Metal complexes with a new N(4)O(3) amine pendant-armed macrocyclic ligand: synthesis, characterization, crystal structures, and fluorescence studies

The synthesis of a new oxaaza macrocyclic ligand, L, derived from O(1),O(7)-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren containing an amine terminal pendant arm, and its metal complexation with alkaline earth (M = Ca(2+), Sr(2+), Ba(2+)), transition (M = Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+)), post-transition (M = Pb(2+)), and Y(3+) and lanthanide (M = La(3+), Er(3+)) metal ions are reported. Crystal structures of [H(2)L](ClO(4))(2).3H(2)O, [PbL](ClO(4))(2), and [ZnLCl](ClO(4)).H(2)O are also reported. In the [PbL] complex, the metal ion is located inside the macrocyclic cavity coordinated by all N(4)O(3) donor atoms while, in the [ZnLCl] complex, the metal ion is encapsulated only by the nitrogen atoms present in the ligand. pi-pi interactions in the [H(2)L](ClO(4))(2).3H(2)O and [PbL](ClO(4))(2) structures are observed. Protonation and Zn(2+), Cd(2+), and Cu(2+) complexation were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. The 10-fold fluorescence emission increase observed in the pH range 7-9 in the presence of Zn(2+) leads to L as a good sensor for this biological metal in water solution.     

Versatility in the binding of 2-pyrazinecarboxylate with iron. Synthesis, structure and magnetic properties of iron(II) and iron(III) complexes

The synthesis and characterization of two new iron(II) complexes, [Fe(pca)2(py)2].py (1) and {[Fe(pca)2(H2O)].H2O}n (2) and one new iron(III) complex, Na2{[Fe(pca)()]2O}.2H2O.2CH3CN (3) (pca- stands for 2-pyrazinecarboxylate), are reported. Complex 1 is obtained from the reaction of iron powder with 2-pyrazinecarboxylic acid. The reaction of Fe(ClO4)3.10H2O with Hpca in the presence of 3 equiv. of Bu4NOH yields 2, whereas the presence of NaOH yields 3. The molecular structure of 1 contains an iron(II) ion with a pseudo-octahedral environment resulting from the coordination of two pca- ligands in a bidentate chelating fashion and two pyridine molecules; pi-pi stacking interactions between pyridine and pyrazine rings lead to a one-dimensional chain. Complex 2 is an iron(II) coordination polymer with an infinite zig-zag motif and an Fe...Fe separation of 7.1 A. In 2, the pi-pi stacking interactions involving the pyrazine rings and the strong hydrogen bonds between the coordinated water molecule and the carboxylate oxygens of two pca- ligands result in a three-dimensional network structure. Complex 3 consists of an anionic micro-oxo-bridged diiron(III) core with two crystallographically distinct iron(iii) ions; the negative charge is compensated by two sodium cations. Complex 3 is assembled in a three dimensional network structure through coordination of Na(I) and hydrogen bond interactions. Temperature dependent magnetic susceptibility and M?ssbauer spectroscopic studies indicate that 1 and 2 have similar magnetic properties. Both complexes are paramagnetic above 12 K, whereas antiferromagnetic ordering is observed below 12 K. The magnetic properties of reveal strong intramolecular antiferromagnetic interactions between the two iron(III) ions with a J value of -221 cm(-1); no long range intermolecular magnetic coupling is observed between 295 and 4.2 K.     

Formation of molecular ladder elements with macrocyclic platforms via linear bifunctional ligands

Reaction between 4-aminopyridine and a dinuclear zinc(II) component of a Robson macrocyclic ligand has resulted in the formation of a molecular ladder element motif. X-ray single crystal structural analysis indicates that two pyridine rings are assembled at the same direction of the macrocycle, which are placed in a nearly parallel way via pi-pi interactions, forming a concavity structure with a macrocyclic base. It is significantly noted that one hydrogen-bond cycle generated from hydrogen atoms of two amino groups with two perchlorate anions has sustained such an assembly of two 4-aminopyridine species to stand in a face to face pattern through a weak molecular interaction on the macrocyclic platform by one-end coordination bonding. The self-assembly of 4-carboxylic pyridine acid and the same macrocyclic component in the presence of sodium hydroxide has yielded an interesting wheel-like complex. Two macrocyclic dinuclear zinc(II) components have been linked through coordination bonding with two pyridine derivatives situated on the same direction of a macrocycle. X-ray structural results suggest that the compound has a unique sandwich-like structure consisting of two macrocyclic covers with two inversely positioned bridging pyridine carboxylic groups in the middle.     

Heteronuclear complexes of macrocyclic oxamide with co-ligands: syntheses, crystal structures, and magnetic properties

Four heteronuclear complexes Mn(CuL)2(SCN)2 (1), {[Mn(CuL)2(mu-dca)2].2H2O}n (2), Zn(CuL)2(SCN)2 (3), and [Fe(CuL)(N3)2]2 (4) incorporating macrocyclic oxamide ligands have been synthesized and structurally characterized. L is the dianion of diethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo[1,4,8,11]-tetraazacyclotetradecine-13,18-dicarboxylate, and dca is the dicyanamide. The structure of 1 or 3 consists of oxamido-bridged trinuclear [MIICuII2] molecules (for 1, M is the manganese(II) ion, and for 3, M is the zinc(II) ion). Both of them consist of 1D supramolecuar chains via pi-pi interactions. The structure of 2 also has the oxamido-bridged trinuclear [MnIICuII2] structure units and consists of 2D layers formed by the linkage of copper(II) and manganese(II) atoms via the oxamido and mu1, 5-dca bridges. Complex 4 consists of oxamido-bridged tetranuclear [FeII2CuII2] molecules and arranges in 1D chains. Different co-ligands may result in different structures in this macrocyclic oxamide system. The variable-temperature magnetic susceptibility measurements (2-300 K) of 1 and 2 both show the pronounced antiferromagnetic interactions between the copper(II) and manganese(II) ions.     

Highly selective recognition of diols by a self-regulating fine-tunable methylazacalix[4]pyridine cavity: guest-dependent formation of molecular-sandwich and molecular-capsule complexes in solution and the solid state

The molecular recognition of methylazacalix[4]pyridine (MACP-4; 1) towards various diols was investigated by using (1)H NMR spectroscopic and X-ray diffraction analysis. As a unique macrocyclic host molecule that undergoes conformational inversions very rapidly in solution, MACP-4 has been shown to self-regulate its conformation, through the formation of different conjugations of the four bridging nitrogen atoms with their adjacent pyridine rings, to form a cavity that best fits the guest species through intermolecular hydrogen-bond, C-H...pi, and pi-pi interactions between the host and guest. As a consequence, depending upon the diol structure and geometry, MACP-4 forms a 1:1 molecular sandwich, 2:1 molecular capsule, and 1:2 butterfly-layered complex with the guests. As a result of favorable enthalpy and entropy effects, MACP-4 exhibits excellent selectivity in the recognition of resorcinol, thus resulting in a very stable 1:1 sandwich complex with resorcinol with a binding constant of 6000 (M-1). The dynamic (1)H NMR spectroscopic study demonstrated that the 1,3-alternate conformation of the macrocyclic ring of the MACP-4resorcinol complex (13) is stable at low temperature (T<243 K), and its conformational inversion requires a larger activation energy (DeltaG++=(45.5+/-2.2) kJ mol(-1)). In the presence of an excess amount of resorcinol, however, the conformational inversion of the MACP-4resorcinol complex proceeds more readily with a decreased activation energy (DeltaG++=(33.5+/-1.5) kJ mol(-1)) owing most probably to the favorable enthalpy effect of the [3...1...3]++transition state.     

Structural and magnetic properties of three one-dimensional azido-bridged copper(II) and manganese(II) coordination polymers

Three one-dimensional (1D) azido-bridged coordination polymers of formula [Cu(L)(N3)2]n (1), [Cu2(Me-L)(N3)4]n (2), and [Mn(L)(N3)2]n (3) have been synthesized and structurally characterized, and their magnetic properties studied, where L and Me-L are 2-(pyrazol-1-ylmethyl)pyridine and 2-(3-methylpyrazol-1-ylmethyl)pyridine, respectively. Compound 1 consists of 1D chains in which the Cu(II) ions with a square pyramidal geometry are alternately bridged by an end-to-end (EE) and an end-on (EO) azido ligands, both adopting a basal-apical disposition. Compound 2 exhibits an unprecedented chain topology built via three different kinds of EO azido bridges. Four Cu(II) ions in the square pyramidal environment are alternately bridged by single and double EO bridges to form a tetranuclear cyclic ring, and neighboring rings are interlinked by double EO bridges to generate a "chain of rings". The intraannular double azido ions are disposed between metal ions in a basal-basal fashion, and the other two kinds of azido ions adopt the basal-apical disposition. Compound 3 consists of 1D concave-convex chains in which cis-octahedrally coordinated Mn(II) ions are alternately bridged by double EE and double EO bridges. There exist pi-pi interactions between the ligands bound to the neighboring Mn(II) ions bridged by the EO bridges. Temperature- and field-dependent magnetic analyses reveal alternate ferromagnetic interactions for 1, dominating ferromagnetic interactions for 2, and alternating ferro- and antiferromagnetic interactions through the EO and EE azido bridges for 3, respectively.     

Cooperative ligation,back-bonding,and possible pyridine-pyridine interactions in tetrapyridine-vanadium(II): a visible and X-ray spectroscopic study

The binding of pyridine by V(II) in aqueous solution shows evidence for the late onset of cooperativity. The K(1) governing formation of [V(py)](2+) (lambda(max) = 404 nm, epsilon(max) = 1.43 +/- 0.3 M(-1) cm(-1)) was determined spectrophotometrically to be 11.0 +/- 0.3 M(-)(1), while K(1) for isonicotinamide was found to be 5.0 +/- 0.1 M(-1). These values are in the low range for 3d M(2+) ions and indicate that V(II).py back-bonding is not significant in the formation of the 1:1 complex. Titration of 10.5 mM V(II) with pyridine in aqueous solution showed an absorption plateau at about 1 M added pyridine, indicating a reaction terminus. Vanadium K-edge EXAFS analysis of 63 mM V(II) in 2 M pyridine solution revealed six first-shell N/O ligands at 2.14 A and 4 +/- 1 pyridine ligands per V(II). UV/vis absorption spectroscopy indicated that the same terminal V(II) species was present in both experiments. Model calculations showed that in the absence of back-bonding only 2.0 +/- 0.2 and 2.4 +/- 0.2 pyridine ligands would be present, respectively. Cooperativity in multistage binding of pyridine by [V(aq)](2+) is thus indicated. XAS K-edge spectroscopy of crystalline [V(O(3)SCF(3))(2)(py)(4)] and of V(II) in 2 M pyridine solution each exhibited the analogous 1s --> (5)E(g) and 1s --> (5)T(2g) transitions, at 5465.5 and 5467.5 eV, and 5465.2 and 5467.4 eV, respectively, consistent with the EXAFS analysis. In contrast, [V(py)(6)](PF(6))(2) and [V(H(2)O)(6)]SO(4) show four 1s --> 3d XAS transitions suggestive of a Jahn-Teller distorted excited state. Comparison of the M(II)[bond]N(py) bond lengths in V(II) and Fe(II) tetrapyridines shows that the V(II)[bond]N(py) distances are about 0.06 A shorter than predicted from ionic radii. For [VX(2)(R-py)(4)] (X = Cl(-), CF(3)SO(3)(-); R = 4-Et, H, 3-EtOOC), the E(1/2) values of the V(II)/V(III) couples correlate linearly with the Hammett sigma values of the R group. These findings indicate that pi back-bonding is important in [V(py)(4)](2+) even though absent in [V(py)](2+). The paramagnetism of [V(O(3)SCF(3))(2)(py)(4)] in CHCl(3), 3.8 +/- 0.2 mu(B), revealed that the onset of back-bonding is not accompanied by a spin change. Analysis of the geometries of V(II) and Fe(II) tetrapyridines indicates that the ubiquitous propeller motif accompanying tetrapyridine ligation may be due to eight dipole interactions arising from the juxtaposed C-H edges and pi clouds of adjoining ligands, worth about -6 kJ each. However, this is not the source of the cooperativity in the binding of multiple pyridines by V(II) because the same interactions are present in the Fe(II)-tetrapyridines, which do not show cooperative ligand binding. Cooperativity in the binding of pyridine by V(II) is then assigned by default to V(II)-pyridine back-bonding, which emerges only after the first pyridine is bound.     

Extreme complementarity in a macrocycle-tweezer complex

[reaction: see text] Interaction of a novel pyrene-based tweezer molecule with a macrocyclic ether-imide-sulfone results in formation of a strongly bound complex (K(a) = 24 000 M(-)(1)) in which binding results not only from pi-pi stacking interactions involving pyrene units as donors and macrocyclic naphthalene-tetracarboximide and biphenylenedisulfone groups as acceptors but also from N-H.O and C-H.O hydrogen bonds and from "reverse" pi-stacking of the electron-poor isophthaloyl residue of the tweezer with an electron-rich 3-aminophenoxy residue of the macrocyclic imide.     

Rare azido-bridged manganese(II) systems: syntheses, crystal structures, and magnetic properties

Two new polymeric azido-bridged manganese complexes of formulas [Mn(N3)2 (bpee)]n (1) and {[Mn(N3)(dpyo)Cl(H2O)2](H2O)}n (2) [bpee, trans-1,2-bis(4-pyridyl)ethylene; dpyo, 4,4'-dipyridyl N,N'-dioxide] have been synthesized and characterized by single-crystal X-ray diffraction analysis and low-temperature magnetic study. Both the complexes 1 and 2 crystallize in the triclinic system, space group P1, with a = 8.877(3) A, b = 11.036(3) A, c = 11.584(4) A, alpha = 72.62(2) degrees, beta = 71.06(2) degrees, gamma = 87.98(3) degrees, and Z = 1 and a = 7.060(3) A, b = 10.345(3) A, c = 11.697(4) A, alpha = 106.86(2) degrees, beta = 113.33(2) degrees, gamma = 96.39(3) degrees, and Z = 2, respectively. Complex 1 exhibits a 2D structure of [-Mn(N3)2-]n chains, connected by bpee ligands, whose pyridine rings undergo pi-pi and C-H...pi interactions. This facilitates the rare arrangement of doubly bridged azide ligands with one end-on and two end-to-end (EO-EE-EE) sequence. Complex 2 is a neutral 1D polymer built up by [Mn(N3)(dpyo)Cl(H2O)2] units and lattice water molecules. The metals are connected by single EE azide ligands, which are arranged in a cis position to the Mn(II) center. The 1D zipped chains are linked by H-bonds involving lattice water molecules and show pi-pi stacking of dpyo pyridine rings to form a supramolecular 2D layered structure. The magnetic studies were performed in 2-300 K temperature range, and the data were fitted by considering an alternating chain of exchange interactions with S = 5/2 (considered as classical spin) with the spin Hamiltonians H = -Ji sigma(S(3i)S(3i+1) + S(3i+1)S(3i+2)) - J2 sigmaS(3i-1)S(3i) and H = -Ji sigmaS(2i)S(2i+1) - J2 sigmaS(2i+1)S(2i+2) for complexes 1 and 2, respectively. Complex 2 exhibits small antiferromagnetic coupling between the metal centers, whereas 1 exhibits a new case of topological ferromagnetism, which is very unusual.     

Layered cobalt(II) and nickel(II) diphosphonates showing canted antiferromagnetism and slow relaxation behavior

Reactions of 2-(1-imidazole)-1-hydroxyl-1,1'-ethylidenediphosphonic acid (ImhedpH4) and cobalt or nickel salts under hydrothermal conditions lead to four new metal phosphonates with two types of structures: M3(ImhedpH)2(H2O)(4).2H2O [M=Co(II) (1) and Ni(II) (2)] and M(ImhedpH3)2(H2O)2 [M=Co(II) (3) and Ni(II) (4)]. Compounds 1 and 2 are isostructural and show a layered structure made up of M3(ImhedpH)2(H2O)4 trimer units. These trimers are connected by edge-sharing of the {Co(2)O6} octahedra, forming an undulating chain. The adjacent chains are fused through the coordination of the phosphonate oxygen atom from one chain to the Co(2) atom of the other, thus generating a two-dimensional layer containing 4-, 8-, and 16-membered rings. The imidazole groups are grafted on the two sides of the layer. Compounds 3 and 4 are also isostructural and show a mononuclear structure with extensive hydrogen bond interactions. Magnetic measurements reveal that both 1 and 2 exhibit canted antiferromagnetism at 2.6 and 5.0 K, respectively. Below these temperatures, slow relaxation is observed from the ac susceptibility measurements corresponding to the spin-glass-like behaviors.     

Monomeric and dimeric copper(II) complexes of a novel tripodal peptide ligand: structures stabilized via hydrogen bonding or ligand sharing

The novel tripodal ligand N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide (Py3AH) affords monomeric and dimeric copper(II) complexes with coordinated carboxamido nitrogens. Although many chloro-bridged dimeric copper(II) complexes are known, [Cu(Py3A)(Cl)] (1) remains monomeric and planar with a pendant pyridine and does not form either a chloro-bridged dimer or the ligand-shared dimeric complex [Cu(Py3A)(Cl)]2 (4) in solvents such as CH3CN. When 1 is dissolved in alcohols, square pyramidal alcohol adducts [Cu(Py3A)(Cl)(CH3OH)] (2) and [Cu(Py3A)(Cl)(C2H5OH)] (3) are readily formed. In 2 and 3, the ROH molecules are bound at axial site of copper(II) and the weak axial binding of the ROH molecule is strengthened by intramolecular hydrogen bonding between ROH and the pendant pyridine nitrogen. Two ligand-shared dimeric species [Cu(Py3A)(Cl)]2 (4) and [Cu(Py3A)]2(ClO4)2 (5) have also been synthesized in which the pendant pyridine of one [Cu(Py3A)] unit completes the coordination sphere of the other [Cu(Py3A)] neighbor. These ligand-shared dimers are obtained in aqueous solutions or in complete absence of chloride in the reaction mixtures.     

Synthesis, X-ray characterization, NMR and ab initio molecular-orbital studies of some cadmium(II) macrocyclic Schiff-base complexes with two 2-aminoethyl pendant arms

Three new pendant arm Schiff-base macrocyclic complexes, [CdLⁿ]²⁺ (n = 5, 6, 7), have been prepared via cyclocondensation of 2,6-diacetylpyridine with three different branched hexaamines in the presence of Cd(II). The ligands are 15-, 16- and 17-membered pentaaza macrocycles having two 2-aminoethyl pendant arms [L⁵ = 2,13-dimethyl-6,9-bis(aminoethyl)-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, L⁶ = 2,14-dimethyl-6,10-bis(aminoethyl)-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadeca-1(19),2,13,15,17-pentaene and L⁷ = 2,15-dimethyl-6,11-bis(aminoethyl)-3,6,11,14,20-pentaazabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene]. All complexes were investigated by IR, ¹H and ¹³C NMR, COSY(H,H) and HETCOR(H,C) spectroscopy and X-ray diffraction. In the solid state structure of each complex the Cd(II) ion is situated centrally within an approximately planar pentaaza macrocyclic ring, binding to the five nitrogen atoms, and also to the two pendant amines which are located on opposite sides of the macrocyclic plane. ab initio HF-MO calculations using a standard 3-21G* basis set have been used to verify that these similar basic structures correspond to energy minima in the gas phase.     

Organic-acid effect on the structures of a series of lead(II) complexes

An investigation into the dependence of coordination polymer architectures on organic-acid ligands is reported on the basis of the reaction of Pb(NO3)2 and eight structurally related organic-acid ligands in the presence or absence of N-donor chelating ligands. Eight novel lead(II)-organic architectures, [Pb(adip)(dpdp)]2 1, [Pb(glu)(dpdp)] 2, [Pb(suc)(dpdp)] 3, [Pb(fum)(dpdp)] . H2O 4, [Pb2(oba)(dpdp)2] . 2(dpdp).2(NO3).2H2O 5, [Pb2(1,4-bdc)2(dpdp)2] . H2O 6, [Pb(dpdc)(dpdp)] 7, and [Pb(1,3-bdc)(dpdp)] . H2O 8, where dpdp = dipyrido[3,2-a:2',3'-c]-phenazine, H2adip = adipic acid, H2glu = glutaric acid, H2suc = succinic acid, H2fum = fumaric acid, H2oba = 4,4'-oxybis(benzoic acid), 1,4-H2bdc = benzene-1,4-dicarboxylic acid, H2dpdc = 2,2'-diphenyldicarboxylic acid, and 1,3-H2bdc = benzene-1,3-dicarboxylic acid, were successfully synthesized under hydrothermal conditions through varying the organic-acid linkers and structurally characterized by X-ray crystallography. Compounds 1-8 crystallize in the presence of organic-acid linkers as well as secondary N-donor chelating ligands. Diverse structures were observed for these complexes. 1 and 5 have dinuclear structures, which are further stacked via strong pi-pi interactions to form 2D layers. 2-3 and 6-8 feature chain structures, which are connected by strong pi-pi interactions to result in 2D and 3D supramolecular architectures. Compound 4 contains 2D layers, which are further extended to a 3D structure by pi-pi interactions. A systematic structural comparison of these 8 complexes indicates that the organic-acid structures have essential roles in the framework formation of the Pb(II) complexes.     

Reactivity of nickel(II) and copper(II) complexes of a β-aminohydrazone ligand with pyridine-2-aldehyde: macrocyclization vs unprecedented pyrazole ring synthesis via C-C bond-forming reaction

The synthesis and characterization of a mononuclear nickel(II) complex [Ni(L(2))](ClO(4))(2) (1) and an analogous mononuclear copper(II) complex [Cu(L(2))](ClO(4))(2) (2) of a 15-membered azamacrocycle (L(2) = 3-(2-pyridyl)-6,8,8,13,13,15-hexamethyl-1,2,4,5,9,12-hexaazacyclopentadeca-5,15-diene) are reported. The macrocyclic ligand is formed during the reaction of 4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dihydrazone (L(1)) with pyridine-2-aldehyde (PyCHO) templated by metal ions. The X-ray crystal structure of 1 exhibits a distorted square-pyramidal coordination geometry, where the metal ion sits in the macrocyclic cavity and the pendant pyridine group of L(2) occupies the axial position. While 1 is stable in the presence of an excess of PyCHO, 2 reacts further with copper(II) salt and PyCHO to form a mononuclear copper(I) complex, [Cu(H(2)L(3))](ClO(4))(3) (3). The structure of the complex cation of 3 reveals a distorted tetrahedral coordination geometry at the copper center with a pseudo 2-fold screw axis. A two-dimensional (2D) polymeric copper(II) complex, {[Cu(2)(L(4))(2)](ClO(4))(2)}(n) (4) is obtained by reacting complex 2 (or [Ni(L(1))](ClO(4))(2)) with copper(II) perchlorate and pyridine-2-aldehyde in a methanol-water solvent mixture. Complex 4 is also obtained by treating 3 with copper(II) perchlorate and pyridine-2-aldehyde in the presence of a base. The X-ray structural analysis of 4 confirms the formation of a pyrazolate bridged dimeric copper(II) complex. The extended structure in the solid state of 4 revealed the formation of a 2D coordination polymer with the dimeric core as the repeating unit. The ligand (HL(4)) in 4 is a 3,4,5-trisubstituted pyrazole ring formed in situ via C-C bond formation and represents an unprecedented transformation reaction.     

Synthesis and characterization of Cd(II) macrocyclic schiff base complex with two 2-Aminoethyl pendant arms

A new pendant armed Schiff base macrocyclic complex of [CdL]²⁺, was prepared via cyclocondensation of 2,6-bis(2- formylphenoxymethyl)pyridine with branched hexaamine in the presence of Cd(II) ion. The ligand was 23-membered oxaazamacrocycle having two 2-aminoethyl pendant arms [L: 3,28-dioxa-14,17-bis(aminoethyl)-11,14,17,20,34- pentaazatetracyclo[34.3.1] tetratriacontane-1(34), 4, 6, 8, 10, 20, 22, 24, 26, 30, 32-undecaene]. The complex was investigated by IR, ¹H NMR, microanalysis and MALDI mass spectroscopy. The structure of the complex was verified by ab initio HF-MO calculations using a standard 3-21G* basis set. This article introduces an unusual seven-membered chelate ring and shows that by its using, the Cd-N bonds lengths within the macrocycle would be longer and also Cd(II)-pendant amine bonds lengths would be shorter.     

New pyridine carboxamide ligands and their complexation to copper(II). X-Ray crystal structures of mono-, di, tri- and tetranuclear copper complexes

Seven new pyridine dicarboxamide ligands H2L(1-7) have been synthesised from condensation reactions involving pyridine-2,6-dicarboxylic acid (H2dipic), pyridine-2,6-dicarbonyl dichloride or 2,6-diaminopyridine with heterocyclic amine or carboxylic acid precursors. Crystallographic analyses of N,N'-bis(2-pyridyl)pyridine-2,6-dicarboxamide monohydrate (H2L8 x H2O), N,N'-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide and N,N'-bis[2-(2-pyridyl)ethyl]pyridine-2,6-dicarboxamide monohydrate revealed extensive intramolecular hydrogen bonding interactions. 2,6-Bis(pyrazine-2-carboxamido)pyridine (H2L6) and 2,6-bis(pyridine-2-carboxamido)pyridine (H2L7) reacted with copper(II) acetate monohydrate to give tricopper(II) complexes [Cu3(L)2(mu2-OAc)2]. X-Ray crystallography confirmed deprotonation of the amidic nitrogen atoms and that the (L6,7)2- ligands and acetate anions hold three copper(II) ions in approximately linear fashion. H2L8. Reacted with copper(II) tetrakis(pyridine) perchlorate to give [Cu(L8)(OH2)]2 x 2H2O, in which (L8)2- was tridentate through the nitrogen atoms of the central pyridine ring and the deprotonated carboxamide groups at one copper centre, with one of the terminal pyridyl rings coordinating to the other copper atom in the dimer. The corresponding reaction using H2L7 gave [Cu3(L7)2(py)2][ClO4]2, which transformed during an attempted recrystallisation from ethanol under aerobic conditions to a tetracopper(II) complex [Cu4(L7)2(L7-O)2].     

Synthesis and crystallographic characterization of low-dimensional and porous coordination compounds capable of supramolecular aromatic interaction using the 4,4'-azobis(pyridine) ligand

Coordination compounds with a 4,4'-azobis(pyridine) (azpy) ligand, {[M2(azpy)6(H2O)5] x 4PF6 x azpy x H2O}n (M = Ni(II) (1) or Co(II) (2)) (0-dimensional (0-D) dimer), {[Zn(azpy)3(H2O)2] x 2PF6 x 2azpy x 4H2O}n (3) (1-dimensional (1-D) fishbone-type chain), {[Ag(azpy)] x PF6}n (4) (1-D linear chain), {[Mn(NCS)2(azpy)2] x azpy}n (5) (2-dimensional (2-D) grid sheet), and {[Ni(NCS)2(azpy)2] x 3toluene}n (6) (2-D grid sheet), were synthesized and structurally characterized. Compounds 1 and 2 have a 0-D dimer motif, in which one M(II) (M(II) = Ni(II) or Co(II)) coordination site is shared by unidentate azpy and H2O ligands, each with half-occupancy, i.e., exhibiting static disorder. Compounds 3 and 4 afford 1-D fishbone-type and 1-D linear chain motifs, respectively. Azpy mediates pi-pi and pi-p interactions between these low-dimensional structures. Compounds 5 and 6 possess a 2-D grid sheet motif. These sheets assemble to form microporous frameworks that incorporate aromatic guests, such as coordination-free azpy (5) and toluene (6). There exist not only pi-pi and pi-p interactions but also CH-pi interactions between the framework azpy ligands and guests. It should be noted that the azpy ligand is a good candidate for the construction of new assembling systems of coordination compounds through its aromatic interactions.     

Synthesis, crystal structures, and magnetic properties of cyano-bridged honeycomblike layers M(V)-Cu(II) (M = Mo, W) chelated by a macrocyclic ligand

Two cyano-bridged Cu(II)-M(V) [M = Mo (2), W (3)] complexes formed by self-assembly of octacyanometalates [M(CN)8]3- (M = Mo, W) with a new molecular precursor [Cu(L2)]2+ (1) (L2 = a macrocyclic ligand) in a 2:3 ratio have been investigated in terms of structures and magnetic behaviors. The M2Cu3 repeating unit of both bimetallic compounds is extended to a two-dimensional honeycomblike layered structure. The pendant ethyl groups on L2 noticeably influence the structural parameters around the Cu center. Compared with the system composed of a macrocycle without a side group, Cu-N(ax) (ax = axial) distances become shorter and the Cu-N(ax)-C(ax) angles are more bent for 2 and 3. The magnetic data denote that the Cu(II) and M(V) spins undergo explicit ferromagnetic interactions via CN bridges. From a structural and magnetic point of view, given that the Cu-N(ax) bond length in the tetragonally distorted octahedral Cu(II) environment is long enough, the overall ferromagnetic character remains despite the variation of Cu-N(ax)-C(ax) angle in this system.     

Effect of intramolecular pi-pi and CH-pi interactions between ligands on structure, electrochemical and spectroscopic properties of fac-[Re(bpy)(CO)3(PR3)]+(bpy = 2,2'-bipyridine; PR3= trialkyl or triarylphosphines)

Intramolecular pi-pi and CH-pi interactions between the bpy and PR3 ligands of fac-[Re(bpy)(CO)3(PR3)]+ affect their structure, and electrochemical and spectroscopic properties. Intramolecular CH-pi interaction was observed between the alkyl groups on the phosphine ligand (R =nBu, Et) and the bpy ligand, and intramolecular pi-pi and CH-pi interactions were both observed between the aryl group(s) on the phosphorus ligand (R =p-MeOPh, p-MePh, Ph, p-FPh, OPh) and the bpy ligand, while no such interactions were found in the trialkylphosphite complexes (R = OiPr, OEt, OMe). The intramolecular interactions distort the pyridine rings of the bpy ligand as long as 3.7 x 10(-2)A in crystals. Molecular orbital calculations of the bpy ligand suggest that this distortion decreases the energy gap between its pi and pi* orbitals. An absorption band attributed to the pi-pi*(bpy) transition of the distorted rhenium complexes, measured in a KBr pellet, was red-shifted by 1-5 nm compared to the complexes without the distorted bpy ligand. Even in solution, similar red shifts of the pi-pi*(bpy) absorption were observed. The redox potential E1/2(bpy/bpy*-) of the complexes with the trialkylphosphine and triarylphosphine ligand are shifted positively by 110-120 mV and 60-80 mV respectively, compared with those derived from the electron-attracting property of the phosphorus ligand. In contrast with these properties, three nu(CO) IR bands, which are sensitive to the electron density on the central rhenium because of pi-back bonding, were shifted to higher energy, and a Re(I/II)-based oxidation wave was observed at a more positive potential according to the electron-attracting property of the phosphorus ligand.     

Control of intramolecular π-π stacking interaction in cationic iridium complexes via fluorination of pendant phenyl rings

Intramolecular π-π stacking interaction in one kind of phosphorescent cationic iridium complexes has been controlled through fluorination of the pendant phenyl rings on the ancillary ligands. Two blue-green-emitting cationic iridium complexes, [Ir(ppy)(2)(F2phpzpy)]PF(6) (2) and [Ir(ppy)(2)(F5phpzpy)]PF(6) (3), with the pendant phenyl rings on the ancillary ligands substituted with two and five fluorine atoms, respectively, have been synthesized and compared to the parent complex, [Ir(ppy)(2)(phpzpy)]PF(6) (1). Here Hppy is 2-phenylpyridine, F2phpzpy is 2-(1-(3,5-difluorophenyl)-1H-pyrazol-3-yl)pyridine, F5phpzpy is 2-(1-pentafluorophenyl-1H-pyrazol-3-yl)-pyridine, and phpzpy is 2-(1-phenyl-1H-pyrazol-3-yl)pyridine. Single crystal structures reveal that the pendant phenyl rings on the ancillary ligands stack to the phenyl rings of the ppy ligands, with dihedral angles of 21°, 18°, and 5.0° between least-squares planes for complexes 1, 2, and 3, respectively, and centroid-centroid distances of 3.75, 3.65, and 3.52 ? for complexes 1, 2, and 3, respectively, indicating progressively reinforced intramolecular π-π stacking interactions from complexes 1 to 2 and 3. Compared to complex 1, complex 3 with a significantly reinforced intramolecular face-to-face π-π stacking interaction exhibits a significantly enhanced (by 1 order of magnitude) photoluminescent efficiency in solution. Theoretical calculations reveal that in complex 3 it is unfavorable in energy for the pentafluorophenyl ring to swing by a large degree and the intramolecular π-π stacking interaction remains on the lowest triplet state.