We will construct infinitely many irreducible symplectic and non-symplectic 4-manifolds that are homeomorphic but not diffeomorphic to (2n-1)CP^2#(2n-1)\bar{CP}^2 for each integer n > 11, and the families of simply connected irreducible nonspin symplectic 4-manifolds that have the smallest Euler characteristics among the all known simply connected 4-manifolds with positive signature and with more than one smooth structure. Our construction uses the complex surfaces of Hirzebruch and Bauer-Catanese on Bogomolov- Miyaoka-Yau line with c_1^2 = 9\chi_h = 45. This is a joint work with A. Akhmedov.