Cobalt(II) coordination networks dependent upon the spacer length of flexible bis(tetrazole) ligands

Four new coordination polymers with flexible bis(tetrazole)alkane ligands as bridges and thiocyanate ions as terminal ligands, [Co(btze) ₂(SCN)₂]_n (1), [Co(btze)₃(SCN) ₂]_n (2), [Co(btzb)₂(SCN)₂] _n (3), and [Co(btzh)₂(SCN)₂]_n (4), have been synthesized and characterized, where btze = 1,2-bis(tetrazol-1-yl) ethane, btzb = 1,4-bis-(tetrazol-1-yl)butane, and btzh = 1,6-bis(tetrazol-1-yl) hexane. The short btze ligand gives singly bridged 2D square grid layers with 2-fold parallel interpenetration (1) or 1D linear chains with deep interdigitation (2), dependent upon the metal-to-ligand ratio used for the synthesis. The btzb ligand links the metal ions into doubly bridged chains composed of bimetallacycles (3). Most interestingly, the long btzh ligand leads to 2D layers with both single and double bridges between Co(II) ions, and the inclined interpenetration of layers generates a 3D polycatenated structure with a high degree of catenation. The results show that the dimensionality and topology of the structures depend strongly upon the length and conformation of the flexible alkyl spacers between the tetrazole rings.