Ligand‐Tuning of the Excitation Wavelength of a Solid state E/Z Isomerization: [Zn(TA)2(2,2′‐Bipyridyl)] in a Supramolecular Framework

The single‐crystal‐to‐single‐crystal (SCSC) E?Z photoisomerization of TA in the supramolecular solid CECR‐[Zn(TA)₂(bpy)]·H₂O (CECR = C‐ethylcalixresorcinarene, HTA = tiglic acid, and bpy = 2,2′‐bipyridine, is induced by 458 nm light, indicating a red‐shift of the photo‐active wavelength on introduction of the aromatic bpy ligand compared with the previously studied reaction of CECR‐[Zn(TA)₂(H₂O)₂] 4H₂O. Theoretical calculations show that the initial excitation involves the bipyridyl ligand, which acts as an intramolecular photosensitizer for the isomerization process. The reaction is topotactic and illustrated by photodifference maps.     

Single-crystal-to-single-crystal E-->Z and Z-->E isomerizations of 3-chloroacrylic acid within the nanocavities of a supramolecular framework

Single-crystal-to-single-crystal E-->Z and Z-->E photo-isomerizations of 3-chloroacrylic acid (HClA) take place with full retention of the crystal lattice in the framework cavities of the supramolecular crystals CECR.HClA.2MeOH.1.5H(2)O (CECR = C-ethylcalix[4] resorcinarene); their progress has been monitored as the reaction proceeds.     

Multiple conformations of benzil in resorcinarene-based supramolecular host matrixes

Six supramolecular complexes incorporating benzil as a guest, CMCR*bipy*benzil (alpha) 1 (CMCR = C-methylcalix[4]resorcinarene), CMCR*bipy*benzil (beta) 2, CMCR*2bpe*benzil*ethanol 3 (bpe = trans-1,4-bis(pyridyl)ethylene), CMCR*2bpe*benzil*2H2O 4, CMCR.2bpeh*benzil*ethanol 5 (bpeh = bis-(1-pyridin-4-yl-ethylidene)-hydrazine), and CECR*2bpe.benzil 6 (CECR = C-ethylcalix[4]resorcinarene), have been synthesized by hydrothermal and conventional methods and characterized by X-ray diffraction. Resorcinarene adopts a boat conformation in 1-4 and a bowl conformation in 5 and 6. Compounds 1-4 show a brick-wall-like framework, in which two benzil molecules are incorporated. For 5, bpeh spacers link CMCR molecules to give a one-dimensional wavelike polymer in which one benzil guest is embedded within the polymer cavity. Complex 6 forms a carcerand-like capsule in which two benzil guests are encapsulated. The O=C-C=O torsion angles vary from 91.8 to 139.3 degrees and correlate with the length of the central C-C bond. The benzil concentration, which is approximately 6.2 mol/L in the neat crystals, varies between 1.01 and 1.51 mol/L in the structures studied, corresponding to a 6-fold dilution. The benzil molecules are disordered in the larger cavities of 4 and 5. The two benzoyl fragments are almost perpendicular in 3, which has the next largest cavity size when solvent volume is excluded, whereas a nearly trans-coplanar conformation occurs for the cavity with the smallest volume in 6.     

Self-encapsulation of [MII(phen)2(H2O)2]2+ (M=Co, Zn) in one-dimensional nanochannels of [MII(H2O)6(BTC)2]4- (M=Co, Cu, Mn): a high HQ/CAT ratio catalyst for hydroxylation of phenols

Four novel three-dimensional (3D) microporous supramolecular compounds containing nanosized channels, namely, [Co(phen)2(H2O)2]2[Co(H2O)6].2BTC.21.5H2O (1), [Co(phen)2(H2O)2]2[Cu(H2O)6].2BTC.21.5H2O (2), [Co(phen)2(H2O)2]2[Mn(H2O)6].2BTC.18H2O (3), and [Zn(phen)2(H2O)2]2[Mn(H2O)6].2BTC.22.5H2O (4), were synthesized from 1,3,5-benzenetricarboxylate (BTC), 1,10-phenanthroline (phen), and the transition-metal salt(s) by self-assembly. Single-crystal X-ray structural analysis showed that the resulting 3D microporous supramolecular frameworks consist of a two-dimensional (2D) hydrogen-bonded host framework of [MII(H2O)6(BTC)2]4- (M=Co for 1, Cu for 2, Mn for 3, 4) with rectangular-shaped cavities containing [MII(phen)2(H2O)2]2+ (M=Co for 1-3, Zn for 4) guests. The guest complex is encapsulated in the 2D hydrogen-bonded host framework by hydrogen bonding and aromatic pi-pi stacking interactions, forming the 3D hydrogen-bonded framework. The catalytic activities of 1, 2, 3, and 4 were studied using hydroxylation of phenols with 30% aqueous H2O2 as a test reaction. The compounds displayed a good phenol conversion ratio and excellent channel selectivity in the hydroxylation reaction, with a maximum hydroquinone (HQ)/catechol (CAT) ratio of 3.9.     

Synthesis, structures, and magnetic properties of metal-coordination polymers with benzenepentacarboxylate linkers

Three hybrid organic-inorganic coordination polymers with benzenepentacarboxylate (BPCA) linkers, [Co3(C6H(COO)5)(OH)(H2O)3] (1-Co), [Zn3(C6H(COO)5)(OH)(H2O)3] (2-Zn), and [Co5(C6H(COO)5)2(H2O)12].(H2O)12 (3-Co), were synthesized hydrothermally and were characterized structurally and magnetically. 1-Co and 2-Zn are isostructural [C2/c; Z=8; 1-Co, a=19.5350(6) A, b=10.4494(4) A, and c=13.2353(5) A, beta=97.2768(8) degrees; 2-Zn, a=19.5418(9) A, b=10.3220(10) A, and c=13.4660(10) A, beta=98.455(10) degrees] with three-dimensional structures that contain [M6] secondary building units bridged by BPCA ligands. A different cobalt-based compound, 3-Co, forms at lower pH and lower reaction temperature. Its structure [P21/c; Z=2; a=12.6162(2) A, b=11.3768(2) A, and c=15.3401(3) A, beta=91.539(1) degrees] is a more loosely packed framework with free (noncoordinated) carboxylic groups pointing at water-filled cavities in the framework. The magnetic phase diagram of 1-Co established through detailed magnetic measurements shows a metamagnetic transition below TN=3.8 K. The less-packed compound 3-Co, on the other hand, remains paramagnetic above 1.9 K. The three compounds are the first examples of coordination polymers with benzenepentacarboxylate linkers and fill the gap of coordination polymers involving benzenepolycarboxylate linkers of the general type C6H6-n(COOH)n, where n=2-6.     

Synthesis,Structure and Luminescent Properties of [Zn(btzb)2Cl2]·2H2O[btzb=1,2-Bis(5-tetrazolyl)benzene]

The title compound[Zn(btzb)2Cl2]·2H2O(1·2H2O,btzb=1,2-bis(5-tetrazolyl)benzene)was synthesized in situ by the[2 3] cycloaddition reaction of phthalonitrile with NaN3 in water in the presence of ZnCl2 under refluxing conditions.1·2H2O crystallizes in the monoclinic system,space group P21/c with a=9.0119(18),b=7.5566(15),c=18.076(5)(A),β=114.67(2)°,V=1118.6(4)(A)3,Z=2,Dc=1.784 g/cm3 T=223(2)K,C16H16N16O2Cl2Zn,Mr=600.74,F(000)=608,μ(MoKα)=1.393 mm-1,S=1.081,R=0.0306 and wR=0.0669 for 1896 observed reflections with Ⅰ ＞2σ(Ⅰ).The Zn2 ion of 1 is coordinated by four N atoms from two btzb ligands and two Cl atoms,forming a distorted octahedral coordination geometry.A number of intermolecular hydrogen bonding interactions between molecules 1 and/or the solvated water molecules result in a 3D hydrogen-bonded structure.The luminescent property of 1·2H2O was also investigated.     

含吡啶-2,5-二羧酸稀土-锌配位聚合物的合成结构和性能（英文）

Gd2O3,Zn(CH3COO)2·2H2O和吡啶-2,5-二羧酸(H2pydc)的水热反应导致一个新颖的钆-锌配位聚合物[La2Zn2(pydc)5(H2O)2]n(1).化合物1的晶体属单斜晶系,空间群P21/c,a=9-5869(1), b=20.4862(3), c=10.1105(2)A,β=97.4890(10)°,V=1968.76(5)A3,Z=4.在同样的条件下,Er2O3或Tb4O7,Zn(CH3COO)2·2H2O和H2pydc的水热反应产生了与化合物1结构不同的配位聚合物[Ln2Zn(pydc)4(H2O)8·H2O]n(Ln=Er(2); Ln=Tb(3)).化合物2和3异质同晶,空间群P1.对2:a=7.8708(7), b=9.2665(8), c=13.0232(11)A, α=75.295(1),β=75.000(2),γ=79.109(2)°,V=879.67(13)A3,Z=1; 对3:a=7.9105(5), b=9.3453(6), c=13.0005(9)A, α=75.3380(10),β=75.0460(10), γ=79.0050(10)°,V=890.17(10)A3,Z=1.X-射线单晶结构研究表明化合物1是一个三维网状结构,而化合物2和3为管状结构.热重分析研究表明所有化合物在380℃以下稳定.     

Hydrothermal Assembly and Structural Characterization of a Novel 3D Coordination Polymer: [Cd_2Zn(BTC)_2(H_2O)_4]_n·2nH_2O

1INTRODUCTIONThehydrothermalsynthesisofmetalsaltsofaro-maticpolycarboxylicacidisattractinginterestinthefieldofcrystalengineeringasaconsequenceoftheirnovelstructuresandpropertiessuchasporosityandmagneticinteractionsbetweenparamagneticmetal-ions[1~7].1,3,5-Benzenetricarboxylicacid(H3-BTC)hasreceivedconsiderableattentionasatridentatearomaticpolycarboxylicligandcapableofformingcoordinationpolymers.Manyscientistshavesuc-ceededinsynthesizingvarietyofporouscoordina-tionpolymerswithhighdimension…     

Hydrothermal Assembly and Structural Characterization of a Novel 3D Coordination Polymer: [Cd2Zn(BTC)2(H2O)4]n·2nH2O

A hydrothermal reaction of 1,3,5-benzene-tricarboxylic acid (H3BTC) with cad- mium acetate, zinc acetate and pyridine led to the formation of pink crystals of [Cd2Zn(BTC)2- (H2O)4]n·2nH2O 1. Single-crystal X-ray diffraction analysis has revealed that 1 (Cd2ZnC18H18O18) crystallizes in the monoclinic system, space group C2/c with a = 19.4328(7), b = 7.1420(3), c = 18.0426(5)(A), β = 118.035(1)o, V = 2210.3(1) (A)3, Mr = 812.49, Dc = 2.442 g/cm3, Z = 4, μ(MoKα) = 3.081 mm-1 and F(000) =1584. A total of 10735 reflections were collected, of which 2544 were unique. The structure was refined to R = 0.0200 and wR = 0.0603 for 2388 observed reflections with I>2σ(I). The crystal structure consists of cadmium(II)/zinc(II) carboxylates of BTC as well as coordination and discrete water molecules. Extension of the coordination geometry around three metal centers (Cd(1), Cd(2) and Zn(1)), two BTC3- ligands and four coordinated water molecules generates a three-dimensional coordination polymer.     

Synthesis and Crystal Structure of a Magnesium Metal-organic Framework

A magnesium metal organic framework, [NH2(CH3)2][N(CH3)4][Mg5(bpdc)3(O2CH)6]· 3H2O (1, bpdcH2 = 4,4′-biphenyldicarboxylic acid), has been solvothermally synthesized and structurally characterized. 1 crystallizes in the trigonal system, space group R-3, with a = 11.3427(3), c = 41.5662(18) , V = 4631.3(3) 3, Z = 3 and the final R = 0.0457. Its structure features a pillared-layered three-dimensional network with 8.21  cavities, in which cationic [NH2(CH3)2]+ or [N(CH3)4]+ and lattice water molecules are located. Thermal stability of the title compound has also been investigated.     

Synthesis and Crystal Structure of a New Complex {[Co~(Ⅲ)L_2]·[Co~(Ⅱ)(H_2O)_6]_(0.5)·2.25H_2O}_4 (H_2L = N-(2-Hydroxyphenyl)salicylidenimine)

The reaction of Co(OAc)2·4H2O with the Schiff base H2L in a methanol solution affords the red crystals of {[CoIIIL2]·[CoII(H2O)6]0.5·2.25H2O}4 1 (H2L = N-(2-hydroxyphenyl) sali-cylidenimine). The molecular and crystal structures were determined by single-crystal X-ray diffraction. The crystal is of monoclinic, space group P21/n, C104H114Co6N8O37, Mr = 2421.61, a = 10.625(3), b = 16.335(4), c = 15.265(4) , β = 102.990(4)o, V = 2581.6(11) 3, Z = 1, Dc = 1.558 g/cm3, μ = 1.034 mm-1, F(000) = 1252, R = 0.0414 and wR = 0.1167 for 5889 reflections. The Co(III) atom is six-coordinated by two nitrogen atoms and four oxygen atoms of two tridentate L ligands. The abundant hydrogen bonding interactions extend the complex into a one-dimensional supra-molecular framework. The uncoordinated water molecules act as space-fillers and consolidate the whole architecture through the hydrogen bonding interactions.     

Synthesis and Crystal Structure of a Zinc(Ⅱ) Complex Salt with the Schiff Base of Picolinaldehyde N-oxide and Semicarbazone

The title zinc(Ⅱ) complex salt [Zn(H2O)6](ClO4)2·(PNOS)4, where PNOS is derived from picolinaldehyde N-oxide with semicarbazone, has been prepared and structurally characterized by X-ray single-crystal analysis. It crystallizes in triclinic, space group P1 with a = 7.529(3),b = 10.206(4), c = 14.678(6) A, α = 86.293(6), β = 87.686(7), γ= 81.382(6)°, C28H44Cl2N16O22Zn,Mr = 1093.06, V= 1112.3(8) A3, Z = 1, Dc = 1.632 g/cm3, S = 1.089,μ(MoKα) = 0.773 mm-1 ,F(000) = 564, the final R = 0.0438 and wR = 0.1076 for 3888 independent reflections with Rint =0.0224. The crystal structure possesses a [Zn(H2O)6]2+ cation, two ClO4- anions and four PNOSs.In the crystal structure, Zn2+ cation is located at the symcenter and coordinated by six water molecules. In [Zn(H2O)6]2+, an elongate octahedral complex cation, the average Zn-O bond length is 2.087(2) A. There exist a lot of H bonds in the structure, linking the cation [Zn(H2O)6]2+, anion ClO4-and PNOS to form a 3D network.     

一种新的有机胺为模板剂的稀土硫酸钐合成，结构表征以及荧光性质

本文采用正丁醇与水的混合溶剂合成一种新的以有机胺为模板剂的硫酸钐盐:[C2N2H10]1.5[Sm(SO4)3(H2O)].2H2O(1),并通过X-射线衍射、红外、热重及元素分析对其进行了表征。该化合物晶体属于单斜晶系,P21/c空间群。其中a=0.65515(9)nm,b=2.648 3(4)nm,c=0.996 15(13)nm,β=104.067 0(10)°,V=1.676 5(4)nm3,Z=4。晶体结构分析显示化合物1中的波浪形层状结构由SmO9多面体与SO4多面体构成,同时非配位水与乙二胺通过氢键连接相邻的两个层。化合物1具有较强的荧光。     

Phototransformations in nonhomogeneous media: cis-trans-isomerization of olefins in inclusion compounds

In order to elucidate photophysical and steric factors influencing extent and reaction pathway of a reaction process involving inclusion compounds the photoisomerization of cis- or trans-stilbene and cis- or trans-methylcinnamate has been studied in cavities of deoxycholic acid or Ni(II)-(4-picoline)₄ -(NCS)₂. The observed isomerization yields have been correlated with the excitation energy transfer processes which occur between host and guest molecules as well as with the symmetry properties of the various species involved during the isomerization process.     

有机-无机复合磷钨酸盐[HTA]3[α-PW12O40]·6H2O的合成与晶体结构（英文）

利用CuCl2·2H2O,1,2,4-三氮唑(TA),L-丝氨酸与Na3[α-PW12O40]·6H2O在乙醇的水溶液中合成了一种有机-无机复合Keggin结构磷钨酸盐[HTA]3[α-PW12O40]·6H2O;利用红外光谱和X射线单晶衍射表征了合成产物的结构,利用元素分析测定了其组成.结果表明,标题化合物属于菱方晶系R-3空间群,晶胞参数为:a=1.793 73(12)nm,b=1.793 73(12)nm,c=2.440 7(3)nm,α=β=90°,γ=120°,Z=6,V=6.800 7(11)nm3,Dc=4.682g·cm-3,GOOF=1.079,R1=0.051 6,wR2=0.137 4.就分子结构而言,标题化合物分子由一个饱和Keggin结构多阴离子[α-PW12O40]3-,三个游离的质子化[HTA]+阳离子和六个结晶水分子组成.     

Synthesis, characterization, and chiral properties of CoIII2AgI3 pentanuclear, CoIII4ZnII4 octanuclear, and CoIII mononuclear complexes with aza-capped hexadentate-N3S3 thiolate ligands: crystal structures of

The reaction of an S-bridged Co2(III)Ag3(I) pentanuclear complex, [Ag3[Co(aet)3]2][BF4]3 (aet = NH2CH2CH2S-), with paraformaldehyde in basic acetonitrile, followed by adding aqueous ammonia, produced an aza-capped Co2(III)-Ag3(I) complex, [Ag3[Co(L)]2]3+ ([1]3+) (L = N(CH2NHCH2CH2S-)3). The crystal structure of [1]3+ was determined by X-ray crystallography. [1][PF6]3 x H2O, empirical formula C18H44Ag3Co2F18N8OP3S6, crystallizes in the tetragonal space group 142m with a = 13.012(1) A, c = 24.707(2) A, and Z = 4. In [1]3+ the two aza-capped [Co(L)] units are linked by three Ag(I) atoms, such that the two Co(III) atoms are encapsulated in a macrobicyclic metallocage, [Ag3(I)(L)2]3-. [1]3+ was converted to an aza-capped Co4(III)Zn4(II) octanuclear complex, [Zn4O[Co(L)]4]6+ ([2]6+), by reaction with I- in the presence of Zn2+ and ZnO in water. The crystal structure of [2]6+ was also determined by X-ray crystallography. [2][PF6]6 x 8H2O, empirical formula C36H100Co4F36N16O9P6S12Zn4, crystallizes in the monoclinic space group P2(1/n) with a = 14.33(7) A, b = 25.67(10) A, c = 24.83(6) A, beta = 101.3(3) degrees , and Z = 4. In [2]6+ each of four [Co(L)] units is bound to each trigonal Zn3(II) face of the tetrahedral [Zn4(II)O]6+ core, such that each Co(III) atom is encapsulated in a macrobicyclic [Zn4(II)O(L)] fragment. Treatment of [2]6+ with a basic aqueous solution resulted in a cleavage of the Zn-S bonds to produce an aza-capped Co(III) mononuclear complex, [Co(L)] ([3]), from which [1]3+ is readily reproduced by the reaction with Ag+ in water. All the reactions were found to proceed with retention of the absolute configuration (delta or lambda) of the Co(III) chiral centers; deltadelta-[1]3+, deltadeltadeltadelta-[2]6+, and A-[3] were derived from deltadelta-[Ag3[Co(aet)3]2]3+. The contributions to circular dichroism (CD) from the triple helicity in [1]3+, besides from the asymmetric N and S donor atoms and the Co(III) chiral centers in [1]3+ and [2]6+, were estimated by comparing the CD spectra of deltadelta-[1]3+, deltadeltadeltadelta-[2]6+, and delta-[3].     

Synthesis and characterization of mono- and micro6-sulfato hexanuclear zinc complexes of a new symmetric dinucleating ligand

Zinc complexes of a new symmetric dinucleating ligand, N,N'-Bis[2-carboxybenzomethyl]-N,N'-Bis[carboxymethyl]-1,3-diaminopropan-2-ol (H5ccdp) with mixed donating groups, have been studied in the solid state as well as in solution. In methanol, the reaction of stoichiometric and substoichiometric amounts of Zn(ClO4)2 x 6H2O and the ligand H5ccdp, in the presence of K2CO3 or Et3N, afforded a mononuclear zinc complex, [Zn(H2O)6][Zn(H2ccdp)(H2O)2]2 x 12H2O (1). The solid state structure of 1 contains two units of the zinc-ligand anion, [Zn(H2ccdp)(H2O)2]-, and one [Zn(H2O)6]2+ counter cation. The Zn(II) center of the anion is in a distorted octahedral geometry. However, in methanol, the reaction of ZnSO4 x 7H2O and the ligand Hsccdp in the presence of NaOH afforded a unique micro6-sulfato hexanuclear zinc complex, Na6[Zn6(ccdp)3(micro6-SO4)](OH) x 10.5H2O (2). The structure of 2 contains a [ZnII6(micro6-SO4)] core unit which is held together by three heptadentate bridging ligands, ccdp5-. Three of the Zn(II) centers are in highly distorted square pyramidal geometry, the other three Zn(II) centers are in a distorted octahedral geometry.     

From chain to network: design and analysis of novel organic-inorganic assemblies from organically functionalized zinc-substituted polyoxovanadates and zinc organoamine subunits

A series of novel organic-inorganic assemblies, [Zn(Meen)2]2[(4,4'-bipy)Zn2As8V12O40(H2O)] (1), [Zn(en)2(H2O)][Zn(en)2(4,4'-bipy)Zn2As8V12O40(H2O)].3H2O (2), [[Zn(en)3]2[Zn2As8V12O40(H2O)]].4H2O.0.25bipy (3) and [Zn2(en)5][[Zn(en)2][(bpe)HZn2As8V12O40(H2O)]2].7H2O (4) [en = ethylenediamine, Meen = 1,2-diaminopropane, 4,4'-bipy = 4,4'-bipyridine, and bpe = 1,2-bis(4-pyridyl)ethane] constructed from organically modified Zn-substituted polyoxovanadates and zinc organoamine subunits have been synthesized. Each anion cluster of compound 1 is directly linked by the 4,4'-bipy ligand into a one-dimensional (1D) straight chain. The secondary metal complex [Zn(Meen)2]2+ acts as an isolated countercation. The 1D chain structure of 2 is similar to that of 1 but sinuate because of the secondary metal complex [Zn(en)2]2+ decorated on the anion cluster. The en ligands covalently bonding to the surface anion of 3 not only support the secondary metal complex [Zn(en)2]2+ but also coordinate to another anion through the secondary metal complex [Zn(en)2]2+ bridge to form an "eight-shaped" chiral helix. The unprecedented 2D layer of compound 4 with large nanosized inner rectangular cavities [33.669(6) x 14.720(8) A] is successfully achieved through the anion clusters polymerized first into chains by flexible organic ligands and then secondary metal complexes bridged between the chains. The different coordination abilities and geometries of the bidentate organodiamine ligands used in the four-reaction systems play important roles in the formation of the final structures: from straight chains to sinuate chains, to helical chiral chains, and finally to a 2D layer with helices.     

Direct observation of change in the molecular structure of benzyl (Z,Z)-muconate during photoisomerization in the solid state

For the solid-state photoisomerization of benzyl (Z,Z)-muconate to the corresponding (E,E)-muconate, the direct observation of a change in the crystal structure has revealed that the isomerization occurs by a topochemical reaction process according to a bicycle-pedal model and is finally accompanied by a phase transition to a stable crystal structure.     

Tetrathiafulvalenenaphthalenophanes: planar chirality and cis/trans photoisomerization

A cyclophane incorporating one 1,5-dioxynaphthalene ring system and one tetrathiafulvalene (TTF) unit bridged by [SCH(2)CH(2)O] linkages has been synthesized. In this cyclophane, the TTF unit can adopt either cis or trans configurations. In addition, the 1, 5-dioxynaphthalene ring system imposes one element of planar chirality on this cyclophane. A second element of planar chirality is introduced by the trans form of the TTF unit. Thus, the cyclophane exists in diastereoisomeric forms as three pairs of enantiomers. The enantiomeric pairs associated with the cis form of the TTF unit, as well as one of those associated with the trans form, have been isolated by crystallization, and their structures assigned in the solid state by single-crystal X-ray analyses. In solution, cis/trans isomerization occurs when either the cis or the trans form of the cyclophane is exposed to light. The photoisomerization reaction can be followed by (1)H NMR and UV-vis spectroscopies, as well as by HPLC. The photoisomerization quantum yield has been measured at two different excitation wavelengths (406 and 313 nm). In both cases, the trans --> cis process (Phi = 0.20 at 406 nm) is much more efficient than the reverse cis --> trans process (Phi = 0.030 at 406 nm). Since the absorption spectra of the trans and cis isomers are different and the quantum yield of the trans --> cis photoisomerization reaction depends on the excitation wavelength, the mole fraction of the two diastereoisomers present at the photostationary state depends on the wavelength of the exciting light. No isomerization occurs when the solutions, regardless of the mole fraction of the two diastereoisomers, are stored in the dark.