New regioregular head-to-tail type poly(6-alkylpyridine-2,5-diyl)s (P6RPys; R = nonyl, dodecyl, and pentadecyl) were prepared by organometallic polycondensation. The head-to-tail (HT) content in the polymers was higher than 95%, as revealed by H-1 NMR spectroscopy. Powder X-ray diffraction data of HT-P6RPys indicated that P6RPys formed a new type of structure composed of an alternating end-to-end packed unit and an interdigitation packed unit. (C) 2004 Wiley Periodicals, Inc.