A cyanide-bridged 1-D helical chain involving both four- and six-coordinate nickel(II)

A cyanide-bridged coordination polymer, {Ni(tren)]Ni(CN)₄]} _n (tren?=?tris(2-aminoethyl)amine), has been synthesized by self-assembly of cis-Ni(tren)]²⁺ and Ni(CN)₄]^2? building blocks. In the molecular structure, the paramagnetic cis-Ni(tren)]²⁺ cations are bridged by diamagnetic Ni(CN)₄]^2? anions through two cis-cyanides to form a 1-D helical chain of {Ni(tren)]Ni(CN)₄]} _n . The compound crystallizes with a centrosymmetrical space group, P2₁ /n, in which the helical chains are packed in alternating right- and left-handed chiralities with a helical pitch of 10.2566(3)?Å (equal to the length of the b-axis), leading to the formation of a racemic compound. The crystal packing is stabilized by moderately strong hydrogen-bonding between primary amines of tren and nitrogens of terminal cyanide.