Cobalt(II) complexes with pentadentate Schiff bases 2,6-diacetylpyridine hydrazones: Syntheses and structures

Seven new cobalt(II) complexes based on the Schiff bases, 2,6-diacetylpyridine bis(isonicotinoylhydrazone) (H₂L¹) and 2,6-diacetylpyridine bis(nicotinoylhydrazone) (H₂L²), are synthesized and studied by X-ray diffraction analysis: [Co(H₂L¹)(NCS)₂] · 2.25H₂O (I), [Co(H₂L²)(NCS)₂] · CH₃OH (II), [Co(H₂L²)(NCS)(H₂O)]NCS (III), [Co(H₄L¹)(NCS)₂](NO₃)₂ · 2H₂O (IV), [Co(H₄L¹)(NCS)₂][Co(NCS)₄] · 0.75H₂O (V), [Co(H₄L²)(NCS)₂][Co(NCS)₄] · 1.75H₂O (VI), and [Co(H₂L²)(NCS)(CH₃OH)]₂[Co(NCS)₄] · 2CH₃OH (VII) (CIF files CCDC 941186 (I), 1457906 (Ia), 1457905 (II), 941187 (III), 1457907 (IV), 1457908 (V), 1457909 (VI), and 941188 (VII)). The organic ligands in the complexes act as pentadentate neutral H₂L or doubly protonated (H₄L)²⁺ coordinated through the same set of donor atoms N₃O₂. In all compounds I–VII, the coordination polyhedron of the Co²⁺ ion in a complex with the Schiff bases has a shape of a pentagonal bipyramid. The hydrazones are arranged in the equatorial plane of the bipyramid. Its axial vertices are occupied by the nitrogen atoms of the NCS￣ anions in compounds I, II, and IV–VI and by the nitrogen atoms of NCS￣ and oxygen of the water molecule in compound III or methanol in compound VII. The NO ₃ ^- anions or [Co(NCS)₄]^2￣ complex anions obtained by the reactions are involved along with the NCS￣ anions in the formation of compounds IV–VII.     

Synthesis and properties of copper(II) complexes with a chiral dioxatetraazamacrocyclic ligand based on a natural monoterpene, (+)-3-carene

The copper(II) compounds [CuL](NO₃)₂ · H₂O (I), [CuL](ClO₄)₂ · H₂O (II), CuLCl₂ · 3H₂O (III), and CuLBr₂ · 4H₂O (IV), where L is a chiral dioxatetraazamacrocyclic ligand based on the natural monoterpene (+)-3-carene, have been synthesized. According to IR and EPR spectroscopy, L acts as a tetradentate chelating ligand coordinated through the N atoms of the NH and C=N groups. The NO ₃ ^? anions in I and the ClO ₄ ^? anions in II are outer-sphere. I and II have a planar coordination core CuN₄, III has a CuN₄ClO coordination core, and IV has a CuN₄Br₂ coordination core.     

Uranyl Methacrylate Complexes with Carbamide and Methylcarbamide: Synthesis and Structure

The synthesis and X-ray diffraction and IR spectroscopic study of (UO₂)₂(mac)₄(L)₃ · H₂O crystals, where mac^– is the methacrylate ion C₃H₅COO^– and L is carbamide (I) or methylcarbamide (II), have been performed. Complexes I and II have a homotypic structure: crystals contain two kinds of mononuclear uranium-containing complexes, i.e., cationic [UO₂(mac)(L)₃]⁺ and anionic [UO₂(mac)₃]^–. The crystallographic formula of complexes in structures I and II is AB⁰¹M ₃ ¹ + AB ₃ ⁰¹ (A =UO₂²⁺ B⁰¹ = mac^–, M¹ = L). The uranium-containing complexes in structures I and II are linked into a framework by means of electrostatic interactions and a system of hydrogen bonds. Despite the similar compositions and structures of the uranium-containing complexes, their packings into a three-dimensional framework appreciably differ from each other.     

Topological insights in polynuclear Ni/Na coordination clusters derived from a schiff base ligand

This article presents the syntheses, crystal structures, topological features and magnetic properties of two Ni^II/Na^I coordination clusters formulated [Ni ₃ ^II Na(L1)₃(HL1)(MeOH)₂] (1) and [Ni ₆ ^II Na(L1)₅(CO₃)(MeO)(MeOH)₃(H₂O)₃]·4(MeOH) 2(H₂O) [2 4(MeOH) 2(H₂O)] where H₂L1 is the semi-rigid Schiff base ligand (E)-2-(2-hydroxy-3-methoxybenzylideneamino)-phenol). Compound 1 possesses a rare Ni ₃ ^II Na^I cubane (3M4-1) topology, and compound 2 is the first example in polynuclear Ni/Na chemistry that exhibits a 2,3,4M7-1 topology.     

Synthesis,crystal structure,and luminescent properties of silver complexes with 2-methylquinoline

The complexes [AgL₂(NO₃)] (I) and [AgL₂(CH₃SO₃)] · H₂O (II) (L is 2-methylquinoline, C₁₀H₉N) have been synthesized and structurally characterized by single-crystal X-ray diffraction. Crystals of I are monoclinic, space group P2₁/n, a = 9.296(1) Å, b = 13.495(1) Å, c = 14.931(1) Å, β = 95.06(1)°, V = 1865.8(3) ų, ρ_calc = 1.624 g/cm³, Z = 4. Crystals of II are monoclinic, space group P2₁/n, a = 13.147(1) Å, b = 11.767(1) Å, c = 13.814(1) Å, β = 96.06(1)°, V = 2124.3(3) ų, ρ_calc = 1.599 g/cm³, Z = 4. Compounds I and II are composed of discrete complexes of similar structure but with different orientation of the methyl groups of ligand L (trans and cis arrangement, respectively). Both anions, NO ₃ ^- and CH₃SO ₃ ^- function as a chelating weakly bound ligand for the Ag⁺ ion. The presence of water molecules in II is favorable for the formation of dimeric supramolecular moieties between the centrosymmetrically arranged Ag⁺ complexes with 2-methylquinoline. The luminescence spectra of solid complexes I and II showed a bathochromic shift as compared to the spectrum of L in acetonitrile. Complexes I and II have been characterized by ¹H and ¹³C{H} NMR spectra in CD₃CN.     

Syntheses,Structures, and Properties of Two Zn(II)/Ag(I) Complexes Assembled from Tetracarboxylic Acids and N-Donor Ligands

Two new complexes {[Zn(H₂L)(Bpp)] · H₂O} _n (I) and {[Ag(H₃L)(Bpp)] · 0.25H₂O} _n (II) (H₄L = 5-(2,3-dicarboxy phenoxy) isophthalic acid, Bpp = 1,3-bis(4-pyridyl)propane) were prepared and characterized by single crystal X-ray diffraction (XRD) (CCDC nos. 1578523 (I), 1578529 (II)), element analysis and powder XRD. Compound I showed a one-dimensional chain structure, in which the zinc(II) ion is fourcoordinated with a tetrahedral geometry. Compound II is a 1D chain structure with the H₃L– suspension arms. Complexes I and II are further extended into three-dimensional supramolecular framework via hydrogen bonds and π–π interactions. The solid state luminescent properties of compounds I and II have been investigated.     

Crystal chemical analysis of structures of the unsaturated tetraazamacrocyclic gold(III) complexes

The detailed comparative study is carried out for crystal structure packings of the following gold(III) complexes with unsaturated ligands: [Au(C₁₄H₂₂N₄)]Br (I), [Au(C₁₄H₂₃N₄)](ClO₄)₂ (II), [Au(C₁₄H₂₄N₄)](H₃O)(ClO₄)₄ (III). The determining role in the topological pattern of packings I–III belongs to the compositions and structures of the cations along with the ability of the ions of the complexes to act as donors and acceptors of hydrogen bonds. The 3D packings of complexes I and II containing iminate six-membered rings are determined and stabilized by a wide network of weak hydrogen bonds (C–H…π, C–H…Au, and C–H…Br(O)) and short contacts Au(N)…O (in structure II). The structure of imine complex III is characterized by one-dimensional piles formed due to hydrogen bonds O(w)–H…O and contacts Au…O of the О(2) atom of anion Сl(1)О ₄ ^- with cations (H₃O)⁺ and [Au(C₁₄H₂₄N₄)]³⁺ (CIF files CCDC 251258 (I), 276132 (II), and 287784 (III)).     

Synthesis and Structure of Different-Metal Different-Ligand Germanium(IV) and Cobalt(II) or Copper(II) Complexes with 1-Hydroxyethylidenediphosphonic Acid and 1,10-Phenanthroline

Different-metal different-ligand complexes [{Co(Phen)₃}₂{Co(Phen)(H₂O)₄}₂][{Ge(μ-OH)(μ- Hedp)}₆Cl₂] (I), [{Cu(Phen)₂(H₂O)}₂(HPhen)₂][Ge(μ-OH)(μ-Hedp)]₆ · 20H₂O (II) (H₄Hedp = 1-hydroxyethylidenediphosphonic acid, Phen = 1,10-phenanthroline) were synthesized and studied by X-ray diffraction. According to X-ray diffraction data (CIF files CCDC nos. 1573112 (I), 1573113 (II)), compounds I and II are cation–anion type complexes in which the anions are represented by {[Ge(μ-OH)(μ-Hedp)]⁶}^6– and, in the case of I, two additional Cl^– ions, while the cations are [Co(Phen)₃]²⁺, [Co(Phen)(H₂O)₄]²⁺ in I and [Cu(Phen)₂(H₂O)]²⁺, HPhen⁺ in II. In the crystals of compounds I and II, the cations, anions, and water molecules are combined by numerous intermolecular hydrogen bonds, giving rise to a 3D network.     

Three metal complexes based on tetrazolyl ligands: Hydrothermal syntheses,crystal structures,and fluorescence properties

Three new complexes based on 1-tetrazole-4-imidazole-benzene (Tibz), namely, [Cd(Tibz)₂(H₂O)₂] _n (I), [Mn(Tibz)₂(H₂O)₄] · 2H₂O (II) and [Co(Tibz)₂(H₂O)₄] · 2H₂O (III) have been synthesized through hydrothermal method and structurally characterized by element analyses, IR spectroscopy and single-crystal X-ray diffraction analyses (CIF files CCDC nos. 1443867 (I), 1443868 (II), 1443869 (III)). Single-crystal X-ray diffraction reveals that complex I is a 1D double-chain architecture, II and III are both mononuclear complexes. The results of single-crystal X-ray diffraction analyses indicate that the hydrogen bond and π··· π stacking exist in the complexes, which make great contribution to the stabilities of complexes I–III. The fluorescent properties of these complexes have also been studied in the solid state at room temperature.     

Supramolecular Heteroleptic Copper(II) Carboxylates: Synthesis,Spectral Characterization,Crystal Structures,and Enzyme Inhibition Assay

Two new complexes of substituted phenyl acetic acids with CuSO₄ · 5H₂O and 2,2′-bipyridine (Bipy) with formula [CuL(Bipy)₂]L · nH₂O, where L = 2-ClC₆H₄CH₂COO^– (I), 2-CH₃-3-NO₂C₆H₃CH₂COO^– (II) and n = 3 (I); 4 (II), have been synthesized. These complexes have been characterized by elemental analysis, FT-IR and X-ray crystal diffraction (CIF file CCDC nos. 1487707 (I), 1487708 (II)). Both complexes are mononuclear and crystallize in the triclinic space group P1?. In both complexes two molecules of Bipy bind equatorially with metal atom and one molecule of substituted phenyl acetic acid binds at axial position giving rise to a distorted five coordinated geometry around copper atom, while the second oxygen atom of carboxylate ligand appears to occupy the sixth position resulting in highly distorted six coordination environments around metal center in both complexes. However, another molecule of substituted phenyl acetic acid along with water molecules lies as co-crystal within the crystal lattice. Two bipyridine molecules in both complexes are lying in different planes and are oriented at dihedral angle of 63.89(8)° and 74.99(11)° in complexes I and II, respectively. Extensive hydrogen bonding because of water molecules present in crystal lattice plays a vital role in the formation of the 3D structure. Additionally, other weak interactions such as π–π interactions markedly influence the supramolecular structure. An investigation of DNA binding ability of both complexes using UV-visible spectroscopy and anti-diabetic capacity is also presented. Results revealed that synthesized complexes bind with SSDNA through intercalation as well as groove binding mode with K_b values of 2.45 × 10⁴ and 7.72 × 10³ M^–1 for complex I and II, respectively. Complex II strongly inhibits in-vitro α-glucosidase with IC₅₀ value of 30.4 μM, while complex I moderately inhibits in-vitro α-amylase with IC₅₀ value of 69.9 μM. Acarbose was employed as standard in both assays.     

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.     

Coordination assemblies of rigid–flexible 1,3-bis(5-(pyridine-2-yl)-1,2,4-triazole-3-yl)propane ligands with MCl<Subscript>2</Subscript> (M = Fe,Co, Cu or Zn): structural diversity and mass spectra

Reactions of the rigid–flexible N-heterocycle 1,3-bis(5-(pyridine-2-yl)-1,2,4-triazole-3-yl) propane (H₂L) with MCl₂ (M = Fe, Co, Cu or Zn) gave coordination complexes, {[Fe ₂ ^III Cl₄(H₂L)₂]·2Cl}·EtOH·H₂O (1), {[Co₃Cl₅(HL)]·H₂O} _n (2), {[Co₄Cl₄(H₂L)₂(H₂O)₄]·[CoCl₄]₂}·H₂O (3), [Cu₂Cl₃(HL)(H₂O)]₆·5H₂O (4), [Cu ₂ ^II Cu^ICl₄(HL)] _n (5), {[Zn₂Cl₂(L)H₂O]·H₂O} _n (6) and [Zn₄Cl₆(HL)₂] (7), which have been characterized by single-crystal X-ray diffraction. Structural analysis reveals that the pyridine triazole ligand attains versatile coordination modes in these complexes. Complexes 1, 3, 4 and 7 consist of 0D clusters with binuclear or tetranuclear units; complex 2 presents a 2D network accompanied by HL^? and chloride bridges; complexes 5 and 6 show 1D chains with [Cu₃] and [Zn₂] subunits. In addition, the electrospray ionization mass spectrometry properties of selected complexes were investigated, revealing the stabilities and structural states of these complexes in solution. These results indicate that H₂L is an excellent multiconnection linker for the construction of diverse coordination complexes.     

Syntheses and crystal structures of hydrated complexes of strontium and barium bromides with 18-crown-6

Two complexes, namely, triaqua(18-crown-6)strontium dibromide monohydrate (I) and diaquabromo(18-crown-6)barium bromide (II), are synthesized. Their crystal structures are determined by X-ray diffraction analyses. For complex I, space group C2/c, a = 17.547 Å, b = 10.246 Å, c = 14.786 Å, β = 123.08°, Z = 4. For complex II, space group Pnma, a = 17.753 Å, b = 17.465 Å, c = 6.629 Å, Z = 4. The structures are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.056 (I) and 0.042 (II) for 2696 (I) and 2440 (II) independent reflections (CAD-4 automated diffractometer, λMoK _α radiation). Both complex cations—randomly disordered [Sr(18C6)(H₂O)₃]²⁺ in complex I and [BaBr(18C6)(H₂O)₂]⁺ in complex II—are of the host-guest type. The Sr²⁺ (Ba²⁺) cation resides in the cavity of the 18-crown-6 ligand and coordinated by all six O atoms. In the structures complexes I and II, the coordination polyhedra of the Sr²⁺ and Ba²⁺ cations (coordination number 9) can be described as distorted hexagonal bipyramids with one apex at the O atom of the water molecule in complex I or at the Br^? ligand in complex II and the other split apex at the O atoms of two water molecules.     

Ln(III) metal-organic frameworks with 5-nitroisophthalate ligands: Crystal structures and luminescent properties

Two new Ln(III) metal-organic frameworks (MOFs) based on 5-nitroisophthalic acid (H₂L), namely [Pr₄(L)₆(H₂O)₄] _n (I) and [Gd(L)(FA)(H₂O)₂] _n (II) (HFA = formic acid), were prepared by solvothermal reactions and structurally characterized by IR, elemental analysis, XRD, and single crystal X-ray diffraction (CIF files CCDC nos. 971379 (I) and 971380 (II)). A 3D {4.6²}{4¹⁰.6¹⁷.8⁹}{4³}₂ topology framework of I and a 3D {4.6² ₂}{4².6¹⁰.8³} topology network of II are constructed respectively with different synthetic conditions. Four kinds of coordination modes are observed for dicarboxylate in these two MOFs in total. Notably, the in situ hydrolysis of DMF solvates leads to the formation of formate ions that was observed in the structure of II. Moreover, the luminescent properties of both complexes and corresponding ligand have been investigated.     

New copper(II) coordination compounds with 1,3-bis(5-(pyridin-2-yl)-1,2,4-triazol-3-yl)propane

Two new copper(II) complexes with 1,3-bis(5-(pyridin-2-yl)-1,2,4-triazol-3-yl)propane (H₂L), [Cu₂(HL)Cl₃] · H₂O (I) and [Cu(H₂L)](ClO₄)₂ (II), were described. The compounds were characterized by elemental analysis, IR spectroscopy, and magnetochemical data. According to X-ray diffraction data (CIF files CCDC nos. 1497511 (I), 1497512 (II)), complex I is binuclear and the metal cations are bound by the nitrogen atoms of the triazole ring and by the chloride anion. Complex II is mononuclear. Analysis of the temperature dependence of the magnetic susceptibility of I attests to the antiferromagnetic coupling of paramagnetic centers (–2J = 18 cm^–1). Exchange channels are analyzed by means of density functional theory (B3LYP/6-311G(d)) using the broken symmetry approach.     

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 and crystal structures of (2.2.2-cryptand)rubidium chloride and bromide hydrates

Two complexes, (2.2.2-cryptand)rubidium chloride and bromide hydrates [Rb(Crypt-222]Hal · 3.5H₂O (Hal = Cl (I) and Br (II)), are synthesized. The structures of isomorphic crystals of compounds I and II are studied by X-ray diffraction analysis. The crystals are trigonal: space group P \(\overline 3 \), Z = 2; I: a = 11.810 Å, c = 11.302 Å; II: a = 11.890 Å, c = 11.402 Å. The structures are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.060 (I) and 0.077 (II) for 2650 (I) and 2700 (II) independent reflections (CAD-4 automated diffractometer, λMoK _α radiation). In crystals of complexes I and II, the [Rb(Crypt-222)]⁺ cation of the host-guest type lies on the crystallographic axis 3 and has the approximate symmetry D ₃. In complexes I and II, the coordination polyhedron of the Rb⁺ cation is a two-base-centered trigonal prism somewhat distorted to an antiprism. The crystals of compounds I and II contain H-bonded disordered cubes of the water molecules and Cl^? or Br^? anions.     

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.     

(18-Crown-6)(nitrato-<Emphasis Type="Italic">O,O</Emphasis>′)potassium and (18-crown-6)(nitrato-O,O′)potassium<Subscript>(0.91)</Subscript>silver<Subscript>(0.09)</Subscript>: Synthesis and crystal structures

Two complexes with similar compositions are synthesized: (18-crown-6)(nitrato-O,O′)potassium (I) and (18-crown-6)(nitrato-O,O′)potassium_(0.91)silver_(0.09) (II). Their isomorphic orthorhombic crystals (space group P2₁2₁2₁, Z = 4) are studied by X-ray diffraction analysis. Structure I (a = 8.553 Å, b = 11.967 Å, c = 17.871 Å) and structure II (a = 8.540 Å, b = 11.956 Å, c = 17.867 Å) are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.044 (I) and 0.055 (II) for all 2385 (I) and 2379 (II) measured independent reflections. Complex molecules [K(NO₃)(18-crown-6)] in structure I and [K_0.91Ag_0.09(NO₃)(18-crown-6)] in compound II are of the host-guest type and rather similar in structure. Their 18-crown-6 and NO ₃ ^? ligands are disordered over two orientations. The K⁺ cation in complex I and the mixed cation (K_0.91Ag_0.09)⁺ in complex II reside in the cavity of the disordered 18-crown-6 ligand and is coordinated by its six O atoms and by two disordered O atoms of the NO ₃ ^? . ligand. The coordination polyhedron (CN = 8) of the K⁺ cation in complex I and that of (K_0.91Ag_0.09)⁺ cation in complex II is a distorted hexagonal pyramid with a base of six O atoms of the 18-crown-6 ligand and a split vertex at two O atoms of the NO ₃ ^? ligand.     

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.