A hexanuclear discrete assembly and a two dimensional coordination polymer constructed from heterotrinuclear [(CuL)2Zn]2+ nodes and dicyanamide spacer (H2L = salen type Schiff base ligands)

Two new Cu(II)–Zn(II) complexes as a discrete hexanuclear cluster {(CuL¹)₂Zn}₂(μ_1,5-N(CN)₂)₂](ClO₄)₂ (1) and a two dimensional (2D) coordination polymer (CuL²)₂Zn(μ_1,5-N(CN)₂)₂]_n (2) have been isolated by mixing two similar tetradentate Schiff bases H₂L¹ (N,N′-bis(ɑ-ethylsalicylidene)-1,3-propanediamine) and H₂L² (N,N′-bis(salicylidene)-1,3-pentanediamine) separately with Cu(ClO₄)₂·6H₂O, Zn(ClO₄)₂·6H₂O and NaN(CN)₂ ?at same reaction condition. The heterometallic complexes have been structurally characterized by single crystal X-ray analyses showing that both are formed by angular trinuclear nodes and μ_1,5-dicyanamide spacers. The trinuclear nodes ((CuL¹)₂Zn]²⁺ in 1 and (CuL²)₂Zn]²⁺ in 2 are produced in situ from their corresponding reactants. The two Schiff base ligands coordinating the Cu(II) ions through the N₂O₂ donor set are additionally bonded to a Zn(II) ion with the four phenoxido oxygen atoms that act as bridging atoms. The zinc ion completes its coordination geometry with two terminal nitrogen atoms of two different dicyanamide spacers. The orientation of spacers from zinc ion are convergent in 1 whereas divergent in 2. Thus, two (CuL¹)₂Zn]²⁺ nodes are interconnected by double μ_1,5-dicyanamide bridges via Zn(II) centres to form discrete hexanuclear assembly of complex 1. On the other hand, (CuL²)₂Zn]²⁺ nodes in 2 are joined by μ_l,5-dicyanamide that bridge Zn(II) to Cu(II) centres of symmetry related units in order to construct a 2D coordination polymer. Consequently, the final coordination environment around Zn(II) is octahedral in both complexes whereas that around Cu(II) are square planar and square pyramidal in 1 and 2 respectively.