Hydrogen-bonded copper(II) and nickel(II) complexes and coordination polymeric structures containing reduced Schiff base ligands

Complexes [Cu(HSas)(H₂O)] · 2H₂O (H₃Sas = N-(2-hydroxybenzyl)-l-aspartic acid) (1), [Cu(HMeSglu)(H₂O)] · 2H₂O (H₃MeSglu = (N-(2-hydroxy-5-methylbenzyl)-l-glutamic acid) (2), [Cu₂(Smet)₂] (H₂Smet = (N-(2-hydroxybenzyl)-l-methionine) (3), [Ni(HSas)(H₂O)] (4), [Ni₂(Smet)₂(H₂O)₂] (5), and [Ni(HSapg)₂] (H₂Sapg = (N-(2-hydroxybenzyl)-l-aspargine) (6) have been synthesized and characterized by chemical and spectroscopic methods. Structural determination by single crystal X-ray diffraction studies revealed 1D coordination polymeric structures in 2 and 4, and hydrogen-bonded network structure in 5 and 6. In contrast to previously reported coordination compounds with similar ligands, the phenol remains protonated and bonded to the metal ions in 2 and 4, and also probably in 1. However, the phenolic group is non-bonded in 6.     

Synthesis, characterization, and magnetic properties of new homotrinuclear bis(oxamato) copper(II) complexes with an asymmetric central N,N′-bridge

The new mononuclear bis(oxamato) complex [n-Bu₄N]₂[Cu(obbo)] (1) (obbo=o-benzyl-bis(oxamato)) has been synthesized as a precursor for trinuclear oxamato-bridged transition metal complexes. Starting from 1 the homotrinuclear complexes [Cu₃(obbo)(pmdta)₂(NO₃)](NO₃)·CH₂Cl₂·H₂O (2) and [Cu₃(obbo)(tmeda)₂(NO₃)₂(dmf)] (3) have been prepared, where pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, tmeda = N,N,N′,N′-tetramethylethylenediamine and dmf = dimethylformamide. The crystal structures of 1-3 were solved. The magnetic properties of 2 and 3 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter values of −111 cm⁻¹ (2) and −363 cm⁻¹ (3) were obtained.     

Synthesis, characterization and magnetic properties of new homotrinuclear copper(II) complexes

Two new mononuclear bis(oxamato) complexes with the formula [nBu₄N]₂[M(nabo)] M = Ni (4), Cu (5), with nabo = 2,3-naphthalene-bis(oxamato) have been synthesized as precursors for trinuclear oxamato-bridged transition metal complexes. Starting from 5 the homo-trinuclear complex [Cu₃(nabo)(pmdta)₂(BF₄)](BF₄) · MeCN · Et₂O (7), with pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, has been prepared. The central N,N′-2,3-naphthalene bridge of 7 is so far the most extended π-conjugated bridge of trinuclear bis(oxamato) type transition metal complexes. The goal of this work was to verify the N,N′-2,3-naphthalene bridge of 7 on its magnetic properties in comparison to the N,N′-o-phenylene bridge of the related homo-trinuclear complex [Cu₃(opba)(pmdta)₂(NO₃)](NO₃) · 2MeCN (6) (opba = o-phenylene-bis(oxamato)). The crystal structures of 4-7 were solved. The magnetic properties of 6 and 7 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, values of −89 cm⁻¹ (6) and −113 cm⁻¹ (7) were obtained. The different J values are discussed based on the crystal structures of 6 and 7.     

Synthesis, crystal structures and properties of novel zinc(II) and cadmium(II) polymeric and cyclic bimetallic complexes with fluconazole and dicarboxylate co-ligands

Four new fluconazole-bridged zinc(II) and cadmium(II) complexes with dicarboxylate co-ligands, namely [Zn(HFlu)(TPA)]_n (1), {[Cd(HFlu)₂(TPA)]·2CH₃OH}_n (2), [Zn(HFlu)₂(Suc)(H₂O)₂]·H₂O (3), and [Cd(HFlu)₂(Suc)(H₂O)₂]·H₂O (4), have been synthesized and characterized by elemental analysis, IR, TG, and single-crystal X-ray diffraction (HFlu = 2-(2,4-difluorophenyl)-1,3-bis(1,2,4-triazol-1-yl)-propan-2-ol, H₂TPA = terephthalic acid, and H₂Suc = succinic acid). Complex 1 displays a 2-D corrugated network with common (4,4) topology, in which two types of grids constructed by two bridging TPA dianions and two HFlu ligands are found. Complex 2 shows an unusual (3,6) coordination layer consisting of alternative PMPM Cd-HFlu helical chains in which the Cd(II) nodes are also fixed by terephthalate dianions in a cis fashion. The isostructural complexes 3 and 4 have 20-membered dimeric macrocyclic motifs with the Zn···Zn and Cd···Cd distances of 11.258(2) and 11.528(2) Å, respectively. The fluorescence and thermal stability of complexes 1-4 have also been investigated.     

Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set

The synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn^III₂(L-3Н)₂(CH₃ОH)₄]·2CH₃ОH (1) and [Mn^III₂(L-3Н)₂(Py)₄]·2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn₂N₄} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = −3.6 cm⁻¹, Θ = −2.02 K for 1 and g = 2.00, J = −3.7 cm⁻¹, Θ = 1.43 K for 2.     

Imidazolium formation from the reaction of N-heterocyclic carbene stabilised group 13 trihydride complexes with organic acids

The reactions of the N-heterocyclic carbene (NHC) stabilised group 13 trihydride complexes [AlH₃(IMeMe)] (1) (IMeMe = 1,3,4,5-tetramethylimidazol-2-ylidene), [AlH₃(IⁱPrMe)] (2) (IⁱPrMe = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with three molar equivalents of phenol, and [InH₃(IMes)] (3) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-ylidene) with one molar equivalent of 1,1,1,5,5,5-hexafluoropentan-2,4-dione (F₆acacH) are presented. These render the imidazolium tetraphenoxyaluminate species; [IMeMe · H][Al(OPh)₄] (4) and [IⁱPrMe · H][Al(OPh)₄] (5), and 1,3-bis(2,4,6-trimethylphenyl)imidazolium 1,1,1,5,5,5-hexafluoropentan-2,4-dionate; [IMes · H][CH{C(O)CF₃}₂] (6), the latter leading to metallohydride decomposition. The molecular structures of 4 and 6 are described.     

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.     

Syntheses, structures, and magnetic properties of 3d-4f heterometallic complexes constructed from pyrazole-bridged CuLn dinuclear units

A series of pyrazole-bridged heterometallic 3d-4f complexes, [CuDy(ipdc)₂(H₂O)₄] · (2H₂O)(H₃O⁺) (1) and [CuLn(pdc)(ipdc)(H₂O)₄] · H₃O⁺ (Ln = Ho (2), Er (3), Yb (4); H₃ipdc = 4-iodo-3,5-pyrazoledicarboxylic acid; H₃pdc = 3,5-pyrazoledicarboxylic acid), {[Cu₃Ln₄(ipdc)₆(H₂O)₁₆] · xH₂O}_n (Ln = Sm (5), x = 8.5; Ln = Eu (6), x = 7; Ln = Gd (7), Tb (8), x = 9), have been synthesized and structurally characterized. Ligand H₃ipdc was in situ obtained by iodination of ligand H₃pdc. Complexes 1-4 are pyrazole-bridged heterometallic dinuclear complexes, and 2-4 are isostructural. Complexes 5-8 are isostructural and comprised of an unusual infinite one-dimensional tape-like chain based on pyrazole-bridged heterometallic dinuclear units. The magnetic properties of compounds 1-4, 7 and 8 have been investigated through the magnetic measurement over the temperature range of 1.8-300 K.     

Synthesis, crystal structures and magnetic studies of terephthalato- and fumarato-bridged dinickel(II) complexes with tripodal poly-benzimidazole ligand

Two novel dinuclear nickel(II) complexes [Ni₂(ntb)₂(μ-tp)(H₂O)_1.61(CH₃OH)_0.39](NO₃)₂·5.13CH₃OH·2.25H₂O (1) and [Ni₂(ntb)₂(μ-fum)(H₂O)(CH₃OH)](NO₃)₂·6CH₃OH·H₂O (2) (tp = terephthalate dianion, fum = fumarate dianion, ntb = tris(2-benzimidazolylmethyl)amine) containing tetradentate poly-benzimidazole ligand were synthesized and structurally characterized by IR spectra, UV-Vis, elemental analysis and X-ray crystallography. The Ni(II) ions in 1 and 2 have distorted octahedral geometry with four nitrogen atoms of ntb, one oxygen atom of water and one oxygen atom supplied by the carboxylate group of the bridged dicarboxylato ligand. Complexes 1 and 2 consist of terephthalato- and fumarato-bridged dinickel(II) centers in bis(monodentate) bonding fashion. The Ni?Ni distances are 11.333 Å for 1 and 8.966 Å for 2. The magnetic susceptibility measurements at variable temperature show that two complexes exhibit weak antiferromagnetic interactions between nickel(II) ions with J values of −0.25 cm⁻¹ and −0.36 cm⁻¹, respectively.     

Different coordination modes of 5,5-diethylbarbiturate in the copper(II) complexes with some aliphatic amines: Synthesis, spectroscopic, thermal and structural studies

Three new copper(II) complexes of 5,5-diethlybarbiturate (barb), [Cu(barb)₂(dmen)]·0.5H₂O (dmen = N,N-dimethylethylenediamine) 1, [Cu(barb)₂(bapa)] (bapa = bis(3-aminopropyl)amine) 2, and [Cu(barb)(apen)](barb)·2H₂O (apen = N,N′-bis(3-aminopropyl)ethylenediamine) 3, have been synthesized and characterized by chemical, spectroscopic and thermal methods. Single crystal X-ray diffraction studies revealed that all complexes are mononuclear. The copper(II) ion exhibits a square-pyramidal coordination geometry in 1 and 3, but a trigonal-bipyramidal geometry in 2. The barb ligand shows different coordination modes. 1 presents the unequal coordination of the barb ligands: one is monodentate (N) and the other one is bidentate (N, O). In 2, both barb ligands are N-coordinated, whereas in 3, one barb ligand is N-coordinated, while the second barb ligand behaves as a counter-ion. The dmen, bapa and apen ligands act as bi-, tri- and tetradentate ligands, respectively. All complexes display a hydrogen-bonded network structure. The IR spectroscopic analysis shows that the ν(CO) stretching frequencies do not correlate predictably with the coordination mode of the barb ligand in 1. Thermal analysis data for 1-3 are in agreement with the crystal structures.     

Analysis of the main structural trends for biscyclometalated dinuclear rhodium compounds of general formula Rh2(O2CR)2(PC)2 · 2H2O

A new series of biscyclometalated dinuclear rhodium (II) compounds with the general formula Rh₂(O₂CR)₂(PC)₂ · 2H₂O, being PC = (C₆H₄)P(C₆H₅)₂, R = CH₃ (1 · 2H₂O), PC = [(p-CH₃ OC₆H₃)P(p-CH₃ OC₆H₄)₂], R = CF₃ (2 · 2H₂O), PC = (C₆H₄)P[CH(CH₃)₂]₂, R = CH₃ (3 · 2H₂O) and PC = (C₆H₄)P(C₆H₅)₂, R = C₆F₅ (4 · 2H₂O) has been obtained. The crystal structures for these compounds have been determined by X-ray diffraction and the main structural trends, bond lengths, bond angles and torsion angles have been analyzed, and have also been compared with the structural parameters for different analogous complexes described previously in the literature.     

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.     

Diiron and diruthenium aminocarbyne complexes containing pseudohalides: stereochemistry and reactivity

Acetonitrile is easily displaced from [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(MeCN)(Cp)₂][SO₃CF₃] (R = 2,6-Me₂C₆H₃ (Xyl) (1a); Me (1b)) upon stirring in THF at room temperature in the presence of [NBu₄][SCN]. The resulting complexes trans-[Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCS)(Cp)₂] (R = Xyl (trans-2a); Me (trans-2b)) are completely isomerised to cis-[Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCS)(Cp)₂] (R = Xyl (cis-2a); Me (cis-2b)) when heated at reflux temperature. Similarly, the complexes cis-[M₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCO)(Cp)₂] (M = Fe, R = Me (4a); M = Ru, R = Xyl (4b); M = Ru, R = Me (4c)) and cis-[M₂{μ-CN(Me)(R)}(μ-CO)(CO)(N₃)(Cp)₂] (M = Fe, R = Xyl (5a); M = Fe, R = Me (5b); M = Ru, R = Xyl (5c)) can be obtained by heating at reflux temperature a THF solution of [M₂{μ-CN(Me)(R)}(μ-CO)(CO)(MeCN)(Cp)₂][SO₃CF₃] (M = Fe, R = Xyl (1a); M = Fe, Me (1b); M = Ru, R = Xyl (1c); M = Ru, R = Me (1d)) in the presence of NaNCO and NaN₃, respectively. The reactions of 5 with MeO₂CCCCO₂Me, HCCCO₂Me and (NC)(H)CC(H)(CN) afford the triazolato complexes [M₂{μ-CN(Me)(R)}(μ-CO)(CO){N₃C₂(CO₂Me)₂}(Cp)₂] (M = Fe, R = Xyl (6a); M = Fe, R = Me (6b); M = Ru, R = Xyl (6c)), [M₂{μ-CN(Me)(R)}(μ- CO)(CO){N₃C₂(H)(CO₂Me)}(Cp)₂] (M = Fe, R = Me (7a); M = Ru, R = Xyl (7b)) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){N₃C₂(H)(CN)}(Cp)₂] (8), respectively. The asymmetrically substituted triazolato complexes 7-8 are obtained as mixtures of N(1) and N(2) bonded isomers, whereas 6 exists only in the N(2) form. Methylation of 6-8 results in the formation of the triazole complexes [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){N₃(Me)C₂(CO₂Me)₂}(Cp)₂][CF₃SO₃] (9), [M₂{μ-CN(Me)(R)}(μ-CO)(CO){N₃(Me)C₂(H)(CO₂Me)}(Cp)₂][CF₃SO₃] (M = Fe, R = Me (10a); M = Ru, R = Xyl (10b)) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){N₃(Me)C₂(H)(CN)}(Cp)₂][CF₃SO₃], 11. The crystal structures of trans-2b, 4b · CH₂Cl₂, 5a, 6b · 0.5CH₂Cl₂ and 8 · CH₂Cl₂ have been determined.     

Diverse coordination of polynuclear copper(II) complexes constructed from benzene tetracarboxylates

The reaction of aqueous solutions of the preformed 1:1 Cu(ClO₄)₂-polydentate amine with tetrasodium 1,2,4,5-benzene tetracarboxylate (Na₄bta) afforded three different types of polynuclear compounds. These include the tetranuclear complexes: [Cu₄(Medpt)₄(μ₄-bta)(ClO₄)₂(H₂O)₂](ClO₄)₂·2H₂O (1), [Cu₄(pmdien)₄(μ₄-bta)(H₂O)₄](ClO₄)₄ (2), [Cu₄(Mepea)₄(μ₄-bta)(H₂O)₂](ClO₄)₄(3), [Cu₄(TPA)₄(μ₄-bta)](ClO₄)₄·10H₂O (4) and [Cu₄(tepa)₄(μ₄-bta)](ClO₄)₄·2H₂O (5), the di-nuclear: [Cu₂(DPA)₂(μ₂-bta)(H₂O)₂]·4H₂O (6), [Cu₂(dppa)₂(μ₂-bta)(H₂O)₂]·4H₂O (7) and [Cu₂(pmea)₂(μ₂-bta)]·14H₂O (8) and the trinuclear complex [Cu₃(dppa)₃(μ₃-bta)(H₂O)_2.25](ClO₄)₂·6.5H₂O (9) where Medpt = 3,3′-diamino-N-methyldipropylamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine, Mepea = [2-(2-pyridyl)ethyl]-(2-pyridylmethyl)methylamine, TPA = tris(2-pyridylmethyl)amine, tepa = tris[2-(2-pyridyl)ethyl)]amine, DPA = di(2-pyridymethyl)amine, dppa = N-propanamide-bis(2-pyridylmethyl)amine and pmea = bis(2-pyridylmethyl)-[2-(2-pyridylethyl)]amine. The complexes were structurally characterized by elemental analyses, spectroscopic techniques, and by X-ray crystallography for complexes 1, 2, 4, 6, 7 and 9. X-ray structure of the complexes reveal that bta⁴⁻ is acting as a bridging ligand via its four deprotonated caboxylate groups in 1, 2 and 4, three carboxylate groups in 9 and via two trans-carboxylates in 6 and 7. The complexes exhibit extended supramolecular networks with different dimensionality: 1-D in 2 and 4 due to hydrogen bonds of the type O-H···O, 2-D in 1 and 7, and 3-D network in 6 as a result of hydrogen bonds of the types N-H···O and O-H···O. Magnetic susceptibility measurements showed very weak antiferromagnetic coupling between the Cu^II ions in 1-5, 7-9 (|J| = 0.02-0.87 cm⁻¹) and weak ferromagnetic coupling for 6 (J = 0.08 cm⁻¹).     

N,N′-Bis(3-methoxysalicylidene)propane-1,2-diamine mononuclear 4f and heterodinuclear Cu-4f complexes: Synthesis, crystal structure and electrochemical properties

Reactions of H₂L [H₂L = N,N′-bis(3-methoxysalicylidene)propane-1,2-diamine] and Ln(NO₃)₃ · 6H₂O give rise to two different mononuclear 4f complexes, namely, {[(H₂L)La(NO₃)₃(MeOH)] · H₂O}_n (1) and [(H₂L)Nd(NO₃)₃] (2). Further additions of Cu(Ac)₂ · H₂O to the mononuclear 4f complexes yield expected heterodinuclear Cu-4f complexes [LCu(Me₂CO)Ln(NO₃)₃] (3, Ln = Nd; 4, Ln = Eu; 5, Ln = Dy). Complex 1 is a unique 1D polymeric chain structure, and 2 is one of the few structurally characterized discrete hexadentate salen-type mononuclear 4f complexes. Complexes 3-5 are similar to their analogues. However, they are prepared by a reversed synthetic route in contrast to their isomorphic complexes. Electrochemical behavior of heterodinuclear Cu-4f complexes 3-5 has been examined by cyclic voltammetry in acetonitrile. The redox potential of heterodinuclear Cu-4f complexes 3-5 shows significant anodic shift comparing to that of mononuclear copper complex (LCu). A tendency of anodic shift was observed in a sequence of 3 < 4 < 5. This results from the modulating effect of coordination geometry around Cu(II) ion on redox potential.     

Structure characterization of two new three-dimensional piperazine-bridged metal-halo coordination polymers

By the simple hydro/solvothermal reaction, two new 3-D metal-halo cluster polymers, [NiCl₂(pip)] (pip = piperazine) (1) and [Cu₂I₂(pip)] (2) were obtained and characterized by IR spectroscopy, CHN analysis and TG analysis. Single-crystal X-ray analysis reveals that, the 3-D network of compounds 1 and 2 are constructed from the 1-D zigzag NiCl₂ chains and the 1-D castellated Cu₂I₂ chains bridged by pip molecules respectively. The μ_eff versus T curve indicates that compound 1 is ferromagnetic when T > 14 K. The photoluminscent spectrum shows that compound 2 possesses the fluorescent property with a broad emission peak at 567 nm upon excision at 397 nm.     

Stereospecific interactions between dinuclear complex cations involving square-planar [Pt(II)(μ-S)2(bpy)] (bpy = 2,2′-bipyridine) frameworks derived from optically active octahedral Co(III) units with d- or l-penicillaminates

The reaction of the octahedral mononuclear complex, trans(N)-[Co(l-pen-N,O,S)₂]⁻ (pen = penicillaminate), with [PtCl₂(bpy)] (bpy = 2,2′-bipyridine) stereoselectively gave an optically active S-bridged dinuclear complex, [Pt(bpy){Co(l-pen)₂}]Cl · 3H₂O (2Cl · 3H₂O), whose structure is enantiomeric to the previously reported [Pt(bpy){Co(d-pen)₂}]Cl · 3H₂O (1Cl · 3H₂O). The mixture of equimolar amounts of 1Cl · 3H₂O and 2Cl · 3H₂O in H₂O crystallizes as [Pt(bpy){Co(d-pen)₂}]_0.5[Pt(bpy){Co(l-pen)₂}]_0.5Cl · 7H₂O (3Cl · 7H₂O), in which the enantiomeric complex cations 1 and 2 are included in the ratio of 1:1. The crystal structures of 2Cl · 3H₂O and 3Cl · 7H₂O were determined by X-ray crystallography, and compared with that of 1Cl · 3H₂O. The structural feature for 2 is essentially consistent with that for 1, except for the absolute configurations around the octahedral Co(III) center. The optically active complex cation 2 exists as a monomer, accompanied by no intermolecular interactions in the π-electronic systems of bpy moieties. In the crystals of 3Cl · 7H₂O, on the other hand, the enantiomeric complex cations, [Pt(bpy){Co(d-pen)₂}]⁺ and [Pt(bpy){Co(l-pen)₂}]⁺, are arranged alternately while overlapping the bpy planes along a axis, and the π electronic system of the bpy framework in [Pt(bpy){Co(d-pen)₂}]⁺ interacts with those in [Pt(bpy){Co(l-pen)₂}]⁺. Differences between the crystal structures of 2Cl · 3H₂O and3Cl · 7H₂O significantly reflect their diffuse reflectance spectra. In aqueous solution, each cation in both 2Cl · 3H₂O and 3Cl · 7H₂O is comparatively put on a free environment without such intermolecular interactions.     

Synthesis, structure, and formation mechanism of the halogen-bridged tricobalt clusters, [Co3Cp3(μ3-CPh)2(μ-X)] (X=Cl, Br, and I)

Reactions of a benzylidyne-capped tricobalt cluster, [Co₃Cp₃(μ₃-CPh)₂] (1), with halogens (X₂ = Cl₂, Br₂, and I₂) in CH₂Cl₂ afforded halogen-adducts of 1. The structure of four isolated salts [Co₃Cp₃(μ₃-CPh)₂(μ-Cl)]PF₆ · MeCN (2PF₆ · MeCN), [Co₃Cp₃(μ₃-CPh)₂(μ-Br)]SbF₆ (3SbF₆), [Co₃Cp₃(μ₃-CPh)₂(μ-I)]SbF₆ · CH₂Cl₂ (4SbF₆ · CH₂Cl₂), and [Co₃Cp₃(μ₃-CPh)₂(μ-I)]I₃ (4I₃) determined by X-ray diffraction can be regarded formally as halide-adducts of 1²⁺. The halogen atom in each structure lies in the Co₃ plane. The halogen-bridged Co-Co edge was elongated (in 2PF₆ · MeCN = 2.6072(4), in 3SbF₆ = 2.6106(7), in 4SbF₆ · CH₂Cl₂ = 2.622(2), and in 4I₃=2.6718(9) Å), and the Co-Co distances that had no halogen-bridge remained unchanged from the Co-Co distance of 1 (2.382(8) Å), (in 2PF₆=2.4037(8) and 2.3948(7), in 3SbF₆=2.3888(6) and 2.4017(7), in 4SbF₆ · CH₂Cl₂ = 2.393(2) and 2.388(1), and in 4I₃ = 2.397(1) and 2.3868(9) Å). The UV-Vis absorption spectra of 2⁺, 3⁺, and 4⁺ had characteristic absorption peaks at 796, 819, and 844 nm, respectively. Cyclic voltammograms of 2PF₆ in CH₂Cl₂ with 0.1 M ⁿBu₄NPF₆ as the supporting electrolyte showed a chemically reversible oxidation (at a potential of 0.75 V versus Fc/Fc⁺), and an irreversible reduction wave at −0.57 V. The irreversible reduction resulted in the recovery of 1. The redox properties of 3⁺ and 4⁺ are very similar to that of 2⁺. Cyclic voltammetry of 1 in 0.1 M ⁿBu₄NCl/MeCN indicates that the formation of 2⁺ is a multi-step reaction. Initially, 1 is oxidized to 1⁺, and then, 1⁺ is coordinated by Cl⁻ followed by immediate oxidation to 2⁺.     

Homochiral metal-organic coordination networks from l-typtophan

Three homochiral metal-organic coordination networks [Co₂(l-Trp)₂(Py)₆] · Py · (ClO₄)₂ (1), [Ni(l-Trp)(Py)₃] · H₂O · ClO₄ (2) and [Co₂(l-Trp)(INT)₂(H₂O)₂(ClO₄)] (3), all containing natural amino acid l-HTrp (l-typtophan), were hydrothermally synthesized and structurally characterized. The compounds 1 and 2 crystallize in the orthorhombic space group C222₁, with a = 10.731(2) Å, b = 19.709(4) Å, c = 27.365(6) Å and Z = 4 for 1 and a = 10.710(10) Å, b = 20.088(18) Å, c = 27.63(3) Å and Z = 8 for 2, respectively. The compound 3 has the monoclinic space group P2₁, with a = 8.1934(14) Å, b = 13.209(2) Å, c = 12.464(2) Å, β = 104.107(3)° and Z = 2. Both 1 and 2 consist of 1D helical chains. Compound 3 is composed of 2D networks, which further assemble into a 3D supramolecular structure via weak interlayer interactions. The optically pure amino acid l-HTrp plays an important role leading to homochiral structures reported here.     

Molecular interactions of zinc(II) cyclams with polycarboxylato ligands

Four new zinc(II) cyclams of the composition {Zn(L)(tp²⁻) · H₂O}_n (1), {Zn(L)(H₂bta²⁻) · 2H₂O}_n (2), [Zn₂(L)₂(ox²⁻)] 2ClO₄ · 2DMF (3), and Zn(L)(H₂btc⁻)₂ · 2DMF (4), where L = cyclam, tp²⁻ = 1,4-benzenedicarboxylate ion, H₂bta²⁻ = 1,2,4,5-benzenetetracarboxylate ion, ox²⁻ = oxalate ion, DMF = N,N-dimethylformamide, and H₂btc⁻ = 1,3,5-benzenetricarboxylate ion, have been synthesized and structurally characterized by a combination of analytical, spectroscopic and crystallographic methods. The carboxylato ligands in the complexes 1-4 show strong coordination tendencies toward zinc(II) cyclams with hydrogen bonding interactions between the pre-organized N-H groups of the macrocycle and oxygen atoms of the carboxylato ligands. The macrocycles in 1, 2, and 4 adopt trans-III configurations with the appropriate R,R,S,S arrangement of the four chiral nitrogen centers, respectively. However, the complex 3 shows an unusual cis V conformation with the R,R,R,R nitrogen configuration. The finding of strong interactions between the carboxylato ligands and the zinc(II) ions may provide additional knowledge for the improved design of receptor-targeted zinc(II) cyclams in anti-HIV agents.