D Hydrogen-Bonded Network Built from Copper ( II ) Complexes of 1 , 3-Propanediamine

A reação entre Cu(NO 3 ) 2 .3H 2 O e 1,3-propanodiamina (pn), na presença de NaN 3 , conduziu à obtenção de um co-cristal 1:1 formado por [Cu(NO 3 ) 2 (pn) 2 ] e [Cu(N 3 )(NO 3 )(pn) 2 ] (1 e 2), os quais foram caracterizados por análise elementar, espectroscopia no IV e difração de raios X por monocristal. Em ambos os compostos, os átomos de cobre(II) encontram-se em um ambiente octaédrico distorcido, com quatro ligações no plano basal formadas por quatro átomos de N de dois ligantes pn bidentados enquanto que as ligações axiais são formadas por dois átomos de O do ligante nitrato em 1 e por um átomo de O do ligante nitrato e um átomo de N do íon azida em 2. A estrutura cristalina consiste em dois complexos (1 e 2) cristalograficamente independentes, que se unem por uma série de ligações de hidrogênio do tipo N–H···O e N–H···N bem como interações por C–H···O. Novos synthons supramoleculares foram identificados pela ocorrência de dois modos geometricamente distintos de reconhecimento molecular envolvendo o íon NO 3 –


Introduction
Much attention has been devoted to the investigation of transition metal-based supramolecular frameworks due to theoretical and challenging aspects in controlling the selfassembly processes, as well the potential uses of such materials in sensing, gas adsorption, magnetic devices, molecular electronics, porous and nanosized materials. 1mong the non-covalent interactions, which play a significant role in the molecular self-recognition of the components, within the crystal, the hydrogen bonding is the most important interaction type, since it combines directionality with strength. 2Within this context, a large number of well-ordered architectures has been successfully built up by assembling discrete coordination compounds via hydrogen bonding motifs. 3n our recent works, 4 we have obtained a series of multidimensional supramolecular systems based on the selfassembly of discrete [Pd(SCN) 2 (3,5- As part of our ongoing investigations on the coordination and supramolecular chemistry of metal pseudohalides complexes, 4,5 we report herein the preparation and crystallographic studies on the co-crystal of [Cu(NO 3 ) 2 (pn) 2 ] [Cu(N 3 )(NO 3 )(pn) 2 ].

Instrumentation
The IR spectrum of the co-crystal was recorded as KBr pellets on a Nicolet IMPACT 400 spectrophotometer in the 4000-400 cm -1 wavelength range, at a resolution of 4 cm -1 .C, H, and N analysis were carried out with a CE Instruments EA1110 CHNS-O microanalyzer.The Cu content was determined following the literature procedure. 6

Crystal structure determination
The data collections for a single crystal were carried out on an Enraf Nonius CAD4 diffractometer, using graphite monochromated MoK α (λ = 0.71073Å) radiation.Twenty five reflections (12.41 < θ < 18.06) were used to determine the cell parameters, at room temperature.During the data collection 3 standard reflections were used with no significant decay.Intensities were corrected by absorption factors [μ(MoK α ) = 1.643 mm -1 ] using the PSISCAN method. 7nformation concerning crystallographic data collection and refinement of the structure are given in Table 1.The structures were solved using the WinGX system 8 by SIR92, 9 and refined by full matrix least squares and difference Fourier synthesis using SHEL97. 10The final residual electronic density, is located around the copper atom.The hydrogen atoms were located in their ideal positions and not refined, with the thermal vibration parameters equal to 1.3 times the isotropic equivalent U of the attached atom.All non-hydrogen atoms were refined anisotropically.The structural analysis was performed by PLATON system. 11

Results and Discussion
During our attempts to synthesize new Cu II azidocomplexes from the reaction between copper(II) nitrate and 1,3-propanediamine (pn) with two equivalents of NaN 3 , in an ethanol:water mixture, we have obtained formulation.The X-ray structural determination of this species was undertaken in order to get a better knowledge of its structure.

X-ray crystallographic studies
The co-crystallization of two different monomeric compounds in the asymmetric unit, [Cu(NO 3 ) 2 (pn) 2 ] (1) and [Cu(N 3 )(NO 3 )(pn) 2 ] (2), was definitely proved by the crystal and molecular structure X-ray analysis, corroborating the important structural features suggested by IR spectroscopy.
The molecular structures of the complexes [Cu(NO 3 ) 2 (pn) 2 ] (1) and [Cu(N 3 )(NO 3 )(pn) 2 ] (2), together with the crystallographic labeling scheme, are shown in Figures 1 and 2, respectively.Selected bond lengths and angles with their estimated standard deviations in parentheses are listed in Table 2 and 3, respectively.
In compound 1, the two axial Cu-O bond distances are very different from each other: Cu1-O3 = 2.927(3) Å and Cu1-O5 = 2.458(3) Å.The former apical Cu-O bond distances for 1 as well that found for 2 (Cu2-O9 = 2.990(4) Å) indicated the existence of very weak covalent interactions between one of the oxygen atom from the nitrate and Cu(II) ion.Despite the fact that these bond lengths are slightly longer than the sum of van der Waals radii of copper and oxygen (2.90 Å), Cu-O values within the range of 2.5-3.0Å have been considered as long coordination distances for copper(II) complexes. 17For instance, Valdéz-Martinez et al. 18 considered the coordination of the NO 3 -groups at the axial positions of [Cu(NO 3 ) 2 (MeTSC) 2 ], which exhibited Cu-O bond length of 2.864(3) Å. Copper-oxygen bond of 2.906 (7) Å was also considered significant in the molecular structure of [Cu(NO 3 ) 2 (py) 2 ] 2 •py (py = pyridine). 19Anyway, if one takes into account that Cu1-O3 and Cu2-O9 are nonbonding distances, the metal coordination polyhedron in 1 and 2 could alternatively be described as distorted square pyramidal.
The azide and nitrate groups participate in a series of hydrogen bonds which are responsible for the stabilization of the crystal structure.Table 4

lists the distances and angles of hydrogen bonds and C-H•••O interactions in the co-crystal.
Table 4. Hydrogen bonds distances and angles for the co-crystal (Å, °)   These intermolecular forces are responsible for the selfassembly of the 1D chains of 1 and 2 into a three-dimensional supramolecular network, which is illustrated in Figure 6.From the crystal engineering point of view, the crystal structure described in this paper clearly demonstrated two geometrically distinct supramolecular synthons (synthons I and II) which are generated from the molecular recognition between the hydrogen bond donating NH 2 groups from chelating 1,3-propanediamine ligands and HB-accepting site of nitrate group (Scheme 1).

IR spectroscopy
The IR spectrum of the co-crystal [Cu(NO 3 ) 2 (pn) 2 ] and [Cu(N 3 )(NO 3 )(pn) 2 ] (1 and 2) displayed a number of absorption bands attributed to vibrational modes of 1,3propanediamine at 3262 cm -1 (ν as NH 2 ), 3157 cm -1 (ν s NH 2 ) and 1580 cm -1 (δNH 2 ).However, the main interest in IR spectrum of the compounds 1-2 lies in the bands associated with the vibrational modes of N 3 and NO 3 -groups as they can be very useful for the diagnosis of their coordination mode.The first feature of the IR spectrum of the co-crystal was the occurrence of a strong band at 2032 cm -1 assigned to ν ass N 3 and indicative of azide group terminally coordinated to the copper atom. 17The presence of the  nitrate group is evidenced by the appearance of a strong and narrow band at 1383 cm -1 (νONO).

Conclusions
In this work, we describe the X-ray structural characterization of an unusual 1: In the context of supramolecular chemistry and crystal engineering of the transition metal-based species, it is of vital importance to identify and understand the role played by new inorganic supramolecular synthons in the molecular aggregation within the crystal since they can be important tools in the rational construction of well-ordered structures.A systematic work on the creation of novel supramolecular architectures is currently underway in our laboratory.

Figure 5 .
Figure 5. ORTEP representation of four molecules of 1 and 2 showing N-H•••O intermolecular hydrogen bonds and C-H•••O interactions.

Figure 6 .
Figure 6.Perspective view of the 3D supramolecular network in the cocrystal.

Table 1 .
Summary of data collection and refinement conditions and analytical evidences of the formation of an unusual compound.Repeated elemental analysis results of the sample were consistent with a C 12 H 40 N 14 Cu 2 O 9 physical

Table 3 .
Selected angles (°) for the co-crystal

Table 2 .
Selected bond lengths (Å) for the co-crystal