Motivated by the magnetic properties of the spin-chain compounds LiCuSbO4≡LiSbCuO4 and Rb2Cu2Mo3O12, we study the ground state of the Heisenberg chain with dimerized nearest-neighbor ferromagnetic (FM) (J1, J 1 < 0) and next-nearest-neighbor antiferromagnetic (J2 > 0) couplings. Using the density-matrix renormalization group technique and spin-wave theory we find a first-order transition between a fully-polarized FM and an incommensurate spiral state at 2α = β/(1 + β), where α is the frustration ratio J2/|J1| and β the degree of dimerization J 1 /J1. In the singlet spiral state the spin-gap is vanishingly small in the vicinity of the FM transition, corresponding to a situation of LiCuSbO4. For larger α, corresponding to Rb2Cu2Mo3O12, and smaller β there is a crossover from this frustration induced incommensurate state to an Affleck-Lieb-Kennedy-Tasaki-type valence bond solid state with substantial spin-gaps. Introduction.-The exotic phenomena emerged by magnetic frustration have long been fascinating subjects of research in condensed matter physics [1]. Nowadays, quasi one-dimensional (1D) frustrated systems, despite their simple structure, are at the center of attention as a playground for novel ground states that can emerge from frustration and strong quantum fluctuations due to low dimensionality. So far, various unconventional magnetic states such as quantum spin liquids [2,3], spin-Peierls states [4], and Tomonaga-Luttinger (TL) liquid phases [5] have been investigated. Currently, among the hottest topics are magnetic multipolar and in particular spin-nematic states [6][7][8][9][10][11] in which magnon bound states are formed from a subtle competition between geometrical balance of ferromagnetic (FM) and antiferromagnetic (AFM) correlations among spins.