Mathematics. pertaining to or using complex numbers: complex methods; complex vector space.
–noun
6.
an intricate or complicated association or assemblage of related things, parts, units, etc.: the entire complex of our educational system; an apartment complex.
7.
Psychology. a system of interrelated, emotion-charged ideas, feelings, memories, and impulses that is usually repressed and that gives rise to abnormal or pathological behavior.
8.
a fixed idea; an obsessive notion.
9.
Mathematics.
a.
an arbitrary set of elements of a group.
b.
a collection of simplexes having specified properties.
10.
Also called coordination compound.Chemistry. a compound in which independently existing molecules or ions of a nonmetal (complexing agent) form coordinate bonds with a metal atom or ion. Compare ligand(def. 2).
11.
Biochemistry. an entity composed of molecules in which the constituents maintain much of their chemical identity: receptor-hormone complex, enzyme-substrate complex.
–verb (used with object)
12.
Chemistry. to form a complex with.
–verb (used without object)
13.
Chemistry. to form a complex.
[Origin: 1645–55; 1905–10 for def. 7; (adj.) < L complexus, ptp. of complectī, complectere to embrace, encompass, include, equiv. to complect- (see complect) + -tus ptp. suffix; (n.) < LL complexus totality, complex (L: inclusion, grasping, embrace), equiv. to complect(ere) + -tus suffix of v. action; reanalysis of the L v. as “to intertwine (completely)” has influenced sense of the adj.]
complex ion, charged molecular aggregate (see ion), consisting of a metallic atom or ion to which is attached one or more electron-donating molecules. In some complex ions, such as sulfate, SO4-2, the atoms are so tightly bound together that they act as a single unit. Many complex ions, however, such as tetrammine zinc (II), Zn(NH3)4+2, are only loosely aggregated and tend to dissociate in a water solution until an equilibrium is established between the complex ion and its components (see chemical equilibrium). Such complex ions, or coordinated complexes as they are also called, generally consist of a positively charged central metal atom or ion, like the zinc in tetramine zinc, surrounded by electron-donating, or basic, groups called ligands; in the tetrammine zinc complex, the NH3 groups are the ligands. The number of bonds connecting the ligands to the central atom or ion is its coordination number, or ligancy. Transition metals (see transition elements) are especially suited for forming complex ions because they have filled or partially filled electron orbitals that can participate in bonding the ligands to the metal. The bonding holding the ligands to the central atom or ion is similar to covalent bonding between atoms but is more complex (see chemical bond). All the ligands surrounding the central ion need not be the same, and some positions can be occupied by solvent molecules. Because ligands remain in a fixed position around a central atom or ion, in many complexes different isomers, or arrangements, of the ligand groups are possible. When there are four or more ligands around a central atom, different stereoisomers, or spatial configurations, are possible (see stereochemistry). Many complex ions are colored; the specific color of a complex depends on both the central atom or ion and the ligands. For example, when cobaltous chloride is dissolved in water, a pale pink solution, sometimes called invisible ink, results because of the presence of the hydrated cobaltous ion, Co(H2O)6+2; this solution does not show up well on paper, but if the paper is heated to drive the water off, visibility improves because of the formation of a blue tetrachlorocobalt (II)-2 complex. Some of the more important complex ions are vitamin B12, chlorophyll, and the heme component of hemoglobin, in which the central metal ions are cobalt, magnesium, and iron, respectively, and the ligands are complex organic systems. Many enzymes contain a metal ion about which parts of the protein are coordinated.
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