Poly[[di-μ3-nicotinato-μ3-oxalato-samarium(III)silver(I)] dihydrate]

In the title three-dimensional heterometallic complex, {[AgSm(C6H4NO2)2(C2O4)]·2H2O}n, the SmIII ion is eight-coordinated by four O atoms from four different nicotinate ligands and four O atoms from two different oxalate ligands. The three-coordinate AgI ion is bonded to two N atoms from two different nicotinate anions and one O atom from an oxalate anion. These metal coordination units are connected by bridging nicotinate and oxalate ligands, generating a three-dimensional network. The uncoordinated water molecules link the carboxylate groups via O—H⋯O hydrogen bonding. The crystal structure is further stabilized by hydrogen bonds between the water molecules.

In the title three-dimensional heterometallic complex, {[AgSm(C 6 H 4 NO 2 ) 2 (C 2 O 4 )]Á2H 2 O} n , the Sm III ion is eightcoordinated by four O atoms from four different nicotinate ligands and four O atoms from two different oxalate ligands. The three-coordinate Ag I ion is bonded to two N atoms from two different nicotinate anions and one O atom from an oxalate anion. These metal coordination units are connected by bridging nicotinate and oxalate ligands, generating a threedimensional network. The uncoordinated water molecules link the carboxylate groups via O-HÁ Á ÁO hydrogen bonding. The crystal structure is further stabilized by hydrogen bonds between the water molecules.

Comment
In the past few years, lanthanide-transition metal heterometallic complexs with bridging multifunctionnal organic ligands have generated much interest, not only because of their impressive topological structures, but also due to their versatile applications in ion exchange, magnetism, bimetallic catalysis and luminescent probe (Cheng et al., 2006;Kuang et al., 2007;Luo et al., 2007;Peng et al., 2008). As an extension of this research, we report here the structure of the title compound, a new heterometallic coordination polymer.
In the title compound ( Fig. 1), there are one Sm III ion, one Ag I ion, two halves of oxalate ligand, two nicotinate ligands, and two lattice water molecules in the asymmetric unit. Each Sm III ion is eight-coordinated by four O atoms from four different nicotinate ligands, and four O atoms of two different oxalate ligands. The Sm center can be described as having a bicapped trigonal prism coordination geometry. The three-coordinate Ag I ion is bonded to two N atoms from two different nicotinate anions and one O atom from an oxalate anion. Thus the Ag I ion is in a T-shaped configuration. These metal coordination units are connected by bridging nicotinate and oxalate ligands, generating a three-dimensional network (Fig.   2). The uncoordinated water molecules link the carboxylate groups by O-H···O hydrogen bonding (Table 1). The crystal structure is further stabilized by hydrogen bonds.

Refinement
H atoms bonded to C atoms were positioned geometrically and refined as riding, with C-H = 0.93 Å and U iso (H) = 1.2 U eq (C). H atoms of water molecules were found from difference Fourier maps and included in the refinements with a restraint of O-H = 0.86 -0.87 Å and U iso (H) = 1.5 U eq (O). The largest residual electron density in the final difference map was located at a distance of 0.82 Å from Ag2 atom and was meaningless.
supplementary materials sup-2 Figures Fig. 1. The molecular structure showing the atomic-numbering scheme and displacement ellipsoids drawn at the 30% probability level. Symmetry codes included in the atomic labels: