Pentagonal Bipyramidal Geometry Research Articles

Syntheses, X-ray crystal structures and spectroscopic characterization of rare μ-di-σ pyrazole based bridging keto carbonyl complexes derived from Cd(II) salts

The pyrazole based ligands (E)-2-(3,5-dimethyl-1H-pyrazol-1-yl)-N′-(pyridin-2-ylmethylene acetohydrazide (N-PzOPyH) and (E)-5-methyl-N′-(pyridin-2-ylmethylene)-1H-pyrazole-3-carbo hydrazide (PzOPyH), a 1:1 condensation product of 2-(3,5-dimethyl-1H-pyrazol-1-yl)aceto hydrazide and 5-methylpyrazole-3-carbohydrazide with pyridine-2-carbaldehyde respectively, and their keto oxygen bridged Cd(II) complexes [Cd2(N-PzOPy)2(H2O)4](ClO4)4 (1), [Cd2(PzOPy)2(H2O)4](ClO4)4 (2) and [Cd2(PzOPy)2(NO3)4] (3)] are reported. They have been characterized structurally and spectroscopically. The potential tetradentate NONN-donor ligands N-PzOPyH and PzOPyH are engaged in the coordination around the cadmium(II) center through the nitrogen atoms of pyrazole, azomethine and pyridine and the ketonic oxygen atom of the carbohydrazide group to form complexes 1, 2 and 3, respectively. These ligands span themselves in the equatorial plane and the pentagonal bipyramidal geometry is completed around the metal centres (with an N3O4 chromophore) with two apical water molecules (for 1 and 2) and with two nitrate ions (for 3). These keto bridged Cd(II) complexes are further stabilised by supramolecular interactions, like π⋯π, C–H⋯π and H-bonding interactions.

A heptadentate ligand possessing two phenol groups: Its diverse coordination chemistry and the catalytic behaviors of its transition complexes towards benzene oxidation

Reacting the heptadentate ligand 2,2′-(((pyridine-2,6-diylbis(methylene))bis((pyridin-2-ylmethyl)-azanediyl))bis(methylene))diphenol (H2L) with one equivalent of CuCl2·6H2O, NiCl2·6H2O and FeCl3·6H2O, followed by anion exchange with PF6−, BPh4− and ClO4− formed three mononuclear complexes [Cu(H2L)](Cl)(PF6) (1), [Ni(HL)](BPh4) (2) and [Fe(L)](ClO4) (3), respectively. Their structures in the solid state were determined by X-ray crystallography. The three metal centers in complexes 1–3 adopt distorted tetragonal pyramidal (Cu2+), octahedral (Ni2+) and pentagonal bipyramidal (Fe3+) geometries, respectively. In addition, the electrochemistry and their catalytic activity in the oxidation reaction of benzene to phenol by H2O2 were investigated.

Effect of metal coordination environment on topology of coordination polymers containing 2,5-thiophenedicarboxylate and long-spanning dipyridine ligands

Hydrothermal reaction of a metal nitrate, 2,5-thiophenedicarboxylic acid (H2tpdc), and bis(4-pyridylmethyl)piperazine (4-bpmp) afforded a series of crystalline coordination polymers with different dimensionality and topology depending on the metal coordination geometry. These materials were characterized by single-crystal X-ray diffraction. [Cu(tpdc)(4-bpmp)(H2O)]n (1), with square pyramidal coordination, shows parallel stacked (4,4) grid motifs. {[Co(tpdc)(4-bpmp)1.5(H2O)2]·4H2O}n (2) exhibits graphitic (6,3) honeycomb layer motifs and octahedral coordination at the metal. {[Cd(tpdc)(4-bpmp)(H2O)]·H2O}n (3) shows pentagonal bipyramidal geometry and manifests (4,4) grid layers as in 1, but with 2D+2D→3D parallel entanglement. [Zn(tpdc)(4-bpmp)(H2O)]n (4), which has distorted “5+1” octahedral coordination at zinc, displays an acentric 66 3-D diamondoid topology. Luminescent properties of 3 and 4 are presented, along with thermal analyses.

Synthetic and structural studies of piperidine carboxamide uranyl ion complexes

New piperidine based ligands of the type [C5H10NCONR2] (where R=CH3 (L1), C2H5 (L2) and iC3H7 (L3)) have been prepared and characterized. The complex chemistry of these ligands with uranyl chloride, bromide, nitrate and β-diketonates has been studied using IR and NMR spectroscopic methods. Crystal structures for the complexes [UO2Cl2(L3)2] (1), [UO2Br2(L3)2] (2) [UO2(NO3)2(L3)2] (5) and [UO2(C4H3SCOCHCOCF3)2(L3)] (8) have been determined by the X-ray diffraction method. The structures of 1 and 2 show that the uranyl ion is surrounded by two of the ligands and two halogen atoms in an octahedral geometry. The structure of 5 shows that the uranyl group is surrounded by two nitrate groups and two ligands in a hexagonal bipyramidal geometry. The structure of 8 shows that the uranyl group is surrounded by two β-diketonates and one ligand in a pentagonal bipyramidal geometry. The structures show that the carboxamide ligands are strongly bonded to the uranyl group, showing a near linear geometry for the U–O–C bond (angle 150–159°). The prepared chloro and bromo compounds are air and moisture stable and show good solubility in normal organic solvents.

Seven-coordinate Co(II), Fe(II) and six-coordinate Ni(II) amide-appended macrocyclic complexes as ParaCEST agents in biological media.

The solution chemistry and solid-state structures of the CoII, FeII, and NiII complexes of 7,13-bis(carbamoylmethyl)-1,4,10-trioxa-7,13-diazacyclopentadecane (L) are reported as members of a new class of paramagnetic chemical exchange saturation transfer (paraCEST) MRI contrast agents that contain transition metal ions. Crystallographic data show that nitrogen and oxygen donor atoms of the macrocyclic ligand coordinate to the metal ions to generate complexes with distorted pentagonal bipyramidal geometry for [Co(L)]Cl2·2H2O or [Fe(L)](CF3SO3)2. The NiII complex [Ni(L)](CF3SO3)2·H2O features a hexadentate ligand in a distorted octahedral geometry. The proton NMR spectra of all three complexes show highly dispersed and relatively sharp proton resonances. The complexes were further characterized by monitoring their dissociation under biologically relevant conditions including solutions containing phosphate and carbonate, ZnCl2, or acidic conditions. Solutions of the paraCEST agents in 20 mM N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid (pH 7.4) and 100 mM NaCl showed highly shifted and intense CEST peaks at 59, 72, and 92 ppm away from bulk water for [Co(L)]2+, [Ni(L)]2+, and [Fe(L)]2+, respectively at 37 °C on a 11.7 T NMR spectrometer. CEST spectra with corresponding rate constants for proton exchange are reported in 4% agarose gel (w/w), rabbit serum, egg white, or buffered solutions. CEST phantoms of 4 mM complex in buffer, 4% agarose gel (w/w), or rabbit serum on a 4.7 T MRI scanner at 37 °C, are compared. The most substantial change was observed for the reactive [Ni(L)]2+, which showed reduced CEST contrast in rabbit serum and egg white. The complexes with the least highly shifted CEST peaks ([Co(L)]2+ and [Ni(L)]2+) showed a reduction in CEST contrast in 4% agarose gel (w/w) compared to that in buffered solutions, while the CEST effect for [Fe(L)]2+ in 4% agarose gel (w/w) was not substantially different.

A two-dimensional Cd(II) coordination polymer with 2,2'-(disulfanediyl)dibenzoate and 1,10-phenanthroline ligands.

In poly[[μ3-2,2'-(disulfanediyl)dibenzoato-κ(5)O:O,O':O'',O'''](1,10-phenanthroline-κ(2)N,N')cadmium(II)], [Cd(C14H8O4S2)(C12H8N2)]n, the asymmetric unit contains one Cd(II) cation, one 2,2'-(disulfanediyl)dibenzoate anion (denoted dtdb(2-)) and one 1,10-phenanthroline ligand (denoted phen). Each Cd(II) centre is seven-coordinated by five O atoms of bridging/chelating carboxylate groups from three dtdb(2-) ligands and by two N atoms from one phen ligand, forming a distorted pentagonal-bipyramidal geometry. The Cd(II) cations are bridged by dtdb(2-) anions to give a two-dimensional (4,4) layer. The layers are stacked to generate a three-dimensional supramolecular architecture via a combination of aromatic C-H···π and π-π interactions. The thermogravimetric and luminescence properties of this compound were also investigated.

Synthesis and structural characterization of [(dpca)MX2] (M = Cu, X = Cl; M = Cd, X = Br and M = Zn, X = NO3) complexes containing N,N-di(2-picolyl)cyclohexylamine (dpca) and their application to methyl methacrylate polymerization

A novel series of [(dpca)MX2] (M=Cu, X=Cl; M=Cd, X=Br and M=Zn, X=NO3) complexes were synthesized through the reaction of N,N-di(2-picolyl)cyclohexylamine (dpca) with the corresponding metal starting materials. X-ray crystallographic analysis determined that the metal center in complexes [(dpca)CuCl2], [(dpca)CdBr2] and [(dpca)Zn(NO3)2] showed a distorted 5-coordinated square pyramidal, trigonal bipyramidal, and 7-coordinated pentagonal bipyramidal geometry, respectively, involving coordination of the nitrogen atom of the cyclohexylamine moiety with the metal center. Specifically, the catalytic activity of [(dpca)Zn(NO3)2] (1.04×105g PMMA/mol Zn·h) for the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60°C was six-fold higher than the reference complex [ZnCl2] (1.73×104g PMMA/mol Zn·h).

Poly[di-ammonium [di-aqua-(μ7-benzene-1,2,3,4,5,6-hexa-carboxyl-ato)tetra-oxido-diuranium(VI)]

Uranyl-carboxyl­ate hybrid materials dominate the catalog of uranyl compounds owing in part to the affinity between COO− functional groups and UO2 2+. Polycarboxyl­ate organic ligands may present a degree of steric hindrance and could thus influence the resulting uranyl topology. Single crystals of the title compound, {(NH4)2[(UO2)2(C12O12)(H2O)2]}n, were synthesized hydro­thermally as a result of reacting uranyl nitrate with benzene-1,2,3,4,5,6-hexa­carb­oxy­lic acid (mellitic acid). The structure is comprised of a single unique monomeric uranyl cation adopting a penta­gonal bipyramidal geometry. The uranyl coordination sphere is composed of four O atoms originating from one half of a fully deprotonated mellitic acid ligand and a single water mol­ecule. The observed axial U—O bonds display an average distance of 1.765 (8) Å, whereas equatorial O atoms are found at an average distance of 2.40 (5) Å. All uranium–oxygen bond lengths are in good agreement with literature values. Furthermore, the coordin­ation between the uranyl penta­gonal bipyramids and the mellitic acid anion constructs a three-dimensional anionic framework which is charge-balanced with ammonium cations. Additional stabilization of the structure is provided by O—H⋯O and N—H⋯O hydrogen bonding inter­actions between the components.

Unusual Seven Coordination of Oxovanadium(V) Oximato Complex: Synthesis and X-Ray Crystal Structure

The new oxovanadium(V) complex, [VO(acac)(dametsc)] (1) (acac = acetylacetonate (-1), H2dametsc = diacetylmonoxime-4-ethylthiosemicarbazone), has been prepared and characterized by studying its physicochemical properties. The X-ray crystal structure of the complex (1) has been determined and showed the presence of vanadium(V) atom in a unique heptacoordination state with distorted pentagonal bipyramidal geometry. The oximato ligand in the pentagonal plane is bonded to the central vanadium atom in dihapto (η2= N,O) manner with the formation of three membered ring, while the other three coordination sites in the plane are occupied by hydrazinic imine nitrogen, thiolate sulfur, and one of the acac oxygen atoms. The axial position sites are defined by the other acac oxygen and the trans oxo-atom. The supramolecular structure of the complex is exclusively constructed by intermolecular interactions, N–H⋯O and C–H⋯O.

Synthesis, Characterization, Crystal Structure, and Cytotoxicity of a Diorganotin(IV) Complex with 2-Acetylpyridine N 4-Phenylthiosemicarbazone

A new diorganotin(IV) complex formulated as [(Me)2Sn(L) (CH3COO)] (1), where HL = 2-acetylpyridine N(4)-phenylthiose micarbazone, has been synthesized and characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction studies. Schiff base in its deprotonated form coordinates to tin(IV) via pyridine nitrogen atom and the nitrogen atom and sulfur atoms of the thiosemicarbazone moiety. The tin(IV) ion is seven-coordinated and adopts a distorted pentagonal bipyramidal geometry. Biological studies, carried out in vitro against the K562 leukemia cells, have shown that the coupling of HL to Me2Sn(IV) leads to an enhancement of the cytotoxicity of the free ligand.

Metal-organic frameworks based on uranyl and phosphonate ligands

Three new crystalline metal-organic frameworks have been prepared from the reaction of uranyl nitrate with nitrilotris(methylphosphonic acid) [H6nmp, N(CH2PO3H2)3], 1,4-phenylenebis(methylene)diphosphonic acid [H4pmd, C6H4(PO3H2)2], and (benzene-1,3,5-triyltris(methylene))triphosphonic acid [H6bmt, C6H3(PO3H2)3]. Compound [(UO2)2F(H3nmp)(H2O)]·4H2O (I) crystallizes in space group C2/c, showing two crystallographically independent uranyl centres with pentagonal bipyramidal coordination geometries. While one metal centre is composed of a {(UO2)O3(μ-F)}2 dimer, the other comprises an isolated {(UO2)O5} polyhedron. Compound [(UO2)(H2pmd)] (II) crystallizes in space group P21/c, showing a centrosymmetric uranyl centre with an octahedral {(UO2)O4} coordination geometry. Compound [(UO2)3(H3bmt)2(H2O)2]·14H2O (III) crystallizes in space group P\bar 1, showing two crystallographically independent uranyl centres. One uranyl centre is a {(UO2)O5} pentagonal bipyramid similar to that in (I), while the other is a {(UO2)O4} centrosymmetric octahedron similar to that in (II). Compounds (I) and (III) contain solvent-accessible volumes accounting for ca 23.6 and 26.9% of their unit-cell volume, respectively. In (I) the cavity has a columnar shape and is occupied by disordered water molecules, while in (III) the cavity is a two-dimensional layer with more ordered water molecules. All compounds have been studied in the solid state using FT-IR spectroscopy. Topological studies show that compounds (I) and (III) are trinodal, with 3,6,6- and 4,4,6-connected networks, respectively. Compound (II) is instead a 4-connected uninodal network of the type cds.

Synthesis, X-ray structure, electrochemical behaviour and fluorescence studies of mononuclear dioxouranium complexes with oxygen donor ligands

Two phenol-based mononuclear dioxouranium complexes [UO2(mdbp)2{OHCH2CMe3}] (1) and [UO2(bdbp)2{OCHNMe2}] (2) (where mdbpH=4-methyl-2,6-dibenzoylphenol and bdbpH=4-tert-butyl-2,6-dibenzoylphendol) have been synthesized and characterized by mass spectrometry, IR, NMR and electronic spectroscopy, cyclic voltammetry and single crystal X-ray diffraction studies. In both the complexes the UVI atom has pentagonal bipyramidal geometry with two apical oxo groups, two chelating dibenzoyl phenolate ligands and one unidentate neopentanol or DMF molecule in the equatorial plane. The electrochemical behaviour of the complexes was investigated by cyclic voltammetry in CH3CN and DMSO. Both complexes exhibited a single quasireversible/irreversible reduction corresponding to the UO22+/UO21+ couple. The potential for 1 in DMSO shifted towards a more positive value by 0.604V, indicating the exchange of coordinated neopentanol with DMSO. The fluorescence of 1 and 2 was studied by fluorometric method and was compared with that observed for the ligand precursors. The results indicated characteristic charge transfer emissions.

ChemInform Abstract: Y, Lu, and Gd Complexes of NCO/NCS Pincer Ligands: Synthesis, Characterization, and Catalysis in the cis‐1,4‐Selective Polymerization of Isoprene.

A series of NCO/NCS pincer precursors, 3-(Ar(2)OCH2)-2-Br-(Ar(1)N=CH)C6H3 (((Ar1)NCO(Ar2))Br, 3a-d) and 3-(2,6-Me2C6H3SCH2)-2-Br-(Ar(1)N=CH)C6H3 (((Ar1)NCS(Me))Br, 4a and 4b) were synthesized and characterized. The reactions of [(Ar1)NCO(Ar2)]Br/[(Ar1)NCS(Me)]Br with nBuLi and the subsequent addition of the rare-earth-metal chlorides afforded their corresponding rare-earth-metal-pincer complexes, that is, [((Ar1)NCO(Ar2))YCl2(thf)2] (5a-d), [((Ar1)NCO(Ar2))LuCl2(thf)2] (6a, 6d), [((Ar1)NCO(Ar2))GdCl2(thf)2] (7), [{((Ar1)NCS(Me))Y(μ-Cl)}2{(μ-Cl)Li(thf)2(μ-Cl)}2] (8, 9), and [{((Ar1)NCS(Me))Gd(μ-Cl)}2{(μ-Cl)Li(thf)2(μ-Cl)}2] (10, 11). These diamagnetic complexes were characterized by (1)H and (13)C NMR spectroscopy and the molecular structures of compounds 5a, 6a, 7, and 10 were well-established by X-ray diffraction analysis. In compounds 5a, 6a, and 7, all of the metal centers adopted distorted pentagonal bipyramidal geometries with the NCO donors and two oxygen atoms from the coordinated THF molecules in equatorial positions and the two chlorine atoms in apical positions. Complex 10 is a dimer in which the two equal moieties are linked by two chlorine atoms and two Cl-Li-Cl bridges. In each part, the gadolinium atom adopts a distorted pentagonal bipyramidal geometry. Activated with alkylaluminum and borate, the gadolinium and yttrium complexes showed various activities towards the polymerization of isoprene, thereby affording highly cis-1,4-selective polyisoprene, whilst the NCO-lutetium complexes were inert under the same conditions.

Synthesis, Structure and Mimic Haloperoxidase Catalytic Activity of Peroxovanadium Complexes

Based on mimicking the environment of the active center of vanadium haloperoxidase( V-HPOs),we designed and synthesized two kinds of peroxovanadium complexes: Na[VO( O2)2( C10H8N2) ]·8H2O( 1)and K3H [( VO)2( O2)4( μ2-O) ]·H2O( 2),which were structurally characterized by X-ray single crystal diffraction,elemental analysis,IR and UV-Vis spectroscopies. Structural analyses reveal that complex 1crystallized in an triclinic system with space group P-1,a = 0. 7213( 2) nm,b = 1. 1269( 4) nm,c = 1. 3728( 4) nm,α = 68. 349( 4) °,β = 89. 178( 4) °,γ = 88. 050( 4) °,V = 1. 0365( 6) nm3 and the complex 2 crystallized in an monoclinic system with space group P21/ c, a = 0. 67047( 12) nm,b = 0. 99503( 18) nm,c = 1. 5817( 3) nm,α = γ = 90°,β = 93. 739( 2) °,V = 1. 0530( 3) nm3. Complex 1 has a distorted pentagonal bipyramidal geometry,while complex 2 has a distorted octahedron geometry. In addition,by studying the bromination reaction activity,it shows that the peroxovanadium complexes can be considered as a potential functional model of bromoperoxidase.

Calcium and strontium salts of (glycinato-κ2N,O)oxidobis(peroxido-κ2O,O′)vanadate(V) tetrahydrate

The title salts calcium (glycinato-κ(2)N,O)oxidobis(peroxido-κ(2)O,O')vanadate(V) tetrahydrate, Ca[VO(O2)2(NH2CH2COO)]·4H2O, and strontium (glycinato-κ(2)N,O)oxidobis(peroxido-κ(2)O,O')vanadate(V) tetrahydrate, Sr[VO(O2)2(NH2CH2COO)]·4H2O, crystallized at pH ca 7.4 with similar lattice parameters. The glycinate anion acts as a bidentate N,O-chelating ligand, and the V atom has a pentagonal bipyramidal geometry, with two η(2)-peroxo groups and the glycinate N atom in the equatorial plane, and one terminal oxo and a glycinate O atom at the axial positions. The H atoms of three of the four water molecules in the strontium salt exhibited disorder over three positions for each molecule.

ChemInform Abstract: Review: Structural Diversity in Organotin(IV) Dithiocarboxylates and Carboxylates

AbstractReview: 81 refs.

Coordination Equilibria Between Seven- and Five-coordinate Iron(II) Complexes

Octahedral, tetrahedral, and square planar geometries are the most often encountered coordination geometries for transition metal complexes. In certain cases, coordination equilibria can exist between different geometries, such as between six- and four-coordinate geometries in nickel(II) complexes, which were discovered half a century ago. Here, we present the first examples of a seven-five coordination equilibrium. Extensive spectroscopic studies in solution have provided evidence for a dynamic equilibrium between two iron(II) complexes, one with a seven-coordinate pentagonal bipyramidal geometry and one with a five-coordinate trigonal bipyramidal geometry.

A Ru(II) Bis-terpyridine-like Complex that Catalyzes Water Oxidation: The Influence of Steric Strain

The complexation of 2,9-dicarboxy-1,10-phenanthroline (DPA) with [Ru(tpy)Cl3] (tpy = 2,2';6,2″-terpyridine) provides a six-coordinate species in which one carboxyl group of DPA is not bound to the Ru(II) center. A more soluble tri-t-butyl tpy analogue is also prepared. Upon oxidation, neither species shows evidence for intramolecular trapping of a seven-coordinate intermediate. The role of the tpy ligand is revealed by the preparation of [Ru(tpy)(phenq)](2+) (phenq = 2-(quinol-8'-yl)-1,10-phenanthroline) that behaves as an active water oxidation catalyst (TON = 334). This activity is explained by the expanded coordination geometry of the phenq ligand that can form a six-membered chelate ring that better accommodates the linear arrangement of axial ligands required for optimal pentagonal bipyramid geometry. When a 1,8-naphthyidine ring is substituted for each of the two peripheral pyridine rings on tpy, increased crowding in the vicinity of the metal center impedes acquisition of the prerequisite reaction geometry.

Hexa- and heptacoordinated manganese(II) dicyanamide complexes containing a tetradentate N-donor Schiff base: Syntheses, composition tailored architectures and magnetic properties

Two 1D coordination polymers [Mn(L)(μ1,5-dca)(MeOH)]n(ClO4)n (1) and [Mn(L)(μ1,5-dca)]n(PF6)n (2) and a dinuclear compound [Mn2(L)2(μ1,5-dca)2(dca)2]⋅H2O (3) [L=N,N′-(bis-(pyridin-2-yl)benzylidene)-ethane-1,2-diamine; dca=dicyanamide] have been isolated using one-pot synthesis of the building components in appropriate molar ratios and characterized. X-ray structural studies reveal that 1 forms a zigzag 1D chain through single Mn-(NCNCN)-Mn units in which each heptacoordinated manganese(II) center adopts a distorted pentagonal bipyramidal geometry with an MnN6O chromophore occupied with four N atoms of L, two nitrile N atoms of monobridged μ1,5-dca and one O atom of MeOH. In 2, each hexacoordinated metal(II) center has a distorted octahedral coordination environment with an MnN6 chromophore bound by four N atoms of L and two nitrile N atoms of two different single bridged μ1,5-dca units; the latter connects other neighboring metal centers in a non-ending fashion affording a linear 1D chain. Complex 3 is dinuclear where two [Mn(L)]2+ units are connected by double μ1,5-dca bridges with a distorted pentagonal bipyramidal environment. Variable-temperature magnetic susceptibility measurements of 1–3 show weak antiferromagnetic interactions among the metal centers through μ1,5-dca bridges.

Dirubidium hexaaquacobalt(II) tetrakis(hydrogen phthalate) tetrahydrate and coordination modes of the hydrogen phthalate anion

The title compound, Rb₂[Co(H₂O)₆](C₈H₅O₄)₄·4H₂O, consists of nearly regular octahedral [Co(H₂O)₆]²⁺ cations with the CoII cations on the inversion centre (special position 2a), Rb⁺ cations, hydrogen phthalate (Hpht⁻) anions and disordered water molecules. The Rb⁺ cation is surrounded by nine O atoms from Hpht⁻ anions and water molecules, with a strongly deformed pentagonal-bipyramidal geometry and one apex split into three positions. The crystal packing is governed by numerous hydrogen bonds involving all water molecules and Hpht⁻) anions. In this way, layers parallel to the ab plane are formed, with the aromatic rings of the Hpht⁻ anions esentially directed along the c axis. While Hpht⁻ anions form the outer part of the layers, disordered water molecules and Rb⁺ cations alternate with [Co(H₂O)₆]²⁺ cations in the inner parts. The only interactions between the layers are van der Waals forces between the atoms of the aromatic rings. A search of the Cambridge Structural Database for coordination modes and types of hydrogen-bonding interaction of the Hpht⁻ anion showed that, when uncoordinated Hpht⁻ anions are present, compounds with intermolecular hydrogen bonds are more numerous than compounds with intramolecular hydrogen bonds. For coordinated Hpht⁻ anions, chelating and bridging anions are almost equally common, while monodentate anions are relatively scarce. The same coordination modes appear for Hpht⁻ anions with or without intramolecular hydrogen bonds, although intramolecular hydrogen bonds are less common.