Coordinated Aqua Ligands Research Articles

Structural and Solution Speciation Studies on fac-Tricarbonylrhenium(I) Complexes of 2,2'-Bipyridine Analogues.

In this study, we report the synthesis and characterization of 12 novel rhenium(I) complexes with the general formula fac-[Re(CO)3(NN)X]n+ where (NN) is a 2,2'-bipyridine analogue ligand, X = Cl-, Br-, or H2O, and n = 0 or 1, focusing on their speciation in an aqueous solution. The prepared organorhenium complexes are stable in a wide pH range in an aqueous solution, and no release of the bidentate ligands or the carbonyl ligands was observed. The stability of the complexes in various biologically relevant matrices (cell culture medium and real blood serum) was also demonstrated. However, the simultaneous substitution of the halido ligand by water and slow hydrolysis of the ester bonds in the ligands were observed, affecting both the solubility and the lipophilicity of the compounds. The aqua complexes became more lipophilic in the presence of chloride ions, while the hydrophilicity increased significantly with time due to the hydrolysis of the ester bonds, which probably contributed to their weak pharmacological activity. The results also showed kinetically hindered aqueous solvation of the halido complexes and low chloride ion affinity of the aqua complexes. The deprotonation of the coordinated aqua ligand in the complexes occurs in the pH = 7-10 range, leading to significant formation (18-30%) of hydroxido species at pH = 7.4. The halido complexes showed somewhat higher cytotoxicity (IC50 = 60-99 μM) on human colon adenocarcinoma cancer cells (Colo205 and Colo320) than the corresponding aqua complexes (IC50 > 100 μM). In all cases, no antibacterial effect was observed (MIC > 100 μM), but some of the complexes showed moderate antiviral activity (IC50 ∼ 50 μM) on Herpes simplex virus 2.

Multifunctional Luminescent Sensor Based on the Pb2+ Complex Containing a Tetrazolato Ligand.

A series of luminescent Pb2+ complexes, [Pb(L1)2]n (1), [Pb(L2)2]n (2), [Pb(L3)(NO3)(H2O)2]n (3), [Pb(L3)(Br)(H2O)]n (4), [Pb(L3)(Cl)(H2O)]n (5), and [Pb(L4)(H2O)2] (6) have been synthesized by treatment of polydentate tetrazolato ligands with various hydrated Pb2+ salts (HL1 = 2-(1H-tetrazol-5-yl)pyridine, HL2 = 3-(1H-tetrazol-5-yl)isoquinoline, HL3 = 6-(1H-tetrazol-5-yl)-2,2'-bipyridine, and H2L4 = 6,6'-bis(1H-tetrazol-5-yl)-2,2'-bipyridine). These complexes have been characterized by IR, TGA, and elemental analysis. Their crystal structures have been determined by X-ray crystallography, and the phase purity of bulk samples were further confirmed by PXRD. Their luminescence properties have been investigated in detail, and their emission origin may involve ligand-centered π-π* transition, metal-centered s-p transition and charge-transfer character. It is interesting to note that 5 exhibits obviously enhanced red-shifted emission, whose photoluminescence quantum yield (PLQY = 16.5%) is much higher than the other compounds (≤2%). Most importantly, the emission property of 5 was strongly affected by temperature. When the temperature rises from 295 to 493 K, the emission maximum gradually shifts to high energy due to the loss of the aqua ligand. In contrast, when the temperature is lowered from 295 to 13 K, two emission bands were observed. The low-energy emission band exhibits a slight blue shift, while a new high-energy emission band appears at around 520 nm, which is assigned to ligand-centered phosphorescence. After removal of the coordinated aqua ligand, the emission of 5-H2O is very sensitive to the vapors of volatile primary amines and acids, although they have different response mechanisms. This result indicates that 5-H2O may be a potential multifunctional sensor for temperature, volatile amines, and acids. To decipher the emission origin, DFT calculations have also been carried out based on the structure units of these compounds.

Gd(III) metal-organic framework as an effective humidity sensor and its hydrogen adsorption properties

Metal-organic frameworks (MOFs) represent a class of nanoporous materials built up by metal ions and organic linkers with several interesting potential applications. The present study described the synthesis and characterization of Gd(III)-based MOF with the chemical composition [Gd(BTC)(H2O)]·DMF (BTC – trimesate, DMF = N,N′-dimethylformamide), known as MOF-76(Gd) for hydrogen adsorption/desorption capacity and humidity sensing applications. The structure and morphology of as-synthesized material were studied using powder X-ray diffraction, scanning and transmission electron microscopy. The crystal structure of MOF-76(Gd) consists of gadolinium (III) and benzene-1,3,5-tricarboxylate ions, one coordinated aqua ligand and one crystallization DMF molecule. The polymeric framework of MOF-76(Gd) contains 1D sinusoidally shaped channels with sizes of 6.7 × 6.7 Å propagating along c crystallographic axis. The thermogravimetric analysis, heating infrared spectroscopy and in-situ heating powder X-ray diffraction experiments of the prepared framework exhibited thermal stability up to 550 °C. Nitrogen adsorption/desorption measurement at −196 °C showed a BET surface area of 605 m2 g−1 and pore volume of 0.24 cm3 g−1. The maximal hydrogen storage capacity of MOF-76(Gd) was 1.66 wt % and 1.34 wt % −196 °C and −186 °C and pressure up to 1 bar, respectively. Finally, the humidity sensing measurements (water adsorption experiments) were performed, and the results indicate that MOF-76(Gd) is a suitable material for moisture sensing application with a fast response (11 s) and recovery time (2 s) in the relative humidity range of 11–98%.

A highly stable terbium(III) metal-organic framework MOF-76(Tb) for hydrogen storage and humidity sensing.

The present study described the synthesis and characterization of MOF-76(Tb) for hydrogen storage and humidity sensing applications. The structure and morphology of as-synthesized material were studied using powder X-ray diffraction, scanning, and transmission electron microscopy. The crystal structure of MOF-76(Tb) consists of terbium(III) and benzene-1,3,5-tricarboxylate(-III) ions, one coordinated aqua ligand and one crystallization N,N´-dimethylformamide molecule. The polymeric framework of MOF-76(Tb) contains 1D sinusoidally shaped channels with sizes of 6.6 × 6.6 Å propagating along c crystallographic axis. The thermogravimetric analysis of the prepared material exhibited thermal stability up to 600 °C. At 77 K and pressure up to 20 bar; 0.6 wt.% hydrogen storage capacity for MOF-76(Tb) was observed. Finally, the humidity sensing measurements (water adsorption experiments) were performed, and the results indicate that MOF-76(Tb) is not a suitable material for moisture sensing applications.

The influence of α,α′-diimine bridging ligand on the reactivity of binuclear para-cymene ruthenium(II) complexes. Kinetic, mechanistic and computational study

Substitution kinetics of the aqua ligands in four binuclear ruthenium(II) para-cymene complexes with different α,α′-diimine bridging ligands [2-pyridylaldazine (Ru-1), p-phenylenebis(picoline)aldimine (Ru-2), p-biphenylenebis(picoline)aldimine (Ru-3) and p-xylenebis(picoline)aldimine (Ru-4)] was investigated as a function of nucleophile concentration and temperature under pseudo-first order conditions using thiourea nucleophiles. The rates of the simultaneous substitution of the aqua ligands decreased in the order: Ru-1 > Ru-4 > Ru-3 > Ru-2. The reactivity of the complexes is controlled by the inherent electronic and steric contributions of the bridging ligand. The strong π-acceptor bridging ligand is responsible for the high reactivity observed in Ru-1 compared to the rest of the complexes. From Ru-2 to Ru-4, the reactivity increases with decrease in steric congestion around the metal centres. The cage effect plays a role in the enhanced reactivity of Ru-4 compared to Ru-3 and Ru-2. Reactivity trends are excellently supported by computational results. All the complexes showed a stepwise deprotonation of the coordinated aqua ligands except Ru-4 and the pKa values increased from Ru-1 to Ru-4 due to progressive increase in σ-donicity of the spacers. The activation parameters (ΔH≠>0, ΔS≠<0) obtained for all the complexes support an associative mechanism of activation.

Experimental and density functional theory studies on the adsorption behavior of selected gas molecules on Mg(II) coordination polymer constructed with 1,3,5-benzenetricarboxylates

An optimized structure of Mg(H2BTC)2(H2O)2, 2 derived from Mg(II)-1,3,5-benzenetricarboxylates with the composition Mg(H2BTC)2(H2O)4, 1 (CCDC 1998471) by elimination of two coordinated aqua ligand, was used to adsorbed selected gas molecules. The adsorption behavior of selected gas molecules (N2, NO2, NO, NH3, H2, O2, CO, CO2) on the optimized structure was investigated using the density functional theory (DFT). Different adsorption configurations screened had favorable adsorption energies while retaining their initial molecular geometries and the gas molecules are said to be physically adsorbed. The quantum chemical descriptors for the adsorbed molecules were studied and analyzed. The density of states (DOS) and the partial density of states (PDOS) calculated for the different adsorption configurations showed that NO2, CO, CO2 interacted strongly with the Mg(H2BTC)2(H2O)2 complex, while the interactions of NH3, NO, H2 and O2 were found to be weak. Overall, the coordination polymer Mg(H2BTC)2(H2O)2 has proven to be good material for storage of gases.

Cyanide-bridged polynuclear heterobimetallic complexes: synthesis, crystal structures, and magnetic properties

The reactions of [MnIII(3-EtOSalen)(H2O)2]ClO4 (Salen=N,N-ethylenebis(salicylideneaminato)dianion) with K3[M(CN)8] (M=Mo, W) have been investigated, from which cyanide-bridged hexanuclear Mo–Mn and binuclear W–Mn complexes formulated as {[Mn(3-EtOSalen)(H2O)]4[Mn(3-EtOSalen)(CH3OH)][MoCN8]}(CN)2·CH3CN·H2O (1) and {[Mn(3-EtOSalen)(H2O)2][Mn(3-EtOSalen)(H2O)(EtOH][MnIII(3-EtOSalen)(H2O) W(CN)8]}·0.5CH3OH (2), respectively, were obtained and characterized by elemental analysis, IR spectroscopy and X-ray crystal structure determination. X-ray diffraction analysis for complex 1 shows that it has a cyanide-bridged cationic hexanuclear Mn5Mo structure in which two free and disordered CN− ions from the cyanide precursor are present as balance anions, while the [Mo(CN)8]3− ion acting as a pentadentate ligand connects five Schiff base manganese(III) units. In complex 2, the [W(CN)8]3− ion is coordinated with a single Schiff base manganese unit by one of its cyanide groups, so forming a cyanide-bridged anionic binuclear structure whose dinegative charge is balanced by two free Schiff base manganese cations. Both of these cyanide-bridged complexes can be considered as self-complementary, such that the coordinated aqua ligand from one complex and the O4 compartment from the Schiff base ligand of the neighboring complex form a supramolecular two-dimensional network and a one-dimensional ladder-like double-chain structure, respectively. Investigation of the magnetic properties of these complexes reveals antiferromagnetic interactions within the cyanide-bridged Mn–Mo/W units. The magnetic susceptibilities of both complexes have been modeled.

A Series of Early Lanthanide Chloranilate Frameworks with a Square Grid Topology

A series of lanthanide chloranilate frameworks containing a (4,4)-net with LaIII, CeIII, NdIII, SmIII, and EuIII have been synthesised and structurally characterised. Two structure types of square grids were obtained for these frameworks. Type 1 consists of the formula (Et4N)[Ln(can)2(H2O)] (Ln=LaIII, CeIII, NdIII; H2can=chloranilic acid) and crystallised in the tetragonal space group I4/m, featuring a nine-coordinate lanthanide ion with a coordinated water molecule and four chloranilate ligands. Type 2, (Et4N)[Ln(can)2] (SmIII and EuIII) crystallised in the I4/mcm space group, and contains an eight-coordinate lanthanide ion without a coordinated water molecule. A single-crystal-to-single-crystal transformation was carried out for (Et4N)[Nd(can)2(H2O)] on removal of the coordinated aqua ligand.

Hydrogen-Bond Directed Cyanide-Bridged Supramolecular 2D and 1D Bimetallic Coordination Polymers: Synthesis, Crystal Structure, and Magnetic Properties

By using K2[Ni(CN)4] as a building block and two Mn(III) compounds containing bicompartimental Schiff-base ligands as assembling segments, two new cyanide-bridged Ni–Mn complexes of the formula {[Mn(L1)(H2O)]4[Ni(CN)4]}[ClO4]2·2CH3CN (1) and {[Mn(L2)(H2O)]2[Ni(CN)4]}·CH3CN H2O (2) (L1 = N,N’-1,2-propylene-bis(3-methoxysalicylideneiminate; L2 = N,N’-1,2-propylene-bis(3-ethoxysalicylideneiminate) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray analysis. Single Xray diffraction analysis revealed the cationic pentanuclear and neutral trinuclear structures for complexes 1 and 2, respectively, and indicated that the structure of the Schiff-base ligand had obvious influence on the structural types of the target cyanide-bridged complexes. Both cyanide-bridged complexes are self-complementary via coordinated aqua ligand from one complex and the free O4 compartment from the neighboring complex, therefore giving supramolecular two-dimensional network and one-dimensional zig-zag chain structure. Study of magnetic properties revealed weak antiferromagnetic coupling within the Mn2 dimer formed by the intermolecular hydrogen bond.

Synthesis, crystal structure, and magnetic characterization of two manganese Schiff-base-containing complexes

The reactions of [MnIII(3-MeOSalen)(H2O)2]+ (Salen = N,N-ethylenebis(salicylideneaminato) dianion) with (Et4N)4[M(CN)8] (M = Mo, W) have been investigated and one mononuclear manganese(II) complex [MnII(Salen)(H2O)] (I) and one bimetallic ion-pair complex [MnIII(3-MeO-Salen)(H2O)2]4[W(CN)8] · DMSO · 4H2O (II) were obtained unexpectedly and characterized by element and single crystal structure analysis. Single crystal X-ray diffraction (CIF files CCDC nos. 1456365 (I) and 1456366 (II)) showed that the Mn2+ ion in complex I is five-coordinated involving in a distorted square pyramid. Furthermore, with the help of the intermolecular hydrogen bond interactions, this complex can be constructed into interesting one-dimensional zig-zag chain structure. For complex II, the coordination sphere of Mn3+ ion is an elongated octahedron. Additional, the four mononuclear manganese(III) units are self-complementary through the coordinated aqua ligand from one molecule and the free O(4) compartment from the neighboring molecule, giving supramolecular dimmers structure. Investigation of the magnetic susceptibility of the two complexes reveals the overall weak antiferromagnetic interactions between the adjacent manganese centers caused by H-bond interactions.

Diphenic acid/nicotinamide complexes of CoII, CuII and ZnII. Synthesis and structural investigation

The complexes of diphenic acid with CoII and CuII metals and diphenic acid/nicotinamide mixed ligand with CoII and ZnII metals were synthesized and characterized of structural properties by elemental analysis, FT-IR spectra, thermo analytic TG-DTG/DTA and crystal X-ray diffraction methods. The pure ligand complexes of diphenic acid (C14H16O8Co (1), C14H16O8Cu (2)) and mixed ligand complexes of diphenic acid/nicotinamide (C40H38N4O14Co (3), C40H38N4O14Zn (4)) are similar to each other and they have P21, P21/n and P1¯ space groups. The diphenic acid ligands in 1 and 2 complexes were coordinated to metal cations as dianionic bridge and in the others complexes (3 and 4) it was involved as monoanionic counter ion. The complexes of 1 and 2 are linked into sheets by a combination of O–H⋯O hydrogen bonds and the others complexes of 3 and 4 are linked into sheets by a combination of O–H⋯O, N–H⋯O and C–H⋯O hydrogen bonds. All of the complexes structures have distorted octahedral geometry. According to TG/DTG-DTA analysis, thermal decomposition of complexes starts with dehydration of coordinated aqua ligands. After the dehydration, neutral nicotinamide ligands start to decompose in mixed ligand complexes. Lastly, anionic diphenic acid ligands decompose and corresponding metal oxides remain as residual products of thermal degradation in reaction vessel.

Cyanide-bridged bi- and trinuclear heterobimetallic Fe(III)–Mn(III) complexes: Synthesis, crystal structures and magnetic properties

By employing trans-dicyano or pentacyanometalate as building block and using a bicompartimental Schiffbase based manganese(III) compound as assemble segment, two new cyanide-bridged heterometallic Fe(III)–Mn(III) complexes {[Mn(L)(H2O)][Febpb(CN)2]}·2CH3OH (1) and {[Mn(L)(H2O)]2··[Fe(CN)5NO]} (2) (bpb2– = 1,2-bis(pyridine-2-carboxamido)benzenate, L = N,N'-ethylene-bis(3-ethoxysalicylideneiminate) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals binuclear FeMn and trinuclear FeMn2 structure, respectively, in which the cyanide precursor acts as mono- or bidentate ligand to connect the Mn(III) Schiff-base unit(s). Furthermore, these two complexes are self-complementary through coordinated aqua ligands from one complex and the free O4 compartments from the neighboring complex, giving dimeric and 1D single chain supramolecular structure. Investigation of the magnetic susceptibility of 1 reveals weak antiferromagnetic coupling between the adjacent Mn(III) ions. Based on the binuclear FeMn model, best fit of the magnetic susceptibilities of 1 leads to the magnetic coupling constants J =–1.37 cm–1 and zJ′ =–0.72 cm–1 (1).

Comments on Proton Cascade in a Molecular Solid: H/D Exchange on Mobile and Immobile Water

Following a previous report of proton transport in a channel-free molecular solid possessing a complex set of water wires, the mechanisms implied by the available neutron diffraction measurements are further developed. Three specific proton transfer pathways along an experimentally observed water wire are proposed. The first is proton transfer involving two aqua ligands coordinated to the same Mn(II) unit and one free water acting as a shuttle. The second mechanism consists of proton transfer between coordinated aqua ligands of distinct molecules, with no shuttle. The third mechanism involves a component of vehicle transport, involving a water molecule that changes position during the process. Geometric parameters of the proposed mechanisms are given.

Synthesis, crystal structure, and magnetic characterization of chiral Schiff-base manganese(III) complex containing cocrystallized crown ether molecule

A chiral Schiff-base Mn(III) compound containing cocrystallized crown ether {Mn[(R,R)-Salcy]·(H2O)2}2(ClO4)2·18-Crown-6 (I), where (R,R)-Salcy = (R,R)-N, N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion, has been synthesized by the reaction of {Mn[(R,R)-Salcy](H2O)2}ClO4 with 18-crown-6 ether and K4[Mo(CN)8]. X-ray diffraction analysis revealed that the cationic mononuclear Mn(III) Schiff-base compounds were self-complementary via intermolecular O-H⋯O H-bond formed by coordinated aqua ligand of one molecule and phenolic oxygen atoms of the neighboring molecule, giving supramolecular dimeric structure. The H-bond between O atoms of the cocrystallized crown molecule and that of the mentioned above dimer supported formation of one-dimensional supramolecular chain structure which can be linked to two-dimensional supramolecular network based on intermolecular O-H⋯Cl weak interactions. Our study of its magnetic properties revealed weak antiferromagnetic coupling between the adjacent Mn(III) ions.

Two binuclear cyanide-bridged Cr(III)-Mn(III) complexes based-on [Cr(2,2'-bipy)(CN)4]- building block: synthesis, crystal structures and magnetic properties.

Tetracyanide building block [Cr(2,2'-bipy)(CN)(4)]- and two bicompartimental Schiff-base based manganese(III) compounds have been employed to assemble cyanide-bridged heterometallic complexes, resulting in two cyanide-bridged CrIII-MnIII complexes: [Mn(L(1))(H(2)O)][Cr(2,2'-bipy)(CN)(4)]·CH(3)OH·2.5H(2)O (1) and [Mn(L(2))(H(2)O)][Cr(2,2'-bipy)(CN)(4)]·CH(3)OH·(3)H(2)O (2) (L1 = N,N'-(1,3-propylene)-bis(3-methoxysalicylideneiminate), L2 = N,N'-ethylene-bis(3-ethoxysalicylideneiminate)). Single X-ray diffraction analysis shows their similar cyanide-bridged binuclear structures, in which the cyanide precursor acting as monodentate ligand connects the manganese(III) ion. The binuclear complexes are self-complementary through coordinated aqua ligand and the free O4 compartment from the neighboring complex, giving H-bond linking dimer structure. Investigation over magnetic properties reveals the antiferromagnetic magnetic coupling between the cyanide-bridged Cr(III) and Mn(III) ions. A best-fit to the magnetic susceptibilities of these two complexes leads to the magnetic coupling constants J = -5.95 cm(-1), j = -0.61 cm(-1) (1) and J = -4.15 cm(-1), j = -0.57 cm(-1) (2), respectively.

Synthesis, Spectral, Thermal Studies of Co(II), Ni(II), Cu(II) and Zn(II)‐arginato Complexes. Crystal Structure of Monoaquabis(arginato‐κO,κN)copper(II). [Cu(arg)2(H2O)].NaNO3

AbstractTransition metal complexes of arginine (using Co(II), Ni(II), Cu(II) and Zn(II) cations separately) were synthesized and characterized by FTIR, TG/DTA‐DrTG, UV‐Vis spectroscopy and elemental analysis methods. Cu(II)‐Arg complex crystals was found suitable for x‐ray diffraction studies. It was contained, one mole CuII and Na+ ions, two arginate ligands, one coordinated aqua ligand and one solvent NO3− group in the asymmetric unit. The principle coordination sites of metal atom have been occupied by two N atoms of arginate ligands, two carboxylate O atoms, while the apical site was occupied by one O atom for CuII cation and two O atoms for CoII, NiII, ZnII atoms of aqua ligands. Although CuII ion adopts a square pyramidal geometry of the structure. CoII, NiII, ZnII cations have octahedral due to coordination number of these metals. Neighbouring chains were linked together to form a three‐dimensional network via hydrogen‐bonding between coordinated water molecule, amino atoms and O atoms of the bridging carboxylate groups. CuII complex was crystallized in the monoclinic space group P21, a = 8.4407(5) Å, b = 12.0976(5) Å, c = 10.2448(6) Å, V = 1041.03(10) Å3, Z = 2. Structures of the other metal complexes were similar to CuII complex, because of their spectroscopic studies have in agreement with each other. Copper complex has shown DNA like helix chain structure. Lastly, anti‐bacterial, anti‐microbial and anti‐fungal biological activities of complexes were investigated.

A tubular one-dimensional polymer constructed from alternating clusters of europium(III)–water and copper(I) chloride bridged by 4-(pyridin-4-yl)benzoate

A new 3d-4f heterometallic polymer, poly[[aqua-μ3-chlorido-[μ3-4-(pyridin-4-yl)benzoato]tris[μ2-4-(pyridin-4-yl)benzoato]dicopper(I)erbium(III)] dihydrate], {[Cu2Er(C12H8NO2)4Cl(H2O)]·2H2O}n, was synthesized by the hydrothermal reaction of Er2O3, CuCl2·2H2O and 4-(pyridin-4-yl)benzoic acid in the presence of HClO4. The asymmetric unit contains one Er(3+) cation, two Cu(+) cations, one Cl(-) anion, four deprotonated 4-(pyridin-4-yl)benzoate ligands, one coordinated aqua ligand and two solvent water molecules. This tubular one-dimensional polymer is constructed from alternating clusters of europium(III)-water and copper(I) chloride bridged by 4-(pyridin-4-yl)benzoate ligands. Extensive hydrogen-bonding interactions involving both the coordinated and the solvent water molecules provide further stabilization to the structure.

Synthesis, Crystal Structures and Magnetic Properties of Cyanide-bridged Trinuclear and Ion-pair Heterometallic Complexes

A cyanide-bridged, trinuclear, heterometallic Pd(II)–Mn(III) complex [{Mn(L)(H2O)}2{(μ-CN)2Pd(CN)2}] and an ion-pair complex [Co(Phen)2(H2O)2][Pd(CN)4]·MeOH have been synthesised (L = N,N-ethylene-bis(3-ethoxysalicylideneiminate; Phen = 1,10-phenanthroline). Single X-ray diffraction analysis reveals the neutral trinuclear complex is self-complementary through coordinated aqua ligands from one complex and the free O4 compartments from the neighbouring complex, thereby giving a 1D single chain supramolecular structure. The ion-pair complex forms a three-dimensional network via intermolecular O…H–N hydrogen bond interactions. Magnetic susceptibility studies show overall weak antiferromagnetic coupling between adjacent Mn(III) ions in the trimeric complex.

Hydrogen-Bond Directed 1D and 3D Cyanide-Bridged Heterometallic Complexes: Synthesis, Crystal Structures and Magnetic Properties

By employing K2[Pd(CN)4] as building block, [Mn(L)(H2O)2]ClO4 or Mn(Phen)2Cl2 (L = N,N-ethylene-bis(3-methoxysalicylideneiminate; Phen = 1,10-phenanthroline) as assembling segment, a trinuclear cyanide-bridged heterometallic Pd(II)-Mn(III) complex {[Mn(L)(H2O)]2[Pd(CN)4]}2·4H2O (1) and a ion-pair complex [Mn(Phen)2(H2O)2][Pd(CN)4] (2) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals the cyanide-bridged trinuclear complex 1 is self-complementary through coordinated aqua ligands from one complex and the free O4 compartments from the neighboring complex, therefore giving 1D single chain supramolecular structure. For complex 2, it is constructed into interesting 3D network depending on the intermolecular O···H–N hydrogen bond interactions. Investigation over magnetic susceptibility of complex 1 reveals the overall weak antiferromagnetic coupling between the adjacent Mn(III) ions. With [Pd(CN)4]2− as cyanide building block and bicompartimental schiff-base manganese(III) compound or Mn(II)-phenanthroline compound as assembling segment, one heterobimetallic cyanide-bridged trinuclear clusters and one heterobimetallic ion-pair complex have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination, in which the trinuclear complex 1 is self-assembled into one-dimensional chain structure by the intermolecular O–H⋯O hydrogen bond interactions, while the ion-pair complex 2 is linked into interesting three-dimensional network supramolecular structure by the intermolecular O–H⋯N hydrogen bond interactions. The trinuclear structure (top) and 1D single chain structure (bottom) constructed by intermolecular hydrogen bond interactions for complex 1. The crystal structure of ion-pair complex 2 (top) and its three-dimensional supramolecular structure constructed by intermolecular O-H⋯N hydrogen bond interactions (a axis (top), b axis (middle), c axis (bottom)). The magnetic property of complex 1.

Selectivity of the Highly Preorganized Tetradentate Ligand 2,9-Di(pyrid-2-yl)-1,10-phenanthroline for Metal Ions in Aqueous Solution, Including Lanthanide(III) Ions and the Uranyl(VI) Cation

Some metal ion complexing properties of DPP (2,9-Di(pyrid-2-yl)-1,10-phenanthroline) are reported with a variety of Ln(III) (Lanthanide(III)) ions and alkali earth metal ions, as well as the uranyl(VI) cation. The intense π-π* transitions in the absorption spectra of aqueous solutions of 10(-5) M DPP were monitored as a function of pH and metal ion concentration to determine formation constants of the alkali-earth metal ions and Ln(III) (Ln = lanthanide) ions. It was found that log K(1)(DPP) for the Ln(III) ions has a peak at Ln(III) = Sm(III) in a plot of log K(1) versus 1/r(+) (r(+) = ionic radius for 8-coordination). For Ln(III) ions larger than Sm(III), there is a steady rise in log K(1) from La(III) to Sm(III), while for Ln(III) ions smaller than Sm(III), log K(1) decreases slightly to the smallest Ln(III) ion, Lu(III). This pattern of variation of log K(1) with varying size of Ln(III) ion was analyzed using MM (molecular mechanics) and DFT (density functional theory) calculations. Values of strain energy (∑U) were calculated for the [Ln(DPP)(H(2)O)(5)](3+) and [Ln(qpy)(H(2)O)(5)](3+) (qpy = quaterpyrdine) complexes of all the Ln(III) ions. The ideal M-N bond lengths used for the Ln(III) ions were the average of those found in the CSD (Cambridge Structural Database) for the complexes of each of the Ln(III) ions with polypyridyl ligands. Similarly, the ideal M-O bond lengths were those for complexes of the Ln(III) ions with coordinated aqua ligands in the CSD. The MM calculations suggested that in a plot of ∑U versus ideal M-N length, a minimum in ∑U occurred at Pm(III), adjacent in the series to Sm(III). The significance of this result is that (1) MM calculations suggest that a similar metal ion size preference will occur for all polypyridyl-type ligands, including those containing triazine groups, that are being developed as solvent extractants in the separation of Am(III) and Ln(III) ions in the treatment of nuclear waste, and (2) Am(III) is very close in M-N bond lengths to Pm(III), so that an important aspect of the selectivity of polypyridyl type ligands for Am(III) will depend on the above metal ion size-based selectivity. The selectivity patterns of DPP with the alkali-earth metal ions shows a similar preference for Ca(II), which has the most appropriate M-N lengths. The structures of DPP complexes of Zn(II) and Bi(III), as representative of a small and of a large metal ion respectively, are reported. [Zn(DPP)(2)](ClO(4))(2) (triclinic, P1, R = 0.0507) has a six-coordinate Zn(II), with each of the two DPP ligands having one noncoordinated pyridyl group appearing to be π-stacked on the central aromatic ring of the other DPP ligand. [Bi(DPP)(H(2)O)(2)(ClO(4))(2)](ClO(4)) (triclinic, P1, R = 0.0709) has an eight-coordinate Bi, with the coordination sphere composed of the four N donors of the DPP ligand, two coordinated water molecules, and the O donors of two unidentate perchlorates. As is usually the case with Bi(III), there is a gap in the coordination sphere that appears to be the position of a lone pair of electrons on the other side of the Bi from the DPP ligand. The Bi-L bonds become relatively longer as one moves from the side of the Bi containg the DPP to the side where the lone pair is thought to be situated. A DFT analysis of [Ln(tpy)(H(2)O)(n)](3+) and [Ln(DPP)(H(2)O)(5)](3+) complexes is reported. The structures predicted by DFT are shown to match very well with the literature crystal structures for the [Ln(tpy)(H(2)O)(n)](3+) with Ln = La and n = 6, and Ln = Lu with n = 5. This then gives one confidence that the structures for the DPP complexes generated by DFT are accurate. The structures generated by DFT for the [Ln(DPP)(H(2)O)(5)](3+) complexes are shown to agree very well with those generated by MM, giving one confidence in the accuracy of the latter. An analysis of the DFT and MM structures shows the decreasing O--O nonbonded distances as one progresses from La to Lu, with these distances being much less than the sum of the van der Waals radii for the smaller Ln(III) ions. The effect that such short O--O nonbonded distances has on thermodynamic complex stability and coordination number is then discussed.