Trans-octahedral Configuration Research Articles

Novel bis(β-diketonato)diorganotin(IV) derivatives containing bulky 4-acyl-5-pyrazolonato ligands: Influence of the steric hindrance of the acyl moiety on the solid state structures of tin complexes and their behaviour in solution

New (Q)2SnR2 derivatives (HQ in general; in detail: HQCHPh2=4-diphenylacetyl-3-methyl-1-phenyl-5-pyrazolone; HQBn=3-methyl-1-phenyl-4-phenylacetyl-5-pyrazolone; HQnaph=3-methyl-4-naphthoyl-1-phenyl-5-pyrazolone; R=CH3, C2H5, C6H11, n- and t-C4H9, C6H5,) have been synthesised and characterised by analytical and spectral techniques. Variable temperature NMR studies of (QCHPh2)2SnR2 derivatives (R=CH3 and C2H5) in chlorohydrocarbon solvents indicate a fluxional behaviour, with rapid interconversion between six- and five-coordinate species, the latter containing a bidentate acylpyrazolonate and a monodentate one. The X-ray crystal structures of the diorganotin(IV) derivatives (QCHPh2)2SnMe2, (QCHPh2)2SnEt2, (QBn)2SnMe2 and (Qnaph)2SnBun2, inclusive of a representative of each Qx family, show the metal centres in a skewed trans octahedral configuration. The 4-acyl moiety of the β-diketonate donor exerts a steric effect which is correlated to structural behaviour in the solid and solution state. A solid state 119Sn CPMAS NMR study of the (QBn)2SnR2 (R=CH3, C2H5, t-C4H9 and C6H5) complexes shows a marked deshielding effect and upfield movement of the 119Sn isotropic chemical shift (δiso) through this series. The 119Sn chemical shift spans (Ω) are the largest reported for directly oxo-coordinated Sn(IV) systems, although the markedly reduced Ω value for the (QBn)2SnPh2 complex may be indicative of a cis octahedral coordination, in contrast to the trans octahedral coordination characterising the other complexes of this suite.

Trinuclear tris-Co(II) and trans-cobaloxime type Co(III) complexes prepared from Co(II) triflate precursor: Synthesis, structure and properties

Three new coordination compounds, [Co 3(DH) 6] · 24H 2O ( I), [Co(DH) 2Tu 2]CF 3SO 3 ( II) and [Co(DH) 2Py 2]CF 3SO 3 ( III) (where DH − = monoanion of dimethylglyoxime, Py = pyridine, Tu = thiourea), were synthesized starting from Co(CF 3SO 3) 2 · 6H 2O as a substrate. The complexes were characterized by X-ray crystallography, spectroscopic methods (IR, UV–Vis, 1H and 13C NMR, MS) and magnetochemistry. Compound I is a neutral, C 3 i symmetrical, trinuclear Co(II) complex with two tris-{Co 2+(μ-DH) 3} units connected to the central Co(II) ion via bridging oxygen atoms, saturating the Co(II) octahedral coordination. In the case of II and III, the complex cations have the usual trans-octahedral configuration with two DH-chelating units in the equatorial plane of the Co(III) ion and the apical coordination sites occupied by two neutral monodentate ligands (Py or Tu).

PREPARATION AND SPECTROSCOPIC STUDY OF 1:2 ADDUCTS OF DIMETHYLTIN(IV)DICHLORIDE WITH AROMATIC N-OXIDES (IQNO, 4-C1QNO, 4-MeQNO, 6-MeOQNO AND 4-PhPyNO). CRYSTAL AND MOLECULAR STRUCTURE OF TRANS-DICHLORODIMETHYL BIS(4-PHENYLPYRIDINE-TV-OXIDE)TIN(IV)

Five adducts of general formula Me2SnCl2L2 [L = IQNO(isoquinoline-N-oxide), 4-C1QNO, 4-MeQNO, 6-MeOQNO (6-methoxyquinoline-N-oxide) and 4-PhPyNO (4-Phenylpyridine-Af-oxide)] have been prepared by the addition of L to chloroform solutions of Me2SnCl2. The adducts have been characterized by analysis and spectroscopic (1R, 1H, 13C and Mössbauer) data. Structural predictions were derived from 119Sn NMR parameters such as 1 J(119Sn-13C) and 2 J(119Sn-1H). The single crystal diffraction study of the adduct Me2SnCl2(4-PhPyNO)2 shows the metal to be six-coordinate inan all trans-octahedral configuration; Sn-O and Sn-CI distances are 2.227(2) and 2.5774(9)Å, respectively, and the CH3-Sn-CH3 bond angle is 180.0°.

Thermal Studies of N-phenylethane-1,2-diamine Complexes of Nickel(II) in the Solid State

[NiL3]X2 (where L=N-phenylethane-1,2-diamine and X=I− and ClO4 −), [NiL2X2] (X is Cl−, Br−, NCS−, 0.5SO4 2− or 0.5SeO4 2−) and [NiL2(H2O)2](NO3)2 have been synthesized from solution and their thermal study has been carried out in the solid phase. [NiL2Cl2] upon heating undergoes irreversible endothermic phase transition (142–152°C, ΔH=0.35 kJ mol−1) without showing any visual colour change. This phase transition is assumed to be due to conformation changes of the diamine chelate rings. NiLCl2 and NiL2.5I2 have been prepared pyrolytically from [NiL2Cl2] and [NiL3]I2 respectively in the solid state. [NiL2(H2O)2](NO3)2 upon heating undergoes deaquation-anation reaction without showing any visual colour change. [NiL2X2] (X is Cl−, Br−, NCS−), [NiL2(H2O)2](NO3)2 and [NiL2(NO3)2] possess trans-octahedral configuration, whereas, [NiL2X2] (X is 0.5SO4 2− or 0.5SeO4 2−) are having cis-octahedral configuration. Amongst the complexes, only NiLCl2 shows unusually high (5.1 BM at 27°C) magnetic susceptibility value.

Thermal studies of N-propylethane-1,2-diamine and N-isopropylethane-1,2-diamine complexes of nickel(II) in the solid state

Abstract [NiL 3 ]X 2 ·2H 2 O (X is Cl − , Br − and ClO − 4 ; L is N -propylethane-1,2-diamine), [NiL 2 (H 2 O) 2 ](ClO 4 ) 2 , [NiL 2 X 2 ] (X is Cl − , Br − , 0.5SO 2− 4 and 0.5SeO 2− 4 ), [NiL′ 2 (H 2 O) 2 ](ClO 4 ) 2 ·2H 2 O (L′ is N -isopropylethane-1,2-diamine), [NiL′ 2 X 2 ] (X is Cl − , Br − , NCS − and 0.5SeO 2− 4 ) and [NiL′ 2 SO 4 ]·3H 2 O have been synthesised from solution and their thermal studies have been carried out in the solid phase. [NiL 2 X 2 ] (X is Cl − and Br − ), NiLCl 2 and NiL'SO 4 have been prepared pyrolytically from their respective parent species in the solid state. [NiL 2 ](ClO 4 ) 2 and [NiL′ 2 ](ClO 4 ) 2 were prepared pyrolytically from their parents species, and also by storing [NiL 2 (H 2 O) 2 ](ClO 4 ) 2 and [NiL′ 2 (H 2 O) 2 ](ClO 4 ) 2 ·2H 2 O in a CaCl 2 desiccator, respectively; these transformations are accompanied by a pink to yellow colour change due to octahedral to square-planar configurational changes. All other bis(diamine) species have octahedral geometry. Among them, [NiL 2 X 2 ] (X is Cl − and Br − ) and [NiL′ 2 X 2 ] (X is Cl − , Br − and NCS − ) possess trans-octahedral configuration, whereas [NiL 2 X] (X is SO 2− 4 and SeO 2− 4 ), [NiL′ 2 SO 4 ]·3H 2 O and [NiL′ 2 SeO 4 ] have cis-configuration. On heating, trans -[NiL′ 2 Br 2 ] and trans -[NiL′ 2 (NCS) 2 ] undergo reversible endothermic phase transitions (86–99°C, ΔH = 0.52 kJ mol −1 for heating, and 92–81°C, ΔH = −0.53 kJ mol −1 for cooling for the former, and 162–224°C, ΔH = 0.27 kJ mol − for heating and 208–150°C, ΔH = −0.25 kJ mol −1 for cooling for the latter), most likely due to conformational changes of the diamine chelate rings.

Preparation, Characterization, and Solid State Thermal Studies of Nickel(II) Iodide Complexes of Ethane-1,2-diamine and Its Derivatives

Abstract [NiL3]I2·2H2O [L = N–methylethane–1,2–diamine (meen) and 2-methylpropane-1,2-diamine (ibn)], [NiL3]I2 [L = ethane–1,2–diamine (en), N-ethylethane-1,2-diamine (eten), N-propylethane-1,2-diamine (pren), and propane-1,2-diamine (pn)], [NiL2(H2O)2]I2 (L = meen and eten), and [Ni2L2]I2 [L = N-isopropylethane-1,2-diamine (ipren) and ibn] have been synthesized from solution and characterized. [NiL2I2] (L = en, meen, eten, and pren] and [Ni(ibn)2]I2 have been isolated in the solid state from their corresponding parent tris(diamine) complex by temperature arrest technique. [NiL2(H2O)2]I2 (L = meen and eten) upon heating undergo deaquation-anation reaction. All the diamine species excepting [Ni(ipren)2]I2 and [Ni(ibn)2]I2 which possess square-planar geometry, are octahedral and both the diaqua and diiodobis(diamine) species possess trans-octahedral geometry showing variation only in [Ni(en)2I2], which is having cis-octahedral geometry. [Ni(meen)2I2] and [Ni(eten)2I2] show irreversible endothermic phase transitions (160—190 °C; ΔH = 5.65 kJ mol−1 and 204—225 °C; ΔH = 4.23 kJ mol−1, respectively) without any visual color change with retention of trans-octahedral configuration. In case of [Ni(eten)2I2] the post phase species reverts to the original diaqua species, [Ni(eten)2(H2O)2]I2 on keeping in open atmosphere whereas the rehydrated species of its meen analogue, [Ni(meen)2(H2O)2]I2 after deaquation does not show the phase transition. On the other hand, corresponding pren analogue shows reversible endothermic phase transition (68—111 °C; ΔH = 2.42 kJ mol−1 for heating and 98—77 °C; ΔH = −1.4 kJ mol−1 for cooling). The occurrence of this type of phase transition is due to the conformational changes in the diamine chelate rings. The square-planar [Ni(ibn)2]I2 undergoes time dependent reversible phase transition (232—248 °C; ΔH = 5.99 kJ mol−1) without any visual color change retaining the original geometry. Here also conformational changes in chelate rings are assumed to be responsible for this transition.

Synthesis and spectral studies of cobalt(II), nickel(II) and copper(II) complexes of 1-(2-hydroxy-1-naphthyl)-3-(4-X-phenyl)-2-propen-1-ones and their pyridine adducts

Metal(II) chelates of the type ML2nB [M = CoII, NiII and CuII; L = 1-(2-hydroxy-1-naphthyl)-3-(4-X-phenyl)-2-pro-pen-1-one, (X = H, Cl or Me); B = H2O or Py; n = 0, 2] have been prepared by in situ ring opening of 5,6-benzofiavanones and also from the corresponding chalcones. Structures have been assessed by magnetic measurements, i.r., electronic and e.p.r. spectra and by thermal studies. The anhydrous CuII chelates are monomers and possess square-planar geometry, while the corresponding CoII and NiII complexes are polymers with a high-spin trans-octahedral configuration. All the base adducts have a high-spin trans-octahedral configuration. I.r. studies indicate that v(C=O) and v(M-O) frequencies are affected by metal-ion and by phenyl substitution and adduct formation. E.p.r. spectral studies indicate a higher degree of covalency in the in-plane σ-bonded pyridine adducts of the copper complexes than do the parent chalcone complexes. The relatively low ligand field strength of 1-(2-hydroxy-l-naphthyl)-3-(4-X-phenyl)-2-propen-l-ones compared to 2′-hydroxychal-cones is attributed to the inhibition of extensive conjugation arising from deviation of the naphthoyl group from planarity.

Synthesis and characterization of potential antitumour and antiviral gallium(III) complexes of N-heterocycles

Ten water-soluble gallium(III) complexes of N-heterocycles were synthesized and characterized by elemental analysis, conductivity measurements, IR spectroscopy, 1H NMR spectroscopy and optical activity measurements. Raman spectra were measured with two complexes and an X-ray singe-crystal study performed with one complex— trans-dichlorotetrakis-(5-methylpyrazole)gallium(III)tetrachlorogallate(III). The gallium(III) complexes had the general formulae: [L 4GaCl 2]GaCl 4 (L = ligand) (L = indazole, 1,2,3-benzotriazole, pyrazole, 5-methylpyrazole, 4-methylpyrazole), having a trans-octahedral structure (symmetry C i ), [L 4GaCl 2]Cl (L = imidazole, benzimidazole), also with a trans-octahedral configuration, and LGaCl 2 (L = 2-α-oxybenzylbenzimidazolato (HBB) and the respective enantiomers d(−)-HBB and l(+)-HBB) having a tetrahedral structure. So far, eight gallium(III) complexes have been tested in the in vitro anti-HIV test (HIV = human immunodeficiency virus) of the National Cancer Institute (NCI) in the U.S.A., and four of these were found to be moderately active: trans-dichlorotetrakis-(5-methylpyrazole)gallium(III) tetrachlorogallate(III), trans-dichlorotetrakis-(4-methylpyrazole)gallium(III)tetrachlorogallate(III), dichloro-(2-α-oxybenzylbenzimidazolato-N,O) gallium (III) and trans-dichlorotetrakis(benzimidazole)gallium(III) chloride, the latter exhibiting the highest therapeutic index (TI) of 77. For comparison, the therapeutic index for 3′-azido-3′-deoxythymidine (AZT) ranges from TI = 1000 to 4000.

Thermal Reactions of N,N-Dimethyl-1,2-ethanediamine Complexes of Nickel(II) in the Solid State

Abstract Complexes [NiL2(H2O)X]X·nH2O (L=N,N-dimethyl-1,2-ethanediamine; n=0 when X=BF4; n=1 when X=Br; n=3 when X= Cl), [NiL2(H2O)Y]·nH2O (n=2 when Y= SeO4; n=5 when Y=SO4), [NiL2(H2O)2](NO3)2·H2O and [NiL2] (ClO4)2 have been synthesized and investigated thermally in the solid state. The complexes [NiL2(H2O)Cl]Cl·3H2O, [NiL2(H2O)Br]Br·H2O, [NiL2(H2O)(SO4)]·5H2O, and [NiL2(H2O(SeO4)]·2H2O possess trans octahedral geometry and undergo deaquation-anation associated with trans→cis isomerization upon heating in the solid state whereas on deaquation the complex [NiL2(H2O)2](NO3)2·H2O retains its trans octahedral configuration. The complex [NiL2(H2O)(BF4)](BF4) possesses cis octahedral geometry and on thermal deaquation it transforms to a square planar complex. The complex [NiL2](ClO4)2 is square planar and undergoes a yellow → red thermochromic phase transition on heating (203–216°C; ΔH=6.9 kJ mol−1). The red isomer is also square planar. The species [NiLCl2], [NiL(SO4)] and NiL0.33Cl2 have been synthesized pyrolytically in the solid state from their corresponding parent diamine complexes. The complexes [NiLCl2] and [NiL(SO4)] possess octahedral geometry. NiL0.33Cl2 possesses an unusually high magnetic moment (4.1 BM at 28°C).

Trans-bis(difluoroborondimethylglyoximato) cobalt(III) complexes containing imidazole and chloride or thiocyanate as axial ligands

Halo- and pseudohalocobaloxime complexes [Co(DH)2(Im)(X)] (X = Cl or CNS), containing imidazole (Im) or its derivatives, interact with BF3·Et2O to form a series of cobalt(III) complexes, [Co(DBF2)2(Im)(X)], that contain a 14-membered macrocyclic ligand. These light coloured microcrystalline solid complexes, stable under ordinary conditions, were characterized on the basis of elemental analyses, conductivity measurements, electronic, IR, NMR and mass spectra, and thermogravimetric and cyclic voltammetric studies, and are shown to posses a six-coordinated trans-octahedral configuration. The mass spectra do not reveal any molecular-ion peak whereas the results of thermolyses reveal the decreased stability of these complexes compared to the corresponding cobaloximes and yield polymeric intermediates, and finally forming Co3O4 as the end product. Cyclic voltammetric studies show four reductive waves and an oxidative wave, confirming an oxidation number of III for the central cobalt atom.

Addition complexes of Co(II) aryl carboxylates with pyridines

A large number of complexes of pyridine ligands have been prepared with different Co(II) aryl carboxylates Co(O 2CC 6H 4R) 2 (where R is H, CH 3- o, Cl- o and m, NO 2- o and m, CH 3O- m). Pyridine (PY), 3-and 4-Methyl Pyridine (3- and 4-MePy) yield bis-amine complexes of 1:2 stoichiometry Co(O 2CC 6H 4R) 2L 2 which have been shown by magnetic and spectral studies to possess a trans octahedral configuration. By contrast, 2-Methyl Pyridine (2-MePy) yields 1:1 complexes which are considered to be monomeric, five coordinate trigonal bipyramidal molecules except that of cobalt( o-toluate) 2 complex which is a dimeric syn-syn carboxylate bridged species.

Cobalt(II), nickel(II) and copper(II) complexes of some o-hydroxycrotonophenones

Metal(II) complexes of the type ML2,nB [M = CuII, NiII, CoII; L = 2- hydroxy-5-X-crotonophenone where X = H, CH3, Cl; B = H2O, pyridine; n = 0, 1, 2] have been obtained and investigated. With the help of element analyses, magnetic measurements, ligand field and infrared spectra and thermal studies, the structure and the nature of bonding have been established. The anhydrous copper(II) chelates are monomeric and possess trans-square-planar configuration while the corresponding cobalt(II) and nickel(II) compounds are polymeric and possess high-spin trans-octahedral configuration. All the base adducts possess high-spin trans-octahedral structure with lesser tendency toward dissociation in solution. Infrared studies indicate that v(C=O) and v(M-O) are affected by metal ion and phenyl substitutions and adduct formation. The order of stabilities, namely Cu > Ni > Co, derived from v(M-O) parallels the crystal field stabilization energies. Substitution in the phenyl ring of the complexes produces shifts in v(M-O) which are related to the resonance capacities of the substituents. ��� The relatively high ligand field strength of o-hydroxycrotonophenone compared to salicylaldehyde is attributed to the conjugation of C=O with C=C which lowers the energy of the π3* orbital leading to extensive back-bonding with dπ orbitals of the metal.

Nickel(II) compounds of three homologous linear tetra-amines, especially solvent effects and configuration

Abstract A comparative study has been made of the 1:1 nickel(II) compounds of three homologous linear tetraamines: 1,4,7,10-tetraazadecane(trien), 1,4,8,11- tetraazaundecane(2,3,2-tet), and 1,5,8,12-tetraazodecane(3,2,3-tet). A range of solid compounds Ni(tetraamine)X 2 (X = Cl, Br, I, NCS, NO 2 , NO 3 , Clo 4 ), a number of which are new, has been prepared from 2,3,2-tet and 3,2,3-tet. These include the structural isomers yellow low-spin [Ni(3,2,3-tet)]I 2 ] and lilac high-spin trans -[Ni(3,2,3-tet)]I 2 ]. The high-spin species have a trans octahedral configuration, except for [Ni(2,3,2-tet)NO 3 ]NO 3 , which appears to have a chelating nitrate. In solution in water, DMF, and DMSO two equilibria of these compounds have been studied under varying conditions: (a) the cis ⇄ trans equilibria of the high-spin [Ni(N 4 )(S) 2 ] 2+ species (S = solvent); and (b) high spin octahedral ⇄ low-spin planar equilibria. It is shown for the first time that equilibria (a) occur in such solutions for both 2,3,2-tet and 3,2,3-tet. The trans isomers are preferred over cis in the orders: (i) (for solvent) H 2 O > DMF > DMSO; and (ii) (for the amines) 3,2,3-tet > 2,3,2-tet ⪢ trien. In concentrated LiNO 3 and LiClO 4 , Ni(trien) 2+ , but not the others, forms high spin cis -[Ni-(N 4 )O 2 ] species which apparently have a chelating anion. For equilibria (b) (the singlet ⇄ triplet equil.) the planar low-spin species are preferred in the order 2,3,2-tet > 3,2,3-tet > trien — an order different from that observed in (a). Difficulties in defining ϵ max for these low-spin species, and hence in quantifying the equilibria are discussed with evidence for the complication. The observations on both equilibria can be rationalised by reference to the steric effects of the amines: 3,2,3-tet has a greater preference thatn 2,3,2-tet for trans high-spin isomers, but it can less easily accomodate to the shorter NiN bond lengths in the low-spin species.

Solid state vibrational spectroscopy of some piperidinium and morpholinium salts of tin(IV), antimony(III) and bismuth(III) halide complexes

Some compounds of the type (LH) 2SnX 6 (X = Cl, Br), (LH) 2SnX 4Y 2 (X ≠ Y = Cl and Br), (LH) 2MX 5 (M = Sb, Bi; X = Cl, Br) and (LH) 3M 2I 9 (M = Sb, Bi) (LH = piperidinium cation (pipdH) or morpholinium cation (morphH)) were prepared and characterized by means of the Raman and far-i.r. spectroscopy. The study of the vibrational spectra suggests for the hexahalo- and mixed-hexahalo-stannates(IV) an octahedral of trans-octahedral configuration, respectively. For the pentahaloantimonates(III) and bismuthates(III) the geometries of the complexes were found to depend on the hydrogen bonding ability of the counter cation. In fact the bismorpholiniumpentahalometallates(III) show square pyramidal configurations while the bispiperidinium complexes show octahedral configurations, in which two halogen atoms bridge the metals. The (LH) 3M 2I 9 (M = Sb, Bi) and the (pipdH) 3Bi 2Br 9 complexes may be interpreted on the basis of D h 3 symmetry.

Pyrazole, 3(5)-methyl pyrazole and 3,5-dimethyl pyrazole complexes of tin(IV) halides

Complexes of tin(IV) halides with pyrazole, 3(5)methyl pyrazole and 3,5-dimethyl pyrazole of the type SnX 4·L 2 were prepared. All the isolated solids were non-electrolytes in acetonitrile. The IR spectra of the complexes (600–180 cm −1 were consistent with a trans-octahedral configuration in the solids state. The dipole moment data suggest that this configuration remains in solution.

The mechanism of formation and crystal structure of trans-dichlorotetrakis-(dimethylphosphine)ruthenium(II), RuCl2[PH(CH3)2

The title compound has been prepared by the reaction of tetramethylbiphosphine and ruthenium trichloride hydrate. When ethanol is present in the reaction medium it is oxidized to acetaldehyde; however, in the absence of ethanol the water of hydration is the source of hydrogen, as shown by incorporation of deuterium, introduced as D 2 0. The single crystal x-ray structural study demonstrates that the compound has a transoctahedral configuration as anticipated from proton nmr. Crystal data: space group, Pbca; a = 11.571(3) Å, b = 12.133(2) Å ; c = 12.831(4) Å ; V = 1801.3(8) Å, Z = 4. The molecule lies on a crystallographic inversion center and has the following metal-ligand bond lengths: Ru-P, 2.323(1) Å , 2.331(1) Å , RuCl, 2.440(1) Å . The PC distances range from 1.837(7) Å to 1.841(7) Å , with a mean of 1.839 Å .

Adducts of Piperidine, Piperazine, Methylpiperazine, and Morpholine with Bis(β-Ketoenolates) of Nickel(II)

The bis(β-ketoenolates)nickel(II) adducts of piperidine, piperazine, methylpiperazine, and morpholine are isolated in the solid state and investigated by magnetic measurements and electronic and i.r. spectra. Magnetic measurements and electronic spectra give evidence of trans-octahedral configuration while i.r. spectra show that the amines are coordinated to the nickel atom towards the nitrogen atom. The new band found in the range 385–300 cm−1 for all complexes can be assigned to Ni—N vibration. In the Ni(DBM)2•4B (B = methylpiperazine and morpholine) the two additional bases are not coordinated to the metal atom.

Mössbauer and infrared spectroscopic studies on complexes of diorganotin(IV) with bis(salicylic aldehyde) ethylenediimine

The infrared spectra and Mössbauer parameters of diorganotin(IV) complexes with the dianion of bis(salicylic aldehyde) ethylenediimine (Salen 2−) are discussed in the light of the molecular structure of Me 2SnSalen derived from X-ray diffraction studies. Infrared data for Me 2SnSalen are found to be fully consistent with the known distorted trans-octahedral configuration. p ]From the temperature dependence of the area under the Mössbauer resonance curve, the intensity asymmetry of the two components of the quadrupole split spectrum, and the value of the QS parameter, n reasonably complete description of the bonding, architecture and vibrational behaviour of Me 2SnSalen emerges. The experimental data are consistent with the presence in the neat solid ofmonomeric molecular units, in which the bonding geometry around the central metal atom reflects the distorted trans-octahedral arrangement. The vibrational amplitude of the metal atom in the range 78 ⩽ T ⩽ 130 K is essentially isotropic. The configuration of Ph 2SnSalen is discussed on the basis of its IR spectrum and QS parameter.

Crystal structure and Mössbauer spectrum of dimethyltin dichloride

The crystal structure of dimethyltin dichloride has been solved and the parameters have been refined by three-dimensional least-squares analysis. The environment of the tin atoms is considerably distorted from the regular tetrahedral co-ordination towards octahedral, because of the association between neighbouring molecules.The Mossbauer spectra of the dialkyltin dichlorides are discussed in terms of this structure, and of the dialkyltin difluorides in terms of a trans-octahedral configuration.

The properties of nitritobis(ethylenediamine)nickelate(II) halides

The properties of a series of complexes [Ni(en)2(ONO)]X, where X = Cl–, Br–, or I–, have been examined and compared with complexes of known crystal structure where X = NO2–, ClO4–, or BF4–. The magnetic data for the halide complexes indicate, a 3A2g ground state for the nickel(II) ion in a magnetically dilute, essentially octahedral environment. The electronic spectra suggest a trans-octahedral configuration for the nickel ion with no evidence that the halide ions are co-ordinated. The electronic and infrared spectra are consistent with a symmetrically bridging nitrito-group.