Tuning of electronic properties of one-dimensional cyano-bridged Cu-Ni, Cu-Pd, and Cu-Pt bimetallic assemblies by stereochemistry of ligands

Preparations, XPS and electronic spectroscopy, and magnetism of seven new one-dimensional cyano-bridged coordination polymers, chiral [Cu(RR-chxn)₂][Pd(CN)₄] · 2H₂O (1), [Cu(trans-chxn)₂][M(CN)₄] · 2H₂O (2, 4, and 6 for M = Pd, Ni, and Pt), and [Cu(cis-chxn)₂][M(CN)₄] · 2H₂O (3, 5, and 7 for M = Pd, Ni, and Pt) (RR-chxn = cyclohexane-(1R,2R)-diamine, trans-chxn = racemic trans-cyclohexane-(1,2)-diamine, and cis-chxn = racemic cis-cyclohexane-(1,2)-diamine) have been reported in view of tuning of their electronic properties by stereochemistry of chxn ligands and metal-substitution. Comparison of Cu 2p_1/2 and 2p_3/2 peaks of XPS and broad d-d bands around 18 000 cm⁻¹ of electronic spectra are described systematically for 1-7. Variable-temperature magnetic measurement shows that complexes 1-7 indicate weak antiferromagnetic interactions via cyano-bridges. Because of semi-coordination coupled with pseudo Jahn-Teller elongation and electrostatic interaction for 1, the axial Cu-N coordination bond distances of 2.330(7) and 3.092(8) Å are considerably longer than those of equatorial ones in the range from 2.016(6) to 2.030(6) Å. The former bond distances of 1 are intermediate values among the related Ni (2.324(6) and 3.120(8) Å) and Pt (2.34(1) and 3.09(1) Å) complexes.     

Two cadmium-thiocyanate coordination polymers with organic cations: Synthesis, crystal structures and luminescent properties

Two new inorganic-organic hybrid polymers [ClBzQl]₂[Cd(SCN)_3.5Br_0.5]·0.25H₂O (1) and [ClBzMePy][Cd(SCN)₃] (2) (ClBzQl = 1-(4′-Cl-benzyl)quinolinium cation and ClBzMePy = 1-(4′-Cl-benzyl)-2-methylpyridinium cation) have been synthesized and characterized by IR, UV, elemental analysis and X-ray crystallography. Crystal structure analyses show that two polymers belong to the monoclinic space group P2/n (1) and P2₁/c (2) with a = 18.548(2) Å, b = 9.526(1) Å, c = 20.689(2) Å, β = 94.008(1)°, V = 3646.6(5) Å³ for 1, and a = 11.195(2) Å, b = 16.415(3) Å, c = 10.751(2) Å, β = 102.930(3)°, V = 1925.7(7) Å³ for 2. The Cd atom exhibits a distorted octahedral coordination geometry for 1 and 2. For 1, a pair of 1,1-μ-SCN⁻ anions and a pair of 1,3-μ-SCN⁻ anions are alternately bridge adjacent Cd centers to form infinite polymeric chains. For 2, adjacent Cd atoms are linked by three 1,3-μ-SCN⁻ anions to form infinite [Cd(SCN)₃⁻]_∞ polymeric chains. The luminescent properties of the two polymers in the solid state at room temperature were investigated.     

Nickel(II) and iron(II) mononuclear complexes with 1-methylimidazole-2-aldoximate: New building units for molecule-assembled magnetic materials

A new class of mononuclear metal complexes with 1-methylimidazole-2-aldoximate (miao) has been synthesized and characterized: trans-Ni^II(Cl)₂(Hmiao)₂ (1), trans-Ni^II(miao)₂(py)₂ (2), NO-trans-Ni^II(miao)₂(phen) (3), and NO-trans-Fe^II(miao)₂(phen) (4). The crystal structures of 2, 3, and 4 have been determined by single-crystal X-ray crystallography. Compound 1 having the protonated miao ligand (i.e., Hmiao) is a precursor for synthesizing 2 and 3. Compound 2 is an octahedral Ni^II complex surrounded by two miao bidentate ligands and two monodentate ligands of pyridine in a trans-arrangement. Compound 3 is a cis-type octahedral Ni^II complex with two miao ligands and a bidentate ligand of 1,10-phenanthroline, in which the ligand arrangement around Ni^II center is found in an NO-trans form. Compound 4 is an isostructural Fe^II derivative of 3. Compounds 1, 2, and 3 exhibit paramagnetic nature with an S = 1 spin and a positive zero-field splitting, among which it for 3 is overlapped with intermolecular ferromagnetic interaction (zJ/k_B = +0.16 K). Compound 4 is diamagnetic due to the existence of low-spin Fe^II ion.     

Variations in the coordination environment of Co, Cu and Zn complexes prepared from a tridentate (imino)pyridine ligand and their structural comparisons

The variations in the coordination environment of Co(II), Cu(II) and Zn(II) complexes with the neutral, tridentate ligand bis[1-(cyclohexylimino)ethyl]pyridine (BCIP) are reported. Analogous syntheses were carried out utilizing either the M(BF₄)₂ · xH₂O or MCl₂ · xH₂O metal salts (where M = Co(II), Cu(II) or Zn(II)) with one equivalent of BCIP. When the hydrated metal starting material was used, cationic, octahedral complexes of the type [M(BCIP)₂]²⁺ were isolated as the tetrafluoroborate salt (4, 5). Conversely, when the hydrated chloride metal salt was used as the starting material, only neutral, pentacoordinate [M(BCIP)Cl₂] complexes (1-3) formed. All complexes were characterized by X-ray diffraction studies. The three complexes that are five coordinate have distortions due mainly to the pyridine di-imine bite angle. The [Cu(BCIP)Cl₂] (2) also exhibits deviations in the Cu(II)-Cl bond distances with values of 2.4242(9) and 2.2505(9) Å, which are not seen in the analogous Zn(II) and Co(II) structures. Similarly, the two six coordinate complexes (5, 6) are also altered by the ligand frame bite angle giving rise to distorted octahedral geometries in each complex. The [Cu(BCIP)₂](BF₄)₂ (6) also exhibits Cu(II)-N_imine bond lengths that are on average 0.14 Å longer than those found in the analogous 5 coordinate complex, [Cu(BCIP)Cl₂]. In addition to X-ray analysis, all complexes were also characterized by UV/Vis and IR spectroscopy with ¹H NMR spectroscopy being used for the analysis of the Zn(II) analogue (3).     

Syntheses, structures, and mesomorphism of a series of Ni(II) salen complexes with 4-substituted long alkoxy chains

A series of nickel(II) salen complexes containing 4-substituted alkoxy chains of aromatic rings, [Ni((4-C_nH_2n + 1O)₂salen)] (n = 3 (1), 4 (2), 6 (3), 8 (4), 10 (5), 12 (6), 14 (7), 16 (8), 18 (9), and 20 (10)), and their parent complex, [Ni((4-HO)₂salen)] (11) (salen = N,N′-ethylenebis(salicylideneiminato)), have been prepared and mesomorphic properties have been investigated. An X-ray crystallographic analysis revealed that complex 11 · 2DMF has one-dimensional stacking structure supported by the π-π interaction between the six-membered chelate and aromatic rings with the NiNi distances of alternatively 3.3957 and 3.7224 Å and that complex 3 is formed by one-dimensional stacking by weak CH?O type hydrogen bonded interaction between the five-membered chelate ring and phenoxo atoms of the dramatically distorted salen moieties with the NiNi distance of 5.994 Å. Complexes 1-6 did not exhibit any mesophases. On the other hand, complexes 7-10 with longer alkoxy chains of n = 14-20 showed an unusual metallomesogen of a lamello-columnar mesophase within the smectic layers with an interlamellar distance of 31.1 Å (7), 33.6 Å (8), 37.1 Å (9), and 39.5 Å (10) and nearly constant stacking distance of 6.19-6.24 Å between the inter-dimers, irrespective of the variation of the alkoxy chain lengths by the X-ray diffraction measurements of the liquid crystal. The relationship between molecular assemblies and mesomorphic properties is discussed.     

Synthesis, structure, and properties of monomeric Fe(II), Co(II), and Ni(II) complexes of neutral N-(aryl)-2-pyridinecarboxamides

We have prepared and structurally characterized six-coordinate Fe(II), Co(II), and Ni(II) complexes of types [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Fe, 1; Co, 3; and Ni, 5) and [M^II(HL²)₃][ClO₄]₂ · MeCN (M = Fe, 2 and Co, 4) of bidentate pyridine amide ligands, N-(phenyl)-2-pyridinecarboxamide (HL¹) and N-(4-methylphenyl)-2-pyridinecarboxamide (HL²). The metal centers in bis(ligand)-diaqua complexes 1, 3 and 5 are coordinated by two pyridyl N and two amide O atoms from two HL¹ ligands and six-coordination is completed by coordination of two water molecules. The complexes are isomorphous and possess trans-octahedral geometry. The metal centers in isomorphous tris(ligand) complexes 2 and 4 are coordinated by three pyridyl N and three amide O atoms from three HL² ligands. The relative dispositions of the pyridine N and amide O atoms reveal that the pseudo-octahedral geometry have the meridional stereochemistry. To the best of our knowledge, this work provides the first examples of structurally characterized six-coordinate iron(II) complexes in which the coordination is solely by neutral pyridine amide ligands providing pyridine N and amide O donor atoms, with or without water coordination. Careful analyses of structural parameters of 1-5 along with that reported in the literature [M^II(HL¹)₂(H₂O)₂][ClO₄]₂ (M = Cu and Zn) and [Co^III(L²)₃] have allowed us to arrive at a number of structural correlations/generalizations. The complexes are uniformly high-spin. Spectroscopic (IR and UV/Vis) and redox properties of the complexes have also been investigated.     

Polymorphism and weak antiferromagnetic interactions in dibromo[(−)-sparteine-N,N]copper(II)

Two polymorphic crystal structures of the title compound, dibromo[(−)-sparteine-N,N^′]copper(II), 1, were determined. The structures of two isomorphs of 1, 1a [orthorhombic, P2₁2₁2₁, a=11.0463(9) Å, b=11.9839(15) Å and c=12.7835(19) Å] and 1b [orthorhombic, P2₁2₁2₁, a=7.6779(9) Å, b=12.0927(14) Å and c=18.090(2) Å], are composed of the same basic structural unit, Cu(C₁₅H₂₆N₂)Br₂. The bond distances in the molecular structures of 1a and 1b are identical to each other within the esds. However, there are slight differences in the bond angles around the Cu(II) center and considerable differences in their packing structure. Crystal 1a exhibits weak anti-ferromagnetism (J=−1.89 cm⁻¹) as opposed to the magnetically isolated paramagnetism observed for the analogous dichloro[(−)-sparteine]copper(II), 2. The results of a magneto-structural investigation of 1a and 2, and other supporting evidence, suggest that the pathway for the weak antiferromagnetic super-exchange in 1a might be through a Cu-Br ? Br-Cu contact.     

Spectroscopic properties of mono- and binuclear platinum(II) alkynyl complexes with phosphine ligands: A theoretical study

Based on their MP2 optimized structures in the ground states, we obtained solution absorption spectra for trans-[Pt^II(CCR)₂(PH₃)₂] (R = H (1) and Ph (2)) and trans-[Pt^II(CCH)₂(PH₂CH₂PH₂)]₂ (3) under the time-dependent density functional theory calculations. These absorptions agree with experimental observations. The unrestricted MP2 optimization performed for 3 in the lowest-energy triplet excited state shows that upon excitation the PtPt distance shortens about 0.347 Å with respect to the 3.188 Å one in the ground state. The UMP2 calculations estimated that its ³[σ^∗(d_z²)σ(p_z)] excited state produces the 531 nm emission, corresponding to the 580 nm one of trans-[Pt^II(CCPh)₂(PPh₂CH₂PPh₂)]₂ in the solid state at 298 K.     

Syntheses, structures, and magnetic properties of two new μ-alkoxo-μ-pyrazolato bridged dicopper(II) complexes

The syntheses, structures, and magnetic properties of two new μ-alkoxo-μ-pyrazolato heterobridged compounds, [Cu ^II₂(L¹-F)(μ-prz)] (1) and [Cu ^II₂(L¹-2OMe) (μ-prz)] · 0.5 CH₃CN (2) (prz=pyrazolato; H₂L¹-F=1,3-bis(3-fluorosalicylideneamino)-2-propanol; H₂L¹-2OMe=1,3-bis(4,6-dimethoxy salicylideneamino)-2-propanol) have been reported. Compound 1 crystallizes in triclinic space group with a=8.6392(10) Å, b=10.6431(9) Å, c=11.6809(13) Å, α=85.972(8)°, β=71.492(9)°, and γ=72.221(9)°, while the unit cell parameters of 2 are as follows: space group: monoclinic C2/c, a=28.2948(5) Å, b=7.3033(2) Å, c=26.3933(5) Å, and β=96.243(1)°. The variable-temperature magnetic susceptibility measurements reveal that the metal centers in both the compounds are antiferromagnetically coupled with J=−200 cm⁻¹ for 1 and J=−175 cm⁻¹ for 2. The magnetic behaviors have been explained on the basis of two opposing factors, complementarity and countercomplementarity of magnetic orbitals.     

Synthesis, spectral (UV-Vis, IR, ESI-MS), magnetic and structural characterizations, and the antimicrobial effect of potassium isothiocyanato-(N-salicylidene-amino-acidato)cuprates

A series of potassium isothiocyanato-(N-salicylidene-amino acidato)cuprates with the general formulas of K₂[Cu₂(sal-aa)₂(μ-NCS)₂]·nH₂O, where n = 0 or 4 and (sal-aa) stands for the dianion of N-salicylideneamino acid derived from glycine (I), dl-α-alanine (II), dl-valine (III), dl-phenylalanine (IV), and {K[Cu(sal-β-ala)(μ-NCS)]}_n for β-alanine (V), respectively, was synthesized and fully characterized by elemental analysis, UV-Vis and IR spectroscopy, ESI-MS spectrometry, magnetic measurements, and X-ray structural analysis (II and IV). It has been found that the copper(II) atom adopts a distorted square-pyramidal surrounding in the dimeric complexes I-IV, while the geometry in the polymeric complex V can be described as distorted square-bipyramidal. The analysis of magnetic properties revealed weak antiferromagnetic exchanges in the dinuclear species I-IV and an alternating ferro/antiferromagnetic exchange in the case of 1D-polymeric compound V. Moreover, the complexes were tested for their antibacterial activity against the G+ bacteria Staphylococcus aureus, G− bacteria Escherichia coli, filamentous fungi Microsporum gypseum, and yeast Candida albicans. The best results were achieved with G+ bacteria S. aureus with MIC values in the range of 0.22-0.57 mmol L⁻¹. It may be concluded that both the antimicrobial and antifungal activity decreased within the tested group of cuprates derived from α-amino acids with the increasing lipophility of the complexes, i.e.I → IV.     

Anionic PAMAM dendrimers as drug delivery vehicles for transition metal-based anticancer drugs

The use of anionic half-generation poly(amidoamine) dendrimers as drug delivery vehicles for [Pt(S,S-dach)(5,6-Me₂phen)]²⁺ (56MESS) (where S,S-dach = 1S,2S-diaminocyclohexane; 5,6-Me₂phen = 5,6-dimethyl-1,10-phenanthroline) and [{Δ,Δ-Ru(phen)₂}₂(μ-bb7)]⁴⁺ (Rubb₇) (where phen = 1,10-phenanthroline; bb7 = 1,7-bis[4-(4′-methyl-2,2′-bipyridyl)heptane]) has been studied by nuclear magnetic resonance spectroscopy. From one- and two-dimensional ¹H NMR spectra both 56MESS and Rubb₇ were found to bind to the surface of generation 3.5, 4.5, 5.5 and 6.5 dendrimers through electrostatic interactions. The higher charge and larger size of Rubb₇ resulted in stronger binding to all dendrimer generations (K_b ? 2 × 10⁵ M⁻¹) compared with 56MESS (K_b ? 1 × 10⁴ M⁻¹). Interestingly, there appeared to be no observable trend between dendrimer size and binding constant strength. The size of the free and 56MESS-bound dendrimers were examined using pulsed-gradient spin-echo NMR. The dendrimers ranged in hydrodynamic diameter from 11 to 20 nm and in all cases were larger than their corresponding full-generation dendrimer. Upon the addition of 56MESS the diameter of the dendrimers increased, consistent with surface binding.     

The role of non-classical supramolecular interactions in the structures of 2-amino-4,6-dimethylpyridinium tetrahalocuprate (II) salts

The compounds [2-amino-4,6-dimethylpyridinium]₂CuCl₄ (1) and [2-amino-4,6-dimethylpyridinium]₂CuBr₄ (2) were prepared from acidic ethanolic media containing CuX₂ and [2-amino-4,6-dimethylpyridine] in the molar ratio 1:1. The compounds were characterized by IR and single-crystal X-ray diffraction and found to be isomorphous in the space group with V = 991.2(10) Å³ for (1) and 1059.26(12) Å³ for (2) . There is no significant difference in the non-classical N-H?X hydrogen bonding between (1) and (2). The anions show essentially the same extent of distortion from tetrahedral geometry with max./min. values for the X-Cu-X bond angles of 139.72(6)°/96.78(6)° for (1) and 139.43(4)°/96.64(3)° for (2). Each [CuX₄]²⁻ anion is hydrogen bonded nonsymmetrically to four cations. In this manner, ladder chains are formed that run along the b-axis, with planar cations falling parallel to the (2, 0, 1) plane. Weaker π-π interactions exist between cations from different chains with centroid to centroid distance of 4.07 Å in (1) and a long 4.594 Å in (2). The X-π electrostatic interactions are surprisingly stronger in (2) than in (1) with a Br to centroid of pyridinic ring distance of 3.890 Å compared with 3.996 Å for the chloride analogue.     

Iron(III), chromium(III) and cobalt(II) complexes with squarate: Synthesis, crystal structure and magnetic properties

The preparation and variable temperature-magnetic investigation of three squarate-containing complexes of formula [Fe₂(OH)₂(C₄O₄)₂(H₂O)₄]·2H₂O (1) [Cr₂(OH)₂(C₄O₄)₂(H₂O)₄]·2H₂O (2) and [Co(C₄O₄)(H₂O)₄]_n (3) [H₂C₄O₄ = 3.4-dihydroxycyclobutene-1,2-dione (squaric acid)] together with the crystal structures of 1 and 3 are reported. Complex 1 contains discrete centrosymmetric [Fe₂(OH)₂(C₄O₄)₂(H₂O)₄] diiron(II) units where the iron pairs are joined by a di-μ-hydroxo bridge and two squarate ligands acting as bridging groups through adjacent oxygen atoms. Two coordinated water molecules in cis position complete the octahedral environment at each iron atom in 1. The iron-iron distance with the dinuclear unit is 3.0722(6) Å and the angle at the hydroxo bridge is 99.99(7)°, values which compare well with the corresponding ones in the isostructural compound 2 (2.998 Å and 99.47°) whose structure was reported previously. The crystal structure of 3 contains neutral chains of squarato-O¹,O³-bridged cobalt(II) ions where four coordinated water molecules complete the six-coordination at each cobalt atom. The cobalt-cobalt separation across the squarate bridge is 8.0595(4) Å. A relatively important intramolecular antiferromagnetic coupling occurs in 1 whereas it is very weak in 2, the exchange pathway being the same [J = −14.4 (1) and −0.07 cm⁻¹ (2), the spin Hamiltonian being defined as ]. A weak intrachain antiferromagnetic interaction between the high-spin cobalt(II) ions occurs in 3 (J = −0.30 cm⁻¹). The magnitude and nature of these magnetic interactions are discussed in the light of their respective structures and they are compared with those reported for related systems.     

Cu(II) complexes with square pyramidal (N2S)CuCl2 chromophore: Jahn-Teller distortion and subsequent effect on spectral and structural properties

One monomeric neutral Cu(II) complex [(pmtpm)CuCl₂] (1) is reported by Lindoy and Livingstone [8]. Two new complexes namely, μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu(Cl)}₂ μ-Cl](ClO₄) (2) and a bis μ-Cl bridged binuclear Cu(II) complex [{(pmtpm)Cu}₂(μ-Cl)₂](ClO₄)₂ (3) derived from a tridentate Schiff base ligand, 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine (pmtpm) were synthesized and characterized by various spectroscopic methods and by X-ray crystallography. (N₂S)CuCl₂ chromophore(s) of distorted square pyramidal coordination geometries around Cu(II) ion(s) have been observed for all the complexes 1-3. The equatorial sites of the square plane comprise two N and a thioether S donor atoms of the pmtpm ligand as well as one Cl⁻ ion (terminal in 1 and 2, and bridging in 3) while the remaining axial site is occupied by a terminal Cl⁻ ion (for 1) or a bridging Cl⁻ ion (for 2 and 3). The equatorial Cu-Cl distances are much shorter [1: 2.2511(4) Å, 2: 2.2307(12) Å, 3: 2.2513(12) Å] than the axial Cu-Cl distances [1: 2.4394(4) Å, 2: 2.5597(9) Å, 3: 2.7037(12) Å]. The correlation of an axial Cu-Cl bond elongation with a lower g_|| value in the solid state EPR spectrum and a blue shifted ligand field transition in the solid and solution phase absorption spectrum has been observed.     

Carboxy-derived (tpy)2Ru complexes as sub-units in supramolecular architectures: The solubilized ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy and its homoleptic Ru(II) complex

We herein describe the synthesis and characterization of a series of homoleptic, Ru(II) complexes bearing peripheral carboxylic acid functionality based upon the novel ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy (L₁), as well as 4′-(4-carboxyphenyl)tpy (L₂) and 4′-(carboxy)tpy (L₃) (where tpy = 2,2′: 6′,2″-terpyridine). Inspection of the metal-based oxidations (E_1/2 = 1.22-1.42 V) indicates an anodic shift (∼0.2 V) for (L₃)₂Ru²⁺ (3b) (E_1/2 = 1.40 V) relative to (L₂)₂Ru²⁺ (2b) (E_1/2 = 1.22 V). The metal-based oxidation (E_1/2 = 1.22 V) and ligand-based reductions (E_1/2 = −1.25 to −1.52 V) of (L₁)₂Ru²⁺ (1) are essentially invariant relative to those of the structural analogue 2b (PF₆)₂, which suggests no significant electronic effect caused by the tert-butyl groups. This is supported by invariance in the metal-to-ligand charge transfer bands in both the electronic absorption (494-489 nm) and emission spectra (654-652 nm). However, contrary to 2b, complex 1 is both very soluble and exhibits a highly porous solid-state structure with internal cavity dimensions of 15 Å × 14 Å due to the preclusion of inter-annular interactions by the bulky tert-butyl substituents.     

Synthesis, characterisation and crystal structures of a few coordination complexes of nickel(II), cobalt(III) and zinc(II) with N′-[(2-pyridyl)methylene]salicyloylhydrazone Schiff base

Four new coordination complexes, Ni^II(L)₂ (1), [Co^III(L)₂]ClO₄ (2), [Zn(HL)(L)]ClO₄ · H₂O (3) and [Zn(L)₂][Zn(L)(HL)]ClO₄ · 7H₂O (4) (where L is a monoanion of a Schiff base ligand, N′-[(2-pyridyl)methylene]salicyloylhydrazone (HL) with NNO tridentate donor set), have been synthesised and systematically characterised by elemental analysis, spectroscopic studies and room temperature magnetic susceptibility measurements. Single crystal X-ray diffraction analysis reveals that 1 is a neutral complex, while 2-4 are cationic complexes. Among them, 4 is a rare type of cationic complex with two molecules in the asymmetric unit. The ligand chelates the metal centre with two nitrogen atoms from the pyridine and imino moieties and one oxygen atom coming from its enolic counterpart. All the reported complexes show distorted octahedral geometry around the metal centres, with the two metal-N (imino) bonds being significantly shorter than the two metal-N (Py) bonds.     

Two-dimensional Cu and first Pb coordination polymers based on a flexible 1,4-cyclohexanedicarboxylate ligand displaying different conformations and coordination modes

Two novel metal-organic hybrid coordination polymers {[Cu(bpo)(chdc)(H₂O)](H₂O)_0.5}_n (1) and [Pb(chdc)(H₂O)]_n (2) have been synthesized under different conditions and structurally characterized by single-crystal X-ray diffraction technique, where H₂chdc refers to a flexible 1,4-cyclohexanedicarboxylic acid ligand and bpo is 2,5-bis(4-pyridyl)-1,3,4-oxadiazole. Complex 1 has a two-dimensional (2-D) grid-like [11.28 × 13.63 Å²] framework in which the Cu^II centers are extended via bidentate bridging ligands bpo and e,e-trans-chdc along two directions, exhibiting large porous cavities. Coordination polymer 2 represents the first Pb^II complex of H₂chdc in which the larger Pb^II centers are connected by e,a-cis-chdc anions to afford a 2-D close-knit structure.     

Synthesis, spectroscopic and structural characterization of the high-spin Fe(II) cyanato-N and thiocyanato-N “picket fence” porphyrin complexes

Two new iron(II) five-coordinated porphyrin complexes [Na(2,2,2-crypt)] [Fe^II(TpivPP)(NCO)] (1) (TpivPP = α,α,α,α-tetrakis(o-pivalamidophenyl) porphyrin known as picket fence porphyrin and 2,2,2-crypt is the cryptand-222) and [K(2,2,2-crypt)][Fe^II(TpivPP)(NCS)] (2) have been prepared and characterized. The UV-Vis and IR spectroscopic data are consistent with a cyanato-N and thiocyanato-N ferrous porphyrinates. The Mössbauer data and the X-ray structural analysis indicate that the Fe(II) cation in 1 and 2 is high-spin (S = 2) and has the (d_xy)²(d_xz)¹(d_yz)¹(d_z²)¹(d_x²-y²)¹ ground state electronic configuration.For complex 1, the average equatorial iron-pyrrole N bond length (Fe-N_p = 2.120(2) Å), the distance between the iron and the 24-atom mean plane of the porphyrin ring (Fe-P_C = 0.6805(7) Å) and the distance between the iron and the plane made by the four pyrrole nitrogens (Fe-P_N = 0.5923(12) Å) are longer than those of complex 2 and similar five-coordinated Fe(II) high-spin porphyrinates. This is probably due to the significant electronic repulsion of the d_x²-y² and d_xy orbitals by the negative charge of the pyrrole N atoms in case of 1.     

Copper(II) chloride/1-methylbenzotriazole chemistry: influence of various synthetic parameters on the product identity, structural and magnetic characterization, and quantum-chemical studies

A systematic investigation of the CuCl₂/Mebta (Mebta = 1-methylbenzotriazole) reaction system is described, involving the determination of the influence of the Cu^II:Mebta ratio, the nature of solvent and the presence of counterions on the identity of the reaction products. As a consequence, complexes [Cu₂Cl₄(Mebta)₄] (1), [CuCl₂(Mebta)₂] (2), {[Cu₂Cl₄(Mebta)₂]}_n (3), [Cu₄OCl₆(Mebta)₄] · 0.25H₂O (4 · 0.25H₂O) and [Cu₂Cl₂(Mebta)₆](ClO₄)₂ (5) have been isolated and structurally characterized by single-crystal X-ray studies. Mebta behaves as a monodentate ligand binding through N(3). 1 is a dinuclear complex, the structure of 2 consists of discrete monomeric units, and that of 3 is composed of linear, well-separated polymeric chains of Cu^II atoms. The molecules of 4 · 0.25H₂O have a central μ₄-oxide ion surrounded tetrahedrally by four Cu^II atoms. In the cations of 5 the two Cu^II centres are asymmetrically bridged by two chloro ligands, with three Mebta molecules completing five coordination at each metal. Complexes were characterized by spectroscopic (IR, far-IR, solution UV/Vis) and thermal decomposition (TG, DTG, and DTA) techniques. Variable-temperature magnetic susceptibility data for 1, 3 and 5 showed intramolecular (1, 5) and intrachain (3) ferromagnetic exchange interactions. Estimates of the Jparameters, experimentally derived, were in close agreement with a new magneto-structural criterion developed by us, holding for bis(μ-chloro) copper(II) dimers. A comparison between the CuCl₂/Mebta and CuBr₂/Mebta systems is also presented.     

New metal complexes with 5-(1H-imidazol-4-ylmethyl)aminoisophthalic acid: Syntheses, structures, electrochemistry and electrocatalysis

Three new coordination polymers {[Cu(HL)(H₂O)]·H₂O}_n (1), [Ag(H₂L)]_n (2), and {[Co(HL)(phen)(H₂O)]·8H₂O}_n (3) [H₃L = 5-(1H-imidazol-4-ylmethyl)aminoisophthalic acid, phen = 1,10-phenanthroline] have been synthesized under hydrothermal conditions. The results of X-ray diffraction analysis revealed that complex 1 displays (3, 3)-connected 2D network with (4, 8²) topology, while complexes 2 and 3 have infinite 1D chain structure, in which one of the two carboxylic groups of H₂L⁻/HL²⁻ is uncoordinated. The 2D layers of 1 or the 1D chains of 2 and 3 are further linked together by hydrogen bonds and π-π interactions to form 3D supramolecular frameworks. Moreover, the electrochemical properties of complexes 1 and 2 have been studied by modified glassy carbon electrodes of 1 (Cu-GCE) and 2 (Ag-GCE), and the results indicate that the Cu-GCE and Ag-GCE show one-electron redox peaks. In addition, both Cu-GCE and Ag-GCE have good electrocatalytic activities toward the reduction of H₂O₂ in phosphate buffer (pH 5.5) solution.