C3H3Nd06, trigonal, Rim (no. 160), a = 10.596(1) Â, c = 4.0588(8) A, V = 394.6 Â3, Z = 3, Rgi(F) = 0.011, wRntfF2) = 0.028, T= 296 K. Source of material Biphenyl-3,3',4,4-tetracarboxylic acid (0.033 g, 0.1 mmol), Nd(N03)3 · 6H2O (0.0876 g, 0.2 mmol), NaOH (0.4 mmol, 0.016 g), DMF (MJV-dimethy lformamide; 1 mL), H2O (6 mL), and HNO3 (0.5 mL, 0.75 M in H2O) were added respectively to a 15 mL Teflon-lined steel autoclave, which was sealed and heated to 443K for 3 days and then cooled to room temperature. Perfect pink block crystals were collected. Chemical analysis — found: C, 12.85 %; H, 1.12 %; calculated forC3H3Nd06: C, 12.90 %, H, 1.08%. The synthesis of the title compound is out of the expectation of our original purpose. The ligand in the complex is a formate, which was not directly introduced as one of the starting reaction materials. The starting materials biphenyl-3,3',4,4'-tetra- carboxylic acid do not take part in the coordination. The synthetic procedure involves DMF and H2O as solvents, and we think the formate group comes from DMF. Similar situation also occurred in other systems (1-3), and it has long been known that DMF can be hydrolyzed to formate and DMA (dimethylamine) and that the rate of this process increases at high temperature and pressure (4). Discussion The title crystal structure, is isotypic with numerous lanthanide formates, like those of La, Ce, Tb and Tm (5). Unit cell data have been reported previously for (Nd(HC02)3)n (6), although the compound was described in that case as a fractional hydrate and atomic coordinates were not determined. The title compound is a 3D neutral framework composed of Nd(H() ions and formate an- ions in a 1 : 3 ratio. The asymmetric unit contains 1/3 neodym- ium(m) cation and one formate HCC>2~ anion. The Nd ion lies on a site of 3m symmetry and is coordinated by nine O atoms from nine HCO2- anions, which lie on mirror planes. The coordinating oxygen atoms of the formate ligand differ with respect to their linkage. Ol forms//2-bridges between neighbouring neodymium centres, while 02 is monocoordinating. Each C atom makes three C-O-Nd linkages through one/^-bridging O atom (Ol) and one μι-bound O atom (02). Three Nd ions and three HCO ~ anions are connected, forming six-membered rings, which are connected by further HCO2 anions, generating a 3D framework. The dis- tance between adjacent Nd ions is 4.0588(8) Â.