Two new 1-D dicyanamide bridged polymeric complexes [Mn(μ1,5- dca)2(salicyh)2]n and {[Ni(μ1,5- dca)(TTA)](ClO4)}n (dca = dicyanamide, N(CN) 2-; salicyh = salicylic hydrazide; TTA = triethylenetetramine): Synthesis, structures and magnetic studies