Analyses of Reaction Mechanisms among Different Sulfonation Reagents and m-Diphenylamine and Crystal Structures of the Formed Compounds

In the traditional process, m-phenylenediamine reacts with fuming sulfuric acid at high temperature to get intermediates, and then after dehydration occurs intramolecular rearrangement to get 2,4-diaminobenzenesulfonic acid. Traditional methods need to consume a lot of fuming sulfuric acid or concentrated sulfuric acid, resulting in high industrial large-scale production cost, more waste, and posing a serious environmental pollution risk. In this thesis, three different sulfonation reagents were used for the sulfonation reaction of m-phenylenediamine, and the reaction mechanisms and crystal structures of the three pathways were investigated. The three routes are: 1) one-step synthesis of monosulfonated compound 1 from raw material and sulfur trioxide (SO3);2) rapid reaction of raw material and chlorosulfonic acid to synthesize bisulfonated compound 2;3) direct eutectic crystallization of raw material and ordinary sulfuric acid to obtain compound 3. The crystal structure of the compounds synthesized by three paths was analyzed by X-ray single crystal diffraction, and compound 1 was characterized by NMR, Fourier infrared spectra, UV-visible spectrum and Mass spectrometry. The one-step synthesis of SO3 as a sulfonation reagent has the advantages of mild reaction conditions, simple operation and low cost.

A review of flotation and selective separation of pyrrhotite:A perspective from crystal structures

Pyrrhotite is an associated mineral that exists widely in sulfide ore. The presence of pyrrhotite will affect the recovery of platinum group minerals. Therefore, researchers have paid increasing attention to the flotation separation of pyrrhotite. Pyrrhotite superstructures owning different Fe/S ratios results in various crystal structures, corresponding to different physical, chemical and electronic properties, and consequently different flotation behavior. In the present paper, a comprehensive review is conducted to discuss the influence of crystal structures on the natural floatability, mineral-reagent interaction, surface oxidation and flotation electrochemistry of pyrrhotite. The selective flotation process of pyrrhotite from its associated minerals is also reviewed in this paper. It is hoped that this review can summarize the newly published research results combined with some representative results from the past, to provide a theoretical basis for the study of the flotation mechanism of pyrrhotite and provide a new direction for future research on pyrrhotite.

Syntheses and Crystal Structures of Four Cobalt Supramolecular Architectures with Hmtyaa Ligand

Four cobalt supramolecular architectures with Hmtyaa（2-（5-methyl-1,3,4-thiadiazol-2-ylthio）acetic acid） ligand have been synthesized.[Co（mtyaa）2（H2O）4]·4（H2O）（1）：triclinic,space group P1 with a = 6.7537（18）,b = 8.591（2）,c = 10.615（3） ,α = 96.495（4）,β = 99.955（5）,γ = 103.615（5）°,V = 581.9（3） 3,Z = 1,Mr = 581.52,Dc = 1.659 g/m3,μ = 1.158 mm-1,F（000） = 301,Rint = 0.0557,R = 0.0377 and wR = 0.1056 for 1854 observed reflections with Ⅰ 〉 2σ（Ⅰ）;{[Co（4,4＇-bipy）（H2O）4]·2（mtyaa）·2（H2O）}n（2）：triclinic,space group P1 with a = 7.669（2）,b = 8.840（3）,c = 11.521（4） ,α = 79.912（5）,β = 73.954（5）,γ = 86.612（6）°,V = 738.9（4） 3,Z = 1,Mr = 701.67,Dc = 1.577 g/m3,μ = 0.924 mm-1,F（000） = 363,Rint = 0.0636,R = 0.0498 and wR = 0.1311 for 2155 observed reflections with Ⅰ 〉 2σ（Ⅰ）;{[Co（4,4＇-bipy）（mtyaa）（H2O）3]（mtyaa）·2（H2O）}（3）：monoclinic,space group Pc with a = 7.7832（17）,b = 11.527（3）,c = 31.483（7） ,β = 91.952（4）°,V = 2822.9（11） 3,Z = 4,Mr = 683.65,Dc = 1.609 g/m3,μ = 0.963 mm-1,F（000） = 1412,Rint = 0.0758,R = 0.0609 and wR = 0.1095 for 5841 observed reflections with I 〉 2σ（I）;{[Co（bpe）（mtyaa）2（H2O）2]}n（4）：monoclinic,space group C2/c with a = 19.290（11）,b = 12.027（7）,c = 14.865（8） ,β = 125.648（8）°,V = 2802（3）3,Z = 4,Mr = 657.66,Dc = 1.559 g/m3,μ = 0.959 mm-1,F（000） = 1356,Rint = 0.0456,R = 0.0332 and wR = 0.0985 for 2299 observed reflections with Ⅰ 〉 2σ（Ⅰ）.

Syntheses and Crystal Structures of Complexes [Cu(C_(14)H_8N_3O_4Br)](C_4H_9NO) and [Ni(C_(14)H_9N_2O_3Br)](C_4H_9NO)

The title compounds, Cu（L1）（C4H8NHO） and Ni（L2）（C4H8NHO） （H2L1 = 5-bromosalicylaldehyde-p-nitrobenzoylhydrazone, H2L2 = 5-bromosalicylaldehyde-p-hydroxybenzoylhydrazone）, have been obtained and characterized by single-crystal X-ray diffraction. Complex 1 belongs to the triclinic system, space group P1 with a = 8.6960（2）, b = 9.957（2）, c = 11.878（2）A, α = 73.36（3）, β = 78.25（3）, γ = 82.64（3）°, V = 962.1（3） A^3, Mr= 512.81, Z = 2, F（000） = 514, Dc = 1.770 g/cm^3,μ（MoKα） = 3.251, R = 0.0337 and wR = 0.0846. Complex 2 is of monoclinic, space group P21/c with a = 13.313（2）, b = 8.2096（1）, c = 21.890（3） A,β = 125.737（3）°, V = 1941.9（4） A^3, Mr= 478.97, Z = 4, F（000） = 968, Dc = 1.638 g/cm^3,μ（MoKα） = 3.085, R = 0.0356 and wR = 0.0817. The ligands form a satisfactory N2O2 square plane around the metal centers in two compounds. Different patterns of hydrogen bonds are observed owing to the presence of different substituents on aromatic ring of the acylhydrazone Schiff bases. In complex 1, square-planar copper（Ⅱ） complexes are linked by intermolecular hydrogen bonds leading to zigzag infinite chains. In complex 2, the metal complexes are linked via hydrogen bonds to form corrugated sheets in a staggered fashion; 3D channels along the b axis are constructed through other non-covalent interactions between the neighboring layers.

Synthesis and Crystal Structures of the α and β Forms of Bis(salicylaldoxime)copper(Ⅱ) Complexes

Modified α and β bis(salicylaldoxime)copper(Ⅱ) have been obtained by recrystallization from ethyl acetate(CCDC Nos. 212157 & 212158). The X-ray analysis reveals that the two modificated forms have the same structure with different geometric parameters. The α form crystallizes in the P2(1)/c space group and the β form in the P1 space group. Both the crystal structures consist of centrosymmetric monomeric molecules of Cu(OC_6H_4CNOH)_2. The IR spectra are in agreement with the structural data.

Syntheses, Crystal Structures and Antifungal Activities of Two Compounds Containing Pyrazole and Pyrethroid Units

Compounds 1 （C15H17C1F3N303, Mr = 379） and 2 （C14H14C1F3N4OS, Mr = 378） have been synthesized and their crystal structures were determined by single-crystal X-ray diffraction. Crystal 1 belongs to the triclinic system, space group P1 with a = 6.0223（19）, b = 9.324（3）, c = 15.936（5） A, a = 80.687（5）, β= 87.289（5）, ）, = 86.097（5）°, V= 880.4（5） A3, Z = 2, Dc = 1.433 g/cm3,μ（MoKa） = 0.266 mm^-1, F（000） = 392, R = 0.0861 and wR = 0.1999 for 2022 observed reflections with I 〉 2o（/）. Crystal 2 belongs to the triclinic system, space group PI with a = 7.7029（15）, b = 8.3371（16）, c = 14.410（3） A, a = 100.672（3）, β= 103.168（3）, ？ = 98.726（3）°, V = 876.1（3） A3, Z = 2, Dc= 1.451 g/cm^3,μ（MoKa） = 0.379 mm^-1, F（000） = 388, R = 0.0672 and wR = 0.2105 for 2725 observed reflections with I 〉 2σ（I）. Although the two compounds are similar with the same pyrazole and pyrethroid units, X-ray analysis reveals that their structures are completely different.

Syntheses, Crystal Structures and Fluorescence Properties of Two Pb(Ⅱ) 1-Naphthoate Complexes

Two new 1-naphthoate-based Pb（Ⅱ） complexes, [Pb（phen）（NA）2]n 1 and [Pb（bpp）（NA）2]n 2 （NA = 1-naphthoate, phen = 1,10-phenanthroline, and bpp = 1,3-bi（4-pyri- dyl）propane）, were hydrothermally synthesized and structurally characterized. 1 is of monoclinic system, space group C2/c with a = 28.114（3）, b = 10.9601（10）, c = 8.6843（8） , β = 93.3760（10）°, V = 2671.3（4） 3, Dc = 1.814 g/cm3, Mr = 729.73, Z = 4, F（000） = 1416, μ = 6.360 mm-1, the final R = 0.0346 and wR = 0.0948 for 2184 observed reflections with I 〉 2σ（I）. Complex 2 crystallizes in monoclinic, space group C2/c with a = 26.491（2）, b = 8.7773（6）, c = 27.893（2） , β = 113.3020（10）°, V = 5956.8（8）3, Dc = 1.668 g/cm3, Mr = 747.78, Z = 8, F（000） = 2928, μ = 5.706 mm-1, the final R = 0.0211 and wR = 0.0493 for 3677 observed reflections with I 〉 2σ（I）. Both complexes present one-dimensional （1-D） zigzag chains extended by anionic NA linkers for 1 and bridged by neutral bpp connectors for 2, which are further aggregated into 2-D supramolecular networks by interchain π···π stacking interactions. In addition, the two solid-state complexes exhibit different strong emissions at room temperature, suggesting their potential applications as fluorescence materials.

Syntheses and Crystal Structures of Two Co(II) Coordination Polymers with 4,4'-(Hexafluoroisopropylidene)bis(benzoic acid)

Two new one-dimensional zigzag chain coordination polymers, [Co（hfipbb）（2,2＇- bpy）（H2O）2]n 1 and [Co（hfipbb）（1,10-phen）（H2O）], 2, have been synthesized under hydrother- mal reactions from COCl2.6H20, 4,4＇-（hexafluoroisopropylidene）bis（benzoic acid） and 2,2＇ -bipyridine or 1,10-phenanthroline ligands, respectively. Single-crystal X-ray analyses revealed that the zigzag chains of 1 and 2 are linked into three-dimensional supramolecular networks by both O-H…O hydrogen-bonds and π…π stacking interactions. Crystal data for 1： CzTHajCoF6N2Os Mr = 641.38, orthorhombic, space group Pnna, a = 9.3820（19）, b = 27.366（6）, c = 10.106（2）A, V = 2594.8（9）A3, Z = 4, Dc = 1.642 g/cm3, F（000） = 1300,/t = 0.752 mm-l, R = 0.0311 and wR = 0.0924. Crystal data for 2： C29H18CoF6N2O5, Mr = 647.38, monoclinic, space group P21/n, a = 7.7626（16）, b = 29.446（6）, c = 11.281（2）A,β= 93.98（3）°, V= 2572.3（9）A3, Z = 4, Dc = 1.672 g/cm3, F（000） = 1308,μ= 0.757 mm-1, R = 0.0403 and wR = 0.0820.

SYNTHESIS,CHARACTERIZATION AND CRYSTAL STRUCTURES OF η~5-CH_3C_5H_4)M(CO)_2NO AND(η~5-CH_3C_5H_4)M(μ_3-NH)(μ_2-NO)(μ_2-CO)Fe_2(CO)_6(M=Mo or W)

Synthesis of complexes（η;-CH;C;H;）M（CO）;NO（M=Mo,I;M=W,II）and clusters（η;-CH;C;H;）M（μ;-NH）(μ;-NO) （μ;-CO）Fe;（CO）;（M=Mo,III:M=W,IV）,based on the reaction of （η;-C5;）M（CO）;Cl with Na[Fe（CO）;NO] at room tem-perature,have been demonstrated,The crystal structures of II and IV arealso presented.

MOLECULAR AND CRYSTAL STRUCTURES OF TETRANUCLEAR MOLYBDENUM CLUSTER[Mo_4(μ_3-O)_2O_4Cl_2(o-CH_3C_6H_4COO)~6]■

The new cluster[Mo_4(μ_3-O)_2O_4Cl_2(o-CH_3C_6H_4COO)_6]has been prepared by the reaction of molybdenum pentachloride and o-methylbenzoic acid.The crystal and molecular structures were determined by the X-ray diffraction method.It crystallizes in the orthorhombic space group Pnna with cell parameters:Mr=1361.6,a=13.792(4), b=17.957(3),c=20.974(9) ,V=5194(2) ~3,Z=4,Dc=1.74/cm^3,F(OOO)=2704,μ(MoK ) =11.0/cm,R=0.074.

Syntheses and Crystal Structures of Two One-dimensional Coordination Polymers Constructed from a Flexible Hinge-like Ligand

By using the flexible hinge-like ligand 2,2＇-bis（3-hydroxy-l,4-naphthoquinone） （H2bhnq）, two isomorphous one-dimensional zigzag chain coordination polymers have been obtained. Single-crystal X-ray analyses revealed that the metal centers in these two complexes are distorted octahedra involving four oxygen atoms of two bhnq2 anions, and two oxygen atoms of two DMF molecules situated in trans positions to one another. Crystal data for [Mn（bhnq）（DMF）2]n 1： C26H22MnN2O8, Mr = 545.40, monoclinic, space group C2/c, a = 14.936（3）, b = 10.362（2）, c = 15.901（3）A., β = 99.86（3）°, V = 2424.7（8）A3, Z = 4, Dc = 1.494 g/cm^3, F（000） = 1124,μ = 0.599 mm^-1, final GOOF = 1.025, R = 0.0654 and wR = 0.1537. Crystal data for [Cd（bhnq）（DMF）2]n 2： C26H22CdN2O8, Mr = 602.86, monoclinic, space group C2/c, a = 14.839（3）, b = 10.493（2）, c = 16.034（3）A, β = 99.40（3）°, V = 2463.1（9）A^3, Z = 4, Dc = 1.626 g/cm^3, F（000） = 1216,μ = 0.941 mm^-1, final GOOF = 1.069, R = 0.0358 and wR = 0.0944.

Crystal Structures and Photoluminescence Properties of Two Lanthanide Complexes Constructed by Flexible 1,2-Phenylenediacetic Ligand

Two 3D Ln-organic coordination frameworks（Ln = Pr3＋ for 1 and Er3＋ for 2） have been constructed. Single-crystal X-ray diffraction analysis reveals that the two complexes have similar structures and belong to the monoclinic C2/c space group. The trans-μ4-（η2：η1）-（η1：η1） 1,2-pda2- anions link the LnIII centers to generate a 2D network containing helical motif. The dimensionality is extended into a 3D architecture through cis-bis（μ2-η2：η1） 1,2-pda2- anions linking. The geometry of Ln3＋ ions is single-capped anti-square prism. Two complexes were characterized by IR spectra and thermogravimetric analysis. The solid fluorescence of 1 and 2 was also investigated at room temperature.

Syntheses,Crystal Structures and Thermal Properties of Two Dicadmiun(II) Complexes Cd_2L_2X_2(HL=N-(3-Methoxylsalicylidene)-3-dimethylaminopropylamine,X = Cl(1),NCS(2))

Two Cd（Ⅱ） complexes, Cd2L2Cl2 （1） and Cd2L2（NCS）2 （2） （HL = N-（3-methoxylsalicylidene）-3-dimethylaminopropylamine） were synthesized and determined by EA, IR, TG and single-crystal X-ray diffraction. The crystallographic data are as follows： monoclinic, space group P21/n, a = 9.2710（9）, b = 18.0069（18）, c = 18.5562（19） A^°, β= 99.741（4）°, V = 3053.1（5）, Z = 4,μ = 1.605, F（000） = 1536, R = 0.0264 and wR = 0.0699 for 1; orthorhombic, space group Pca21, a = 16.196（3）, b = 11.506（2）, c = 36.126（7） A^°, V = 6732（2）, Z = 8,μ = 1.428, F（000） = 3264, R = 0.0376 and wR = 0.0877 for 2. There are two geometrically different octahedral Cd（Ⅱ） atoms, with N4O2 and O4Cl2 donor sets for 1 while N4O2 and N2O4 for 2. In the dinuclear Cd（Ⅱ） centers, the Cd（Ⅱ） atoms are held together by two deprotonted phenolate oxygen atoms from tetradentate L^- ligands. The thermal gravity data show two step decompositions with the residues of CdO for two complexes.

SYNTHESIS AND CRYSTAL STRUCTURES OF {Pr[(C_2H_5O)_2POO]_3}_n

The synthesis, characterization and crystal structure of rare earth coordination complex of {Pr[（C;H;O）;POO];};has been studied. It is triclinic with space group P1 in a unit cell of dimensions a=11.788（5）, b=12.536（3）, c=10.262（2.） , α=112.21（2）, β=93.01（3）, γ=109.94（3）°; V=1290.9（8）;, Z=2. As shown in Fig. 1, each Pr atom is connected with other two Pr atoms through three "O-P-O" bridging groups to form a long chain polymer. The coordination number of Pr is six. The six coordinated O atoms form an octahedron. The average bond distance of Pr-O is 2.333 A. The complex has been also studied by infrared spectroscopy and thermal analyses.

Syntheses and Crystal Structures of Two Zn(Ⅱ) Coordination Polymers Constructed with 4,4'-(Dihydroxymethylene)dibenzoic Acid

Two new isomorphous metal-organic coordination polymers, [Zn（dhmdb）（2,2＇- bpy）]n 1 and [Zn（dhmdb）（1,10-phen）]n 2, have been obtained under hydrothermal reactions from 4,4＇-（dihydroxymethylene）dibenzoic acid （H2dhmdb）, Zn（NO3）2·6H2O and 2,2＇-pyridine or 1,10- phenanthroline, respectively. Compounds 1 and 2 have been characterized by FT-IR spectroscopy, thermal analysis and single-crystal X-ray diffraction. The zigzag chains of 1 and 2 are linked into three-dimensional supramolecular networks by both O–H…O hydrogen bonds and π…π stacking interactions. Crystal data for 1： ZnC25H18N2O6, Mr = 507.78, orthorhombic, space group Pbca, a = 14.031（3）, b = 10.826（2）, c = 27.343（6）, V = 4153.5（14）3, Z = 8, Dc = 1.624 g/cm3, F（000） = 2080, μ = 1.231 mm-1, R = 0.0699 and wR = 0.1829. Crystal data for 2： ZnC27H18N2O6, Mr = 531.80, orthorhombic, space group Pbca, a = 13.796（3）, b = 10.809（2）, c = 28.612（6）, V = 4266.8（15）3, Z = 8, Dc = 1.656 g/cm3, F（000） = 2176, μ = 1.203 mm-1, R = 0.0454 and wR = 0.1399.

Four New Cu(Ⅱ) Complexes with Benzotriazole-based Ligands: Syntheses, Crystal Structures and Theoretical Investigations

Four new Cu（Ⅱ） complexes with two benzotriazole-based ligands, [Cu2（L^1）2（NO3）2]· 2H2O （1）, [Cu2（L^1）2]·2ClO4·2H2O （2）, [Cu2（HL^2）2（NO3）4]·2CH3COCH3 （3） and [Cu（HL^2）2（Cl）]·Cl·2CH2Cl2 （4）, where HL^1 = 1,3-bis（benzotriazol-2-yl）-2-propanol and HL^2 = 1,3-bis（benzotriazol-1-yl）-2-propanol, were synthesized and structurally characterized by elemental analyses, IR and single-crystal X-ray diffraction analyses. It is revealed that complexes 1～3 have dinuclear structures, while 4 possesses a one-dimensional （1-D） chain structure, which extends in two orthogonal orientations. In 1～4, the coordination numbers of Cu（Ⅱ） centers range from four to six, which may be attributed to the different geometries and coordination abilities of the ligands and anions. The L^1 ligand in complexes 1 and 2 adopts a tridentate di-chelating coordination mode, whereas ligand HL^2 in complexes 3 and 4 has a bidentate bridging coordination mode. The different coordination modes of these two ligands may be explained by the different charges of nitrogen donor atoms in the benzotriazole ring, which has been investigated by density functional theory （DFT） calculations.

Investigation on Molecular and Crystal Structures of Metal Complexes with Aminopolycarboxylic Acids(Ⅰ)─Synthesis and Structure of Na_2[Fe~Ⅲ(ida)2]2·3H_2O

The crystal structure of the title complex salt has been determined by single-crystal X-ray structure analysis. The crystal data are as follows; Monoclinic, P21/c, a=15.6480(10)A,b=16.7870(10)A, c=10.347(2)A, β=90.790(10), V=2717.7(6)A3, Z=3, and R=0.0333 for 4789 unique reflections. The complex anion has a pseudo-octahedral structure distorted more than the CrⅢand CoⅢ analogs, in which cach iminodiacetato ligand (ida2-) is coordinated in a facial fashion with the two N atoms in a cis configuration, resulting in an unsyin-fac structure.

Ionothermal Syntheses and Crystal Structures of Two Cobalt(Ⅱ) Compounds:Co(2,2'-bpy)_2Br_2 and Co(1,10-phen)_2Br_2

Two cobalt（Ⅱ） compounds,Co（2,2-bpy） 2 Br 2 （1,2,2-bpy=2,2-bipyridyl） and Co（1,10-phen） 2 Br 2 （2,1,10-phen=1,10-phenanthroline）,have been prepared under ionothermal reactions using the 1-propyl-3-methylimidazolium bromide ionic liquid solvent.Single-crystal X-ray analyses reveal that 1 crystallizes in a monoclinic space group P2 1 /c,with a=8.5509（13）,b=14.804（2）,c=15.650（2）,β=97.119（2） o,V=1965.8（5） 3,Z=4,C 20 H 16 Br 2 N 4 Co,M r=531.12,D c=1.795 g/cm 3,μ=4.950 mm-1,F（000）=1044,the final R=0.0467 and wR=0.0736 for 2291 observed reflections with I 2σ（Ⅰ）.Complex 2 crystallizes in a monoclinic space group P2 1 /n,with a=10.4237（8）,b=16.8657（12）,c=12.4945（9）b,β=102.110（1） o,V=2147.7（3） 3,Z=4,C 24 H 16 Br 2 N 4 Co,M r=579.16,D c=1.791 g/cm 3,μ=4.540 mm-1,F（000）=1140,the final R=0.0431 and wR=0.1042 for 3470 observed reflections with I 2σ（Ⅰ）.The mononuclear molecules of 1 are linked by the C-H···Br hydrogen bonds and π-π interactions to form a three-dimensional supramolecular framework structure.The C-H···Br hydrogen bonds and π-π interactions link the mononuclear molecules of 2 to give a two-dimensional layer structure.

Fault-Tolerant Resolvability of Certain Crystal Structures

An ordered set W of vertices of a graph G is called a resolving set, if all the vertices of G are uniquely determined by the vector of distances to the vertices in W. The metric dimension of G is the minimum cardinality of a resolving set of G. A resolving set W for G is fault-tolerant if W\{v} is also a resolving set, for each v in W, and the fault-tolerant metric dimension of G is the minimum cardinality of such a set. In this paper we determine the metric dimension and fault-tolerant metric dimension problems for the graphs of certain crystal structures.

Crystal Structures of Two Compounds from a Rapid and One-pot Synthesis Method

Compounds 1 （C17H22N2,Mr =254.37） and 2 （C13H16N2,Mr=200.28） have been synthesized and their crystal structures were determined by single-crystal X-ray diffraction.Crystal 1 belongs to triclinic,space group P（1） with a =6.524（2）,b =8.987（3）,c =12.746（5） A,α =95.220（7）,β =90.055（6）,γ =104.431（6）°,V =720.5（4） A^3,Z =2,Dc =1.173 g/cm^3,μ（MoKα） =0.069 mm1,F（000） =276,R =0.0578 and wR =0.1221 for 1487 observed reflections Ⅰ 〉 2o（Ⅰ）.Crystal 2 is of tetragonal system,space group Ⅰ41/a with a =20.763（10）,b =20.763（10）,c =11.427（6） A,V=4926（4） A3,Z =16,Dc =1.080 g/cm^3,μ（MoKα） =0.065 mm-1,F（000） =1728,R =0.0581 and wR =0.1288 for 1408 observed reflections with Ⅰ 〉 2σ（Ⅰ）.Although the two compounds are similar with the same pyrazole and benzene ring units,X-ray analysis reveals that their structures are completely different maybe caused by steric effects.