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The structures of the novel compounds K3Ln(AsS4)2 (Ln = Nd, Sm, Gd) contain infinite straight (1)infinity[Ln(AsS4)2]3- anionic chains which are composed of interconnected LnS8 polyhedra and AsS4 tetrahedra. The compounds were synthesized via reactions of Ln metals with in-situ-formed potassium polythioarsenate fluxes.
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Five new coordination compounds were prepared, structurally characterized, and investigated for their thermal properties. In the structure of the ligand-rich 4:9 compound, tetra(mu2-chloro)bis(mu2-2,3-dimethylpyrazine-N,N')tetrakis(2,3-dimethylpyrazine-N)tetracopper(I) tris(2,3-dimethylpyrazine)solvate (I), discrete complexes are formed by build up of two [(CuCl-(2,3-dimethylpyrazine)2]2 dimers, which are connected by two 2,3-dimethylpyrazine ligands via mu-N,N' coordination. In the 1:1 compound poly[mu2-chloro-mu2-2,3-dimethylpyrazine-N,N'-copper(I)] (II), (CuCl)2 dimers are found, which are connected by the 2,3-dimethylpyrazine ligands into layers. For this composition, a second polymorphic modification was found (III), which exhibits a different topology of the coordination network and a different packing of the layers. In the most stable 3:2 compound catena[tri(mu2-chloro)bis(mu2-2,3-dimethylpyrazine-N,N')tricopper(I)] (IV), six-membered rings of (CuCl)3 are found, which are connected by the 2,3-dimethylpyrazine ligands into chains. In the ligand-deficient 2:1 compound, poly[di(mu3-chloro)(mu2-2,3-dimethylpyrazine-N,N')dicopper(I)] (V), CuCl double chains are found, which are connected by the 2,3-dimethylpyrazine ligands into layers. On heating, compound I transforms quantitatively into the 3:2 compound IV without the formation of II or III as intermediates. Compound IV is also obtained by heating either the 1:1 compound II or III. On further heating, the 3:2 compound IV loses additional ligands, forming the ligand-deficient 2:1 compound V, which then decomposes into CuCl. The stability, thermal reactivity, and the transition behavior of all compounds were investigated using different thermoanalytical methods. These results are compared with those previously reported for the structurally similar CuCl(2-ethylpyrazine) coordination compounds. The formation and the stability of the different compounds in solution were also investigated.
The five zinc(II) halide pyrazine coordination compounds poly-bis(mu2-pyrazine)-dichloro-zinc(II) (I), poly-(mu2-pyrazine-N,N')-dichloro-zinc(II) (II), poly-bis(mu2-pyrazine-N,N')-dibromo-zinc(II) (III), catena-(mu2-pyrazine-N,N')-dibromo-zinc(II) (IV), and catena-(mu-pyrazine)-diiodo-zinc(II) (V) were prepared by the reaction of ZnX2 (X = Cl, Br, I) with pyrazine in acetonitrile. In the crystal structure of compound I, the zinc atoms are coordinated by two chlorine atoms and two pyrazine ligands within distorted tetrahedra. The zinc atoms are linked by the N-donor ligands into layers. The crystal structure of compound III is very similar to that of compound I. The structure of compound III was originally reported in space group Ccca with similar a and b axes, but it was proved that the correct space group is I4/mmm. Ligand-poor compound V is isotypic to compound IV, in which ZnX2 units (X = Br, I) are connected by the pyrazine ligands into chains. It was originally reported in the noncentrosymmetric space group P2(1), but we found that the correct space group is P2(1)/m. If ligand-rich 1:2 compounds I and III are heated in a thermobalance, different mass steps are observed. We have proven that in the first step, ligand-poor compounds II and IV are formed in quantitative yields. On further heating, a second mass step occurs that leads to the formation of two new compounds of composition (ZnCl2)2(pyrazine) (VI) and (ZnBr2)2(pyrazine) (VII). However, the mass step is not well-resolved. and the new compounds are not phase-pure after the thermal event. If ligand-poor 1:1 compound V is investigated by thermogravimetry, a not-well-resolved single mass step is observed in which new ligand-poor 2:1 compound (ZnI2)2(pyrazine) (VIII) is formed. On further heating, all 2:1 compounds lose their remaining ligands and transform into the pure zinc(II) halides.
Heilbronner in 1964 predicted that annulenes with ".. a planar perimeter of N=4r AO's, which would yield an open shell configuration when occupied by 4r electrons, can be twisted into a closed shell Möbius strip perimeter without loss in pi electron energy". We have been able to synthesize the first [4n]annulene with such a Möbius topology and now present further Möbius isomers and the details of their preparation as stable compounds. To address the question whether the twist in the pi system has an effect on the properties we systematically investigate energy, geometry and magnetic parameters of a large number isomers of [16]annulenes. The Möbius twisted annulenes are consistently more aromatic than the non-twisted isomers. This is true for the parent as well as our benzoannelated systems. Our results are in contrast to those published recently by C. Castro, W. L. Karney, P. von R. Schleyer et al.
The title compound, C(24)H(24)N(2)O(2), crystallizes as a triclinic polymorph from dimethylformamide and a monoclinic polymorph from ethanol. In both forms, the molecule displays crystallographic inversion symmetry, and the packing involves translationally related 'ladders' of molecules connected by N-H...O=C hydrogen bonds. Differences between the structures can be rationalized in terms of weak C-H...O contacts. Powder and differential scanning calorimetry investigations of new samples gave no evidence for the triclinic form, and it seems to represent a disappearing polymorph.
The glucocorticoide triamcinolone diacetate was investigated for polymorphism. Crystallization experiments in different solvents performed at room-temperature reveal that in most cases solvates has formed (form B) which are isotypic and which crystallize in the orthorhombic space group P2(1)2(1)2(1). In their crystal structure channels are formed in which the solvent molecules are located. In some other solvents the commercial available form A is the thermodynamic most stable form. On heating form A using differential scanning calorimetry (DSC) the compound melts at a peak temperature of 136 degrees C without any further polymorphic transformation. If the solvents are removed at higher temperatures using simultaneous differential thermoanalysis and thermogravimetry coupled to mass spectroscopy (DTA-TG-MS) the remaining residues are amorphous against X-rays because the compound melts directly after desolvation. If the desolvation process is investigated by DSC measurements the same is observed for most solvents but in some cases different peaks for desolvation and melting are observed. In this case a new modification can be isolated after removing the solvent (form C). If the solvent are removed in vacuum or by storage at room-temperature always the commercial available form A is obtained, whereas desolvation experiments at 80 degrees C indicate the formation of a further polymorphic modification (form D).
The two novel compounds, [Mn(tren)]Sb2S4 (1 and 2), were obtained by the reaction of elemental Mn, Sb, and S in aqueous solutions of tren (tren = tris(2-aminoethyl)amine, C6H18N4) after different reaction times. Compound 1 is formed up to a reaction time of 13 d, and an extension of the reaction time leads to the formation of 2. Both compounds crystallize in monoclinic space groups (1, P2(1)/c; 2, C2/c). In 1, the two unique SbS3 trigonal pyramids share a common S atom to form a Sb2S5 unit. Two S atoms of this group have a bond to Mn2+ yielding a MnSb2S3 heteroring in the boat conformation. The Sb2S5 moieties are joined via common corners into the final undulated [Sb2S4]2- anion which is directed along [001]. The structure of 2 contains the [Mn(tren)]2+ ion, one SbS3 pyramid, and a SbS4 unit. Two symmetry-related SbS4 groups share an edge, forming a Sb2S6 group containing a Sb2S2 ring. This group is joined via corners to two SbS3 pyramids on both sides producing a Sb4S4 ring. The Sb2S2 and Sb4S4 rings are condensed into the final [Sb2S4]2- anion which runs along [010]. The [Mn(tren)] groups are bound to the thioantimonate(III) backbone on opposite sides of the Sb4S4 ring, and a small MnSbS2 ring is formed. In both structures, weak S...H bonds are found which may contribute to the stability of the materials. The two compounds decompose in one step upon heating, and only MnS and Sb2S3 could be identified as the crystalline part of the decomposition products. Both compounds can also be prepared under solvothermal conditions using MnSb2S4 as starting material. Compounds 1 and 2 are obtained from this ternary material in a high yield.
In this paper, the differences in the spectroscopic properties and electronic structures of five- and six-coordinate iron(II) porphyrin NO complexes are explored using [Fe(TPP)(NO)] (1; TPP = tetraphenylporphyrin) and [Fe(TPP)(MI)(NO)] (2; MI = 1-methylimidazole) type systems. Binding of N-donor ligands in axial position trans to NO to five-coordinate complexes of type 1 is investigated using UV-vis absorption and 1H NMR spectroscopies. This way, the corresponding binding constants Keq are determined and the 1H NMR spectra of 1 and 2 are assigned for the first time. In addition, 1H NMR allows for the determination of the degree of denitrosylation in solutions of 1 with excess base. The influence of the axial ligand on the properties of the coordinated NO is then investigated. Vibrational spectra (IR and Raman) of 1 and 2 are presented and assigned using isotope substitution and normal-coordinate analysis. Obtained force constants are 12.53 (N-O) and 2.98 mdyn/A (Fe-NO) for 1 compared to 11.55 (N-O) and 2.55 mdyn/A (Fe-NO) for 2. Together with the NMR results, this provides experimental evidence that binding of the trans ligand weakens the Fe-NO bond. The principal bonding schemes of 1 and 2 are very similar. In both cases, the Fe-N-O subunit is strongly bent. Donation from the singly occupied pi* orbital of NO into d(z2) of iron(II) leads to the formation of an Fe-NO sigma bond. In addition, a medium-strong pi back-bond is present in these complexes. The most important difference in the electronic structures of 1 and 2 occurs for the Fe-NO sigma bond, which is distinctively stronger for 1 in agreement with the experimental force constants. The increased sigma donation from NO in 1 also leads to a significant transfer of spin density from NO to iron, as has been shown by magnetic circular dichroism (MCD) spectroscopy in a preceding Communication (Praneeth, V. K. K.; Neese, F.; Lehnert, N. Inorg. Chem. 2005, 44, 2570-2572). This is confirmed by the 1H NMR results presented here. Hence, further experimental and computational evidence is provided that complex 1 has noticeable Fe(I)NO+ character relative to 2, which is an Fe(II)NO(radical) complex. Finally, using MCD theory and quantum chemical calculations, the absorption and MCD C-term spectra of 1 and 2 are assigned for the first time.
Vibrational properties of the five-coordinate porphyrin complexes [M(TPP)(Cl)] (M = Fe, Mn, Co) are analyzed in detail. For [Fe(TPP)(Cl)] (1), a complete vibrational data set is obtained, including nonresonance (NR) Raman, and resonance Raman (RR) spectra at multiple excitation wavelengths as well as IR spectra. These data are completely assigned using density functional (DFT) calculations and polarization measurements. Compared to earlier works, a number of bands are reassigned in this one. These include the important, structure-sensitive band at 390 cm(-1), which is reassigned here to the totally symmetric nu(breathing)(Fe-N) vibration for complex 1. This is in agreement with the assignments for [Ni(TPP)]. In general, the assignments are on the basis of an idealized [M(TPP)]+ core with D(4h) symmetry. In this Work, small deviations from D(4h) are observed in the vibrational spectra and analyzed in detail. On the basis of the assignments of the vibrational spectra of 1, [Mn(TPP)(Cl)] (2), and diamagnetic [Co(TPP)(Cl)] (3), eight metal-sensitive bands are identified. Two of them correspond to the nu(M-N) stretching modes with B(1g) and Eu symmetries and are assigned here for the first time. The shifts of the metal sensitive modes are interpreted on the basis of differences in the porphyrin C-C, C-N, and M-N distances. Besides the porphyrin core vibrations, the M-Cl stretching modes also show strong metal sensitivity. The strength of the M-Cl bond in 1-3 is further investigated. From normal coordinate analysis (NCA), force constants of 1.796 (Fe), 0.932 (Mn), and 1.717 (Co) mdyn/A are obtained for 1-3, respectively. The weakness of the Mn-Cl bond is attributed to the fact that it only corresponds to half a sigma bond. Finally, RR spectroscopy is used to gain detailed insight into the nature of the electronically excited states. This relates to the mechanism of resonance enhancement and the actual nature of the enhanced vibrations. It is of importance that anomalous polarized bands (A(2g) vibrations), which are diagnostic for vibronic mixing, are especially useful for this purpose.
The structures of the title complexes, (C6H15N2)2[MoS4], (I), and (C6H16N2)[MoS4], (II), can be described as consisting of discrete tetrahedral [MoS4]2- dianions that are linked to the organic ammonium cations via weak hydrogen-bonding interactions. The asymmetric unit of (I) consists of a single (+/-)-trans-2-aminocyclohexylammonium cation in a general position and an [MoS4]2- anion located on a twofold axis, while in (II), two crystallographically independent trans-cyclohexane-1,4-diammonium cations located on centres of inversion and one [MoS4]2- anion in a general position are found. The differing dispositions of the amine functionalities in the organic cations in the title complexes lead to different crystal packing arrangements in (I) and (II).
The molybdenum and tungsten dialkylhydrazido complexes [M(dppe)2 (NNC5H10)]2+ (M = Mo, W; compounds A(Mo) and A(W)) and their two-electron-reduced counterparts [M(dppe)2 (NNC5H10)] (compounds B(Mo) and B(W)) are characterized structurally and spectroscopically. The crystal structure of B(W) indicates a geometry between square pyramidal and trigonal bipyramidal with the NNC5H10 group in the apical position and in the trigonal plane of the complex, respectively. Temperature-dependent 31P NMR spectra of B(Mo) show that this geometry is present in solution as well. At room temperature, rapid Berry pseudorotation between the "axial" and "equatorial" ligand positions gives rise to a singlet in the 31P NMR spectrum. This exchange process is slowed at low temperature, leading to a doublet. The N-N distance of B(W) is 1.388 A, and the W-N distance is 1.781 A. Infrared and Raman spectroscopy applied to A(W), B(W), and their 15N isotopomers reveals extensive mixing between the N-N and W-N vibrations of the metal-N-N core with the modes of the piperidine ring. The N-N force constant of A(W) is determined to be 6.95 mdyn/A, which is close to the values of the Mo and W NNH2 complexes. In B(W), the N-N force constant decreases to 6.4 mdyn/A, which is between the values found for the Mo/W NNH3 and NNH2 complexes. This allows us to attribute N-N double bond character to A(W) and intermediate character between the double and single bonds for the N-N bond of B(W). These findings are supported by DFT calculations. More importantly, the HOMO of B(W) corresponds to a linear combination of the metal d(sigma) orbital with a ligand orbital having N-N sigma* character, inducing a weakening of the N-N bond. This contributes to the cleavage of the N-N bond taking place upon protonation of B(W) at the Nbeta atom of the NNC5H10 group.
The spectroscopic properties and the electronic structure of the only nitrous oxide complex existing in isolated form, [Ru(NH(3))(5)(N(2)O)]X(2) (1, X = Br(-), BF(4)(-)), are investigated in detail in comparison to the nitric oxide precursor, [Ru(NH(3))(5)(NO)]X(3) (2). IR and Raman spectra of 1 and of the corresponding (15)NNO labeled complex are presented and assigned with the help of normal coordinate analysis (NCA) and density functional (DFT) calculations. This allows for the identification of the Ru-N(2)O stretch at approximately 300 cm(-)(1) and for the unambiguous definition of the binding mode of the N(2)O ligand as N-terminal. Obtained force constants are 17.3, 9.6, and 1.4 mdyn/A for N-N, N-O, and Ru-N(2)O, respectively. The Ru(II)-N(2)O bond is dominated by pi back-donation, which, however, is weak compared to the NO complex. This bond is further weakened by Coulomb repulsion between the fully occupied t(2g) shell of Ru(II) and the HOMO of N(2)O. Hence, nitrous oxide is an extremely weak ligand to Ru(II). Calculated free energies and formation constants for [Ru(NH(3))(5)(L)](2+) (L = NNO, N(2), OH(2)) are in good agreement with experiment. The observed intense absorption at 238 nm of 1 is assigned to the t(2g) --> pi(*) charge transfer transition. These data are compared in detail to the spectroscopic and electronic structural properties of NO complex 2. Finally, the transition metal centered reaction of nitrous oxide to N(2) and H(2)O is investigated. Nitrous oxide is activated by back-donation. Initial protonation leads to a weakening of the N-O bond and triggers electron transfer from the metal to the NN-OH ligand through the pi system. The implications of this mechanism for biological nitrous oxide reduction are discussed.
Infrared and Raman spectra of Fe(4)(S/Se)(4) clusters with terminal halide ligands and MoFe(3)S(4) clusters with terminal thiolate and halide ligands are presented and interpreted on the basis of the force fields determined in the accompanying paper. The Raman spectra of halide coordinated Fe(4)(S/Se)(4) clusters are characterized by the fact that vibrations of the terminal ligands appear with little or vanishing intensity. Infrared and Raman spectra of MoFe(3)S(4) clusters with terminal thiolates are correlated to those of corresponding Fe(4)S(4) systems, which were investigated in part 1 of this study and interpreted with normal coordinate analysis. Band assignments are checked by employing MoFeS(4) clusters with terminal halide ligands. Spectra of these systems are in turn compared to those of their Fe(4)S(4) counterparts, i.e., Fe-S cubane clusters with chloro, bromo, and iodo ligands. A consistent interpretation of all spectra is presented. General implications of these results are discussed.
A series of Fe-S and Fe-Se cubane clusters containing all four combinations of the general formula [Fe(4)X(4)(Y-CH(3))(4)](2)(-) (X = S/Se, Y = S/Se) is investigated with FTIR and Raman spectroscopy. The terminally selenolate coordinated clusters (Y = Se) are prepared by a new synthetic route. All four cluster compounds are structurally characterized by X-ray single-crystal structure determination. Infrared and Raman spectra of all compounds are presented and interpreted with normal coordinate analysis. The corresponding force fields are based on that developed for the Fe(4)S(4)-benzyl cluster (Czernuszewicz, R. S.; Macor, K. A.; Johnson, M. K.; Gewirth, A.; Spiro, T. G. J. Am.Chem. Soc. 1987, 109, 7178-7187). An empirical procedure is presented to convert Fe-S into Fe-Se force constants. Only minor changes in force constants are found upon S --> Se exchange, reflecting the similarity of the Fe-S and Fe-Se bonds. The drastic frequency shifts in the metal-ligand region observed upon substitution of sulfur by selenium are, therefore, primarily due to the corresponding mass changes.
Two new neutral thioantimonates(III) were first prepared by the reaction of elemental manganese, antimony, and sulfur in tren (tren = tris(2-aminoethyl)amine, C6H18N4) at 140 degrees C. In the amine-rich compound [Mn(tren)]2Sb2S5 (1) the trigonal SbS3 pyramids are connected via common corners (S(3)) into the tetradentate [Sb2S4]4- anion. Four S atoms have bonds to the manganese atoms of the [Mn(tren)2+] cations. A special structural feature is the large Sb-S(3)-Sb(a) angle of 134 degrees. Density functional calculations clearly demonstrate that this large angle results from the steric interactions between the two Mn(tren) subunits. In the crystal structure of the amine-poorer compound [Mn(tren)]2Mn2Sb4S10 (2), MnS4 tetrahedra and SbS3 pyramids are linked via common corners and edges to form a new heterometallic [Mn2Sb4S10] core. The [Mn(C6H18N4)2+] cations are located at the periphery of the core and are bound to the [Mn2Sb4S10] unit via two S atoms. The thermal behavior of both compounds was investigated using simultaneous thermogravimetry (TG), differential thermoanalysis, and mass spectroscopy. The amine-richer compound 1 decomposes in three steps upon heating. After the first TG step an intermediate phase is formed, which was identified as the amine-poorer compound 2 by X-ray diffraction. Reaction of compound 2 at 140 degrees C with an excess of tren forms the amine-rich compound 1.
The reaction of Ta with an in situ formed polythiophosphate melt of Cs2S3, P2S5, and S yields the two new quaternary tantalum thiophosphates Cs2Ta2P2S12 (I) and Cs4Ta4P4S24 (II). Both compounds were obtained with the same stoichiometric ratio but at different reaction temperatures. Compound I was prepared at 873 K and crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 8.862(2) A, b = 12.500(3) A, c = 17.408(4) A, beta = 99.23(3) degrees, and Z = 4. Compound II was prepared at 773 K and crystallizes in the monoclinic space group P2(1)/n (No. 14) with a = 14.298(3) A, b = 17.730(4) A, c = 16.058(3) A, beta = 106.19(3) degrees, and Z = 4. The two structures are closely related and exhibit two-dimensional anionic layers consisting of dimeric [Ta2S11] units which are linked by two tetradentate and two tridentate [PS4] tetrahedra. The significant difference between these two compounds is the orientation of the [Ta2S11] units in infinite [Ta2S4(PS4)]x chains which are subunits of both structures. The specific orientation of the [Ta2S11] blocks in compound I leads to the formation of one cavity in the 2(infinity)[Ta2P2S12]2- layers, whereas in compound II two types of cavities are observed in the 2(infinity)[Ta4P4S24]4- layers. The Cs+ ions are located between the layers above and below the cavities. The compounds were characterized with infrared spectroscopy in the MIR region, Raman spectroscopy, and UV/Vis diffuse reflectance spectroscopy. When Cs4Ta4P4S24 (II) is heated at the synthesis temperature of compound I it is fully converted into compound I.
In the crystal structure of the title compound, [Cu(NCS)(C(4)H(4)N(2))](n), each Cu atom is coordinated by one N atom of one pyridazine ligand and by one N and two S atoms of three symmetry-related thiocyanate anions within a distorted tetrahedron. Only one N atom of the pyridazine ligand is involved in Cu coordination. The Cu atoms are connected via the thiocyanate anions, forming layers parallel to the ab plane.