Chiral one- and two-dimensional silver(I)–biotin coordination polymers
Authors: Altaf Muhammad , Stoeckli-Evans Helen 
Published: January 2013

Reaction of biotin {C10H16N2O3S, HL; systematic name: 5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoic acid} with silver acetate and a few drops of aqueous ammonia leads to the deprotonation of the carboxylic acid group and the formation of a neutral chiral two-dimensional polymer network, poly[[{μ3-5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoato}silver(I)] trihydrate], {[Ag(C10H15N2O3S)]·3H2O}nor {[Ag(L)]·3H2O}n, (I). Here, the AgIcations are pentacoordinate, coordinated by four biotin anionsviatwo S atoms and a ureido O atom, and by two carboxylate O atoms of the same molecule. The reaction of biotin with silver salts of potentially coordinating anions,viz.nitrate and perchlorate, leads to the formation of the chiral one-dimensional coordination polymerscatena-poly[[bis[nitratosilver(I)]-bis{μ3-5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoato}] monohydrate], {[Ag2(NO3)2(C10H16N2O3S)2]·H2O}nor {[Ag2(NO3)2(HL)2]·H2O}n, (II), andcatena-poly[bis[perchloratosilver(I)]-bis{μ3-5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoato}], [Ag2(ClO4)2(C10H16N2O3S)2]nor [Ag2(ClO4)2(HL)2]n, (III), respectively. In (II), the AgIcations are again pentacoordinated by three biotin moleculesviatwo S atoms and a ureido O atom, and by two O atoms of a nitrate anion. In (I), (II) and (III), the AgIcations are bridged by an S atom and are coordinated by the ureido O atom and the O atoms of the anions. The reaction of biotin with silver salts of noncoordinating anions,viz.hexafluoridophosphate (PF6−) and hexafluoridoantimonate (SbF6−), gave the chiral double-stranded helical structurescatena-poly[[silver(I)-bis{μ2-5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoato}] hexafluoridophosphate], {[Ag(C10H16N2O3S)2](PF6)}nor {[Ag(HL)2](PF6)}n, (IV), andcatena-poly[[[{5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoato}silver(I)]-μ2-{5-[(3aS,4S,6aR)-2-oxohexahydro-1H-thieno[3,4-d]imidazol-4-yl]pentanoato}] hexafluoridoantimonate], {[Ag(C10H16N2O3S)2](SbF6)}nor {[Ag(HL)2](SbF6)}n, (V), respectively. In (IV), the AgIcations have a tetrahedral coordination environment, coordinated by four biotin moleculesviatwo S atoms, and by two carboxy O atoms of two different molecules. In (V), however, the AgIcations have a trigonal coordination environment, coordinated by three biotin moleculesviatwo S atoms and one carboxy O atom. In (IV) and (V), neither the ureido O atom nor the F atoms of the anion are involved in coordination. Hence, the coordination environment of the AgIcations varies from AgS2O trigonal to AgS2O2tetrahedral to AgS2O3square-pyramidal. The conformation of the valeric acid side chain varies from extended to twisted and this, together with the various anions present, has an influence on the solid-state structures of the resulting compounds. The various O—H...O and N—H...O hydrogen bonds present result in the formation of chiral two- and three-dimensional networks, which are further stabilized by C—H...X(X= O, F, S) interactions, and by N—H...F interactions for (IV) and (V). Biotin itself has a twisted valeric acid side chain which is involved in an intramolecular C—H...S hydrogen bond. The tetrahydrothiophene ring has an envelope conformation with the S atom as the flap. It is displaced from the mean plane of the four C atoms (planeB) by 0.8789 (6) Å, towards the ureido ring (planeA). PlanesAandBare inclined to one another by 58.89 (14)°. In the crystal, molecules are linkedviaO—H...O and N—H...O hydrogen bonds, enclosingR22(8) loops, forming zigzag chains propagating along [001]. These chains are linkedviaN—H...O hydrogen bonds, and C—H...S and C—H...O interactions forming a three-dimensional network. The absolute configurations of biotin and complexes (I), (II), (IV) and (V) were confirmed crystallographically by resonant scattering.