Crystal structure of poly[[μ3-(S)-2-amino-3-hydroxy­propano­ato]-cis-di-μ-chlorido-caesium­palladium(II)]

Bhadbhade, M.M.; Charlson, A.J.

doi:10.1107/S2056989017016164

research communications

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Volume 73| Part 12| December 2017| Pages 1898-1902

https://doi.org/10.1107/S2056989017016164

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Crystal structure of poly[[μ₃-(S)-2-amino-3-hydroxypropanoato]-cis-di-μ-chlorido-caesiumpalladium(II)]

Mohan Madhav Bhadbhade ^a and Alexander J. Charlson ^b ^*

^aMark Wainwright Analytical Centre, University of New South Wales, Sydney, NSW 2052, Australia, and ^bDepartment of Chemistry and Biomolecular Sciences, Macquarie University, North Ryde, NSW 2109, Australia
^*Correspondence e-mail: alec.charlson@gmail.com

Edited by W. Imhof, University Koblenz-Landau, Germany (Received 16 August 2017; accepted 9 November 2017; online 21 November 2017)

The structure of the title compound, [CsPd(C₃H₆NO₃)Cl₂]_n, previously shown to have anticancer activity in rodent test systems and recently found to have antifungal activity, has been determined. The Pd centre is in a square-planar coordination environment with two chlorine atoms in cis positions and the remaining two coordination sites being coordinated by N and O atoms from deprotonated L-serine. Each of the Cs cations shows ninefold coordination with six chlorine and three O atoms resulting in a coordination environment that is similar to the well known Cs₂SO₄ structure. X-ray crystal structures of only three dichloridopalladium(II)–amino acid complexes have been determined so far and the present paper describes one of those.

Keywords: palladium–amino acid complex; L-serine; single-crystal X-ray structure; palladium complex.

CCDC reference: 1584689

1. Chemical context

The X-ray crystal structure of potassium-L-alaninato-dichloroplatinate(II) has been published (Schiesser et al., 2012 ). Two complexes of L-serine with palladium(II), bis(L-serinato) palladium(II) and caesium cis-dichloro-L-serinato palladium(II), were synthesized (Charlson et al., 1981 ) and an X-ray crystal structure determination of bis (L-serinato) palladium(II) has been performed (Vagg, 1979 ). Previously it was shown that caesium cis-dichloro-L-serinato palladium(II) produced filamentous growth in Escherichia coli (E.coli) bacteria (Charlson et al., 1981), markedly modified the interior of E.coli bacteria cells (McArdle et al., 1984 ), increased the lifespan of solid murine tumors Ca-755 and RShM-5 (Treschalina et al., 1994 ) and had radio-modifying properties (Treshalina et al., 1995 ). Recently it was found that caesium cis-dichloro-serinato palladium(II) had antifungal activity in the Candida albicans and Cryptococcus neoformans test-systems and was non-cytotoxic against human kidney cells at the dose levels used (Elliott, 2016 ). The antimicrobial screening was performed by CO–ADD (The Community for Antimicrobial Drug Discovery) funded by the Welcome Trust (UK) and the University of Queensland (Australia). In the publication describing the synthesis of caesium cis-dichloro-L-serinato palladium(II), the empirical formula of the compound was deduced on the basis of the percentages of carbon, hydrogen, chlorine and nitrogen that were obtained by micro analysis (Charlson et al., 1981) The present X-ray crystal structure was performed in order to establish the molecular and structural formulae of caesium cis-dichloro-L-serinato palladium(II).

2. Structural commentary

The palladium(II) serine complex ion shows a square-planar coordination of palladium with the two chloro ligands being in cis positions relative to each other and the remaining two coordination sites being coordinated by the nitrogen atom (N1) and one of the carboxylato oxygen atoms (O1) of the deprotonated amino acid L-serine. The view of the asymmetric unit is given in Fig. 1 and the ninefold coordination (three oxygen and six chlorine atoms) of caesium is shown in Fig. 2. A summary of significant bond distances is given in Table 1. The two Pd—Cl bonds are of slightly different bond length. The longer bond [Pd1—Cl1 = 2.305 (4) A] is trans to nitrogen and the shorter one [Pd1—Cl2 = 2.287 (4) A] is trans to the oxygen atom. The same behaviour was observed in the structure of barium dichloro(glycinato) palladium(II)·2H₂O (Baidina et al., 1980a ). The five membered ring Pd1–O1–C1–C2–N1 is planar with the hydroxymethyl substituent in a gauche–gauche orientation that is very similar with the conformation of one of the ligands in the structure of bis(L-serinato) palladium(II) (Vagg, 1979).

Table 1
Selected bond lengths (Å)

Cs1—Cs1ⁱ	4.421 (2)	Cs1—O2	3.117 (10)
Cs1—Pd1ⁱⁱ	3.8755 (17)	Cs1—O2^vi	2.962 (10)
Cs1—Cl1ⁱⁱⁱ	3.528 (4)	Cs1—O3	3.349 (10)
Cs1—Cl1^iv	3.572 (4)	Cs1—C1	3.654 (15)
Cs1—Cl1ⁱⁱ	3.740 (4)	Pd1—Cl1	2.305 (4)
Cs1—Cl1^v	3.698 (4)	Pd1—Cl2	2.287 (4)
Cs1—Cl2ⁱⁱ	3.510 (4)	Pd1—O1	1.993 (9)
Cs1—Cl2^v	3.901 (4)	Pd1—N1	2.000 (12)
Symmetry codes: (i) -x+1, -y, z; (ii) $[-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z+1]$ ; (iii) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+2]$ ; (iv) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ ; (v) $[-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z+2]$ ; (vi) x, y, z+1.

Figure 1
ORTEP representation of the asymmetric unit showing atom labelling (ellipsoids drawn at 50% probabilities).

Figure 2
Caesium coordination and packing of cations and anions in the unit cell.

3. Supramolecular features

The cation and anion assembly, viewed along the twofold axis (the c axis) is shown in Fig. 3. Chains of complex anions related by a 2₁ screw axis along the b axis link double rows of caesium cations (Fig. 4). The caesium ions are bridged by chlorine atoms along and across the rows. The successful crystallization with larger Cs ions, which failed with smaller K ions, can be rationalized with this lattice arrangement. Larger cations with higher coordination capability can engage four molecules of complex anions acting as a nucleator in forming the lattice much better compared to smaller cations such as Na or Li.

Figure 3
The cation and anion assembly viewed along the twofold axis (the c axis).

Figure 4
Chains of complex anions related by a 2₁ screw axis along the a axis linking double rows of caesium cations (blue spheres).

In the crystal, extensive O—H⋯O, N—H⋯Cl and C—H⋯O hydrogen bonds (Table 2, Fig. 5) link the molecules, forming a two-dimensional network parallel to (010).

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3⋯O1^iv	0.91 (1)	2.07 (2)	2.750 (14)	131 (3)
O3—H3⋯O2^iv	0.91 (1)	2.60 (2)	3.479 (15)	163 (3)
N1—H1A⋯Cl2^vii	0.91	2.62	3.471 (13)	156
N1—H1B⋯Cl2^viii	0.91	2.51	3.388 (13)	163
C2—H2⋯O3^vii	1.00	2.58	3.255 (19)	125
Symmetry codes: (iv) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]$ ; (vii) x, y, z-1; (viii) -x+1, -y+1, z.

Figure 5
A view of the packing illustrating the hydrogen bonding (dashed lines; see Table 2

4. Database survey

The planarity of the chelate ring M–N–CH(R)–C–O is thought to be a relevant structural parameter in correlating biological activities and was examined in the structures of Pd (36 hits) and Pt (49 hits) complexes from the Cambridge Structural Database (CSD; Groom et al. 2016 ) using CONQUEST (Version 1.19; Bruno et al., 2002 ). However, there are very few structure determinations of Pd or Pt complexes with amino acids as the organic ligands, only five having been reported for Pt and three for Pd. Table 3 details these structures and their chelate ring geometry parameters in relation to their planarity. It appears from Table 3 that the planarity of the five-membered ring is dependent on the hybridization state of the carboxylate moiety after it has coordinated to the metal ion. Thus longer C—O bonds (associated with shorter exocyclic ones) give rise to larger O—C—C—N torsion angles (and non-planarity), whereas more equal C—O bonds form planar five-membered rings. For example, structure ACEMEC (Schiesser et al., 2012) has the highest torsion angle (25.85°) accompanied by a quite long C—O bond length (1.304 Å) whereas structure BAGLPD (Baidina et al., 1980a) shows the smallest torsion angle (5.36°) together with a slightly shorter C—O bond length (1.284 Å). Irrespective of its causes (electronic factors during the complex formation), this parameter could be an important feature while modelling the interaction of the complexes with DNA for biological activities.

Table 3
Molecular geometry (Å, °) of the five-membered ring in MCl₂ (amino acid) complexes with Pt and Pd

Data obtained from a search of the CSD (Groom et al., 2016).

CCDC refcode	Reference	Structure	C—O	C=O	C—C	C—N	O—C—C—N (τ)
ACEMEC	Schiesser et al., (2012)	K[Pt(L-alaO)Cl₂]	1.304	1.223	1.528	1.480	25.85
GAWYOS	Bino et al., (1988 )	[PtCl₂(N,O-Dap)]	1.313	1.232	1.543	1.499	19.44
GAWYUY	Bino et al., (1988)	[PtCl₂(N,O-Lys)]·H₂O	1.300	1.219	1.500	1.557	13.66
GAWYPS	Bino et al., (1988)	[PtCl₂(N,O-Lys)]·H₂O	1.315	1.227	1.457	1.436	15.72
KCGLPD	Baidina et al., (1980b )	K[Pd(Gly)Cl₂]·H₂O	1.285	1.216	1.518	1.490	11.74
BAGLPD	Baidina et al., (1980a)	Ba[Pd(Gly)Cl₂]·2H₂O	1.268	1.194	1.526	1.484	−13.69
BAGLPD	Baidina et al., (1980a)	Ba[Pd(Gly)Cl₂]·2H₂O	1.284	1.233	1.503	1.507	5.36

5. Biological considerations

Caesium cis-dichloro-L-serinato platinum(II) has been shown to increase the lifespan of P-388 leukemic mice. It also has anti-tumor activity in the MBG5 Supernal Capsule MX-1 mammary carcinoma xenograph mouse test-system (Charlson & Shorland, 1984 ). An X-ray crystal structure determination of caesium cis-dichloro-L-serinato platinum(II) has not been performed. Since caesium cis-dichloro-L-serinato platinum(II) and caesium cis-dichloro-L-serinato palladium(II) both show anticancer activity in mouse test-systems, it may be anticipated that the platinum(II) complex also has a planar five-membered ring system. Recently, there has been a report on the structure of potassium (2-amino-3-hydroxypropanoato)dichloroplatinum(II) (Fabbiani et al., 2015 ) in which one molecule has a planar ring. Potassium cis-dichloro-glycinato platinum(II) has also been shown to increase the lifespan of P-388 leukemic mice (Charlson & Shorland, 1984). Therefore the hydroxyl group in caesium cis-dichloro-L-serinato platinum(II) plays little or no part in the anti-tumor activity shown by this complex. In the publication by Schiesser et al. (2012), the authors mentioned that some platinum(II) complexes with amino acid ligands showed moderate cytotoxicity toward tumor cells. However, they did not mention whether potassium-L-alaninato-dichloro platinum(II) has been tested or not in any of the rodent test-systems. It should also be mentioned that potassium cis-dichloroglycinato platinum(II) and caesium cis-dichloro-L-serinato platinum(II) have not been screened for possible antifungal activity. The X-ray crystal structure of bis(phenylglycinato)palladium(II) containing two molecules of dimethyl sulfoxide has been determined (Gao et al., 2009 ). These authors also synthesized bis(phenylglycinato)platinum(II), which also contains two molecules of dimethyl sulfoxide, and showed that this platinum complex had a stronger binding affinity to fish-sperm DNA than the corresponding palladium complex. Both complexes added to DNA by a strong intercalating mode and both complexes could cleave pBR 332plasmid DNA. (A plasmid is a small DNA molecule within a cell that is physically separated from chromosomal DNA and replicates independently. Plasmids are commonly found in bacteria as circular double-stranded DNA. Plasmid DNA can also be found in fungi and higher plants.) The palladium and platinum complexes are also cytotoxic to HeLa, Hep-G2, KB, and AGZY-83a tumor cells, with the platinum complex being more effective than the palladium complex. X-ray crystal structures have been reported for the palladium(II) complexes of glycine with 2,2′-bipyridine, 1,10-phenathroline or 2,2′-bipyridylamine with chloride counter-ions (Yodoshi & Okabe, 2008 ). Each of the complexes was shown to be capable of intercalative binding to calf thymus DNA and could enhance the cleavage of pBR 332 plasmid DNA in the presence of hydrogen peroxide and ascorbic acid (Yodoshi & Okabi, 2008) . Small molecules can intercalate DNA by fitting in between base pairs in the two different DNA strands. Generally these molecules are planar or nearly planar. In the case of the palladium(II) complex with glycine and bipyridine, the central palladium(II) atom has a distorted square-planar geometry. Furthermore, the two five-membered rings formed by the bipyridine and the glycine ligands are almost planar and the two pyridine rings are planar (Yodoshi & Okabe, 2008).

6. Synthesis and crystallization

Poly{caesium [cis-dichloro-(S-2-amino-3-hydroxypropanoate-κ²N,O)palladate(II)]} was synthesized by a previously described method (Charlson et al., 1981). Using a procedure similar to the method described for the synthesis of potassium-L-alaninato-dichloroplatinum(II) (Ley & Ficken, 1912 ), a crude amorphous sample of potassium cis-dichloro-L-serinato palladium(II) was obtained. Therefore, the potassium salt was converted by a known method (Cleare, 1977 ) into crystalline caesium cis-dichloro-L-serinato palladium(II), which could be purified by recrystallization from water. In a typical preparation, a solution of L-serine (2.1 g) and potassium tetrachloropalladate(II) (3.2 g) in water (60 mL) was heated for 3h under reflux on a boiling water bath. Absolute ethanol (450 mL) was added to the filtered reaction mixture and the light-orange precipitate (1.7 g) was filtered off. This potassium salt of the palladium L-serine complex was reprecipitated from water (10 mL) with ethanol (40 mL). Small quantities of solid caesium chloride were added to a stirred solution of the potassium salt (1.5 g) in water (10 mL) until the solution became dark red. A brick-shaped red crystalline caesium salt (1.2 g) was obtained by keeping this solution for 24 h at 278 K. The caesium complex was purified by two recrystallizations from water (yield 0.2 g). Analysis found: C, 8.83; H, 1.55; Cl, 17.2; N, 3.43. Calculated for C₃H₆Cl₂NO₃PdCs: C, 8.70; H, 1.46; Cl, 17.1; N, 3.38%.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 4. All H atoms were positioned geometrically with d(N—H) = 0.91 Å, for Csp³—H, d(C—H) = 0.99 Å and (O—H) = 0.87 Å and with U_iso(H) = 1.2U_eq(C,N) or 1.5U_eq(O).

Table 4
Experimental details

Crystal data
Chemical formula	[CsPd(C₃H₆NO₃)Cl₂]
M_r	414.30
Crystal system, space group	Orthorhombic, P2₁2₁2
Temperature (K)	150
a, b, c (Å)	11.594 (4), 17.072 (5), 4.4739 (12)
V (Å³)	885.6 (5)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	6.71
Crystal size (mm)	0.08 × 0.07 × 0.03

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2016 )
T_min, T_max	0.499, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	5126, 1546, 1212
R_int	0.125
(sin θ/λ)_max (Å⁻¹)	0.595

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.039, 0.076, 0.83
No. of reflections	1546
No. of parameters	91
No. of restraints	13
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	1.64, −1.24
Absolute structure	Flack x determined using 375 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] (Parsons et al., 2013 )
Absolute structure parameter	−0.02 (5)
Computer programs: APEX2 and SAINT (Bruker, 2016), SHELXT (Sheldrick, 2015a ), SHELXL2014 (Sheldrick, 2015b ) and OLEX2 (Dolomanov et al., 2009 ).

Supporting information

CCDC reference: 1584689

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989017016164/im2483sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989017016164/im2483Isup2.hkl

Table 2. DOI: https://doi.org/10.1107/S2056989017016164/im2483sup3.pdf

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2016); cell refinement: SAINT (Bruker, 2016); data reduction: SAINT (Bruker, 2016); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Poly[[µ₃-(S)-2-amino-3-hydroxypropanoato]-cis-di-µ-chlorido-caesiumpalladium(II)] top

Crystal data top

[CsPd(C₃H₆NO₃)Cl₂]	D_x = 3.107 Mg m⁻³
M_r = 414.30	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P2₁2₁2	Cell parameters from 360 reflections
a = 11.594 (4) Å	θ = 2.4–20.1°
b = 17.072 (5) Å	µ = 6.71 mm⁻¹
c = 4.4739 (12) Å	T = 150 K
V = 885.6 (5) Å³	Plate, light yellow
Z = 4	0.08 × 0.07 × 0.03 mm
F(000) = 760

Data collection top

Bruker APEXII CCD diffractometer	1212 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.125
Absorption correction: multi-scan (SADABS; Bruker, 2016)	θ_max = 25.0°, θ_min = 2.1°
T_min = 0.499, T_max = 0.746	h = −13→13
5126 measured reflections	k = −20→16
1546 independent reflections	l = −5→3

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.039	w = 1/[σ²(F_o²)] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.076	(Δ/σ)_max = 0.001
S = 0.83	Δρ_max = 1.64 e Å⁻³
1546 reflections	Δρ_min = −1.24 e Å⁻³
91 parameters	Absolute structure: Flack x determined using 375 quotients [(I⁺)-(I^-)]/[(I⁺)+(I^-)] (Parsons et al., 2013)
13 restraints	Absolute structure parameter: −0.02 (5)

Special details top

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

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Cs1	0.38524 (10)	0.10339 (5)	0.6704 (2)	0.0179 (3)
Pd1	0.28780 (11)	0.41984 (6)	0.5719 (2)	0.0097 (3)
Cl1	0.1180 (4)	0.4294 (2)	0.8375 (9)	0.0184 (9)
Cl2	0.3493 (4)	0.5375 (2)	0.7574 (8)	0.0164 (10)
O1	0.2471 (9)	0.3141 (6)	0.415 (2)	0.016 (3)
O2	0.3137 (9)	0.2136 (6)	0.147 (2)	0.020 (3)
O3	0.5412 (9)	0.2649 (6)	0.538 (2)	0.016 (2)
H3	0.6175 (15)	0.2695 (16)	0.579 (8)	0.024*
N1	0.4279 (10)	0.4068 (7)	0.316 (3)	0.014 (2)
H1A	0.430153	0.446008	0.178195	0.017*
H1B	0.492081	0.410758	0.431882	0.017*
C1	0.3228 (14)	0.2811 (9)	0.245 (3)	0.012 (4)
C2	0.4286 (13)	0.3293 (8)	0.158 (4)	0.014 (2)
H2	0.424782	0.339538	−0.061897	0.017*
C3	0.5389 (14)	0.2847 (9)	0.222 (3)	0.016 (2)
H3A	0.541636	0.236400	0.099494	0.019*
H3B	0.606568	0.317387	0.170155	0.019*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cs1	0.0240 (7)	0.0163 (5)	0.0134 (5)	0.0002 (5)	−0.0022 (5)	−0.0020 (4)
Pd1	0.0094 (7)	0.0098 (6)	0.0097 (6)	0.0012 (6)	0.0003 (6)	0.0000 (5)
Cl1	0.015 (2)	0.0202 (19)	0.020 (2)	0.001 (2)	0.003 (2)	−0.0022 (17)
Cl2	0.016 (3)	0.0124 (19)	0.021 (3)	−0.0018 (19)	0.0006 (18)	−0.0039 (15)
O1	0.009 (6)	0.015 (5)	0.025 (7)	−0.003 (5)	0.011 (5)	−0.005 (5)
O2	0.024 (8)	0.013 (5)	0.024 (6)	−0.001 (5)	−0.010 (6)	−0.003 (5)
O3	0.010 (5)	0.022 (5)	0.016 (5)	0.002 (4)	0.000 (4)	0.002 (4)
N1	0.008 (5)	0.018 (5)	0.017 (6)	0.002 (4)	−0.004 (5)	−0.001 (5)
C1	0.008 (9)	0.021 (9)	0.007 (9)	−0.001 (7)	0.005 (6)	0.003 (6)
C2	0.008 (5)	0.018 (5)	0.017 (6)	0.002 (4)	−0.004 (5)	−0.001 (5)
C3	0.010 (5)	0.022 (5)	0.016 (5)	0.002 (4)	0.000 (4)	0.002 (4)

Geometric parameters (Å, º) top

Cs1—Cs1ⁱ	4.421 (2)	Pd1—O1	1.993 (9)
Cs1—Pd1ⁱⁱ	3.8755 (17)	Pd1—N1	2.000 (12)
Cs1—Cl1ⁱⁱⁱ	3.528 (4)	O1—C1	1.291 (17)
Cs1—Cl1^iv	3.572 (4)	O2—C1	1.238 (18)
Cs1—Cl1ⁱⁱ	3.740 (4)	O3—H3	0.907 (12)
Cs1—Cl1^v	3.698 (4)	O3—C3	1.458 (18)
Cs1—Cl2ⁱⁱ	3.510 (4)	N1—H1A	0.9100
Cs1—Cl2^v	3.901 (4)	N1—H1B	0.9100
Cs1—O2	3.117 (10)	N1—C2	1.500 (17)
Cs1—O2^vi	2.962 (10)	C1—C2	1.53 (2)
Cs1—O3	3.349 (10)	C2—H2	1.0000
Cs1—C1	3.654 (15)	C2—C3	1.52 (2)
Pd1—Cl1	2.305 (4)	C3—H3A	0.9900
Pd1—Cl2	2.287 (4)	C3—H3B	0.9900

Pd1ⁱⁱ—Cs1—Cs1ⁱ	70.48 (4)	O3—Cs1—C1	48.1 (3)
Pd1ⁱⁱ—Cs1—Cl2^v	65.76 (6)	C1—Cs1—Cs1ⁱ	141.5 (2)
Cl1^v—Cs1—Cs1ⁱ	50.56 (7)	C1—Cs1—Pd1ⁱⁱ	115.0 (2)
Cl1ⁱⁱⁱ—Cs1—Cs1ⁱ	54.04 (6)	C1—Cs1—Cl1ⁱⁱ	109.9 (2)
Cl1^iv—Cs1—Cs1ⁱ	54.55 (6)	C1—Cs1—Cl1^v	167.2 (3)
Cl1ⁱⁱ—Cs1—Cs1ⁱ	51.09 (7)	C1—Cs1—Cl2^v	116.3 (3)
Cl1^iv—Cs1—Pd1ⁱⁱ	94.97 (7)	Cl1—Pd1—Cs1^vii	69.20 (10)
Cl1ⁱⁱⁱ—Cs1—Pd1ⁱⁱ	116.25 (7)	Cl2—Pd1—Cs1^vii	63.44 (11)
Cl1ⁱⁱ—Cs1—Pd1ⁱⁱ	35.18 (7)	Cl2—Pd1—Cl1	90.97 (14)
Cl1^v—Cs1—Pd1ⁱⁱ	60.77 (7)	O1—Pd1—Cs1^vii	120.7 (3)
Cl1ⁱⁱⁱ—Cs1—Cl1^v	60.58 (12)	O1—Pd1—Cl1	92.5 (3)
Cl1ⁱⁱⁱ—Cs1—Cl1^iv	78.11 (9)	O1—Pd1—Cl2	175.4 (3)
Cl1^iv—Cs1—Cl1^v	105.11 (6)	O1—Pd1—N1	83.7 (4)
Cl1ⁱⁱⁱ—Cs1—Cl1ⁱⁱ	105.13 (6)	N1—Pd1—Cs1^vii	110.5 (3)
Cl1^v—Cs1—Cl1ⁱⁱ	73.95 (7)	N1—Pd1—Cl1	175.3 (4)
Cl1^iv—Cs1—Cl1ⁱⁱ	59.79 (11)	N1—Pd1—Cl2	93.0 (3)
Cl1ⁱⁱⁱ—Cs1—Cl2^v	94.47 (10)	Cs1^viii—Cl1—Cs1^ix	119.79 (11)
Cl1^v—Cs1—Cl2^v	50.97 (8)	Cs1^x—Cl1—Cs1^ix	75.40 (8)
Cl1ⁱⁱ—Cs1—Cl2^v	99.35 (9)	Cs1^ix—Cl1—Cs1^vii	73.95 (7)
Cl1^iv—Cs1—Cl2^v	154.03 (9)	Cs1^x—Cl1—Cs1^vii	119.82 (11)
Cl1ⁱⁱⁱ—Cs1—C1	127.5 (3)	Cs1^viii—Cl1—Cs1^vii	74.36 (8)
Cl1^iv—Cs1—C1	87.0 (3)	Cs1^x—Cl1—Cs1^viii	78.11 (9)
Cl2^v—Cs1—Cs1ⁱ	100.91 (6)	Pd1—Cl1—Cs1^vii	75.62 (10)
Cl2ⁱⁱ—Cs1—Cs1ⁱ	102.14 (7)	Pd1—Cl1—Cs1^viii	107.83 (14)
Cl2ⁱⁱ—Cs1—Pd1ⁱⁱ	35.65 (6)	Pd1—Cl1—Cs1^x	164.55 (15)
Cl2ⁱⁱ—Cs1—Cl1ⁱⁱⁱ	151.89 (9)	Pd1—Cl1—Cs1^ix	111.88 (14)
Cl2ⁱⁱ—Cs1—Cl1^v	93.39 (9)	Cs1^vii—Cl2—Cs1^ix	74.06 (8)
Cl2ⁱⁱ—Cs1—Cl1ⁱⁱ	53.58 (9)	Pd1—Cl2—Cs1^ix	105.91 (14)
Cl2ⁱⁱ—Cs1—Cl1^iv	100.86 (10)	Pd1—Cl2—Cs1^vii	80.92 (12)
Cl2ⁱⁱ—Cs1—Cl2^v	74.06 (8)	C1—O1—Pd1	116.2 (9)
Cl2ⁱⁱ—Cs1—C1	80.1 (3)	Cs1^xi—O2—Cs1	94.8 (3)
O2—Cs1—Cs1ⁱ	129.96 (19)	C1—O2—Cs1^xi	145.3 (10)
O2^vi—Cs1—Cs1ⁱ	132.5 (2)	C1—O2—Cs1	105.8 (9)
O2^vi—Cs1—Pd1ⁱⁱ	124.7 (2)	Cs1—O3—H3	124.3 (19)
O2—Cs1—Pd1ⁱⁱ	98.06 (19)	C3—O3—Cs1	110.7 (8)
O2^vi—Cs1—Cl1ⁱⁱⁱ	82.3 (2)	C3—O3—H3	101 (2)
O2—Cs1—Cl1ⁱⁱ	91.2 (2)	Pd1—N1—H1A	109.2
O2—Cs1—Cl1^iv	79.5 (2)	Pd1—N1—H1B	109.2
O2—Cs1—Cl1^v	158.4 (2)	H1A—N1—H1B	107.9
O2^vi—Cs1—Cl1ⁱⁱ	159.9 (2)	C2—N1—Pd1	111.9 (9)
O2—Cs1—Cl1ⁱⁱⁱ	140.2 (2)	C2—N1—H1A	109.2
O2^vi—Cs1—Cl1^v	94.5 (2)	C2—N1—H1B	109.2
O2^vi—Cs1—Cl1^iv	140.3 (2)	O1—C1—Cs1	101.0 (8)
O2^vi—Cs1—Cl2ⁱⁱ	112.3 (2)	O1—C1—C2	117.5 (13)
O2—Cs1—Cl2^v	118.8 (2)	O2—C1—Cs1	55.1 (8)
O2—Cs1—Cl2ⁱⁱ	65.0 (2)	O2—C1—O1	123.8 (15)
O2^vi—Cs1—Cl2^v	61.0 (2)	O2—C1—C2	118.7 (14)
O2^vi—Cs1—O2	94.8 (3)	C2—C1—Cs1	114.9 (9)
O2—Cs1—O3	60.9 (3)	N1—C2—C1	110.5 (13)
O2^vi—Cs1—O3	75.8 (3)	N1—C2—H2	108.0
O2—Cs1—C1	19.0 (3)	N1—C2—C3	111.1 (12)
O2^vi—Cs1—C1	78.0 (3)	C1—C2—H2	108.0
O3—Cs1—Cs1ⁱ	109.42 (18)	C3—C2—C1	111.0 (13)
O3—Cs1—Pd1ⁱⁱ	153.60 (18)	C3—C2—H2	108.0
O3—Cs1—Cl1ⁱⁱⁱ	80.07 (19)	O3—C3—C2	108.4 (14)
O3—Cs1—Cl1ⁱⁱ	123.52 (19)	O3—C3—H3A	110.0
O3—Cs1—Cl1^iv	66.99 (18)	O3—C3—H3B	110.0
O3—Cs1—Cl1^v	140.51 (19)	C2—C3—H3A	110.0
O3—Cs1—Cl2^v	136.84 (18)	C2—C3—H3B	110.0
O3—Cs1—Cl2ⁱⁱ	125.87 (19)	H3A—C3—H3B	108.4

Symmetry codes: (i) −x+1, −y, z; (ii) −x+1/2, y−1/2, −z+1; (iii) x+1/2, −y+1/2, −z+2; (iv) x+1/2, −y+1/2, −z+1; (v) −x+1/2, y−1/2, −z+2; (vi) x, y, z+1; (vii) −x+1/2, y+1/2, −z+1; (viii) x−1/2, −y+1/2, −z+1; (ix) −x+1/2, y+1/2, −z+2; (x) x−1/2, −y+1/2, −z+2; (xi) x, y, z−1.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3···O1^iv	0.91 (1)	2.07 (2)	2.750 (14)	131 (3)
O3—H3···O2^iv	0.91 (1)	2.60 (2)	3.479 (15)	163 (3)
N1—H1A···Cl2^xi	0.91	2.62	3.471 (13)	156
N1—H1B···Cl2^xii	0.91	2.51	3.388 (13)	163
C2—H2···O3^xi	1.00	2.58	3.255 (19)	125

Symmetry codes: (iv) x+1/2, −y+1/2, −z+1; (xi) x, y, z−1; (xii) −x+1, −y+1, z.

Molecular geometry (Å, °) of the five-membered ring in MCl₂ (amino acid) complexes with Pt and Pd top

Data obtained from a search of the CSD (Groom et al., 2016).

CCDC refcode	Reference	Structure	C—O	C═O	C—C	C—N	O—C—C—N (τ)
ACEMEC	Schiesser et al., (2012)	K[Pt(L-alaO)Cl₂]	1.304	1.223	1.528	1.480	25.85
GAWYOS	Bino et al., (1988)	[PtCl₂(N,O-Dap)]	1.313	1.232	1.543	1.499	19.44
GAWYUY	Bino et al., (1988)	[PtCl₂(N,O-Lys)]·H₂O	1.300	1.219	1.500	1.557	13.66
GAWYPS	Bino et al., (1988)	[PtCl₂(N,O-Lys)]·H₂O	1.315	1.227	1.457	1.436	15.72
KCGLPD	Baidina et al., (1980b)	K[Pd (Gly) Cl₂]·H₂O	1.285	1.216	1.518	1.490	11.74
BAGLPD	Baidina et al., (1980a)	Ba[Pd (Gly) Cl₂]·2H₂O	1.268	1.194	1.526	1.484	-13.69
BAGLPD	Baidina et al., (1980a)	Ba[Pd (Gly) Cl₂]·2H₂O	1.284	1.233	1.503	1.507	5.36

Acknowledgements

We thank the Johnson and Matthey Company in Reading, England, for supplying the potassium tetrachloropalladate(II) that was used in the preparation of caesium cis-dichloro-L-serinatopalladium(II) on their loan scheme. We also thank Dr Alysha Elliott from the CO-ADD of the University of Queensland for giving us the results of the antifungal testing and Dr Andrew Piggott of the Department of Chemistry and Biological Sciences for taking an interest in this work. In addition, we thank Dr Christopher Marjo, Head of the Division (SSEAU), Mark Wainwright Analytical Centre, UNSW for his encouragement and support.

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