cis-(3-Hydroxy­cyclo­butane-1,1-di­car­box­yl­ato-κ²O,O′)bis­(2-methyl­pyridine-κN)platinum(II)

In the crystal structure of the title compound, [Pt(C₆H₆O₄)(C₆H₇N)₂], the platinum(II) ion is tetra­coordinated in a square-planar coordination. The structure involves intra­molecular C—H...O hydrogen bonds.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.022 Å
• R factor = 0.053
• wR factor = 0.150
• Data-to-parameter ratio = 19.0

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT220_ALERT_2_B Large Non-Solvent    C     Ueq(max)/Ueq(min) ...       3.51 Ratio
PLAT342_ALERT_3_B Low Bond Precision on C-C Bonds (x 1000) Ang ...         22
PLAT420_ALERT_2_B D-H Without Acceptor       O5     -   H5     ...          ?

Alert level C
PLAT094_ALERT_2_C Ratio of Maximum / Minimum Residual Density ....       2.24
PLAT222_ALERT_3_C Large Non-Solvent    H     Ueq(max)/Ueq(min) ...       3.49 Ratio
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for         C8
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C5
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        C11

Alert level G
ABSTM02_ALERT_3_G  The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
            Tmin and Tmax reported:      0.271     0.367
            Tmin and Tmax expected:      0.187     0.286
            RR =      1.127
            Please check that your absorption correction is appropriate.
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           28.33
           From the CIF: _reflns_number_total               4511
           Count of symmetry unique reflns         2701
           Completeness (_total/calc)            167.01%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured      1810
           Fraction of Friedel pairs measured     0.670
           Are heavy atom types Z>Si present        yes
PLAT794_ALERT_5_G Check Predicted Bond Valency for Pt1         (2)       2.26

   0 ALERT level A = In general: serious problem
   3 ALERT level B = Potentially serious problem
   5 ALERT level C = Check and explain
   3 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   6 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

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S1. Comment

In an attempt to overcome drawbacks of cisplatin, numerous analogues have been prepared and evaluated in a search for an alternativeactive agent. Among them, cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II) (Carboplatin) is commonly used for the treatment of testicular and ovarian cancer as well as cervical, bladder and head and neck tumors. It has proven to be the only second-generation platinum complex commercially available worldwide at present (Jakuper et al., 2003). But the application of Carboplatin in therapy is limited by the dose-dependent nephrotoxicity and other side effects. Therefore, the search for the new potent platinum complexes possessing high antitumor activity and lack of cross-resistance is needed. The title compound is a new soluble carboplatin analogue containing an asymmetric chelating malonate anion as its carrier and anticancer tests are presently being carried out.

The title complex consists of discrete monomeric units where the Pt(II) is coordinated by two crystallographically independent 2-methylpyridine ligands and 3-hydroxy-1,1-cyclobutanedicarboxylate anions with a square planar geometry (Table 1, Fig. 1) The 1,1-cyclobutanedicarboxylate ligand displays similar features to those described in the literature (Tu et al., 2004; Zhang et al., 2002; Ali et al., 2002). The six-membered chelate ring built up of the Pt(II) atom and the 3-hydroxy-1,1-cyclobutanedicarboxylate anion adopts a boat conformation and the two 2-methylpyridine liagnds are oriented perpendicular to each other.

Related literature

For related literature, see: Ali et al. (2002); Jakuper et al. (2003); Tu et al. (2004); Zhang et al. (2002).

S2. Experimental

Potassium tetrachloroplatinate(II) (5 g, 12 mmol) was dissolved in water (50 ml) and treated with KI (12 g, 72 mmol). After left in a dark for 30 min at room temperature, a solution of 2-methylpyridine (1.08 g, 12 mmol in 50 ml water) was added dropwise. The mixture was stirred for 4 h and the yellow precipitate was filtrated off. Then to a suspension of di(2-methylpyridine)PtI₂ (2.5 g, 0.044 mmol) in 75 ml water was added (1.36 g, 3.65 mmol) disilver 3-hydroxy-1,1-cyclobutanedicarboxylate, and the reaction mixture was stirred at 323 K for 72 h. Then the AgI formed was filtrated off and the filtrate was condensed at 313 K under reduced pressure to 5 ml, and a colourless crystalline product was precipitated. The compound was recrystallized from water to obtain crystals suitable for X-ray structure analysis.

S3. Refinement

All H atoms were initially located in a difference Fourier map but were positioned with idealized geometry and refined isotropic with U_iso(H) = 1.2U_eq(C) (1.5 for methyl H atoms) using a riding model with C—H = 0.93 and 0.97 Å).

Computing details

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 2000); software used to prepare material for publication: SHELXTL (Sheldrick, 2000).

Figures

Fig. 1. Molecular structure of (I) with the atomic labelling scheme. Displacement ellipsoids are shown at the 30% probability level.

cis-(3-Hydroxycyclobutane-1,1-dicarboxylato-κ²O,O')bis(2-methylpyridine- κN)platinum(II)

Crystal data

[Pt(C6H6O4)(C6H7N)2]	F(000) = 1040
Mr = 539.45	Dx = 1.874 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P2ac2ab	Cell parameters from 4511 reflections
a = 9.5157 (7) Å	θ = 2.0–28.3°
b = 13.1417 (9) Å	µ = 7.37 mm^−1
c = 15.2884 (11) Å	T = 298 K
V = 1911.9 (2) Å^3	Block, colourless
Z = 4	0.24 × 0.22 × 0.17 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer	4511 independent reflections
Radiation source: fine-focus sealed tube	3991 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.054
φ and ω scans	θmax = 28.3°, θmin = 2.0°
Absorption correction: numerical (APEX2; Bruker, 2004)	h = −12→12
Tmin = 0.271, Tmax = 0.367	k = −17→16
16189 measured reflections	l = −20→20

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.053	H-atom parameters constrained
wR(F^2) = 0.151	w = 1/[σ^2(Fo^2) + (0.1024P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max = 0.002
4511 reflections	Δρmax = 4.96 e Å^−3
238 parameters	Δρmin = −2.22 e Å^−3
0 restraints	Absolute structure: Flack (1983), with how many Friedel pairs?
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.03 (2)

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 F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Pt1	0.11187 (4)	0.91536 (3)	0.94090 (2)	0.03526 (14)
N1	0.2783 (10)	0.9230 (10)	0.8607 (6)	0.048 (2)
N2	0.2200 (10)	0.8622 (7)	1.0440 (6)	0.0370 (19)
O1	−0.0012 (9)	0.9638 (7)	0.8395 (5)	0.0448 (19)
O2	−0.0581 (9)	0.9143 (8)	1.0179 (6)	0.0482 (19)
O3	−0.2424 (12)	1.0008 (9)	1.0680 (8)	0.073 (3)
O4	−0.1914 (11)	1.0397 (9)	0.7953 (6)	0.063 (3)
O5	−0.1137 (19)	1.3303 (7)	0.9751 (9)	0.086 (4)
H5	−0.1290	1.3371	0.9226	0.104*
C1	0.3516 (16)	1.0153 (14)	0.8581 (11)	0.066 (4)
H1	0.3235	1.0688	0.8939	0.079*
C2	0.4629 (17)	1.0274 (15)	0.8039 (12)	0.073 (5)
H2	0.5208	1.0841	0.8092	0.087*
C3	0.4895 (19)	0.9557 (18)	0.7413 (14)	0.085 (6)
H3	0.5567	0.9695	0.6988	0.103*
C4	0.4248 (17)	0.8695 (16)	0.7389 (10)	0.073 (5)
H4	0.4459	0.8217	0.6960	0.088*
C5	0.3196 (16)	0.8488 (11)	0.8039 (9)	0.057 (3)
C6	0.249 (2)	0.7510 (17)	0.8104 (16)	0.123 (10)
H6A	0.2251	0.7379	0.8704	0.185*
H6B	0.3105	0.6983	0.7895	0.185*
H6C	0.1651	0.7520	0.7757	0.185*
C7	0.3179 (18)	0.9235 (11)	1.0828 (10)	0.064 (4)
H7	0.3370	0.9855	1.0560	0.077*
C8	0.388 (2)	0.9018 (15)	1.1558 (13)	0.093 (7)
H8	0.4519	0.9479	1.1795	0.111*
C9	0.3624 (18)	0.8037 (12)	1.1973 (13)	0.077 (5)
H9	0.4081	0.7839	1.2483	0.092*
C10	0.2683 (16)	0.7436 (11)	1.1568 (10)	0.061 (3)
H10	0.2503	0.6800	1.1810	0.073*
C11	0.1944 (12)	0.7709 (8)	1.0794 (7)	0.039 (2)
C12	0.0894 (18)	0.6987 (9)	1.0333 (10)	0.065 (4)
H12A	−0.0046	0.7235	1.0416	0.098*
H12B	0.0974	0.6317	1.0578	0.098*
H12C	0.1101	0.6962	0.9719	0.098*
C13	−0.1430 (12)	0.9925 (10)	1.0153 (7)	0.042 (3)
C14	−0.1268 (10)	1.0706 (7)	0.9431 (7)	0.036 (2)
C15	−0.2338 (13)	1.1622 (9)	0.9461 (9)	0.047 (3)
H15A	−0.2537	1.1920	0.8893	0.057*
H15B	−0.3198	1.1475	0.9777	0.057*
C16	−0.1254 (17)	1.2203 (9)	0.9991 (10)	0.059 (4)
H16	−0.1411	1.2118	1.0621	0.070*
C17	−0.0093 (13)	1.1523 (8)	0.9672 (9)	0.044 (3)
H17A	0.0549	1.1303	1.0127	0.053*
H17B	0.0412	1.1789	0.9170	0.053*
C18	−0.1097 (14)	1.0224 (8)	0.8538 (7)	0.039 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Pt1	0.0451 (2)	0.02367 (19)	0.0370 (2)	0.00148 (15)	0.00061 (16)	−0.00037 (16)
N1	0.045 (5)	0.059 (7)	0.041 (5)	0.008 (5)	0.002 (4)	0.006 (6)
N2	0.041 (5)	0.027 (4)	0.043 (5)	−0.001 (3)	−0.004 (4)	0.001 (4)
O1	0.052 (5)	0.052 (5)	0.030 (4)	0.010 (4)	−0.003 (3)	−0.004 (3)
O2	0.049 (4)	0.042 (4)	0.053 (5)	0.006 (4)	0.011 (4)	0.016 (5)
O3	0.075 (6)	0.060 (6)	0.085 (7)	0.011 (5)	0.044 (6)	0.015 (6)
O4	0.072 (7)	0.065 (6)	0.052 (5)	0.014 (5)	−0.012 (5)	−0.002 (5)
O5	0.131 (11)	0.029 (5)	0.099 (8)	0.010 (6)	0.038 (9)	−0.013 (5)
C1	0.061 (9)	0.069 (10)	0.068 (9)	−0.014 (7)	0.006 (7)	−0.009 (8)
C2	0.057 (9)	0.078 (11)	0.083 (12)	−0.016 (8)	0.007 (8)	0.006 (9)
C3	0.055 (9)	0.110 (15)	0.091 (13)	−0.001 (10)	0.033 (9)	0.028 (11)
C4	0.067 (10)	0.100 (13)	0.052 (8)	−0.010 (9)	0.011 (7)	−0.011 (8)
C5	0.066 (8)	0.050 (8)	0.055 (7)	−0.006 (6)	−0.002 (6)	−0.014 (6)
C6	0.134 (18)	0.085 (14)	0.15 (2)	−0.036 (14)	0.093 (17)	−0.066 (15)
C7	0.098 (11)	0.034 (7)	0.061 (8)	0.002 (7)	−0.016 (7)	0.002 (6)
C8	0.097 (13)	0.086 (13)	0.096 (13)	−0.040 (11)	−0.057 (11)	0.042 (10)
C9	0.087 (12)	0.045 (8)	0.099 (12)	−0.009 (7)	−0.029 (10)	0.016 (8)
C10	0.086 (9)	0.026 (6)	0.070 (9)	0.010 (6)	−0.003 (7)	0.007 (6)
C11	0.055 (7)	0.024 (5)	0.036 (5)	0.005 (4)	−0.002 (4)	0.005 (4)
C12	0.101 (12)	0.018 (5)	0.077 (9)	−0.003 (6)	0.000 (8)	0.005 (5)
C13	0.045 (7)	0.043 (6)	0.037 (6)	0.004 (5)	0.005 (5)	0.005 (5)
C14	0.038 (5)	0.026 (5)	0.042 (5)	0.001 (4)	0.007 (4)	−0.003 (4)
C15	0.048 (6)	0.039 (6)	0.055 (7)	0.013 (5)	0.000 (6)	0.011 (6)
C16	0.083 (11)	0.034 (7)	0.059 (7)	0.005 (6)	0.014 (8)	−0.009 (6)
C17	0.049 (6)	0.021 (5)	0.063 (8)	−0.013 (4)	0.007 (5)	0.003 (5)
C18	0.050 (6)	0.028 (5)	0.040 (5)	−0.001 (5)	−0.006 (5)	0.002 (4)

Geometric parameters (Å, º)

Pt1—O1	1.992 (8)	C6—H6C	0.9600
Pt1—O2	2.001 (8)	C7—C8	1.33 (2)
Pt1—N1	2.005 (10)	C7—H7	0.9300
Pt1—N2	2.008 (9)	C8—C9	1.46 (2)
N1—C5	1.364 (17)	C8—H8	0.9300
N1—C1	1.40 (2)	C9—C10	1.34 (2)
N2—C11	1.338 (13)	C9—H9	0.9300
N2—C7	1.368 (18)	C10—C11	1.422 (18)
O1—C18	1.306 (15)	C10—H10	0.9300
O2—C13	1.307 (15)	C11—C12	1.548 (19)
O3—C13	1.248 (15)	C12—H12A	0.9600
O4—C18	1.207 (15)	C12—H12B	0.9600
O5—C16	1.495 (18)	C12—H12C	0.9600
O5—H5	0.8200	C13—C14	1.515 (15)
C1—C2	1.35 (2)	C14—C18	1.513 (15)
C1—H1	0.9300	C14—C15	1.577 (14)
C2—C3	1.37 (3)	C14—C17	1.593 (14)
C2—H2	0.9300	C15—C16	1.52 (2)
C3—C4	1.29 (3)	C15—H15A	0.9700
C3—H3	0.9300	C15—H15B	0.9700
C4—C5	1.44 (2)	C16—C17	1.502 (18)
C4—H4	0.9300	C16—H16	0.9800
C5—C6	1.45 (2)	C17—H17A	0.9700
C6—H6A	0.9600	C17—H17B	0.9700
C6—H6B	0.9600
O1—Pt1—O2	91.4 (4)	C8—C9—H9	122.2
O1—Pt1—N1	86.3 (4)	C9—C10—C11	124.3 (13)
O2—Pt1—N1	177.0 (5)	C9—C10—H10	117.9
O1—Pt1—N2	177.7 (4)	C11—C10—H10	117.9
O2—Pt1—N2	87.1 (4)	N2—C11—C10	118.2 (11)
N1—Pt1—N2	95.3 (4)	N2—C11—C12	118.8 (10)
C5—N1—C1	117.3 (12)	C10—C11—C12	122.9 (11)
C5—N1—Pt1	125.5 (10)	C11—C12—H12A	109.5
C1—N1—Pt1	117.0 (10)	C11—C12—H12B	109.5
C11—N2—C7	118.4 (10)	H12A—C12—H12B	109.5
C11—N2—Pt1	122.5 (8)	C11—C12—H12C	109.5
C7—N2—Pt1	119.0 (8)	H12A—C12—H12C	109.5
C18—O1—Pt1	119.0 (7)	H12B—C12—H12C	109.5
C13—O2—Pt1	118.4 (7)	O3—C13—O2	121.1 (11)
C16—O5—H5	109.5	O3—C13—C14	119.2 (11)
C2—C1—N1	120.6 (16)	O2—C13—C14	119.5 (9)
C2—C1—H1	119.7	C18—C14—C13	112.6 (9)
N1—C1—H1	119.7	C18—C14—C15	114.5 (9)
C1—C2—C3	119.5 (17)	C13—C14—C15	115.5 (9)
C1—C2—H2	120.3	C18—C14—C17	114.5 (9)
C3—C2—H2	120.3	C13—C14—C17	111.1 (9)
C4—C3—C2	122.5 (16)	C15—C14—C17	86.1 (8)
C4—C3—H3	118.8	C16—C15—C14	87.7 (9)
C2—C3—H3	118.8	C16—C15—H15A	114.0
C3—C4—C5	118.6 (16)	C14—C15—H15A	114.0
C3—C4—H4	120.7	C16—C15—H15B	114.0
C5—C4—H4	120.7	C14—C15—H15B	114.0
N1—C5—C4	120.4 (14)	H15A—C15—H15B	111.2
N1—C5—C6	117.1 (13)	O5—C16—C17	116.1 (12)
C4—C5—C6	122.4 (14)	O5—C16—C15	113.9 (13)
C5—C6—H6A	109.5	C17—C16—C15	91.5 (9)
C5—C6—H6B	109.5	O5—C16—H16	111.3
H6A—C6—H6B	109.5	C17—C16—H16	111.3
C5—C6—H6C	109.5	C15—C16—H16	111.3
H6A—C6—H6C	109.5	C16—C17—C14	87.7 (9)
H6B—C6—H6C	109.5	C16—C17—H17A	114.0
C8—C7—N2	125.5 (14)	C14—C17—H17A	114.0
C8—C7—H7	117.3	C16—C17—H17B	114.0
N2—C7—H7	117.3	C14—C17—H17B	114.0
C7—C8—C9	117.9 (16)	H17A—C17—H17B	111.2
C7—C8—H8	121.0	O4—C18—O1	119.6 (11)
C9—C8—H8	121.0	O4—C18—C14	121.4 (11)
C10—C9—C8	115.6 (15)	O1—C18—C14	118.9 (10)
C10—C9—H9	122.2

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C15—H15B···O3	0.97	2.48	2.826 (16)	101
C12—H12A···O2	0.96	2.58	3.170 (16)	120