Studies of two lanthanide coordination polymers built up from dinuclear units

The two three-dimensional oxo-bridged lanthanides {[Ln2(C4H2O4)3(H2O)4]·3H2O}3∞, with Ln=Ho3+ (1); Gd3+ (2), are isomorphous. They have layer-type structures built up from non-centrosymmetric dinuclear unit Ln2O12(H2O)4, beside three lattice H2O molecules stabilizing the 3D open-framework. The building entities are linked through one classical syn-anti μ2-carboxylato-K1O:K1O' bridge. Within the bi-polyhedra, two double μ2-O'; μ2O';,K2O,O' bridges and a syn-syn classical one, support the magnetic measurements carried out on holmium compound indicating relatively weak anti-ferromagnetic interactions. The comparison with magnetic studies on the almost similar reported Gd(III) compound, suggested that concomitant antiferromagnetic and ferromagnetic properties could not be excluded. The two distinct thermal behaviors evidenced the higher metal-water bond strength with the smaller cation, and revealed the great supramolecular effects generated by hydrogen-bonding patterns.