Trigonal Prismatic Environment Research Articles

Na-deficient P2-type layered oxide cathodes for practical sodium-ion batteries

Sodium-ion batteries (SIBs) have attracted enormous attention as candidates in stationary energy storage systems, because of the decent electrochemical performance based on cheap and abundant Na-ion intercalation chemistry. Layered oxides, the workhorses of modern lithium-ion batteries, have regained interest for replicating their success in enabling SIBs. A unique feature of sodium layered oxides is their ability to crystallize into a thermodynamically stable P2-type layered structure with under-stoichiometric Na content. This structure provides highly open trigonal prismatic environments for Na ions, permitting high Na+ mobility and excellent structural stability. This review delves into the intrinsic characteristics and key challenges faced by P2-type cathodes and then comprehensively summarizes the up-to-date advances in modification strategies from compositional design, elemental doping, phase mixing, morphological control, and surface modification to sodium compensation. The updated understanding presented in this review is anticipated to guide and expedite the development of P2-type layered oxide cathodes for practical SIB applications.

Tuning the interplay of spin-orbit coupling and trigonal crystal-field effect in the Ising-like spin system Ca3Co2O6

In the ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2}{\mathrm{O}}_{6}$ (CCO) system, the large contribution of the orbital moment to the magnetization and the strong magnetocrystalline anisotropy (MCA) are considered to give rise to the Ising magnetism. In this study, the dominant role of both spin-orbit-coupling (SOC) and crystal-field (CF) effects behind this Ising character of magnetism is qualitatively elucidated from the temperature and field dependence of magnetization in the presence of hydrostatic pressures up to 1.04 GPa in a CCO single crystal (SC). The local trigonal prismatic environment is compressed with the application of high pressure, resulting in higher trigonal CF as compared to ambient conditions. It reduces the effect of SOC due to the initiation of orbital quenching that finally decreases orbital moment contributions to both the magnetization and the MCA, respectively. This interplay of triagonal CF and SOC effects is further shown from the detailed quantitative analysis of the field-dependent magnetization in different orientations of CCO and ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{1.8}{\mathrm{Fe}}_{0.2}{\mathrm{O}}_{6}$ (CCFO) SCs at ambient pressure by employing a simple classical model and second-order perturbative analysis of SOC. The complete quenching of the orbital moment of ${\mathrm{Fe}}^{3+}$ ($S=5/2$) in CCFO weakens the MCA and also helps in deducing the SOC effect. Furthermore, the estimated anisotropic constants using density functional theory very well capture the Ising magnetism in CCO and deviation from it in CCFO compared to that of classical results.

Synthesis, biological activities and theoretical studies of a new macroacyclic Schiff base ligand and its related Co(II), Ni(II), and Cu(II) complexes: The X-ray crystal structure of the Co(II) complex

A new symmetrical macroacyclic Schiff base ligand (H2L) was prepared by the condensation reaction of 2-(4-(2-aminophenyl)piperazin-1-yl)benzeneamine and 2-hydroxy-5-nitro-benzaldehyde which was then used to synthesize the Co(II), Ni(II) and Cu(II) complexes. The new compounds were characterized by Mass spectrometry, IR, 1H NMR and 13C NMR spectroscopy and elemental analyses. The single crystal X-ray structural analysis of [CoL] showed that the Cobalt atom was in a slightly distorted trigonal prismatic environment coordinated by the four amine nitrogen atoms and two phenol oxygen atoms of the ligand; the nitro groups are not coordinating to the metal atom. The in vitro antioxidant attributes of the synthesized compounds were evaluated, using DPPH free radical scavenging with the lowest IC50 reported for [CuL]. The cytotoxicity of the compounds was also evaluated against A-549 lung adenocarcinoma cells, which showed the H2L and [CuL] were more effective than the other two compounds. NBO, EDA, and EDA-NOCV studies were used to look at the type of metal–ligand interactions in these complexes.

Synthesis and characterization of a new piperazine containing macroacyclic ligand and its Cu(ii) and Co(ii) complexes: An investigation of the ligand's silver specific fluorescent properties

A new Schiff base ligand (H2L) was designed and synthesized by the condensation of 2,2′-(piperazine-1,4-diyl)dianiline and 2‑hydroxy-3-methoxybenzaldehyde. The copper(II) and cobalt(II) complexes were synthesized by direct reaction the metal ions and the ligand in 1:1 molar ratio in ethanol. The molecular structures of H2L and the cobalt(II) complex were determined by single crystal X-ray diffraction analyses, showing that the cobalt(II) in a relatively rare trigonal prismatic environment coordinated by all six donor atoms of the (N4O2) hexadentate ligand. The study of the photophysical properties shows that H2L has a medium fluorescence emission at 440 nm, which is strongly enhanced in the presence of silver, meaning that the ligand may be able to be used as a chemosensor for detection of Ag+ions in the environment.

Re‐investigation of Barium‐Gold(I)‐Tetra‐Thiostannate(IV), Ba[Au2SnS4], with Short AuI···AuI Separation Showing Luminescence Properties

New investigations combining single crystal‐ and synchrotron‐based powder X‐ray diffraction data revealed that Ba[Au2SnS4] crystallizes in the orthorhombic crystal system in space group C2221 instead of P21212 as reported earlier. While the principle crystal structure is not altered, there are significant differences of the interatomic distances Au‐S and Sn‐S. A salient property of this crystal structure is the partial framework composed of AuS2 dumbbells and SnS4 tetrahedra to form chains [(Au2SnS4)2–]∞ propagating in the [100] direction. Within the chains a short Au···Au separation of 2.9538(13) Å is observed, while the interchain Au···Au separation is longer at 3.383 Å. The Ba2+ cation is eightfold coordinated by S2– anions in a distorted bicapped trigonal prismatic environment BaS8. These polyhedra share all S2– anions thus generating a three‐dimensional network. This connection Scheme generates voids along [100] hosting [(Au2SnS4)2–]∞ chains. In addition, the compound has been shown to be luminescent at the blue‐green spectral range with emission maximum at approximately 21000 cm–1.

Polypyridines, Picrates, Lanthanides: A Plethora of Stacks?

Reactions of the lanthanide(iii) picrates (picrate=2,4,6-trinitrophenoxide=pic) with 1,10-phenanthroline (phen) and 2,2′:6′,2′′-terpyridine (terpy) in a 1:2 molar ratio have provided crystals suitable for X-ray structure determinations in instances predominantly involving the lighter lanthanides. In all, the aza-aromatic ligands chelate the lanthanide ion, none being found as ‘free’ ligands within the lattice. The complexes of 1,10-phenanthroline have been characterised in two forms, one unsolvated (Ln=La, Sm, Eu; monoclinic, C2/c, Z 8), one an acetonitrile monosolvate (Ln=Gd; monoclinic, P21/a, Z 4), the latter being the only previously known form (with Ln=La). In both forms, the LnIII is nine-coordinate, in an approximately tricapped trigonal-prismatic environment, with two picrate ligands chelating through phenoxide and 2-nitro group oxygen atoms, the third being bound through phenoxide-O only. The 2,2′:6′,2′′-terpyridine complexes, all acetonitrile monosolvates defined for Ln=La, Gd, Er, and Y (monoclinic, C2/c, Z 4), are ionic, one picrate having been displaced from the primary coordination sphere. For Ln=La, the two bound picrates are again chelating, making the LaIII 10-coordinate in a distorted bicapped square-antiprismatic environment but in the other species they are bound through phenoxide-O only, making the LnIII ions eight-coordinate in a distorted square-antiprismatic environment. Stacked arrays of the ligands can be found in both series of complexes, with intramolecular picrate–picrate and picrate–aza-aromatic stacks being prominent features.

Mononuclear transition metal adamantane-1-carboxylates

A procedure was developed for the synthesis of mononuclear first row transition metal coordination compounds with adamantane-1-carboxylate (AdCO2), which allowed the synthesis of complexes NBu4[M(AdCO2)3], where MII = Mn, Ni, Co, Zn. The X-ray diffraction study showed that all AdCO2 act as chelating ligands, which is the main distinguishing structural feature of the synthesized compounds. The formation of four-membered metallocycles leads to a small O—M—O angle (58.4–63.0°), resulting in the distorted trigonal-prismatic environment of the central atom in the coordination anions [M(AdCO2)3]−. Under similar conditions of the synthesis, CuII forms the complex (NBu4)2[Cu(AdCO2)2(SO4)] existing in two differently colored modifications (green and light blue), which is due to a small difference in the environment of CuII in the solid state. Upon heating above 150°C, the light blue modification is transformed into the green modification. Using 1,3-diphenyltriazene (HL), it was demonstrated that the developed synthetic approach is applicable to the preparation of compounds, in which the coordination anions [ML3]− also contain only four-membered chelate metallocycles with the N—M—N angle tightened at the metal atom. The compounds NBu4[ML3], where MII = Co and Ni, were isolated in individual state and were structurally characterized.

Crystal Growth and Magnetic Properties of Pr3Co2+xGe7 and the Sn-Stabilized Ln3Co2+xGe7–ySny (Ln = Pr, Nd, Sm)

Single crystals of the ternary Pr3Co2+xGe7 and Ln3Co2+xGe7–ySny (Ln = Pr, Nd, Sm) adopting a disordered version of the La3Co2Sn7 structure type have been prepared via flux-growth methods and characterized by single crystal X-ray diffraction. The structure consists of two lanthanide crystallographic sites with one occupying a cuboctahedral coordination environment and a second in a trigonal prismatic environment. The structure can also be described as an intergrowth of AuCu3 and CeNiSi2 structure types, and the stability of the germanide analogues requires Sn incorporation and Co site preferences. Magnetic properties of the Pr3Co2+xGe7–ySny series are highlighted with the Sn-substituted Pr3Co2.514(5)Ge6.66(7)Sn0.360(2) orders magnetically near 5.8 K, while the germanide Pr3Co2.3376(5)Ge7.056(7) exhibits magnetic transitions at 5.3 and 9.3 K, arising from the magnetic sublattices with field-dependent magnetization revealing three metamagnetic transitions at 0.46, 0.80, and 2.1 T.

Lanthanide Organophosphate Spiro Polymers: Synthesis, Structure, and Magnetocaloric Effect in the Gadolinium Polymer.

Spirocyclic lanthanide organophosphate polymers, {[Ln(dipp)(dippH)(CH3OH)(H2O)2](CH3OH)2}n [Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11)], have been prepared from the reaction of Ln(NO3)3·xH2O with sterically hindered 2,6-diisopropylphenyl phosphate (dippH2) using aqueous NaOH as the base. The one-dimensional chainlike lanthanide (III) organophosphate coordination polymers have been characterized with the aid of analytical and spectroscopic methods. The single crystal structure determination of polymers (2-5 and 7-11) reveals that in these compounds the hydrophobic organic groups of the phosphate provide a protective coating for the inorganic lanthanide phosphate polymeric chain. The encapsulation of inorganic lanthanide phosphate core, which has very low solubility product, within the organic groups assists in the facile crystallization of the polymers. The di- and monoanionic organophosphate ligands dipp2- and dippH- display [2.111] and [2.110] binding modes, respectively, in 2-5 and 7. However, they exhibit only [2.110] binding mode in the case of 8-11. This results in the formation of two different types of polymers. While the lighter rare-earth metal ions in 2-5 and 7 display eight coordinate biaugmented trigonal prismatic geometry, the heavier rare-earth metal ions in 9-11 exhibit a seven coordinate capped trigonal prismatic environment. The Tb(III) ion in 8 displays distorted pentagonal bipyramidal geometry. Magnetic studies reveal the presence of weak antiferromagnetic interactions between the Ln(III) ions through the organophosphate ligand. The isotropic Gd(III) polymer 7 exhibits a maximum entropy change of 17.83 J kg-1 K-1 for a field change of 7.0 T at 2.5 K, which is significant considering the high molecular weight of the organophosphate ligand. These polymers represent the first family of any structurally characterized rare-earth organophosphate polymers derived from monoesters of phosphoric acid.

Complexations of Ln(III) with SnS4H and Sn2S6: Solvothermal syntheses and characterizations of lanthanide coordination polymers with thiostannate and polyamine mixed ligands

Polymeric lanthanide complexes with thiostannate and polyamine mixed ligands, [Ln(peha)(μ–SnS4H)]n [Ln=La (1a), Nd (1b)] and [{Ln(tepa)(μ–OH)}2(μ–Sn2S6)]nnH2O [Ln=Nd (2a), Sm (2b), Gd (2c), Dy (2d)] (peha=pentaethylenehexamine, tepa=tetraethylenepentamine) were respectively prepared in peha and tepa coordinative solvents by the solvothermal methods. In 1a and 1b, the Ln3+ ions are coordinated by a hexadentate peha ligand forming [Ln(peha)]3+ units. The [SnS4H]3− anion chelates a [Ln(peha)]3+ unit via two S atoms and coordinates to another [Ln(peha)]3+ unit via the third S atom. As a result, the [Ln(peha)]3+ units are connected into coordination polymers [Ln(peha)(μ–SnS4H)]n by an unprecedented tridentate μ–η1,η2–SnS4H bridging ligands. In 2a–2d, the Ln3+ ions are coordinated by a pentadentate tepa ligand, and two [Ln(tepa)]3+ units are joined by two μ–OH bridges to form a binuclear [{Ln(tepa)(μ–OH)}2]4+ unit. Behaving as a bidentate μ–η1, η1–Sn2S6 bridging ligand, the Sn2S6 unit connects [{Ln(tepa)(μ–OH)}2]4+ units into a neutral coordination polymer [{Ln(tepa)(μ–OH)}2(μ–Sn2S6)]n via the trans S atoms. The Ln3+ ions are in distorted monocapped square antiprismatic and bicapped trigonal prismatic environments in [{Ln(peha)(μ–SnS4H)]n and [{Ln(tepa)(μ–OH)}2(μ–Sn2S6)]n, respectively. The denticities of ethylene polyamine play an important role on the formation and complexation of the thiostannate in the presence of lanthanide ions. Compounds 1a–2d show well-defined absorption edges with band gaps between 2.81 and 3.15eV.

Hydro-thermal synthesis and crystal structure of a new lanthanum(III) coordination polymer with fumaric acid.

The title compound, poly[di­aqua­tris­(μ4-but-2-enedioato)(μ2-but-2-enedioic acid)dilanthanum(III)], [La2(C4H2O4)3(C4H4O4)(H2O)2]n, was synthesized by the reaction of lanthanum chloride penta­hydrate with fumaric acid under hydro­thermal conditions. The asymmetric unit comprises an LaIII cation, one and a half fumarate dianions (L 2−), one a half-mol­ecule of fumaric acid (H2 L) and one coordinated water mol­ecule. Each LaIII cation has the same nine-coordinate environment and is surrounded by eight O atoms from seven distinct fumarate moieties, including one proton­ated fumarate unit and one water mol­ecule in a distorted tricapped trigonal–prismatic environment. The LaO8(H2O) polyhedra centres are edge-shared through three carboxyl­ate bridges of the fumarate ligand, forming chains in three dimensions to construct the MOF. The crystal structure is stabilized by O—H⋯O hydrogen-bond inter­actions between the coordin­ated water mol­ecule and the carboxyl­ate O atoms, and also between oxygen atoms of fumaric acid

Pr3S2Cl2[AsS3]: A Praseodymium(III) Sulfide Chloride Thioarsenate(III) with Double Chains of Condensed [SPr4]10+ Tetrahedra

AbstractSingle crystals of Pr3S2Cl2[AsS3] were obtained by reacting praseodymium sesquisulfide and trichloride with arsenic and sulfur (molar ratio: 7:4:6:9) in torch‐sealed evacuated silica ampoules at 850 °C for a week and subsequent slow cooling to room temperature. The transparent, pale yellowish green platelets crystallize monoclinically (Pr3S2Cl2[AsS3]: a = 2190.96(9) pm, b = 685.49(3) pm, c = 701.87(3) pm, β = 98.752(3)°) in the non‐centrosymmetric space group Cc with Z = 4. The crystal structure of Pr3S2Cl2[AsS3] comprises three crystallographically different Pr3+ cations. (Pr1)3+ and (Pr2)3+ exhibit bicapped trigonal prismatic environments of five sulfur and three chlorine atoms (C.N. = 8) each, whereas only seven sulfur atoms arranged as capped trigonal prism (C.N. = 7) are present in the case of (Pr3)3+. Two of the five crystallographically different sulfur atoms (S1 and S2) are coordinated by four Pr3+ cations, each in the shape of slightly distorted [SPr4]10+ tetrahedra (d(S–Pr) = 278–294 pm). Hence, the crystal structure of Pr3S2Cl2[AsS3] contains double chains with the composition 1∞{[S2Pr3]5+}, consisting of two parallel edge‐fused chains of anti‐SiS2‐analogous single strands 1∞{[SPr2]4+}, formed by trans‐edge sharing [SPr4]10+ tetrahedra. The arrangement of the 1∞{[S2Pr3]5+} double chains running along [001] can be described as a hexagonal rod‐packing. Chloride anions (Cl1 and Cl2) as well as the isolated, ψ1‐tetrahedral thioarsenate(III) groups [AsS3]3– (d(As–S) = 228–229 pm) consisting of three sulfur atoms (S3, S4, and S5) and an As3+ cation carrying a stereochemically active non‐bonding electron pair take care of the three‐dimensional interconnection and the charge balance of the 1∞{[S2Pr3]5+} double chains. All lone pairs at the As3+ cations of the [AsS3]3– pyramids point in the same direction parallel to the c axis of the acentric crystal structure of Pr3S2Cl2[AsS3].

A linear heterometallic bismuth-copper coordination polymer containing two types of organic ligands.

In the linear coordination polymer catena-poly[[[aqua(1,10-phenanthroline-κ(2)N,N')copper(II)]-μ-pyridine-2,6-dicarboxylato-κ(4)O(2):O(2'),N,O(6)-[(nitrato-κ(2)O,O')bismuth(III)]-μ-pyridine-2,6-dicarboxylato-κ(4)O(2),N,O(6):O(6')] dihydrate], {[Bi(III)Cu(II)(C7H3NO4)2(NO3)(C12H8N2)(H2O)]·2H2O}n, the Bi(III) cation is O,N,O'-chelated by the two pyridine-2,6-dicarboxylate ligands and O,O'-chelated by the nitrate anion, the nine coordinating atoms conferring a tricapped trigonal prismatic environment on the metal centre. Each pyridine-2,6-dicarboxylate ligand uses one of its carboxylate O atoms to bind to an aqua(1,10-phenanthroline)copper(II) unit, the Cu-O dative bonds giving rise to the formation of a ribbon motif. The Cu(II) cation exhibits a square-pyramidal geometry. The ribbon motif propagates along the shortest axis of the triclinic unit cell and the solvent water molecules are hydrogen bonded to the same ribbon.

Tridentate benzimidazole-pyridine-tetrazolates as sensitizers of europium luminescence.

We report on new anionic tridentate benzimidazole-pyridine-tetrazolate ligands that form neutral 3:1 complexes with trivalent lanthanides. The ligands are UV-absorbing chromophores that sensitize the red luminescence of europium with energy-transfer efficiency of 74-100%. The lifetime and quantum yield of the sensitized europium luminescence increase from 0.5 ms and 12-13% for the as-prepared solids to 2.8 ms and 41% for dichloromethane solution. From analysis of the data, the as-prepared solids can be described as aqua-complexes [Ln(κ(3)-ligand)2(κ(1)-ligand)(H2O)x] where the coordinated water molecules are responsible for the strong quenching of the europium luminescence. In solution, the coordinated water molecules are replaced by the nitrogen atoms of the κ(1)-ligand to give anhydrous complexes [Ln(κ(3)-ligand)3] that exhibit efficient europium luminescence. X-ray structures of the anhydrous complexes confirm that the lanthanide ion (La(III), Eu(III)) is nine-coordinate in a distorted tricapped trigonal prismatic environment and that coordination of the lanthanide ion by tetrazolate is weaker than by carboxylate.

Di-aqua-bis-(cinnamato-κ(2) O,O')cadmium.

The title complex, [Cd(C9H7O2)2(H2O)2], was obtained as an unintended product of the reaction of cadmium nitrate with hexa­methyl­ene­tetra­mine and cinnamic acid. The CdII ion lies on a twofold rotation axis and is coordinated in a slightly distorted trigonal–prismatic environment. In the crystal, the V-shaped mol­ecules are arranged in an inter­locking fashion along [010] and O—H⋯O hydrogen bonds link the mol­ecules, forming a two-dimensional network parallel to (001).

A Series of Exceptionally Robust Luminescent Coordination Polymers Based on a Bipyridyldicarboxylate Ligand and Rare‐Earth‐Metal Ions

AbstractA series of three‐dimensional rare‐earth coordination polymers, [M2(bpdc)3(H2O)4] (M = Y [1], Sm [2], Eu [3], Gd [4], Tb [5], Dy [6], Er [7], and Yb [8]) were synthesized by solvothermal reactions of 2,2′‐bipyridine‐5,5′‐dicarboxylate (bpdc) with corresponding metal salts. Single‐crystal and powder X‐ray diffraction analyses demonstrated that these coordination polymers are isostructural. The carboxyl groups of the bpdc ligand are coordinated to metal ions and the 2,2′‐bipyridine moieties are left free due to the preferable affinity of rare‐earth metals for oxygen‐donor atoms. The adjacent eight‐coordinate MO8 cores show dicapped trigonal prismatic environments; they are interconnected by carboxyl groups and are further bridged through the bipyridyl linkers to give quite dense three‐dimensional networks. Photoluminescent studies at room temperature reveal intense red and green luminescent emissions for EuIII and TbIII analogues, respectively. Furthermore, it is noteworthy that bpdc shows an effective antenna effect in sensitizing emissions from EuIII and TbIII ions. Thermogravimetric analyses demonstrate that these coordination polymers exhibit exceptional thermal stability (decomposing at T > 580 °C under N2 for compound 1). Water‐resistance measurements of these coordination polymers show excellent hydrothermal stability.

Synthesis and Crystal Structure of the New Samarium Oxyhydroxide, SmO(OH)

A single crystal of SmO(OH) was grown out of a high temperature lithium hydroxide melt and characterized by single crystal X-ray diffraction. SmO(OH) crystallizes in the monoclinic space group P21/m with a = 4.3605(3) A, b = 3.7725(3) A, c = 6.1490(4) A, and β = 108.4500(10)°. The material exhibits a three-dimensional crystal structure consisting of corner- and edge-shared SmO7 polyhedra. The samarium cation is observed in a distorted monocapped trigonal prismatic coordination environment. Two kinds of oxygen atoms are found, and these represent oxide (O2−) and hydroxide (OH−) ligands, respectively. The synthesis and crystal structure of a new samarium oxyhydroxide, SmO(OH) is reported.

Catena-Poly[[tris(acetonitrile-κN)praseodymium(III)]tris(μ-trifluoromethanesulfonato-κ2O:O′)

In the colourless title compound, [Pr(CF3O3S)3(CH3CN)3]n, the three trifluoro­methane­sulfonate anions form three bridges via O:O′-coordination between two PrIII atoms. The structure contains [Pr(NCMe)3-μ2(OTf)3—Pr(NCMe)3-μ2(OTf)3]n (NCMe is acetonitrile; OTf is trifluoromethanesulfonate) chains parallel to the a axis. The PrIII atom is nine-coordinate in a distorted tricapped trigonal-prismatic environment.

Bis-o-semiquinonato complexes of transition metals with 5,7-di-tert-butyl-2-(pyridine-2-yl)benzoxazole

New cobalt(II) (1), iron(II) (2) and manganese(II) (3) complexes of M(3,6-SQ)2L type containing 3,6-di-tert-butyl-o-benzosemiquinonato ligands (3,6-SQ) and 5,7-di-tert-butyl-2-(pyridine-2-yl)benzoxazole (L) were synthesized and characterized in details. Magnetic susceptibility measurements and spectroscopic studies have shown that all complexes include metal(II) in the high-spin state and two radical-anionic o-semiquinonato ligands. The antiferromagnetic ligand–ligand coupling in cobalt(II) and iron(II) complexes takes place, while manganese(II) complex demonstrates metal–ligand antiferromagnetic interactions. Molecular structure of Co(3,6-SQ)2L was determined by X-ray analysis. Cobalt(II) atom has a distorted trigonal prismatic environment.

Novel tris-o-semiquinonato cobalt complexes, where quinonato fragments are modified by cyclic substituents

Octacarbonyldicobalt reacts with tricyclic 5,8-di(tert-butyl)-2,3-dihydro-1,4-ethanoquinoxaline-6,7-dione and 5,8-di-tert-butyl-2,3-dihydrobenzo[b][1,4]dioxine-6,7-dione to give tris-o-semiquinonato complexes (1 and 2, respectively). X-ray structural study indicate exact trigonal prismatic environment of cobalt in 1 and slightly twisted one in 2. Rigid and flexible steric configurations of N,N′-piperazino- and O,O′-ethane-1,2-diolato-cyclic fragments of ligands are responsible for trigonal prismatic molecular geometry of 1 and twisted one for 2. Magnetic moment temperature dependences have very close shapes for 1 and 2 and correspond to S=1/2 ground state. High temperature limits exceed spin-only value calculated for three noninteracting spins on three semiquinones. Precision calorimetric study of temperature dependence of heat capacity of 1 does not detect significant anomalies.