Synthesis,crystal structures,and properties of copper(II) dicarboxylate complexes with [bis(2-pyridylcarbonyl)amido]

Four new complexes, [Cu₂(Bpca)₂(L¹)(H₂O)₂] · 3H₂O (I), [Cu₂(Bpca)₂(L²)(H₂O)₂] (II), [Cu₂(Bpca)₂(L³)] · 2H₂O (III), [Cu₂(Bpca)₂(L¹)(H₂O)] · 2H₂O (IV) (Bpca = bis(2-pyridylcarbonyl)amido, H₂L¹ = glutaric acid, H₂L² = adipic acid, H₂L³ = suberic acid, H₂L⁴ = azelaic acid) have been synthesized and characterized by single-crystal X-ray diffraction methods (CIF files CCDC nos. 1432836 (I), 1432835 (II), 817411 (III), and 817412 (IV)), elemental analyses, IR spectra. Structural analyses reveal that compounds I, II, and IV have similar structures [Cu(Bpca)]⁺ units bridged by dicarboxylate forming dinuclear units, whereas the dinuclear of compound III are edge-shared through two carboxylate oxygen atoms of different suberate anions. Hydrogen bonds are response for the supramolecular assembly of compounds I to IV. The temperature-dependent magnetic property of III was also investigated in the temperature range of 2 to 300 K, and the magnetic behaviour suggests weak antiferromagnetic coupling exchange.     

Zn-containing double complex salts formed by Keggin type polyoxotungstates: Synthesis and crystal structure

Novel double complex salts, [Zn(DMF)₆]₂[SiW₁₂O₄₀] · 2H₂O (I) and [Zn(H₂O)₂(DMF)₄][Zn(DMF)₆]₂[PW₁₂O₄₀]₂ · 6DMF (II) (DMF = N,N-dimethylformamide), were prepared by the reaction of Zn²⁺ and heteropoly acids H_x[EW₁₂O₄₀] · xH₂O (E = P, X = 3, E = Si, X = 4) in DMF. Compounds I and II were studied by X-ray diffraction (СIF files CCDC nos. 1497570 (I) and 1497571 (II)) and IR spectroscopy.     

Three cobalt(II) coordination polymers constructed from flexible bis(thiabendazole) and dicarboxylate linkers: crystal structures,fluorescence, and photocatalytic properties

Three Co(II) coordination polymers, namely, {Co(btbb)_0.5(ndc)(H₂O)}_n (1), {[Co(btbb)(bpdc)]·1.5H₂O}_n (2), and {[Co(btbp)₂(3-npa)]·2H₂O}_n (3) (btbb = 1,4-bis(thiabendazole)butane, btbp = 1,3-bis(thiabendazole)propane, H₂ndc = 2,6-naphthalenedicarboxylic acid, H₂bpdc = 4,4′-biphenyldicarboxylic acid and 3-H₂npa = 3-nitro phthalic acid) were synthesized under hydrothermal conditions. Their X-ray crystal structures show that complexes 1 and 2 both have 2D uninodal 3-connected hcb (honeycomb) structures. Complex 1 is further extended into a threefold interpenetrating 3D 4,4-connected mog (moganite) supramolecular architecture with the point symbol of {4.6⁴.8}₂{4².6².8²} by O–H···O hydrogen bonding interactions. Complex 2 shows a 3D supramolecular framework involving π···π stacking interactions. Complex 3 features a uninuclear structure, which is further assembled into an ordered 2D hydrogen-bonded-driven pattern with O–H···O and O–H···N hydrogen bonding interactions. The fluorescence spectra and photocatalytic properties of complexes 1–3 for degradation of methyl orange were investigated.     

Syntheses and luminescence of four supramolecular coordination complexes with flexible ligand

Four d ¹⁰-based complexes with chemical formulae {[Zn(L¹)₂(H₂O)₂(4,4′-Bipy)₂] (I), {[Zn₂(L¹)₄(Mi)] · 4H₂O} (II), {[Zn(L¹)₂(Phen)] · H₂O} (III) {[Cd(L¹)₂(Phen)] · 2H₂O} (IV) (HL¹ = p-hydroxy phenylacetic acid, 4,4′-Bipy = 4,4′-bipyridine, Phen = 1,10-phenanthroline, Mi = 1,4-bis(imidazol-1-yl)butane) have been synthesized and structurally characterized by single crystal X-ray diffraction (CIF files CCDC nos. 1047119 (I), 1047120 (II), 1047121 (III), 1047122 (IV)). The significant effect of assistant ligands and metal ions on assembly of I?IV has been demonstrated, which leads to the formation of distinct crystalline products. Complexes I?IV show various coordination motifs with different existing forms and coordination modes of the organic ligands. Furthermore, extend supramolecular networks are connected by secondary interactions such as hydrogen-bonding and aromatic stacking. The thermal stability and luminescent properties of the compounds were discussed in detail.     

Synthesis,crystal structures,and luminescent properties of three cluster-based heterometallic and monometallic compounds

Two heterometallic cluster compounds and one monometallic cluster compound, namely [Ni₉Co₆(PMIDA)₆(BTC)₂(H₂O)₁₂]·6H₂O (1), [Co₁₃Zn₂(PMIDA)₆(H₂O)₁₈]·6NO₃·15H₂O (2), and [Fe₁₅(PMIDA)₆(BTC)₂(H₂O)₂₂]·38H₂O (3), have been obtained under hydrothermal conditions using N-(phosphonomethyl)imino-diacetic acid (H₄PMIDA) and 1,3,5-benzenetricarboxylate acid (H₃BTC) as ligands, and structurally characterized by X-ray crystallography. Compound 1 exhibits a 3D open framework constructed from [Ni₉Co₆(PMIDA)₆(H₂O)₁₂]⁶⁺ heteronuclear clusters and BTC^3? ligands. Compounds 2 and 3 are both zero-dimensional polynuclear clusters, further extended into 3D supramolecular structures via hydrogen-bonding interactions. However, there are some differences in their crystal structures; compound 2 features an isolated spherical heteronuclear cation cluster based on PMIDA^4? ligands, such that the NO₃ ^? anions only balance the charge, whereas compound 3 is characterized as a neutral monometallic cluster incorporating two different types of organic acid ligands, namely PMIDA^4? and BTC^3?, and the two BTC^3? ligands exhibit regular distribution in each cluster. The luminescence properties of all three compounds have been investigated at room temperature.     

Syntheses,structures and properties of complexes of indole-3-propionic acid

Three complexes [Zn₂(IPA)₂(phen)₄](HIPA)₂(NO₃)₂·H₂O (1), {[Zn(IPA)₂(bipy)]·3H₂O}_n (2), and {[Mn(IPA)₂(bipy)(H₂O)]·2H₂O}_n (3) (HIPA = indole-3-propionic acid, phen = 1,10-phenanthroline, bipy = 4,4′-bipyridine) were synthesized and characterized by physico-chemical and spectroscopic methods. Complex 1 displays a zero-dimensional structure, whilst 2 and 3 show one-dimensional chains, which are linked into supramolecular networks through hydrogen bonding interactions and/or π···π stacking interactions. The luminescence properties of complexes 1 and 2 were investigated.     

Polyoxometalate-based supramolecular hybrids composed of Cu/2, 2′-dimethyl-4, 4′-bithiazole fragments extended via non-bonding S···O interactions

Four polyoxometalate-based complexes, namely [Cu^I(dm4bt)₂]₃[PMo₁₂O₄₀] (1), H₂[Cu^I(dm4bt)₂]₂{[Cu ₂ ^I (dm4bt)₃]₂[SiW₁₂O₄₀]}[SiW₁₂O₄₀] (2), [Cu^I(dm4bt)₂]₅ {[Cu^I(dm4bt)][P₂W₁₈O₆₂]} (3) and {Cu ₂ ^II (dm4bt)₂[Mo₆O₂₀]} (4) (dm4bt = 2,2′-dimethyl-4,4′-bithiazole), were synthesized hydrothermally from copper nitrate and various polyoxoanions. X-ray crystal structural analysis reveals that all four complexes have supramolecular structures, in which the dm4bt ligands coordinate with the Cu atoms to give different Cu/dm4bt fragments, which are further connected into supramolecular structures via non-bonding S···O interactions between Cu/dm4bt fragments and polyoxoanions. The crystal structures also reveal the crucial role of S···O interactions in the packing structures of complexes 1–4. The electrochemical and electrocatalytic properties of 1–3 with respect to bromate reduction were investigated.     

Synthesis,crystal structures and photocatalytic properties of four silver(I) coordination polymers based on semirigid bis(pyrazole) and carboxylic acid co-ligands

Four Ag(I) coordination polymers, formulated as [Ag(L1)(tpa)_0.5] _n (1), {[Ag(L2)(ndc)_0.5]·0.5H₂ndc} _n (2), [Ag(L3)_0.5(ndc)_0.5] _n (3) and {[Ag(L3)]·H₃bptc} _n (4) (L1 = 4,4′-bis(pyrazole-1-ylmethyl)-biphenyl, L2 = 4,4′-bis(3,5-dimethylpyrazol-1-ylmethyl)-biphenyl, L3 = 1,4-bis(3,5-dimethylpyrazol-1-ylmethyl)benzene, H₂tpa = terephthalic acid, H₂ndc = 2,6-naphthalenedicarboxylic acid, H₄bptc = 3,3′,4,4′-biphenyltetracarboxylic acid), have been hydrothermally synthesized and structurally characterized. Complex 1 features the rare binodal (4,4)-connected 2D 4,4L10 topological network with a point symbol of {3²·4.6²·7}₂{3²·6²·7²}. Complex 2 has a folded ladder-like chain structure, which is further extended into a 3D supramolecular network via O–H···O hydrogen bonding and π···π stacking interactions. Complexes 3 and 4 both possess 1D zigzag chain structures. Complex 3 is further extended into a binodal (3,4)-connected network with the point symbol of {4.8⁴·10}{6²·8²}₂ by Ag···O weak interactions, while complex 4 is further connected through O–H···O hydrogen bonding and π···π interactions to afford a 2D supramolecular structure. The photoluminescence spectra and photocatalytic properties of these complexes for degradation of methylene blue and methyl orange are reported.     

Crystal structure,spectroscopic and thermal properties of copper(II) and manganese(II) coordination polymers based on triazole-benzoic acid ligands

Two transition metal coordination polymers {[Cu(tba)₂(H₂O)]·2H₂O} _n (1) and {[Mn(Htta)₂(H₂O)₂]·2H₂O} _n (2) {Htba = 3-[1,2,4]triazol-1-yl-benzoic acid, H₂tta = 2-[1,2,4]triazol-1-yl-terephthalic acid} have been synthesized under solvothermal conditions. Both complexes have been characterized by single-crystal X-ray diffraction, X-ray powder diffraction, elemental analysis and FTIR spectroscopy. Complex 1 has a 1-D chain structure in which Cu(II) atoms are doubly bridged by tba^? ligands, which is further stabilized by hydrogen bonding and π–π stacking interactions to give a 3-D supramolecular framework. In complex 2, Mn(II) atoms are doubly bridged by Htta^? ligands to form 1-D chains, which are further connected by intermolecular hydrogen bonds to form a 3-D supramolecular framework. The electronic spectra and thermal behaviors of complexes 1 and 2 are also reported.     

Structure Modulation in Four New Coordination Polymers by In Situ Ligands Synthesis of Anthracene Derivatives and Various Auxiliary N-donor Ligands

Four novel coordination polymers, [Zn(HL¹)₂(phen)₂]·2CH₃OH·2H₂O (1), [ZnCl(HL¹)(4,4′-bipy)_0.5] _n (2), [Cd(HL¹)(L²)_0.5(2,2′-bipy)₂]·3H₂O (3), [Zn(L³)_0.5(N₃)_1.5(phen)] _n (4) (H₂L¹ = 9-(1H-tetrazole-5-yl)-10-carboxyl anthracene, H₂L² = 9,10-di-(1H-tetrazole-5-yl) anthracene, HL³ = 9-(1H-tetrazole-5-yl)-10-cyan anthracene, 1,10-phen = 1,10-phenanthroline, 4,4′-bipy = 4,4′-bipyridine, 2,2′-bipy = 2,2′-bipyridine), have been constructed by in situ ligands synthesis system. The formation of tetrazole-based ligands H₂L¹, H₂L² and H₂L³ involves the in situ Sharpless [2 + 3] cycloaddition reaction between 9,10-dicyanoanthracene (DCA) and NaN₃ in the presence of Zn²⁺/Cd²⁺ ions as Lewis-acid catalysts under hydro/solvothermal conditions. At the same time, there is also another in situ carboxyl ligand synthesis reaction by hydrolysis from nitrile in compounds 1 and 2. The four compounds have been characterized by elemental analysis, IR and single-crystal X-ray diffraction analysis. Compound 1 exhibits a butterfly-shaped mononuclear structure. Compound 2 represents a 2D framework constructed by six-membered {Zn₆} rings as secondary building units (SBUs). Compound 3 presents a dinuclear {Cd₂} structure with two butterflies “flying side by side” fashion. While compound 4 displays a 1D chain structure based on a dinuclear {Zn₂} SBUs. Moreover, the luminescence properties of 1–4 have been also investigated.     

New Thiocyanatocadmate and Halo-thiocyanatocadmates Modified by Imidazole or Triazole Derivatives: Synthesis,Structural Characterization,and Photoluminescence Property

At pH 2, the simple room-temperature self-assemblies between Cd²⁺ salts, SCN^? and organic bases created one new thiocyanatocadmate as [H₂(L1)][Cd₂(SCN)₆] (L1?=?1,4-bis(2-methyl-1H-imidazol-1-ylmethyl)benzene) 1, and two new halo-thiocyanatocadmates as [H₂(L2)][CdI₂(SCN)₂]·H₂O (L2?=?3,5-bis (4-pyridyl)-1,2,4-triazole) 2, and [CdCl(SCN)(L3)] (L3?=?3-pyrazinyl-1,2,4-triazole) 3. X-ray single-crystal diffraction analysis reveals that (a) in 1, with H₂(L1)²⁺ as the countercation, the SCN^? groups tri-bridge the Cd²⁺ centers into a 1-D chained thiocyanatocadmate; (b) 2 is only a mononuclear iodo-thiocyanatocadmate, and H₂(L2)²⁺ acts as the countercation. But via the π···π and N_pyridyl–H···N_SCN interactions, H₂(L2)²⁺ and CdI₂(SCN) ₂ ^2? aggregate together to form a 1-D supramolecular tube. Amongst the tubes, a chained water cluster with a zig-zag shape is observed; (c) 3 is an organically extended chloro-thiocyanatocadmate. Note that the report on this type of material is rather rare. It possesses a 3-D network structure with a dia topology, in which a castellated CdCl⁺ single chain is observed. L3 and Cl^? act as a mixed bridge, whereas SCN^? just serves as a terminal ligand in 3. The photoluminescence analysis indicates that the title compounds 1–3 all emit light (green light for 1, blue light for 2 and 3), which should be attributed to the ligand-centered electronic excitations.     

One Novel 3D Supramolecular Network Based on Dicobalt-Carboxylate Secondary Building Units with Polycarboxylate Ligands 1, 2, 3, 4-Butanetetracarboxylic Acid

A novel cobalt–carboxylate framework constructed from secondary building units (SBUs), {[Co₁₆(btca)₈(H₂O)₄₀]·16H₂O}_n (1) (H₄btca = 1,2,3,4-butanetetracarboxylic acid) has been hydrothermally synthesized and characterized by techniques of single-crystal X-ray diffraction analyses, elemental analyses, infrared spectra, powder X-ray diffraction and thermogravimetric analyses. The complex exhibits 2D 4-connected sql net with (4⁴ × 6²) topology symbol built from [Co₂(COO)₄(H₂O)₅] SBUs and is further extended into a 3D supramolecular architecture via strong O–H···O hydrogen bonds. Moreover, the magnetic measurements indicate complex 1 exhibit antiferromagnetic behavior.     

Co(II) and Ni(II) complexes with imidazole-containing ligands: Synthesis,structural characterization,and magnetic property

Hydrothermal reaction of Co(II) salt with 1,4-di(1-imidazolyl)benzene (L¹) and 4,4’-oxydiphthalic acid (H₄OA) yields a new complex [Co₃(HOA)₂(L¹)₄(H₂O)₄] (I). [Ni(L²)₂SO₄] · 0.5H₂O (II) can be obtained via the hydrothermal reaction of NiSO₄ · 6H₂O with 1,3-di(1H-imidazol-4-yl)benzene (L²). Complexes I and II have been characterized by single-crystal and powder X-ray diffraction (CIF files CCDC nos. 1019291 (I) and 1019292 (II)), IR, elemental, and thermogravimetric analyses. Complex I exhibits the uninodal six-connected 3D pcu framework structure of I with (4¹² · 6³) topology; Complex II consists of the uninodal four-connected 2D sql (4⁴ · 6²) networks. In addition, magnetic property of I was investigated.     

Syntheses,Crystal Structures and Luminescent Properties of Drum and Ladder-Like Organooxotin Clusters with Carbazole Ligand

Four new Organooxotin Clusters: [(p-MeC₆H₄)Sn(O)L¹]₆ (1) (HL¹ = 2-(9H-carbazol-9-yl)acetic acid), [PhSn(O)L²]₆·2C₆H₆·2H₂O (2) (HL² = 3-(9H-carbazol-9-yl)propanoic acid), [n-BuSn(O)L²]₆ (3), [(c-Hex₂Sn)₂(L¹)O(OH)]₂·3C₆H₆ (4), were synthesized with benzene being used as solvent in the reaction and characterized by elemental analysis, IR, NMR spectroscopy and X-ray crystallography diffraction analyses. Complexes 1–3 are hexanuclear organotin complexes with drum structure. Complex 4 is dimeric carboxylate tetraorganodistannoxane and shows a ladder structure. There are four crystallographically unique Sn centers in the structure of 4, which consists of a Sn₄O₂(OH)₂ ladder unit, and the ladder consists of four tins held together by four µ₃-oxygens. All the complexes show an extensive supramolecular organization in the solid state and form 1D or 2D supramolecular assembly mediated by C–H…O, C–H…π or π…π interactions. Moreover, complexes 1 and 4 exhibit good fluorescence properties in the solid state revealed by the luminescent investigation. The experimental results show the complexes may be explored for potential luminescent materials.     

Uranyl oxamate hydrates: hydrothermal synthesis,crystal structure,photophysical properties,and selective crystallization

Presented here are two isostructural uranyl coordination polymers [UO₂(EDO)(H₂O)]·H₂O (1) and [UO₂(BDO)(H₂O)]·2H₂O (2) (EDO^2-=ethylene-1,2-dioxamate; BDO^2-=butylene-1,2-dioxamate) with identical stepwise zigzag chain structure and distinct interchain hydrogen bonding interaction, prepared from hydrothermal reaction of DEEDO or DEBDO (DEEDO=diethyl ethylene-1,2-dioxamate; DEBDO=diethyl butylene-1,2-dioxamate) with uranyl ions. The monomeric uranyl-based fluorescence emissions of compounds 1 and 2 are red-shifted by about 6 and 5 nm respectively, compared to that of uranyl nitrate hexahydrate. Compound 1 has stronger emission than compound 2, but both their emissions exhibit triple-exponential decay. The photophysics of uranyl oxalate trihydrate was also investigated for comparison. The selective crystallization of compound 1 in alkaline solution was applied to the sequestration of uranyl ions, showing a kinetic preference.     

Four novel metal–organic frameworks based on 3,4,7,8-tetramethyl-1,10-phenanthroline: Syntheses,structures, and thermal properties

Four novel metal–organic frameworks, [Cu(Tmp)₂(H₂O)] · NO₃ (I) (Tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline), [Mn(Tmp)₂(H₂O)₂] · 2NO₃ · H₂O (II), [Pb(Tmp)(CH₃COO)₂] · 3H₂O (III) and [Zn(Tmp)₂(H₂O)₂] · 2NO₃ · 2H₂O (IV), have been synthesized and characterized by single crystal X-ray diffraction (CIF files CCDC nos. 88362–88365 for I–IV, respectively), IR spectroscopy, elemental analysis and thermogravimetric analysis. Both I and II complexes are crystallized in monoclinic system with space groups C2/c, P2₁/c, respectively, while III and IV complexes are crystallized in triclinic system with space groups \(P\overline 1 \). Generally, these crystal structures are stabilized by O–H···O hydrogen bonds and π–π interactions between the phenanthroline rings of neighboring molecules. Thermogravimetric analyses of compounds I–IV display considerable thermal stability.     

Examples of cation exchange in new ionic oxovanadium(IV) complexes with anions of cyclobutane-1,1-dicarboxylic acid

The results on the synthesis and study of the crystal structures of compounds based on anionic fragments {VO(Cbdc)₂}^2– formed by oxovanadium(IV) (vanadyl, VO²⁺) and two chelate-bound anions of cyclobutane-1,1-dicarboxylic acid (H₂Cbdc = C₄H₆(COOH)₂) are presented. The use of ammonium cation NH₄⁺ as a counterion in the synthesis leads to the formation of the mononuclear complex (NH₄)₂[VO(Сbdc)₂(H₂O)] · 2H₂O (I). In the case of K⁺ cation, compound [K₄(VO)₂(Сbdc)₄(H₂O)₄] _n (II) with the 3D polymeric crystal structure is formed. The reaction of compound II with Mg(NO3)2 · 6H₂O in an aqueous solution involves the partial substitution of K⁺ by Mg²⁺ cations to form 1D polymeric compound {[KMg_0.5(VO)(Сbdc)₂(H₂O)_6.5] · 3H₂O} _n (III), while a similar reaction of compound I does not afford the product of substitution of NH₄⁺ by Mg²⁺ cations (CIF files CCDC 1551021–1551023 for compounds I–III, respectively).     

Synthesis,crystal structures,luminescence, and photocatalytic properties of two 1D Co(II) coordination polymers constructed with semirigid bis(benzimidazole) and dicarboxylate ligands

Two ternary cobalt(II) coordination polymers (CPs), namely [Co(L1)(npht)] _n (1) and {[Co₂(L2)₂(npht)₂(H₂O)]·H₂O} _n (2) (L1 = 4,4′-bis(benzimidazol-1-ylmethyl)biphenyl, L2 = 1,2-bis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene, and H₂npht = 4-nitrophthalic acid) have been synthesized and structurally characterized by X-ray crystallography. Both CPs feature similar 1D infinite chains containing two distinct loops. CP 1 further forms a 3D supramolecular network via weak C–H···O hydrogen bond interactions. CP 2 shows a 1D two-layer chain structure, assembled through π–π stacking interactions. The electrochemical, luminescence, and photocatalytic activities of the two CPs for the removal of methylene blue under visible or UV light were investigated. Possible photocatalytic mechanisms are discussed.     

Syntheses,crystal structures,and properties of three two-dimensional complexes constructed by flexible (2,3-pyridylmethyl)amine

Three two-dimensional coordination polymers [Cd(2,3-Pyma)Cl₂] _n (I), {[Cd(2,3-Pyma)(1,4-Chdc)] · 4H₂O}n (II) and {[Zn₂(2,3-Pyma)(1,2,4,5-Bttc)(H₂O)₄] · 6H₂O} _n (III) (2,3-Pyma = (2,3-pyridylmethyl) amine, H₂-1,4-Chdc = 1,4-cyclohexanedicarboxylic acid, and H₄-1,2,4,5-Bttc = 1,2,4,5-benzenetetracarboxylic acid) have been synthesized and structurally characterized by single crystal X-ray crystallography (CIF files CCDC nos. 989461 (I), 1055685 (II) and 1055686 (III)). Three complexes are all twodimensional layer networks bridged by the flexible 2,3-Pyma ligands or the carboxylate ligands. It is noted that the flexible 1,4-Chdc ligands bind the Cd²⁺ ions into a helical chain structure in complex II. The photoluminescence and thermal properties are investigated.     

New complexes of tris(2-aminoethanolato-O,N)cobalt(III) sulfates: Synthesis and structure

The reaction of [Co(Etm)₃] · 3H₂O (I) with sulfuric acid affords [Co(HEtm)₃]₂(SO₄)₃ · 4H₂O (II). The change in the synthesis procedure (the direction interaction of cobalt(II) sulfate with β-aminoethanol (HEtm)) makes it possible to isolate [Co(HEtm)₃](SO₄)(HSO₄) · H₂O (III) and {[Co(HEtm)₃][Co(Etm)₃]}₂(SO₄)₃ · 7.75H₂O (IV). The X-ray diffraction analyses of compounds II–IV show that all of them are of the ionic type. In compounds II and III, the ionic structure consists of the [Co(HEtm)₃]₃₊ cations and sulfate anions in a ratio of 2: 3 and 1: 2, respectively. The basic difference in compounds II and III is the different degrees of deprotonation of the acid residues. In complex II, two anions SO ₄ ^2? are doubly deprotonated. In complex III, of the four anions found in the independent part of the unit cell of the sulfate anion two anions are monodeprotonated. In structure IV, two crystallographically independent complexes [Co(HEtm)₃]³⁺ and [Co(Etm)₃] are joined into a dimer through the O-H?O hydrogen bonding.