni₂(3,3,3-tet)₂(μ-tp)(H₂O)₂](ClO₄)₂ · 2H₂O (3), where tp = terephthalate dianion, cyclen = 1,4,7,10-tetraazacyclododecane, trpn = tris(3-aminopropyl)amine and 3,3,3-tet = 1,5,9,13-tetraazatridecane, were synthesized and structurally characterized by X-ray crystallography. Their magnetic susceptibilities were also determined at variable temperatures over the range 2-300 K. The structures of these complexes consist of μ-tp bridging two Ni(II) centers in a bis(bidentate) bonding fashion in 1 and in bis(monodentate) bonding fashion in 2 and 3. The coordination geometry around the Ni(II) ions in these compounds has a distorted octahedral geometry with four nitrogen atoms from the amine ligand (cyclen, trpn or 3,3,3-tet) and two coordinated oxygen atoms supplied by the chelated carboxylate group of the bridged terephthalate ligand in 1, and by one tp-carboxylate-oxygen in 2 and 3. The sixth coordination site in the last two complexes 2 and 3 is achieved via an oxygen atom from a coordinated water molecule. The intradimer Ni…Ni distances in these complexes are 10.740, 11.428 and 11.537 Å for 1, 2 and 3, respectively. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Ni(II) centers. Also, the analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(bidentate) and bis(monodentate) coordination modes for the bridged terephthalate ligand in 1, 2 and 3, respectively. Despite the different coordination modes of the tp bridging ligand in these complexes, they all exhibit very weak antiferromagnetic coupling. The coupling constants J were found to be −2.2, −0.6 and −1.5 cm³ K mol⁻¹ for the complexes 1, 2 and 3, respectively. The structural and magnetic results of 1-3 are discussed in relation to the other related published μ-terephthalato dinuclear Ni(II) compounds.     

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.     

Interaction of free functional group with platinum(II) center in cyclometalated complexes: A structural and photophysical property investigation

A series of flexible multidentate ligands containing N,P-donor, 2-[N-(diphenylphosphino)methyl]amino-pyridine (L¹), 2-[N-bi-(diphenylphosphino) methyl]amino-pyridine (L²), 2-[N-(diphenylphosphino)methyl]amino-7-methyl-1,8-naphthyridine (L³) and 4-[(N-diphenylphosphino)methyl]amino-pyridine) (L⁴) have been synthesized. The mono- and dinuclear cyclometalated platinum(II) complexes [Pt(C^N^N)L¹]ClO₄ (HC^N^N = 6-phenyl-2,2′-bipyridine), [Pt₂(C^N^N)₂L¹](ClO₄)₂, [Pt₂(C^N^N)₂L²](ClO₄)₂, [Pt(C^N^N)L³]ClO₄ and [Pt₂(C^N^N)₂L⁴](ClO₄)₂ were prepared and their structures determined by X-ray crystal analysis. These complexes exhibit long-lived bright orange emissions ranging from 560 to 610 nm in the solid state at room temperature. In solution, dinuclear complexes have emissions with higher quantum yields than mononuclear complexes. This can be attributed to intramolecular interaction of free functional group with Pt(II) at axial position, resulting in the quenching of phosphorescence for platinum(II) complexes in the ³MLCT excited state.     

Cd(II)-ethylenediamine mono- and bimetallic complexes - Synthesis and characterization by Cd NMR spectroscopy and single crystal X-ray diffraction

Formation of three Cd(II)-ethylenediamine (en) complexes ([Cd(en)_n]²⁺, n = 1-3) in aqueous solution and in DMSO solvent has been established by means of ¹¹³Cd NMR spectroscopy. It is clearly shown that Cd(II)-en complexes form primarily in basic solutions. A correlation between the ¹¹³Cd NMR chemical shifts and the ethylenediamine (en) coordination number has been observed and discussed. Two single crystals with the composition [Cd₂(en)₅](ClO₄)₄ (1) and [Cd(en)₃](ClO₄)₂ (2) were prepared from aqueous solution, and their structures were determined by single crystal X-ray diffraction. Cd(II) ions are coordinated by six atoms in both compounds, 1 and 2: via five N-donor atoms and one O-donor atom forming a bimetallic complex 1, and via six N-donor atoms forming a distorted octahedral monometallic complex 2. Raman spectra of complexes 1 and 2 also provide additional evidence that the cis-form of the bridging en is present in complex 1.     

Structure and spectroelectrochemical property of a ruthenium complex containing phenanthroline-quinone, and assembly of the complexes on a gold electrode

Ruthenium complexes containing pdon (pdon = 1,10-phenanthroline-5,6-dione) were synthesized. Their spectroscopic and electrochemical properties were examined. The molecular structure with [Ru(pdon)(bpy)₂](ClO₄)₂ ([1](ClO₄)₂) (bpy = 2,2′-bipyridyl) was determined by single crystal X-ray diffraction. The optically transparent thin-layer electrochemical measurements confirm that the quinone form of [1](ClO₄)₂ is reduced to the semi-quinone state in acetonitrile (E°′ = −8 mV). Comparing the model complex, [1](ClO₄)₂, and metal-free pdon, the positive charge on two carbon atoms of the o-quinone group is bigger than that of metal-free pdon. The assemblies of the complexes were finally examined using ligand substitution.     

Reaction of [MCl2(CH3CN)2] (M = Pd(II), Pt(II)) compounds with N1-alkylpyridylpyrazole-derived ligands

Palladium(II) and platinum(II) complexes with N-alkylpyridylpyrazole-derived ligands, 2-(1-ethyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L¹) and 2-(1-octyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L²), cis-[MCl₂(L)] (M = Pd(II), Pt(II)), have been synthesised. Treatment of [PdCl₂(L)] (L = L¹, L²) with excess of ligand (L¹, L²), pyridine (py) or triphenylphosphine (PPh₃) in the presence of AgBF₄ and NaBPh₄ produced the following complexes: [Pd(L)₂](BPh₄)₂, [Pd(L)(py)₂](BPh₄)₂ and [Pd(L)(PPh₃)₂](BPh₄)₂. All complexes have been characterised by elemental analyses, conductivity, IR and NMR spectroscopies. The crystal structures of cis-[PdCl₂(L²)] (2) and cis-[PtCl₂(L¹)] (3) were determined by a single crystal X-ray diffraction method. In both complexes, the metal atom is coordinated by one pyrazole nitrogen, one pyridine nitrogen and two chlorine atoms in a distorted square-planar geometry. In complex 3, π-π stacking between pairs of molecules is observed.     

Pd(II) complexes containing N-alkyl-3-pyridine-5-trifluoromethyl pyrazole ligands: Synthesis, NMR studies and X-ray crystal structures

Palladium [PdCl₂(L)] complexes with N-alkylpyridylpyrazole derived ligands [2-(5-trifluoromethyl-1H-pyrazol-3-yl)pyridine (L¹), 2-(1-ethyl-5-trifluoromethyl-1H-pyrazol-3-yl)pyridine (L²), 2-(1-octyl-5-trifluoromethyl-1H-pyrazol-3-yl)pyridine (L³), and 2-(3-pyridin-2-yl-5-trifluoromethyl-pyrazol-1-yl)ethanol (L⁴) were synthesised. The crystal and molecular structures of [PdCl₂(L)] (L = L², L³, L⁴) were resolved by X-ray diffraction, and consist of monomeric cis-[PdCl₂(L)] molecules. The palladium centre has a typical square-planar geometry, with a slight tetrahedral distortion. The tetra-coordinate metal atom is bonded to one pyridinic nitrogen, one pyrazolic nitrogen and two chlorine ligands in cis disposition. Reaction of L (L², L⁴) with [Pd(CH₃CN)₄](BF₄)₂, in the ratio 1M:2L, gave complexes [Pd(L)]₂(BF₄)₂. Treatment of [PdCl₂(L)] (L = L², L⁴) with NaBF₄ and pyridine (py) and treatment of the same complexes with AgBF₄ and triphenylphosphine (PPh₃) yielded [Pd(L)(py)₂](BF₄)₂ and [Pd(L)(PPh₃)₂](BF₄)₂ complexes, respectively. Finally, reaction of [PdCl₂(L⁴)] with 1 equiv of AgBF₄ yields [PdCl(L⁴)](BF₄).     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.