Trinuclear N,N-bridged copper(II) complexes involving a Cu3OH core: [Cu3(mu3-OH)L3A(H2O)2 ]A.(H2O)x [L= 3-acetylamino-1,2,4-triazolate; A = CF3SO3, NO3, ClO4; x =0,2]. Synthesis, X-ray structures , spectroscopy and magnetic properties