Control of dimensionality through nitrogen donor disposition in divalent metal perchlorate bis(pyridylmethyl)piperazine coordination polymers

Slow diffusion of aqueous solutions of metal perchlorates with alcoholic solutions of bis(4-pyridylmethyl)piperazine (4-bpmp) or bis(3-pyridylmethyl)piperazine (3-bpmp) afforded crystalline coordination polymer phases whose dimensionality and topology is determined largely by the pyridyl nitrogen donor disposition within the imine components. {[M(H₂O)₄(4-bpmp)](ClO₄)₂·4-bpmp·4H₂O}_n (M = Co, 1-Co; M = Zn, 1-Zn) are isostructural, displaying cationic [M(H₂O)₄(4-bpmp)]_n²ⁿ⁺ 1-D coordination polymer chains connected through extensive hydrogen-bonding pathways involving unligated species. In contrast, use of the 3-bpmp isomer generated compounds with formulation of {[M(H₂O)₂(3-bpmp)₂](ClO₄)₂·8H₂O}_n (M = Co, 2-Co; M = Zn, 2-Zn), which manifest achiral 3-fold interpenetrated 6⁶ diamondoid lattices. The zinc derivatives undergo modest blue-violet luminescence on exposure to ultraviolet light.     

Luminescent cadmium and zinc diphenate coordination polymers containing pyridyl-piperazine type ligands: Grids, diamondoid lattices, and a rare 4-connected net

Hydrothermal synthesis has afforded five d¹⁰ configuration divalent metal diphenate coordination polymers containing pyridyl-piperazine type ligands, which were structurally characterized by single-crystal X-ray diffraction. {[Cd(diphenate)(3-bpmp)(H₂O)]·0.5H₂O}_n (1, 3-bpmp = bis(3-pyridylmethyl)piperazine) has a double layer topology. Its perchlorate-containing analog {[Cd₃(diphenate)₄(H₂3-bpmp)(H3-bpmp)(H₂O)₂](ClO₄)·7H₂O}_n (2) possesses a very rare 4-connected 6⁵8 dmp topology based on anionic trinuclear nodes. {[Cd(diphenate)(4-bpfp)]·H₂O}_n (3, 4-bpfp = bis(4-pyridylformyl)piperazine) manifests a non-interpenetrated diamondoid lattice, while the related compound [Cd(diphenate)(4-bpmp)(H₂O)]_n (4, 4-bpmp = bis(4-pyridylmethyl)piperazine) has a simple (4,4) grid topology. {[Zn(diphenate)(4-bpmp)]·0.5H₂O}_n (5) displays a 2-fold interpenetrated diamondoid lattice. Luminescent properties of these materials are also reported.     

Zinc and cadmium flexible-arm ortho-dicarboxylate bis(pyridyl)piperazine coordination polymers with rare two- and three-dimensional topologies

Hydrothermal reaction of a d¹⁰ configuration divalent metal precursor with flexible-arm aromatic ortho-dicarboxylates and a bis(pyridyl)piperazine-type neutral co-ligand has generated four coordination polymers, some with rare topologies. {[Cd(hmph)(4-bpmp)_1.5]·4H₂O}_n (1, hmph = homophthalate, 4-bpmp = bis(4-pyridylmethyl)piperazine) manifests a new 3-fold interpenetrated uninodal 5-connected 3-D net with a very simple 4⁴6⁶ topology, different from the usual sqp 5-connected topology. [Cd₂(hmph)₂(4-bpfp)]_n (2, 4-bpfp = bis(4-pyridylformyl)piperazine) displays a rare 4,5-connected binodal tcs net with (4⁴6²)(4⁴6⁶) topology. [Zn₂(1,2-phda)₂(4-bpmp)(H₂O)₂]_n (3, 1,2-phda = 1,2-phenylenediacetate) possesses an uncommon 3,4-connected binodal 2-D layer with (4²6)(4²6³8) (V₂O₅ prototype) topology. [Zn₂(hmph)₂(4-bpfp)]_n (4) has a decorated (4,4) grid topology with embedded [Zn₂(OCO)₄] paddlewheel clusters. All materials exhibit ligand-centered fluorescent behavior. Thermal degradation behavior of the 3-D network materials is reported.     

Synthesis and characterization of cobalt(II)-salicylate complexes derived from N4-donor ligands: Stabilization of a hexameric water cluster in the lattice host of a cobalt(III)-salicylate complex

The syntheses and structural characterization of four cobalt(II)-salicylate complexes, [(TPA)Co^II(HSA)](ClO₄) (1), [(isoBPMEN)Co^II(HSA)](BPh₄) (2), [(TPzA)Co^II(HSA)](ClO₄) (3) and [(6Me₃TPA)Co^II(HSA)](BPh₄) (4) [TPA = tris(2-pyridylmethyl)amine, isoBPMEN = N¹,N¹-dimethyl-N²,N²-bis(2-pyridylmethyl)ethane-1,2-diamine, TPzA = tris((3,5-dimethyl-1H-pyrazole-1-yl)methyl)amine and 6Me₃TPA = tris(6-methyl-2-pyridylmethyl)amine] are described. While 2, 3 and 4 are unreactive towards dioxygen, 1 reacts slowly with molecular oxygen to a cobalt(III)-salicylate complex, [(TPA)Co^III(SA)](ClO₄) (1a). Two different crystalline forms, 1a and 1a·4H₂O were isolated depending upon the condition of oxidation and crystallization. The solid-state structures of cobalt(III)-salicylate unit in both 1a and 1a·4H₂O show a six-coordinate distorted octahedral coordination geometry at the cobalt(III) center ligated by the tetradentate ligand (TPA) where the dianionic salicylate (SA) binds in a bidentate fashion through one carboxylate and one phenolate oxygen. The hydrated form 1a·4H₂O reveals a hexameric water cluster formation in the inorganic lattice host. The complex cation and the perchlorate counterion are involved in stabilizing the (H₂O)₆ cluster in a rare ‘pentamer planar+1’ conformation. A one-dimensional water tape consisting of edge-shared water hexamers is observed. The water tape represents a subunit of ice structure.     

Intramolecular ether oxygen coordination in the zinc complexes with dipicolylamine (DPA)-derived ligands

The ether oxygen coordination to the zinc center in the complexes with dipicolylamine (DPA)-derived ligands, N-(2-methoxyethyl)-N,N-bis(2-pyridylmethyl)amine (L), N-(3-methoxypropyl)-N,N-bis(2-pyridylmethyl)amine (L′), and N-{3-(2-pyridylmethyloxy)propyl}-N,N-bis(2-pyridylmethyl)amine (L^Py) has been discussed. Upon chelation of the oxygen atom, L forms a five-membered chelate ring with respect to the 2-aminoethyl ether moiety whereas L′ forms a six-membered chelate in 3-aminopropyl ether unit. This difference was highlighted by the crystal structures of ZnCl₂ complexes, in which [Zn(L)Cl₂] (1) exhibited ether oxygen coordination but [Zn(L′)Cl₂] (2) had the ether oxygen non-coordinated. The terminal pyridyl group of L^Py facilitates the ether oxygen atom coordination via a metal binding from the basal plane trans to the aliphatic nitrogen.     

Chiral and achiral layered divalent metal aromatic ortho-dicarboxylate coordination polymers with bis(4-pyridylmethyl)piperazine ligands: Luminescent behavior and magnetic properties

Four divalent metal coordination polymers containing bis(4-pyridylmethyl)piperazine (4-bpmp) and the ortho-dicarboxylate ligands phthalate (pht) or 4-methylphthalate (mpht) have been prepared by solvent diffusion or hydrothermal methods. {[Cu₂(pht)₂(H4-bpmp)₂(H₂O)₂](NO₃)₂·H₂O}_n (1) and {[Cu₂(pht)₂(H4-bpmp)₂(H₂O)₂](SO₄)·2H₂O}_n (2) possess chiral cationic layer motifs formed by the junction of [Cu(H₂O)(pht)]_n chains by tethering curled-conformation H4-bpmp⁺ ligands. {[Co(pht)(H₂O)(4-bpmp)]·5.5H₂O}_n (3) displays a (4,4) grid constructed from anti-syn carboxylate-bridged {Co₂(H₂O)₂(pht)₂} dimeric clusters linked by open-conformation 4-bpmp ligands. {[Cd₂(mpht)₂(H₂O)₂(4-bpmp)(H4-bpmp)]ClO₄·4H₂O}_n (4) manifests cationic layered motifs based on neutral [Cd₂(H₂O)₂(mpht)₂] dinuclear units with {CdOC₄O}₂ 12-membered circuits, linked by open-conformation 4-bpmp and H4-bpmp⁺ ligands. Variable-temperature magnetic data indicate likely concomitant zero-field splitting and ferromagnetic coupling in 3. Violet light emission is observed when 4 is subjected to ultraviolet irradiation.     

Effect of pendant arm length and nitrogen donor disposition on the topology of luminescent cadmium phenylenedicarboxylate coordination polymers with bis(pyridylmethyl)piperazine co-ligands

Hydrothermal synthesis has afforded divalent cadmium coordination polymers containing bis(pyridylmethyl)piperazine (bpmp) tethers and either phenylenediacetate (phda) or phenylenedipropionate (phdp) ligands. {[Cd(1,4-phda)(4-bpmp)]·1.5H₂O}_n (1) displays a (4,4)-grid layered structure based on 4-connected {Cd₂O₂} dimeric units. Extension of the pendant arms generated {[Cd(1,4-phdp)(H4-bpmp)](ClO₄)·3.5H₂O}_n (2, phdp = phenylenedipropionate), which possesses a rare (3,6) 2D trigonal lattice based on 6-connected {Cd₂O₂} dimers. Changing the nitrogen donor atom disposition by using 3-bpmp as the nitrogen co-ligand yielded [Cd(1,4-phdp)(3-bpmp)(H₂O)]_n (3), which crystallizes in a 3-fold interpenetrated achiral diamondoid lattice. [Cd(1,3-phda)(4-bpmp)]_n (4) adopts a very similar structure to that of 1. Complexes 1-4 undergo blue-violet luminescence upon exposure to ultraviolet radiation.     

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.     

Syntheses, structures, and properties of Co(III) complexes derived from polypyridine ligands containing one carboxamido nitrogen donor

Four cobalt(III) complexes containing the polypyridine pentadentate ligands N,N-bis(2-pyridylmethyl)amine-N′-ethyl-2-pyridine-2-carboxamide (PaPy₃H), N,N-bis(2-pyridylmethyl)amine-N′-[1-(2-pyridylethyl)acetamide (MePcPy₃H), and N,N-bis(2-pyridylmethyl)amine-N′-(2-pyridylmethyl)acetamide (PcPy₃H), have been synthesized. All three ligands bind the Co(III) center in the same fashion with the exception of loss of conjugation between the carboxamide moiety and the pyridine ring in the latter two. The structures of [(PaPy₃)Co(OH)][(PaPy₃)Co(H₂O)](ClO₄)₃ · 3H₂O (1), [(PaPy₃)Co(NO₂)](ClO₄) · 2MeCN (2), [(MePcPy₃)Co(MeCN)](ClO₄)₂ · 0.5MeCN (3), and [(PcPy₃)Co(Cl)](ClO₄) · 2MeCN (4) have been determined. These ligands with strong-field carboxamido N donor stabilize the +3 oxidation state of the Co center as demonstrated by the facile oxidation of the corresponding Co(II) complexes (prepared in situ) by H₂O₂, [Fe(Cp)₂](BF₄), or nitric oxide (NO). The Co-N_amido bond distances of 1-4 lie in the narrow range of 1.853-1.898 Å. ¹H NMR spectra of these complexes confirm the low-spin d⁶ ground states of the metal centers.     

Synthesis and characterization of three mononuclear Fe(III) complexes containing bipodal and tripodal ligands: X-ray molecular structure of the dichloro[N-propanamide-N,N-bis-(2-pyridylmethyl)amine]iron(III) perchlorate

In this work, we present the synthesis and characterization of three mononuclear iron(III) complexes: dichloro[N-propanamide-N,N-bis-(2-pyridylmethyl)amine]iron(III) perchlorate (1), trichloro[N-methylpropanoate-N,N-bis-(2-pyridylmethyl)amine]iron(III) (2) and trichloro[bis-(2-pyridylmethyl)amine]iron(III) (3). The complexes were characterized by cyclic voltammetry, conductivimetry, elemental analyses, and by electronic, infrared and Mössbauer spectroscopies. Complex 1 was also characterized by X-ray structural analysis, which showed an iron center coordinated to one amide, one tertiary amine, two pyridine groups and two chloride ions. While for 1 the X-ray molecular structure and the infrared spectrum confirm the coordination of the amide group by the oxygen atom, the infrared spectrum of 2 indicates that the ester group present in the ligand is not coordinated, resulting in a N₃Cl₃ donor set, similar to the one present in 3. However, in 3 there is a secondary amine while in 2 a tertiary amine exists. These structural differences result in distinguishable variations in the Lewis acidity of the iron center, which could be evaluated by the analysis of the redox potential of the complexes, as well as by Mössbauer parameters. Thus, the Lewis acidity decreases in the following order: 1 > 2 > 3. It is important to notice that 1 has the amide group coordinated to the iron center, a feature present in metalloenzymes as lipoxygenase and isopenicillin N synthase, and in a small number of mononuclear iron(III) complexes.     

One-dimensional helical coordination polymers of cobalt(II) and iron(II) ions with 2,2′-bipyridyl-3,3′-dicarboxylate (BPDC)

One-dimensional (1-D) helical coordination polymers, [M^II(H₂O)₃(BPDC)]_n · nH₂O (M = Co (1), Fe (2)), have been prepared by the self-assembly of cobalt(II) and iron(II) ions, respectively, with 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂BPDC) in an aqueous solution. X-ray crystal structures of compounds 1 and 2 show that each metal ion displays a distorted octahedral coordination geometry including three water oxygen atoms, one oxygen atom of the carboxylate of a BPDC²⁻ belonging to the adjacent metal ion and two nitrogen atoms from the BPDC²⁻ acting as a chelating ligand. In 1 and 2, one carboxylate oxygen atom of coordinated BPDC²⁻ binds to the neighboring metal ion, which give rise to 1-D helical coordination polymers. The helical chains of 1 and 2 are linked by the hydrogen bonding interactions between the carboxylate oxygen atom of the BPDC²⁻ ion belonging to a chain and the water molecule of the adjacent helical chain, which lead to 2-D networks extending along the ab plane. The supramolecules 1 and 2 show isomorphous structures regardless of the metal ions.     

Platinum(II) and technetium(I) complexes anchored to ethynylestradiol: a way to drug targeting and delivery

Starting from ethynylestradiol (1), or, more precisely, from its 3,17β-bis-(triethylsilyloxy) derivative 2, two new ligands containing the ethylenediamino motif were synthesised by a Mannich aminomethylation, namely N-methyl-N-(prop-2-ynyl-3-(17α-estradiolyl))-N^′,N^′-dimethylethylenediamine (3) and N-(prop-2-ynyl-3-(17α-estradiolyl))-N^′-methylpiperazine (4). The corresponding platinum(II)-malonato complexes (7 and 8) were prepared through the PtI₂ intermediates (namely 5 and 6) by Dhara’s method. The structures of the two platinum complexes were energy-minimised by molecular mechanics employing the Amber force field. Both ligands were joined to the [^99mTc(CO)₃Cl] moiety, ^99mTc being the chief γ-emitter employed in nuclear medicine. Unfortunately, piperazine ligand 4 afforded complexes that were unstable under physiological conditions. The RBA values for both ligands and complexes derived from 3, measured for the two forms of estrogen receptor, were less than 1%. Such a poor degree of ligand recognition may be due to the partial protonation of the amino groups at physiological pH, making the carrier quite hydrophilic, therefore unsuitable for entering the hydrophobic pocket of estrogen receptors.     

Divalent metal 1,3-phenylenediacetate coordination polymers with rigid or flexible dipyridyl tethers: Chains, layers, and interpenetrated networks

Hydrothermal synthesis has afforded four divalent metal 1,3-phenylenediacetate (1,3-phda) coordination polymers containing different dipyridyl-type ligands. {[Cu(1,3-phda)(dpa)(H₂O)]·H₂O}_n (1, dpa = 4,4′-dipyridylamine) exhibits a simple 2-D (4,4) rhomboid grid structure. {[Co(1,3-phda)(bpy)]·1.5H₂O}_n (2, bpy = 4,4′-bipyridine) also possesses a (4,4) layer structure, but with syn-syn bridged {Co₂(OCO)₂} dimeric kernels serving as 4-connected nodes. {[Co(H₂O)₄(3-bpmpH₂)](1,3-phda)₂·8H₂O}_n (3, 3-bpmp = bis(3-pyridylmethyl)piperazine) manifests cationic 1-D [Co(H₂O)₄(3-bpmpH₂)]_n⁴ⁿ⁺ chains linked into higher dimensionality by unligated 1,3-phda anions and curled tetrameric water molecule units. {[Ni(1,3-phda)(4-bpmp)(H₂O)₂]·2H₂O}_n (4, 4-bpmp = bis(4-pyridylmethyl)piperazine) has an underlying twofold interpenetrated 6⁵8 (cds) 3-D network topology. Variable temperature magnetic susceptibility studies revealed the presence of weak antiferromagnetic coupling and zero-field splitting (J = −1.65(4) cm⁻¹ and D = 30.9(7) cm⁻¹ with g = 2.20(1)) within the {Co₂(OCO)₂} dimers in 2.     

Construction of 1-2D Cu(or Cu) metal-organic architectures with metal thiocyanates and bipyridyl spacers: Syntheses, structures, and thermal properties

Three new coordination polymers based on IB metal thiocyanates, [Cu^II(NCS)₂(DMSO)₄(meso-dpb)]_n (1), (2), [Cu^I(NCS)(pia)]_n (3) (dpb = 2,3-di(4-pyridyl)-2,3-butanediol, bpp = 1,3-bis(4-pyridyl)propane, pia = N,N′-(1,2-phenylene)diisonicotinamide), have been synthesized by the pre-assembly method and characterized by X-ray crystallography. In 1, Cu^II cations are bridged by meso-dpb ligands to form a one-dimensional (1D) linear chain. Compound 2 consists of 2D undulated layers of (4, 4) topology that show twofold parallel interpenetration. In the case of 3, the M^I center adopts tetrahedral coordination geometry and the 2D networks are formed by organic ligand with “folding ruler-shaped” NCS⁻-M chains. The thermal properties of 1-3 were also investigated.     

Crystal structure of six and seven coordinate manganese(II) complexes with penta and hexadentate pyridylmethyl ligands

Two six-coordinated manganese(II) complexes [Mn(pydien)Cl](ClO₄) · C₂H₅OH (1), [Mn(pydien)NCS](ClO₄) (2) and two seven-coordinated manganese(II) complexes [Mn(pydado)Cl](ClO₄) (3), [Mn(pydado)NCS](ClO₄) (4) have been obtained using linear penta and hexadentate ligands pydien and pydado (pydien: 1,7-bis(2-pyridylmethyl)-1,4,7-triazaheptane and pydado: 1,10-bis(pyridylmethyl)-1,10-diaza-4,7-dioxadecane). The crystal structures for all compounds have been determined. 1 and 3 crystallize in the triclinic space group , 2 crystallizes in the orthorhombic space group Pbca, whereas 4 crystallizes in the monoclinic space group P2₁/c. The bound anion (chloro or isothiocyanato) in complexes 1 and 2 has no influence on the geometry of six-coordinate manganese(II) complexes, whereas the geometry and the wrapping of the hexadentate ligand (pydado) around Mn²⁺ cation depend on the nature of the bound anion. The complex 3 has a capped octahedron geometry with the two pyridyl groups in trans position, while the geometry of complex 4 can be described as pentagonal bipyramid with one pyridyl group and a thiocyanate anion in the axial positions.     

Anion binding studies of tris(2-aminoethyl)amine based amide receptors with nitro functionalized aryl substitutions: A positional isomeric effect

Syntheses and crystal structures of tren-based amide, L¹, N,N′,N″-tris[(2-amino-ethyl)-4-nitro-benzamide] and L², N,N′,N″-tris[(2-amino-ethyl)-2-nitro-benzamide] are reported and compared with previously published tripodal amide receptor L³, N,N′,N″-tris[(2-amino-ethyl)-3-nitro-benzamide]. The crystallographic results show intramolecular and intermolecular hydrogen-bonding interactions between two arms of the tripodal receptor and two other adjacent molecules in cases of L¹ and L² whereas in addition to the above interactions an aromatic π···π stacking among tripodal arms is also observed in L³. Receptors L¹, L² and L³ having electron withdrawing -NO₂ substituted (para, ortho and meta, respectively) phenyl moieties are explored toward their solution state anion binding properties and selectivity studies. The substantial changes in chemical shifts are observed for the amide protons (-NH) and aromatic protons (-CH) with F⁻ and Cl⁻ in cases of L¹ and L³, and only with F⁻ for L², indicating the participation of -NH and -CH protons in the solution state binding events. Binding constants for the above cases are calculated by ¹H NMR titration upon monitoring the -NH signal. Receptor L² shows exclusive selectivity toward F⁻ in dimethyl sulfoxide (DMSO). The structural aspects of binding I⁻, ClO₄⁻ and SiF₆²⁻ with the monoprotonated L¹, L¹H⁺·I⁻·DMF (1), L¹H⁺·ClO₄⁻·DMF (2) and L¹H⁺·0.5SiF₆²⁻·H₂O (3), respectively are examined crystallographically. Anion binding with multiple receptor units is observed via amide N-H···anion as well as aryl C-H···anion hydrogen-bonding interactions in all the complexes as observed in cases of previously reported crystal structures of anionic complexes of protonated L³. The aryl group having nitro functionality that contributes to solution state anion binding with the neutral receptor and solid state coordination in complexes 1-3 through CH···anion interactions is noteworthy.     

Molecular structures of nickel(II) monochelates of a racemic tridentate ligand and co-ligand induced structural variations

Using a racemic mixture of the tridentate ligand, (((2-pyridyl)ethylamine)methyl)phenolate ion (L⁻) and , NCS⁻, (NC)₂N⁻, OAc⁻ as coligands, complexes having the formula [Ni(L)(N₃)] (1), [Ni(L)(NCS)]₂ (2), [Ni₂(L)₂(OAc)(N(CN)₂)]_n (3) were prepared and structurally characterized. In 1, Ni(II) has a square planar geometry and phenolate oxygen is involved in dipolar ?N^δ+ interaction with electrophilic central nitrogen atom of coordinated azide ion. Complex 2 is dimeric in nature and nickel(II) is penta-coordinated. Compounds 1 and 2 exist as centrosymmetric dimers made up of a pair of R and S enantiomers of L. In 3, an acetate and phenoxo bridged dinickel complex is present which is further linked to a zig-zag coordination polymer by the dicyanamide ion. In a given chain of 3, both L have same enantiomeric form and either RR or SS dimers are repeated along the chain. The magnetic properties are described.     

Unprecedented formation of binuclear copper(II) complex with a perylene derived ligand by the oxidative reaction

A new perylene-pendent tridentate ligand, N-(3-perylenylmethyl)-N,N-bis(2-pyridylmethyl)amine (perbpa) 1 and its Cu(II) complex, [Cu(perbpa)Cl₂] (2) were prepared and structurally characterized by the X-ray diffraction method. In the packing structure of ligand 1, perylene groups were aggregated to form a π-π stacked layer of dimerized pelylene moieties similar to the packing of pristine perylene. This result suggests both that the π-π interactions among the perylene moieties predominate for the arrangement of perbpa molecules in the crystal and that this ligand is a good candidate for constructing electron conducting path. A complex 2 was prepared from the ligand 1 and a copper(II) chloride dehydrate. Complex 2 had a mononuclear and 5-coordinate distorted square pyramidal structure with a perbpa and two coordinated chloride ions. The chemical oxidation of 2 by iodine resulted in the unprecedented binuclear Cu(II) species, [Cu₂(μ-Cl)₂(perbpa)₂](I₃)₂, 3·(I₃)₂. An X-ray crystal structure analysis of 3·(I₃)₂ revealed the binuclear structure bridged by the chloride ions. A temperature dependent magnetic susceptibility measurement of 3 showed a weak ferromagnetic exchange interaction with S = 1 ground state, g = 2.12 and J = +1.17 cm⁻¹, based on H = −2JS₁ · S₂. The UV-Vis absorption and the EPR spectra of 3 showed that the perylene groups are not oxidized. These results indicate a couple of Cu(II) constructed S = 1 ground state with intermolecular ferromagnetic interaction. The electrochemical study suggested that the crystallization of 3·(I₃)₂ was initiated by the oxidation of the N,N-bis-(2-pyridylmethyl)amino (bpa) groups of 2 by I₂.     

Biomimetic zinc(II) and cobalt(II) complexes with tri-tert-butoxysilanethiolate and imidazole ligands - Structural and spectroscopic studies

New, heteroleptic zinc and cobalt complexes with tri-tert-butoxysilanethiolate and imidazole co-ligands are characterized by crystal structure studies. The ligands exhibit different coordination modes to Co(II) ions: NOS₂ (with methanol as O-donor ligand) in 2′, NO₂S₂ in 2′′, N₂S₂ in 1, and to Zn(II) ions: N₂S₂ in 3 and N₃S in 4. Complex 2′ is a structural analog of cobalt-substituted active site of alcohol dehydrogenase. All four-coordinate Co(II) and Zn(II) complexes have tetrahedral geometry. Solution and solid state electronic spectra of cobalt(II) complexes are discussed and compared to literature data available for the cobalt-substituted liver alcohol dehydrogenase and sorbitol dehydrogenase. The EPR spectra of all cobalt complexes exhibit at 77 K a characteristic broad signal with g ∼3.6 and 5.6, strongly indicating a high-spin state, S = 3/2, of Co(II) complexes.     

Zinc(II) and mercury(II) coordination architectures with two pyridyl/benzimidazol-1-yl-based ligands: Crystal structures and photoluminescent properties

In our efforts to investigate the relationships between the structures of ligands and their complexes, two structurally related ligands, 1-(2-pyridylmethyl)-1H-benzimidazole (L¹) and 1-(4-pyridylmethyl)-1H-benzimidazole (L²), and their four complexes, [Zn(L¹)₂Cl₂] (1), [Hg(L¹)Br₂]_∞ (2), {[Zn(L²)Cl₂](CH₃CN)}_∞ (3) and [Hg(L²)Br₂]₂(CH₃CN)₂ (4) were synthesized and structurally characterized by elemental analyses, IR spectra and single-crystal X-ray diffraction analysis. Structural analyses show that 1 has a mononuclear structure, and 2 and 3 both take 1D structure. While 4 takes a dinuclear structure. 1, 2 and 4 were further linked into higher-dimensional supramolecular networks by weak interactions, such as C-H?Cl and C-H?Br H-bonding, C-H?π, and π?π stacking interactions. The structural differences of 1-4 may be attributed to the difference of the spatial positions of the terminal N donor atoms in the pendant pyridyl groups in L¹ and L², in which the pyridine rings may act as the directing group for coordination and the benzimidazole rings act as the directing group for π?π stacking and C-H?π interactions. The luminescent properties of the corresponding complexes and ligands have been further investigated.