We have synthesized a new spinel oxide LiRh2O4 with a mixed-valent configuration of Rh 3+ and Rh 4+ . At room temperature it is a paramagnetic metal, but on cooling, a metal-insulator transition occurs and a valence bond solid state is formed below 170 K. We argue that the formation of valence bond solid is promoted by a band Jahn-Teller transition at 230 K and the resultant confinement of t2g holes within the xy band. The band Jahn-Teller instability is also responsible for the observed enhanced thermoelectric power in the orbital disordered phase above 230 K.Among the wide variety of structural categories of complex transition metal oxides, spinel, with chemical formula AB 2 O 4 , is one of the most common structures and provides a unique playground for the physics of geometrical frustration. The B-sublattice of the spinel structure consists of a three-dimensional network of tetrahedra, known as the pyrochlore lattice and can underpin strong geometrical frustration effects. When antiferromagnetically coupled spins are placed on the pyrochlore lattice, long range magnetic ordering is suppressed substantially leading to, amongst other things, quantum spin liquid behavior [1]. In many cases, however, a nontrivial self-organized state of spins marginally emerges by means of coupling with lattice distortion and/or orbital ordering [2]. In analogy with spins, when a spinel B-sublattice is occupied by ions with a formally half-integer valence, suppression of charge ordering and the eventual formation of a nontrivial state of charges results. Such charge frustration has attracted much interest since the discovery of Verwey ordering in the spinel

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