Structure and magnetic behaviour of [{Mn2(3-Et,4-Mepy)6(μ1,1-N3)2(μ1,3-N3)}n][PF6]n and [{Mn2(3-ampy)4(μ1,1-N3)2(μ1,3-N3)(N3)(H2O)· 4H2O}n], two alternating ferro–antiferromagnetic one-dimensional compounds