Copper 5-sulfoisophthalato quasi-planar squares in coordination polymers modulated by alkaline-earth metals:: a way to molecular squares?

Two copper-sip coordination polymers (sip(3)-= 5-sulfoisophthalic anion), [Ca(H2O)(3)Cu-2(H2O)(6)(sip)(2)]center dot 2H(2)O 2a, and [Sr(H2O)(4)Cu-2(H2O)(6)(sip)(2)]center dot H2O 2b, have been synthesized at room temperature. Single-crystal X-ray diffraction reveals that the structures of complexes 2a and 2b are 2-D coordination layer structures, containing [Cu-4(sip)(4)] molecular squares linked by calcium (2a) or strontium (2b) bridges. The coordination layers display 3,6-connected topologies if the [Cu-4(sip)(4)] molecular squares and alkaline-earth metals are considered as nodes, or (4,4) nets if alkaline-earth metals are considered to be part of the [Cu-4(sip)(4)] squares. In comparison with the more commonly encountered Cu-sip zigzag chain subunits in copper-sip coordination polymers, the [Cu-4(sip)(4)] square subunits in 2a and 2b represent similar coordination fashions and connecting modes while creating singular examples of new subunits in coordination complexes of the copper-sip system. Variable temperature magnetic susceptibility of 2a indicated that antiferromagnetic interactions dominate between the Cu(II) ions bridged by sip(3)-ligands.