Synthesis and transport properties of perovskite-like phases (Sr,Ba)<Subscript>4</Subscript>E<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>11 ± δ</Subscript> (E = Mn,Cr, Cu)

Synthesis of (Sr, Ba)₄Э₂Nb₂O_{11 ± δ} where E = Mn, Cr, Cu and solid solution (Sr_1?y Cu_y)_{6 ? 2x} Nb_{2 + 2x} O_{11 + 3x} is performed. By measuring the overall conductance of some solid-solution compositions it is established that the conductance increases with the cubic-lattice parameter and concentration of oxygen vacancies. Values of the conductance in humid air at T < 700°C are shown to increase as compared with dry air. Mass spectrometry analysis confirms the possibility of water incorporation into the complex-oxide structure out of a gas phase. Complex certification of samples of the composition (Sr, Ba)₄E₂Nb₂O₁₁ where E = Mn, Cr, Cu is performed. It is established that the decrease in the overall electroconductance occurs in the series Sr₄Mn₂Nb₂O₁₁ > Ba₄Mn₂Nb₂O₁₁ > Sr₄CrMnNb₂O₁₁ > Sr₄Cu₂Nb₂O₁₁. Investigation of the overall electroconductance in dry and moist atmospheres shows that the effect of humidity exerts no influence on the values of the overall electroconductance. The oxygen-ion constituent of conductance is determined by the Arzhannikov method and is also evaluated from a σ,pO₂ dependence. It is established that the presence of an element with a variable oxidation degree for compositions of the type Sr₄E₂Nb₂O₁₁ leads to an increase in the contribution made by the electronic constituent. In so doing, the magnitude of the oxygen-ion conductance practically does not alter. Thermal and mass spectrometry analyses show that, for the Sr₄E₂Nb₂O₁₁ compositions where E = Mn, Cr, Cu, there occurs no water intercalation into structure, correspondingly, there is observed no appearance of a protonic constituent of conduction.     

Geometric and electronic structure of an N,N′-ethylene-bis(salicylaldiminato) zinc(II) molecule,ZnO<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>16</Subscript>H<Subscript>14</Subscript>

Gas electron diffraction at a temperature T of 641(5) K is used to study the structure of an N,N′-ethylenebis(salicylaldiminato) zinc(II) molecule, ZnO₂N₂C₁₆H₁₄, further Zn(salen). The structure of a gaseous Zn(salen) complex has C ₂ symmetry and is characterized by a substantial turn of two chelating fragments of the ligand with respect to each other, and also by a big difference in the length of coordination bonds: r _h1(Zn-O)=1.902(7) Å r _h1(Zn-N)= 2.027(7) Å. Results of the DFT/B3LYP calculation with 6-31G* and CEP,TZV basis sets of the molecule structure well agree with the experimental data. The electronic structure of Ni(salen), Cu(salen), Zn(salen), and Zn(acacen) molecules is considered.     

Synthesis,characterization, spectroscopic,and thermal studies of imidazole complexes of metal benzenesulfonates. Crystal structure of [M(imH)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>]·(BS)<Subscript>2</Subscript> [M=Ni(II) and Co(II)]

Four novel transition metal benzenesulfonate (BS) complexes of imidazole (im) with a general formula [M(imH)₃(H₂O)₃]·(BS)₂ [M=Mn(II) (1), Ni(II) (2), Co(II) (3)] and [Cu(BS)(imH)₃]·(BS) (4) have been synthesized and characterized by physicochemical and spectroscopic methods. The complexes 2 and 3 have also been characterized by single X-ray diffraction technique. The BS anion in complexes 1–3 acts as a counter anion, while in complex 4, it acts as both ligand and counter anion. The Ni and Co complexes are isomorphous, crystallizing in the monoclinic crystal system with C2/c space group. Each metal(II) atom in 2 and 3 is octahedrally coordinated by three imidazole and three aqua ligands, adopting a mer-coordination mode with Ni(II) or Co(II) centers. In both 2 and 3, the H2C atom has bifurcated donor (O3 and O5) atoms, forming a bifurcated hydrogen bond. This hydrogen bond links the complex cation and BS anion, forming one-dimensional hydrogen-bonded supramolecular chains. The complexes exhibit different decomposition characteristics. Magnetic susceptibility measurement shows that complex 3 has orbital interactions.     

Crystal structures of chiral (R/S) (C<Subscript>8</Subscript>H<Subscript>11</Subscript>N)<Subscript>2</Subscript> · Zn(OAc)<Subscript>2</Subscript>

Two opposite configuration (R/S) of chiral complexes (C₈H₁₁N)₂ · Zn(OAc)₂ (Ia and Ib—L-(−)-) and D-(+)-isomer) were synthesized by a simple one-pot method. The crystal structures of Ia and ib determined by X-ray crystallography.     

Stable triangle (LiF)<Subscript>2</Subscript>–(KI)<Subscript>2</Subscript>–Li<Subscript>2</Subscript>CrO<Subscript>4</Subscript> of the quaternary reciprocal system Li,K∥F,I,CrO<Subscript>4</Subscript>

The quaternary reciprocal system Li,K||F,I,CrO₄ was partitioned into stable simplexes using graph theory. The system consists of five stable tetrahedra separated by four stable triangles. The chemical interaction between components was described based on the material balance written with account for occurring chemical reactions. Phase equilibria in the quasi-ternary system (LiF)₂–(KI)₂–Li₂CrO₄ were studied for the first time; in this system, the temperature and composition of a ternary eutectic were determined. The limited solubility of two liquid phases manifests itself in the concentration region adjacent to the LiF–KI quasibinary system. A three-dimensional model of the phase complex of the system was constructed in temperature– concentration coordinates.     

Study of the formation temperature of mixed LaREO<Subscript>3</Subscript> (RE ≡ Dy,Ho, Er,Tm, Yb,Lu) and NdGdO<Subscript>3</Subscript> oxides

Mixed LaREO₃ (RE ≡ Dy, Ho, Er, Tm, Yb, Lu) and NdGdO₃ oxides were prepared by thermal decomposition of the corresponding co-precipitated mixed oxalates. The decomposition of La/RE and Nd/Gd oxalates was studied by means of differential thermal analysis and thermogravimetric (DTA-TG) measurements; in particular the last step, consisting of the loss of a CO₂ molecule from the corresponding oxycarbonate, has been thoroughly investigated, as it is particularly interesting for the study of the formation temperature of mixed rare earth oxides. After the release of CO₂, the oxides crystallize in a distorted perovskitic cell or one of the structures typical of rare earth sesquioxides, depending on the cationic size difference and on the average cationic radius. The mixed rare earth oxycarbonate decomposition has been studied in comparison to the decomposition of single rare earth oxycarbonates. A trend of the mixed oxides formation temperature as a function both of the average cationic size and of the cationic sizes difference has been observed and compared to the behaviour of single rare earth oxides.     

Synthesis,structure, and properties of LnBiI<Subscript>6</Subscript>•13H<Subscript>2</Subscript>O (Ln = La,Nd)

Two new iodobismuthates with the composition LnBiI₆?13H₂O (Ln = La, Nd) were synthesized and their crystal structures were determined. The compound LaBiI₆?13H₂O crystalizes in the orthorhombic space group Pna2₁, a = 24.206(5), b = 8.405(1), c = 26.360(5) Å; the compound NdBiI₆?13H₂O crystalizes in the monoclinic space group P2₁/n, a = 14.553(3), b = 13.386(3), c = 27.541(6) Å, β = 92.80(3)°. In both crystal structures, the cations Ln(H₂O)₉³⁺ and the anions BiI₆^3– alternate, forming a NaCl-type structure, and the structures themselves differ in the arrangement of water of crystallization that leads to the formation of dissimilar systems of hydrogen bonds. Both compounds undergo decomposition when heated, which is accompanied first by a partial liberation of water molecule, followed by pyrohydrolysis to form oxoiodides LnOI as final solid products. According to optical measurements, the band gap of the obtained compounds was equal to 1.78 (La) and 1.71 (Nd) eV.     

Synthesis,properties, and crystal structure of diphenylguanidinium bis(citrato)germanate hydrate (HDphg)<Subscript>2</Subscript>[Ge(HCit)<Subscript>2</Subscript>] · 1.08H<Subscript>2</Subscript>O

Diphenylguanidinium bis(citrato)germanate hydrate (HDphg)₂[Ge(HCit)₂] · 1.08H₂O (I) was prepared for the first time (H₄Cit is citric acid, Dphg is diphenylguanidine). The composition of I was determined using elemental analysis and thermogravimetry; the coordination sites of H₄Cit and the protonation sites of Dphg were identified by IR spectroscopy. Compound I was studied by X-ray diffraction. The crystals are monoclinic, a = 11.179(2) Å, b = 7.6081(15) Å, c = 23.529(5) Å, β = 95.38(3)°, V = 1992.3(7) ų, Z = 2, space group P2₁/c, R = 0.0339 for 2498 reflections with I>2σ(I). In the [Ge(HCit)₂]^2? complex anion, the Ge atom is bond to a distorted octahedral array of six O atoms of the two tridentate chelating HCit^3? ligands (Ge-O, 1.8045–1.9555 Å). In the crystal of I, the anions and cations are combined into layers by a system of hydrogen bonds.     

Thermodynamic investigation of MF-MgF<Subscript>2</Subscript> (M = Na,K) system

The molar Gibbs energy of formation of NaMgF₃(s) in NaF-MgF₂ system and KMgF₃(s) and K₂MgF₄(s) in KF-MgF₂ system has been determined using an electromotive force (e.m.f.) technique. For this purpose, fluoride cell has been constructed for each compound using CaF₂(s) as the solid electrolyte. From the measured e.m.f. values and required Gibbs energy data available in the literature, ?_fG^o_m(T) for NaMgF₃(s), KMgF₃(s), and K₂MgF₄(s) have been calculated. To determine the stability domains of NaMgF₃(s), KMgF₃(s), and K₂MgF₄(s), the binary phase diagram NaF(s)-MgF₂(s) and KF(s)-MgF₂(s) and ternary phase diagram Na-Mg-F₂ and K-Mg-F₂ have been calculated and chemical potential diagrams of Na-Mg-F-O and K-Mg-F-O system were calculated.     

Reactions of 2,2′-Pyridyl with the cadmium(II) compounds: Synthesis,crystal structure,and luminescence properties of [Cd(Pic)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>] · H<Subscript>2</Subscript>O

The reactions of 2,2'-pyridyl, (2-Py)C(O)C(O)(2-Py), with the Cd(II) compounds under various conditions are studied. The medium and nature of the anions exert a decisive effect on the compositions and structures of the formed cadmium complexes. The reaction of cadmium diacetate with 2,2'-pyridyl in an aqueous-alcohol medium in air affords coordination compound [Cd(Рic)₂(H₂O)₂] · H₂O (I) (Pic^? is picolinate ion, CO₂C₅H₄N), and its crystal structure is determined. The crystals are monoclinic: space group P2₁/c, a = 7.499(1), b = 15.676(1), с = 12.719(1) Å, β = 94.79(1)°, V = 1490.0(2) Å3, Z = 4, ρ_calcd = 1.502 g/cm³. The molecular packing of compound I is a supramolecular 3D framework consisting of discrete complexes [Cd(Pic)₂(H₂O)₂] linked by hydrogen bonds O–H…O. The coordination sphere of Cd²⁺ contains two O atoms and two N atoms of the ligand and two water molecules. The coordination polyhedron of Cd²⁺ is a distorted octahedron.     

Study of Acidic (Tetracaprolactam) Dodecamolybdosilicate of the Composition (C<Subscript>6</Subscript>H<Subscript>11</Subscript>NO)<Subscript>4.5</Subscript>Н<Subscript>4</Subscript>[SiМо<Subscript>12</Subscript>O<Subscript>40</Subscript>]

New caprolactam dodecamolybdosilicate of the composition (C₆H₁₁NO)_4.5Н₄[SiМо₁₂O₄₀] (I) is synthesized. Chemical and crystallographic analyses, NMR and IR spectroscopic studies are performed. Compound I is found to crystallize in the monoclinic system with the space group P2₁/n. Unit cell parameters are: a = 19.945(4) Å, b = 13.340(3) Å, c = 28.110(6) Å, β = 110.75(3)°, ρ_calc = 2.232 g/cm³, М = 2350.63, Z = 4, V = 6994(3) ų.     

Reduction of Oxide Mixtures of (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + CuO) and (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) by Low-Temperature Hydrogen Plasma

The paper presents experimental results pertaining to the reduction of oxide mixtures namely (Fe₂O₃ + CuO) and (Fe₂O₃ + Co₃O₄), by low-temperature hydrogen plasma in a microwave hydrogen plasma set-up, at microwave power 750 W and hydrogen flow rate 2.5 × 10^?6 m³ s^?1. The objective was to examine the effect of addition of CuO or Co₃O₄, on the reduction of Fe₂O₃. In the case of the Fe₂O₃ and CuO mixture, oxides were reduced to form Fe and Cu metals. Enhancement of reduction of iron oxide was marginal. However, in the case of the Fe₂O₃ and Co₃O₄ mixture, FeCo alloy was formed within compositions of Fe₇₀Co₃₀, to Fe₃₀Co₇₀. Since the temperature was below 841 K, no FeO formed during reduction and the sequence of Fe₂O₃ reduction was found to be Fe₂O₃ → Fe₃O₄ → Fe. Reduction of Co₃O₄ preceded that of Fe₂O₃. In the beginning, the reduction of oxides led to the formation of Fe–Co alloy that was rich in Co. Later Fe continued to enter into the alloy phase through diffusion and homogenization. The lattice strain of the alloy as a function of its composition was measured. In the oxide mixture in which excessive amount of Co₃O₄ was present, all the Co formed after reduction could not form the alloy and part of it appeared as FCC Co metal. The crystallite size of the alloy was in the range of 22–30 nm. The crystal size of the Fe–Co alloy reduced with an increase in Co concentration.     

Structural features of phases (Na<Subscript>0.5</Subscript>R<Subscript>0.5</Subscript>)MO<Subscript>4</Subscript> and (Na<Subscript>0.5</Subscript>R<Subscript>0.5</Subscript>)MO<Subscript>4</Subscript>:R′ (R = Gd,La; R′ = Er,Tm, Yb; M = W,Mo) of the scheelite family

The structural data for single crystals of (Na_0.5R_0.5)MO₄ and (Na_0.5R_0.5)MO₄:R′ (R = La, Gd; R′ = Er, Tm, Yb; M = W, Mo) grown by the Czochralski method were studied by X-ray diffraction and analyzed. The structural characteristics of these compounds depend on the sort of cations M and R. The formation of superstructures was found in the scheelite structure, and distortion of the scheelite structure depending on the composition and preparation conditions was established (with unit cell rotation by 45° and triclinic distortion of the scheelite structure for (Na_0.5Gd_0.5)WO₄:Tm, with doubled unit cell compared to the scheelite type structure for (Na_0.5Gd_0.5)WO₄ and (Na_0.5Gd_0.5)WO₄:Yb). In the case of overstoichiometric oxygen content in the crystal, the unit cell symmetry increases to space group I4₁/amd or (Na_0.5Gd_0.5)WO₄:Yb without considerable change in the cell parameters. On the basis of experimental data, a transformation scheme for the structures in the system Na ₂ ⁺ M⁶⁺O_4?-“R³⁺M⁵⁺O₄” was proposed.     

Bis(citrato)germanates of bivalent 3<Emphasis Type="Italic">d</Emphasis> metals (Fe,Co, Ni,Cu, Zn): Crystal and molecular structure of [Fe(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>][Ge(HCit)<Subscript>2</Subscript>] · 4H<Subscript>2</Subscript>O

In continuation of a systematic study of bis(citrate)germanates, we synthesized a number of heterometallic germanium(IV) and 3d metal complexes based in citric acid (H₄Cit) with the molecular formula [M(H₂O)₆][Ge(HCit)₂] · nH₂O, where M = Fe, n = 4 (I); Co, n = 2 (II); Ni, n = 2 (III); Cu, n = 1 (IV); Zn, n = 3 (V). The complexes were characterized by elemental analysis, X-ray diffraction, thermogravimetry, and IR spectroscopy. The X-ray diffraction analysis of compound I was performed. Crystals are monoclinic, a = 10.091(4) Å, b = 11.126(4) Å, c = 10.996(4) Å, β = 100.966(6)°, V = 1212.1(8) ų, Z = 4, space group P2₁/n, R1 = 0.0561 for 2266 reflections with I > 2σ(I). Compound I is composed of centrosymmetric octahedral complexes-[Ge(HCit)₂]^2? anions and [Fe(H₂O)₆]²⁺ cations—and crystallization water molecules. Structural units in compound I are combined by a hydrogen bond system.     

Synthesis and spectral studies on NiS<Subscript>4</Subscript>, NiS<Subscript>2</Subscript>PN,NiS<Subscript>2</Subscript>P<Subscript>2</Subscript> chromophores: Single-crystal X-ray structure of [Ni(dbpdtc)<Subscript>2</Subscript>] (dbpdtc = benzyl(4-(benzylamino)phenyl)dithiocarbamate)

Three complexes of a dithiocarbamate ligand (dbpdtc = benzyl(4-(benzylamino)phenyl)dithiocarbamate), namely [Ni(dbpdtc)₂] (1), [Ni(dbpdtc)(NCS)(PPh₃)] (2) and [Ni(dbpdtc)(PPh₃)₂]ClO₄ (3) have been prepared. The complexes were characterized by IR, electronic spectroscopy and cyclic voltammetry. A single-crystal X-ray structural analysis was carried out for complex 1 and showed that the nickel is in a distorted square planar environment with a NiS₄ chromophore. For the two mixed ligand complexes, the thioureide ν _C–N values were shifted to higher wavenumbers compared to [Ni(dbpdtc)₂], suggesting increased strength of the thioureide bond due to the presence of the π-accepting phosphine. Electronic spectral studies suggest square planar geometries for the complexes. Cyclic voltammetry showed easier reduction of nickel(II) to nickel(I) in the mixed ligand complexes compared to [Ni(dbpdtc)₂].     

Preparation specifics and properties of AMn<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript> (А = Ca,Ce, and Sm) high-pressure phases

Perovskite-like phases AMn₃V₄O₁₂ (A = Ca, Ce, and Sm) were prepared under borothermic conditions (p = 7.0–9.0 GPa, T = 700–1100°C). Their X-ray diffraction structure (space group Im \(\bar 3\), Z = 2) was determined, and unit cell parameters were calculated: for CaMn₃V₄O₁₂: а = 7.40824(3) Å, for SmMn₃V₄O₁₂: а = 7.45280(8) Å, and for CeMn₃V₄O₁₂: а = 7.46965(4) Å. The temperature-dependent electrical resistivity (10–300 K) and magnetic susceptibility (2–300 K) of the prepared phases were studied.     

Synthesis,properties, and molecular and crystal structure of diantipyrylmethanium Bis(μ-tartrato)dihydroxydigermanate(IV) tetrahydrate (HDAm)<Subscript>2</Subscript>[Ge<Subscript>2</Subscript>(μ-L)<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>] · 4H<Subscript>2</Subscript>O

The complex (HDam)₂[Ge₂(μ-L)₂(OH)₂] · 4H₂O (I) (H₄L is tartaric acid, Dam is diantipyrylmethane) was synthesized for the first time. The individual character and composition of I was established by elemental analysis and X-ray diffraction. The thermal stability of I was studied. The coordination sites of H₄L in the germanium complex were determined by IR spectroscopy. The structure of I was determined by X-ray crystallography. The crystals of I are triclinic: a = 9.3098(10) Å, b = 9.8088(10) Å, c = 17.6869(10) Å, α = 84.009(10)°, β = 77.926(10)°, γ = 67.088(5)°, V = 1454.3(2) ų, Z = 2, space group P \(\bar 1\), R = 0.0628 for 6343 reflections with I > 2σ(I). The compound is composed of the complex anions [Ge₂(μ-L)₂(OH)₂]^2?, the HDam⁺ cations, and crystal water molecules. In the dimeric anion, the metal atoms are bound to two completely deprotonated ligands L^4?. The latter are coordinated to the metal through the carboxyl (av. Ge-O, 1.911(6) Å) and hydroxyl (av. Ge-O, 1.768(6) Å) oxygen atoms. The coordination of each Ge atom is completed to trigonalbipyramidal by the O atom of the hydroxy ligand in the axial position (av. Ge-O, 1.748(7) Å). Both L^4? ligands are D isomers. In the crystal, the complex anions and crystal water molecules are combined by a system of hydrogen bonds.     

Synthesis and physicochemical study of M<Subscript>4</Subscript>Na<Subscript>2</Subscript>V<Subscript>10</Subscript>O<Subscript>28</Subscript> · 10H<Subscript>2</Subscript>O (M=K,Rb, NH<Subscript>4</Subscript>)

The formation conditions and physicochemical properties of binary decavanadates M₄Na₂V₁₀O₂₈ · 10H₂O (M=K, Rb, NH₄), synthesized by crystallization from saturated solutions of the NaVO₃-MH₂AsO₄-H₂O systems, were studied by chemical analysis, X-ray powder diffraction, microscopy, thermogravimetry, and IR spectroscopy. To optimize the synthesis conditions of M₄Na₂V₁₀O₂₈ · 10H₂O, the ( 1-x)NaVO₃ · 2H₂O · xMH2AsO4-H₂O (0.2 ≤ x ≤ 0.8) isomolar series method was applied to studying the interaction in the NaVO₃-MH₂AsO₄-H₂O systems (M = K, Rb, Cs) at the 0.4 mol/L total molar concentration of NaVO₃ and MH₂AsO₄ in solutions. The studied M₄Na₂V₁₀O₂₈ · 10H₂O compounds were shown to be isostructural with triclinic crystals (Z= 1, space group P $ \bar 1 $ \bar 1 ), and their unit cell parameters were estimated.     

On the kinetics and thermodynamics of S–X (X = H,CH<Subscript>3</Subscript>, SCH<Subscript>3</Subscript>, COCH<Subscript>3</Subscript>, and CN) cleavage in the formation of self-assembled monolayers of alkylthiols on Au(111)

Abounding potential technological applications is one of the many reasons why adsorption of aliphatic thiols on gold surface is a subject of intense research by many research groups. Understanding and exploring the nature of adsorbed species, the site of adsorption and the nature of interaction between adsorbed species and the gold surface using experimental and theoretical investigations is an active area of pursuit. However, despite a large number of investigations to understand the atomistic structures of thiols on Au(111), some of the basic issues are still unaddressed. For instance, there is still no clear information about the mechanism of adsorption of alkylthiol on gold surface. Furthermore, the reactivity and mechanism of adsorption of alkylthiol is likely to differ when gold adatoms and/or vacancies in the gold layers are considered. In this work, we have tackled these issues by computing the stationary states involved in the thiols adsorption in order to shed light on the kinetics aspects of adsorption process. In this respect, we have considered a variety of thiols into consideration such as methylthiol, dimethylsulfide, dimethyldisulfide, thioacetates, and thiocyanates. We have also considered the cleavage mechanism in the clean and the reconstructed surface scenario and the structure, energetics and spin densities have been computed using electronic structure calculations. For all the studied cases, an homolytic cleavage of CH₃S–X (X = H, CH₃, SCH₃, CN, and COCH₃) bond has been found to occur upon adsorption on the gold surface.     

Exploring the Reactivity of Rh<Subscript>2</Subscript> (OAc)<Subscript>4</Subscript> with 2, 2′ -Dipyridylamine

A series of three new compounds obtained from the reaction of Rh₂(OAc)₄ and 2, 2 -dipyridylamine (Hdpa) under various conditions have been characterized. All are diamagnetic and have a Rh–Rh single bond. In Rh₂(dpa)₄, 1, there are four bridging dpa anions which bind the two Rh atoms through one pyridyl N atom and one amido N atom though two of these ligands interact further with a rhodium atom through the third N atom. In the other two compounds the Hdpa ligand is neutral. Thus Rh₂(OAc)₄(Hdpa)₂, 2, is an adduct of the well known complex dirhodium tetraacetate in which the two Hdpa ligands occupy axial positions. In the third compound, Rh₂(Hdpa)₂(OAc)₂Cl₂, 3, only two acetate bridges are present. One Hdpa molecule chelates equatorially each rhodium atom and the chloride ions are axially coordinated. The Rh–Rh distances are 2. 4005(6) and 2. 4042(8) Å for 1 and 2, respectively. For 3, the Rh–Rh distance of 2. 593(1) Å is significantly longer than those in 1 and 2 because of the presence of fewer bridging ligands.