Transition elements have greater tendency to form complexes because

.Transition metals are d-block elements with valence shell configuration ns2(n−1)d1−10. These metals and their ions easily coordinate to a number of negative ions or neutral molecules having lone pairs of electrons to form complex. This is due to
(i) Small size and high nuclear charge of these metals.
(ii) Availability of vacant d-orbitals of suitable energy to accommodate lone pairs of electrons donated by the ligands.