Planar to linear structural transition in small boron-carbon mixed clusters: C(x)B(5-x)- (x = 1-5).

Bulk carbon and boron form very different materials, which are also reflected in their clusters. Small carbon clusters form linear structures, whereas boron clusters are planar. For example, it is known that the B(5)(-) cluster possesses a C(2v) planar structure and C(5)(-) is a linear chain. Here we study B/C mixed clusters containing five atoms, C(x)B(5-x)(-) (x = 1-5), which are expected to exhibit a planar to linear structural transition as a function of the C content. The C(x)B(5-x)(-) (x = 1-5) clusters were produced and studied by photoelectron spectroscopy; their geometric and electronic structures were investigated using a variety of theoretical methods. We found that the planar-to-linear transition occurs between x = 2 and 3: the global minimum structures of the B-rich clusters, CB(4)(-) and C(2)B(3)(-), are planar, similar to B(5)(-), and those of the C-rich clusters, C(3)B(2)(-) and C(4)B(-), are linear, similar to C(5)(-).