Metal complexes of 1-methyl-3,4-diphenylpyrazole,a ligand formed by the reaction between benzil and N,N,-dimethylhydrazine

New complexes of the general formulae MnX₂L₂ (X = Cl,Br), MnBr₂L₃, CoX₂L₂ (X = Cl, Br, I, NCS, NO₃), NiX₂L₂ (X = Cl, NO₃), NiBr₂L₃·H₂O, NiL₂L₄·H₂O, CuCl₂L, CuBr₂L₂·H₂O, Cu(NO₃)₂L₂, ZnX₂L₂ (X = Cl, Br, NO₃, Zn(NCS)₂L₂·H₂O, CdX₂L₂ (X = I, NO₃) and HgCl₂L, where L is 1-methyl-3,4-diphenylpyrazole, have been prepared and characterized by elemental analysis, conductivity measurements, magnetic moments and spectral (¹H-NMR, IR and electronic) studies. The ligands is formed by the reaction between benzil and N,N-dimethylhydrazine. The nitrogen of the >CN bond is the donor atom to the metal ions. The bis-ligand halide complexes are pseudotetrahedral, while the nitrate complexes contain octahedrally coordinated metal ions. The IR spectra of MCl₂L (M = Cu, Hg) are indicative of the presence of both terminal and bridging metal-halogen bonds supporting polymeric structures. The stereochemistry and the nature of the nickel(II) complexes are markedly dependent upon the anions; the chloride complex is pseudotetrahedral, the iodide square planar, the nitrate polymeric octahedral, while the proposed structural formula for NiBr₂L₃·H₂O comprises Nickel(II) atoms present in both square planar and octahedral coordination environments.     

Coordinated 2-halo-1,3,2-dioxaphosphorinane ligands. II. Syntheses and 13C, 31P and 95Mo NMR and IR spectroscopic characterization of some Cr and Mo pentacarbonyl complexes of 2-substituted-4-methyl-1,3,2-dioxaphosphorinanes

A study of the reactions of M(CO)₅(P(OCH₂CH₂CH(Me)O)Cl) (M=Cr, Mo) with a variety of nucleophiles of the type HER (E=NH, O, S; R=H, alkyl, aryl) is reported. The ¹³C, ³¹P and ⁹⁵Mo NMR and IR spectral data for the M(CO)₅(P(OCH₂CH₂CH(Me)O)ER) complexes is presented and compared to that previously reported for some Mo(CO)₅(P(OCH₂CMe₂CH₂O)ER) complexes. This comparison provides insight into the manner in which variations in the metal and in the substitution on the 1,3,2-dioxaphosphorinane ring affect the electron density distribution within these complexes.The results from a study of the rates of chloride substitution by n-propylamine in the M(CO)_s(P(OCH₂CH₂CH(Me)O)Cl) complexes are also presented. These rates are compared with those previously reported for chloride substitution by n-propylamine in the Mo(CO)₅(P(OCH₂CMe₂CH₂O)Cl) and Mo(CO)₅(Ph₂PCl) complexes. These comparisons, in conjunction with the NMR and IR studies, suggest that both the position of the Me groups on the phosphorinane ring and the amount of electron density on the P have significant effects upon the rate of chloride substitution in these complexes.     

Synthetic, EPR spectroscopic, magnetic and X-ray crystallographic structural studies on copper(II) complexes of the tridentate N2S donor ligand formed from 6-methyl-2-formylpyridine and S-methyldithiocarbazate (Hmpsme)

New copper(II) complexes of general empirical formula, Cu(mpsme)X · xCH₃COCH₃ (mpsme = anionic form of the 6-methyl-2-formylpyridine Schiff base of S-methyldithiocarbazate; X = Cl, N₃, NCS, NO₃; x = 0, 0.5) have been synthesized and characterized by IR, electronic, EPR and susceptibility measurements. Room temperature μ_eff values for the complexes are in the range 1.75-2.1 μ_B typical of uncoupled or weakly coupled Cu(II) centres. The EPR spectra of the [Cu(mpsme)X] (X = Cl, N₃, NO₃, NCS) complexes reveal a tetragonally distorted coordination sphere around the mononuclear Cu(II) centre. We have exploited second derivative EPR spectra in conjunction with Fourier filtering (sine bell and Hamming functions) to extract all of the nitrogen hyperfine coupling matrices. While the X-ray crystallography of [Cu(mpsme)NCS] reveals a linear polymer in which the thiocyanate anion bridges the two copper(II) ions, the EPR spectra in solution are typical of a magnetically isolated monomeric Cu(II) centres indicating dissociation of the polymeric chain in solution. The structures of the free ligand, Hmpsme and the {[Cu(mpsme)NO₃] · 0.5CH₃COCH₃}₂ and [Cu(mpsme)NCS]_n complexes have been determined by X-ray diffraction. The {[Cu(mpsme)NO₃] 0.5CH₃COCH₃}₂ complex is a centrosymmetric dimer in which each copper atom adopts a five-coordinate distorted square-pyramidal geometry with an N₂OS₂ coordination environment, the Schiff base coordinating as a uninegatively charged tridentate ligand chelating through the pyridine and azomethine nitrogen atoms and the thiolate, an oxygen atom of a unidentate nitrato ligand and a bridging sulfur atom from the second ligand completing the coordination sphere. The [Cu(mpsme)(NCS)]_n complex has a novel staircase-like one dimensional polymeric structure in which the NCS⁻ ligands bridge two adjacent copper(II) ions asymmetrically in an end-to-end fashion providing its nitrogen atom to one copper and the sulfur atom to the other.     

N-(2-Pyridyl)acetamide complexes of palladium(II), cobalt(II), nickel(II), and copper(II)

N-(2-Pyridyl)acetamide (aapH) complexes of palladium(II), cobalt(II), nickel(II), and copper(II) have been studied by means of magnetic susceptibilities, and infrared, electronic, and PMR spectra. In the octahedral complexes M(aapH)₂X₂(M = Co, Ni, Cu; X = Cl, Br, NCS, NO₃), bidentate aapH is chelated through the pyridine-N and amid-O atomes, whereas in the square-planar Pd(aapH)₂X₂ (X = Cl, Br) unidentate aapH is coordinated through the pyridine-N atom alone. Under alkaline conditions aapH is deprotonated in the presence of palladium(II) to form Pd(aap)₂·4H₂O, aap being an anionic bidentate ligand and chelating through the pyridine-N and amide-O atoms.     

The preparation and structural elucidation of uranium (VI) complexes and salts of the phosphorus ylides Ph3PCHCOPh, Ph3PC(COMe)(COPh) and Ph3PCHCOOCH2CH3

The reaction in methanol of the phosphorus ylides Ph₃PCHCOPh, benzoylmethylenetriphenylphosphorane (BPPY), and Ph₃PC(COMe)(COPh), α-acetyl-α-benzoylmethylenetriphenylphosphorane (ABPPY) with UO₂(NO₃)₂ · 6H₂O at 273 K leads to the formation of O-coordinated bis(ylide)-uranium (VI) complexes of the type [UO₂(ylide)₂(NO₃)₂], whereas the reaction of BPPY and UO₂(NO₃)₂ · 6H₂O under reflux in benzene yields the salt . The reaction of Ph₃PCHCOOCH₂CH₃, carbethoxymethylenetriphenylphosphorane (EPPY) with UO₂(CH₃COO)₂ · 2H₂O produces the salt [H-EPPY]⁺[UO₂(CH₃COO)₃]⁻. The structures of the free ylides ABPPY and EPPY are also discussed.     

The synthesis and characterisation of some MnLnX2 complexes (n = 1, L = pyridine, 4-pyrrolidinopyridine,X = Cl,Br, I,NCS; n = 1, L = EtOH,X = Cl,Br; n = 2, L = EtOH,X = I,NCS)

Mono-ligand complexes MnLX₂ (L = pyridine, 4-pyrrolidinopyridine, X = Cl, Br, I, NCS) have been prepared. The pyridine complexes contain only bridging halide and pseudohalide groups, whereas the 4-py complexes contain both bridging and terminal bound anions. Ethanol is coordinated in Mn(EtOH)X₂ (X=C1, Br) and Mn(EtOH)₂X₂ (X=I, NCS). Although the MnLX₂ complexes have the same stoichiometry as the Mn(PR₃)X₂complexes none show any activity towaxds binding dioxygen either in the solid state or in solution.     

Synthesis, structure and properties of di- and mononuclear ruthenium(III) complexes with N-(benzoyl)-N′-(salicylidene)hydrazine and its derivatives

The reactions of [Ru(PPh₃)₃Cl₂], N-(benzoyl)-N′-(5-R-salicylidene)hydrazines (H₂bhsR, R = H, OCH₃, Cl, Br and NO₂) and triethylamine (1:1:2 mole ratio) in methanol afford mononuclear ruthenium(III) complexes having the general formula trans-[Ru(bhsR)(PPh₃)₂Cl]. In the case of R = H, a dinuclear ruthenium(III) complex of formula [Ru₂(μ-OCH₃)₂(bhsH)₂(PPh₃)₂] has been isolated as a minor product. The complexes are characterized by elemental analysis, magnetic, spectroscopic and electrochemical measurements. The crystal structures of the dinuclear complex and two mononuclear complexes have been determined. In the dinuclear complex, each metal centre is in distorted octahedral NO₄P coordination sphere constituted by the two bridging methoxide groups, one PPh₃ molecule and the meridionally spanning phenolate-O, imine-N and amide-O donor bhsH²⁻. The terminal PPh₃ ligands are trans to each other. In the mononuclear complexes, bhsR²⁻ and the chlorine atom form an NO₂Cl square-plane around the metal centre and the P-atoms of the two PPh₃ molecules occupy the remaining two axial sites to complete a distorted octahedral NO₂ClP₂ coordination sphere. All the complexes display ligand-to-metal charge transfer bands in the visible region of the electronic spectra. The cryomagnetic measurements reveal the antiferromagnetic character of the diruthenium(III) complex. The low-spin mononuclear ruthenium(III) complexes as well as the diruthenium(III) complex display rhombic EPR spectra in frozen solutions. All the complexes are redox active in CH₂Cl₂ solutions. Two successive metal centred oxidations at 0.69 and 1.20 V (versus Ag/AgCl) are observed for the dinuclear complex. The mononuclear complexes display a metal centred reduction in the potential range −0.53 to −0.27 V. The trend in these potential values reflects the polar effect of the substituents on the salicylidene moiety of the tridentate ligand.     

Heterobinuclear Zn‐Ln (Ln = La,Nd, Eu,Gd, Tb,Er and Yb) complexes based on asymmetric Schiff‐base ligand: synthesis,characterization and photophysical properties

With a novel asymmetric Schiff‐base zinc complex ZnL (H₂L = N‐(3‐methoxysalicylidene)‐N′‐(5‐bromo‐3‐methoxysalicylidene)phenylene‐1,2‐diamine), obtained from phenylene‐1,2‐diamine, 3‐methoxysalicylaldehyde and 5‐bromo‐3‐methoxysalicylaldehyde, as the precursor, a series of heterobinuclear Zn‐Ln complexes [ZnLnL(NO₃)₃(CH₃CN)] (Ln = La, 1; Ln = Nd, 2; Ln = Eu, 3; Ln = Gd, 4; Ln = Tb, 5; Ln = Er, 6; Ln = Yb, 7) were synthesized by the further reaction with Ln(NO₃)₃·6H₂O, and characterized by Fourier transform‐infrared, fast atom bombardment mass spectroscopy and elemental analysis. Photophysical studies of these complexes show that the strong and characteristic near‐infrared luminescence of Nd³⁺, Yb³⁺and Er³⁺ with emissive lifetimes in the microsecond range has been sensitized from the excited state of the asymmetric Schiff‐base ligand due to effective intramolecular energy transfer; the other complexes do not show characteristic emission due to the energy gap between the chromophore and lanthanide ions. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and characterization of uranyl(VI) and thorium(IV) complexes with phosphine oxides. The crystal structure of UO2(NO3)2(NO2-C6H4Ph2PO)2

Uranyl(VI) and thorium(IV) complexes of the type UO₂(NO₃)₂(L¹)₂, UO₂(NO₃)₂(L²)₂, UO₂(CH₃COO)₂L¹, UO₂(CH₃COO)₂L², Th(NO₃)₄(L¹)₂ and Th(NO₃)₄(L²)₂ (L¹ = (2-nitro)phenyl-bis-phenyl phosphine oxide, L² = triferrocenylphosphine oxide) are reported, together with their physico-chemical properties.The crystal structure of UO₂(NO₃)₂(L¹)₂ is also reported. The crystals are monoclinic, space group P2₁/n with a = 17.78(1), b = 13.88(1), c = 17.37(1) Å, β = 114.8(1)° for Z = 4. The uranium atom is 8-coordinated, the uranyl(VI) group being equatorially surrounded by an irregular hexagon of six oxygen atoms from two trans neutral ligands and two nitrato groups.     

Preparation and characterisation of Ni(II), Pd(II) and Pt(II) complexes of 1-diphenylphosphino-2-bis (m -trifluoromethylphenyl)phosphinoethane,(m -CF3 P-P)

A series of four-coordinate, square-planar, dia- magnetic 1-diphenylphosphino-2-bis(_m-trifluoro- methylphenyl)phosphinoethane complexes of type cis-[MX₂(_m-CF₃P-P)] (M = Ni, Pd, Pt; X = Cl, Br, I or NCS) have been prepared. These complexes have been characterized by ³¹P {₁H} NMR, ¹H NMR, IR and UV spectroscopy, elemental analyses and magnetic susceptibility measurements. The effects of various substituents on the phenyl groups of the ditertiary phosphines on the solubility characteristics of the metal complexes are discussed.     

Synthesis, characterization and thermal decomposition of dioxouranium(VI) complexes with N,N-diarylidene-S-propyl-thiosemicarbazone: Crystal structure of [UO2(L)(C4H9OH)]

Reactions of salicyl- and 3,5-dichlorosalicylaldehyde-S-propyl-thiosemicarbazones with salicyl- and 3,5-dichlorosalicylaldehyde in the presence of UO₂(CH₃COO)₂ in different alcohols yielded stable solid complexes corresponding to the general formula [UO₂(L)ROH] (R: propyl-, butyl-, pentyl-, and octyl-). The complexes were characterized by means of elemental analysis, IR and ¹H NMR spectroscopies. The thermal stabilities of the alcohol solvated complexes were investigated in air and nitrogen atm., and determined their decomposition phases. In the crystal structure of the [UO₂(L)(C₄H₉OH)], the U(VI) centre is seven-coordinated in a distorted pentagonal bipyramidal geometry involving O,O,N,N atoms of two phenolic and two imine groups and one oxygen atom of alcohol molecule in basal plane and two O atoms of dioxo group in apical positions. The title structure is stabilized by one intramolecular interaction of types C-H?Cl and by two intermolecular interactions of types O-H?O and C-H?π (benzene) leading to the molecular chain along the [0 1 0] direction.     

Synthesis, characterization and structural studies of new palladium(II) complexes including non-symmetric phosphorus ylides

The reaction of the non-symmetric phosphorus ylides, Ph₂P(CH₂)_nPPh₂C(H)C(O)PhR [Y₁-Y₄: n = 1, R = Cl, Br, NO₂, OCH₃ and Y₅-Y₈: n = 2, R = Cl, Br, NO, OCH₃] with dichloro(1,5-cyclooctadiene)palladium(II) in dichloromethane under mild conditions afford the monomeric P-C chelated complexes, [(Y)PdCl₂] (Y = Y₁-Y₈). These complexes were fully characterized by elemental analysis and spectroscopic techniques such as IR, ¹H, ³¹P, and ¹³C NMR. In addition, the identity of complexes [(Y₅)PdCl₂] (1b) and [(Y₈)PdCl₂] (4b) was unequivocally determined by single crystal X-diffraction techniques, both structures consisting of six-membered rings formed by coordination of the ligands through the phosphine group and the ylidic carbon atom to the metal center. The coordination geometry around the Pd atoms in both these complexes be defined as slightly distorted square planar. Furthermore, their electrochemical behavior was also investigated by cyclic voltammeters, thus the cyclic voltammetry of complex [(Y₁)PdCl₂], in dichloromethane solution with Pt electrode, shows that the redox reaction of the pair Pd(II)/Pd(0) is irreversible with the cathodic peak potential at −1.08 V versus Ag wire.     

Synthesis and structural characterization of zwitterionic oxorhenium(V) complexes with 2-hydroxypyridine

[ReOX₃(PPh₃)₂] complexes (X = Cl and Br) react with equivalent amounts of 2-hydroxypyridine (Hhp) under formation of the mono-substituted, zwitterionic complexes mer-[ReOCl₃(Hhp)(PPh₃)] (1) and mer-[ReOBr₃(Hhp)(PPh₃)] (2). Crystal structure determinations of 1 · CH₂Cl₂ and 2 revealed the Cl and Br ligands adopt a mer arrangement. The Hhp ligands coordinate neutral and monodentate via their exocyclic oxygen atoms in axial positions, trans to the oxo groups. The distorted octahedral coordination sphere of the rhenium(V) complexes is completed by the phosphorus atom of the remaining PPh₃ ligand.     

A patch-clamp study of the ionic selectivity of the large conductance,ca-activated chloride channel in muscle vesicles prepared fromAscaris suum

Summary Plasma membrane vesicles prepared from the bag re gion of the somatic muscle cell of the parasiteAscaris suum contain a large conductance, voltage-sensitive, calcium-activated chloride channel. The ability of this channel to conduct a variety of anions has been investigated using the patch-clamp technique on isolated inside-out patches of muscle membrane. Symmetrical Cl solutions (140 mm) produced single-channel I/V plots with reversal potentials of 0 mV, substitution of bath Cl by 140 mM NO₃, Br and I caused depolarizing shifts in the reversal potentials. Replacement of the internal Cl by F (140 mM) caused a large hyperpolarizing shift in the reversal potential. The channel dis played a permeability sequence of I > Br = NO₃> Cl > F which differed from the corresponding conductance sequence Cl > NO₃ = Br = I > F. The ionic environment within the channel pore has been investigated using Reuter and Stevens (1980) plots to describe the selectivity and “fluidity” of the channel pore. In addition, the approach of Wright and Diamond (1977) was employed to estimate the number of cationic binding sites within the channel pore. The channel is relatively fluid but the number of cationic binding sites varies inversely with the ionic radius of the anion from 2.15 for F to 0.89 for the large planar anion NO₃     

Co-ordination compounds derived from dimethylhydrazones of cyclohexane-1,2-dione, 2-acetyl- and 2-benzoylpyridines and 4-bezoylpyridine

The 1,1-dimethylhydrazones of cyclohexane-1,2-dione (CDDMH), 2-acetylpyridine (APDMH) and 2-benzoylpyridine (2BPDMH) from tetrahedral complexes MX₂L (M = Co(II), Zn(II); X = Cl, Br) in which the ligand is chelating through the methylene nitrogen atoms (CDDMH) or one methylene and one pyridine nitrogen atom (APDMH, 2BPMDH). Octahedral complexes CoX₂L₂ (X = Cl, NCS; L = APDMH, 2BPDMH) have also been isolated but no tris-ligand complexes. The ligand 4-benzoylpyridine-dimethylhydrazone (4BPDMH) does not chelate but forms tetrahedral complexes MX₂(4BPDMH)₂ in which the unidentate ligand co-ordinates through the pyridine nitrogen atom.     

Main group metal halide complexes with sterically hindered thioureas. VIII. Complexes of lead(II) halides with 1,3-dimethyl-2(3H)-imidazolethione

Two new complexes of 1,3-dimethyl-2(3H)- imidazolethione (dmit) and lead(II) halides have been synthesized and characterized. Addition of dmit in molar excess to PbX₂ (X = Cl, Br, I, SCN) solutions in hot water yielded PbCl₂dmit and Pb(NCS)₂(dmit)₂. No adducts were isolated for PbBr₂ or PbI₂. Complexes were characterized via standard methods including both solid state and solution state information. Both complexes were high melting solids and appeared to be polymeric in the solid state, and IR data indicated polymerization occurred through halogen (of pseudohalogen) bridges only. Thiocyanate was N-bonded to the metal. Solution studies concluded that both were dissociated in DMF with PbCl₂dmit being a non-electrolyte and Pb(NCS)₂(dmit)₂ acting like a 1:1 electrolyte.     

Sugar interaction with uranium ion. Synthesis,spectroscopic and stmctural analysis of UO2-sugar complexes containing D-glucuronate moiety

Interaction between D-glucuronic acid and hydrated uranyl salts has been studied in aqueous solution and solid complexes of the type UO₂(D- glucuronate)X·2H₂0 and UO₂(D-glucuronate)₂·2H₂O, where X = CI⁻, Br⁻ or NO₃⁻, are isolated and characterized by means of FT-IR and proton-NMR spectroscopy.On comparison with the structurally identified Ca(D-glucuronate)Br·3H₂O compound, it is concluded that the UO₂²⁺ cation binds to two D- glucuronate moieties in uranylsugar complexes via O6, O5 oxygen atoms (ionized carboxyl group) of the first and O6′, 04 (non-ionized carboxyl group) of the second sugar moiety, whereas in the UO₂(D- glucuronate)₂·2H₂O salt the uranyl ion is bonded to two sugar anions through O6, O6′ oxygen atoms of the ionized carboxyl group, resulting in a six- coordination geometry around the uranium ion. The strong intermolecular hydrogen bonding network of the free acid is rearranged upon sugar metalation and the sugar moiety showed β-anomer conformation both in the free acid and in these uranylsugar complexes.     

Titanium, zirconium and hafnium halide complexes of trithioether and triselenoether ligands

The reaction of TiX₄(X=Cl or Br) with the tripodal ligands MeC(CH₂SMe)₃ or MeC(CH₂SeMe)₃, (L³) in anhydrous n-hexane or CH₂Cl₂ produced the extremely moisture sensitive complexes [TiX₄(L³)]. These were characterised by microanalysis, IR, UV-Vis and variable temperature ¹H,¹³C{¹H} and ⁷⁷Se NMR spectroscopy. The NMR studies showed that in solution in CH₂Cl₂ the complexes contain L³ bound as bidentates, and that pyramidal inversion and exchange between the free and coordinated chalcogen donors is rapid at room temperature. Ligand dissociation/exchange increases TiCl₄<TiBr₄ and MeC(CH₂SMe)₃<MeC(CH₂SeMe)₃ and attempts to isolate TiI₄ analogues were unsuccessful. The reactions of [MCl₄(Me₂S)₂] (M=Zr or Hf) with (L³) in anhydrous CH₂Cl₂ produces white or cream 7-coordinate [MCl₄(L³)], which are insoluble in chlorocarbon solvents. The reactions of TiX₄ (X=Cl, Br or I) with the trithia-macrocycles [9]aneS₃ and [10]aneS₃ produced [TiX₃([n]aneS₃)]X, whilst reaction of TiCl_4, SbCl₅ and [9]aneS₃ in anhydrous CH₂Cl₂ gave [TiCl₃([9]aneS₃)]SbCl₆. Spectroscopic studies suggest these macrocyclic compounds contain 6-coordinate cations, [TiX₃([n]aneS₃)]⁺ (n=9 or 10) but with Zr and Hf the complexes [MCl₄([n]aneS₃)] are 7-coordinate and neutral.     

Interaction between alkaline earth cations and oxo-ligands. DFT study of the affinity of the Ca<Superscript>2+</Superscript> cation for carbonyl ligands

The affinity of the Ca²⁺ ion for a set of substituted carbonyl ligands was analyzed with both the DFT (B3LYP/6-31+G(d)) and semi-empirical (PM6) methods. Two types of ligands were studied: a set of monosubstituted [O=CH(R)] and a set of disubstituted ligands [O=C(R)₂] (R=H, F, Cl, Br, OH, OCH₃, CH₃, CN, NH₂ and NO₂), with R either directly bound to the carbonyl carbon atom or to the para position of a phenyl ring. The interaction energy was calculated to quantify the affinity of the Ca²⁺ cation for the ligands. Geometric and electronic parameters were correlated with the intensity of the metal-ligand interaction. The electronic nature of the substituent is the main parameter that determines the interaction energy. Donor groups make the interaction energy more negative (stabilizing the complex formed), while acceptor groups make the interaction energy less negative (destabilizing the complex formed).     

Interactions between alkaline earth cations and oxo ligands. DFT study of the affinity of the Mg²+ cation for phosphoryl ligands

DFT (B3LYP/6-31+G(d)) calculations of Mg²⁺ affinities for a set of phosphoryl ligands were performed. Two types of ligands were studied: a set of trivalent [O = P(R)] and a set of pentavalent phosphoryl ligands [O = P(R)₃] (R = H, F, Cl, Br, OH, OCH₃, CH₃, CN, NH₂ and NO₂), with R either bound directly to the phosphorus atom or to the para position of a phenyl ring. The affinity of the Mg²⁺ cation for the ligands was quantified by means of the enthalpy for the substitution of one water molecule in the [Mg(H₂O)₆]²⁺ complex for a ligand. The enthalpy of substitution was correlated with electronic and geometric parameters. Electron-donor groups increase the interaction between the cation and the ligand, while electron-acceptor groups decrease the interaction enthalpy.