The mer ‐Triaquatrichloroiron(III) Molecule in Triethylenediammonium and Piperazinium Chloride Matrices

The neutral mer ‐triaquatrichloroiron(III) molecule, mer ‐[(H 2 O) 3 FeCl 3 ], has been structurally defined, co‐crystallized with a pair of organic‐cation/chloride salts, from hydrochloric acid solution in each case. The array {[HN(CH 2 CH 2 ) 3 NH]Cl 2 }{ mer ‐[(H 2 O) 3 FeCl 3 ]}, ( 1 ) has been previously described in a room‐temperature study in terms of orthorhombic Pnma symmetry; here, at low‐temperature ( ca. 153 K), the description is in terms of P 2 1 2 1 2 1 , with the complex of quasi‐m symmetry. Full m symmetry is achieved in the second complex, {[H 2 N(CH 2 CH 2 ) 2 NH 2 ]Cl 2 }{ mer ‐[(H 2 O) 3 FeCl 3 ]}, ( 2 ) which crystallizes in space group P 2 1 / m . Fe–Cl and Fe–O(H 2 ) are very tightly ranged in 1 , < > 2.3359(6), 2.051(5) Å, respectively, less so in 2 (2.326(1), 2.340(1); 2.049(2)–2.080(2) Å), despite strong hydrogen‐bonding in the lattice between the hydrogen atoms of the coordinated water molecules and the uncoordinated chloride ions. A redetermination of the structure of FeCl 3 ·6H 2 O ( 3 ), trans ‐tetraquadichloroiron(III) chloride dihydrate, is also recorded; at 100 K,Fe–Cl,O are 2.2830(4), 2.0543(9) Å.