Syntheses and crystal structures of the one-dimensional coordination polymers formed by [Ni(cyclam)]2+ cations and 1,3-bis-(3-carb-oxy-prop-yl)tetra-methyl-disiloxane anions in different degrees of deprotonation

From Amorphous Silicones to Si-Containing Highly Ordered Polymers: Some Romanian Contributions in the Field

Polydimethylsiloxane (PDMS), in spite of its well-defined helical structure, is an amorphous fluid even at extremely high molecular weights. The cause of this behavior is the high flexibility of the siloxane backbone and the lack of intermolecular interactions attributed to the presence of methyl groups. These make PDMS incompatible with almost any organic or inorganic component leading to phase separation in siloxane-siloxane copolymers containing blocks with polar organic groups and in siloxane-organic copolymers, where dimethylsiloxane segments co-exist with organic ones. Self-assembly at the micro- or nanometric scale is common in certain mixed structures, including micelles, vesicles, et cetera, manifesting reversibly in response to an external stimulus. Polymers with a very high degree of ordering in the form of high-quality crystals were obtained when siloxane/silane segments co-exist with coordinated metal blocks in the polymer chain. While in the case of coordination of secondary building units (SBUs) with siloxane ligands 1D chains are formed; when coordination is achieved in the presence of a mixture of ligands, siloxane and organic, 2D structures are formed in most cases. The Romanian research group's results regarding these aspects are reviewed: from the synthesis of classic, amorphous silicone products, to their adaptation for use in emerging fields and to new self-assembled or highly ordered structures with properties that create perspectives for the use of silicones in hitherto unexpected areas.

Crystal structure of the one-dimensional coordination polymer formed by the macrocyclic [Ni(cyclam)]2+ cation and the dianion of di-phenyl-silanediylbis(4-benzoic acid)

The asymmetric unit of the title compound, catena-poly[[[(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)nickel(II)]-μ-4,4'-(di-phenyl-silanedi-yl)dibenz-o-ato-κ2 O:O'] sesquihydrate], {[Ni(C26H18O4Si)(C10H24N4)]·1.5H2O} n , consists of the halves of the centrosymmetric macrocyclic cation and the C 2-symmetric di-carboxyl-ate dianion and of the water mol-ecule of crystallization. The Ni2+ ion is coordinated by the four secondary N atoms of the macrocyclic ligand characterized by the most energetically favourable trans-III conformation and two mutually trans O atoms of the carboxyl-ate, forming a slightly tetra-gonally elongated trans-N4O2 octa-hedron. The crystals are composed of parallel polymeric chains of the macrocyclic cations linked by the anions of the acid running along the [101] direction. Each polymeric chain is bonded to four neighbouring ones via water mol-ecules providing O-H⋯O hydrogen bonds to the non-coordinated carboxyl O atoms to form a three-dimensional supra-molecular network.