Four structurally closely related one-dimensional coordination polymers (CPs) have been synthesised, constituted by pyrazine (pyz) and the group 13 metal halides AlCl3, AlI3, InBr3, and InI3. Three CPs are isotypic: [ AlCl 3 ( pyz ) ] ∞ 1 CH21317_IE1.gif, [ AlI 3 ( pyz ) ] ∞ 1 CH21317_IE2.gif, [ InBr 3 ( pyz ) ] ∞ 1 CH21317_IE3.gif. Alike [ InI 3 ( pyz ) ] ∞ 1 CH21317_IE4.gif, they form linear chains. Hereby, each M3+ ion is trigonal-bipyramidally coordinated by three halido ligands and two N-atoms of two pyz serving as linear nodes with twofold connectivity (2-c). The CPs were characterised by SCXRD, PXRD, elemental-analysis, simultaneous DTA/TG and IR-spectroscopy. In addition, two complexes [(AlCl3)2(pyz)5] and [(InI3)2(pyz)] with octahedrally coordinated Al3+ and unprecedented tetrahedrally coordinated In3+ ions were structurally characterised by SCXRD.