SYNTHESIS, STRUCTURE AND INVESTIGATION OF GERMANIUM(IV) AND COPPER(II) COMPLEXES WITH MALIC ACID AND 1,10’-PHENANTHROLINE

Two crystalline compounds of germanium(IV) with malic acid (H3Mal) and 1,10’-phenanthroline (phen) [Ge(HMal)2(phen)]·phen·2H2O (1) and [CuCl(phen)2][Ge(OH)(HMal)2] (2) were synthesized for the first time and characterized by elemental analysis, IR spectroscopy and thermogravimetric analysis. Using single crystal X-ray diffraction, two different forms of germanium were elucidated: Ge (1) and hydrolyzed GeOH (2) with a distorted octahedron and pyramid surrounding geometry, respectively.


Introduction
In the course of our systematical research towards complex formation of germanium(IV) with hydroxycarboxylic acids, which are different by the number and mutual position of hydroxyl and carboxyl groups, our group have previously synthesized and structurally characterized different ligand and heteronuclear coordination compounds with citric [1,2], tartaric [3,4] and xylaric acids [5,6]. Unexpectedly, it was not possible to obtain germanium(IV) complex with the monohydroxydicarboxylic malic acid under the same conditions. At the same time, such research is of great interest because of the properties of malic acid that plays the key role in plants and animals metabolism, and is involved in many biochemical processes, e.g., the Krebs cycle [7]. It is also a versatile polydentate ligand, a large number of mono-, di-and polymeric coordination compounds of different metals with H 3 Mal have been already structurally characterized [8][9][10][11].
In the past few years, there were synthesized a number of complex compounds containing the divalent tris ( [14]. As a result, the idea for obtaining the complexes of germanium(IV) with malic acid by reactions in GeO 2 -H 3 Malphenwater and GeO 2 -H 3 Mal -CuCl 2phenwater systems has appeared. Here, the synthesis, structural characterization and properties of the new complexes in the solid state and also their comparison with the previously obtained coordination compounds of germanium(IV) with hydroxycarboxylic acids is reported.

Instrumentation
Elemental analysis for germanium and copper was performed using inductively coupled plasma atomic emission spectroscopy (PerkinElmer Optima 2000 DV instrument), chlorine was quantified by mercurometry. The C, H, and N analysis was performed using Elemental Analyzer CE-440.
Thermogravimetric analysis (TGA) was carried out using a Q-1500D device at a heating rate of 10 °C/min, in air, in 20-1000 °С temperature range.
The IR spectra in the 4000-400 cm -1 range were recorded as potassium bromide pellets on a PerkinElmer Frontier spectrometer (The absorption bands were attributed according to the reference data for the starting malic acid and our earlier obtained germanium(IV) coordination compounds with hydroxycarboxylic acids [1-6] (s.strong, m.middle, w.weak).
Crystal data for structures 1 and 2 were measured on an Xcalibur-3 diffractometer (graphite monochromated Mo-Kα radiation, CCD detector, φ and ω-scanning). The structures were solved by the direct method using SHELXTL package [15]. Full-matrix least-squares refinement against F 2 in anisotropic approximation was used for non-hydrogen atoms. Positions of hydrogen atoms were located from the electron density difference maps and refined by "riding" model with Uiso = nUeq of the carrier atom (n = 1.5 for hydroxyl groups and n = 1.2 for other hydrogen atoms). CCDC 1513407-1513408 contain the supplementary crystallographic data for 1 and 2, respectively. These data can be obtained, free of charge, via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Full use of the CCDC package was also made for searching in the CSD Database [16].

[CuCl(phen) 2 ][Ge(OH)(HMal) 2 ] (2)
In the first step, GeO 2 (104.6 mg, 1 mmol) and malic acid (268.2 mg, 2 mmol) were dissolved in 100 mL of hot water to make first working solution, which was then concentrated to 25 mL (50°C). In the second step, weighted portions of 1,10'-phenanthroline (360 mg, 2 mmol) and CuCl 2 ·2H 2 O (170.5 mg, 1 mmol) were added to 25 mL of ethanol and then heated at 40 °C until the reagents were completely dissolved. In the third step, two working solutions cooled to the room temperature were mixed to allow obtaining the mild after 2 days, from which blue crystals were collected mechanically and analyzed by X-ray crystallography.
The thermal decomposition of 1 starts with an endotherm peak in the temperature range 80-230 °C, which is coming along the elimination to the gas phase of two molecules of crystal water (calc. m=4.92%). While heating, further in a temperature range from 270 to 360 °C, complex 1 eliminates one molecule of phenanthroline and two СО 2 molecules from the malate ligands (calc. m=36.56%).
According to the calculated weight loss of the thermogravimetric curve of complex 2, the first endotherm peak is accompanied by elimination of one water molecule to the gas phase (calc. m=2.2%). That molecule is formed by an interaction of the carboxyl proton with the inner sphere OH group bound to germanium [3]. The second endotherm peak from the thermogravimetric curve of 2 corresponds to the loss of two phenanthroline molecules (calc. m=44.3%).
Finally, complexes 1 and 2 undergo oxidative thermal degradation and combustion of the organic part of their molecules, with the corresponding one (for 1) and two exothermic peaks (for 2).
The presence in IR spectra of 1 and 2 (C=O),  as (COO -) and  s (COO) absorption bands, which are typical for COOH and COO  groups, shows the presence of nonequivalent carboxyl groups (free and bound) in the complexes. The conclusion about how these groups are bonded with germanium is also made on the basis of the band corresponding to the Ge-O stretching vibrations, which is emergence in the IR spectra of complexes. The presence of the band responsible for the Ge-O-H bending vibrations implies the presence of the hydrolyzed form of germanium in the complex 2.
In the structures of complexes 1 and 2 two different forms of germanium are implemented: Ge 4+ (1) and hydrolyzed GeOH 3+ (2), wherein neutral complex and anion are formed, respectively. In 1 coordination number is 6, in 2 -5, where germanium atom is coordinated with two malate anions HMal 2in both cases and binds with 1,10'-phenanthroline in 1 and with hydroxyl group in 2.
The compound 1 exists as a monohydrate of co-crystal with 1,10'-phenanthroline in 1:1 ratio (Figure 1). Molecules of complex and uncoordinated 1,10'-phenanthroline are in particular position on the axis of second-order symmetry. In crystal structure of the molecules of coordination compound 1 and water are connected with intermolecular hydrogen bonds (Table 2) and form the three-dimensional network (Figure 2). structures 1 and 2 ( 1 -x, 1-y, -z).
In the crystal structure of 2 anions and cations form three types of alternating layers, parallel along the аb crystallographic plane ( Figure 5): the first layer type is formed by anions A, the second layer type includes both cations (A and B) and the third layer type is organized by anions B. All anions within the layers are connected by the О-Н…О intermolecular hydrogen bonds (Table 2).

Conclusions
Using 1,10'-phenanthroline, for the first time it was possible to get two different types of malatogermanate complexes of germanium: the different-ligand compound 1 by the self-assembly method from the water solution and the differentmetal compound 2 by stepwise synthesis method from the water-ethylene solution. The feature of compound 1 is that 1,10'-phenanthroline enters the inner sphere and coordinates in a bidentate fashion to Ge(IV) by two N atoms, though in water solutions Ge rather coordinates with oxygen-containing organic molecules, such as malic acid in complex anion [Ge(OH)(HMal) 2 ] -(2). The big interest also represents the differences in crystal structures of synthesized complexes: three-dimensional net, in the cavities of which uncoordinated 1,10'-phenanthroline molecules are located in 1, and fiber structure of alternating topological isomeric cations and anions A and B in 2.