Crystal structures of {[Cu(Lpn)2][Fe(CN)5(NO)]·H2O}n and {[Cu(Lpn)2]3[Cr(CN)6]2·5H2O}n [where Lpn = (R)-propane-1,2-diamine]: two heterometallic chiral cyanide-bridged coordination polymers

Two new chiral cyanide-bridged bimetallic coordination polymers involving the ligand (R)-propane-1,2-diamine (Lpn) are described. One compound is a zigzag cyanide-bridged chain polymer in which the asymmetric unit consists of two independent chiral {[Cu(Lpn)2][Fe(CN)5(NO)]} units and two water molecules, while the second compound is a two-dimensional cyanide-bridged coordination polymer, in which the asymmetric unit consists of two chiral {[Cu(Lpn)2][Cr(CN)6]}− anions bridged by a chiral [Cu(Lpn)2]2+ cation and five water molecules.

The Fe III atoms have distorted octahedral geometries, while the Cu II atoms can be considered to be pentacoordinate. In the crystal, however, the units align to form zigzag cyanidebridged chains propagating along [101]. Hence, the Cu II atoms have distorted octahedral coordination spheres with extremely long semicoordination Cu-N(cyanido) bridging bonds. The chains are linked by O-HÁ Á ÁN and N-HÁ Á ÁN hydrogen bonds, forming two-dimensional networks parallel to (010), and the networks are linked via N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds, forming a three-dimensional framework. Compound (II) is a two-dimensional cyanidebridged coordination polymer. The asymmetric unit is composed of two chiral {[Cu(Lpn) 2 ][Cr(CN) 6 ]} À anions bridged by a chiral [Cu(Lpn) 2 ] 2+ cation and five water molecules of crystallization. Both the Cr III atoms and the central Cu II atom have distorted octahedral geometries. The coordination spheres of the outer Cu II atoms of the asymmetric unit can be considered to be pentacoordinate. In the crystal, these units are bridged by long semicoordination Cu-N(cyanide) bridging bonds forming a two-dimensional network, hence these Cu II atoms now have distorted octahedral geometries. The networks, which lie parallel to (101), are linked via O-HÁ Á ÁO, O-HÁ Á ÁN, N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds involving all five non-coordinating water molecules, the cyanide N atoms and the NH 2 groups of the Lpn ligands, forming a threedimensional framework.

Chemical context
The design of multi-dimensional molecular systems is closely linked to their unique bulk physicochemical properties, such as magnetism (Kahn, 1993). Examples of these systems include cyanide-bridged complexes, in which a cyanidometallate anion serves as the bridging moiety in a multidimensional structure with a second coordination centre (Fukita et al., 1998;Ohba et al., 1999;Tanase & Reedijk, 2006;Zhang & Luo, 2006). In this context, heterometallic and chiral frameworks are of particular interest (Cui et al., 2002;Mironov et al., 2004). A chiral network would allow selective binding of chiral guests, and the presence of different types of metal ions may enable specific tuning of the electronic properties. However, only a few examples of chiral cyanide-bridged bimetallic complexes have been published so far (Coronado et al., 2003;Imai et al., 2004;Kaneko et al., 2006). We report herein on the synthesis and crystal structures of two new chiral cyanide-bridged heterometallic coordination polymers, (I) and (II), synthesized using the chiral ligand (R)-propane-1,2diamine. Compound (I) is isotypic with [Cu(1,2-pn) 2 ]-[Fe(CN) 5 NO]ÁH 2 O, synthesized using the racemic form of the same ligand propane-1,2-diamine (Smé kal et al., 2000).

Structural commentary
The asymmetric unit of complex (I) (Fig. 1) is composed of two independent cation-anion units of [Cu(Lpn) 2 ] 2+ Á-[Fe(CN) 5 )(NO)] 2À ÁH 2 O. Atoms Fe1 and Fe2 have distorted octahedral geometries being coordinated by five C atoms from the cyanide ligands (two cyanido groups are bridging and two terminal) and by one N atom, N2 and N12, respectively, from the nitrosyl group. The average Fe-N distance [1.657 (14) Å ] is much shorter than the Fe-C distances, which are between 1.926 (5) and 1.954 (6) Å . These values are in good agreement with those reported for other polymeric structures involving nitroprusside (Shyu et al., 1997;Chen et al., 1995). Atoms Cu1 and Cu2 are pentacoordinate. Atom Cu1 has a perfect squarepyramidal geometry with a value of 0 (Addison et al., 1984), while atom Cu2 has a distorted square-pyramidal geometry with a value of 0.23. The Cu-N(Lpn) bond lengths vary between 1.998 (5) and 2.026 (5) Å , while the axial bond length Cu1-N1 is 2.333 (5) Å and Cu2-N11 is 2.290 (5) Å . The asymmetric unit of complex (II) (Fig. 2) consists of two chiral {[Cu(Lpn) 2 ][Cr(CN) 6 ]} À anions bridged by a chiral [Cu(Lpn) 2 ] 2+ cation. There are also five water molecules of crystallization present. The coordination sphere of the central Cu II atom, Cu3, can be described as elongated octahedral, generated by four N atoms of the Lpn ligands and two cyanide N atoms. The outer atoms Cu1 and Cu2 are pentacoordinate; atom Cu1 has a distorted square-pyramidal geometry with a value of 0.14 (Addison et al., 1984), while atom Cu2 has an almost perfect square-pyramidal geometry with a value of 0.04. The Cu-N(Lpn) bond lengths vary between 1.960 (12) and 2.020 (10) Å , which is similar to the bond lengths observed in (I) and in a copper(II) complex involving (S)-

Figure 1
A view of the asymmetric unit of compound (I), showing the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
A view of the asymmetric unit of compound (II), showing the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. Water molecules and the C-bound H atoms have been omitted for clarity.

Figure 4
Crystal packing of compound (I), viewed along the a axis. Hydrogen bonds are shown as dashed lines (see Table 1 for details) and C-bound H atoms have been omitted for clarity. Àx + 2, y + 1 2 , Àz + 1]. Thus, as for complex (I), atoms Cu1 and Cu2 have octahedral coordination spheres with a strong pseudo-Jahn-Teller effect. Closely related two-dimensional bimetallic systems have been found in iron(III) analogues, where [Fe(CN) 6 ] 3À anions binds to three adjacent nickel atoms (Kou et al., 1999(Kou et al., , 2000. The two-dimensional networks of (II) (Fig. 5) are linked by a series of O-HÁ Á ÁO, O-HÁ Á ÁN, N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds, involving the water molecules, the cyanide N atoms and the NH 2 groups of the Lpn ligands, forming a three-dimensional framework ( Fig. 6 and Table 2).

Synthesis and crystallization
Compound (I): (R)-propane-1,2-diamine (Lpn) was synthesized according to a reported procedure (Bernauer, 1971). The pH of an aqueous solution of LpnÁHCl (0.1 mmol in 1 ml of water) was adjusted to 7-8 by the addition of an aqueous solution of KOH (0.12 mmol in 0.3 ml of water  Crystal packing of compound (II), viewed along the a axis. Hydrogen bonds are shown as dashed lines (see Table 2 for details) and C-bound H atoms have been omitted for clarity.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 3. For both compounds, the water molecule H atoms were located in difference Fourier maps and refined with distance restraints of O-H = 0.84 (2) Å and with U iso (H) = 1.5U eq (O). The N-and C-bound H atoms were included in calculated positions and treated as riding atoms:

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.