A co-crystal of 1,10-phenanthroline with boric acid: a novel aza-aromatic complex

The title compound, C12H8N2·2B(OH)3, is best described as a host–guest complex in which the B(OH)3 molecules form a hydrogen-bonded cyclic network of layers parallel to the ab plane into which the 1,10-phenanthroline molecules are bound. An extensive network of hydrogen bonds are responsible for the crystal stability. No π-stacking interactions occur between the 1,10-phenanthroline molecules.

The title compound, C 12 H 8 N 2 Á2B(OH) 3 , is best described as a host-guest complex in which the B(OH) 3 molecules form a hydrogen-bonded cyclic network of layers parallel to the ab plane into which the 1,10-phenanthroline molecules are bound. An extensive network of hydrogen bonds are responsible for the crystal stability. No -stacking interactions occur between the 1,10-phenanthroline molecules.

Related literature
For the design and synthesis of novel systems of non-covalent hosts involving hydrogen bonds, see: Pedireddi et al. (1997). In the field of supermolecular synthesis, recognition between the complementary functional groups is a main factor for the evaluation of influence of noncovalent interactions in the formation of specific architecture, see: Lehn (1990). The ability of the -B(OH) 2 functionality to form a variety of hydrogen bonds through different conformations makes it a very suitable moiety for the synthesis of novel molecular complexes, see: Lee et al. (2005). It is known to have an affinity for pyridyl N atoms, often forming O-HÁ Á ÁN hydrogen bonds, as observed in some crystals of boronic acids with aza compounds (Talwelkar & Pedireddi, 2010). Non-covalent hosts are generally designed and synthesized by employing appropriate functional groups at required symmetry positions to form a cyclic network through the hydrogen bonds, see: Pedireddi (2001). This effect has been observed in simple molecular adducts such as 1,10-phenanthroline and water (Tian et al., 1995).  Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx; Ày þ 1; Àz þ 1; (ii) Àx þ 1; Ày; Àz þ 1; (iii) x; y À 1; z.

Experimental
Data collection: CrysAlis PRO (Oxford Diffraction, 2011); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: publCIF (Westrip, 2010). The design and synthesis of novel systems of noncovalent hosts involving hydrogen bonds is a vast research area in both molecular and supermolecular chemistry, see Pedireddi et al. (1997). In the field of supermolecular synthesis, recognition between the complementary functional groups is a main factor for the evaluation of influence of noncovalent interaction in the formation of specific architecture, see: Lehn (1990). In recent times, boric acid derivatives have been well considered to be potential co-crystal formers. In fact, the ability of -B(OH) 2 functionality to form a variety of hydrogen bonds through different conformations makes it a very suitable moiety for the synthesis of novel molecular complexes, see Lee et al. (2005). The -B(OH) 2 moiety is known to have an affinity for pyridyl N-atoms, often forming O-H···N hydrogen bonds, as observed in some crystals of boronic acids with aza compounds,see Talwelkar & Pedireddi (2010).
Non-covalent hosts are generally designed and synthesized by employing appropriate functional groups at required symmetry positions to form a cyclic network through the hydrogen bonds, see Pedireddi (2001). This effect has been observed vividly in simple molecular adduct such as 1,10-phenanthroline and water, see Tian et al. (1995). In this complex, a water molecule interacts with a molecule of 1,10-phenanthroline through O-H···N hydrogen bonds and an unique aza-aromatic complex is formed. In the latter, 1,10-phenanthroline could be considered as a host. Herein, we report the crystal structure of boric acid with 1,10-phenanthroline as an aza-donor compound.
As seen in Figure 1, the phen molecule forms a H-bonded adduct via two B-O-H···N interacts from one of the included B(OH) 3 moieties. A strong network of hydrogen bonds among the B(OH) 3 units forms a layered structure with alternating B(OH) 3 and phen layers that reside in the ab planes ( Figure 2). The B(OH) 3 layers alone can be described as a cyclic network formed by hydrogen bonding interactions as can be seen in Figure 3. There are not any significant π-stacking interactions between the phen molecules.

Experimental
(CH 3 ) 3 NBH 3 (0.73 g, 10 mmol) and iodine (2.54 g, 5 mmol) were dissolved in toluene (4 ml) and stirred for 30 min. A solution of 1,10-phenanthroline (1.98 g, 10 mmol) in toluene (4 ml) was added, and the mixture refluxed overnight. The solution was cooled to room temperature, during which process orange-brown crystals were formed. The product was recrystallized twice from CH 3 CN to obtain analytically pure, red-brown crystalline product.

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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.