Comment on μ_1,3-azido-di­azido­tetra­kis­(1,10-phenanthroline)­dicopper(II) azide tetrahydrate

The supramolecular structure of the title dimeric azido complex of copper(II), [Cu₂(μ_1,3-N₃)(N₃)₂(phen)₄](N₃)·4H₂O (phen is 1,10-phenanthroline, C₁₂H₈N₂) [Cheng, Hu, Wang & Ye (2002). Acta Cryst. C58, m12–m13], which was originally described in terms of hydrogen-bonded chains, has been re-interpreted as two-dimensional hydrogen-bonded sheets built from R(12) and R(28) rings, taking into account the complete hydogen-bonding pattern.

1. Comment

In a recent paper, Cheng et al. (2002) reported a dimeric azido complex of copper(II), viz. [Cu₂(μ_1,3-N₃)(N₃)₂(phen)₄](N₃)·4H₂O. Although the correct formula was given, the molecular unit was described as being comprised of a dimeric cation, two azide anions and four water mol­ecules. However, re-examination of the structure using the deposited coordinates shows that the molecular unit possesses a dimeric cation along with only one azide anion and four water mol­ecules. This is evident from the fact that both the central N2 and N11 atoms of the two azide ions lie on the special positions at (0,0,½) and (0,0,0), respectively.

The authors also showed that there were hydrogen-bonding and aromatic π–π interactions producing, respectively, a one-dimensional chain and a two-dimensional supramolecular array. However, re-examination using PLATON (Spek, 2001) clearly reveals further relatively strong hydrogen bonds that were overlooked in the original report, namely the O1W—H1WA⋯O2Wⁱ and O2W—H2WA⋯N10ⁱ hydrogen bonds [symmetry code: (i) 1 − x, −y, −z]. These intermolecular hydrogen bonds are involved in the formation of a two-dimensional sheet consisting of R(12) and R(28) rings (Fig. 1) (Etter, 1990; Bernstein et al., 1995). The R(12) rings adopt a chair conformation and if the weak O1W—H1WA⋯O2Wⁱ component of the nearly planar three-centre hydrogen-bonding system is also considered, then this ring is itself divided into three smaller rings (Fig. 1), one of the R⁴₄(8) type and two of the R²₂(4) type.

Thus, the structure is now correctly described with a complete hydrogen-bonding pattern which dominates the overall structure and plays an important role in the crystal packing (Jeffrey, 1997).

Table 1
Hydrogen-bonding geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1W—H1WA⋯N10	0.94	2.25	2.792 (7)	116
O1W—H1WA⋯O2W^i	0.94	2.53	3.369 (6)	149
O1W—H1WB⋯N1	0.94	2.24	2.908 (6)	128
O2W—H2WA⋯N10^i	0.94	2.33	3.245 (8)	163
O2W—H2WB⋯O1W	0.94	1.92	2.857 (6)	178
Symmetry code: (i) 1-x,-y,-z.

Supporting information

Computing details

 

Footnotes

‡The author is currently a postdoctoral fellow.