Conformational stabilities of dimethylmethoxyphosphine and dimethyl(methylthio)phosphine from temperature dependent infrared spectra of rare gas solutions

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500 to 400 cm⁻¹) of dimethylmethoxyphosphine, (CH₃)₂POCH₃ and dimethyl(methylthio)phosphine, (CH₃)₂PSCH₃ dissolved in liquid krypton and/or xenon have been recorded. From these data, the enthalpy differences have been determined to be 393±50 cm⁻¹ (4.71±0.60 kJ/mol), for (CH₃)₂POCH₃ with the near-cis conformer the more stable rotamer and 80±10cm⁻¹ (0.96±0.12 kJ/mol) for (CH₃)₂PSCH₃ with the cis conformer the more stable form. Complete vibrational assignments are presented for both molecules, which are consistent with the predicted frequencies obtained from the ab initio MP2/6-31G(d) calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules.     

On the vibrational spectra and conformational stability of 1,1-dimethylhydrazine from temperature dependent FT-IR spectra of krypton solutions and ab initio calculations

Variable temperature (−105 to −150 °C) studies of the infrared spectra (3500–400 cm⁻¹) of 1,1-dimethylhydrazine, (CH₃)₂NNH₂, in liquid krypton have been carried out. No convincing spectral evidence could be found for the trans conformer which is expected to be at least 600 cm⁻¹ less stable than the gauche form. The structural parameters, dipole moments, conformational stability, vibrational frequencies, and infrared and Raman intensities have been predicted from MP2/6-31G(d) ab initio calculations. The predicted infrared and Raman spectra are compared to the experimental ones. The adjusted r₀ parameters from MP2/6-311+G(d,p) calculations are compared to those reported from an electron diffraction study. The energy differences between the gauche and trans conformers have been obtained from MP2 ab initio calculations as well as from density functional theory by the B3LYP method calculations from a variety of basis sets. All of these calculations indicate an energy difference of 650–900 cm⁻¹ with the B3LYP calculations predicted the larger values. The potential function governing the conformational interchange has been predicting from both types of calculations and comparisons have been made. The barrier to internal rotation by the independent rotor model of the inner methyl group is predicted to have a value of 1812 cm⁻¹ and that of the outer one of 1662 cm⁻¹ from ab initio MP2/6-31G(d) calculations. These values agree well with the experimentally determined values of 1852±16 and 1558±12 cm⁻¹, respectively, from a fit of the torsional transitions with the coupled rotor model. For the coupled rotor model the predicted V′₃₃ (sin 3τ₀ sin 3τ₁ term) value which ranged from 190 to 232 cm⁻¹ is in reasonable agreement with the experimental value of 268±3 cm⁻¹ but the predicted V₃₃ (cos 3τ₀ cos 3τ₁ term) value of −73 to −139 cm⁻¹ is 25% smaller and of the opposite sign of the experimental value of 333±22 cm⁻¹. These theoretical and spectroscopy results are compared to similar quantities of some corresponding molecules.     

Thermotropic phase behaviour of sodium oleate as studied by FT-Raman spectroscopy and X-ray diffraction

The thermotropic behaviour of sodium oleate (NaOl) has been studied in the temperature range 10–125°C by using Fourier transform-Raman spectroscopy, X-ray diffraction and differential scanning calorimetry (DSC). The temperature dependence of conformationally sensitive bands in the CH₂ stretching (2800–2900 cm⁻¹), C–C stretching (1050–1150 cm⁻¹) and CH₃ rocking region (830–900 cm⁻¹) has been used to characterize the order/disorder behaviour of alkyl chains. It is found that in phase I, NaOl exhibits the crystalline ordered lamellar structure with a repeat period of 4.51 nm. The first broad peak in the DSC trace is due to superposition of two transitions (phase I to phase II and phase II to phase III), therefore, it is not possible to determine the lamellar structure of phase II. This broad transition from phase I to phase III is associated with the melting of methyl-sided chains and increase in gauche conformers in carboxylate-sided chains. Finally, NaOl undergoes a transition from crystalline to a liquid crystalline phase IV, which is associated with the melting of the carboxylate-sided chain.     

Study of the N2 bΠu state via 1 + 1 multiphoton ionization

Medium-resolution spectra of the N₂ b¹Π_u-X¹Σ_g⁺ band system were recorded by 1 + 1 multiphoton ionization. In the spectra we found different linewidths for transitions to different vibrational levels in the b ¹Π_u state: Δν₀ = 0.50 ± 0.05 cm⁻¹, Δν₁ = 0.28 ± 0.02 cm⁻¹, Δν₂ = 0.65 ± 0.06 cm⁻¹, Δν₃ = 3.2 ± 0.5 cm⁻¹, Δν₄ = 0.60 ± 0.07 cm⁻¹, and Δν₅ = 0.28 ± 0.02 cm⁻¹. From these linewidths, predissociation lifetimes τ_ν were obtained: τ₀ = 16 ± 3 ps, τ₁ > 150 ps, τ₂ = 10 ± 2 ps, τ₃ = 1.6 ± 0.3 ps, τ₄ = 9 ± 2 ps, and τ₅ > 150 ps. Band origins and rotational constants for the b ¹Π_uν = 0 and 1 levels were determined for the ¹⁴N₂ and ¹⁴N¹⁵N molecules.     

Proton transfer between hydrogen halides and dimethylether in nitrogen matrices. An example of infrared-induced transfer

The infrared absorption of mixtures of dimethyl ether and hydrogen halide (HX) in nitrogen at 13 K display relatively narrow bands in the range 650–800 cm⁻¹ with an isotopic ratio ν_H/ν_D larger than 1.4 and weakly halogen dependent; these features are assigned to the antisymmetric O…H…O stretching within the [(CH₃)₂ O…H…O(CH₃)₂]⁺X⁻ ion pair. With HI—ether mixtures, the intensity of the 660 cm⁻¹ band decreases under infrared irradiation of the matrix, which might be due to the transfer of the proton back to the I⁻ anion.     

The dehydroxylation of basic aluminum sulfate: An infrared emission spectroscopic study

The tridecameric aluminum polymer [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ was prepared by forced hydrolysis of Al³⁺ up to an OH/Al molar ratio of 2.2. Upon addition of sulfate, the tridecamer crystallized as the monoclinic basic aluminum sulfate Na_0.1[AlO₄Al₁₂(OH)₂₄(H₂O)₁₂](SO₄)_3.55. The dehydroxylation of the basic aluminum sulfate has been studied by Fourier transform in-situ infrared emission spectroscopy over a temperature range of 200° to 750°C at 50°C intervals. The spectrum is characterized by the sulfate ν₁ (1024 cm⁻¹), ν₃ doublet (1117 and 1168 cm⁻¹) and the ν₄ doublet (568 and 611 cm⁻¹) modes. Furthermore, minor bands assigned to nitrate are observed. Upon heating from ≈350° to 400°C major changes are observed, especially in the bandwidth and band intensities. The bands in the hydroxyl stretching region due to the Al₁₃ group disappear, whereas the bands around 1050 cm⁻¹ display various changes in bandwidths, intensities and positions associated with the dehydration and dehydroxylation of the basic sulfate and the changing of the structure into an aluminum oxosulfate. The nitrate bands diminish upon heating.     

Vibrational disequilibrium in a low-pressure Na-Catalyzed CO---N2O Flame

A high-resolution emission spectrum of a low-pressure Ar-diluted CO + N₂O → CO₂ + N₂ flame catalyzed by Na metal vapor has been obtained and examined for vibrational disequilibrium. Emission in the 1900-2400 cm⁻¹ spectral region, which includes the fundamental and “hot” bands of CO, CO₂(ν₃), and N₂O(ν₃), was recorded with high resolution and the CO emission was analyzed in detail to determine vibrational and rotational temperatures which were found to be unequal, T_v = 2050°K and T_R = 1100°K. An examination of vib-vib and vib-trans energy transfer mechanisms results in the conclusion that an excess of 14% of the chemical energy is preferentially deposited in the resonantly-coupled N₂, CO, CO₂ (ν₃), and N₂O(ν₃) vibrational modes. It is further observed that CO vibrational levels for ν > 4 are excessively populated, presumably due to quenching of Na*(3p) by CO; the flame is accompanied by intense Na D-line chemiluminescence.     

The beryllium dimer potential

The convergence of ab initio calculations of the beryllium dimer potential is examined with several basis sets orders of perturbation theory. When the atomic pair natural orbital basis set calculations are extrapolated to the complete basis set and full CI limits, the calculated parameters: R_e=2.447 Å, D_e=827 cm⁻¹, ν₀₁=212.7 cm⁻¹, ν₁₂=167.2 cm⁻¹, ν₂₃=121.5 cm⁻¹ and ν₃₄=77.7 cm⁻¹ are in good agreement with the experimental parameters: R_e=2.45 Å, D_e=839±10 cm⁻¹, ν₀₁=223.2 cm⁻¹, ν₁₂=169.7 cm⁻¹, ν₂₃=122.5 cm⁻¹, and ν₃₄=79 cm⁻¹.     

Synthesis and magnetism of the first tetranuclear copper(II)–iron(III) complexes of macrocyclic oxamides

Four novel tetranuclear macrocyclic complexes of the formula [(CuLⁱ)₃Fe](ClO₄)₃·3H₂O (i=1–4, Lⁱ are the dianions of the [14]N₄ and [15]N₄ macrocyclic oxamides, namely 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene, 2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene and 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene] have been prepared and characterized. These complexes are the first examples of oxamido-bridged Cu(II)–Fe(III) heterometallic species. Cryomagnetic studies on [(CuL¹)₃Fe](ClO₄)₃·3H₂O (1) and [(CuL³)₃Fe](ClO₄)₃·3H₂O (3) (77–300 K) revealed that the Cu(II) and Fe(III) ions interact antiferromagnetically through the oxamido bridge, with the exchange integral J=−30.8 cm⁻¹ for 1 and J=−28.7 cm⁻¹ for 3 based on . The interaction parameters have been compared with that of the related [Cu₃Mn] compound.     

Structural, spectral and thermal properties of a polymeric nickel(II) complex containing two-dimensional network

The structure of the complex [Ni(hmt)(NCS)₂(H₂O)₂]_n, assembled by hexamethylenetetramine (hmt) and octahedral Ni(II), is reported. Crystal data: Fw 351.07, a=9.885(10) Å, b=12.06(1) Å, c=12.505(8) Å, β=114.41(4)°, V=1357(1) ų, Z=4, space group=C2/c, T=173 K, λ(Mo−K)=0.71070 Å, ρ_calc=1.718 gcm⁻¹, μ=17.44 cm⁻¹, R=0.099, Rw=0.145. The tetrahedral assembling template effect of the hmt molecule is completed by two coordination bonds and two hydrogen interactions. The UV–vis absorption spectrum of this complex [Ni(hmt)(NCS)₂(H₂O)₂]_n with a two-dimensional network is determined in the range of 5000–35000 cm⁻¹ at room temperature. The observed spectrum is discussed and explained perfectly by the scaling radial theory proposed by us. The two-dimensional structure has no apparent effects on the d–d transitions of the central Ni(II) ion. The IR spectrum and the GT curve of the complex were also measured and clearly reflect its structural properties.     

Electronic absorption spectrum of Ba(MnO4)2·3H2O/Ba(ClO4)2·3H2O

Polarized absorption spectra of Ba(MnO₄)₂·3H₂O/Ba(ClO₄)₂·3H₂O mixed single crystals are reported at 4.2°K. Previous ¹T₂ → ¹A₁ assignments for the 5200 Å and 3000 Å absorption bands of MnO₄⁻ are substantiated; further support is provided for the ¹T₁ → ¹A₁ assignment of the 3600 Å absorption band of MnO₄⁻. The site-splitting of the 5200 Å ¹T₂ state is E(¹E)−E(¹A) ≈ −150 cm⁻¹; that of the 3000 Å ¹T₂ state is E(¹E)−E(¹A) ≈ 300 cm⁻¹. A significant e vibronic intensity component is observed in the 5200 Å ¹T₂ state.     

Crystalline calcium phenylphosphonate—thermodynamic data on n-alkylmonoamine intercalations

Lamellar crystalline calcium phenylphosphonate, as anhydrous Ca(HO₃PC₆H₅)₂ and hydrated Ca(HO₃PC₆H₅)₂·2H₂O compounds, were used as hosts for intercalation of polar n-alkylmonoamine molecules of the general formula CH₃(CH₂)_nNH₂ (n=0–4, 7) in water or 1,2-dichloroethane. An increase in the interlayer distance was observed. The exothermic enthalpic values for intercalation increased with the number of carbon atoms and with increasing concentration of the amines. The intercalation followed by a titration procedure in the solid/liquid interface with Ca(HO₃PC₆H₅)₂·2H₂O and Ca(HO₃PC₆H₅)₂ gave the enthalpy/number of carbons correlations: Δ_intH=−(1.74±0.43)–(1.30±0.13)n_c and Δ_intH=−(4.15±0.15)–(1.07±0.03)n_c, for water and 1,2-dichloroethane, respectively. A similar correlation Δ_intH=−(4.27±0.80)–(1.85±0.21)n_c was obtained in water by using the ampoule breaking procedure for Ca(HO₃PC₆H₅)₂·2H₂O. The increase in exothermic enthalpic values with the increase in n-aliphatic carbon atoms is more pronounced for the anhydrous compound and also when using the ampoule breaking procedure. The Gibbs free energies are negative. Positive entropic values favor intercalation in these systems.     

Strong antiferromagnetism in the dinuclear 2-pyridone complex with N–C–O bridges: A paddle-wheel analogue of the dinuclear tetracarboxylates

A novel dinuclear complex [Cu₂(μ-L)₄(HL)₂] (1) was isolated from starting 2-pyridone (HL) via a resonance and a tautomeric transformation. Each copper centre is in a square-pyramidal coordination sphere, defined by two oxygen atoms (Cu–O4 1.978(5), Cu–O11 1.964(4) Å) and two nitrogen atoms (Cu–N2 2.003(5), Cu–N3 2.007(5) Å) of four bridging deprotonated pyridin-2-olates and an oxygen atom on the top from a neutral 2-pyridone (Cu–O2 2.227(5) Å), analogous to tetracarboxylate paddle-wheel complexes. Compound 1 was compared with mixed pyridin-2-olato/methanoato analogues [Cu₂(μ-HCO₂)₂(μ-L)₂(HL)₂] · 2CH₃CN (2) and [Cu₂(μ-HCO₂)₂(μ-L)₂(HL)₂] (2a) (2a is an air stable form obtained from 2 outside mother-liquid). The EPR spectra of air stable 1 and 2a show three signals H_z1, H₂ and H_z2, typical for the binuclear systems with spin S = 1, both revealing strong antiferromagnetism 2J = −334 (1) and −324 cm⁻¹ (2a). Interestingly, only for 1 additional H₁ signal at 100 mT is noticed (D(1) = 0.293 cm⁻¹ < hν = 0.320 cm⁻¹ < D(2a) = 0.347 cm⁻¹). On the other hand, several broad signals in the 100–450 mT region, only in the high temperature spectrum for 2a are observed. These results are in agreement with the magnetic susceptibility analysis.     

Preparation and X-ray characterization of two-coordinate Cu(I) complex of aliphatic thiolato ligand: Effect of steric bulk on coordination features

We have synthesized in a single-step procedure from available copper(I) precursor at RT two Cu(I) thiolato clusters of the formula [Cu₄(μ-SCH(CH₃)₂)₆]²⁻ and [Cu₅(μ-SC(CH₃)₃)₆]⁻ as revealed by X-ray crystallography, where increased steric bulk leads to a bigger cage with some two-coordinate metal centers. In addition, we identified a mononuclear two coordinate thiolato complex with the bulkier ligand, of the formula NEt₄[Cu(SC(CH₃)₃)₂]. This is only the second example of such a complex of an aliphatic ligand that is structurally characterized. The X-ray structure reveals an S–Cu–S angle of 176.7–179.5°, with Cu–S distances of 2.14 Å.     

Preparation, properties, and reactions of metal-containing heterocycles: Part CV. Synthesis and structure of polyoxadiphosphaplatinaferrocenophanes

A series of novel heterobimetallic crown ether-like polyoxadiphosphaplatinaferrocenophanes cis-[1,1′-Fc(CH₂O(CH₂CH₂O)_nCH₂CH₂PPh₂)₂]PtCl₂ (n=1–3) (4a–c) was synthesized in good yield by cyclization of the bis(phosphine) ligands 1,1′-Fc(CH₂O(CH₂CH₂O)_nCH₂CH₂PPh₂)₂ (n=1–3) (3a–c) and (PhCN)₂PtCl₂ under high dilution conditions in CH₂Cl₂. The bisphosphines 3a–c are obtained by reaction of the corresponding diols 1,1′-Fc(CH₂O(CH₂CH₂O)_nCH₂CH₂OH)₂ (n=1–3) (1a–c) with: (i) CH₃SO₂Cl in CH₂Cl₂ and (ii) LiPPh₂ in THF. Although the X-ray crystal structure of 4a shows that the cavity is large enough for the encapsulation of small metal cations, inclusion experiments of 4a–c with Group 1 cations, and Mg²⁺, or NH₄⁺ in solution applying NMR titration and cyclovoltammetric methods reveal no evidence for the formation of host–guest complexes for 4a,b. In the case of 4c only the addition of Na⁺ or K⁺ leads to an insignificant effect.     

The electrolyte NRTL model and speciation approach as applied to multicomponent aqueous solutions of H2SO4, Fe2(SO4)3, MgSO4 and Al2(SO4)3 at 230–270 °C

This work presents chemical modeling of solubilities of metal sulfates in aqueous solutions of sulfuric acid at high temperatures. Calculations were compared with experimental solubility measurements of hematite (Fe₂O₃) in aqueous ternary and quaternary systems of H₂SO₄, MgSO₄ and Al₂(SO₄)₃ at high temperatures. A hybrid model of ion-association and electrolyte non-random two liquid (ENRTL) theory was employed to fit solubility data in three ternary systems H₂SO₄–MgSO₄–H₂O, H₂SO₄–Al₂(SO₄)₃–H₂O at 235–270 °C and H₂SO₄–Fe₂(SO₄)₃–H₂O at 150–270 °C. Employing the Aspen Plus™ property program, the electrolyte NRTL local composition model was used for calculating activity coefficients of the ions Al³⁺, Mg²⁺ Fe³⁺ and SO₄²⁻, HSO₄⁻, OH⁻, H₃O⁺, respectively, as well as molecular species. The solid phases were hydronium alunite (H₃O)Al₃(SO₄)₂(OH)₆, hematite Fe₂O₃ and magnesium sulfate monohydrate (MgSO₄)·H₂O which were employed as constraint precipitation solids in calculating the metal sulfate solubilities. A correlation for the equilibrium constants of the association reactions of complex species versus temperature was implemented. Based on the maximum-likelihood principle, the binary interaction energy parameters for the ionic species as well as the coefficients for equilibrium constants of the reactions were obtained simultaneously using the solubility data of the ternary systems. Following that, the solubilities of metal sulfates in the quaternary systems H₂SO₄–Fe₂(SO₄)₃–MgSO₄–H₂O, H₂SO₄–Fe₂(SO₄)₃–Al₂(SO₄)₃–H₂O at 250 °C and H₂SO₄–Al₂(SO₄)₃–MgSO₄–H₂O at 230–270 °C were predicted. The calculated results were in excellent agreement with the experimental data.     

Electron transfer in organometallic clusters : XI. Redox chemistry of M3(CO)12(M = Ru, Os) and PPh3 derivatives; mechanism of catalysed nucleophilic substitution

The generality of a two-electron reduction process involving an mechanism has been established for M₃(CO)₁₂ and M₃(CO)₁₂−n(PPh₃)_n (M = Ru, Os) clusters in all solvents. Detailed coulometric and spectral studies in CH₂Cl₂ provide strong evidence for the formation of an ‘opened’ M₃(CO)₁₂²⁻ species the triangulo radical anions M₃(CO)₁₂^−· having a half-life of < 10⁻⁶ s in CH₂Cl₂. However, the electrochemical response is sensitive to the presence of water and is concentration dependent. An electrochemical response for “opened” M₃(CO)₁₂²⁻ is only detected at low concentrations < 5 × 10⁻⁴ mol dm⁻³ and under drybox conditions. The electroactive species ground at higher concentrations and in the presence of water M₃(CO)₁₁²⁻ and M₆(CO)₁₈²⁻ were confirmed by a study of the electrochemistry of these anions in CH₂Cl₂; HM₃(CO)₁₁⁻ is not a product. The couple [M₆(CO)₁₈]^−/2− is chemically reversible under certain conditions but oxidation of HM₃(CO)₁₁⁻ is chemically irreversible. Different electrochemical behaviour for Ru₃(CO)₁₂ is found when [PPN][X] (X = OAc⁻, Cl⁻) salts are supporting electrolytes. In these solutions formation of the ultimate electroactive species [μ-C(O)XRu₃(CO)₁₀]⁻ at the electrode is stopped under CO or at low temperatures but Ru₃(CO)₁₂^−· is still trapped by reversible attack by X presumably as [η¹-C(O)XRu₃(CO)₁₁]⁻. It is shown that electrode-initiated electron catalysed substitution of M₃(CO)₁₂ only takes place on the electrochemical timescale when M = Ru, but it is slow, inefficient and non-selective, whereas BPK-initiated nucleophilic substitution of Ru₃(CO)₁₂ is only specific and fast in ether solvents particulary THF. Metal---metal bond cleavage is the most important influence on the rate and specificity of catalytic substitution by electron or [PPN]-initiation. The redox chemistry of M₃(CO)₁₂ clusters (M = Fe, Ru, Os) is a consequence of the relative rates of metal---metal bond dissociation, metal-metal bond strength and ligand dissociation and in many aspects resembles their photochemistry.     

The rovibrational analysis of the high-resolution IR spectrum of CD2HF below 1200 cm: an interacting tetrad of vibrational levels

The spectrum of CD₂HF was measured by high-resolution interferometric Fourier-transform IR (FTIR) spectroscopy (apodised instrumental band with:0.004 cm⁻¹ fwhm) between 800 and 1200 cm⁻¹ covering the four lowest fundamentals. A complete rotational analysis using a semi-automatic assignment procedure yields accurate band centres (ν₉: 912.2028 cm⁻¹, ν₆:964.4994 cm⁻¹, ν₅: 1050.5104 cm⁻¹, ν₄: 1093.8632 cm⁻¹) and a complete set of first-order Coriolis coupling constants. The most important couplings occur between ν₉ and ν₆ (ξ_a= 1.069 cm⁻¹, ξ_c= −0.3535 cm⁻¹) and between ν₅ and ν₄ (ξ_b= −0.80606 cm⁻¹). The analysis was guided by and compared with results from our ab initio calculations for Coriolis constants and transition moments using CADPAC at TZP/MP2 level.     

Optimised hydrothermal synthesis of multi-dimensional hybrid coordination polymers containing flexible organic ligands

In this paper, we summarise our recent research interest in the hydrothermal synthesis and structural characterisation of multi-dimensional coordination polymers. The use of N-(phosphonomethyl)iminodiacetic acid (also referred to as H₄pmida) in the literature as a versatile chelating organic ligand is briefly reviewed. This molecule plays an important role in the formation of centrosymmetric dimeric [V₂O₂(pmida)₂]⁴⁻ anionic units, which were first used by us as building blocks to construct novel coordination polymers. Starting with [V₂O₂(pmida)₂]⁴⁻ in solution, we have isolated [M₂V₂O₂(pmida)₂(H₂O)₁₀] species (where M²⁺ = Mn²⁺, Co²⁺ or Cd²⁺) via the hydrothermal synthetic approach, which were then employed for the construction of [CdVO(pmida)(4,4′-bpy)(H₂O)₂]·(4,4′-bpy)_0.5·(H₂O), [CoVO(pmida)(4,4′-bpy)(H₂O)₂]·(4,4′-bpy)_0.5, [Co(H₂O)₆][CoV₂O₂(pmida)₂(pyr)(H₂O)₂]·2(H₂O) and [Cd₂V₂O₂(pmida)₂(pyr)₂(H₂O)₄]·4(H₂O) by the inclusion of bridging organic ligands in the reactive mixtures, such as pyrazine (pyr) and 4,4′-bipyridine (4,4′-bpy). These materials can contain channel systems, and exhibit magnetic behaviour, not only due to the V⁴⁺ centres but also to the transition metal centres which establish the links between neighbouring dimeric [V₂O₂(pmida)₂]⁴⁻ anionic units. A closely related anionic moiety, [Ge₂(pmida)₂(OH)₂]²⁻, was engineered to allow the study of such crystalline hybrid materials using one- and two-dimensional high-resolution solid-state NMR.     

Tetra(μ3-hydroxo)hexa(μ2-carboxylato-O,O′)-bridged tetranuclear terbium(III) cubane complex

A novel tetranuclear terbium(III) complex [Tb₄(OH)₄(pybet)₆(H₂O)₈][Tb₄(OH)₄(pybet)₆(H₂O)₇ (NO₃)](ClO₄)₁₄·6H₂O has been synthesized and shown by X-ray crystallography to have a cubane-like Tb₄(μ₃-OH)₄(μ₂-carboxylato-O,O′)₆ core. The ligand pybet is pyridinoacetate, C₅H₅⁺N-CH₂CO₂⁻. Magnetic susceptibility data were measured for this Tb₄ complex in the range of 2.0–320 K and in fields of 1.0 G to 50.0 kG. It is concluded that either there is very weak antiferromagnetic exchange interaction (J = −0.015 cm⁻¹) or there is a small crystal-field splitting of the ⁷F₆ Tb^III ground state.