supramolecular organic 
 assemblies , including single - component and 
 multiple - component complexes , are a family of crystalline materials 
 composed of molecular species held together in the solid state by 
 long - range , noncovalent interactions . the 
 crystal engineering of organic assemblies is developing apace due 
 to the increasing knowledge of the underlying supramolecular chemistry 
 that directs the assembly and packing of molecules in the sold state . this defines their crystal structures and underpins the design and 
 synthesis of new organic supramolecular materials , which 
 have found applications in a wide range of areas including host guest 
 recognition , proton conductivity , and gas adsorption and separations . among them , the hydrogen bonded supramolecular organic frameworks 
 ( sofs , also referred to as hofs ( hydrogen bonded organic frameworks ) ) 
 have received attention due to their design potential and their structural and conceptual similarities to metal  organic 
 frameworks ( mofs ) , which can also function as porous substrates / absorbent . however , most hydrogen bonds are primarily electrostatic 
 in nature and vary in strength according to the different donor and 
 acceptor properties of functional groups and their environment , and 
 thus prediction of structures of supramolecular organic arrays driven 
 by hydrogen bonding can be challenging . predicting and understanding the packing of molecular assemblies 
 is , therefore , a practical target toward the goal of designing and 
 engineering solid - based materials . thermodynamically stable 
 and crystalline supramolecular organic 
 assemblies are most often prepared from the solutions using appropriate 
 solvents through conventional crystallization under ambient conditions . 
 in this context , some subtle factors , for example the acid  base 
 properties of the solvent mixtures and the interaction of solvent 
 molecules with the organic host , may be essential for the successful 
 crystallization of the material in the solid state . moreover , in situ transformations of organic hosts have 
 been observed , and study of in situ transformations 
 and their effect on resultant products and their relationship with 
 precursors in terms of functional groups , supramolecular interactions , 
 packing patterns , and order are of interest . we report herein the 
 structures of four organic assemblies , 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)benzene 
 ( [ c40h24n10]2dmf , 12dmf ) , 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)benzene 
 ( [ c40h20n10 ] , 2 ) , 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)phenylbenzene 
 ( [ c46h28n10]2dmf , 32dmf ) , and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)phenylbenzene 
 ( [ c46h24n10]dmf , 4dmf ) , in which 2 and 4 were prepared 
 in situ from 1 and 3 , respectively , under 
 solvothermal conditions ( scheme 1 ) . commercially available 
 reagents and organic solvents were used as received without further 
 purification . elemental analyses ( c , h , and n ) were carried out on 
 an elementar vario el iii analyzer . infrared ( ir ) spectra were recorded 
 with a perkinelmer spectrum one as kbr pellets in the range 4004000 
 cm , and h nmr spectra on a bruker 
 dpx-400 spectrometer . thermal gravimetric analyses ( tga ) were performed 
 under a flow of n2 ( 20 mlmin ) 
 with a heating rate of 10 cmin using 
 a ta sdt-600 thermogravimetric analyzer , and x - ray powder diffraction 
 ( pxrd ) measurements were carried out at room temperature on a panalytical 
 xpert pro diffractometer using cu k radiation (  
 = 1.5418  ) at 40 kv , 40 ma , at a scan speed of 0.02/s 
 and a step size of 0.005 in 2. 4-cyanopyridine 
 ( 104 mg , 1.0 mmol ) , in mecn ( 82 mg , 2.0 mmol ) , and potassium tert - butoxide ( 336 mg , 3.0 mmol ) were added to toluene ( 40 
 ml ) , and the reaction mixture stirred at ambient temperature for 48 
 h. saturated nahco3 solution ( 200 ml ) was used to quench 
 the reaction , and the resultant solid crude product of 3-amino-3-(4-pyridinyl)propionitrile 
 collected by filtrations , washed three times with nacl solution , and 
 dried in air . h nmr ( dmso - d6 ) : 8.63 ( d , j = 6.3 hz , 2h , 2,6-pyridyl - h ) ; 7.57 
 ( d , j = 6.0 hz , 2h , 3,5-pyridyl - h ) ; 7.01 ( s , 2h , 
 nh ) , 4.4 ( s , 1h , = c  h ) ppm . hrms ( ei- ) : m / z 439.0403 [ m + h ] . ir ( kbr , max , cm ) : 2801 ( w ) , 2759 ( w ) , 2256 ( m ) , 
 2194 ( s ) , 1942 ( m ) , 1670 ( s ) , 1593 ( s ) , 1530 ( s ) , 1502 ( s ) , 1425 ( s ) , 
 1335 ( m ) , 1271 ( m ) , 1222 ( m ) , 1146 ( m ) , 1069 ( m ) , 992 ( s ) , 874 ( m ) , 
 839 ( s ) , 670 ( s ) , 650 ( s ) , 609 ( s ) , 573 ( s ) . elemental analysis for 
 c8h7n3 ( found / calcd ) : c , 66.15/66.19 ; 
 h , 4.83/4.86 ; n , 28.94/28.95% . 3-amino-3-(4-pyridinyl)propionitrile ( 580 
 mg , 4.0 mmol ) and 1,4-benzenedialdehyde ( 134 mg , 1.0 mmol ) were added 
 to glacial acetic acid ( 10 ml ) which had been degassed for 10 min 
 under n2 flow . the reaction mixture was refluxed at 120 
 c for 48 h , and the light yellow precipitate of 1 was collected by filtration , washed with hot acetic acid , etoh , 
 and distilled water , and dried in air . crystals of 12dmf 
 suitable for single crystal x - ray diffractions were obtained by dissolving 1 ( 33 mg ) in n , n - dimethylformamide 
 ( dmf ) ( 3 ml ) and slowly concentrating the solution by evaporation . h nmr ( dmso - d6 ) : 10.41 ( s , 2h , 
 dihydropyridyl - nh ) , 8.76 ( d , j = 5.9 hz , 8h , py - h ) , 
 7.70 ( d , j = 4.7 hz , 8h , py - h ) ; 7.65 ( s , 4h , ar - h ) , 
 4.90 ( s , 2h , dihydropyridyl - ch ) ppm . ir ( kbr , max , cm ) : 2207 ( s ) , 1641 ( m ) , 1595 ( m ) , 1545 ( m ) , 
 1499 ( s ) , 1406 ( m ) , 1335 ( m ) , 1289 ( s ) , 1222 ( w ) , 1193 ( w ) , 1154 ( w ) 
 1068 ( w ) , 987 ( m ) , 830 ( s ) . elemental analysis for 12dmf , 
 c46h38n12o2 ( found / calcd ) : 
 c , 68.99/69.86 ; h , 4.27/4.84 ; n , 19.34/21.25% . 50 mg of 1 was added to dmf 
 ( 2 ml ) , sealed in a 15 ml pressure tube , and heated in an oil bath 
 at 90 c under autogenous pressure for 3 days . colorless crystals 
 of 2 suitable for single crystal x - ray diffraction were 
 collected by filtration , washed with etoh and distilled water , and 
 dried in air . h nmr ( dmso - d6 ) : 8.98 ( d , j = 4.9 hz , 8h , py - h ) , 8.20 ( s , 4h , 
 ar - h ) , 8.08 ( d , j = 4.9 hz , 8h , py - h ) ppm . ir ( kbr , 
 max , cm ) : 2207 ( s ) , 1645 ( m ) , 
 1595 ( m ) , 1538 ( m ) , 1499 ( s ) , 1470 ( m ) , 1413 ( m ) , 1382 ( m ) , 1289 ( s ) , 
 1217 ( w ) , 11893 ( w ) , 1154 ( w ) 1125(w ) , 1062 ( m ) , 994 ( s ) , 834 ( m ) , 
 803(s ) . elemental analysis for 2 , c40h20n10.2h2o ( found / calcd ) : c , 71.02/71.00 ; 
 h , 4.14/3.57 ; n , 20.47/20.69% . 3 was prepared via a similar 
 procedure to that of 1 but using 4,4-biphenyldicarbaldehyde 
 instead of benzene-1,4-benzenedicarbaldehyde . the light - yellow crystalline 
 product of 32dmf was collected by filtration , washed 
 with hot acetic acid , etoh , and distilled water , respectively , and 
 dried in air . h nmr ( dmso - d6 ) : 10.37 ( s , 2h , dihydropyridyl - nh ) , 8.878.71 ( m , 8h , py - h ) , 
 7.87 ( d , j = 8.2 hz , 4h , ar - h ) ; 7.787.62 
 ( m , 8h , py - h ; 4h , ar - h ) , 4.93 ( s , 2h , dihydropyridyl - ch ) ppm . ir ( kbr , 
 max , cm ) : 2203 ( s ) , 1648 ( m ) , 
 1552 ( w ) , 1513 ( s ) , 1409 ( m ) , 1346 ( w ) , 1293 ( m ) , 1218 ( w ) , 1186 ( w ) , 
 1150 ( w ) 1072 ( w ) , 1005 ( w ) , 880 ( w ) , 827 ( s ) . elemental analysis 
 for 32dmf , c55h49n13o3 ( found / calcd ) : c , 70.12/70.27 ; h , 4.54/5.25 ; n , 18.39/19.37% . 3 ( 50 mg ) was added to dmf 
 ( 2 ml ) , sealed in a 15 ml pressure tube , and heated in an oil bath 
 at 90 c under autogenous pressure for 3 days . colorless crystals 
 ( 4dmf , suitable for single crystal x - ray diffraction ) 
 were collected by filtration , washed with etoh and distilled water , 
 respectively , and dried in air . ir ( kbr , max , cm ) : 2235 ( s ) , 1598 ( m ) , 1559 ( w ) , 1524 ( s ) , 1488 ( m ) , 
 1470 ( m ) , 1414 ( m ) , 1387 ( s ) , 1325 ( w ) 1222 ( w ) , 1193 ( w ) , 1157 ( w ) , 
 1126 ( w ) , 1065 ( m ) , 997 ( m ) , 869 ( w ) , 837 ( s ) , 803 ( s ) . elemental 
 analysis for 42.5dmf , c55h45n13o3 ( found / calcd ) : c , 71.13/71.44 ; h , 3.22/4.65 ; 
 n , 19.56/19.46% . tga plots of all four 
 compounds are shown in figure s2 in the supporting 
 information . for compound 2 , which contains no 
 solvent molecules in the crystal lattice , the weight loss observed 
 after 320 c corresponds to structural decomposition . for compounds 12dmf , 32dmf , and 4dmf , the first weight losses of 17.5% , 17.2% , and 9.1% before 130 c 
 are assigned to the loss of solvent dmf molecules ( calculated ca . 
 18.4% , 16.8% , and 9.2% , respectively ) , followed by stability between 
 130 and 250 c and followed by thermal decomposition . the number 
 of solvent molecules associated with crystals of 14 has been determined by single crystal x - ray diffraction 
 with electron densities calculated by the platon / squeeze routine . for bulk materials , where variability in solvent 
 of crystallization was observed due to the synthesis and solvent volatility , single crystal x - ray data for 
 compounds 12dmf , 2 , and 32dmf were collected on agilent supernova atlas diffractometers , 
 while the diffraction data for compound 4dmf was 
 acquired using an oxford diffraction xcalibur eos instrument . the 
 structure was solved by direct methods and developed by difference 
 fourier techniques , both using the shelxl software package . hydrogen atoms of the ligands were placed geometrically 
 and refined using a riding model . the unit cell volume of compounds 3 and 4 includes disordered solvent molecules 
 ( dmf ) which could not be modeled as discrete atomic sites . we therefore 
 employed platon / squeeze to calculate 
 the contribution of the solvent region to the diffraction and thereby 
 produced a set of solvent - free diffraction intensities . the solvent 
 molecules of compounds 3 and 4 were not 
 included in the structural models but are included in the formulae . ccdc 980607 ( 1 ) , 980562 ( 2 ) , 980572 ( 3 ) , and 980586 ( 4 ) contain the supplementary crystallographic data 
 for this paper . data can be obtained free of charge from the cambridge 
 crystallographic data centre via www.ccdc.cam.ac.uk/data_request/cif . the 1,4-bis-(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl ) derivatives 
 ( 1 and 3 , scheme 1 ) were prepared from the reaction of 3-amino-3-(4-pyridinyl)propionitrile 
 with 1,4-benzenedicarbaldehyde or 4,4-biphenyldicarbaldehyde 
 in glacial acetic acid at 120 c , respectively . solvothermal 
 reactions of appropriate amount of 1 or 3 in n , n - dimethylformamide ( dmf ) 
 yielded colorless crystalline solid of 2 or 4 in a yield of ca . 12% , and these products are insoluble in water 
 and common organic solvents at room temperature . the structural transformation 
 of 1 to 2 and 3 to 4 via oxidative dehydrogenation under solvothermal conditions has 
 been confirmed by nmr spectroscopy and single crystal x - ray diffraction . the supramolecular chemistry of all four compounds has been comprehensively 
 studied , and it has been found that the oxidative products , 2 and 4 , are somewhat elongated due to the aromatization 
 of the dihydropyridyl rings located on each end of the parent molecules 
 ( 1 and 3 ; figure 1 ) , moreover , structures of 2 and 4 are distinct in that they are more linear than 
 their parent zigzag dihdropyridyl parent molecules in terms of the 
 hierarchical assemblies via hydrogen bonds . 12dmf crystallizes 
 in monoclinic space group p21/c with the asymmetric unit containing one 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)benzene 
 molecule and two solvent dmf molecules . a feature of 1 is that the two dihydropyridyl rings are nearly perpendicular ( dihedral 
 angle of ca . 83.34 ) to the central phenyl ring as a result of 
 the sp carbon at the 4-position of each dihydropyridyl 
 ring . h groups on the dihydropyridyl rings expected to 
 act as dominant hydrogen bond donors , and the exo - pyridyl and lateral cyano groups behaving as potential hydrogen 
 bond acceptors . each molecule of 1 interacts with two 
 solvent dmf molecules via hydrogen bonds from dihydropyridyl groups 
 to amide groups ( n  ho interactions , 1.934(11 ) 
 /1.971(15 )  ; table 2 and table s1 in the supporting information ) . two of the four exo - pyridyl groups of 1 interact with two neighboring ones via hydrogen bonds from phenyl 
 groups to pyridyl groups ( c  hn interactions , 
 2.502(5 )  to 2.775(6 )  ) . although dmf molecules block 
 the connection of 1 to a neighboring molecule from the 
 primary hydrogen bond donating sites , the pyridyl hydrogen bond accepting 
 groups generate secondary c  hn interactions 
 and direct the assembly of 1 into a 2d hydrogen bonded 
 square layer ( figure 2 ) . a 3d supramolecular organic framework structure is thus formed 
 through complex hydrogen bond and  stacking 
 interactions . compound 1 : # 1 : 1 
 + x , + y , + z. # 2 : 
 2  x , 1  y , z . compound 2 : # 1 : 1/2 
  x , 1/2 + y , 1/2 z. compound 3 : # 1 : 1  x , 1/2 
 + y , 1/2  z. # 2 : x , 1/2 + y , 1/2  z. compound 4 : # 1 : 3/2 
  x , y , 1/2 + z. # 2 : 1/2 + x , 1/2  y , 1  z. view of hydrogen bonded square layer structure of compound 1 . 2 possesses a linear 
 central backbone with 
 the two external pyridyl rings twisting around the central phenyl 
 ring due to the rotation about c  c single bonds ( torsion angles 
 of 62.14 and 66.50 ) . 2 lacks the primary 
 n  h hydrogen bond donating groups unlike its precursor 1 due to the oxidation of dihydropyridyl groups , and thus 
 the exo - pyridyl and lateral cyano hydrogen bond accepting 
 groups interact mainly with the c  h groups of pyridyl or phenyl 
 moieties ( table 2 and 
 table s1 in the supporting information ) . a 2d supramolecular network can be identified through hydrogen bond 
 interactions from the pyridyl groups on the central backbones of 2 to the pyridyl / phenyl c  h groups of neighboring ones 
 ( figure 3 ) . the cyano 
 groups decorate the 2d layers and interact with the c  h groups 
 in the adjacent layers through c hn hydrogen 
 bonds ( table 2 and 
 table s1 in the supporting information ) . thus , a complex 3d supramolecular organic framework structure is formed 
 through hydrogen bonding as well as  stacking 
 interactions between adjacent aromatic rings ( pyridyl and/or phenyl ) . the longer 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)phenylbenzene 
 molecule ( 3 ) assembles into a 3d porous organic framework 
 via hydrogen bonding . single crystal x - ray diffraction confirms that 
 compound 3 crystallizes in monoclinic space group p21/c and adopts a zigzag configuration 
 due to the sp carbon at the 4-position on each dihydropyridyl 
 ring . the two central phenyl rings are coplanar and the two dihydropyridyl 
 rings are nearly perpendicular to the central phenyl rings ( dihedral 
 angle of ca . h 
 groups on the dihydropyridyl rings of 3 participate in 
 primary n  hn hydrogen bond interactions ( 2.019(14 ) 
  , table 2 and 
 table s1 in the supporting information ) 
 with the pyridyl n atoms , which leads to the formation of a 2d hydrogen 
 bonded square layer structure ( figure 4a ) . hn interactions 
 ( table 2 and table 
 s1 in the supporting information ) between 
 the lateral cyano and c  h groups on the skeleton of 3 account for the formation and stabilization of a 3d supramolecular 
 organic framework with free pyridyl functional groups pointing toward 
 the 1d channels along the crystallographic b axis 
 ( figure 4b ) . the opening 
 to these channels is estimated to be ca . 2.5  
  5.0  and the total solvent accessible volume of compound 3 after the removal of guest dmf molecules was estimated to 
 be ca . view of the 2d hydrogen bonded square layer structure in 3 ( a ) and 3d hydrogen bonded supramolecular organic framework 
 in 3 ( b ) . 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)phenylbenzene 
 ( 4 ) crystallizes in the orthorhombic space group pbca as 4dmf . unlike 3 , the two phenyl 
 rings of 4 are twisted from each other with a torsion 
 angle of ca . 46.38 and the neighboring pyridyl rings have torsion 
 angles of ca . 45.09 and 47.36 with respect to each phenyl 
 ring . one molecule of 4 interacts with four others , two 
 at each end via c hn interactions between 
 the n - donors and c  h groups on the pyridyl rings ( figure 5 , inset ) . in this 
 way , a 3d supramolecular framework with 1d channels along the crystallographic a axis is formed ( figure 5 ) . the opening of the channels is estimated to be 7.0 
   9.2  . in addition , 4 incorporates 
 two identical 3d supramolecular nets that interpenetrate through each 
 other with interactions observed through c 8% of solvent accessible volume in the solvent - free 
 structure of 4 as confirmed by platon / void calculation . it has been found that 2 and 4 are longer 
 than the parent molecules 1 and 3 ( figure 1 ) due to the oxidative 
 dehydrogenation of the dihydropyridyl moieties to form pyridyl rings . the supramolecular structures of the four molecules have been interpreted 
 in terms of their hydrogen bonded structures in the sold state . among 
 the multiple hierarchical hydrogen bonds which direct the self - assembly 
 of the solvated compounds , n  ha ( a = n or 
 o ) appear to be the strongest amd most prevalent . compounds 1 and 2 assemble into nonporous close - packed 
 structures , whereas the biphenyl analogues , 3 and 4 , build into potential porous phases . the supramolecular 
 structure of 32dmf is reminiscent of the organic 
 framework material sof-1 in which a similar molecular 
 tecton with an extra central anthracene moiety was used . however , 32dmf shows fairly 
 poor framework stability on solvent exchange and desolvation , probably 
 due to the lack of strong  stacking interactions , 
 which are observed in sof-1 , and we argue that it is 
 these  interactions that are responsible for 
 the exceptionally high thermal stability of sof-1 . 4dmf possesses a promising porous 3d hydrogen bonded 
 substructure ; however , the observed framework interpenetration severely 
 reduces the structural porosity . thus , the balance between molecular 
 size and topology of tectons and observed structural porosity of the 
 resultant solid - state materials is crucial for the design and practical 
 application of supramolecular organic assemblies . in summary , the present work explores the supramolecular structures 
 of two organic multiple - pyridyl derivatives , 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)benzene 
 ( 1 ) and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)phenylbenzene 
 ( 3 ) , as well as the in situ formation of their elongated 
 pyridyl analogues , 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)benzene 
 ( 2 ) and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)phenylbenzene 
 ( 4 ) . it has been shown the dihydropyridyl groups in 1 and 3 offer reliable hydrogen bond donating 
 sites that give primary and strong hydrogen bonding interactions to 
 o-/n - containing hydrogen bond acceptors ; secondary c the current research offers a possible 
 route to the design of supramolecular organic assemblies from structural 
 transformations of organic modules with similar functionalities . the 
 structures of these organic solid materials are stabilized by hierarchical 
 hydrogen bonds generated from more favorable functional groups .
the crystallization of two dihydropyridyl 
 molecules , 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)benzene 
 ( [ c40h24n10]2dmf , 12dmf ; dmf = dimethylformamide ) and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)phenylbenzene 
 ( [ c46h28n10]2dmf , 32dmf ) , and their respective oxidized pyridyl analogues , 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)benzene 
 ( [ c40h20n10 ] , 2 ) and 
 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)pyridyl)phenylbenzene ( [ c46h24n10]dmf , 4dmf ) , 
 has been achieved under solvothermal conditions . 
 the dihydropyridyl 
 molecules are converted to their pyridyl products via in situ oxidative 
 dehydrogenation in solution . 
 the structures of the four molecules 
 have been fully characterized by single crystal and powder x - ray diffraction . 
 the oxidized pyridyl products , 2 and 4 , 
 are more elongated due to aromatization of the dihydropyridyl rings 
 at each end of their parent molecules 1 and 3 , respectively . 
 the solid - state supramolecular structures of the 
 pyridyl molecules are distinct from the dihydropyridyl molecules in 
 terms of their hierarchical assembly via hydrogen bonding due to the 
 loss of primary n  h hydrogen bond donors in the two electron 
 oxidized tectons . 
 overall , the geometrically shorter molecules 1 and 3 display close - packed structures , whereas 
 the more extended 2 and 4 assemble into 
 more open supramolecular systems .