Lead Tetrakis(imidazolyl)borate Solids: Anion Exchange, Solvent Intercalation, and Self Assembly of an Organic Anion

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.

A novel 3-D lead-iodide polymer based on the linkage of rare binuclear [Pb2I]3+ cations and anionic bis(pyrazinyl)-trizole bridges

A novel 3-D lead-iodide polymer [Pb₂I(μ-bpt-z)₃]_n (1, Hbpt-z = 3,5-bis(pyrazinyl)-1,2,4-trizole) has been hydrothermally prepared and structurally characterized. 1 offers the first example of a 3-D lead-iodide polymer built up from the linkage of rare binuclear [Pb₂I]³⁺ cations and anionic bis(pyrazinyl)-trizole bridges. 1 exhibits photoluminescent and photocurrent response properties, and its density functional theory calculation was also studied.

A charge-separated diamondoid metal–organic framework

Metal–organic framework with diamondoid structure constructed with precisely placed tetrahedral borate anions and copper(i) cations.

μ-Oxalato-κ(4)O(1),O(2):O(1'),O(2')-bis-[aqua-(2,2'-bipyridine-κN)(nitrato-κ(2)O,O')lead(II)]

The title compound, [Pb₂(C₂O₄)(NO₃)₂(C₁₀H₈N₂)₂(H₂O)₂], was synthesized hydro­thermally. The binuclear complex mol­ecule is centrosymmetric, the inversion centre being located at the mid-point of the oxalate C—C bond. The Pb^II ion is hepta­coordinated by the O atom of one water mol­ecule, two oxalate O atoms, two nitrate O atoms and two 2,2′-bipyridine N atoms, forming an irregular coordination environemnt. Inter­molecular O—H⋯O hydrogen bonds between water mol­ecules and oxalate and nitrate ions result in the formation of layers parallel to (010). π–π inter­actions between pyridine rings in adjacent layers, with centroid–centroid distances of 3.584 (2) Å, stabilize the structural set-up.

catena-Poly[[(benzoato-κO,O')(2,2'-bipyridine-κN,N')lead(II)]-μ(3)-nitrato-κO:O,O':O'']

In the title coordination polymer, [Pb(C₇H₅O₂)(NO₃)(C₁₀H₈N₂)]_n, the Pb^II ion is eight-coordinated by two N atoms from one 2,2′-bipyridine ligand, two O atoms from one benzoate anion and four O atoms from three nitrate groups (one chelating, two bridging) in a distorted dodecahedral geometry. Adjacent Pb^II ions are linked by bridging nitrate O atoms through the central Pb₂O₂ and Pb₂O₄N₂ cores, resulting in an infinite chain structure along the b axis. The crystal structure is stabilized by π–π stacking inter­actions between 2,2′-bipyridine and benzoate ligands belonging to neighboring chains, with shortest centroid–centroid distances of 3.685 (8) and 3.564 (8) Å.

Bis(benzoato-κO,O')(1,10-phenanthroline-κN,N')lead(II) benzoic acid mono-solvate

The reaction of lead acetate, benzoic acid and 1,10-phenanthroline (phen) in aqueous solution yielded the title complex, [Pb(C₇H₅O₂)₂(C₁₂H₈N₂)]·C₇H₆O₂. In the crystal, the Pb^II ion is hexa­coordinated by two N atoms from one 1,10-phenanthroline ligand and four O atoms from two chelate benzoate anions. If the second benzoate ligand is treated as one coordination site, the overall coordination may be represented as a distorted pseudo-square pyramid. An inter­molecular O—H⋯O hydrogen bond links the solvent benzoic acid mol­ecule with a metal-coordinated benzoate ligand. The shortest Pb⋯Pb distance is 3.864 (4) Å, indicating a weak metal–metal inter­action. Two complex mol­ecules related by an inversion centre form dimeric units via Pb⋯O inter­actions of 3.206 (4) Å.

Bis(benzoato-κO,O')(2,2'-bipyridine-κN,N')lead(II) benzoic acid monosolvate

The reaction of lead acetate, benzoic acid and 2,2'-bipyridine (bipy) in aqueous solution yielded the title complex, [Pb(C(7)H(5)O(2))(2)(C(10)H(8)N(2))]·C(7)H(6)O(2). The asymmetric unit contains two independent complex mol-ecules as well as two independent benzoic acid solvent mol-ecules, one of which is disordered over two positions with almost equal occupancies [0.504 (5) and 0.496 (5)]. The two complex mol-ecules have similar configurations with the hexa-coordinated environment of the Pb(II) atom formed by four carboxyl-ate O atoms of two chelate benzoate ligands and two N atoms of the bipy ligand. The Pb-O bonds involving one of the benzoate ligands are almost coplanar with Pb-N bonds to the bipy ligand [dihedral angles of 12.67 (11) and 14.73 (11)°] ; if the second benzoate ligand is treated as one coordination site, the overall coordination may be represented as a distorted pseudo-square pyramid. Weak inter-molecular Pb⋯O inter-actions [3.046 (3) and 3.359 (3) Å] link each of the complex mol-ecules into two symmetry-independent centrosymmetric dimers. Hydrogen bonds involving the carboxyl H atoms of solvent benzoic acid mol-ecules and metal-coordinated carboxyl-ate O atoms link complex mol-ecules and benzoic acid solvent mol-ecules into insular aggregates.

(2,2'-Bipyridine-κN,N')bis-(4-methyl-benzoato-κO,O')lead(II)

In the title compound, [Pb(C₈H₇O₂)₂(C₁₀H₈N₂)], the Pb^II ion is coordinated by two N atoms from one 2,2′-bipyridine ligand and four O atoms from two 4-methyl­benzoate anions in a distorted pseudo-square-pyramidal environment, considering one of the carboxyl­ate anions as an apical ligand. Pairs of complex mol­ecules related by inversion centers are organized into dimers via pairs of Pb⋯O inter­actions [3.185 (2) Å] and stacking interactions between 2,2′-bipyridine and 4-methyl­benzoate ligands, with a mean distance between their planes of 3.491 Å.

(2,2'-Bipyridine-κN,N')bis-(4-hydroxy-benzoato-κO,O')lead(II) monohydrate

The reaction of lead acetate, 4-hydroxy­benzoic acid and 2,2′-bipyridine in aqueous solution gave the title complex, [Pb(C₇H₅O₃)₂(C₁₀H₈N₂)]·H₂O. The asymmetric unit contains one Pb^II atom, two 4-hydroxy­benzoate ligands, one 2,2′-bipyridine ligand and one uncoordinated water mol­ecule. The Pb^II atom is hexa­coordinated in a distorted tetra­gonal-bipyramidal geometry and is chelated by four carboxyl­ate O atoms and two N atoms. O—H⋯O hydrogen-bonding inter­actions, involving the uncoordinated water, the carboxyl­ate O atoms and hydr­oxy O atoms, produce a three-dimensional supra­molecular structure.

Pb···π Aryl Interactions as Supramolecular Synthons

A survey of lead (Pb) structures containing Pb···π aryl interactions has been conducted. Such contacts usually lead to zero- or one-dimensional aggregates with rare examples of two- and three-dimensional architectures. The Pb···π aryl interactions are found only in crystal structures containing lead(ii) centres and arise as a result of electron donation of the lead-bound lone pair of electrons to the lowest unoccupied molecular orbital of the accepting aryl ring. The prevalence of Pb···π interactions as a supramolecular synthon is relatively low, occurring in ~3% of all structures containing lead and at least one aryl ring, but these are more likely to form compared with Sn···π interactions.

catena-Poly[[aqua-(3-methyl-benzoato-κO,O')lead(II)]-μ-3-methyl-benzoato-κO:O,O':O']

The reaction of lead(II) acetate and 3-methyl­benzoic acid (MBA) in aqueous solution yielded the title polymer, [Pb(C₈H₇O₂)₂(H₂O)]_n. The asymmetric unit contains two Pb^II atoms, four MBA ligands and two water mol­ecules. Each Pb^II cation is hepta­coordinated and chelated by four carboxyl­ate O atoms from two MBA ligands. The Pb atoms are bridged through the carboxyl­ate O atoms from another two MBA ligands, leading to a central Pb₂O₂ core. The Pb—O bond lengths are in the range 2.325 (3)–2.757 (4) Å. The intra- and inter­dimer Pb⋯Pb distances are 4.2942 (3) and 4.2283 (3) Å, respectively, indicating little direct metal–metal inter­action. The coordinating water mol­ecules and carboxyl­ate O atoms are involved in extensive O—H⋯O hydrogen-bonding inter­actions. The complex has an extended ladder-like chain structure and the chains are assembled by hydrogen bonds and π–π inter­actions [centroid–centroid distance = 3.6246 (3) Å] into a three-dimensional supra­molecular structure.

Zeolitic boron imidazolate frameworks

B-hive? A family of crystalline materials analogous to porous AlPO(4) but based on boron imidazolate frameworks (BIFs) can be formed by the crosslinking of various presynthesized boron imidazolates with monovalent cations (Li(+) and Cu(+), see picture). This synthetic method is capable of generating a large variety of open frameworks, ranging from the four-connected zeolitic sodalite type to the three-connected chiral (10,3)-a type.

Investigating the topochemical polymerization of aniline derivatives in Pb(II) borate scaffolds

Three different aniline derivatives, namely m- and p-aminobenzoic acids and m-amino benzenesulfonic acid, were sequestered in between layers of a borate-based coordination polymer, based on lead(II) tetrakis(imidazolyl)borate. The aniline derivatives pre-organized in the interlayer spacing of the coordination polymer, and the reactivity of these pre-organized anionic monomers in the crystalline state was studied. We found that thermally activated reactivity under ambient atmospheric oxygen promotes what appears to be polymerization, and that the most reactive species is m-aminobenzenesulfonic acid monomer due to its increased mobility within the layers of the polymer.

Probing lead(II) bonding environments in 4-substituted pyridine adducts of (2,6-Me2C6H3S)2Pb: an X-ray structural and solid-state 207Pb NMR study

The effect of subtle changes in the sigma-electron donor ability of 4-substituted pyridine ligands on the lead(II) coordination environment of (2,6-Me(2)C(6)H(3)S)(2)Pb (1) adducts has been examined. The reaction of 1 with a series of 4-substituted pyridines in toluene or dichloromethane results in the formation of 1:1 complexes [(2,6-Me(2)C(6)H(3)S)(2)Pb(pyCOH)](2) (3), [(2,6-Me(2)C(6)H(3)S)(2)Pb(pyOMe)](2) (4), and (2,6-Me(2)C(6)H(3)S)(2)Pb(pyNMe(2)) (5) (pyCOH = 4-pyridinecarboxaldehyde; pyOMe = 4-methoxypyridine; pyNMe2 = 4-dimethylaminopyridine), all of which have been structurally characterized by X-ray crystallography. The structures of 3 and 4 are dimeric and have psi-trigonal bipyramidal S(3)N bonding environments, with the 4-substituted pyridine nitrogen and bridging sulfur atoms in axial positions and two thiolate sulfur atoms in equatorial sites. Conversely, compound 5 is monomeric and exhibits a psi-trigonal pyramidal S(2)N bonding environment at lead(II). The observed structures may be rationalized in terms of a simple valence bond model and the sigma-electron donor ability of the 4-pyridine ligands as derived from the analysis of proton affinity values. Solid-state (207)Pb NMR experiments are applied in combination with density functional theory (DFT) calculations to provide further insight into the nature of bonding in 4, 5, and (2,6-Me(2)C(6)H(3)S)(2)Pb(py)(2) (2). The lead chemical shielding (CS) tensor parameters of 2, 4, and 5 reveal some of the largest chemical shielding anisotropies (CSA) observed in lead coordination complexes to date. DFT calculations using the Amsterdam Density Functional (ADF) program, which take into account relativistic effects using the zeroth-order regular approximation (ZORA), yield lead CS tensor components and orientations. Paramagnetic contributions to the lead CS tensor from individual pairs of occupied and virtual molecular orbitals (MOs) are examined to gain insight into the origin of the large CSA. The CS tensor is primarily influenced by mixing of the occupied MOs localized on the sulfur and lead atoms with virtual MOs largely comprised of lead 6p orbitals.

Anion Separation by Selective Crystallization of Metal−Organic Frameworks

A novel approach for the separation of anions from aqueous mixtures was demonstrated, which involves their selective crystallization with metal-organic frameworks (MOFs) containing urea functional groups. Self-assembly of Zn2+ with the N,N'-bis(m-pyridyl)urea (BPU) linker results in the formation of one-dimensional MOFs including various anions for charge balance, which interact to different extents with the zinc nodes and the urea hydrogen-bonding groups, depending on their coordinating abilities. Thus, Cl-, Br-, I-, and SO4(2-), in the presence of BPU and Zn2+, form MOFs from water, in which the anions coordinate the zinc and are hydrogen-bonded to the urea groups, whereas NO3- and ClO4- anions either do not form MOFs or form water-soluble discrete coordination complexes under the same conditions. X-ray diffraction, FTIR, and elemental analysis of the coordination polymers precipitated from aqueous mixtures containing equivalent amounts of these anions indicated total exclusion of the oxoanions and selective crystallization of the halides in the form of solid solutions with the general composition ZnCl(x)Br(y)I(z).BPU (x + y + z = 2), with an anti-Hofmeister selectivity. The concomitant inclusion of the halides in the same structural frameworks facilitates the rationalization of the observed selectivity on the basis of the diminishing interactions with the zinc and urea acidic centers in the MOFs when going from Cl- to I-, which correlates with decreasing anionic charge density in the same order. The overall crystal packing efficiency of the coordination frameworks, which ultimately determines their solubility, also plays an important role in the anion crystallization selectivity under thermodynamic equilibration.

Lead(II) Complexes of Pyridinedicarboxylates — Lattice Interactions and Metal Ion Stereochemistry

Crystal structure determinations of the Pb(ii) complexes of the isomeric 2,3-, 2,4-, and 2,5-pyridinedicarboxylates (pdca) of composition Pb(2,3-pdca), Pb(2,4-pdca)·H2O, and Pb(2,5-pdcaH)2·2H2O show that, as in the known 2,6-pyridine-dicarboxylate (dipicolinate, commonly designated ‘dipic’ but here, for the sake of consistency, as 2,6-pdca) complexes Pb(2,6-pdca)(2,6-pdcaH2)·3H2O and Pb(2,6-pdca), stacking of the aromatic moieties is a prominent feature of the lattices. Structural evidence can also be discerned for the possible influence of other forces such as Pb···Pb bonding and lone-pair repulsions, but the lattices differ markedly in these regards.

The assembly of organic radical anions between metal-borate scaffolds

Metal-organic frameworks based on the Pb[B(Im)(4)](+) unit form layered structures analogous to those observed in clays and double layered hydroxide minerals. These layers can act as scaffolds for the organization of anionic organic guests. In this report, we use this scaffold to assemble TEMPO and PROXYL carboxylates in the interlayer spacings of Pb[B(Im)(4)](4-carboxy-TEMPO) 1 and Pb[B(Im)(4)](3-carboxy-PROXYL)(H(2)O)2, respectively. The resultant materials are paramagnetic, and the organization of the radical units differs between the two compounds. This results in changes in electronic structure of the radical unit, as observed by EPR spectroscopy.